planning and plant layout

7.1 Introduction Plant layout can affect the total operation of a company, including the production processes, equipment, storage, dispatch and administration. It has a direct effect upon production efficiency and economics of the operation, the morale of employees and can affect the physical health of operatives.

A production facility will be considered as a facility for processing pharmaceuticals or food products or manufacturing engineering products or consumer goods. The facility must utilize real estate, equipment, materials and labor to generate profit for investors and, philosophically, to enrich the life of all associated with it.

Layout planning involves knowledge of a wide range of technologies that will extend beyond those of individual planners and the full range of expertise may not exist in a production facility. Consultants can provide the expertise but guidance can be found in the published works listed in the References.

The design methods presented here allow a layout plan to be quickly formulated. The methods rely upon a thorough understanding of factory operations gained from experience and a good understanding of the relationship between people and equipment. When such an understanding is not present, a more rigorous approach is rec- ommended. Muther 1 published a formalized procedure in 1973, Tompkins, and White 2 a more academic method in 1984, both valuable contributions to problems of layout planning.

The first step in any design is to identify the real need, and this is often the most difficult task. Without it, designs can be produced which do not satisfy the requirements and the result is often unsatisfactory. It is essential to clearly define the objectives of the task and to re-confirm the objectives as time progresses. A useful aid is a value analysis at the end of the concept design stage. This assesses the design for value for money while meeting the defined project objectives. A good source document is A Study of Value Management and Quantity Surveying Practice, published by The Royal Institute of Chartered Surveyors.

A criterion of effective plant operation used to be effi- cient utilization of capital equipment. The main requirement is now recognized as short door-to-door times, not short floor-to-floor times. The prime need is therefore to achieve a plant layout that facilitates reception of raw materials and dispatch of finished goods in the shortest possible time with minimum capital tied up in work in progress (WIP). This involves access to the site, reception of goods vehicles, raw material goods storage and issue to production, procurement of component parts and sub- assemblies from sub-contractors, process technology and process routes, integrating the sub-contractors' supplies, finished goods storage and dispatch to the customer.

Layout planning concepts 7/69

These developments, employed by companies now called World Class Manufacturers (WCM), 3 must be examined by the company management who are contemplating establishing a new factory or expanding or reorganizing an existing plant.

Much of the new thinking on strategy has centered on advanced technology and the exploitation of the computer, but the following recommendations, requiring minimum investment in new plant, should be considered first:

1. Establish the operational priorities: (a) Production to be sales driven; (b) Make only what can be immediately sold; (c) Make every part right first time.

2. Reorganize production equipment: (a) Consider process orientation but employ product-

oriented flow when possible; (b) Organize products into groups that require the

same manufacturing equipment; (c) Arrange equipment into product cells.

3. Re-form the structure of production teams: (a) Form accountability teams for each product; (b) Bring staff functions onto the shop floor and into

the teams, form quality circles and establish total quality control (TQC).

These ideas, interestingly described by Goldratt and Cox, 4 provide flexible production and cater for customer requirements. They have become known as just in time (JIT) manufacture, but are often overlooked by many that think that investment in computer-controlled equipment is the only way to go. The concept, simplify before you automate, can provide significant improvements in production and can point the way to later advanced manufacturing where:

1. Equipment cells can be replaced by computer-coordinated machines- direct numerical control (DNC), flexible manufacturing systems (FMS), flexible manufacturing cells (FMC);

2. Warehousing automated to include computer-controlled storing and retrieval (AS/AR) and movement by auto- matic guided vehicles (AGV);

3. Whole manufacturing processes computer linked (CAM);

4. Computer-aided design (CAD); 5. Sales and management computerized, leading to com-

puter-integrated manufacture (CIM).

The development of these technologies can be followed in the proceedings of the professional institutions and the many magazines, some available free. You should define the state of technological awareness in the company and consider how this affects the plant layout.

7.2 Technological development and its effect upon plant layout There have been important world developments in the phi- losophy of factory operation and they affect plant layouts.

7.3 Layout planning concepts A process of analysis often executes designs. The methods vary from the traditional and well tried to experimental techniques. These include:

7/70 Planning and Plant Layout

1. A conventional plan drawing; 2. Cardboard cut-outs depicting blocks of buildings

pinned to an outline drawing of the site; 3. Three-dimensional scale models; 4. Software calculation and simulation packages.

Proprietary systems are available 10,11 employing Lego type blocks which can be constructed and placed on a baseboard to represent a three-dimensional visualization of the layout. Another system employs aluminum castings of the actual items of equipment and operatives. Cardboard cutouts have been the most commonly used method, particularly with those who rarely plan layouts.

The above methods allow proposed layouts to be visualized, analyzed and altered. These methods are often a try-it-and-see process, and the associated analysis is rarely structured. The old saying that 'If it looks right, it is right' is often used to justify results, but it may be more true to say that if it looks fight it is conventional, and the analysis method will rarely produce something original. This applies, of course, to any design activity, whether it is a plant layout, a piece of machinery or a consumer product.

Computer-aided methods are increasingly being used to assist design and a process of synthesis, described later, employs techniques to produce a design that will satisfy predetermined criteria. This produces a layout that can be subjected to critical review, and suggested changes to the layout can be examined for violation of the criteria.

The introduction of computers to many companies allows proprietary software to be used for layout design. 5 Spreadsheet, mathematical modeling and computer-aided design (CAD) techniques are available and greatly assist the design process, and have added to the resources available to planners. However, the traditional scale models described above will still be useful to present the result to management and shop floor personnel.

7.4 Plant data

7.4.1 Collection

The objective of the production process is to produce the fight goods of the right quality and at the fight price in order to generate a financial profit from the capital investment, but the plant layout fundamentally affects this objective.

The essential requirement for any design exercise is a thorough understanding of the working medium. For layouts, this means collecting sufficient data to describe those characteristics of the company which affect the layout. Data collection is time consuming and difficult, and it requires the contribution of factory personnel from many departments. The data required includes:

1. The company organization structure All departments, including maintenance This should be readily available from the personnel department but may need to be updated.

2. Number of employees in each department and shift Administration staff Technical staff

Factory workers direct Factory workers indirect This and the next item will be obtained from the personnel department, but the actual working situation will probably need to be confirmed with the individual managers of the various process departments.

3. Hours and the arrangements for shift working Administration and technical staff on day shift Difficulty is often experienced when workers are shared between departments. Some information will not be documented but since employees are generally paid for attendance hours these are meticulously recorded. Factory workers on each of the worked shifts Consider the arrangements for holidays Quantify work contracted to outside organizations Work contracted out is usually difficult to quantify. The accounts department will probably have records of the cost of such work and this can be employed to provide an indication of the significance of the work in relation to the operations within the company.

4. Process flow diagram Description of the products Description of the processes

Flow diagram showing process material flow, scrap and recycled material. Brief descriptions of the products are usually sufficient for the early stages of analysis of the company operation. The information will be amplified during the subsequent stages of the study.

