Welding / Welders

• FOR FILTER LENS SHADE NUMBERS >AIR CARBON ARC TORCHES & ELECTRODE GUIDE
• SILVER SOLDERING COPPER TO COPPER BRAZING
• WELDING MACHINE DUTY CYCLES
• WELDING ELECTRODE STORAGE CONDITIONS
  RE-DRYING PROCEDURES - HOT BOXES AND OVENS
• GAS WELDING & CUTTING SAFETY PRACTICES
• STAINLESS STEEL WELD CLEANER
• WELDING SAFETY INFORMATION
• TROUBLESHOOTING GUIDE ON WELDING EQUIPMENT
• GAS TUNGSTEN ARC WELDING (GTAW)
  TUNGSTEN INERT GAS (T.I.G.) WELDING
• GAS METAL ARC WELDING (GMAW)
  METAL INERT GAS WELDING (M.I.G.)
• CONSEQUENCES RESULTING FROM INCORRECT USE OF WELDING ACCESSORIES
• DIRECT CURRENT (D.C.) STICK INVERTERS

WELDING SAFETY CHECKLIST

GUIDE FOR FILTER LENS SHADE NUMBERS

As a rule of thumb, start with a shade that is to dark to see the weld / cut zone.

Then go to a lighter shade which gives sufficient view of the weld zone without going below the minimum recommended shade .

AIR CARBON ARC TORCHES & ELECTRODE GUIDE

The ARC AIR gouging process does not depend on oxidation and therefore works well on all metals regardless of how rapidly they oxidize. Metal can be removed at approximately 5 times faster by arc gouging than other mechanical means. For example, a 9.5mm groove can be gouged at a speed of more than 300mm per minute. The depth of cut/gouge can be controlled closely and welding slag does not deflect or hamper the cutting/gouging action, as it would be for cutting tools. The cost of operating gouging equipment is generally less than for chipping/cutting tools or gas cutting system and the arc equipment require less space. An arc air gouged surface is clean and smooth and can usually be welded without further preparation.

The correct use of arc-air gouging with carbon based electrodes apparently causes no ill effects insofar as carbon pick-up, corrosion resistance or distortion are concerned. The chemical changes produced by the process are similar to those produced by the arc welding process, that is, a thin hardened zone may appear on some metals but the subsequent welding re-melts this zone and reduces the hardness. Copper contamination from the copper cladding on the electrode has not been detected. Heat penetration is shallower than with oxygen/acetylene cutting/gouging, so arc-air gouging produces less distortion. Machinability of low carbon non-hardenable steel is not affected by arc-air gouging. The surface of cast iron and high carbon steel may be rendered un-machinable by the process. This hard layer, however, is generally Excluding - 0.15mm thick and can be easily removed by a cutting tool set to penetrate beyond this depth.

Any process where molten metal is spewed about presents a hazard and normal precautions of removing flammable materials, wearing proper protective clothing, and eye protection (shade 14 lens recommended) should be worn. Primary and secondary cables should be of the proper size in relation to the amperage being used and be protected from the molten slag being spewed about. The operator should not be working on wet surfaces, ventilation and operator respiratory masks must be adequate as the process causes more fumes than with normal welding.

The process requirements are a D.C. RECTIFIER with minimum 60 open circuit voltage, however, for a given size of carbon electrode the power requirement is normally considerably higher than for arc welding (see electrode amperage recommendations in chart below.) It is recommended that the power source has overload protection in the output circuit. High current surges of short duration occur with arc gouging and these surges can overload the power source. Compressed air is commonly used and air pressure requirements are 5.6 to 7 Kg/cm2 (80 to 100 P.S.I.) for optimal removal of molten slag from the gouged groove or cut. A standard workshop compressor with minimum of 2.9 to 5.5 Kw can be used with a flow rate of 28 to 36 Cfm (1.0 to 1.1 m3 min.)

TECHNIQUES USED FOR SPECIFIC MATERIALS:

CARBON STEEL: This material can be easily gouged or cut using DCEP (reverse Excluding polarity). Normal conditions use a 35° electrode to work angle with a maximum of 18cm electrode stick out. The air blast flow is always positioned between the electrode and workpiece.

STAINLESS STEEL: On these alloys use the same techniques as described above.

HIGH NICKEL ALLOYS: The higher the nickel content the harder the material is to gouge. By using an even lower angle to workpiece can assist the gouging operation.

ALUMINIUM: The electrode stick-out should be no more than 8cm. Be careful not to touch the electrode to the work surface, as carbon deposit will occur. The finish of the groove/cut will require a stainless steel brush to remove the black oxide (oxides not carbon) from the area. Recommend using DCEP (reverse Excluding polarity) or if this does not work well, then switch to DCEN ( – polarity).

GRAY, DUCTILE & MALLEABLE CAST IRON: These materials require a special operating procedure when attempting to gouge. It is recommended that the current range be 1000 amps or higher and this requires a carbon size of 13mm or larger. Attempts to gouge with smaller size carbon will deposit refractory slag (gray crystalline surface) resulting in little or no gouging progress while burning up carbons.

COPPER BASE ALLOYS: Heat dissipation due to high conductivity of these materials makes them more difficult to cut or gouge than carbon steel. Use DCEN (straight – polarity) at the maximum amperage rating of the electrode.

