Aluminum Castings repaired:

Aluminum Alloy castings scrapped in the foundry since of surface defects and lack of dimensional integrity can be recovered by welding apart from if they present massive porosity.

Gas tungsten arc welding (GTAW) with high frequency stabilized Alternating Current is usually used to fix sound castings. Inclusions are supposed to be disallowed by taking care to avoid touching the surface with the pure tungsten electrode.

Argon with or without helium can be used as a shield. Helium helps produce a hotter arc if essential. To arrange for welding one should remove defects, particularly cracks, by dry chipping with a rounded tool or by hand milling, to get a smooth area. One ought to by no means attempt to weld on the original casting outside rough surface with no first removing the oxidized coating.

Removal of oil and grease is performed using steam degreasing or clean solvents. Use of acid etch is not suggested. If impregnation was applied, it should be removed previous to welding. A spotless stainless steel wire brush should be used to clean thick oxide layers just earlier than welding.

Filler material alloy is regularly the same as that of the casting. Preheating is wanted only in outstanding cases to conquer difficulties.

On correctly prepared surfaces of sound castings, with oxide coatings thoroughly cleaned, one should be able to weld as with no trouble as on wrought alloys. It would be fine practice to look for cracks in the weld by using penetrant inspection.
Radiographic check may be necessary by contract in sure cases.

If the original castings are to be warmth treated, also the fixed ones should go after the same procedure. Weld repairing of heat treated casting would impair their mechanical properties.

The possibility of repair of aluminum alloy castings that were previously heat treated and machined is doubtful since of stresses and deformations likely to develop during welding.

Welding on Aluminum Castings

Grind off sand from rough castings. Smooth in areas to be welded. There are grinding wheels for 4- 1/2” and larger grinders made specifically to grind aluminum.

Castings that are dirty or oily need special care. You can plasma cut a crack out if possible.This cleans out the oil in the crack. Drill holes at the ends of cracks or they will continue on after the repair is made. Clean the surface with alcohol or similar cleaner. Carefully heat the area with a oxy-acetylene torch to cook out the oil. Go over the crack with the TIG torch with low heat. Use a small tungsten electrode. These are called cleanup passes. Do not add welding rod. Every time you go over aluminum it should get cleaner. You will see black discolored aluminum in the beginning. Weld; grind; weld; grind. Eventually the aluminum will be shiny silver color, then you can weld with rod and larger tungsten.

You can use sanding discs on aluminum to metal finish; spray WD40 on the disc and the part to keep it from loading up.

Gas Welding Welders

Gas Welding Equipment Safety Tips

Acetylene cylinders should be secured in an upright position prior to and during use. Acetylene is packaged in a cylinder filled with Diatemaceous Earth. The acetylene is dissolved in acetone and the solution is then pumped into the cylinder. If the cylinder is placed on its side and then set upright again, it takes some time for the system to reequilibrate and for the acetone to drain out of the dip tube in the valve. If welding is done during this period, the weld will be high in carbon due to the acetone. If welding is done with the cylinder on its side, you may get "spitting".

All cylinders that are not connected for use must be capped. Stored oxygen cylinders must be separated from stored fuel gas cylinders or combustibles by at least 20 feet or by a 5-foot high, fire-resistant barrier with a 30-minute rating.

All cylinders that are connected for use must be lashed or chained; cylinders must be clearly marked to identify the contents. Mark empty tanks with the letters MT, and close the valves and replace the caps securely. Empty cylinders should never be placed where they could become part of an electrical circuit.

Because regulators are delicate, they must be handled carefully. Never use pliers or pipe wrench to attach them. Never pound valves equipped with wheels to open or close them. "Creeping" regulators must be repaired immediately.

Hoses should be color coded to avoid using the wrong hose. Any hoses with leaks, worn spots or burns must be replaced or repaired before use.

Oxygen hose connections are threaded right-handed. Acetylene and other fuel gas hose connections are threaded left-handed. This helps prevent accidentally switching oxygen and fuel gas hoses.

Hoses can be tested for leaks by immersing them in tap water or grease-free soapy water. Do not try to repair hoses with tape.Use only fittings that are bronze or brass (less than 65 percent copper). Never use copper because it forms copper acetylide, which can explode. Never use oil, grease or a similar substance on torches or regulators, because in the presence of oxygen they may burn, or if ignited, explode.

