Las OAW (LAS OXY ACETYLENE WELDING)
Welding carbide acetyline
Oxy-acetyline welding is a manual welding process by heating the metal surface to be welded or connected until it melts by flame gasacillin through combustion of C2H2 with O2 gas with or without filler metal. The connection process can be done with pressure (pressed), very high so that it can melt the metal.
Welding with Oxy-acetylene Gas
Carbide welding or acetylene welding is one of the most frequently used workshop tools. Its operation is easy enough to make it often used to connect dual metal or welding. In general, acetylene welding tools are metal connectors through the process of melting metal using heat energy from combustion of acetyline gas mixture dangas oxygen. The carbide welding workshop device is used to cut and connect workpieces made of metal (iron plate, pipe and shaft)
Gas welding is done by burning gas fuel mixed with oxygen (O2) so as to cause a high temperature flame (3000o) which is able to melt the parent metal and filler metal. The type of gas fuel used is acetylene, propane or hydrogen, so this welding method is called oxy-acetylene welding or known as carbide welding.
The acetylene flame is obtained from the flame of a mixture of oxygen and acetylene gas used to heat the metal until it reaches the melting point of the parent metal. Welding can be done with or without filler metal.
Oxygen is obtained from the electrolysis process or air liquefaction process. Commercial oxygen generally comes from the process of air liquefaction where oxygen is separated from nitrogen. This oxygen is stored in a steel cylinder at a pressure of 14 MPa. Acetylene gas (C2H2) is produced from the reaction of calcium carbide with water. Gas bubbles rise and the precipitate that occurs is quicklime. The reactions that occur in the acetylene tube are:
CaC2 + 2H2O ® Ca (OH) 2 + C2H2 calcium carbide quick water Acetylene gas lime
When calculated it turns out that 1 kg of CaC2 produces approximately 300 liters of acetylene. The nature of acetylene (C2H2) which is a fuel gas is colorless, non-toxic, smelly, lighter than air, tends to break away in the event of an increase in pressure and temperature (above 1.5 bar and 350 ° C), can dissolve in a porous mass (acetone).
Hard calcium carbide, similar to stone, is gray and formed as a result of the reaction between calcium and coal in an electric kitchen. The results of this reaction are then ground, selected and stored in a tightly closed steel drum. Acetylene gas can be obtained from acetylene generators that produce acetylene gas by mixing carbide with water or can now be purchased in ready-made gas cylinders. To be safe the pressure of acetylene gas in the tube must not exceed 100 Kpa, and be stored mixed with acetone. The acetylene tube is filled with a porous filler material which is saturated with acetone, then filled with acetylene gas. This type of tube is capable of accommodating acetylene gas up to 1.7 MPa.
The principle of welding is not too complicated. Only by regulating the amount of acetylene gas and oxygen, then the tip is brought close to the flame, there will be a flame. But the amount of acetylene gas and oxygen must be arranged in such a way by rotating the pressure regulator little by little. If only acetylene gas is turned on, the flame is in the form of ordinary flame by removing soot. If too little acetylene gas is rotated, the weld will not light up.
The speed of gas recovery per hour from an acetylene cylinder must not be greater than 20% (one fifth) of its contents, so that acetone gas can be flowed (the acetylene cylinder must always be perpendicular).
The combustion flame in oxy-acetylene welding can change depending on the ratio between oxygen gas and acetylene gas. There are three types of flame in the oxy-acetylene welding as shown in the figure below:
a. More acetylene flame (carburizing flame)
If too many comparisons of acetylene gas are used then between the inner cone and the outer cone there will be a new blue flame cone. Between the flaming cones and the outer sheath there will be a whitish cone between them, whose length is determined by the amount of excess acetylene. This will cause carburization in the molten metal. This flame is widely used in welding monel, nickel, various types of steel and various non-ferous surface hardening materials.
b. More oxygen flame (oxidation flame)
When oxygen gas is more than needed to produce a neutral flame, the flame becomes short and the color of the inner cone turns purple. This flame will cause oxidation or decarburization in the molten metal. This oxidizing flame must be used in fusion welding of brass and bronze but is not recommended for other welding.
c. Neutral flame
This flame occurs when the ratio between oxygen and acetylene is around one. Nyala consists of a cone in a white glow and a clear blue outer cone. The oxygen needed by this flame comes from the air. The maximum temperature as high as 3300 to 3500 oC is reached at the end of the cone flame.