MAXWELD & BRAZE offers the following INCLUDING FULL SPARES COVERAGE :

POWER SOURCES: THERMADYNE DC THYRISTOR CONTROLLED RECTIFIERS

TORCHES:

STOCK CODE: 100152: K4000 ARCAIR ANGLE – ARC TORCH (1000 amp maximum) works efficiently with the natural angle and movement of the arm and wrist.

STOCK CODE: 100151: K5000 STRAIGHT HANDLE TORCH (1250 amp maximum)

STOCK CODE: 100135: TRI-ARC FOUNDRY TORCH (2200 amp maximum) offers one torch that accepts three types of heads for defect removal, pad washing or general purpose cleaning (13, 16 or 19mm carbons)

These torches offer excellent torch air flow from four barrel air nozzle - optimized air flow where noise level does not exceed 115 decibels - positive on and shut-off air control - improved cable electrical conduction - improved durable outer cable cover - insulated connection boot and hook up kit . These torches are highly effective metal removal tools for use in steel fabrication plants, foundries, shipyards, railroads, construction plants, farms …. Anywhere industry needs to remove metal fast, efficiently and to save time and money. Ideal for almost all metals with little or no deformation, due to low heat input.

SILVER SOLDERING COPPER TO COPPER BRAZING

1. SILVER SOLDER FLUXES

The most critical consideration in obtaining a successful silver solder joint is in the use of a good quality flux. The flux used must be active up to Excluding - 870° C, covering most general purpose alloy applications. The flux will absorb and protect the weld surface from impurities and oxides up to this temperature. The flux also assists in the capillary flow of the molten alloy. Special fluxes are used for alloys requiring specialized procedures or when used to join Titanium, Tungsten or Chrome Carbide components.

Once the brazing temperature exceeds 870° C the flux is saturated with impurities and no longer protects the weld area and will not assist with the normally good capillary flow of the alloy. The flux burns and leaves a hard residue that is difficult to remove. The alloy flow becomes sluggish and penetration though the gap is suspect. Flux residues on well executed weld joints is easily removed using warm water or if difficulty is encountered, immerse in 10% caustic soda.

The flux acts as a temperature indicator and once it melts the correct brazing temperature is reached and the alloy can be introduced. At this point it is important to maintain the heat by moving the flame in a sweeping motion so that no overheating is achieved in one area. The flux acts like a carrier of the molten alloy (capillary flow) and is pushed away in front of the molten alloy leaving a solid homogenous weld joint. Silver solder flows towards heat therefore it is good practice to introduce the alloy from the opposite side from where you are heating. This will ensure that the alloy is drawn through the joint towards the heat source and enhances the capillary flow to enable the alloy to flow both horizontally and vertically. Weld joints should be designed so that the flux can escape at the end of the joint and not be entrapped.

2. SILVER SOLDER ALLOYS

Selection of the correct silver solder for the application is based on a number of considerations.

• The joining of most ferrous and non-ferrous metals (except aluminium) is possible as well as the joining of dissimilar alloys to each other.
• Tight fitting joints (0.05 – 0.10 mm) requires an alloy (50 or 40% Ag) with thin flowing properties, good capillary flow and with a narrow plastic range (the temperature between liquidus (when alloy melts) and solidus (when alloy freezes). Tight fitting joints normally have the highest strength and elongation joints possible. These alloys have a melting range between 620 and 730° C.
• Joints with bad fit up (0.10 – 0.25 mm) requires an alloy (30 or 20% Ag) with a wider plastic range i.e. more sluggish flow, that is able to bridge gaps and enables the operator to manipulate the alloy through the joint. These alloys have a melting range between 680 and 780° C.
• Alloys that give good color match to the base metal.
• Alloys for corrosion resistance to various requirements.
• Alloys with very narrow plastic range to protect adjacent areas from prolonged heat or not to re-melt existing joints.
• Alloys suitable for Tungsten/Chrome Carbide brazing, furnace or vacuum brazing etc.
• Alloys with higher strength and/or elongation requirements.
• Generally the general purpose alloys stocked are Cadmium free for use on Hospital and Food utensils. The alloys without Cadmium are toxic free, have the same strength and capillary flow as those containing Cadmium and melts at slightly higher temperatures. The fumes given off with Cadmium containing alloys are toxic to the operator.

3. COPPER TO COPPER BRAZING ALLOYS

Copper phosphorus alloys are recommended for flux-less brazing of copper to copper. The phosphor content of up to 8% acts as a deoxidizer to the surface of the copper being joined and therefore no flux is needed. When joining dissimilar metal i.e. Brass and Bronze, the use of a good silver solder flux is necessary. Copper phosphorous alloys should not be used on ferrous alloys or nickel-bearing copper alloys.

The copper phosphorus brazing alloys that contain no silver should be used on joints that are not subjected to any stress levels or vibration. They are ideal for static joints as found in gas and water pipes fixed in static positions.

Copper phosphorus brazing alloys containing 2 to 15% silver are more ductile and are recommended for use on joints that will be subjected to significant stress / elongation levels and vibration.

The above alloy range contains between 90 & 94% copper and gives good color match to copper.