Before hookup always make sure the cylinder outlets are pointing away from each other. This prevents improper mixtures in case a leak occurs. When opening the cylinder valve, never face the gauge--stand to one side to prevent injury caused by malfunctioning valves.

Anyone looking directly at the flame should have eye protection with dark lenses, and if near the torch, a hood to protect against slag. Flash burns are the most common injury associated with welding; they are caused by exposure to ultraviolet light and can affect anyone near the welder even if you are not looking at the welding flame. Although this usually occurs with arc welding, anyone within about 20 feet of a welder should have polycarbonate safety glasses wih side shields, which will block ultraviolet light. Dark glasses are not required to prevent uv burns.

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Welding on Aluminum Casting

• Grind off sand from rough castings. Smooth in areas to be welded. There are grinding wheels for 4-1/2” and larger grinders made specifically to grind aluminum.
  


• Castings that are dirty or oily need special care. You can plasma cut a crack out if possible. This cleans out the oil in the crack. Drill holes at the ends of cracks or they will continue on after the repair is made. Clean the surface with alcohol or similar cleaner. Carefully heat the area with a oxy-acetylene torch to cook out the oil. Go over the crack with the TIG torch with low heat. Use a small tungsten electrode. These are called cleanup passes. Do not add welding rod. Every time you go over aluminum it should get cleaner. You will see black discolored aluminum in the beginning. Weld; grind; weld; grind. Eventually the aluminum will be shiny silver color, then you can weld with rod and larger tungsten.
  


• You can use sanding discs on aluminum to metal finish; spray WD40 on the disc and the part to keep it from loading up.

Welding Women

Welding Tragedies

Gas Welding Safety

Storage and Handling

• Keep cylinders away from physical damage, heat, and tampering.
• Securely chain equipment to prevent falling.
• Store away from flammable and combustible materials.
• Store extra gas and oxygen cylinders separately.
• Store in an upright position.
• Close cylinder valves before moving.
• Protective caps or regulators should be kept in place.
• Roll cylinders on bottom edges to move—Do not drag.
• Allow very little movement when transporting.

General Gas Welding Safety Tips

• Inspect equipment for leaks at all connections using approved leak-test solution.
• Inspect hoses for leaks and worn places.
• Replace bad hoses.
• Protect hoses and cylinders from sparks, flames and hot metal.
• Use a flint lighter to ignite the flame.
• Stand to the side (away from the regulators) when opening cylinder valves.
• Open cylinder valves very slowly to keep sudden high pressures from exploding the regulators.
• Only open the acetylene cylinder valve 1/4 – 3/4 turn; leave wrench in place so the cylinder can be quickly closed in an emergency.
• Open and light acetylene first, then open and adjust oxygen to a neutral flame.
• Follow the manufacturer's recommendations for shutting off the torch. If the guidelines are not readily available, the common accepted practice is to close the oxygen valve first.
• When finished, close cylinder valves, bleed the lines to take pressure off regulators, neatly coil hoses and replace equipment.
• Have a fire extinguisher easily accessible at the welding site.

Personal Protective Equipment:

• Infrared radiation is a cause of retinal burning and cataracts. Protect your eyes with safety glasses.
• Protect your body from welding spatter and arc flash with protective clothing. Such as:
• Woolen clothing
• Flame-proof apron
• Gloves
• Properly fitted clothing that is not frayed or worn.
• Shirts should have long sleeves.
• Trousers should be straight-legged and covering shoes when arc welding.
• Fire resistant cape or shoulder covers are needed for overhead work.
• Check protective clothing equipment before each use to make sure it is in good condition.
• Keep clothes free of grease and oil.

Proper Ventilation
Be sure there is adequate ventilation available when welding in confined areas or where there are barriers to air movement. Natural drafts, fans and positioning of the head can help keep fumes away from the welder’s face.

Ventilation is sufficient if:

• The room or welding area contains at least 10,000 cubic feet for each welder.
• The ceiling height is not less than 16 feet.
• Cross ventilation is not blocked by partitions, equipment, or other structural barriers.
• Welding is not done in a confined space.

**If these space requirements are not met then the area needs to be equipped with mechanical ventilating equipment that exhausts at least 2000 cfm of air for each welder, except where local exhaust hoods or booths, or air-line respirators are used.

MIG Aluminum Welding

The Ternary Gas Plasma Welding Torch

The increase in performance that the Ternary Gas Plasma Welding Torch achieves is attributed to a secondary inert gas acting in conjunction with the primary inert gas to provide a substantially "stiffer" arc from the electrode of the torch than a typical single inert gas provides.

