Transiflo and MACuGuard

Mechanical Plating

And

Galvanising

March 2003

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All statements, technical information and recommendations contained herein are

based on tests we believe to be reliable, but the accuracy or completeness thereof is

not guaranteed. No statement or recommendation shall constitute a representation

unless set forth in an agreement signed by the officers of seller and manufacturer.

The following warranty is made in lieu of all other warranties, express, implied or

statutory:

Products are warranted to be free from defects in material and workmanship at the

time sold. No warranty is made regarding the performance of any product. The

sole obligation of the seller and manufacturer under this warranty shall be to

replace any product defective at the time sold. Under no circumstances shall

manufacturer or seller be liable for any loss, damage or expense, direct or

consequential, arising out of the use of or inability to use the product.

No suggestion for product use nor anything contained herein shall be construed as a

recommendation to use any product in infringement of any patent rights, and seller

and manufacturer assume no responsibility or liability for any such infringement.

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Contents Page

General Description

Mechanical Plating

Mechanical Galvanising

Advantages of the Transiflo Mechanical Plating Process

Advantages of Macuguard Mechanical Galvanising

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History

Avoiding Hydrogen Embrittlement

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Other Transiflo and Macuguard Benefits

Mixed Metal Coatings

Thicker Coatings

Sheradizing Disadvantages

Hot Dip Galvanising Disadvantages

Mechanical Plating/Galvanising

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Theoretical Principle of Mechanical Plating 11

The Principle of Mechanical Plating Chemistry

The Surface Conditioning Steps/Removal of Oxide

Application of Copper Flash

Promoter and Flash Coat Step

The Mechanical Deposition Step

Principle Process of Application

Surface Conditioner – Acid Descale

Surface Conditioner – Copper Flash

Mechanical Plating Promoter

Flash Metal Coating

Zinc Metal Plating

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Typical Mechanical Plating Cycle

Zinc Plating 6 – 20 microns

Inverplex Plating 10 microns

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Liquid Delivery System 19

Ancillary Process Additives

Macuguard FP

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Equipment for Mechanical Plating

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Plant Schematic Drawings 21-22

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General Description of the Process

Mechanical Plating

Mechanical Plating is a method of plating,which utilises mechanical energy to deposit

metal coatings onto metal parts. In general, parts, glass beads, water, chemicals, and

metal powder are tumbled together in rotating barrels to obtain the desired coating. The

process is used primarily to provide ferrous-based parts with protective coatings of zinc,

aluminium* and tin* as single layers or in combination. Decorative coatings of brass are

also available. Parts treated by this method are most often small parts, which are typically

handled in bulk.

Parts which have been degreased are tumbled in chemically resistant lined barrels with

water, glass bead impact media, and surface conditioners which clean and activate the

base metal before the addition of a promoter. The promoter chemical serves to clean the

metal powders and control the size of the metal powder agglomerates that are formed.

The mechanical energy generated from the barrel's rotation is transmitted through the

glass impact media and causes the clean metal powder to be cold welded to the clean

metal parts, thereby providing an adherent, metallic coating. The Transiflo Mechanical

Plating System is economically beneficial over previous Mechanical Plating methods in

that the rinsing stages between descaling, coppering and the plating steps are eliminated,

saving both water and time.

Single layers of aluminium or tin do not sacrificially protect steel substrates.

Mechanical Galvanising

Modification of the Transiflo chemistry has allowed the mechanical zinc plating thickness

range (6-25 microns) to be extended to cover the range 25-110 microns.

Mechanically deposited coatings of zinc within this range are known as MACuGuard

Mechanical Galvanising. The principle of the process is exactly the same as for

mechanical plating except that:

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a) Modified chemicals are used,

and

b) Multiple additions of zinc powder are added during the cycle.

Advantages of the Transiflo Mechanical Plating Process

Produces corrosion resistant coatings to satisfy most specifications.

Excellent adhesion and uniformity.

Freedom from hydrogen embrittlement.

Easily plates sintered metal parts, without the need to impregnate.