4. GENERAL PURPOSE BRAZING ALLOYS AND FLUXES

Bronze Brazing Alloy (BBR) is a general purpose fusion bronze brazing alloy used for joining and building up on Steel, Cast / Malleable Irons and Copper based alloys. Not recommended to join copper to copper pipes. This alloy has medium strength, good elongation and thick flowing properties. Used either in flux coated alloy or with MAXBRAZE BRAZING FLUX.

FLUXWELD 110 is a high tensile bronze brazing alloy containing 10% nickel for applications requiring excellent wear resistance. The alloy has work hardening properties and is ideal for building up worn parts, broken gear teeth and for high tensile brazed joints on low and medium carbon steels.

WELDING MACHINE DUTY CYCLES

Arc welding machines of all types are rated according to their maximum current (amperage) output.

This rating is generally set by the manufacturers of the specific equipment in accordance with standards established by the NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION (NEMA).

These standards are established on a conservative basis, requiring a rating below the maximum overload capacity of the welding machine so that it will provide safe operation efficiently over a long period of time.

The duty cycle of a welding machine is the percentage of a (10) ten minute welding cycle that the welding machine can operate at it's given maximum output current. For example, if a welding machine is rated at 160 amp maximum at a 60% duty cycle, it means that the machine can be operated safely at maximum welding current (160 amp) for (6) six minutes out of every (10) ten minutes and would need to cool down, theoretically, for the remainder of (4) four minutes.

Welding machines are generally protected against overloading by thermal overload devices. This means that once the given duty cycle is exceeded, the excess heat being generated will activate the thermal overload device and shut of the power supply to the welding machine, preventing the overheating and failure of components. Once the thermal overload is activated the machine should be left to cool down for the remainder of minutes out of (10) ten i.e. 60% actual welding time = (6) six minutes therefore the machine should be left to cool down for a further (4) four minutes. HOWEVER, THIS OVERHEATING TIME PERIOD REACHED AND COOLING DOWN TIME PERIOD CAN BE INFLUENCED BY HOW WELL THE MACHINE IS MAINTAINED. Should the machine be located in a badly ventilated area or the ambient temperature where the machine is located is above 30 ° C, the fan cooling of components may not be sufficient and overheating of components can occur before the (6) six minute maximum welding cycle is reached. Another influencing factor of overheating and cool down period, is whether the inside of the machine is cleaned out on a regular basis by using, for example, compressed air to remove dust and air-born metal particles that may have settled on the components of the machine.

If the welding amps required for a particular application is lower than the maximum output welding amps of the machine, the duty cycle is increased proportionately.

THE WELDING MACHINE WILL NOT OPERATE ONCE THE THERMAL OVERLOAD AND OVERLOAD SIGNAL ON THE FRONT PANEL OF THE MACHINE IS ACTIVATED. THE MACHINE WILL OPERATE AGAIN AFTER THE NECESSARY COOLING DOWN PERIOD IS ACHIEVED AND THE OVERLOAD DEVICE IS DE – ACTIVATED.

WELDING ELECTRODE STORAGE CONDITIONS
RE-DRYING PROCEDURES - HOT BOXES AND OVENS 

GENERAL

To obtain a good quality weld using the MMAW (Manual Metal Arc Welding – stick) process depends on the composition and condition of the electrode coating. Because the flux coating and the alloy content in some of the flux coatings play such an important role in the welding process, no attempt should be made to weld with electrodes that have their coating wholly or partly damaged. The efficiency of an electrode will also be impaired if the coating is allowed to get wet or damp. Dampness causes water vapour to be generated within the arc shield and adversely affects the weldability and quality of the weld deposit. This is eespecially important with all electrodes manufactured with coating of LOW HYDROGEN (Basic coated) specifications. Hydrogen in the coating has an adverse effect on the welds requiring a tensile strength of 70,000 psi or more and causes internal and external porosity, underbead cracking and poor weldability.

STORAGE CONDITIONS

To prevent moisture pick-up, eespecially on LOW HYRDOGEN (Basic coated) electrodes, the electrodes should be stored in dry conditions, off the floor on pallets or racks, in their original packaging. Hydrogen controlled basic coated electrodes are packed in cardboard cartons with a moisture resistant sealed polythene wrapping. Further protection is provided by packing these cartons into rigid outer shippers. Once the polythene wrapping is removed the electrodes will, depending on the type of storage conditions, regain moisture from the surrounding air. It is therefore good practice to place the opened electrodes into a holding oven (HOTBOX) during welding and to re-seal unused electrodes in polythene sealed wrapping for storage and later use. LOW HYDROGEN basic coated electrodes SHOULD NOT be STORED or SOLD UNLESS PROPERLY SEALED.

RE-DRYING AND RE-BAKING OF ELECTRODES

Electrodes that are suspected of possible dampness should be re-dried before use. The large range of electrodes that are manufactured with LOW HYROGEN controlled basic coatings need to be re-dried at varying temperatures. Electrodes that have been subjected to severe dampness or in contact with water need special re-baking procedures and it is recommended that your supplier be contacted for further information, inspection or advice.

GAS WELDING & CUTTING SAFETY PRACTICES

Applying and observing basic safety measures during GAS WELDING AND CUTTING operations is a pre-requisite in preventing - serious injury or even death of the operator - damage to expensive equipment - facilities - costly downtime.

