320102b. Agricultural Equipment Technician. Oxy-Fuel Equipment. Electric Welding and Oxy-Fuel Cutting. First Period

Transcription

1 320102b Agricultural Equipment Technician Oxy-Fuel Equipment Electric Welding and Oxy-Fuel Cutting First Period

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3 Table of Contents Objective One... 2 Oxygen... 2 Acetylene (C 2 H 2 )... 4 Propane... 8 Objective Two The Oxy-Fuel Outfit Regulators Hoses Check Valves Torch Handle Welding and Heating Tips Objective Three Oxyacetylene Set-Up Prior to Use Balance the Pressures for Welding and Heating Flame Types Oxy-Fuel Cutting Factors for a Quality Cut Objective Four Goggles Objective Five Cutting Common Cutting Faults Fusion Welding Steel Brazing Braze Welding Objective Six Effect of Heat on Metal Rules to Remember when Welding Self-Test Self-Test Answers... 57

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5 Oxy-Fuel Equipment NOTES Rationale Why is it important for you to learn this skill? Oxy-fuel equipment is used in many phases of agricultural equipment repair. You must know the safety requirements, heat control, and cutting principles for using oxy-fuel equipment in order to make these necessary repairs. This module provides the information required to perform heating and cutting operations safely. Outcome When you have completed this module you will be able to: Demonstrate the use of the torch for welding, heating, brazing and cutting. Prerequisites In order for you to fully understand the information presented in this module, you must first complete the following module: a Welding Safety Objectives 1. Describe the characteristics and safe handling procedures for gases and cylinders. 2. Describe care and maintenance procedures for the oxy-fuel outfit. 3. Demonstrate equipment set-up, adjustment and shut down procedures. 4. Demonstrate use of personal protective equipment and safe operating procedures. 5. Perform heating, welding and cutting operations using oxy-fuel equipment. 6. Describe temperature indicators and the effect of heat on metal. Introduction This module will cover safe set-up and use of oxyacetylene equipment, including the techniques required to perform heating, welding and cutting operations on metals. 1

6 Objective One When you have completed this objective you will be able to: Describe the characteristics and safe handling procedures for gases and cylinders. Oxygen Oxygen (O 2 ) is a colourless, odourless and tasteless gas. It is not flammable itself but supports combustion of other materials. Atmospheric air is composed of approximately 21% oxygen. Oxygen used for oxy-fuel equipment is 99.5% pure. In this nearly pure form, oxygen must be considered a potential danger because it greatly speeds up combustion of known flammable materials. It combines readily and often violently with many other materials including some that are not generally considered combustible. Rubber, burning in pure oxygen, burns rapidly with a white flame, practically no smoke and little odour. Fabric burns rapidly in oxygen with intense heat. If your clothing is saturated with oxygen, a spark or misdirected flame could easily ignite the fabric causing severe burns to your body. If oil or grease is exposed to pure oxygen under pressure or friction, it can spontaneously explode without external ignition. When steel is heated to a red heat and oxygen is applied, it oxidizes quite rapidly, reducing the reacted metal to iron oxide or ash. This is the principle behind the cutting torch. DANGER Keep oxy-fuel equipment away from oil, grease, cleaning fluids and gasoline! Never oil regulators or torch parts. Do not use compressed air to blow out oxy-fuel equipment. O 2 + Oil = Explosion Oxygen Cylinders Oxygen for oxy-fuel equipment is stored as a compressed gas in a seamless cylinder. Oxygen cylinders come in several different sizes. The two most popular sizes being the K (241 cu ft or 6.82 cu m) and the M (121 cu ft or 3.43 cu m). When an oxygen cylinder is filled, the gas is compressed to approximately 2200 psi ( kpa) at 21 C. Half size and smaller cylinders will carry the same pressure as larger cylinders and their construction is very similar. Although the preferred orientation of the oxygen cylinder is upright, it can be used in any position. The contents of the cylinder are indicated by a WHMIS label stating that the cylinder contains oxygen. The colour of the cylinder is not a reliable indicator of its contents. 2

7 A typical oxygen cylinder with the valve and protective cap installed is shown in Figure 1. NOTES Figure 1 - Oxygen cylinder with protective cap installed. Valve The valve on an oxygen cylinder has a right-hand (RH) thread to connect the regulator (Figure 2). The oxygen cylinder is protected from extreme pressure, or pressure rise caused by heat or fire, by a safety device known as a frangible disk, a fusible metal rupture disk. This disk is mounted between the cylinder valve and a drilled nut on the rear side of the cylinder valve opening. The melting point of fusible metal is around 115 C. Its purpose is to melt or burst, as the case may be, and allow for slow controlled escape of gas, thus avoiding the violent bursting of the cylinder. Figure 2 - Oxygen cylinder valve. The oxygen cylinder valve is a double seated valve. One seat seals to prevent the flow of oxygen from the cylinder when the cylinder valve is closed. The other seat seals when the cylinder valve is fully open to prevent leakage around the stem of the valve. Since there can be leakage around the valve stem, it is recommended the oxygen valve be fully open when using the oxy-fuel equipment. 3

