Читать книгу The Art of Welding - William Galvery - Страница 11
ОглавлениеOxygen and acetylene gases when combined, in the proper proportions in the torch handle’s mixing chamber, produce an approximately 5,600°F (3,100°C) flame at the torch tip. This flame melts the edges of the base metals to be joined into a common pool. Sometimes additional filler metal is added to the molten pool from a welding rod. When this common pool cools and the metal freezes solid, the joined metals are fused together and the weld complete. Other fuel gasses can be used in place of acetylene—and often are for soldering or brazing—but their maximum heat potential is below the heat output required for welding steel. The American Welding Federation (AWF) uses the abbreviation OAW for oxyacetylene welding.
WHAT ARE THE APPLICATIONS THAT OAW IS BEST SUITED FOR?
WHAT METALS CAN THE OAW PROCESS READILY WELD?
WHAT ARE SOME BASIC SAFETY PROCEDURES?
WHAT TYPES OF EQUIPMENT ARE NEEDED?
HOW DO YOU SELECT FILLER METAL (WELDING ROD)?
HOW IS THE EQUIPMENT SET UP?
WHAT ARE THE SPECIAL PREPARATIONS FOR WELDING?
HOW ARE WELD RESULTS ACCESSED?
WEST COAST CUSTOMS WELDING TIPS
OXYACETYLENE WELDING TIPS FROM WEST COAST CUSTOMS
Figure 3-2 OAW does not require electrical power, so it is extremely portable.
What are the applications that OAW is best suited for?
If you have many different types of projects or repairs, OAW processes work well, particularly if you are not near an electrical power source. Unlike other welding processes, OAW does not require electrical power. Use it for welding thin sheet, tubing, and small-diameter pipe.
Pros and Cons of OAW Process
Advantages
•Low cost
•Readily portable
•Excellent control of heat input and puddle viscosity
•No external power required
•Good control of bead size and shape
•Fuel mixture is hot enough to melt steel
Disadvantages
•Not economical to weld thick pieces of metal compared with other processes
•Slowest of the welding processes
What metals can the OAW process readily weld?
•Copper
•Low alloy steels
•Bronze
•Wrought Iron
•Lead
•Cast steel
Aluminum and Stainless Steel
These metals are usually not welded using the OAW process, but they may be welded provided one or more of the following steps are taken: preheat, postheat, use of fluxes, or special welding techniques. The reason is that aluminum does not change color prior to melting, so it requires extra welder skill to control heat input. It lacks strength at high temperatures. And exposed aluminum has a very thin oxide layer that requires the use of flux and also the oxide surface does not let the welder see a wet-looking molten weld pool.
What are some basic safety procedures?
All construction projects require a group of safe practices, and welding is no exception. Chapter 1 covered general safety measures for welding, but there are additional practices and equipment that are specific to OAW processes.
Essential Pieces of Safety Equipment
•Non-synthetic fabric (cotton or wool) long-sleeved shirt buttoned to the top to prevent sparks from entering.
•Tinted welding goggles with minimum of number 5 shade lenses.
•Leather gloves.
•Spark igniter.
•Pliers for moving hot metal.
Figure 3-2 Leather gloves.
Photo courtesy of Hobart Welders.
Figure 3-3 Cotton welding shirt.
Photo courtesy of Hobart Welders.
Figure 3-4 Tinted welding goggles.
Photo courtesy of Hobart Welders.
Figure 3-5 Spark igniter for lighting welding torch.
Photo courtesy of Hobart Welders.
Preventing Accidents
•External eye injuries from welding or grinding sparks are prevented by using welding goggles, safety glasses, or safety shields.
•Internal (retinal) eye damage from viewing hot metal and the radiation being emitted during welding and while cooling (until the metal is no longer red), prevented by using a number 5 tinted lens.