Listed below is a number of important steps that should be taken when fitting and before the actual use of the gas equipment. These steps, if strictly applied, will ensure that the correct flow, regulation and mixing of the gases is obtained and that the ignition of the flame is done safely.

1. No gas equipment repairs should be attempted on site and worn or leaking components should be replaced immediately.
2. The pressure regulators are precision instruments and should not be exposed to shocks, vibration or impact caused by the sudden opening of the cylinder valves while the regulator diaphragm is under pressure.
3. Gas bottles with regulators fitted to them and with safety caps in place should always be secured with chains or fitted securely onto cylinder trolleys. Always store and use the cylinders in the upright position.
4. Never lubricate components using oil, grease or hydrocarbon or let similar organic materials come in contact with the gas equipment. It can cause a violent explosion. Do not use oil based P.T.F.E. tape to stop leaks, rather replace the component.
5. When testing for leaks or cleaning the equipment, use a soapy water solution.
6. Do not use regulators on any gas other than the one that it is designed for.
7. Never operate the equipment at pressures exceeding those that are recommended by the manufacturer.
8. Where practical avoid using long lengths of hose as they are vulnerable to mistreatment i.e. stepped on, run over, kinked, tangled, sparks, hot slag, hot/sharp edges, open flames, exposed to sun for long periods etc. Keep hose away from oil and grease. Purge gas from pipes after use. Never use steel or copper pipe to make a joint. Do not repair hose with tape. Regular inspection of hose quality and soundness of connections will prevent costly down time.
9. The gas cylinders and the bullnose on the regulators have their own seat and may not seat properly the first time. To ensure that proper seating is achieved when fitting the regulator, the following procedure is recommended:
   (a) Fit the regulator bullnose to the cylinder valve and tighten the regulator nut slightly. Turn the regulator clock and anti – clock wise a number of times.
   (b) Remove the regulator and inspect the seating marks achieved on the bullnose. This should indicate if proper seating is being achieved, thereby avoiding leaks. Some cylinder valve seats may be damaged.
   (c) Damaged bullnose stem faces and regulator nuts should be replaced as this is the main cause of leakages.
   (d) Before refitting the regulator, open and shut the cylinder valve to remove any dirt or foreign particles that may have lodged in the valve.
   (e) Once proper seating is achieved, re-fit the regulator and tighten the nut securely.
10. The same procedure is recommended to attain proper seating of the cutting nozzles to the torch head. This procedure will also ensure proper gas flow, no leakage and reduce the possibility of flash backs.
11. Ensure that the gas hoses from the regulator to the torch are in good condition and that all connections are secured, to avoid possible leakages.
12. It is highly recommended, to ensure operator safety, to fit flash back arrestors to the regulator and torch flow system.
    THE FOLLOWING PROCEDURE IS RECOMMENDED TO ENSURE THAT THE DIAPHRAGM OR GAUGES OF THE REGULATOR IS NOT DAMAGED.
13. Before opening the cylinder valves, release the pressure valve on the regulator by turning the pressure knob anti-clock wise. This will ensure that the sudden high pressure loading from the cylinder does not damage the regulator diaphragm or gauges. On opening the cylinder valve the high pressure gauge will indicate the content capacity of the cylinder. The low pressure gauge should be on zero.
14. Stand to the side of the regulators when opening the cylinders. Avoid being behind or in front of the regulator gauges. This is for your own safety.
15. Open the cylinder valves slowly.
16. Set the regulator low pressure required for the size of nozzle and job at hand.
17. When lighting the torch, open the acetylene torch valve first and when the job is finished close the acetylene torch valve first.
18. After the job is completed, close the cylinder valves first, purge the gas from the hoses by opening the torch valves and finally release the pressure valve of the regulator's diaphragm. This will ensure that the next time the system is used the correct safety procedures are re-applied.
19. Finally, ensure that the operator has adequate eye protection fitted with the correct shade lenses, adequate ventilation and/or correct respiratory protection, safety gloves, safety shoes, shoe spats, leather apron and flame retardant overalls, without pockets and / or turn-up hems or sleeves where sparks or hot metal can collect and cause burns or fires.
20. Do not weld, cut or heat near flammable material and at all times be safety conscious.

THESE SAFETY PRACTICES WILL ONLY TAKE A COUPLE OF MINUTES OF YOUR TIME AND WILL ENSURE YOUR SAFETY AND PREVENT COSTLY DOWN TIME DUE TO EQUIPMENT FAILURE.

STAINLESS STEEL WELD CLEANER 

DESCRIPTION

Stainless Steel Weld Cleaner is a thickened solution of special acids used for the removal of the black oxide marks or burn scale left during the welding of stainless steel.

After the use of Stainless Steel Weld Cleaner the weld area treated should have the same appearance as the rest of the stainless steel being used. The stainless steel weld area will have a clean professional surface finish.

PHYSICAL PROPERTIES

Boiling point : N/A

Specific Gravity : 1.24 - 1.26

Water Solubility : MISCIBLE

pH (as supplied) : < 1.0

Appearance / colour : OPAQUE, YELLOW ACIDIC, PUNGENT ACIDIC ODOUR

METHOD OF APPLICATION

1. Clean the weld area carefully using a stainless steel brush.
2. Stir the content of the container with a flat plastic or wooden stick to ensure a smooth consistency, eespecially if the product has not been used for a long time.
3. Ensure that the surface is cool before applying paste.
4. Apply weld cleaner to the area to be cleaned, using a non – metallic applicator.
5. Leave paste on the surface for 1 to 5 minutes, depending on the severity of the oxide scale or burn marks. Care should be taken to avoid getting excess paste onto bright or polished surfaces, as this may cause stains or unsightly dull patches.
6. Remove residue by rinsing with water. It may be necessary to scrub the area with a stainless steel wire brush to remove any visible etching to match the remaining surface.