Different metal coatings can be applied on a batch to batch basis in the same

equipment.

Eliminates analytical process control requirements.

Simple waste treatment; no cyanides or complexing chemicals.

Mixed metal coatings or sandwich coatings may be applied to meet specific higher

corrosion resistant applications.

Thicker coatings can be applied without significant cost increases.

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Advantages of MACuGuard Mechanical Galvanising

Improved coating uniformity compared with other traditional thick zinc coating

processes.

Excellent part to part coating thickness consistency.

Low energy, room temperature process.

Freedom from hydrogen embrittlement.

No stickers.

Small components can be easily processed.

Coating thickness can be accurately controlled at any value within the range 20-110

microns.

No softening of hardened components.

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History

Avoiding Hydrogen Embrittlement:

Sacrificially protective coatings of zinc and cadmium have long been established as the

satisfactory choice for a protection system for steel, especially for those components such

as nails, screws, washers etc., that could be damaged during assembly. Today cadmium is

out of favour due to the health and safety aspects of the metal, whereas zinc alone or co-

deposited with other metals and topcoats has been found to be acceptable for use.

The established technique for applying thin coatings of zinc has been that of

electrodeposition, on parts racked or bulk processed in barrels. Electrodeposition of zinc

has taken place in aqueous solutions based on alkaline cyanide, alkaline zincate or

chloride zinc, together with proprietary brightener systems which have produced bright

metallic coatings at a reasonable cost. These types of solutions have proven to be the

work-horse of the corrosion protection industry.

Unfortunately the use of these solutions and their associated process systems will by their

electrochemical behaviour, produce hydrogen during deposition of the zinc, i.e. cathode

efficiencies of less than 100%. With unhardened steel this hydrogen does not normally

cause a problem. Hardened steel components however, of hardness greater than

Rockwell 32C, (318 Vickers or 301 Brinell) or tensile strength of greater than 1000

N/mm2 can be affected by this hydrogen.

Hydrogen absorbed into hardened steel structures can cause a brittle fracture mechanism

known as ‘hydrogen embrittlement’ whereby components unexpectedly break under load

conditions much less than the design maxima of the unplated parts. This phenomenon

can be explained more, in the attached study, carried out using different protective

finishes.

Therefore for safety critical applications, i.e. automotive braking steering, seat belt

components etc., this risk of hydrogen embrittlement failure is unacceptable.

The Transiflo Mechanical Plating Process was developed to offer the automotive

engineer, the first, commercially available, non-electrolytic technique for applying

corrosion protective coatings of zinc on critical hardened steel components. Since its

inception the Transiflo Mechanical Plating System has gained the acceptance and

confidence of the worlds automotive manufacturers as a method of applying corrosion

resistant coatings without the risk of hydrogen embrittlement.

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Other Transiflo and MACuguard Benefits

As well as the major feature of the mechanical plating process avoiding hydrogen

embrittlement, there are further features for which the design engineer should be made

aware.

The Transiflo Mechanical Plating Process does not suffer from ‘line of sight’ or throwing

problems. Internal diameters can be better plated, than by electroplating processes; thread

profiles are more uniformly plated.

As a result, several applications exist where tubes and other parts with holes in them have

been mechanically plated successfully. Also, mechanically plated bolts and/or nuts can

be tightened more securely at lower torque loadings.

Normally difficult substrates such as castings or porous materials, such as sintered metals,

can be mechanically plated easily. The process does not suffer any hydrogen overvoltage

problems like electroplating zinc, and because the mechanical plating process operates at

a ‘constant’ pH and temperature, it stops ‘pores’ acting as thermal pumps, entrapping

incompatible hot and/or cold chemicals within the structure of the base material. There is

no ‘spotting out’.

Mixed Metal Coatings

Most soft, easily chemically cleaned metals can be deposited using the mechanical plating

process.

Applications exist where specific mixtures or layers of coatings are applied, e.g.

