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Upon completion of this chapter, students should be able to:- Explain Oxy Acetylene Welding(Gas Welding) ◦ Types of Gas Welding ◦ Gas Welding Operation ◦ Gas welding equipment ◦ Identify the basic components of an Oxy Acetylene welding ◦ Types of flame ◦ Typical startup procedures
CHAPTER 7
Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. fuel gas (i.e. acetylene, hydrogen propane or butane)
Definition; “The oxy-acetylene welding process uses a combination of oxygen and acetylene gas to provide a high temperature flame to weld & cut metals.” cutting metal as well as welding, this is because the welding torch(andang) generates enough heat to bring the metal up to melting temperature. In this process, acetylene is mixed with oxygen in correct proportions in the welding torch and ignited (dinyalakan). The flame resulting at the tip of the torch is sufficiently (cukup) hot to melt and join the parent metal.
The oxyacetylene flame reaches a temperature of about 3300°C and thus can melt most of the ferrous and nonferrous metals in common use. A filler metal rod or welding rod is generally added to the molten metal pool to build up the seam (jahitan) slightly for greater strength. Oxyacetylene welding does not require electricity and is typically used for maintenance, in body shops, and the repair of small parts where other welding process are too expensive. Oxyacetylene welding equipment can also be used for preheating, cutting metal, case hardening, and annealing.
• A metal joining process, the method of heating the two metal parts to be connected, until melted and merged into one.
• Receive acetylene gas supply from gas fired acetylene, a pressure less than 1.0 bar. Lowpressure gas welding. • Receive gas from the gas generator acetylene, with pressure from 1-15 bar. Highpressure gas Welding
• Metal fabrication work involving the sheet metal thickness greater than 1.0mm up to 3.0mm. For example, • In the work of the vehicle body repair work involves knocking and pasting portions of the damaged vehicle bodies. • Piping air-conditioning system , Oil and Gas piping ,etc .
The welding profession provides a wide range of career options. Many welding jobs are associated with high-risk work environments such as underwater commercial diving or oil pipeline construction. Expert welders, such as those working on pipelines or in underwater environments, are qualified for the most difficult and, therefore, highest paying jobs.
Metal Fabrication Welders that work in metal fabrication are responsible for the assembly, shaping and welding of metal pieces incorporated in structures and machinery. From architecture and building construction to automobile and airplane manufacturing, metal fabrication is a crucial process. Pipeline Welding Pipeline welders -- or pipe "fitters" as they are often called -- are responsible for producing secure pipelines used for transporting water, oil, gases and other hazardous materials. The degree of difficulty in pipeline welding is higher than most other welding jobs because many pipeline welding projects take place outdoors where welders are exposed to unpredictable weather conditions. Underwater Welding Underwater welders are trained to be proficient in "wet welding" and "dry welding" techniques. Wet welding involves a special electrode with DC power and dry welding takes place in a hyperbaric chamber filled with a breathable mixture of helium and oxygen.
Fuel gas cylinder with pressure regulator Oxygen cylinder with pressure regulator Welding torch Blue/green oxygen hose Red fuel gas hose Trolley for transportation of the gas cylinders Check Valve Non-return Valve Welding Torch
All threaded fittings oxygen right direction All threaded fittings acetylene right direction
Oxygen and acetylene pressure regulators perform two functions: ◦ Control the flow of gas from the cylinder to maintain the required working pressure. ◦ Produce a steady flow of gas under varying cylinder pressures.
Equipped with two gauges: ◦ A cylinder pressure gauge, which indicates the actual pressure in cylinder ◦ Working pressure, which shown the working, or line, pressure used at the torch.
Single Stage Regulators Two Stage Regulators
• has a high pressure area where the high pressure of the cylinder directly into this space. • pressure readings can be seen on the needle ready regulators and reduced the pressure to work in accordance with appropriate adjustments using the adjustment screw regulators pad. • Regulators security level is lower than the two-stage Regulators
• has two chambers of pressure and low pressure area. • High pressure area at regulators accept the high pressure in the cylinder and the pressure readings can be read on the pressure gauge. • While the low-pressure area to receive the controlled admission of gas from high pressure column by adjusting the adjustment screw on the regulators according to the required working pressure. • The level of security is better than regulators one stage.