5. Layout plans for all areas of the site Calculate the covered areas for all process areas. Cal- culate the areas taken up by services such as the boiler house, fuel-storage farm, etc. Layout plans are often available but the areas devoted to the various activities in the plant will need to be discussed with the individual area managers. The actual area in square meters or square feet will need to be esti- mated by scaling from the drawings and measure- ment on site. List the items of equipment on the site. Identify the location of the items on the layout plan. This information may exist. It will be needed for designing the layouts of the internals of the factory buildings and it is useful to initiate the quest for the information during the early stages of the project.

6. Vehicle movements The types and numbers of vehicles moving around the site and vehicles arriving from outside the plant must be considered. Identify interdepartmental vehicle movements. It is useful to start with the records from the gatehouse, which will indicate the number of vehicles arriving at the plant each day. This will need to be confirmed with the plant manager who will know if abnormal conditions existed during the time for which the records are valid. Aim to establish average and maximum numbers.

7. Consumables The quantities of main consumables used. Electricity, water and gas will be included in this item but of more importance to the plant layout are those items that occupy site space. Fuel oil is such an item, and it is

important to establish whether the existing facilities, e.g. a fuel-storage farm, are sufficient for the planned operations in the factory.

8. Effluent It should be established whether the area allocated to effluent treatment is sufficient, whether the technology is up to date and determine what influence the findings will have upon the effluent treatment area and the whole plant layout.

9. Site features Site features can be obtained by observation and ord- nance maps may be available from the drawing office. The features that need to be recorded are listed in Section 7.7.2.

10. Future plans It might be assumed that if an examination of the plant layout is being carried out, the future plans, as they affect the site layout, will be known. This is not always the case; therefore, management should be questioned at the beginning of the project. Particular attention should be paid to hazardous substances that may be used on the site, and the health and safety document 6 should be consulted.

Pareto, the Italian economist, observed that 85 per cent of wealth is owned by 15 per cent of the population, and it is sometimes stated that 15 per cent of a company's products generate 85 per cent of the turnover. Some workers have interpreted this to mean that 15 per cent of the data will suffice, but Tompkins and White 2 demonstrated that

Description: Manufacturer:

Sketches or Manufacturing l i te ra ture attached Y/N: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dimensions: Equipment S ize (m)

Working envelope (m) . . . L x W x H Equipatent weight (kg) . . . . . . . . . . . . . . . . . . . . . . . .

LOCATION: Bu i ld ing NO: Zone:

ELECTRIC ITY :

SingLe phase, isolated . . . . . . . . . . . . . . . . . . .

Three phase, isolated . . . . . . . . . . . . . . . . . . . .

Three phase & neutraL, isolated . . . . . . . . . .

Direct current . . . . . . . . . . . . . . . . . . . . . . . . . . .

Waterproof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Clean supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Spec ia l earthing . . . . . . . . . . . . . . . . . . . . . . . . .

Uninterrupt ibte supply . . . . . . . . . . . . . . . . . . .

Flameproof (Zone 1) . . . . . . . . . . . . . . . . . .

Flameproof (Zone 2) . . . . . . . . . . . . . . . . . .

Emergency supply . . . . . . . . . . . . . . . . . . . . .

Controls required . . . . . . . . . . . . . . . . . . . .

Emergency stop . . . . . . . . . . . . . . . . . . . . . . .

Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power requirement (kW) . . . . . . . . . . .

Other voltage . . . . . . . . . . . . . . . . . . . . . . . .

Other frequency . . . . . . . . . . . . . . . . . . . . . .

WATER: FLOW: t i t / sec PRESSURE: bar CONNECTION: Deta i ls

Cotd/hot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Soft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Deminerati~ed . (S i l i ca free Y/N . . . ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dis t i t ted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Drinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circu lat ing Cooling . . . . . . . . (Softened Y/N . . . . . . . )

Flow temp ( *C) . . Return temp ( *C) . . . . . . . DRAINAGE:

Gravity . . . . . . . . . . . . . . . . . . . . Discharge flow rate ( t i t res /min) . . . . . . . . . . .

Pumped . . . . . . . . . . . . . . . . . . . . . Discharge temperature ( *C) . . . . . . . . . . . . . . . . .

Solids/Sediments . . . . . . . . . . . Outlet connection size (mm) . . . . . . . . . . . . . . . . . . . .

Oil/Grease/Wax . . . . . . . . . . . . . Number of out let connections . . . . . . . . . . . . . . . . . . .

Cottection Tank . . . . . . . . . . . .

Hazardous (eg. radioactive~solvent~biological~chemical) give deta i l s . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

STEAM:

CONDENSATE RECOVERY: Y /N [g/hour psi

COHPRESSED A IR : t i t res /sec bar

NATURAL GAS: t i t res /sec bar

Figure 7.1 Equipment data sheet

Plant data 7/71

this is not always true, so data collectors should use their judgement regarding what is sufficient.

The data needed to plan the site layout are shown in the form of a questionnaire in Figure 7.1.

After the site layout has been determined, the layout of equipment inside the buildings will need to be considered. Details of the individual items of equipment will be needed, and Figure 7.2 lists the required information in the form of a questionnaire.

The areas for administration and amenities will need to be identified and in some countries, space will be required for accommodation and a mosque.

7.4.2 Ana lys is

The collection and tabulation of data will provide an opportunity to become familiar with the company and will generate a good understanding of the operation of the plant. Much of the data will be needed to establish the models needed to size the various areas of the plant. For instance, hours worked should be analyzed to identify shift work, direct and indirect effort, and the normal and overtime activity. Outside contractors may be employed, and this contribution will need to be determined, sometimes by visiting the contractor's facilities. When expansions are being planned, it may be necessary to discuss the contributions that outside contractors make to the factory and assess the increase which they can accommodate.

Model No . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment Ident i f i ca t ion No . . . . . . .

SPECIAL GASES: . . . . . . . . Y /N I f YES complete separate SPECIAL GASES DATA SHEET

FUME EXTRACTION:

Located in fume cup l~ard . . . . . . . Y /N I f YES complete FUHE CUPBOARD DATA SHEET

Fume hood . . . . . . . Y /N I f YES complete FUHE/DUST HOOD DATA SHEET

Local extract ductwork required . . . . . . . . . . . . . Scrubbing required . . . . . . . . . . . . . . . . . .

Discharge to central system . . . . . . . . . . . . . . . . . F i l t ra t ion require~ . . . . . . . . . . . . . . . . . . . J

Discharge through watt ( inbu i t t fan) Extract ion rate (m /s ) . . . . . . .

Connection of ductwork to equipt . . . . . .

Connection s ize and type . . . . . . . Type of fumes . . . . . . . . . . . . . . . . . . .

MOUNTING:

Free standing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Watt mounting . . . . . . . . . . . . . . . . . . . . . . .

Static~Mobile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ant iv i rbat ion mounts ( type) . . . . . . . . . Floor f i x ing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete pt inth (m) . . . . . L x W x H . . .

Bench mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Depth of ent)edment of botts . . . . . . . . .