SAFETY PRECAUTIONS

1. The Stainless Steel Weld Cleaner contains a mixture of NITRIC ACID, HYDROFLUORIC ACID, HYDROCHLORIC ACID and is EXTREMELY CORROSIVE.
2. Avoid contact with the skin and eyes by wearing protective clothing, eye protection and breathing apparatus at all times when working with this product.
3. Do not use near open flames or cutting torches, since hazardous flammable gas can be generated.
4. Keep out of reach of children and give all personnel suitable instructions regarding the dangers before allowing them to work with the product.
5. In case of accidental contact with the skin or eyes, wash immediately with water for 15 minutes and seek medical attention. Physicians should treat for Hydrofluoric acid burns.
6. In case of accidental spillage - SMALL SPILL: Take up with sand or other non – combustible absorBent material and place in container for later disposal – LARGE SPILL: Ensure that clean – up is conducted by trained personnel. Contain spill with earth, sand or absorBent material that does not react with the product. Do not use organic material such as sawdust.
7. Do not store or use below 5º C.

THE RECOMMENDATIONS CONTAINED HEREIN ARE BASED ON TESTS AND IN – FIELD EXPERIENCE AND ARE TO THE BEST OF OUR KNOWLEDGE ACCURATE. SINCE CONDITIONS OF ACTUAL USE ARE BEYOND OUR CONTROL, ALL RECOMMENDATIONS ARE MADE WITHOUT WARRANTY, EXPRESS OR IMPLIED.

WELDING SAFETY INFORMATION

HIGH VOLTAGE AND ELECTRIC SHOCK CAN KILL

PRIMARY INPUT VOLTAGE

The primary voltage shock is very hazardous because it is much greater than the welding machine secondary voltage. You can receive a shock from the primary (input) voltage if you touch a lead inside the welding machine with the power to the welder “on” while you have your body or hand on the welding machine case or other grounded metal. Remember that turning the welding machine power switch “off” does not turn the power off inside the welding machine. The input power cord must be unplugged or the power disconnect switch turned off. This also applies when you remove the welding machine panels. Should a problem occur with the welding machine it is always advisable to have a qualified electrician repair the unit. It is also good practice to have your welding machine installed by a qualified electrician so that it is correctly wired for the primary voltage supply recommended by the manufacturer and that the case be connected to an earth ground. The case must be grounded so that if a problem develops inside the welding machine, a fuse will blow, letting you know that the welding machine needs attention. Never ignore a blown fuse as it is a warning that something is wrong .

SECONDARY OUTPUT VOLTAGE

A secondary voltage shock occurs when you touch a part of the electrode circuit while at the same time another part of your body is touching the metal upon which you are welding . To receive a shock your body must touch both sides of the welding circuit i.e. electrode and ground (workpiece) at the same time. To prevent secondary voltage shock you must develop and use safe work habits:

Wear dry gloves and clothes, in good condition, when welding

Do not touch the electrode or metal parts of the electrode holder with your skin or wet clothing.

Ensure that the electrode holder jaws, handle and cable insulation is in good condition.

Never weld on wet or metal floors without proper dry insulation i.e. wood or rubber mats, between your body (including arms and legs) and the metal workpiece being welded.

Do not rest your body, arms or legs on the workpiece, eespecially if your clothing – gloves are wet or bare skin is exposed.

Remember that the (stick) electrode is always “electrically hot” when the welding machine is switched on and should be treated with respect.

These rules are basic to all welding processes and you will probably not experience a shock if you adhere to them.

TROUBLESHOOTING GUIDE ON WELDING EQUIPMENT

GAS TUNGSTEN ARC WELDING (GTAW)
TUNGSTEN INERT GAS (T.I.G.) WELDING

POWER SOURCES

DC Rectifier or Inverter power sources without high frequency facility can be used for scratch start DC welding. The connection is torch power cable to the negative (-) connection of the machine and earth cable to the positive (Excluding) connection. The machine has no solenoid gas valve and gas flow is controlled manually by the operator by turning the knob, mounted on the torch, to the required volume.

DC Rectifier or Inverter power sources with high frequency facility are used for automatic arc ignition T.I.G. welding. The connection can be either electrode positive (Excluding) or negative (-) as described below. These machines are fitted with a contactor and a means of controlling arc current as well as a solenoid valve for automatic gas flow control by the welder. The control of arc current can either be pre – set at the machine or through current control mounted on the torch or by using a foot control unit. These machines normally also have pre – set control of gas flow before starting the arc and gas flow off after completing the weld. An additional feature can be included to pulse the weld which allows root pass welds, welds on thin material and overhead welds to be made with less chance of melt through.