•Burns from weld sparks and hot metal prevented by leather or heavy cotton welding gloves, fire retardant clothing, leathers or specially treated welding jacket or cape-sleeves and bibs when working overhead, cuffless pants, high-top leather shoes.
•Fume hazards from the vapors of metals and flux must be avoided by proper ventilation, fume filters, and welder air supplies to the welding hood.
•Fires from the welding process prevented by moving flammables away from the weld zone and having water or fire extinguishers close at hand.
16-Step Safety Plan
•Never use oxygen in place of compressed air.
•Never use oxygen for starting engines or cleaning clothing.
•Store and use acetylene and propane cylinders valve end up.
•Secure cylinders to prevent them from being knocked over in use.
•Use valve protection caps on cylinders while moving them.
•Use a striker to light an oxyfuel torch. Never use a match or cigarette lighter because these can can cause a large fire or explosion with the potential power of a half-stick of dynamite.
•Never leave a lighted torch unattended.
•When a cylinder is empty, close the valve and mark it EMPTY (MT).
•Do not attempt repair of cylinder valves or regulators; send them to a qualified repair shop.
•Never use compressed gas cylinders as rollers.
•Never attempt welding on a compressed gas cylinder.
•Keep power and welding cables away from compressed gas cylinders.
•Prevent sparks from falling on other persons, combustible materials, or falling through cracks in the floor.
•On old-style acetylene cylinders with a removable valve wrench, always leave the wrench in place when using the equipment so that it can be shut off quickly in an emergency.
•When transporting compressed gas cylinders by vehicle have the cylinder caps in place and secure the cylinders so they will not move around as the vehicle starts and stops. Never transport cylinders with the regulators in place.
•Never carry compressed gas cylinders inside a car or car trunk.
Welding Sealed Cylinders or Other Containers
Never weld on a sealed container regardless of its size. Even if the vessel is clean and empty, penetration of the shell could release hot gases from the interior. They could also drive the torch flame back towards the welder. If the cylinder is empty and contains no residual vapors, vent it to atmosphere by opening a valve, hatch, bung, or by drilling a hole. An even more dangerous situation results when the cylinder contains residual flammable vapors whether it is vented to atmosphere or not. This will almost certainly result in an explosion. Clean or purge the cylinder with an inert gas, then have it checked for explosive vapors by a qualified person. Vent it to the atmosphere and begin welding. In some cases filling the vessel with water or other liquid and welding below the liquid is acceptable, but this is an area for experienced, knowledgeable welders.
Ventilation
Make sure the welding area is well ventilated to draw the weld fumes away from the welder. Many fumes from the welding process are poisonous and must be avoided. Welding fumes from cadmium plating, galvanized sheet metal, lead, brass (which contains zinc), and many fluxes (especially those containing fluorine) are poisonous. They can have both immediate and long-term adverse health effects. Welding supply companies, welding equipment manufacturers, and materials suppliers will provide MSDSs (Material Safety Data Sheets) on request. Often they are available for downloading via the Internet from the manufacturer. They detail the hazards of materials and equipment and show how to deal with them safely. They are particularly helpful in understanding the fume hazards of fluxes, solders, and brazing materials.
What types of equipment are needed?
Compressed Gas Cylinders
Both oxygen and acetylene are shipped and stored in special cylinders. Oxygen cylinders are seamless vessels of special high-strength alloy steel. They are made from a single billet by a draw-forming process and they contain no welds. Acetylene cylinders are fabricated and contain welds.
Frequently, oxygen cylinders are painted green or have a green band, but the only sure way to determine the contents of a compressed gas cylinder is to read the adhesive label on it. This label is required by law and should not be removed. Do not go by its color as there is no color code. Unlike civilian industry, the US armed forces do color code their cylinders.
Figure 3-6 Here is a basic OAW setup. It includes cylinders of oxygen and acetylene, regulators for the tanks, hoses, igniter, and welding torch with interchangeable tips.
Photo courtesy of Hobart Welders.