Specify spec i f i c spacing or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

access requirements

SAFETY AND OPERATIONAL CONSIDERATIONS:

Heat (kW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . .

pn Noise (dec ibels) . . . . . . . . . . . . . . . . . . . . . . Dust/Fumes/Vapeurs . . . . . . . . . . . . . . . . . . Chemical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F ire/Explosion . . . . . . . . . . . . . . . . . . . . .

Moving parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biological . . . . . . . . . . . . . . . . . . . . . . . . .

Vibrat ion (frequency) . . . . . . . . . . . . . . . . . . . . . . . Others (speci fy) . . . . . . . . . . . . . . . . . . .

(amplitude) . . . . . . . . . . . . . . . . . . . . . . . (accelerat ion) . . . . . . . . . . . . . . . . . . . . .

ADDIT IONAL INFORMATION/COHNENTS:

Frequency of use of equipment . . . . . . . . . . . . . . . . . . . . . . . . . . .

Duration of usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Please l i s t other users of th is equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wilt th is equipment require: Specia l ist disconnection? . . . . . . . . . . . . . . . . . . . . . . .

Speciat ist reconnection? . . . . . . . . . . . . . . . . . . . . . . . .

Specia l is t commissioning? . . . . . . . . . . . . . . . , . . . . . . .

Specia l is t transport? . .


DEPARTMENT/SECTION - NAME: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

STAFF LEVELS: Indicate split function/responsibilities of staff.

Grade Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FLOOR AREA: (square metres) excluding corridors and common areas etc.

Current/Projected Current /P ro jec ted Of f i ce . . . . . . . . . . . . . . . . . Workshop . . . . . . . . . . . . . . . .

Machine Room . . . . . . . . . . . . . . . . . Lab Wash-Up . . . . . . . . . . . . .

Clean Room . . . . . . . . . . . . . . . . . Computer Room . . . . . . . . . . .

Tank Farm . . . . . . . . . . . . . . . . . S torage - Genera l . . . . . . .

Lockers . . . . . . . . . . . . . . . . . - D isks . . . . . . . . .

Fuel . . . . . . . . . . . . . . . . . - Ac id . . . . . . . . . .

Solvent . . . . . . . . . . . . . . . . . - Pa in t . . . . . . . . .

Temp. Controtted . . . . . . . . . . . . . . . . .

- Process areas - L i s t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Car park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Other - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FLOOR TYPE: No Special Requirement . . . . . . . . . . . . . . . . . . . . . . . . . .

Vehicu lar t ra f f i c (deta i l heavy, tong, awkward toads) . . . . . . . . . . . . . . . . .

Fork L i f t . . . . . . . . . . . . . . . . . . . . Dra in . . . . . . . . . . . . . . . . 9 . . . . . . . . . . . . . . . . . .

Ac id Res is tant . . . . . . . . . . . . . . . So lvent res i s tant . . . . . . . . . . . . . . . . . . . . . .

Stat i c Conductive . . . . . . . . . . . . Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

REQUIRED LOCATION:

Ground F loor . . . . . . . . . . . . . . . . . F i r s t F loor . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Basement . . . . . . . . . . . . . . . . . . . . . . Not Cr i t i ca l . . . . . . . . . . . . . . . . . . . . . . . . . . .

Prox imity to other fac i l i t i es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Other eg. prox imity to other fac i l i t i es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CE IL ING: No special requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Special requirement - act as plenum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

L ight ing - No specia l requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In tegra l . . . . . . . . . . . . . . . . . . . . . . tear drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ye l low . . . . . . . . . . . . . . . . . . . . . . . f l ameproof . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Non-F luorescent . . . . . . . . . . . . . . o ther . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

L ight ing Levels see Room Env i ronment

Figure 7.2 Basic user requirements schedule

7.5 Process/site layout modeling Site and factory layout designs are needed when new installations are being planned or changes to existing facilities are investigated. New layouts are examined when increased efficiency is being sought and when plant managers are planning expansions to the existing installations. There is also a need for plant managers to anticipate the changing requirements of both site and plant over future years.

When a new installation is being planned, the site requirements will be predetermined, but when future expansions are being investigated, a model for sizing is invaluable.

7.5.1 Computer mode l ing

The use of computer models to assist in plant layout decisions can often be helpful, but a clear understanding of what they can and cannot do is needed. Used blindly, they can lead to solutions which are, in some sense, optimal but which have little practical merit.

In discussing the benefits and limitations of modeling we distinguish between three types:

INTERNAL WALLS AND WINDOWS:

In terna l Wat ts - Standard par t i t ion watts unless otherwise stated.

Acoustic . . . . . . . . . . . . . . . . . . . . . Soundproof . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sta in less Steel . . . . . . . . . . . . . . . E lec t ro ~tat i c Discharge . . . . . . . . . . . . . . . .

Other - Non Ref lec t ive? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

EXTERNAL WINDOWS: No Special Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Special Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fixed . . . . . . . . . . . . . . . . . . . . . . . . . Opening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Seated . . . . . . . . . . . . . . . . . . . . . . . . Gr i l l es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Blinds . . . . . . . . . . . . . . . . . . . . . . . . Curtains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

INTERNAL DOORS: No Speciat Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Special Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ROOM ENVIRONMENT: - Not c r i t i ca l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Noise Level 4bdBA ... 4~BA ... 50dBA ... 55dBA .. . 6~BA ... Other ...

Temperature - Non criticat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Special requ i rement . . . . . . . . Temp "C . . . . . . . . . . . to le rances . . . . . . . . . . .

Relative Humidity

Not Critical ................. Special Requ i ren~nt . . . . . . . . . . . . . . . . . . . %

Lighting Leve ls (LUX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cleanliness Based on British Standard 5295 measured at working l eve l :

Class 1 . . . . . . . . . . 2 . . . . . . . . . . 3 . . . . . . . . . . . 4 . . . . . . . . . . . 5 . . . . . . . . .

A i r Lock . . . . . . . . . . . . . . . . . . . . . . A i r shower . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Storage - Lockers . . . . . . . . . . Overa l l s . . . . . . . . . . . . . . . Other . . . . . . . . . .

Secur i ty - secure Area . . . . . . . . . . . . . . . . . . . . . Cont raband . . . . . . . . . . . . . . . .

No Smoking . . . . . . . . . . . . . . . . . . . . . . Controtted . . . . . . . . . . . . . . . . . . . . . . . . . . .

Recorded Access . . . . . . . . Locks . . . . . . . . . . . Gr i l l es . . . . . . . . . . . . . . . . . . . .

Secure Communicat ions System . . . . . . . . . . . . . Other . . . . . . . . . . . . . . . . . . . . . .

GASES:

Oxygen . . . . . . . . . . . . . . . . . . . . . . . Carbon D iox ide . . . . . . . . . . . . . . . . . . . . . . . . .

Nitrogen - Ord inary . . . . . . . . . . High pur i ty . . . . . . . . . . U l t ra pure . . . . . . .

Hydrogen . . . . . . . . . . . . . . . . . . . . . Helium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A rgon . . . . . . . . . . A i r : . . . . . . . . . . . P ress . . . . . . . . . . . (Bars ) . . . . . . . . . . . . .

Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Optimizing calculations for plant layout; 2. Flowsheet models for sizing the individual items of

equipment; 3. Simulation models for understanding the interaction

between different manufacturing units.

Optimizing plant layouts Historically, modeling techniques have had little impact on the problem of designing plant layouts. This has been for two reasons. First, the calculations are difficult, and second, practical constraints and considerations essential to the decision are often ignored.

To understand the mathematics, consider a large empty space into which a number of production units are to be placed, and assume that the major variable to be optimized is the cost of transporting materials between them. If the manufacturing process is essentially a flow-line operation, then the order in which units should be placed is clear (from the point of view of transport costs), and the problem is simply to fit them into the space available. In a job-shop, where materials are flowing between many or all the production units, the decision is more difficult. All the potential combinations of units and locations

SERVICES SUPPORT:

Vacuum pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Water - Town mains ............. Specific pressure . . . . . . . . . . . . . . . . . . .

- So f tened . . . . . . . . . . . . . . . De -minera l i=ed . . . . . . . . . . . . . . . . . . . . . .

-Ch i t ted (open circuit) . Distitted . . . . . . . . . . . . . . . . . . . . . . . . . . .

- Heat ing . . . . . . . . . . . . . . . .

Process cooling water (closed circuit) . . . . . . . . . . . . . . . . . . . . . . .

Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fume Cupboards Ordinary ...... Ordinary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Acid ......................... Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Water Drench . . . . . . . . . . . . . . . . . Rad ioact ive . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

EXTRACTS:

to atmosphere ................ scrubbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

filtered ..................... dedicated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CRANES: (Tonnes)

Overhead ..................... Gantry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Manual ....................... Electric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ELECTRICS:

Total power KW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Process/machine toad KW . . . . . . . No of machines . . . . . . . . . . . . . . . . . . . . . .

Other toad KW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Bus bar system/Trunking system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Phase . . . . . . . . . . . . . . . . . . . . . . 3 phs + Neut ra l . . . . . . . . . . . . . . . . . . . . . . . .

Clean SuppLy ................. Uninterruptabte . . . . . . . . . . . . . . . . . . . . . . . .

Stand-by Generator ........... Emergency Lighting . . . . . . . . . . . . . . . . . . . . .

13A Sockets (do not specify number) ....... with RCC8 . . . . . . . . . . . . . . . . .

Earthing requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Faraday Cage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Special Lightening requirements ...... Other . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONTAMINAT ION: DO you need to be separate from:

Noise ........................ Vibration . . . . . . . . . . . . . . . . ~ : . . . . . . . . . . . .

Electricat Interference ...... Fumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Gases ........................ Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Vibration Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Equipment Specific ........... Room in total . . . . . . . . . . . . . . . . . . . . . . . . . .

Detune S t ruc ture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electro Magnetic Interference Counter-Measures . . . . . . . . . . . . . . . . . . . . . . . .

Electro Magnetic Interference from Satellites aircraft etc . . . . . . . . . . . .

Screened enclosures . . . . . . . . . . GHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 7.2 continued

Process/site layout modeling 7/73

WASTE AND EFFLUENT: (Large quant i t ies - please specify)

Paper ........................ Cardboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Glass ........................ Metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Solvents ..................... Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cutting Fluids ............... Other . . .~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Powders ...................... Radioactive material . . . . . . . . . . . . . . . . . . .

Special wastes . . . . . . . . . . . . . . .

Do you generate contamination? Please specify levels where known:

Noise ........................ Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electrical Interference ....... Fumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Gases ........................ Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

F IRE :

Local Fire regulations wilt apply throughout but special

requirements which need to be drawn to the Fire Adviser~ attention

should be stated below:

No Speciat Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Speciat Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SAFETY HAZARDS - not brought out in answers above: . . . . . . . . . . . . . . . . . . . .

FLEX IB IL ITY : How often do you anticipate changing your layout ... yrs

could be enumerated on a computer and the resultant cost of each option obtained. The number of combinations quickly becomes large, however, and more sophisticated methods, such as branch-and-bound techniques, are required for complex problems.

Alternatively, the location of subsets of plant, within which the layout is assumed to be fixed, could be optimized.

Solutions of this nature ignore practical considerations of noise, hazardous areas, etc. unless these are specif- ically entered as constraints. Furthermore, if the site is geometrically complex, then additional detail will need to be included in the problem formulation.

Flowsheet models for plant sizing

The consistent sizing (i.e. balancing the capacities) of the equipment that is to make up a plant is obviously of importance in the overall design. Models used for this type of decision are usually an extension of the manual calculations that a designer would normally make.

They are based on a network of activities (or machines) with flows of materials between them. Relationships between the activities are expressed in terms of yields or unit consumption and, for a given output of finished products, the required output from each of the other activities can be calculated.

The complexity of the plant and the type and number of sensitivity tests to be carried out will determine whether a formal model or a simple calculation is needed.

Flowsheet models assume that activities operate at a constant rate. This is an important limitation, and may be an oversimplification. To overcome this, simulation techniques can be employed.

These models, however, can be useful if estimates are to be made of operating costs. By assigning fixed and variable costs to each activity, average and marginal unit costs at each stage of the process can be easily calculated, which will assist in decisions regarding pricing policies or whether to buy in components and materials or make them on site. ATPLAN 12 is an example of a network- based model of this type.


Simulation models

Simulation models aim to replicate the workings and logic of a real system by using statistical descriptions of the activities involved. For example, a line may run at an average rate of 1000 units per hour. If we assume that this is always the case, we lose the understanding of what happens when, say, there is a breakdown or a halt for routine maintenance. The effect of such a delay may be amplified (or absorbed) when we consider the effect on downstream units.

A simulation model has 'entities' (e.g. machines, materials, people, etc.) and 'activities' (e.g. processing, transporting, etc.). It also has a description of the logic governing each activity. For example, a processing activity can only start when a certain quantity of working material is available, a person to run the machine and an empty conveyor to take away the product. Once an activity has started, a time to completion is calculated, often using a sample from a statistical distribution.

The model is started and continues to run over time, obeying the logical rules that have been set up. Results are then extracted concerning throughputs, delays, etc.

It is clear that simulation models can replicate a complex production system. They can be used to indicate the level of shared resources needed by the operation (e.g. forklift trucks or operators), the speed of lines, sizes of vessels or storage tanks, etc.

A number of packages are available for quickly building simulation models. HOCUS 13 and SEEWHY TM are two major UK systems. They allow graphical displays to be used to show, for example, the movement of staff and materials between machines. This can be useful for understanding the way in which the operation is reacting to particular adverse circumstances and can assist in designing methods of avoiding them (for example, by building in redundancy).

Simulation models can be expensive to build and the results obtained need to be analyzed with care because they are statistical in nature. For example, two runs of the model may give different results- just as the performance on two real days in a factory can vary. Sufficiently large samples need to be taken therefore for a proper understanding of the performance of the plant.