8 A drawing of an oxygen cylinder valve is shown in Figure 3. \ Figure 3 - Oxygen cylinder valves: closed, partially open and fully open. Acetylene (C 2 H 2 ) Acetylene is a colourless, flammable gas and has a strong pungent odour. Acetylene is an endothermic compound, which means it absorbed extra heat energy at some stage during its formation. When acetylene is burned, this endothermic heat is released along with the heat generated by burning the carbon and hydrogen, which forms the acetylene gas. This endothermic heat contributes to the high temperature of the oxyacetylene welding flame (3300 C), making it the most efficient fuel gas for welding purposes. This gas is very unstable when compressed beyond 15 psi (100 kpa). The critical point for acetylene is reached at 28 psi (193 kpa) with a minimum temperature of 21 C. At this critical point, acetylene will ignite spontaneously in the presence of air. This critical point lowers as the temperature of the gas rises. Because of this, the maximum safe working pressure is considered to be 15 psi (100 kpa). DANGER Do not set acetylene operating pressure in hoses or manifold systems above 15 psi (100 kpa). Acetylene gas is highly flammable and, compared with other fuel gases, has the widest explosive range when mixed with air. As little as 2.5% acetylene in air is an explosive mixture. Unlike other combustible gases, these explosive mixtures continue right up the scale as the acetylene content is increased and the air is decreased. 4 This flammability of all the fuel gases listed in Table 1 is greatly magnified when mixed with pure oxygen. You should treat all mixtures of acetylene and air or oxygen as being explosive. Acetylene gas is approximately the same weight as air and tends to collect in pockets rather than dissipate into the air. If you can smell acetylene, do not take any chances. Extinguish all open flames and ventilate the room before turning on a light switch. Test for leaks by brushing soapy water onto suspected joints or areas. Watch for bubbles. Never test for leaks with an open flame.

9 Fuel Type Range of Flammability (% Gas in Air) Propane % Butane % Natural Gas 5-15% MAPP Gas % Acetylene 2-89% Table 1 - Range of flammability of common fuel gases. Over time, moist acetylene gas under pressure will react with copper. The endothermic heat will be released. Pressure will rise, which will possibly lead to an explosion. Never use copper or red brass fittings or tubing for acetylene pipeline systems or for hose splices. NOTES NOTE Use only yellow brass, steel or stainless steel fittings and piping for acetylene systems. Never use copper or red brass. Acetylene Cylinders An acetylene cylinder has a WHMIS label indicating that it contains acetylene. Two types of acetylene cylinders are shown in Figure 4. Acetylene cylinders are completely filled with a porous filler mass. This material can be asbestos, balsa wood, corn pith or many other products. This serves to break up the large cylinder cavity into tiny cells. Acetylene is most unstable when compressed in a large cavity. The voids within the porous material of an acetylene cylinder are then filled to approximately 40% capacity with acetone. Acetone is an alcohol derivative that has the ability to absorb large volumes of acetylene. When gaseous acetylene is pumped into the cylinder, the acetylene is absorbed into the acetone. The cylinders are filled by weight. The combination of a porous filler and acetone allows acetylene to be stored safely in the cylinder at high pressures (250 psi [approximately 1700 kpa]). Because the acetone is a liquid, it is essential to use acetylene cylinders in a vertical position to prevent acetone from being drawn off as the acetylene gas is used. It is thought that the action of lying a cylinder and standing it up can contribute to the acetylene (C 2 H 2 ) compound disassociating, relative to its critical pressure point, resulting in a time delayed pressure increase and subsequent cylinder rupture. DANGER Keep acetylene cylinders upright at all times during transport, storage and use. Acetylene cylinders come in several different sizes, the two most popular sizes being: WK (300 cu ft or 8.5 cu m) and WS (130 cu ft or 3.7 cu m). Half sized and smaller cylinders will carry the same pressure as a full sized cylinder and their construction is very similar. 5

10 When acetylene is drawn out of a cylinder, it is possible for acetone to be drawn out of the cylinder with the acetylene. It takes time for the acetylene to bubble out of the liquid acetone. The maximum amount of acetylene that can be taken from the acetone is referred to as the draw limit. To prevent drawing off acetone with the gas, a cylinder must be emptied no faster than one-seventh of its capacity per hour (or less than 7 hours). When large tips are used with small size cylinders, the draw limit can be exceeded. Fuel consumption specifications for heating and cutting tips are available from the manufacturer. Use a cylinder that has a large enough capacity to supply the largest tip in your outfit. When the heating and cutting equipment requires larger volumes than can be supplied from one cylinder, two or more cylinders must be connected together using an approved manifold system. Minimum cylinder size (cu ft) = tip consumption (cu ft per hr) x 7 Acetone drawn with the acetylene will produce a flame that is cooler and can be identified by a pale blue colour with orange flecks. The acetone, being a solvent, will cause damage to any plastic or rubber parts in the regulator, hoses and torch assembly. Loss of acetone from the cylinder will also reduce the safety factor of that cylinder. Fusible metal plugs are installed in the cylinder to allow a controlled release of acetylene in the event of a fire. The plugs will melt out at 100 C and allow acetylene to discharge. Common locations for the plugs are: on the concave bottom of the cylinder, a filled passage on the back side of the cylinder valve, on the reinforcing collar or neck ring or the shoulders of the cylinder. Figure 4 - Acetylene cylinders. 6

11 Valves Generally, two styles of valves are used. These are shown in Figure 5. Acetylene cylinder valves use a left-hand (LH) thread to connect the regulator. The cylinder with the recessed top uses a special wrench to operate the valve. NOTES NOTE The wrench should be attached to the valve whenever the cylinder is in use. Figure 5 - Acetylene cylinder valves. The most commonly used acetylene valve is the exposed type as shown in Figure 6. Figure 6 - Acetylene valve. Unlike an oxygen cylinder valve, the acetylene valve does not have a double seating system and thus, is not required to be fully open when acetylene is being used. The cylinder valve should be opened only about 1 to 1 1 / 2 turns to allow enough fuel flow for the heating or cutting operation. In the event of a fire, this allows the cylinder valve to be closed quickly. 7