AC / DC Rectifiers or Inverter power sources with high frequency facility is the most versatile machine used for T.I.G. welding of all ferrous (steel) based metals including non – ferrous metals i.e. Aluminium, Copper, Nickel etc. The DC welding side is as per the above comments. For AC welding the high frequency is on continuously and the power supply can vary the positive and negative half cycles of AC current to favor either cleaning action or penetration. This feature is useful for welding aluminium where adjustments must be made based on the thickness and cleanliness of the joint. Current and gas flow control is as per above.

DIRECT CURRENT (D.C.) T.I.G. WELDING

In direct current welding (D.C.), the welding current circuit may be hooked up as either “straight – negative (-)” or “reverse - positive (Excluding)” polarity. The D.C. welder connection for direct current straight polarity “DCSP negative (-)” welding is electrode negative and workpiece positive. In other words, the electrons flow from the electrode to the workpiece, as shown in figure 1-1 above. For direct current reverse polarity “ DCRP reverse (Excluding)” the connections are the opposite i.e. the electrons flow from the plate to the electrode, as shown in figure 1 – 2 above.

In negative polarity welding, the electrons exert a considerable heating effect on the plate. In positive polarity welding the electrode acquires this extra heat which then tends to melt off the end of the electrode. In the case of DCSP (-) approximately 70% of the heat is developed at the workpiece and 30% at the electrode, so the electrode tip will not melt and will maintain the conical shape when used within the recommended current range. For any given welding current, DCRP (Excluding) requires a larger diameter electrode than DCSP (-). These opposite heating effects of DCRP (Excluding) and DCSP (-) influence not only the welding action but also the shape of the weld obtained (see weld result drawing). One other effect of DCRP (Excluding) welding should be considered namely the so – called plate cleaning effect which occurs. The exact reason for this surface cleaning action is not known. The electrons and gas ions tend to remove the surface oxides and scale usually present.

When using a DC welder without high frequency facility , the arc can be stuck on the workpiece or on a piece of copper or steel (scratch start) and then carried to the weld starting point. Do not use a carbon block for starting the arc as the electrode becomes contaminated causing the arc to wander. The T.I.G. torches used in this case has a mechanical gas valve on the torch that is opened manually by the operator before striking the arc.

When using a welder fitted with high frequency facility it eliminates the need for touching the workpiece as the high frequency is automatically turned on to assist in establishing the arc and is automatically turned off as soon as the arc is established. The welder also has a solenoid valve that opens to allow gas flow when triggered on the torch and shuts off after the trigger is released. If water cooler is fitted to the system a water cooled torch is required and water flow is continuous while the circulator pump is running.

ALTERNATING CURRENT (AC) WELDING

In alternating current (AC) welding, the welding current circuit is hooked up to the “straight (-) polarity terminal. The high frequency facility on these AC/DC type welders jumps the gap between electrode and the workpiece, burns through the tough oxide skin during the “reverse polarity phase - positive (Excluding)” of the AC cycle and creates a clean path for the welding current that follows. The depth of penetration results from the heat produced during the electrode negative (-) portion of the AC cycle. Because cleaning action is inherent in electrode positive welding, any oxide film on the work is broken up during the electrode-positive portion of the AC cycle. Zirconiated tungsten electrodes are generally used when welding aluminium due to being able to carry slightly higher currents and have a longer life than pure tungsten electrodes. The AC welders with high frequency facilities are normally fitted with solenoid valves that regulate the gas flow through torch trigger activation. If water cooler is fitted to the system a water cooled torch is required and water flow through the torch is continuous while the circulator pump is running.

APPLICATIONS

The main feature of the GTAW (T.I.G.) process is the high quality welds achieved on almost all commercially available metals and alloys. Freedom of contamination from the atmosphere is achieved eespecially on critical alloys where small amounts of oxygen, nitrogen and carbon can cause embrittlement and loss of corrosion resistance. The process is ideal for welds on thin material, root passes and small parts where quality and finish is important. The ability of adding filler metal independently of the arc current, that can be operated at very low amperages, with very little spatter loss and with a stable arc, is a strong consideration eespecially on small thin walled parts.

The only disadvantages of the T.I.G. process is the greater skill required by the operator and the low rate of filler metal being applied.

TECHNIQUES

The technique of manually feeding the filler wire into the weld puddle is illustrated in the drawing above. The filler rod end should not be moved out of the inert gas shielding area of the torch. This is to prevent the hot end from oxidizing with the resultant contamination in the weld pool, when it is dipped into it. Pre-flow of gas before the arc is established and post-flow after the weld is completed also prevents oxidation and allows the filler alloy to wet and flow properly. At the end of the weld the current should be decreased gradually to avoid a crater forming with the possibility of crater crack developing. Adding a small amount of filler metal at the end of the weld, just before the arc is extinguished, is good practice. Many joints of thin material can be joined without adding filler material by fusing them together such as corner joints, edge joints etc. On establishing the arc, the torch is moved at a constant speed to the end of the weld.

CHARACTERISTICS OF THE GAS TUNGSTEN ARC (T.I.G.) WELDING PROCESS FOR ALUMINIUM (ALL AT SAME CURRENT)

GAS METAL ARC WELDING (GMAW)
METAL INERT GAS WELDING (M.I.G.)

GAS METAL ARC WELDING (GMAW) (M.I.G) PROCESS

Gas metal arc welding, commonly known as M.I.G., welding consists of various components as indicated in the drawing above. The system uses continuous small diameter solid wire and an externally supplied gas or mixtures of gasses. The shielding gas can be Helium, Argon, Carbon dioxide or mixtures thereof.