7.5.2 Model construction

A simple model can be produced using the areas required for the various site activities for different scenarios. These might include redistribution of a company's manufacturing facilities, changes in the market demand, or simply increased factory output.

Constructing the model is an area where innovative effort is needed to maximize the validity of the model. The model will vary from industry to industry, but a simple one can start with a relationship between the number of employee hours and the output produced in each discrete activity area on the site, e.g.

Activity area Output Manning hours Raw material Tonnage/volume No. and shift no.

store handled

Process areas Output tonnage No. and shift no. or volume

Finished goods Tonnage/volume No. and shift no. store handled

Maintenance Specific area No. and shift no. output

Service facilities, electrical sub-station, water treatment, fuel storage, etc. will depend upon process parameters, mainly tonnage or volume handled, and may need to be assessed from the summation of the individual activity areas, but it will be affected by technology when improved techniques are being introduced.

Office accommodation will depend upon the factory manning and the car parking facilities upon the total manning during the day shift.

7.5.3 Model for change

The recent introduction of inexpensive desktop computers has allowed their extensive use throughout many companies. The standard spreadsheet packages which accom- pany these machines enables the above data to be laid out in an interactive way, so that 'what if' situations can be explored at the planning stage and the implications of, for example, market trends in the food industry, to be examined over the long term for its effect on the plant layout. The model may include a factor to take into account improvements in technology and working practices in both the office and factory.

In determining the area required for increased production the relationship between the output and the area may not be linear, and needs to be examined in some detail. When the output required exceeds the maximum output of a process line then increased shift working may be considered. Alternatively, a second process line may be needed.

The model for the maintenance requirements of a large metallurgical plant was recently constructed by relating the man-hours to the production output, but the relationship was not linear, and a more sophisticated model was needed to examine the site requirements for different output tonnage.

Mechanical wear is a feature which is significant among the causes of machinery failure and the James Clayton Lecture delivered to the Institution of Mechanical Engi- neers in 1981 discussed friction and wear and identified tribological losses as 45-50 per cent of all maintenance costs in metallurgical plants. This suggested that mechanical transmission of energy could be investigated to obtain the relationship between production output and the maintenance requirements.

The model equation produced was:

.2 . , xKx

2

107

8

~ 5 =~ 4 0 e- -~.E_ ii 3

2

10 6

Process/site layout modeling 7/75

Efficiency rating (h/ton)

654 3 2

/ / / / / / _ / / / / /.

/ / / / / / / i i / / / / / / / / / /

/ / / I / / I. I I / /

/ / / z

5 6789106 2 3 4 5 6 789107 2

2 1

Y//// /

1.00.9 /0 .8 10.7

v

10.6 10.5

10.4

10 .3

i 0.2 ~

~o.1 ~-

Figure 7.3 (a) Model of manning requirements related to plant output; (b) Sankey diagram of the changing manning requirement in an expanding plant


where

H2 : Future man hours,

H 1 -- Current man hours,

K -- Technology or practices factor,

P2 -- Future production output,

P1 = Current production output.

This produces a global requirement chart and a chart showing the discrete, departmental requirements in Figure 7.3.

New plants and expanding plants rarely produce maximum output on start-up. In large capital plants, it may need many months for staff training and equipment commissioning before output is sufficient to need maximum manning. The technology factor K in the above equation can be used to reflect this. In Figure 7.3(a) a technology factor of 0.9 has been used.

It is important to test models, and in the above case, figures were obtained for other plants and the validity of the model confirmed.

7.5.4 Determination of factory areas

When existing factories are being examined, the floor areas occupied by the various items of equipment can be measured on site during the data-collection period. It is important to consider and include the equipment outline (maximum travels), space for maintenance activity, operator movement and the handling of material and workpieces. In many cases, the space needed for handling exceeds that required accommodating the operative part of the equipment. Aisle space is also needed for through- shop movement.

When planning new installations, manufacturers' cata- logues may be the only information source of equipment data, but they rarely indicate the space needed outside the equipment outline. This requires careful consideration from an experienced facility planner to establish realistic space requirements.

In the absence of reliable information and during the preliminary planning stage (feasibility studies, etc.) the following occupancy values can be employed:

Activity Occupancy (m2/person)

Service industries 15- 30

Manufacturing 20- 35 Machine tool shop 20 Electrical/plastics 25 Mechanical fitting 27 Pottery/glass 35

Transport 30-65 Cars/mobiles 33 Locos 37 Wagon shop 55 Lorries 65

Distributive trades (average) -80

These values will change with the future move towards unmanned factories.

Dividing the areas established in Section 7.5.3 by these occupancy values will give building areas. Bay widths can be established for each type of building and dividing the areas by this width will establish a building length that can be arranged into a convenient building block shape.

7.6 Design synthesis 7.6.1 Plant activities and intercommunications

In 1973, Richard Muther 1 published a method of ana- lyzing the interrelationships of activities within industrial plants, and the method allows a high degree of detail to be examined. The method proposed here is similar in that a relationship grid is constructed, but this technique employs the power of the modem desktop computer to rapidly examine alternative layouts to obtain best solutions.

The design synthesis starts by listing the activities or areas in the plant and indicating the access, which each activity needs to the other activities. The access may be required for internal process, traffic, and people movement or plant services. Rather than go into the detail of examining all interrelationships for all of the above requirements, the experienced layout planner can decide which requirement predominates and employ it to produce quick results. The method allows inexperienced planners to iteratively examine the implications of changing requirements as the project proceeds and plant knowledge increases.

Table 7.1 shows the construction of a typical activity chart using one of many computer spreadsheet packages. The cross (+) identifies an activity in the plant and stars (*) in the vertical lines denote where access to other activities is needed or an interrelationship exists. A wide scat- tering of the stars away from the diagonal line of crosses indicates large distances between the activities and thus large communicating distances.

A feature of PC spreadsheets is that the position of rows or columns can be changed at the touch of a key, so the sequence of the rows of activities can be rapidly altered, and the position of the columns varied to preserve the diagonal pattern of crosses. This exercise can be exe- cuted a number of times to reduce the scatter of the stars away from the diagonal line and reduce the communicating distances between the activities. This has been carried out, and the result is shown in Table 7.2, where it can be seen that the stars are clustered more closely around the diagonal line. The list now shows the activities arranged in a preferred order of sequence.

7.6.2 Location criteria and boundary groups

There may be reasons why individual activities cannot be located near to those which are adjacent in the determined sequential list, so design criteria are needed to determine which activities are compatible and can be near, and which are incompatible and cannot.