12 Propane There are other fuel gases available for use in the welding industry (see Table 1). Propane (C 3 H 8 ) (liquid petroleum gas (LPG)) is the most common and is readily available. The other gases function similar to propane. Propane is colourless with an added odour. The advantages of propane over acetylene is that it is more stable to handle and store, it is less expensive and is more readily available. Propane can be purchased at your local gas station and you do not require a rental contract for the cylinders. The disadvantage is that the oxy-propane flame is not hot enough (2500 C) nor concentrated enough for welding. It can, however, be effective for heating and cutting applications. The oxyacetylene equipment, in general, will work with propane. The propane cylinder will receive a normal acetylene regulator and similar gas pressures are used. It is necessary to use specific heating and cutting tips designed specifically for propane. The oxy-propane flame requires slightly different techniques to light and adjust compared to oxyacetylene. You are advised to handle propane with the same safety procedures and precautions as are described for acetylene. Handling Compressed Gas Cylinders Normally, you purchase a yearly lease agreement (contract) with a gas supply company for all your welding gases. That contract entitles you to have possession of specified cylinders. When a cylinder is empty, you return the empty cylinder to the supplier, trade it for a full cylinder and pay for the gas in the full cylinder. To avoid mixing empty cylinders with full cylinders, it is helpful to mark a large "MT" (which means empty) with chalk or soapstone on the empty cylinder when the regulator is removed. Leave the valve closed on an empty cylinder to prevent contamination of the cylinder. Cylinders should not be stored or used in close quarters with welding activities or machines. If the cylinder should become grounded, any contact made with the electrode or electrode holder could result in an arc being struck against the cylinder. A flame, hot slag or sparks directed at a cylinder could result in damage to the valve, cylinder or equipment. A cylinder damaged in any way is very unsafe and could easily explode. Any cylinder that is faulty, leaks or is damaged, must be taken out of service and isolated for safety reasons. Place it outside away from buildings, combustible material and any source of ignition. Tag it as to the type of fault and notify the supplier. Do not attempt any repairs to cylinders. Cylinders must be fastened in place or supported in a cart when in use. When supported, the caps can be removed. Figure 7 shows how acetylene, propane and oxygen cylinders can be secured to a cart. 8

13 Figure 7 - Cylinders secured to cart. For safety reasons, it is very important you adhere to the following guidelines. Store cylinders in a cool, dry, well-ventilated location. Store oxygen and fuel gas cylinders separately (a minimum of 6 m (20 ft) apart). Store, transport and use acetylene cylinders in the vertical position. Keep protective caps on the cylinders during transportation and storage. Keep cylinders tied in place during transport, storage and use. Do not attempt to transfer acetylene from one cylinder to another. Do not drop, bump or pound on cylinders of either type. Do not use cylinders as rollers, dollies or supports. Do not attempt to interchange equipment (such as regulators or hose) from one type of gas to another type. Call the gases by their proper names. Do not refer to acetylene as gas or oxygen as air. Operate cylinder valves according to instructions. Keep oxy-fuel equipment away from oil or grease. Do not use compressed air to blow out oxy-fuel equipment. The air may contain oil from the compressor. Do not use oxygen for dusting purposes or for blowing off mechanical parts. Keep oxy-fuel equipment clear of electric arc welding equipment. An accidental arc strike against the cylinder could cause a fire or serious explosion. Avoid directing a flame, hot slag or sparks at the oxy-fuel equipment. Do not attempt any repairs to cylinders. Do not attempt to use oxygen or fuel gas directly from the cylinder at cylinder pressures. Always use a proper pressure regulator. Close empty cylinder valves snugly and place protective caps on the cylinders to protect the valves. This will prevent contamination of the cylinder by moisture, dust and foreign gases. Cylinder valves left open are always an explosive hazard since a change in temperature could cause the release of gas from within the cylinder. When lifting cylinders with a crane, use a properly designed cradle. 9

14 Objective Two When you have completed this objective you will be able to: Describe care and maintenance procedures for the oxy-fuel outfit. The Oxy-Fuel Outfit The combination oxy-fuel outfit consists of the following and are shown in Figure one oxygen and one acetylene regulator, 2. a torch handle complete with torch valves, 3. cutting tips, 4. a cutting attachment, 5. welding tips with individual gas mixers, 6. an accessory package (includes hose, goggles, spark lighter and tip cleaners) and 7. one set of check valves. Figure 8 - Oxyacetylene outfit. Regulators Pressure regulators are used on both the oxygen and fuel cylinders. They are required to reduce cylinder pressure to an usable working pressure. They are designed to maintain a constant delivery pressure regardless of pressure changes in the cylinders. 10

15 Two gauges are mounted on the regulator. The high pressure gauge indicates the pressure in the oxygen or fuel cylinder (pressure into the regulator). The low pressure gauge indicates the regulated hose or working pressure. NOTES Pressure regulators have a non-serviceable filter at the inlet fitting to prevent foreign particles from entering the regulator. Types Although similar in design, the oxygen and fuel regulators are not interchangeable. An oxygen regulator has right-hand threads on both the inlet and outlet fittings and generally has green markings. The gauges are calibrated with high reading numbers. An oxygen regulator is shown in Figure 9. Figure 9 - Oxygen regulator. The fuel regulator has left-hand threads on both the inlet and outlet fitting and generally has red markings. The gauges are calibrated with lower reading numbers. An acetylene regulator is shown in Figure 10. Figure 10 - Acetylene regulator. 11