M.I.G. welding is suitable for use on all major commercial metals i.e. Low Carbon, Low and High Alloy Steels, Stainless Steels, High Strength quenched and tempered steels, Aluminium, Magnesium, Copper, Titanium, etc. With these various metals the welding techniques and weld procedures may vary widely.

Carbon – Dioxide or Argon – Oxygen mixtures are suitable as shielding gasses on low carbon and low alloy steels, whereas pure inert gas (Argon – Helium) is used when welding high alloyed steels and alloys of Aluminium, Magnesium, Copper, Titanium, Stainless Steel and the Nickel Based alloys.

Welding is either semi-automatic, using a hand-held torch (manual) through which the wire is fed automatically, or fully-automatic equipment can be used.

Metal transfer achieved using the M.I.G. process is done by one of two methods, namely, “spray arc” or short circuiting (globular). With spray arc, drops of molten metal detach from the wire and move through the arc column to the workpiece. With the short circuiting method, metal is transferred to the workpiece when the tip of the wire contacts the molten metal.

In short – circuit welding (globular), lower current, low voltages and small diameter wire is used and the metal is transferred with each short – circuit rather than across the arc as in spray arc welding. This method results in low heat input with the minimum of distortion and used on thin or poor fit-ups and bridging wide gap applications.

Spray arc M.I.G. welding produces a very hot, high voltage arc and gives a higher deposition rate than short circuit welding. The spray arc method is normally recommended for thicker sections requiring heavy single or multi-pass applications where deposition rate is important.

Gas Metal Arc (M.I.G.) welding is done with Direct Current (D.C.) rectifier power sources, using reverse polarity, wire positive (Excluding) and this provides a stable arc, smooth metal transfer, relatively low spatter loss and good weld bead.

Some manufacturers also provides Spot Welding features on there equipment which replaces either riveting or where T.I.G. spot welding is not suitable such as in joining Aluminium or on poor fit-ups and where cleanliness requirements are not as important or on thicker materials.

As with all welding processes, the correct setup and maintenance of M.I.G. welding equipment is vitally important to ensure continuous automatic feeding and successful weld deposits. This equally applies to the M.I.G. torch and ensuring that the torch system is clean, with no obstructions and current carrying parts, that are relatively inexpensive, are replaced frequently. It is also good practice to have the torch cable as straight as possible to ensure continuous successful wire feeding.

When welding non-ferrous metals i.e. Aluminium, Copper or Nickel alloys it is highly recommended to use a Octarate torch specifically for these alloys, than the one used on steel alloys, and that the torch cable length is as short as possible and kept as straight as possible.

CONSEQUENCES RESULTING FROM INCORRECT USE OF WELDING ACCESSORIES

ELECTRICAL CONDUCTIVITY OF METALS

Electrical conductivity is the efficiency of a metal in conducting electrical current. The conductivity of electrolytic tough pitch copper (ETP) is 101% of the International Annealed Copper Standard (IACS). Other metals compare as follows:

ALUMINIUM (99.9%) 65%

ALUMINIUM ALLOYS 35%

MILD STEEL 15%

STAINLESS STEEL (300 SERIES) 2.5%

WELDING CABLE

The first item on both sides of the welding machine (power source) is the cable required for conveying the electrical current. The cable from the welding machine to the electrode holder carries the current to the electrode via the electrode holder to the arc and on to the workpiece. The cable from the welding machine to the workpiece is the earth cable and completes the circuit from workpiece back to the welding machine.

The electrical conductors of the cable are fine strands of copper (preferred) or aluminium. The quality, size and length of the conductors are extremely important to ensure the efficiency, success and quality of welding. The insulating material of rubber or synthetic rubber over the copper strands provides adequate insulation and flexibility needed. The size of cable used depends on the current (amperage) to be carried and the total length of the electrical circuit. The longer the circuit, the larger the size of the conductors needed to prevent voltage drop and the dissipation of energy by resistance heating within the conductor. DAMAGED INSULATION, BROKEN CONDUCTORS INSIDE THE INSULATION, TO SMALL CONDUCTORS CARRING THE CURRENT WILL CAUSE HEAT BUILD UP, COPPER SCALING, WITH THE RESULTANT POOR CONDUCTIVITY AND WELDING EFFICIENCY.

ELECTRODE HOLDERS

The electrode holder is a clamping device that grips the welding electrode between the jaws that conducts the current through the electrode to the workpiece. Electrode holders are rated according to their current carrying capacity. By choosing the correct rated size holder and cable , that the cable connection to the holder is sound and the metal used by the manufacturer on the holder's body/jaws , carrying the current, has good electrical conveying and gripping properties , will ensure that the electrode holder does not overheat . Quality electrode holders have good handle and jaw insulation and the screws holding these parts are well recessed thereby protecting the welder from electrical shock or accidentally touching the workpiece causing a short circuit. THE EFFICIENCY, COMFORT AND WELD QUALITY PRODUCED BY THE WELDER GREATLY DEPENDS ON THE QUALITY OF THE ELECTRODE HOLDER AND SOUND CONNECTING SYSTEM.

