1. Teknologi Dan Rekayasa
OXY-ACETYLENE WELDING

2. The setting of oxy-acetylene welding equipment
OBJECTIVE :
After studying this lesson, the students can be to explain the setting of oxy-acetylene welding equipment.
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3. The oxy-acetylene welding set
The high pressure oxy-acetylene welding set is consist of two steel cylinders that contain oxygen and acetylene gases.
Attached to these cylinders are two regulators. The function of these regulators is to reduce the cylinder pressure to a suitable working pressure and hold that pressure constant regardless of the size of flame being used.
The regulators are connected by two rubber hoses to a hand torch.
The torch has two valves to control the gas flow and interchangeable tips of different sizes to provide different sizes of flame.
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4. The oxy-acetylene welding set
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5. Safety precautions of the oxygen cylinder
Cylinders should not be used as rollers or anvils as this may damage the case. Also, if the brass valve is broken off the cylinder, the gas will exhaust at a violent rate.
The cylinder valve should be opened only two or three turns. If gas leaks around the valve stem, the brass gland-nut should be tightened.
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6. Safety precautions of the oxygen cylinder
No oil or grease should be used on oxygen or other gas connections. If even a very small quantity of oil is placed under pressure in glass line, it will explode in much the same way as the oil fuel in a diesel engine cylinder.
Note that gas connections are all made of brass, so oil is not needed to join these together.
Cylinders should not be heated as this tends to expand their contents with sub-sequent risk of explosion.
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7. Safety precautions of the oxygen cylinder
Liquid Oxygen.
When oxygen is compressed and cooled to liquid state, there are 814 litres of gas available from every litre of liquid. For this reason. It is very economical to transport large quantites of oxygen in liquid form.
Large users of oxygen may have an insulated container of liquid oxygen installed on their premises together with an evaporator unit that turns the liquid oxygen back into oxygen gas.
The insulated storage tank is kept filled by and insulated road tanker from the manufacturer.
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8. Safety precautions of the oxygen cylinder
Precautions with Liquid oxygen.
Liquid oxygen is intensely cold and must never be allowed to touch human flesh. The temperatures involved can cause human tissue to freeze and be permanently destroyed.
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9. Oxygen and acetylene cylinder
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10. Safety precautions of the acetylene cylinder
Acetylene cylinders must not be used as anvils or rollers. This is because a dent in the cylinder may pulverize some of the porous filling and increase the size of the storage voids to a dangerous level.
Cylinders must not be heated either in the hot sun or by a flame. The contents could explode if heated. Each cylinder contains fusible safety plugs that will melt at 100° C if the cylinder is heated, these plugs melt and release the gas, preventing dangerous pressure from building up within the cylinder that could explode violently.
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11. Faults in Gas Regulators
Regulators are generally very reliable in service but may suffer at times from the following faults :
Creep or surge : The torch pressure may creep up when the torch is turned off or may surge up and down during flame adjustment. This is caused by a leaking regulator valve or seat.
Cure : Replace regulator valve and/or seat.
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12. Faults in Gas Regulators
Freezing : Regulators may freeze at very high flow rates.
Cure : Turn off and allow to thaw or pour hot water over the regulator case. Alternatively, the flow may be reduced by using a number of cylinders with separate regulators to supply the necessary flow. A two stage regulator will carry larger flows without freezing.
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13. Faults in Gas Regulators
Leaking Bullnose Spigot : The bullnose may leak even though it is very tight in the cylinder fitting. This is caused by damage to the brass face of the cylinder O ring or by dirt deposited in the valve.
Cure : renew or remachine the bullnose face and remove dirt before inserting valve.
Note : The practice of using a lead washer between a leaking bullnose and cylinder valve is to be discouraged as it can cause a blockage in the valve or regulator.
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14. Safety with Regulators
No oil or grease should be used on any part of the regulator or bullnose. This is because oil subjected to high pressure can explode
The regulator adjusting knobs should never be screwed into their limit and left there. This is because this can stop the regulating valve from working, and a blocked blowpipe tip can allow high pressure oxygen to enter the acetylene line with risk of explosion.
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15. Safety with Hoses
The gas is carried between the regulators and the blowpipe by flexible reinforced rubber hoses.
Rubber hoses should not be used for liquified petroleum gas as this gas causes deterioration of the rubber.
Hose connections are made of brass and have threads. Because interchanging of the hoses could cause dangerous gas mixtures and pressures, the acetylene connections always have left hand threads.

16. Lighting the Blowpipe
With a valve key open the valve on each cylinder slowly. This allows the gas to fill the regulators.
The regulators adjusting knobs are screwed in until the working pressure gauge reads the correct pressure for the welding blowpipe –34 kPa for acetylene and 69 kPa for oxygen.
Having screwed a welding tip onto the torch (say, a size 15), turn on the blowpipe acetylene and light the gas flowing from the tip. A sooty, yellow flame will result.
Gradually turn on the blowpipe oxygen and outer cone. If the flame is too fierce, turn both blowpipe valves off a little. If the flame is too small, turn both blowpipe valves on little.

17. To Turn Off the Blowpipe
Turn off the blowpipe acetylene valve. (This stops the flame immediately).
Turn off the blowpipe oxygen valve
Turn off the gas at the cylinder with the cylinder key.
Open and close the blowpipe valves one by one to remove the gas from the regulators and hoses.
Unscrew both regulator adjusting knobs so that there is no spring tension remaining against the diaphragm.
Always turn off the welding set and remove the gas and the tension from each regulator diaphragm. This prevent gas leakage and stops excessive wear of the regulator valves seats.

18. Flame Adjustment
The flame used for welding must be hot enough to easily raise the metal to be welded to its melting point.
There are three types of oxy-acetylene welding flames. These are called neutral, oxidising and carburising.
The blowpipe flame may be adjusted to a neutral, oxidising or carburising flame. Each type of flame has its own special use, and careful adjustment it necessary before welding commences.

19. Short fierce inner cone
Flame Adjustment
Neutral flame
Hottest part of flame
5 mm
Oxidising flame
Short fierce inner cone
Carburising flame
Unburnt gases

20. Flame Adjustment Neutral flame :
Equal volumes of oxygen and acetylene. Greatest heat 5 mm from end of inner cone. Used for welding.
Oxidising flame :
Excess oxygen causes oxidation of the weld pool. Used for brazing.
Carburising flame :
Excess of acetylene turns into carbon which mixes with the weld pool. Used for Linde welding.

21. THE END
THANK YOU
Teknologi dan Rekayasa