16 Single Stage Single stage regulators change cylinder pressure to operating pressure in one step. Using the hand, (adjusting screw), clockwise rotation increases pressure and counter-clockwise rotation reduces pressure. When the hand control is turned fully counter clockwise until it freewheels the outlet pressure is reduced to zero. The operating principle of a single stage regulator is shown in Figure 11. Single stage regulators are the most common and function well for general cutting and heating applications. Figure 11 - Single stage regulator. Two-Stage Two-stage regulators, as shown in Figure 12, have two diaphragms, two metering needles and two seats. The first stage reduces the high gas pressure that comes from the cylinder to some intermediate pressure. The second stage is the low-pressure stage that reduces the intermediate pressure to a constant volume and pressure needed by the torch. The second stage can be adjusted to the desired pressure in the same way a single stage regulator is adjusted. The two-stage regulator provides more consistent delivery flow and pressure and would be chosen for high quality welding applications. 12

17 Figure 12 - Two-stage regulator. Regulators are available in several different levels of quality. Generally speaking, if you use industrial quality regulators, observe safe handling practices and operate them according to manufacturer's recommendations, you will experience few, if any, regulator malfunctions. They are precision-built instruments. If your regulator malfunctions, you should send it to an authorized service centre for repairs. Regulator Malfunctions Creep is a condition where the low pressure gauge, which indicates working pressure, slowly rises when the torch valves are shut off. It is possible for the working pressure to rise as high as cylinder pressure. This high pressure could rupture the diaphragm, the low pressure gauge or the hose. Creep is caused when the regulator valve does not seat completely, possibly from dirt or scarring. Surge is a condition where the regulator does not provide a constant pressure and flow. This is indicated by the flame not staying where it is set. The flame changes from neutral to carburizing or oxidizing without you touching the torch valves. The internal mechanism is not moving freely. CAUTION Do not attempt to repair a faulty regulator yourself. Send it to an authorized service centre for repair. Attempting a regulator repair without proper training and equipment may lead to equipment being damaged and/or serious injury. 13

18 Hoses Hoses are made of neoprene rubber and linen braid. They are flexible, durable, resistant to gas and oil and able to withstand pressures up to 400 psi (2760 kpa). The hoses may be individual lines, but most often the oxygen and fuel hoses are bonded together. Table 2 is a quick resource for identifying oxygen and fuel hoses. Oxygen Hose Connections have right-hand thread. The colour of the hose is green. Acetylene Hose Connections have left-hand thread. An annular groove is cut in the hexagonal of the fitting. The colour of the hose is red. Table 2 Position the hoses to avoid damage from the flame, hot slag, welding sparks, falling steel and traffic. Hoses should be checked periodically for physical damage or signs of aging. The hoses in Figure 13 show cracking due to normal use and aging and should be replaced. Figure 13 - Cracked hoses. When making repairs and modifications to the oxy-fuel hoses, use the approved fittings (shown in Figure 14), available at your gas or welding supply outlet. 14 Figure 14 - Oxy-fuel hose fittings.

19 CAUTION NOTES Never use copper tubing to repair acetylene hoses because acetylene and copper react together causing explosive conditions. Check Valves One-way check valves (flash back arrestors) help minimize mixing of the fuel gas and oxygen in the hoses or regulators by disallowing the flow of gas backwards up into the hose. The gas is allowed to flow from the cylinder source through the hose and exit out the torch assembly. The most common location for the check valve is at the torch as shown in Figure 15. Figure 15 - One-way valves installed at torch. The construction and operation of a check valve are illustrated in Figure 16. Figure 16 - Check valve construction and operation. 15

20 Torch Handle The torch handle shown in Figure 17 provides a mounting area for heating or welding tips and for the cutting attachment. The valves on the torch handle are needle valves that allow fine, individual adjustment of oxygen and fuel gas flow. The oxygen and fuel gases flow through separate tubes through the length of the handle. Typically, torch handles are constructed from brass, thus, they are easily damaged if dropped or abused. Figure 17 - Torch assembly. Welding and Heating Tips The tip and mixer combination (Figure 18) is installed as a unit onto the torch handle and held in place by the retaining nut, which should only be hand-tightened. The mixing chamber attaches into the torch handle. Its function is to mix the combustion gases as they enter the welding tip. The mixing chamber is calibrated to match a specific tip size. Do not interchange tip and mixer sizes. The tips are made of copper to dissipate heat rapidly. Figure 18 - Heating tip installed on torch handle. Typical welding tips designed for use with acetylene gas are shown in Figure 19. Tips are available in numerous sizes. Tip numbering systems are not standardized amongst manufacturers; however, a larger number on a tip indicates a larger orifice. A larger orifice is capable of providing more heat. Tips and torch handle combinations are not interchangeable amongst manufacturers. 16

21 Figure 19 - Welding tips showing sizes. A Rosebud or multi-flame heating tip is shown in Figure 20 and Figure 21. These are also available in a variety of sizes and are commonly used for heating applications requiring high heat inputs. Figure 20 - Multi-flame tip. Figure 21 - Intense acetylene heating flame. NOTE Welding, heating and cutting tips are specifically designed for use with each fuel gas. You will experience less than satisfactory results, for example, if you use propane with tips designed for acetylene. 17