EARTH (GROUND) CLAMP

Proper earth (ground) of the system cannot be over emphasized to its importance in achieving quality and efficient welding. The earth completes the electrical circuit back to the welding machine. Any resistance i.e. earth not firm enough or insufficient cross sectional area surface contact in relation to the cable size will cause electrical resistance, voltage drop will occur with the resultant heat build up in the cable and earth clamp and poor arc characteristics. Since the conductivity of copper is almost 7 times that of mild steel, the cross sectional area of any common steel grounding bar should be at least 7 times the cross section of the welding cable conductor. It is good practice to ensure that the area of earth contact is adequate, free from scale, rust, oil, grease, oxides, or dirt that would act as areas of insulation. PROPER EARTH IN ALL WELDING SYSTEMS IS A PRE-REQUISITE IN OBTAINING GOOD ARC CHARACTERISTICS AND WELD QUALITY.

CABLE CONNECTORS

Connecting the current conducting welding cable to either the welding machine or extending the length of welding cable is normally done by either using cable lugs or cable connectors. Again the cross sectional area and soundness of the connection of the cable to these connectors is important in assuring good electrical flow and reducing the possibility of resistance, heat build up, voltage drop and poor arc characteristics. ADEQUATE AND UNINTERUPTED ELECTRICAL FLOW ENSURES GOOD ARC CHARACTERISTICS AND WELD QUALITY.

DIRECT CURRENT (D.C.) STICK INVERTERS

The THERMADYNE D.C. STICK INVERTER range consists of 140 amp, 160 amp and 200amp output capacity welding machines, all suitable for use on 220 volt input supply and generally used for maintenance applications. For production use we have a 250 amp and 400 amp, both suitable for use on 380 volt input supply . All units are rated at 60% duty cycle, are lightweight and have low amperage capabilities (i.e. 20 to 30 amps depending on the unit).

INVERTER welding machines are state of the art technology and makes use of solid state switching and rectification and filtration of the input voltage to produce very stable D.C. voltage and current. The input line voltage can either be single phase (220 volt or three phase 380/525 volt). Solid state control circuits are incorporated to provide excellent arc characteristics and line voltage compensation.

IMPORTANT FEARURES

• Lightweight portability is one of the main features to be considered when purchasing a welding machine for use on a specific range of applications.
• Input voltage covers all power input supplied in South Africa .
• The components can absorb up to 15% under or over line voltage variations.
• Inverters produce a stronger, more concentrated, smooth and state arc with excellent striking and re-striking capabilities.
• Inverters are ideally suited and versatile for use on all commercially available ferrous and non-ferrous metals. It will weld electrodes of different specifications, including basic (low hydrogen) and cellulosic types. Fine adjustment through the current range allows for precision welding on complex alloys.
• The stick Inverters (no high frequency facility) can be used for scratch start D.C. T.I.G. welding using straight (Negative -) electrode polarity when T.I.G. welding ferrous (steel) metals. (See INFOMAX No. 12)
• On thin metals using mild steel electrodes , the polarity can be reversed i.e. electrode negative (-) and ground (earth) (Excluding). This allows for less burn through possibilities.
• The Inverter is fitted with a V.R.D. (voltage reduction device) switch located at the back of the Inverter. This is a safety feature and when switched to the “ON” position, it reduces the initial open circuit voltage and safeguards the operator from electrical shock when welding in wet of damp areas. It effectively means that the voltage needed to start the arc is reduced and no arcing is established until (within a couple of seconds) the voltage increases to the level needed to establish the arc. This can also be used as a feature for use by an operator who wears a standard helmet (not required when using a automatic Solar Helmet) as the arc delay gives the operator time to down his helmet.
• The Inverters are fitted with an overload protection switch that is activated once the components reach overheating levels or the duty cycle is exceeded. (See INFOMAX No. 6.)

PROVENTATIVE MEASURES AND MAINTENANCE

• Inverters should be used in dry environments, with humidity levels of 90% max.
• The ambient room temperature should be between 10 to 40 ºC.
• The Inverter should not be used in rain or drizzle.
• Do not use the Inverter in corrosive areas.
• The cooling fan fitted to the Inverter needs to keep the unit cooled to required limits, therefore, the intake air vents must not be obstructed, always clean and not within 0.3 meter to the nearest object. The WARRANTY of the Inverter allows for the operator to remove the cover to blow out excessive dust and metal dust particles (using dry compressed air with reasonable pressure level) that may damage the electrical components. However, the WARRANTY will be nul and void if any component is changed or altered. Care should be taken that the cover is fitted back correctly as this can influence the correct air flow.
• The duty cycle of the Inverter should not be exceeded.
• The input voltage should always be within the Excluding - 15% under of over allowable constant supply. Using input power cable exceeding 15 meters may cause the voltage to drop below this level and may damaged the electronic components. (See INFOMAX No. 3. for cable information.)
• When the overload protection device is activated (front indicator light will come on) the Inverter will switch off and the power will only be re-activated (front indicator light off) for further welding once the component temperature reaches safe levels. The cool down time may vary according to the conditions under which the Inverter is used.
• Prevent water or steam from entering the Inverter. Should this happen, remove the power supply from the mains and dry properly.
• Inverters should not be used using power generators unless expensive voltage equalizers are fitted. The electronic components fitted to Inverters cannot absorb the excessive voltage variations found with this type of power supply.