Zinc-Tin

Tin-Zinc

Zinc-Aluminium

Zinc-Brass

All can be tailored to suit particular environments, or for such applications whereby steel

fasteners are used to fasten into aluminium substrates.

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Thicker Coatings

Zinc is one of the most widely accepted coatings for protecting steel against corrosion.

In principle, the protection offered by zinc, is proportional to the coating weight or

thickness applied.

Although the electroplating process is the most commonly used coating technique, it is

only economically viable for applying thin coatings (12-15 microns maximum).

For coatings thicker than this it is normal to use other methods of applying zinc metal.

The thicker coatings utilise hot dip galvanising whilst the intermediate coating

thicknesses use sherardizing.

Each method of coating process has its own advantages and disadvantages. The main

advantages are theoretical cheapness; the disadvantages are as follows:

Sherardizing Disadvantages:

Iron-zinc alloy coating

Dusty surface

Difficult to apply uniformly

High temperature process, can cause softening and/or distortion of components

High energy consumption

Hot-dip Galvanising Disadvantages

Brittle intermetallic Fe/Zn compound formed

Difficult to apply smoothly or uniformly onto small components

Sensitive to certain silicon ‘killed’ steels

Distorts components such as nails

High temperature process can soften components

Flat or small components tend to stick together

High energy consumption

Use of scrubbers for fume emissions

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Short plant life

Molten zinc is hazardous

Coating thickness, is controlled by shape, and heat capacity of the component

Mechanical Plating/Galvanising

Transiflo and MACuguard Mechanical Plating Processes have become established as a

universal zinc coating technique with the versatility of using one piece of equipment to

provide a range of zinc thicknesses from plating to galvanising, and not just an eliminator

of permanent hydrogen embrittlement, for the reasons of:

It is a room temperature process which cannot soften or distort components

Small parts cannot stick together

Coating thicknesses can be controlled to an average value between 5 and 110 microns

Smooth, uniform and consistent part-to-part coating thicknesses can be applied

Simple, low cost, low energy use

Less hazardous equipment required

100% metallic zinc coating

Equal or better thickness for thickness corrosion resistance than other zinc coating

processes

The same piece of equipment can also be used for applying other finishes, whether single

or mixed metal, layered or co-deposited.

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Theoretical Principle of Mechanical Plating

As the name of the process suggests, mechanical plating takes place by the transfer of

energy from a multi-sided barrel into an impact and sliding energy of contact between a

glass bead, a metal powder particle and a prepared component surface.

The diagram represents the point of energy of contact between a 6 micron particle of zinc

powder particle and a 200 micron diameter glass bead, (one of up to four different sizes in

a standard mix. The largest being 4.5mm diameter).

Cohesive bonding takes place between the lattice of the particle, and the lattice of the

substrate surface. The continuing mechanism of particle attachment forms adhesion and

compaction thus building layers of particles to achieve plating thickness.

Substrate

Copper Layer

Flash Coat

6 Metal

Particle

200

Glass

Bead

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The factors required for this mechanism to take place are:

Correctly cleaned and prepared component surfaces

Correct chemical environment

Clean metallic powder of the correct shape, size and purity

Clean glass media

Sufficient glass media of the correct shape, size and possessing sufficient impact

energy

If one or more of the above requirements are not met, then the process of metal deposition

will be impaired or not take place.

1. Principle of The Mechanical Plating Chemistry

The Transiflo and MACuguard Mechanical Plating systems utilise the following process

steps:

1) Surface Conditioning

2) Promoter and Flash Coating

3) Mechanical Deposition

Note:

Steps 1 and 2 are mainly chemical functions, whereas step 3 is mainly a

mechanical and chemical function. All the steps occur in a rotating multi-sided

barrel in the presence of glass beads. The processing steps are sequential, i.e.

there is no intermediate rinsing or removal of the parts from the barrel.

