teknologi las kapal shielded metal arc welding. teknologi dan rekayasa shielded metal arc welding...

Teknologi Las Kapal

Shielded Metal Arc WeldingShielded Metal Arc Welding

Teknologi dan Rekayasa

Shielded Metal Arc Welding(SMAW)

Manual arc welding Heat for welding generated by electric arc established

between flux-covered consumable metal rod (electrode) and work

Called stick electrode welding Combustion and decomposition of electrode creases

gaseous shield Protects electrode tip, weld puddle, arc, and highly heated

work from atmospheric contamination• Additional shielding provided by covering of molten slag

(flux)


SMAW


SMAW Advantages

Equipment less complex, more portable and less costly

Can be done indoors or outdoors, in any location and any position

Electrodes available to match properties and strength of most base metals

Not used for welding softer metals Not as efficient in deposition


SMAW Operating Principles

Sets up electric circuit

Includes welding machine, work, electric cables, electrode holder and electrodes, and a work clamp

Heat of electric arc brings work to be welded and consumable electrode to molten state

Heat intense: as high at 9,000ºF at center


Welding Process

Electric arc started by striking work with electrode Heat of arc melts electrode and surface of base

metal Tiny globules of molten metal form on tip of

electrode and transferred by arc into molten pool on work surface

After weld started, arc moved along work


SMAW Operating Principle


AC Welding Machine

Most common type found in homes, farms, etc.

Good for farm repairs, light jobs.

Low cost


DC Welding Machine

Often generator type machines

Diesel or gasoline engine driven

Portable Expensive


AC/DC Welding Machine

Can weld in AC or DC polarity

Less expensive than DC machine

Quieter than DC machine


Welding Power Sources

Each type of power source has fundamental electrical differences that best suit particular processes

Welding machine

Must meet changing arc load and environmental conditions instantly

Must deliver exact amount of electric current precisely at right time to welding arc

Available in wide variety of types and sizes


Welding Power Sources

Also known as power supplies and welding machines Two classifications

Output slope• Whether constant current or constant voltage

Power source type• Transformer• Transformer-rectifier• Inverter• Generator


Type of Output Slope

Two basic types

Constant current

• Referred to as variable voltage

Constant voltage

• Referred to as constant potential


Output Slope

Relationship between output voltage and output current (amperage) of machine as current increased or decreased

Also called volt-ampere characteristic or curve Largely determines how much welding current will

change for given change in load voltage

Permits welding machine to control welding heat and maintain stable arc

Indicates type and amount of electric current designed to produce


Typical Output Slopes


Four Types of Power Source

Engine-driven generators

Powered by gas or diesel combustion engine Can be found with a.c. or d.c. electric motor

• No longer being manufactured and rarely found Transformer-rectifiers

Use basic electrical transformer to step down a.c. line power voltage to a.c. welding voltage

Welding voltage then passed through rectifier to convert a.c. output to d.c. welding current

May be either d.c. or a.c.-d.c. machines


Four Types of Power Source

A.C. transformers

Used to step down a.c. line power voltage to a.c. welding voltage

Inverters

Increases frequency of incoming primary power

Constant current, constant voltage, or both

Produce a.c. or d.c. welding current


Constant Current Welding Machines

Used for shielded metal arc welding

Current remains fairly constant regardless of changes in arc length

Called drooping voltage, variable voltage, or droopers

• Load voltage decreases as welding current increases


Constant Current Output Slope

Constant current welding machines

Steep output slope Available in both d.c. and a.c. welding current

Steeper the slope, the smaller current change Enables welder to control welding current in specific

range by changing length of arc


Constant Current Output Slope


Open Circuit and Arc Voltage

Open circuit voltage runs between 50-100 volts Drops to arc voltage when arc struck

Arc voltages

Range: 36 volts (long arc) to 18 volts (short arc) Determined by arc length held by welder and type of

electrode used Arc lengthened, arc voltage increases and current

decreases


Open Circuit and Arc Voltage

Open circuit voltage on constant current machines higher than on most constant voltage machines

Arc voltage depends on physical arc length at point of welding and controlled by welder

Shielded metal arc welding Arc voltage much lower than open circuit voltage


Polarity Switch

Electrode negative and electrode positive used in d.c. welding

DCEN (d.c. electrode negative)

Electrode connected to negative terminal of power source and work connected to positive terminal

DCEP (d.c. electrode positive)

Electrode connected to positive terminal of power source and work connected to negative terminal