Table 7.1 Plant activity intercommunications: first design criteria

Design synthesis 7/77

Activity Access to each other

Heavy p lant repai rs + 9 9 9 9

Veh ic le hot wash ing 9 + 9 9

Veh ic le co ld wash ing 9 + 9 9

Pub l i c hea l th repairs 9 9 + 9

Store for large t ires 9 9 +

Serv ice stat ion 9 9 +

E lec t r i ca l repai rs 9

Bus washer

Veh ic le test area 9 9

Mechan ica l repa i rs 9

T i re shop 9 9

We ld ing shop 9 9

Pane l beater 9

Rad ia tor shop 9 9

Pa in t area

+ 9

+ 9 9 9 9 9

+ 9 9 9 9

9 + 9 9 9 9 9

9 + 9 9 9 9

9 + 9 9 9

, 9 + 9 9 9 9

Compressor house 9 9 9 9 9 9 9 9 9 9 9 9 +

Tai lor + * * *

Carpenter + * * *

S tore -carpenter * + * *

S tore - t i res 9 9 + * *

S tore - ta i lo r * + * *

S tore -pa in t * + * *

S tore -genera l 9 9 9 9 9 9 9 9 9 9 9 * * * * * * * + *

Admin is t ra t ion b lock 9 9 9 9 9 9 9 9 9 9 9 9 9 * * * * * * * * +

F i l l i ng stat ion

Veh ic le park 9 * -t-

Table 7.2 Rearranged activities to improve plant operation

Activity Access to each other

F i l l ing stat ion + 9

Veh ic le park 9 + 9

Bus washer 9 +

Veh ic le hot wash ing

Veh ic le co ld wash ing

Serv ice stat ion

T ire shop

Store - t i res

Veh ic le test area

Compressor house

Admin is t ra t ion b lock

S tore -genera l

Heavy p lant repai rs

Pub l i c hea l th repai rs

Store for large t ires

E lec t r i ca l repa i rs

Mechan ica l repa i rs

Weld ing shop

Rad ia tor shop

Pane l beater

Pa in t area

Store -pa in t

Carpenter

S tore -carpenter

Tai lor

S tore - ta i lo r

-t- , 9 9 9 9 9

-t- , 9 9 9 9 9 9 + * 9 9

+ * 9 , 9 9

9 + * 9 9

9 9 + * 9 9

, 9 9 9 9 + * 9 9 9 9 9 9 9

9 * * * * * -t- * * * * * * * * * * * * * * * 9 * * * * ~ * * * * * * * * * * * * * *

9 9 9 9 9 9 -t- , 9 9 9 9 9 9 + * 9 9 9

, 9 9 , +

9 9 9 9 + *

9 9 9 9 + * 9

9 9 9 9 , 9 q- , 9

9 9 9 9 9 9 -q-

9 * * * * -t- * 9 9 9 9 9 + *

9 * * -t-

* +

-t- ,

, -t-


Particular plants will have characteristics which will determine the importance of particular criteria, but typical criteria will include the following:

1. The hazardous nature of the activity; 2. The ease of access to the entry gate which the activity

needs; 3. The amount ut~'c uli'a'-"t iaiiu~-'a . . . . . . [#utciitxial:~l contamination "'--'tllttt

the activity would generate; 4. The amount of noise and potential disturbance that the

activity will normally generate.

Each of the listed plant activities can be assessed for each of the chosen criteria and a star rating determined for each assessment. An experienced engineer will find that a qualitative assessment is sufficient, but quantitative measurements can be used if necessary. The results of this exercise are shown in Figure 7.4.

For each of the criteria a two-star rating difference between an activity and an adjacent activity is taken to indicate incompatibility. Activities that are hazardous, dirty, noisy or needing good access to the entry/exit gate are consequently rated with many stars. In the site layout they should not be located near other activities with fewer stars because they could adversely affect that activity. However, an activity that is not critical and has a low star rating may be located next to an activity with many stars.

Boundary maps can be drawn around groups of stars which are compatible and horizontal lines drawn through the incompatibility points to show groups of compatible activities on the fight-hand side of the chart Figure 7.4.

Groups of compatible activities together with their major characteristic can be listed, e.g. for a transportation maintenance facility, as follows:

Boundary group Characteristic Filling station Hazardous Vehicle park High traffic density Servicing faeilitia.~ . . . . l')irtva Administration and stores Quiet and clean Repair facilities Medium traffic, dirt and noise Body shop Noisy Accommodation Quiet

The synthesized layout can be described in terms of the characteristics of the various zones within a hypothetical site boundary as shown in Figures 7.5 and 7.6.

Administ ing

Repairs ~t ~ / /~ Park

Filling \ / s a,,on Figure 7.5 Synthesized location of plant activities

Activity Hazardous Gate Access

Dirty Noisy Boundary groups

Filling station Vehicle park Bus washer Vehicle hot washing Vehicle cold washing Service station Tire shop Store - tires Vehicle test area Compressor house Administration block Store - general Heavy plant repairs Public health repairs Store for large tires Electrical repairs Mechanical repairs Welding shop Radiator shop Panel beater Paint area Store - paint Carpenter Store - carpenter Tailor Store - tailor

***K

**** I*1

***F I * **** *** / I * **** ***_J I * **** ** / I*LI ** / I*L

I*****I I***I **i***** I***I I*****, I***I I*I P**I I'***I l***_J I****I I**I I****I I**I- l****k I * * I - -~ I*****I I * * , *1 ~ I *L.. I * * i - / * *1 '

I**I ~ l**['.,,'

i '

i::1

Filling station Vehicle park,

Wash

Tyres Store Test Compressor

Servicing

Admin & Store

Store Electric Repairs

Denter Painter Store

Store

Store

Body shop

Figure 7.4 Compatible activities and boundary groups: secondary design criteria

Quiet, ~ . cl

Low ~ I Medium traff ic~ / t ra f f i c

\ / H~gh. Noise ~ traffec

Hazardous

Figure 7.6 Characteristics of the synthesized layout

7.7 S i te layout rea l i za t ion

7.7.1 Process and traffic flows

Traffic and material movement is a major consideration, and should be arranged so that cross flows are minimized and the potential for congestion and accidents reduced. Much useful information on both the analysis and practice of movements is contained in the References.

Using the example of a transportation maintenance facility, Figure 7.7 shows that a counter-clockwise rotation of the traffic flow could achieve minimum crossing and give a graduation of decreasing traffic density in the counter-clockwise direction as vehicles are diverted off the main stream (Figure 7.8).

The circulation diagram indicates that, in a left-hand drive environment, activities with a high traffic density

Figure 7.7 Ideal traffic or material flow

' ~ ' , ,

I

Site layout realization 7/79

Decreasing traffic density

Low traffic

density

P " - v v v

High traffic

density

v v t v v

Exit/entry

Figure 7.8 Traffic density zones

should be located on the right-hand side of the traffic circulation diagram and the activities with low traffic on the left-hand side.

With this arrangement, the vehicle needing no servicing or maintenance could be parked on the right-hand side of the site in a park designated 'overnight park', and the filling station which handles all the vehicles could be located towards the center of the site in the flow line of the vehicles leaving the area.

The servicing area could be located on the fight-hand side of the site but remote from the gate, and part of the park near to the servicing area could be allocated to vehicles that arrive for their scheduled routine service.

The left-hand side of the site has a reducing traffic density and could thus accommodate the vehicle repair shops. The body shop is a repair function, and thus would be located on the left-hand side but remote from the existing administration office.

The technical administration office needs to be quiet, clean, and central to the facilities that it administers. Hence, it should be located in the central area between the service and repair shops. This is remote from the dirty washing facility and the noisy body shop while providing good access to the gate.