22 Checking Seals Prior to installing a heating tip, welding tip, or cutting attachment, you should check for and replace damaged O-ring seals. A damaged O-ring can allow gas leakage resulting in a fire where the tip connects to the torch handle. Figure 22 shows good O-rings and one broken O-ring. Figure 22 - Good O-ring seals and bad O-ring seals. Tip Cleaning A tip cleaner is shown in Figure 23. Tip cleaners are designed to remove foreign material from the tip. You should use the largest tip cleaner that will just fit the tip. You can draw it back and forth in the tip. The tip cleaner is designed to minimize removal of copper from the tip. Do not use too small or too large a tip cleaner as this will tend to cause more tip damage. Use the small file with the tip cleaner to polish the end of the tip. It is optional to maintain a small flow of oxygen through the tip during the cleaning procedure to remove foreign material from the tip. Figure 23 - Tip cleaner with file. NOTE The copper tips and brass torches are soft and easily damaged. Take care when handling and cleaning. 18

23 Safe Handling of Oxy-Fuel Equipment The following techniques and procedures will help maximize the performance and safety factor relative to the operation of your oxy-fuel outfit. When shutting the outfit down, bleed the gas pressures down to zero and turn out the regulator adjusting screws, thus leaving no tension on the spring and diaphragm. When opening the cylinder supply valve, first ensure that the regulator adjusting screw is in the neutral position, then open the cylinder valve slowly to prevent a sudden surge of pressure which could do damage to the diaphragm and gauges. Do not stand directly in front of the regulator when opening the cylinder valve. Send malfunctioning regulators out for repair by trained technicians via your gas supply dealer. Do not attempt to repair regulators yourself. Crack the cylinder valve (open and close briefly) to blow dust out of the valve before installing the regulator. Do not force the threads on any part of the equipment. Tighten all connections firmly. Check for leaks with soapy water. Position the outfit and hoses to avoid damage from hot slag, sparks, flame or falling metal parts. Coil up hoses off the floor away from the shop traffic. Close torch valves firmly with your finger tips. Overtightening will cause damage to the valve seat and will stretch the stem threads. Adjust the packing gland nut on the torch valves so the valves are comfortable to manipulate; yet their setting will not be inadvertently altered by a light touch of a sleeve or glove. Provide a secure storage apparatus for the torch and tips so they are readily available and to prevent accidental damage. Do not use the torch assembly as a hammer. Clean the tips gently and sparingly with the correct sized tip cleaner. Do not use copper tubing or red brass fittings to repair or modify oxy-fuel hoses. Use approved hose fittings. NOTES 19

24 Objective Three When you have completed this objective you will be able to: Demonstrate equipment set-up, adjustment and shut down procedures. Oxyacetylene Set-Up Prior to Use A complete oxyacetylene outfit is shown in Figure 24. This will be useful in understanding the following information. 20 Figure 24 - Complete oxyacetylene outfit equipped for heating and welding. Prior to using oxyacetylene equipment or after any components are changed, the following set-up procedure should be followed. 1. Secure the cylinders in the vertical position to a wall, stand or cart. 2. Uncap the cylinders. Check all fittings and remove oil, grease or other contaminants with a clean cloth or shop towel. 3. Crack the cylinder valves (open momentarily and close) to blow out dust or dirt from the cylinder valve openings. 4. Attach the pressure regulators to the cylinders and tighten the fittings. 5. Attach the hoses to the regulators and then attach the check valves and torch handle to the hoses. Tighten all fittings. 6. Install desired cutting attachment or heating tip. 7. Ensure that all torch valves are closed. 8. Ensure that the regulator adjusting screws are fully released (turn counterclockwise until they turn freely).

25 9. Open the cylinder valves slowly to the desired amount (oxygen fully open and acetylene to a maximum of 1 1 / 2 turns). 10. Turn in the regulator adjusting screws (clockwise) to set the approximate working pressures for the job at hand. 11. Flush or purge each individual hose to remove all foreign gases that may be within that hose. This is done by opening each torch valve individually (one at a time) and allow sufficient time for the gas to flush from the cylinder through the entire length of the hose (5 seconds for each 3 m of hose length). Close that torch valve and repeat purging procedure for the other torch valve. 12. Check the entire system for leaks with soap and water. Correct any leaks before proceeding. NOTES Balance the Pressures for Welding and Heating When performing welding or heating operations, it is recommended that the working pressures of oxygen and acetylene be equal to each other. This enhances the safety factor of the system by reducing the possibility of a higher pressured gas forcing its way back into the line of the other gas. This balancing procedure also establishes the correct working pressure for any specific tip size. The following procedures are to be performed subsequent to the above set-up procedures or at the start of a work project. 1. Select and install the desired sized welding or heating tip. 2. Set the working pressure of both oxygen and acetylene to be approximately 3 psi (20 kpa). 3. Purge each hose individually. Set Maximum Acetylene Pressure To set the maximum acetylene pressure, follow these steps. 1. Open the acetylene torch valve 1 / 4 turn and then ignite the torch with the flint lighter. (Figure 25). Figure 25 - Flint lighter. 2. Open the acetylene torch valve fully (about 3 turns). 3. Increase the acetylene pressure with the regulator adjusting screw to a point where there is a gap of 5 mm to 8 mm between the base of the flame and the copper tip. This can be referred to as blowoff and is shown in Figure 26. Note: excessive blowoff may cause the flame to blow out when setting the oxygen pressure in subsequent steps. A larger tip will require more pressure to establish the correct blowoff than does a smaller tip. Normal welding tips will require from 3 psi to 6 psi (20 kpa to 40 kpa) and large rosebud heating tips may require up to 10 psi (65 kpa). 21