Acetylene will form explosive mixtures with air at all concentrations between 2.5 and 80%. This is the widest range of any common gas and almost insures an explosion if leaking gas is ignited. At 70°F (21°C), the acetylene should show 225 psi (15.5 bar) and the oxygen 2,250 psi (155 bar). Note that these pressures will fluctuate with ambient temperature.
Acetylene, like most other fuel gas handling equipment, has a notch or groove cut in the middle of the edges of the hexagonal faces of the swivel nut. This is a flag for a left-handed thread. See Figure 3-7.
Figure 3-7 This illustration compares connector nuts for acetylene and oxygen equipment.
Tank Cross Sections
Safety valves and plugs prevent the cylinder bursting from overpressure when it is heated. Oxygen cylinders have a small metal diaphragm in a section of the valve which ruptures, releasing cylinder pressure to the atmosphere and preventing a cylinder burst. Disk rupture occurs above 3,360 psi (232 bar), the cylinder test pressure.
Acetylene cylinders contain one to four fusible safety plugs depending on their capacity. These fusible plugs, made of a special metal alloy, melt at 212°F (100°C).
They also release the cylinder contents to atmosphere to prevent rupturing (and then exploding) when the cylinder is exposed to excessive temperatures, usually from a fire. Acetylene cylinders may have the plugs on the top, or top and bottom.
Figure 3-8 Detail of pressure safety relief on oxygen valve
Figure 3-9 Cross sections of an oxygen and acetylene cylinders
Transporting Cylinders. If an acetylene cylinder has been incorrectly transported on its side, the welder avoid using it immediately. The acetylene gas and the acetone in which it is dissolved may become mixed in the area just below the valve, resulting in both gaseous acetylene and liquid acetone at the top of the cylinder. This is where acetylene exits the cylinder and goes through the valve to enter the regulator. Both acetylene gas and liquid acetone will be drawn into the regulator possibly ruining the rubber components of the regulator and torch and creating a safety hazard. The weld metallurgy may also be contaminated.
To use the cylinder, stand it upright and wait at least one-half hour before connecting and using the cylinder to allow the liquid phase of the acetone to separate from the acetylene gas in the upper portion of the cylinder. That way no acetone will be drawn into the regulator possibly damaging its seals. Also, acetone in the weld flame will contaminate the weld pool and spoil the weld.
Reading High-Pressure Cylinders
The stampings indicate which US Department of Transportation specifications the cylinder meets, what type steel was used, who fabricated it, and when.
•Steel stamp markings such as “DOT-3A-2400” indicate the cylinder was made to US Government Department of Transportation (DOT) specifications, the “3A” denotes chrome manganese steel (or “AA” for molybdenum steel), and the “2400” the maximum filling pressure in psi.
The oldest date indicates the month and year of manufacture. Subsequent dates, usually at five year intervals, indicate when mandatory hydrostatic pressure testing was performed and by whom. See Figures 3-10 and 3-11.
Figure 3-10 High-pressure cylinder markings
Figure 3-11 Acetylene cylinder markings
Common Cylinder Sizes
A 55 ft3 (1557 liter) oxygen cylinder would last under two hours cutting 1/8 inch (3 mm) steel plate. For the larger cylinders, their size and weight can be major drawbacks. In general the mid-sized cylinders offer the best compromise of economy and convenience.
Figure 3-12 Oxygen cylinder sizes
Figure 3-13 Acetylene cylinder sizes
Other Fuel Gases can be used in place of acetylene, but their maximum heat potential is below that required for welding steel. Acetylene is the best gas for welding because it:
•Has the highest temperature of all fuel gases.
•Acetylene delivers a higher concentration of heat than other fuel gases.
•Has the lowest chemical interaction with the weld pool’s molten metal than all other gases.