The remaining corner on the left-hand side of the site can be arranged to be sufficient distance from the body shop so that it can be quiet and thus suitable for staff accommodation and the plant administration office. Thus, the synthesized layout becomes as shown in Figure 7.9.

7.7.2 Site constraints

The real design must consider design criteria derived from the physical constraints of the chosen site and the current operating procedures. In this exercise, the site must be examined to list the features of the site, which will affect the plant layout. These will include the contour of the site and the location of the following:


Low traffic

density

Repair area

Store admin.

Repair area

Repaired park

v v v

Garage admin.

Filling station

Service park

~.r~l r _..dr .

Service park

Overnight park

v v v vP . . - -

Low traffic

density

Exit/entry

Figure 7.9 Combination of synthesized layout and ideal flows- garage layout

1. Main highways and access to the site area 2. The main and other gates to the plant 3. Factories near the boundary of the plant 4. Domestic dwellings near the boundary 5. Natural features such as streams 6. Effluent routes 7. Prevailing wind directions.

These can be drawn onto a plan of the site area, which does not show the existing or any proposed arrangement of the plant layout (Figure 7.10).

The site constraints must be considered for their effect upon the design and the practicality of implementing the design. When the plans are for an existing plant, the implementation must consider the minimum disturbance

Domestic ,,,~,

) actories

tl" Effluent Gate

~ R o a d

to the everyday functioning of the existing plant. These limitations can be listed as follows:

1. The location of the gate; 2. The existing buildings that have been found, during the

structural survey, to be structurally sound and which will be retained;

3. The logistics of erecting new buildings and rearrang- ing the plant with minimum disturbance to the plant functions;

4. The requirement to allow for future expansion of the production and subsequent activities in the plant.

As an example, the synthesized design considers all these limitations in the following ways:

1. The gate is taken as a starting point for realization of the layout and high traffic densities are placed near to it;

2. The structural survey dictates which of the existing buildings will be replaced;

3. The final report will need to include a detailed description of the implementation procedure to demonstrate that the synthesized layout is feasible.

The final layout characteristics are shown in Figure 7.11.

7.7.3 Ease of expansion Layout planners normally have to consider that activities within the site may change in the future. The changes may be the result of increased product demand or the introduction of new product lines. They may be predicted from the model designed in Section 7.5.2 or allowance for unpredictable changes may be needed.

The dilemma facing the planner is between designing the layout with minimum distance between buildings and allocating free space between buildings to accommodate future process units. Often the problem becomes one of providing a single building for economy or multiple separate buildings for ease of expansion.

The solution may be a policy decision, but this decision will be assisted by the results of the internal layout con- figurations, which may indicate how simply or otherwise expansion can be accommodated.

c -

.o r

o~ .Q

o

Dirty ~ Traffic

Noise

Figure 7.10 Site constraints Figure 7.11 Conceptual layout design on the real site

7.7.4 Options

Management usually wishes to see alternatives to a particular design in order to say that the alternatives have been considered. Unique design solutions are rare; consequently, the layout planner will normally be able to interpret the results of the finding of the study to show alternative possibilities. Each alternative option should be accompanied by a critique listing the advantages and dis- advantages.

7.8 Internal layouts of buildings Material, traffic and people are involved, and the constraints on internal layouts will be different to those for site layouts but will not affect the design process. The constraints will include organization of the factory work tasks, which may involve trade practices and the type of organization adopted for the control of the process equipment. This is discussed in Section 7.2.

7.8.1 Process flows and performance indicators

The same method as described above can be employed to plan the layout of factory building interiors. Establishing the interior activities and characteristics of the activities must, however, derive from a thorough understanding of the products and processes.

The management of production is well described by Hill, 7 but the prime consideration is product flow, and all features of the layout must assist flow. There are some indicators which can be used to measure the quality of the production facilities, and these can be employed to demonstrate the viability of the proposed new layout.

Performance indicators

The relative importance of each indicator will vary according to the type, quantity, end quality, variety and value of the product and the capital cost, flexibility and required utilization level of the plant. Three variables will serve most industrial processes:

1. The stock value. The value of the stores stock represents a significant investment for many manufacturers and financing the work in progress can represent a significant cost. It is a useful indicator of the financial health of a company and is a prime target for cuts in the drive for increased economic efficiency. Section 7.2 highlighted this.

2. The cycle time. This represents the maximum time interval between the start of a single operation on a product on a particular flow line and the start of the same operation on the next product on the same flow line. The cycle time is calculated by dividing the target production volume (annual or monthly) by the working time (hours, minutes or seconds) and then adjusting for the reject rate and the per centage of lost time (down- time). If every operation is conducted within the cycle time then the steady-state functioning of the flow line will produce the required production rate. The number

Internal layouts of buildings 7/81

of sequential process operations multiplied by the cycle time is the actual process time.

3. The door-to-door time. This represents the total elapsed time from the delivery of the raw materials or component parts to the dispatch of the finished product. This figure can be adjusted to control the value of the stock of materials, parts, work-in-progress (WIP), and finished goods in the process. Dividing the door-to-door time by the actual process time and multiplying the result by the stock value can find the gross excess stock carried. The difference between the gross and the net excess stock values will depend on individual circumstances. Reducing these figures to a minimum requires strategies for purchasing, stock-level monitoring and process control.

7.8.2 Process equipment

When the idealized flow routing has been determined, the equipment must be located and the practicalities of the interrelationships between, and integration of, equipment, services and people must be considered.

Equipment information would have been collected during the data-gathering exercise described in Section 7.4, but a thorough understanding of the process is vital during this phase of the work. Adequate space for the equipment must include:

1. The machine itself with the maximum movement of all machine elements;

2. Space for maintenance activities, withdrawing shafts, etc.;

3. Process material movement; 4. Operator mobility.

7.8.3 Material handling

Knowledge of material-handling techniques is vital to the layout planner, and detailed consideration will need to be given to the various techniques and equipment, which are available. References 2, 8 and 9 contain valuable information and trade journals report the current state of the market.

In the absence of reliable information and during the preliminary planning stage (feasibility studies, etc.) the following space requirements for aisles can be employed:

Traffic type Aisle width (m) Tow tractor 3.7 3-ton forklift truck 3.4 2-ton forklift truck 3.0 1-ton forklift truck 2.75 Narrow-aisle truck 1.85 Manual truck 1.6 Personnel 1.0 Access to equipment 0.85 Allow extra for door openings

7.8.4 Storage

Storage in plants range from simple facilities to fully automated flow-through warehouses. Simple facilities are


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(Site boundary)

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I I

11 kV/415 V transformer

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~" Factory 11 kV distribution

I 11 kV/415 kV transformers / x

MCC boards

Figure 7.12 Typical power distribution system

installed to contain the day-to-day requirements of, for instance, maintenance workers, and the just-in-time supply of components on the production floor. Fully automated flow-through warehouses are employed in the food industry where the shelf life of many products is short and a high throughput is involved. Much has been written about storage and References 8 and 9 are excellent.