26 DANGER Do not set acetylene pressure over 15 psi (100 kpa). There should never be an occasion when you need more than 10 psi (65 kpa). Figure 26 shows blowoff. Figure 26 - Blowoff. Set Matching Oxygen Pressure To set matching oxygen pressure, follow these steps. 1. Close the acetylene torch valve until the base of the flame returns to the tip. Then, open the acetylene torch valve sufficiently for the flame to burn smokefree. 2. Open the oxygen torch valve to achieve an approximate neutral flame. 3. Open the individual torch valves alternately (acetylene, then oxygen) small increments at a time, keeping between a neutral flame and a 4X carburizing flame, until both torch valves are at full volume (about 3 turns). 4. With both torch valves wide open, adjust the oxygen regulator screw until a neutral flame is achieved (when the feather has just disappeared into the primary flame). NOTE Your original oxygen working pressure setting may have been too high. In this case, an oxidizing flame will be formed before you have the oxygen torch valve opened to full flow. You must reduce the oxygen pressure at the regulator until you can open the oxygen torch valve to full flow and have a feather showing on the flame. Then, with both torch valves fully open, slowly increase oxygen pressure at the regulator until the feather just disappears. You have now established a neutral flame. 22 The oxygen regulator is now set at the same pressure as is the acetylene pressure. The torch is said to be balanced with equal pressures in each hose. This is the maximum pressure required for that tip. You will seldom use a welding tip with the torch handle valves wide open as in the balancing procedures.

27 With the valves wide open, the subsequent noisy aggressive flame causes excessive turbulence to the molten puddle. It is best to operate in the mid-range of the available pressure setting. If you feel you require the torch valves to be wide open to achieve sufficient heat, you will experience better puddle control by using a bigger tip and balance the pressures accordingly. Once the gas pressures are balanced for any given sized tip, you should not need to readjust the pressures at the regulator for the duration of the job. You must, however, repeat the above-described procedure when changing to a larger tip size. NOTES Extinguish Flame To extinguish a flame, follow these steps. 1. Close the acetylene torch valve to extinguish the flame quickly without leaving carbon deposits within the tip. 2. Close the oxygen torch handle valve. Set Welding Flame To set a welding flame, follow these steps. 1. Light the torch, acetylene only, and adjust the acetylene torch handle valve until the black smoke just disappears. This establishes a heat setting that you can repeat each time you light the torch. If you operate the torch below the black smoke range, the torch will backfire excessively. 2. Open the oxygen torch handle valve, slowly increasing the flow of oxygen until a neutral flame is achieved (when the feather has just disappeared into the primary flame). 3. If you would like more heat, simply open the acetylene torch handle valve to create a carburizing feather of a length that you determine will produce sufficient heat. 4. Then, open the oxygen torch handle valve until a neutral flame is achieved. NOTE You must be specific when setting a neutral flame. Add oxygen to the point when the feather just disappears; no more, no less. A neutral flame is the choice for most of your welding and cutting applications. Carburizing and oxidizing flames produce detrimental effects. 23

28 Shutdown After a leak check is performed and any time cutting or heating operations are terminated, follow these steps to shut down the outfit. 1. Extinguish the flame. 2. Close both the cylinder supply valves. 3. Open the torch handle valves, one side at a time, to bleed all gas pressure from the respective hose and regulator. Close each torch handle valve when the pressure reads zero. It is not important which side of the system is bled first, but it is critical while bleeding one side that the opposing side remains closed. 4. Unscrew the regulator adjusting screws until they turn free in the neutral position. 5. Remove the tip from the torch handle. Place the tip in its storage holder and coil up the hoses neatly. 6. Check again to ensure that you have closed the cylinder supply valves, closed the torch handle valves and backed off the regulator adjusting screws. Flame Types The four types of flame you will encounter are: acetylene flame, carbonizing flame, neutral flame and oxidizing flame. Acetylene Flame The flame burning with acetylene (Figure 27) only has the following characteristics. The flame is yellow and bushy. The flame temperature is 800 C. This type of flame is not successfully used for heating applications. Figure 27 - Acetylene flame. 24

29 Carbonizing Flame When oxygen is added to the acetylene flame and as the oxygen flow approaches the preset flow of the acetylene, the flame becomes carbonizing (carburizing). The carbonizing oxyacetylene flame shows as a feather on the end of the cone (Figure 28). The amount of feather indicates the amount of excess acetylene in the flame. Excess acetylene produces excess carbon in the flame and hence the title carbonizing flame. The whole flame in general takes on a blue colour. A white feather encloses and extends beyond the primary flame cone as shown. NOTES Figure 28 - Carbonizing flame. A longer feather indicates a surplus of acetylene versus oxygen being consumed within the flame. The flame temperature is cooler than a neutral flame. A carbonizing flame adds carbon to the molten puddle and thus has limited use. There are a wide variety of tip sizes and types and each one has its own length of cone and feather. Therefore, the comparison of the amount a flame is carbonizing is made in relation to the length of the neutral cone, regardless of tip size. This method of comparison is known as the X system of carbonizing flames. Thus with a 2X flame, the feather and cone are equal in length. With a 3X flame, the feather is twice as long as the neutral cone and with a 1 1 / 8 X flame, the feather is 1 / 8 the length of the neutral cone (Figure 29). Figure 29 - Carbonizing flame. 25