However, other gases such as natural gas, methylacetylene-propradene stabilized (also called MPS or MAPP® gas), propane, hydrogen, and proprietary gases based on mixtures of these are frequently used for other non-welding processes for cost reasons. They work well for soldering, brazing, preheating, and oxygen cutting, and are seldom used for welding. Small changes, like different torch tips, may be necessary to accommodate alternate fuel gases. Table 3-1 shows the maximum temperature achievable with different fuel gases. Where even lower temperatures are needed (sweating copper tubing and many small soldering tasks) a single cylinder of fuel gas using only atmospheric oxygen is effective and economical.
Figure 3-14 Two-stage regulator
Regulators
Regulators reduce the pressures of welding gases from the very high cylinder pressures to the low pressures needed by the torch to function properly. Also, as the cylinder pressure falls with gas consumption, the regulator maintains the constant pressure needed by the torch, even though the cylinder supply pressure drops greatly. For example, an oxygen cylinder may contain oxygen at 2,250 psi (155 bar) and the torch requires about 6 psi (0.4 bar) to operate. Similarly, a full acetylene tank may contain gas at 225 psi (15.5 bar) and the torch needs fuel gas at 6 psi (0.4 bar).
There are single-stage and two-stage regulators available. The two-stage regulator’s advantage is that a higher volume of gas may be withdrawn from the cylinder with less pressure fluctuation than produced by a single-stage regulator. The combination of two regulators working together in series maintains a very constant torch pressure over wide cylinder pressure changes. Its disadvantage is cost. They are only needed when large gas volumes are needed as with multiple stations or rosebud tips.
Figure 3-15 This is an oxygen tank regulator
Torches, Tips, and Hoses
Shown below is the most common oxyacetylene torch design. Other designs are available. Some have very small flames for jewelry and instrument work, while others take no accessories and are much lighter in weight than standard torch designs to reduce operator fatigue. Some torch handles can accommodate cutting heads.
Matching the size of the flame, which is controlled by the torch tip, and the resulting volume of gas to the thickness of the metal in the weld is important. Too much flame and the base metal around the weld may be damaged, too little and there is inadequate heat to melt metal for full penetration.
Figure 3-16 Tank hoses are sold in 25 and 50-foot lengths
Figure 3-17 Oxyacetylene torch handle
Figure 3-18 Cutting head attachment
Figure 3-19 Oxyacetylene torch and tip
Figure 3-20 Welding tip
Photos courtesy of Hobart Welders.
Torch Tip Sizes
There is no industry standard; each torch manufacturer has its own numbering system. Cross-reference tables compare each manufacturer’s tip sizes with numbered drill sizes.
The American Welding Society (AWS) has been urging tip manufacturers to stamp tips with the material thickness size to eliminate the confusion of tip size numbers. The AWS C4.5M Uniform Designation System for Oxy-Fuel Nozzles calls for tips to be stamped with the name of the manufacturer, a symbol to identify the fuel gas, the maximum material thickness, and a code or part number to reference the manufacturer’s operating data; many manufacturers are not in compliance. Most companies making welding tips do provide information booklets available to cross reference their tip sizes to tip drill sizes. See Table 3-2.
Table 3-2 Matching welding tip size to weld material thickness
Finding the Drill Size of a Tip
Using a tip cleaner find the round file which fits into the tip easily but snuggly then check the drill size of that file listed on the body of the tip cleaner cover.
TOOL TIP
Cleaning Tips
When sparks from the weld puddle deposit carbon inside the nozzle and on the tip face, they act as spark plugs and cause premature ignition of the gas mixture. Torch tips should be cleaned at the start of each day’s welding and whenever flashback occurs, the flame splits, or when the sharp inner cone no longer exists. To clean, select the largest torch tip cleaning wire file that fits easily into the nozzle and use the serrated portion to remove any foreign material. Be careful not to bend the tip cleaner file into the tip which can cause the cleaning file to break inside the tip; if the breaks inside the tip it is nearly impossible to remove. Also be sure not to enlarge the existing hole. Then touch up the face of the tip with a file or emery cloth to remove any adhering dirt. Use compressed air or oxygen to blow out the tip. Never use a twist drill to clean the tip; it will cause bell-mouthing.