7.8.5 Electrical distribution

The plant layout design and whether the processes involve dry, wet or contaminated environments with possibly elevated temperatures will affect the principles adopted

for the support and containment of electric cables and bus bars. Cables from the incoming supply sub-station to load centers would normally be run in the ground, either directly buried with suitable route marking and protection, or in ducts or concrete trenches. Depending on the number of cables, the latter may incorporate support trays or cleats fixed to the trench walls.

Inside the factory buildings, below-floor trenches are frequently the preferred method for main routes, but where there is danger of flooding, due to storms or process fluids, aboveground routing must be considered. Single or few cable runs could be clipped to walls and building struc- tures but multiple cable runs need tray work, involving

space equivalent to major pipes and air ducting, and routing must be coordinated with other services.

Busbar trunking systems are frequently employed in machine shops to facilitate relocation of the equipment. The busbars are located overhead, suspended from the roof structure, and arranged, in conjunction with the lighting system, in a suitable grid pattern. Fused plugs and sockets provide outlets to individual items of equipment.

In some installations (e.g. clean rooms), the electrical distribution system can be located in the sealed ceilings, allowing maintenance access without affecting the clean facilities (Figure 7.12).

7.8.6 Building utilities

These include the canteen, toilets, workers' rest rooms, access routes and the car parks. Hygiene, traffic density, traffic flow and sizing need to be addressed and have been discussed in the section on the sizing model.

7.9 Selling the concept The site layout needs to be presented to management, union, staff and possibly others to obtain approval, and the design procedure described here, together with visualization, will assist the presentation.

Photographs of the proposed site are useful and a site layout drawing is needed, but a perspective artistic impression showing buildings with architectural facades, vehicles and other site activities improves the presentation. Employing three-dimensional models 1~ discussed in Section 7.3 helps communication and allows layout options to be easily demonstrated and discussed.

7.10 Implementation One of the principal tasks facing the manager responsible for implementing a new plant layout is the planning and scheduling of the many activities involved in the project. Modern computerized systems have evolved into easy- to-use tools that avoid the need for a detailed technical knowledge of planning techniques.

Project plans for the installation and commissioning of new plant should be prepared in order to:

1. Provide a readily understood and concise description of the scope of work for all involved in the project in order to facilitate easy communication between all parties;

2. Provide an informative management tool for the monitoring and control of progress, including the effect of changing circumstances that so often occur in the form of extended delivery time scales, revised requirements and new external constraints on the project completion date.

The project plan should be started as soon as possible so that all aspects of the early layout planning can be incorporated into the plan.

Consultants 7/83

Most detailed programs for plant-related projects are prepared using simple critical path analysis (CPA) techniques. CPA is a well-known and familiar technique to most engineers and is incorporated into most modem PC- based planning and scheduling systems. Such a system typically has the following features that a plant project manager will find useful:

1. Easy screen-based data entry of related task details; 2. Ability to allocate material and labor resources to each

activity to allow a picture to be built of the total resource requirements over time;

3. Simple production of bar charts or Gantt charts detail- ing the task time scales;

4. The ability to schedule the tasks logically within the constraints of available resources.

The definition of what constitutes a resource from a scheduling point of view may vary, but would normally include materials, labor, special tools, temporary services and also access to space on the plant floor if the layout is particularly tight. This last item is of great importance, as it is easy to forget that a given amount of space will limit the number of people working in it, and the scheduling system can take it into account when re-scheduling start dates.

For the more sophisticated requirements of complex one-off projects, techniques such as PERT, resource, lev- eling and precedence diagrams should be investigated. 15

The most important aspect of planning the work is that the plan should be constantly monitored for progress and the individuals responsible for particular areas of work should be kept well informed regarding delays or advances in the program.

Frequent updates and reports will ensure that surprises are kept to a minimum and allow smooth progress of the project towards completion. Should problems occur in the project at any time, the modem planning systems allow rapid changes to the logic or task details and the consequent update to the project program.

7.11 Consu l tants

7.11.1 Justification for consultants

Planning the layout of a manufacturing facility should be an infrequent activity for an operational manufacturing company. The staff of such a company will normally be fully committed to the day-to-day activity of assisting factory output, and they will rarely have the time to consider the design problems associated with plant layout. They do have intimate knowledge of the products and processes but not the practice and techniques of the design of plant layout. In these circumstances, it is normal to engage the services of a firm of consultants.

The consultants will need to conduct in-depth discussions with company personnel to acquire the data described above, but will bring to the task the skills of years of practice, often employing modem computing techniques, knowledge of industrial trends and undivided attention to the task.


The best way to select a consultant is to seek recommendations from other companies who are known to have carried out a similar exercise. Failing this, a useful guide is the Association of Consulting Engineers Year- book, which lists the consultants classified according to the type of engineering work they engage in and their specialist discipline. An altemative approach is to con- tact associations set up to serve particular industries (e.g. the Production Engineering Research Association (PERA) in Melton Mowbray for engineering production and the Rubber and Plastics Research Association (RAPRA)).

The consultant will discuss and determine the objectives of the activity, but it is useful if a specification is prepared in advance of the consultant being engaged.

7.11.2 Specification

After a short introduction to the company and its products, the specification should describe in some detail the reasons why a new layout is needed. This will vary from the introduction of, or change to, new products, the establish- ment of a new factory or the need to explore the changing future demands on an existing site because of changing technology or market forces and opportunities. (Contracts are described in detail in Chapter 8.)

References

Literature

1 Muther, R., Systematic Layout Planning, Van Nostrand Reinhold, New York.

2 Tompkins, J. A. and White, J. A., Facilities Planning, John Wiley, New York; see also Neufert, E., Architects' Data, Halsted Press, New York.

3 Schonberger, R. J., Worm Class Manufacturing, The Free Press, New York.

4 Goldratt, M. and Cox, J., The Goal, Scheduling Tech- nology Group Ltd, Middlesex.

5 Francis, R. L. and White, J. A., Facility Layout and Location, Prentice-Hall, Hemel Hempstead.

6 Health and Safety; The Control of Substances Hazardous to Health Regulations 1988, HMSO, No. 0110876571.

7 Hill, T. J., Production~Operations Management, Pren- tice-Hall, Hemel Hempstead.

8 Drury, J., Factories Planning, Design and Moderniza- tion, The Architectural Press, London.

9 Material Handling, Reed Business Publishing, Surrey.

Scale models (proprietary systems)

10 Modulux Systems Ltd, Northampton; Lego symbolic constructions on a fiat baseboard.

11 Visual Planning Systems Ltd; Cast aluminum scale models of actual equipment.

Software programs

12 ATPLAN; W. S. Atkins Consultants Ltd, Woodcote Grove, Ashley Road, Epsom, Surrey KT18 5BW.

13 HOCUS; PE Consultants, Egham, Surrey. 14 SEE-WHY; ISTEL, Redditch, Warwickshire. 15 PERTMASTER; Pertmaster Intemational Ltd,

Bradford.

planning and plant layout

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