Welding Basics, Part 3

Oxy-acetylene Welding - Part One

In our series on welding we have taken a brief look at AC and DC arc welding along with basic techniques and safety equipment required for safe usage. Since our premise is to cover welding types that might best be used on a farm environment we have kept our overview purposefully simple and general.

The second type of welding that this observer finds quite useful in working with older equipment on the farm is that of oxy-acetylene welding. Commonly called gas welding it can readily be used for repairing lighter gauge steel as found on body parts or exhaust systems along with difficult to repair delicate parts like dash parts and special light weight holding devices. Lets take a brief overview of oxy units and their usefulness on the farm.

The term gas welding is not really limited to the use of oxygen and acetylene. By definition it is the burning of a gas flame, such as natural gas, LP, hydrogen or acetylene, in the presence of an oxygen source either from natural air, compressed air or pressurized pure oxygen. For our purposes it is most convenient to focus on acetylene gas and pressurized pure oxygen as our gas source since it gives us the hottest flame capable of melting the common metals encountered on the farm.

Our term gas welding, therefore, is the art of joining various metals together by melting and fusing their adjoining surfaces by using an intense, concentrated gas flame as the heating medium.

Lets take a quick look now at the equipment involved with an oxy-acetylene setup. The most obvious items noticed are the tanks that store the two gases. It should always be remembered that the pressurized oxygen and acetylene tanks are to be respected and taken care of. They can be quite lethal if dropped or misused. The acetylene tank is usually the smaller and chunkier of the two tanks. Acetylene gas is highly unstable at pressures over 15 psi so it is stored in an unusual manner. The stubby tank contains an inert substance like fullers earth or lime silica, which absorbs acetone. The acetone absorbs the acetylene and kind of keeps it in suspension preventing accumulating pockets of high-pressure gas thus stabilizing the explosive tendencies of the gas. Be careful not to lay the tanks on their side as this will permit some of the acetone to enter the valves, lines, and gauges and contaminate the system. A purplish flame color at the torch is an indication of this contamination. Also note that the shutoff valve on the acetylene tanks have left handed threads so the appropriate regulator and corresponding hardware can be properly installed. It is recommended that this valve only be opened an average of one half turn when in use so it can be quickly turned off in case of emergency.

The other cylinder in the pair is the oxygen tank. This can almost be characterized as a loaded bomb. The gas in a fully charged cylinder has more than one ton of pressure for every square inch of surface area. The gas is an oxidizer that supports common combustion to the extreme and will make typical items burn with an unbelievable violence and intensity. It should be respected as such and measures should be taken to ensure a secure storage and usage environment. When not in use with the corresponding regulator the oxygen cylinder, as with the acetylene tank, has a heavy-duty screw on cap that protects the valve. It should always be used. In addition the cylinders should always remain securely fastened to a wall or similar structure to keep them from tipping over.

Since the various gases are stored at considerably higher pressures than are used in the welding process a pressure regulating mechanism must be provided. Pressure regulators that fasten to the respective cylinders of gas provide this function. They reduce the cylinder pressure to a working pressure and also maintain a constant gas pressure at the torch even though the cylinder pressure may vary. Most regulators are a two-gauge unit, the high pressure or primary gauge reflecting the cylinder pressure, the low pressure or secondary gauge showing the delivery pressure to the torch hose. Once again, the oxygen fittings are right hand thread, the acetylene are left hand threads. Take care fastening the respective gauges to their cylinders and hoses. Dont over tighten and make sure to use the correct wrench to avoid curling the brass nuts and fittings. Check to make sure the regulator-adjusting valve is screwed out all the way to prevent premature charging of the secondary circuit. Charge the gauges by slowly cracking the cylinder valves open to prevent pinging of the gauge needles or melting of the seats due to sudden heat compression in the gauge. Never use any type of oil or grease in conjunction with oxy-acetylene fittings or related components. Once again, make sure all tanks are securely fastened to a wall or supporting structure to prevent them from tipping over. Keep in mind that acetylene gas is highly unstable at pressures over 15 psi. Make sure the secondary gauge measuring the acetylene gas going to the torch hosing never goes over that pressure.

The hoses delivering the gases from the tanks to the torch should be of a regular welding type. The rubber is designed not to break down by the respective gases and already has the correct fittings pre-fitted on the ends. Take care not to kink the hose or step on it as it stretches across the work area. Also try to protect it from melted metal globules that are produced in the welding process. Once again the fittings are either left or right hand threads matching the corresponding gas used. The hose fittings screw into the respective left or right hand receptacles of the gas torch.

The torch is where the gases are mixed and delivered to the torch tip where they are ignited and used for welding purposes. The gases are directed into the torch base and through respective shut off valves. These valves serve two purposes: one for shutting off and on the gas stream the other for throttling the gas flow to give the flame the correct characteristics for proper burning. From the valves the gases flow into the main body of the torch and into the mixing chamber. Then on through the torch barrel to the tip where it is expelled through a drilled hole called the orifice. The orifice size depends on the type, and thickness of metal being welded along with the rod diameter and heat/pressure requirements. Keeping the orifice cleaned and free of welding debris will assure a clean and properly formed flame.

As with any welding proper safety gear should be mentioned before the welding procedure takes place. Make sure and wear the correct protective eyewear. The flame and puddle of molten metal emits both ultraviolet and infrared rays that may cause eye injury if viewed at close distance. The goggles also protect the eyes from flying sparks and the occasion popping of overheated metal. Generally speaking the thicker the metal to be welded and the more heat produced by the torch requires a darker shade for eye protection. A number of 4-5 is a good all around shading for the casual gas welder. Protective clothing consists of heavy leather gloves with a gauntlet covering the wrists, a non-flammable shirt or jacket and flame resistant trousers without cuffs. Good heavy leather shoes with thick soles will award a little more time if one accidentally steps on a hot piece of metal. Also be aware to not wear accessories like pens and other pocket items on your person when welding. A carefully misplaced spark in an oxygen rich environment might cause a quick burn scenario that could create a potential problem. Acquire and use a flint and steel lighter for igniting the torch. The steel cup tends to trap a small amount of gas that quickly and safely ignites when sparked.

Weve taken some time to give a brief overview of the oxy-acetylene welding unit and offered some safety advice. In the next part of this series we will look into the welding process and finish up with a few tips on using the cutting torch.

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