Figure 3-22 Here is a collection of torch cleaning files.
Photo courtesy of Hobart Welders.
Flashback and Backfire
Flashback occurs when a mixture of fuel and oxygen burns inside the mixing chamber in the torch handle and reaches the hoses to the regulators or cylinders. Such burning in the hoses is extremely dangerous and will lead to serious injury. If either through operator horseplay (like turning on both the acetylene and the oxygen with the torch tip blocked) or through regulator failure, an explosive mixture of acetylene and oxygen is forced back toward the cylinders. When the torch is lit, this explosive mixture will go off. See Figure 3-23.
Figure 3-23 How flashback can occur
Flashback is easily prevented by installation of flashback arrestors consisting of both a check valve and a flame arrestor. These devices are about the diameter of the gas hoses and about 1 3/4 inches long. Some newer torch designs incorporate check valves and flashback arrestors into the torch handle itself. Some arrestors fit between the regulator and the hose. See Figure 3-24. The best arrestors include a thermally-activated, spring-loaded shut-off valve which closes on sensing a fire.
A backfire is a small explosion of the flame at the torch tip. The biggest hazard is that the detonation from the tip may blow molten weld metal five to ten feet from the weld and injure someone. Also, a series of repeated, sustained backfires, which can sound like a machine gun, may overheat the tip or torch, permanently damaging them.
Figure 3-23 Reverse-flow check valve flashback arrestor cross section
Figure 3-25 The flashback arrestor on the right is for an oxygen line; the one on the left is for acetylene.
Photo courtesy of Hobart Welders.
The most frequent cause of backfire is pre-ignition of the mixed acetylene and oxygen. Here are the most common causes of pre-ignition and their solutions:
•The mixed welding gases are flowing out through the tip more slowly than the flame front burns and the flame front ignites the gas in the tip and/or mixing chamber causing a pop. Solution: Slightly increase both the oxygen and acetylene pressures and if this results in too large a flame for the job, reduce the torch tip size.
•The tip may be overheated from being held too close to the weld or from working in a confined area like a corner. Solution: Let the tip cool off and try again holding the tip farther from the weld pool.
•Carbon deposits or metal particles inside the tip act like spark plugs prematurely igniting the mixed gases. Solution: Let the tip cool, then clean it thoroughly with your tip cleaning kit.
How do you select filler metal (welding rod)?
Usually the filler metal is a close match to the base metal. Sometimes the filler metal will have deoxidizers added which will improve the weldmore than just a base metal match. Rod diameters vary from 1/16 to 3/8 inch diameter. The prefix R in the description of the oxy-acetylene welding wire means rod which is followed by two or three numbers designating the ultimate tensile strength of the as welded filler material in thousands of pounds per square inch (ksi). See Table 3-3.
Table 3-3 Oxyacetylene steel welding rods
Procedures and Material Selections
Before welding, remove all surface dirt, scale, oxide, grease, and paint. Refer to Table 3-4 for suggestions on welding common metals. See Figure 3-25.
Figure 3-25 Before welding, clean metal thoroughly to remove grime and mill scale.
Table 3-4 Information for welding various metals
SR = Slightly Reducing SO = Slightly Oxidizing N = Neutral
Figure 3-26 Be sure you have the right type flame for the job at hand. For additional information on torch flames see pages 55 and 56.
Here are the steps for beginning the OAW process.
•Put on your welding safety equipment: tinted safety goggles (or tinted face shield), cotton or wool shirt and pants, high-top shoes, and welding gloves at a minimum.
•Make sure the valves on previously used or empty cylinders are fully closed and their valve protection covers are securely screwed in place. Then remove the empty cylinders from the work area and secure them against tipping during the wait for a refill shipment. Secure the newly replaced or full cylinders to a welding cart, building column, or other solid anchor to prevent the cylinders from tipping over during storage or use.