Benefits

• Improves weld quality through a stiffer more controllable arc
• Reduces cost through reduction in weld "cutting" defects
• Reduces welding times
• Narrower weld with greater penetration at any given electrical current setting
• More desirable Heat Affected Zone (HAZ)
• Reduces dependency on operator's skills
• Expands the capabilities for joining thicker materials with relatively low heat inputs.

The Technology

The Ternary-Gas Plasma Arc Welding (TGPAW) torch functions by utilizing three gases: a primary inert plasma gas, a secondary inert plasma gas, and an inert shielding gas. The primary inert plasma gas is directed through the body of the welding torch and out of the body across the tip of a welding electrode disposed at the forward end of the body. The second plasma gas is disposed for flow through a longitudinal bore in the electrode. It is directed through the electrode to co-act with the arc to produce equivalent defect free welds in types and thickness of metals (ferrous and non-ferrous) with less total heat input per inch of weld (i.e. less current/voltage output and/or high travel speeds). The completed weld is narrower with greater penetration at any given electrical current setting, thereby producing a more desirable Heat Affected Zone (HAZ) and greater ultimate tensile strength values. In addition, the secondary inert plasma gas compliments the primary inert gas to provide a "stiffer" arc, less subject to becoming skewed and unequal in dimensional shape. This characteristic aids alleviating weld "cutting" defects caused by an asymmetrical arc and subsequent asymmetrical heating pattern at the weld joint. The secondary plasma gas may be any of the inert gases or semi-reactive gases or a mixture of two or more of these, however the choice is dependent on the material being welded and the results desired. The process can be applied to Direct Current Straight Polarity and Variable Polarity Welding Modes. The third inert plasma gas is "shield" gas that is directed through the torch body for circulating around the head of the torch adjacent to the electrode tip. The following diagram illustrates the Ternary Gas system:

Settings for TIG Welding Stainless Steel

In the TIG (tungsten inert gas) welding process, an essentially non-consumable tungsten electrode is used to provide an electric arc for welding. A sheath of inert gas surrounds the electrode, the arc, and the area to be welded. This gas shielding process prevents any oxidization of the weld and allows for the production of neat, clean welds.

Electric welding Accessories

An electrical appliance which—

(a) is for use in the electric arc welding process;

(b) is for connection to single phase low voltage supply;

(c) is fitted with a flexible cord and plug rated at not more than 16 A;

(d) can easily be moved from one place to another while it is connected to supply; and

(e) has, for GMAW (gas metal arc welding), GTAW (gas tungsten arc welding), and FCAW (flux cored arc welding) machines, a 100% output rating not exceeding 65 A. The 100% rating is calculated from the square root of the marked duty cycle expressed in decimal form multiplied by the marked output current associated with the duty cycle in amperes;

but does not include—

(f) an arc welding machine promoted exclusively to industry.
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Gas Tungsten arc welder

The team’s first experiments examined titanium welds. Titanium is popular in manufacturing because of its corrosion resistance and light weight. Also, titanium has two well-characterized solid-phase transitions at ambient air pressure before it melts. In pure titanium, the alpha phase exists from room temperature to 882°C. At these temperatures, titanium has a hexagonal-close-packed crystalline structure.

Using the experimental setup shown in the figure below, a metal bar rotates under a Gas Tungsten arc, taking 6 minutes for a full revolution. An intense x-ray beam from the synchrotron source passes through a pinhole to allow researchers to resolve features as small as 180 micrometers. During welding, the x-ray beam is aimed at specific points around the heat source. A silicon photodiode linear array detector records the diffraction patterns during the experiment.

Phase mapping experiments performed using the SRXRD method are useful for observing phase changes under quasi-steady-state heating and cooling conditions. The next step was to examine the changes that occur at a single spot as a function of time. Wong developed a time-resolved x-ray diffraction (TRXRD) technique that takes a set of x-ray diffraction patterns at a single location adjacent to or within a stationary spot weld.

When the detector is clocked for durations of tens to hundreds of milliseconds, phase transformation may be observed on a much shorter time scale than is possible with moving welds. Changes in the diffraction pattern show directly how phase changes are taking place as a function of time and temperature. As the temperature goes up and then down, the metal at the weld becomes liquid and then solidifies. With TRXRD, the Livermore team has been able to examine the solidification and subsequent solid-state phase transformations in a number of different materials for the first time.

Vibra-Free High Speed Aluminium Machining