Most regulators have two stages: the first stage of the regulator is a fixed-pressure regulator whose function is to release the gas from the cylinder at a constant intermediate pressure, despite the pressure in the cylinder falling as the gas in the cylinder is used. The adjustable second stage of the regulator controls the pressure reduction from the intermediate pressure to the low outlet pressure. The regulator has two pressure gauges, one indicating cylinder pressure, the other indicating hose pressure. The adjustment knob of the regulator is sometimes roughly calibrated for pressure, but an accurate setting requires observation of the gauge.
Common gauge settings for cutting ◦ 1/4” material Oxy 30-35psi Acet 3-9 psi ◦ 1/2” material Oxy 55-85psi Acet 6-12 psi ◦ 1” material Oxy 110-160psi Acet 7-15 psi Check the torch manufactures data for optimum pressure settings
The hose pipes are used for the supply of gases from the pressure regulators. Hoses are are fabricated from rubber Oxygen hoses are green in color and have right hand thread. Acetylene hoses are red in color with left hand thread. Left hand threads can be identified by a grove in the body of the nut and it may have “ACET” stamped on it
A connection consists of a nipple that is forced into the hose and a nut that connects the nipple to the regulator and the torch. The acetylene nut can be distinguished from the oxygen nut by the notch that runs around the center, indicating a lefthand thread.
It is a tool for mixing oxygen and acetylene in correct proportion and burning the mixture at the end of a tip. Gas flow to the torch is controlled with the help of two needle valves in the handle of the torch.
The torch is the part that the welder holds and manipulates to make the weld. It has a connection and valve for the fuel gas and a connection and valve for the oxygen, a handle for the welder to grasp, a mixing chamber (set at an angle) where the fuel gas and oxygen mix, with a tip where the flame forms.
A small welding torch, with throttle valves located at the front end of the handle. Ideally suited to sheet metal welding. Can be fitted with cutting. attachment in place of the welding head shown. Welding torches of this general design are by far the most widely used. They will handle any oxyacetylene welding job, can be fitted with multiflame (Rosebud) heads for heating applications, and accommodate cutting attachments that will cut steel 6 in. thick. A full-size oxygen cutting torch which has all valves located in its rear body. Another style of cutting torch, with oxygen valves located at the front end of its handle.
The tip sizes are identified by the diameter of the opening. The diameter of the tip opening used for welding depends upon the type of metal to be welded. Welding on different thicknesses of metal is possible because torches are equipped with different size heads or tips.
Manifold system ◦ Allows the necessary volume to be supplied to work area. Flash arrestor(perangkap) ◦ Safety device that prevents an explosion or a backfire in the torch or torch head from reaching the regulator and acetylene cylinders.
Flame is the most important means to control the welding joint and the welding process. The correct type of flame is essential (penting) for the production of satisfactory welds. The flame must be of the proper size, shape and condition in order to operate with maximum efficiency.
There are three basic types of oxy-acetylene flames: 1.Neutral welding flame (Acetylene and oxygen in equal proportions). 2. Carburizing welding flame or reducing (excess of acetylene). 3. Oxidizing welding flame (excess of oxygen).
Verify that equipment visually appears safe IE: Hose condition, visibility of gauges Clean torch orifices with a “tip cleaners” (a small wire gauge file set used to clean slag and dirt form the torch tip) Crack (or open) cylinder valves slightly allowing pressure to enter the regulators slowly Opening the cylinder valve quickly will “Slam” the regulator and will cause failure.
Never stand directly in the path of a regulator when opening the cylinder Check for leaks using by listening for “Hissing” or by using a soapy “Bubble” solution Adjust the regulators to the correct operating pressure Slightly open and close the Oxygen and Acetylene valves at the torch head to purge any atmosphere from the system. Always use a flint and steel spark lighter to light the oxygen acetylene flame. Never use a butane lighter to light the flame