30 Neutral Flame A neutral flame, such as that shown in Figure 30, occurs when the oxygen flow, relative to the preset acetylene flow, is increased to the point when the feather just disappears into the primary flame. The primary flame is bright, luminous and has a distinct round tipped cone shape about 1 cm long. The secondary flame (envelope) is bluish in colour with red flecks and extends 20 cm to 30 cm beyond the primary flame. Figure 30 - Neutral flame. The flame temperature is approximately 3300 C. A neutral flame is the recommended flame for heating and cutting mild steel. The neutral flame adds nothing nor takes anything away from the steel. Oxidizing Flame An oxidizing flame (Figure 31) occurs when the oxygen flow, relative to the preset acetylene flow, is increased beyond the point when the feather disappears. The primary flame cone becomes shorter, sharper and paler blue than a neutral flame. The secondary flame becomes shorter. This flame type is accompanied by a harsh sound. There is an excess of oxygen versus acetylene being consumed within the flame. Figure 31 - Oxidizing flame. The flame temperature is hotter than a neutral flame. Carbon will be oxidized and removed from steel. Avoid using an oxidizing flame. 26

31 Backfires A backfire occurs when the flame backs up into the tip and mixer. See Figure 32. This results in a small explosion within that area where the gases are normally mixed. You hear a loud snap or pop and the flame goes out. The flame re-establishes itself almost instantly from the hot steel. Other than the loud pop, this is generally not a serious malfunction. When a backfire occurs, correct the cause and continue heating. NOTES Figure 32 - Backfires occur in the torch where shown. Backfires are caused by the following conditions. Too slow gas flow may occur when lighting the torch if you do not open the acetylene torch valve enough. (Adjust the gas flow to above the black smoke range.) Obstruction of gas flow, such as when holding the torch tip too close to the work, can cause backfire. Loose or faulty seat connections between the tip and mixer will cause backfire. A dirty tip, such as metal particles collecting on the tip end, tends to retard gas flow and cause backfires. A worn out tip will have an enlarged orifice allowing the gases to flow slower and thus backfire easier. Worn tips should be replaced as required. Use recommended tip maintenance procedures to maximize the life of your tips. A hot tip can be caused by working in deep grooves or blind holes. The hot tip pre-ignites the gases in the tip. The flame burns inside the tip and a rapid series of backfires occurs. Continuous Backfire and Burnback A continuous backfire is a rapid, repeated backfiring (popping) within the tip and mixer. A burnback is continuous combustion within the tip and mixer, indicated by a screeching sound as well as black smoke emitted from the tip. The probable cause is a hot tip preigniting the gases. The tip and torch handle become hot immediately. If the condition continues, the torch could melt down within a few seconds. Both the acetylene and oxygen torch valves should be closed immediately stopping the flow of gases to extinguish the combustion. To cool a hot tip, close the torch valves, open the oxygen valve and quench the torch in water. The oxygen will blow the water out of the tip. Shut off the oxygen and re-light the torch. 27

32 Figure 33 shows continuous backfire, burnback and flashback. Figure 33 - Continuous backfire, burnback and flashback. Flashback Under normal operating conditions, the oxygen and acetylene gases remain separate and pure in their respective hoses including the torch handle, hose and regulator. It is possible; however, for the gases to become mixed, such as oxygen in the acetylene hose and acetylene in the oxygen hose. A flashback is the combustion or explosion that can occur within the hoses when this gas mixture is ignited. This is a very serious malfunction that will do major damage to the equipment. If a flashback has occurred and the ruptured hoses are burning, shut off the cylinder supply valves. Flashback occurs within oxyacetylene equipment in the areas shown in Figure 33. Flashbacks can only occur if the gases have become mixed in the separate lines. The gases can become mixed due to the following situations. Grossly unequal pressures. The higher pressure gas backs up into the lower pressure hose. Mildly unequal pressure plus an obstruction. Should tip blockage occur, always close off both torch valves immediately. Then you can clean the tip. Failure to purge each hose individually before lighting the torch. A torch that has been sitting idle for awhile may have an explosive mixture present in one or both hoses. Faulty manipulation of valves. This may occur by lighting a torch with both torch valves open or otherwise failing to operate equipment in the recommended manner. 28 Use these methods to avoid flashbacks. Purge each hose individually and thoroughly before lighting the torch. Install one-way check valves. Closely adhere to recommended set-up and operating procedures. Keep equipment in good repair. Balance gas pressures when heating and welding.

33 Oxy-Fuel Cutting Steel is heated until it reaches its kindling temperature (red heat). Then, a stream of pure oxygen is introduced which rapidly oxidizes (burns) the steel in its path. The molten iron oxide is removed by the stream of oxygen resulting in a kerf or cut gap. Heat from the burning process helps preheat the steel ahead so the cut is continuous and progressive. The temperature of the burning steel is lower than the melting point of steel; thus, the edges of the kerf remain square. Ferrous materials (iron and steel) can be cut with the oxy-fuel cutting process. Cast iron, stainless steels and non-ferrous metals will not burn progressively and thus, cannot be cut. NOTES The cutting attachment (Figure 34) fixes to the torch handle in the same manner as a welding or heating tip. The cutting attachment channels the fuel, as controlled by the torch handle fuel valve, directly to the preheat holes of the cutting tip. When using the cutting attachment, keep the oxygen torch handle valve fully open (3 or 4 complete turns). The cutting attachment directs the oxygen flow through two different paths. When you open the oxygen preheat valve located on the cutting attachment, oxygen flows to the preheat holes on the cutting tip and mixes with the fuel to feed the preheat flames. When you depress the oxygen cutting lever, the oxygen cutting valve opens and allows a large volume of oxygen to flow through the oxygen outlet at the centre of the tip to form the cutting stream. Propane is a popular alternative to acetylene as a fuel for cutting applications. Select the appropriate tip type designed for the gas being used. Various tip sizes and styles are available for various job applications. Figure 34 - Cutting attachment. Figure 35 shows cutting tip outlets. Figure 35 - Cutting tip outlets. 29