•Momentarily open each cylinder valve to the atmosphere and reclose the valve quickly purging the valve; this is known as cracking a valve. Cracking serves to blow out dust and grit from the valve port and to prevent debris from entering the regulators and torch.
•With a clean, oil-free cloth, wipe off the cylinder valve-to-regulator fittings on both cylinders to remove dirt and grit from the fittings’ connection faces and from the fittings’ threads. Do the same to both regulators’ threads and faces. Remember, never use oil on high-pressure gas fittings. Oxygen at high pressures can accelerate combustion of oil into an explosion.
•Make sure reverse-flow check valves are installed on the torch or the regulators.
•Check to see that both the oxygen and acetylene regulator pressure adjustment screws are unscrewed, followed by threading each regulator to its respective cylinder. Snug up the connections with a wrench. Caution: Oxygen cylinder-to-regulator threads are right-handed; so are oxygen hose to-torch screw fittings. Acetylene cylinder-to-regulator fittings and acetylene hose-to-torch fittings threads are left-handed.
•Stand so the cylinders are between you and the regulators, S-L-O-W-L-Y open the oxygen cylinder valves. Open the oxygen cylinder valve until it hits the upper valve stop and will turn no further. Also standing so the cylinders are between you and the regulator, open the acetylene cylinder valve gradually and not more than 1 1/2 turns. If there is an old-style removable wrench on the acetylene cylinder, keep it on the valve in case you must close it in an emergency. Standing so that the cylinders are between you and the regulators offers some protection should the regulator fail and the housing and gauges explode.
Figure 3-27 With the tank valves closed, back out the pressure adjusting screws on the regulators. When opening the tank valves, stand to the side or behind the tank in case the regulator malfunctions and explodes.
•Look at the high-pressure—cylinder side—pressure gauges to indicate about 225 psi (15.5 bar) in the acetylene cylinder and 2,250 psi (155 bar) in the oxygen cylinder. Note: 1 bar = 1 atmosphere = 14.5 psi = 0.1 MPa. Cylinder pressures vary with ambient temperature. The pressures given above are for full cylinders at 70°F (21 °C).
•Purge each torch hose of air separately: Open the oxygen valve on the torch about three-quarters of a turn, then screw in the pressure control screw on the oxygen regulator to your initial pressure setting—about 6 psi (0.4 bar). After several seconds, close the torch valve. Do the same for the acetylene hose. Comment: We do this for two reasons, (1) to make sure we are lighting the torch on just oxygen and acetylene, not air, and (2) to set the regulators for the correct pressure while the gas is flowing through them.
Caution: never adjust the acetylene regulator pressure above 15 psi (1 bar) as an explosive disassociation of the acetylene could occur.
•Recheck the low-pressure gauge pressures to make sure the working pressures are not rising. If the working pressure rises, it means the regulator is leaking. Immediately shut down the cylinders at the cylinder valves as continued leaking could lead to a regulator diaphragm rupture and a serious accident. Replace and repair the defective regulator.
•Test the system for leaks at the cylinder-to-regulator fittings and all hose fittings with special leak detection solutions; bubbles indicate leaks.
TOOL TIP
Adjusting the Torch to a Neutral Flame
Open the acetylene valve no more than 1/16 turn and use a spark lighter to ignite the gas coming out of the tip. A smoky orange flame will be the result, Figure 3-28 (A).
Continue to open the acetylene valve until the flame stops smoking (releasing soot). Another way to judge the proper amount of acetylene is to open the acetylene valve until the flame jumps away from the torch tip, leaving about 1/16 inch gap (1.6 mm), Figure 3-28 (B). Then close the valve until flame touches the torch tip.