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The Surface Conditioning Steps

Removal of Oxide

The chemical equation controlling this step is represented by:

FeO + 2H+ Fe + H2O

Fe2O3 + 6H+ 2Fe+++ + 3H2O

At this preliminary stage there are other chemicals present which:

Act as detergents to remove light surface oils

Provide inhibitors to prevent the formation of hydrogen, as represented by-

Fe + 2H+ Fe++ + H2

Inhibitor

Application of Copper Flash

An adherent immersion copper deposit is applied to the oxide-free surface, as represented

by:

Cu++ + Fe Cu + Fe++

Reaction rate is controlled by the inhibitor, which is contained in the first surface

conditioner.

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Promoter and Flash Coat Step

A salt of a noble metal is added followed by an addition of metal powder to produce a

metallic ‘flash’ coating, as follows:

M++ + Zn M + Zn++

The Mechanical Deposition Step

The process operating in an inhibited acid environment permits:

ZnO + 2H+ Zn++ + H2O

to leave a clean oxide free zinc surface, but prevents:

Zn + 2H+ Zn++ + H2

Inhibitor (from the promoter)

The acid environment must be maintained at a pH of <2.0 for the zinc surfaces to remain

clean and active, for cold welding to take place.

Principle Process of Application

All the process chemistry described previously is provided by the sequential addition of

specially formulated MacDermid chemicals and zinc powder.

The overall function of these chemicals can be described as:-

Surface Conditioner – Acid Descale

The range of Transiflo and Macuguard liquid surface conditioners, are formulated with

mineral acids, surfactants and inhibitors. The consumption of surface conditioner is

added at a specific ml/sqm addition rate dependent upon the system being employed.

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The function of this material is to remove surface oxides and to control the pH of the

process, maintaining it <2.0 during the subsequent metal deposition step.

Surface conditioners are only designed to remove light oil traces and light scale, heavier

contaminants should be removed in a suitable pre-cleaning step before loading into the

mechanical plating barrel.

Normal Processing Time is 5-10 minutes.

Surface Conditioner – Copper Flash

Copper flash additives have been formulated in both liquid and solid form dependent

upon the Transiflo or MACuguard system being employed. They are formulated using

either mineral acids or acid salts together with a source of copper ions and an inhibitor.

The addition rate in units/sqm of the copper flash material used varies with the system

employed and to some degree the base material being processed.

The function of the copper flash material is to further remove oxides from the surface of

the steel components and, when clean, deposit a thin adherent layer of copper metal.

This surface eliminates any metallurgical variations, in the components to be plated, e.g.

high/low carbon steels, sintered metals, castings, etc., and provides a consistent

chemically active surface to initiate further mechanical/chemical reactions.

The speed of deposition and the colour of the metallic copper coating serves as an

indicator of the activity of the surface and the cleanliness of the plating environment, e.g.

beads, part surface, etc.

Normal Processing Time is 5 – 10 minutes

Mechanical Plating Promoter

The promoter chemistry used in the Transiflo and MACuguard processes is supplied as a

liquid or solid product dependent upon the mechanical plating system being used. It

contains a salt of a noble metal, an inhibitor and a dispersant.

The addition rate of this material in units/sqm varies with the mechanical plating system

being employed.

The function of the promoter is to provide a source of noble metal ions, to disperse and to

maintain the subsequently added zinc powder free from oxide. The inhibitor is designed

to slow the dissolution of zinc, in the acidic plating environment.

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Normal Processing Time is 1 – 2 minutes

Flash Metal Coating

Zinc metal powder to MacDermid Specification MP15 is added at the rate of 4.6g/m2 of

component surface area contained within the barrel.

The function of the MP15 zinc powder at this stage is to initiate the deposition of the

noble metal ions in the solution as an adherent thin metal film on the coppered surface of

the steel components.

Normal Processing Time is 5 minutes

Zinc Metal Plating

Zinc metal powder (to MacDermid Specification MP15) is added to the barrel at a rate of

7.7g zinc/square metre of work in the barrel/micron of deposit required. As an example

of this; if the load surface area is 20 sqm and the desired thickness of zinc deposit is 10

microns, the calculation would be:

7.7 x 20 x 10 = 1540

Therefore the required amount of zinc powder added to achieve the desired thickness of

deposit, (10 microns) would be 1540gms.