Switch changes to either electrode positive or electrode negative


Volt-Ampere Meters

Sometimes serve dual purpose

Can indicate polarity as well as current Others, individual meters for volts and amperes Some, single meter that indicates both volts and

amperes• Button engaged to get individual readings• Would need second person for monitoring

Increased demand for additional devices so meters have been discontinued by some manufacturers


Current Controls

Amperage Quantity of current Determines amount of heat produced at weld

Voltage Measure of force of current Determines ability to strike an arc and maintain its

consistency Two types of dual control generators

Tapped-step current control Continuously variable current control


Dual Continuous Control

Coarse adjustment dial continuously adjusts current Fine dial adjusts both current (amperage) and open

circuit voltage

Operator adjusts output slope for given current setting by manipulating both coarse and fine adjustment dials together

Wheel or knob on both amperage and voltage setting devices gives welder continuous control of both


Power Supply Ratings

Standards set The National Electrical manufacturers Association Occupational Safety and Health Administration

Provide guidelines for manufacture and performance of power sources

Rated by Current output Open circuit voltage Duty cycle


Current Output

Rated on basis of current output in amperes Amperage range

200 amperes or less for light or medium work


Open Circuit Voltage

Maximum allowable used for manual welding

80 volts for a.c. or a.c.-d.c. machines 100 volts for d.c. machines

• Very smooth output (less than 2% ripple) Automatic machine welding

Some constant current machines rated up to 125 Constant voltage types normally rated from

15 to 50


Duty Cycle

Percentage of any given 10-minute period that machine can operate at rated current without overheating or breaking down Rating of 100% means machine can be used at rated

amperage on continuous basis• Required by continuous, automatic machine

welding Rating of 60% means machine can be used at its

capacity 6 out of every 10 minutes without damage• Satisfactory for heavy SMAW


Efficiency

Relationship of secondary power output to primary power input

Indicated in percent Determined by losses through machine when

actually welding at rated current and voltage Average efficiencies

Motor generator welding machines: 50% Transformer-rectifier: 70% Inverter: 85%


Power Factor

Measure of how effectively welding machine makes use of a.c. primary line power Primary power used divided by amount total drawn Expressed in percent

Three-phase d.c. transformer-rectifiers: 75% Single-phase a.c. power units: 55% Welding machines can be purchased with power

factor correction


Power Cable

Conductors of ample capacity and adequately insulated for voltage transmit power

Necessary to ground frame of welding machine

Portable cable with extra conductor fastened to machine frame on one end and solid ground on other

Important cable adequately insulated with tough abrasion-resisting insulation

Stand up under rough usage in welding shops


Electrode and Work Cable

Required to complete electric circuit between welding machine and work

Electrode cable (welding cable) attached to electrode holder

Work cable attached to work Rubber-covered multistrand

copper cable generally used

Must have high flexibility


Cable Core Construction

Woven of thousands of very fine copper wire

Greater the number of strands the more flexible Components

A.Wires stranded for extra flexibility

B.Paper wrapping around wiresallows conductor to slip withinrobber covering when bent

C.Extra strength from open-braidedreinforcement of extra cotton cords

D.Special composition and curing of heavy rubber covering


Work Cable

Not necessary to have flexibility of electrode cable Usually same cable used

Important considerations Amperage of welding machine Distance from work

Larger cable Greater the amperage and greater the distance Resistance increases as diameter of cable decreases


Cable Lugs

Required on both electrode cable and work cable

Soldered or fastened mechanically Connections MUST be tight and secure


Work Clamps

Variety of structures to be welded; many types of clamps may be used

Copper hook, heavy metal weight, C-clamp Specialized work clamps

Lenco dba NLC. Inc.

Lenco dba NLC. Inc.

Spring loaded C-clamp


Metal Electrode Holders

Device used for holding electrode mechanically Conveys electric current

from welding cable to electrode Insulated handle protects hand from heat Jaws of holder grip electrode at any angle Made of metal with high electrical conductivity and

ability to withstand high temperatures


Metal Electrode Holders

Jaws can be replaced with new ones Should be light in weight, well-balanced and have

comfortable grip Size of holder must be in line with size of welding

machine Fully insulated so stays cool even with high duty

cycles


Spring Type Electrode Holder


Short-stub Electrode Holder

Cable connections

Special extruded copper-alloy body

High welding current conductanceOne-ton pressure contact

Lifeguard insulation

Entirely insulatedBernard Welding Equipment Co.

Holds electrodes burned to very short stub.Twist-type locking device permits electrode-gripping power in excess of 2,000 pounds.


Knowledge is the key to success

teknologi las kapal shielded metal arc welding. teknologi dan rekayasa shielded metal arc welding...

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