Open the oxygen valve slowly. As the oxygen is increased, the orange acetylene flame turns purple and a smaller, white inner cone will begin to form. With the further addition of oxygen, the inner cone goes from having ragged edges, Figure 3-28 (C), to sharp, clearly defined ones. The flame is now neutral and adding oxygen will make an oxidizing flame, Figure 3-28 (D).
If a larger flame is needed while keeping the same tip size, the acetylene may be increased and the oxygen further increased to keep the inner cone’s edges sharp. This process of increasing the acetylene, then the oxygen is usually done in several cycles before the maximum flame available from a given tip is achieved. Adjusting the flame below the minimum flow rate for the tip orifice permits the flame to ignite inside the nozzle. This is flashback and makes a popping sound. If you need a smaller flame, use a smaller torch tip. See the section on flashback.
Figure 3-28 Shows flame adjustments from carburizing to a neutral flame
Flame Temperatures
The tip of the inner cone is the hottest part of the flame. The inner cone is where the optimum mixture of oxygen and acetylene burn. The outer envelope where any unburned acetylene burns with oxygen from the atmosphere. A neutral flame is when enough oxygen is present in the flame to be burning all of the acetylene gas and is used for most welding processes. See Figure 3-29.
Figure 3-29 Graph of an oxyacetylene flame temperature profile
TOOL TIP
Lighting a Multi-Flame (Rosebud) Tip
This type of tip produces a large flame for heating metal prior to welding, bending, or brazing. When using a multi-flame tip you first set the acetylene pressure at or just below 15psi (1 bar) and the oxygen pressure at 30psi (2 bar); open the acetylene torch valve far enough to light the acetylene flame. Once the flame is ignited, open the acetylene valve until you have full flow of gas; now you can open the oxygen torch valve and adjust the flame to slightly carburizing. You may now use the multi-flame (rosebud) to heat materials but keep the sharp inner cone flame away from the material and only touch the carburizing flame to the material being heated. A heat sensing device such as a pyrometer or temperature sensing stick can be applied to the material to indicate the temperature of the material being heated.
Figure 3-30 A rosebud tip is often used to preheat materials prior to welding
Photo courtesy of Hobart Welders
How is the equipment shut down?
First turn off the oxygen and then the acetylene with the torch handle valves. Turning off the acetylene first can cause a flashback.
Turn off the oxygen and acetylene cylinder valves at the upstream side of the regulators.
Separately, open and reclose the oxygen and acetylene valves on the torch handle to bleed the remaining gas in the hoses and regulator into the atmosphere. Verify that both the high-pressure and low-pressure gauges on both regulators indicate zero.
Unscrew the regulator pressure adjustment screws on both cylinders in preparation for the next use of the equipment. The regulator screws should be loose but not about to fall from their threads.
What are the joint preparations for welding?
Refer to Figure 3-31.
Figure 3-31 Preparation for OAW butt welds
For butt welds, here are examples of a correct weld, poor penetration weld, excessive reinforcement, undercutting, and excessive root reinforcement. See Figure 3-32.
Figure 3-32 Correct and defective butt weld profiles
Producing a good weld bead is a combination of four main factors: the distance between the torch tip and the work, the angle at which you hold the torch, your speed when moving the torch along the weld area, and the heat produced by the torch. Getting everything right takes practice, so always test your technique on scrap metal first.
Figure 3-33 Create a puddle at the start of the bead. Keep the tip steady until a puddle begins to form. Begin making a circular motion with the torch, slowly moving the torch tip in the direction of the bead. Keep the distance to the work and the speed of your movements consistent.
Figure 3-34 Now try it with a filler rod. The goal is to intermittently dip the end of the rod into the puddle to add material to the weld. Dip the end of the rod into the puddle while making a circular motion with the torch. This will help blend the filler material into the weld. Withdraw the rod from the puddle, but keep it close to the end of the torch to keep it preheated. Don’t directly heat the end of the rod with the torch.
Figure 3-35 The finished bead should be even throughout its length. The ripples created by the circular motion of the torch tip should be consistent.