34 Set-Up Procedure Follow the same basic set-up procedures for the oxy-fuel outfit as described earlier in this objective. 1. Install the cutting attachment onto the torch handle. 2. Select the cutting tip size for the job at hand. 3. Ensure torch valves and cutting attachment valves are closed and regulator adjusting screws are fully released. 4. Open the cylinder valves slowly to the desired amount (oxygen fully open and acetylene to a maximum of 1 1 / 2 turns). 5. Set approximate regulator pressures for the job at hand relative to metal thickness and tip size. (See Table 3 for approximate sizes.) 6. Purge both oxygen and fuel gas lines individually before lighting the torch. Approximate Cutting Torch Gas Pressures Metal Thickness (Inches) 1 /4 3 /8 1 /2 3 / /2 2 Cutting Tip Size * Oxygen Pressure psi (kpa) (124 kpa) (138 kpa) (145 kpa) (159 kpa) (172 kpa) (193 kpa) (207 kpa) Acetylene Pressure psi (kpa) (34 kpa) (34 kpa) (34 kpa) (34 kpa) (34 kpa) (41 kpa) (41 kpa) *Cutting tip sizes may vary from manufacture to manufacture. Table 3 - Approximate cutting torch measures. Lighting the Torch Follow these procedures when lighting the torch. 1. Open the oxygen torch handle valve fully (3 to 4 complete turns) and leave it open until you are shutting the torch down. 2. With the preheat oxygen valve closed, open the acetylene torch valve about one half turn and ignite the flame. Increase acetylene flow to desired proportions, but do not attempt to take the flame beyond the smoke range or preheat will likely be excessive. 3. Add oxygen to preheat flames by slowly opening the oxygen preheat valve on the cutting attachment. Continue to adjust the oxygen preheat valve until the preheat flames are neutral. 4. Depress the cutting lever and adjust the preheat oxygen valve to achieve a neutral flame while cutting. Be specific; add oxygen to the point when the feather just disappears. Extinguish Flame To extinguish the flame, follow these steps. 1. Close the acetylene torch valve to extinguish the flame quickly without leaving carbon deposits within the tip. 2. Close the oxygen preheat valve on the cutting attachment. Leave the oxygen torch handle valve open until you are shutting down the outfit. Shut Down Procedures Follow the same shut down procedures for the oxy-fuel outfit as described earlier in this objective. 30

35 Factors for a Quality Cut There factors that determine a quality cut are outlined in this section. NOTES Clean Tip Before beginning the cut, inspect the preheat flame inner cones, as in Figure 36). When set at a neutral flame, they should be equal in length, size and adjustment. If the primary flame cones are malformed or of different lengths, this may be caused by an obstruction to the preheat orifice or there may be a build-up of carbon fluff within the length of the tip. Shut off the torch and carefully clean the preheat orifices with tip cleaners. The carbon fluff can be cleaned out by removing the tip, disassembling and blowing out the orifices with compressed air. Figure 36 - Unequal length preheat inner flame cones. CAUTION The fine tip cleaners are easily wedged and broken off inside the preheat holes. Avoid cleaning the preheat holes, if possible. Try scraping the spatter from the end of the tip first. The larger cutting orifice can be cleaned with less risk. A straight oxygen stream (Figure 37) is most important for a good quality cut. Depress the cutting oxygen lever and observe the oxygen jet stream. The jet stream should be straight through the length of the secondary flame and you should hear an aggressive raspy sound. If the cutting jet stream is not straight and you hear a hissing sound, shut off the torch and clean the cutting orifice in the tip. A worn or abused tip may not provide a straight jet stream with a crisp sound and will need to be replaced for best results. 31

36 Figure 37 shows an oxygen jet stream. Figure 37 - Oxygen jet stream. Correct Gas Pressures Approximate gas pressures are indicated in Table 3, but you can establish more precise pressures using flame characteristics as indicators. Oxygen pressure is most critical to the cut quality. You can establish the precise oxygen pressure by listening to the sound emitted from the torch. Using a clean tip with an appropriate cutting flame lit, depress the cutting lever and make adjustments to the oxygen regulator adjusting screw while observing the sound of the torch. When the oxygen pressure is too low, the sound will be soft, lazy and non-aggressive. When the oxygen pressure is too high, the torch will have an aggressive hissing sound. There will be a range between too low and too high where the torch will have a crisp, raspy sound. Set the oxygen pressure within that range to suit your needs with respect to the limits of that tip size. Set toward the lower end for cutting thin metals and through one layer of a lamination (removing a bearing). Set toward the higher limit when cutting thick objects. Set in the middle for medium thicknesses. The acetylene gas pressure can be established in the same manner as described in the balancing procedures using a welding tip. Light the cutting torch with acetylene only. Open the acetylene torch valve 3 to 4 complete turns. Adjust the acetylene regulator to a point where there is a gap of approximately 5 mm between the base of the flame and the copper tip. When using propane, a gap of 2 cm to 3 cm. will provide the correct results. 32 Heat Build-Up When the heat build-up within the object being cut is just right, the cutting speeds will be efficient, the kerf marks will be smooth, uniform and straight, the top edge of the plate will be square, the bottom edge will be relatively slag free and clean up will be minimal. Heat build-up is determined by the selected tip size and flame setting, by the amount of preheat and by the rate of travel. A little preheat (200 C to 300 C) will allow the cut to initiate easily and to progress smoothly and efficiently across the plate. Not enough heat (small tip, small flame setting) will make it difficult to start the cut and will require slow rate of travel to keep the cut going. Too much heat (large tip, big flame, slow travel) will cause the top edge of the plate to melt and large amounts of slag to hang up on the bottom.