The function of the MP15 zinc powder is to provide sufficient metal powder particles to

be cold welded, and compacted to produce a uniform zinc coating of the desired

thickness.

With mechanical plating systems the maximum zinc thickness obtained is 25 microns.

No more than 5 micron equivalent amounts of zinc powder should be added at any one

time. There should also be an interval of up to 7.5 minutes between zinc additions

dependent upon the energy available in the barrel. Once the last addition of zinc powder

has been added to the barrel, the zinc metal should be allowed to deposit and compact

over a period of 10-30 minutes dependent upon part type.

At the end of the plating sequence there is a nominal 10 minute plate down time to allow

maximisation of metal powder deposition and the compaction of the deposit to the

component substrate.

Once complete either before or after the first decant of chemistry water is added to the

barrel and the parts, media and liquid are tumbled slowly to polish the surface of the

components. This may take 5 – 10 minutes.

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Typical Mechanical Plating Process Cycle

Zinc Plating 6 – 20 Microns

1. Load oil free parts and media

2. Adjust water level (18C - 25C)

barrel angle and speed

3. Add appropriate surface conditioner

at calculated addition 5 – 10 mins

4. Add coppering agent at calculated addition 4 – 8 mins

5. Add promoter at calculated addition 0’30 – 2 mins

6. Add zinc flash at 4.6gm/m2 5 mins

7. Add zinc plating metal at 7.7gm/m2/micron 15 – 30 mins

** The pH must be maintained below 2.0 preferably below 1.5 for the above

processing stages.

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Inverplex Plating 10 Microns

1. Load oil free parts and media

2. Adjust water level (18C - 25C)

barrel angle and speed

2. Add appropriate surface conditioner

at calculated addition 5 – 10 mins

3. Add coppering agent at calculated addition 4 – 8 mins

5. Add promoter at calculated addition 0’30 – 2 mins

6. Add zinc flash at 4.6gm/m2 5 mins

7. Add zinc plating metal at 53.9gm/m2 10 – 20 mins

8. Add tin plating metal at 24.3gm/m2 15 – 30 mins

** The pH must be maintained below 2.0 preferably below 1.5 for the above

processing stages.

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Liquid Delivery System

The development of liquid chemicals was in response to an industry need for automation.

Machine sizes utilising load weights of 1000Kg have become more common. This in

turn can equate to zinc additions of up to 100Kg per load. Operators can be relieved of

some of the repetitive tasks by use of the LDS system. The process cycle is more

accurately controlled and the operator becomes more productive.

Ancillary Process Additives

MACuGuard FP (Torque/Tension Additive)

MACuGuard FP is a product that is added during the plating cycle, which becomes an

integral part of the coating system. The resultant lubricated coating is dry (non-tacky),

non-evaporating, non-toxic and colourless. It does not affect post chromate treatments

and will remain on the parts indefinitely, until ready to use, even if the parts become wet

before assembly.

As with any mating surfaces the lubricant film should be applied to all components so

that the application torques are completely reproducible, and able to meet virtually any

industry standard torque tension requirement.

Recommended Quantities

The amount of MacuGuard FP required will depend on a number of variables:

The particular torque-tension relationship required

The type of plated surface to be treated

Generally the amount of MACuGuard FP will be determined by experimentation. It has

been found that most applications require between 0.5-5.0gm/m2 to provide adequate

lubricity.

Recommended Process Cycle

MACuGuard FP is added directly to the mechanical plating barrel normally being mixed

and added with the last 5 microns equivalent of metal powder. Once the plating cycle is

complete, the parts may be rinsed and separated from the media, chromated (if required)

and dried.

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Equipment For Mechanical Plating

MacDermid do not manufacture mechanical plating equipment, but work closely with the

manufacturers, in order to provide the best suitable equipment for the plater.

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Courtesy of NES Equipment

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Courtesy of NES Equipment