Because of its nature which can change the composition of the molten metal, the excess acetylene flame and excess oxygen flame cannot be used to weld steel. Temperature At the inner cone tip is about 3000 ° C and in the middle of the outer cone is about 2500 ° C.
In the welding position with the oxy acetylene the welding direction and the inclination of the burner can affect the speed and quality of the weld. In welding techniques there are several methods, namely:
a. Under hand welding
Under hand welding is a welding process that is carried out under the hand and the workpiece is located on a flat plane. The angle of the burner tip (brander) is located between 60 ° and the filler wire (filler rod) is tilted with an angle between 30 ° - 40 ° with the workpiece. The position of the burner tip to the angle of the connection with a distance of 2-3 mm to allow maximum heat to the connection. At the outer corner connection, the flame is directed to the center of the connection and the movement is straight.
b. Horizontal (horizontal) welding
In this position the workpiece stands upright while welding is done in a horizontal direction so that the welding fluid tends to flow downward, for this reason the brander's swing should be as small as possible. Brander's position on the workpiece angles 70 ° and tilts approximately 10 ° below the horizontal line, while the filler wire is tilted at an angle of 10 ° above the horizontal line.
c. Upright welding (vertical)
In welding in an upright position, the welding direction goes up or down. The filler wire is placed between the flame and the angle of the connection is 45 ° -60 ° and the brander angle is 80 °.
d. Over head welding
Welding with this position is the most difficult compared to other positions where the workpiece is above the head and welding is done from below. In this position welding the brander angle is tilted 10 ° from the vertical line while the filler wire is behind it angled 45 ° -60 °.
e. Welding in the left direction (forward)
This welding method is most widely used where the flame is directed to the left by forming an angle of 60 ° and welding wire 30 ° to the workpiece while the transverse angle is perpendicular to the direction of welding. This method is widely used because the method of welding is easy and does not require a difficult position when welding.
f. Welding in the right direction (backward)
This method of welding is the opposite direction than the welding direction to the left. Welding in this way is needed for steel welding that is 4.5 mm thick and above.
The advantages and uses of oxy-acetylene welding are numerous, including:
Equipment is relatively inexpensive and requires minimal / little maintenance.
How to use it is very easy, does not require high welding techniques so it is easy to learn.
Easy to carry and can be used in the field or in the factory or in workshops because the equipment is small and simple.
With the right welding technique, almost all types of metal can be welded and this tool can be used for cutting or connecting.
a. Oxides of Oxy-acetylene In this process an oxygen gas mixture with acetylene gas is used. The sound can reach 3500 degrees Celsius.
Welding can be done with or without filler metal. Acetylene gas (C2H2) is produced by the reaction of calcium carbide with water with the following reactions: C2H2 + 2 H2O Ca (OH) 2 + C2H2
Picture of oxygen tube form and acetyline tube:
Figure: Acetylene tube and oxygen for oxyacetylene welding
In order to be safe to use acetylene gas in a tube the pressure must not exceed 100 kPa and be stored mixed with acetone. The acetylene tube is filled with a porous filler material which is saturated with acetone, then filled with acetylene gas. The acetylene tube is resistant to 1.7 MPa. The welding flame scheme and the gas connection can be seen in the picture:
Figure: Oxyacetylene welding flame scheme and gas connection
In the oxyacetylene gas flame can be obtained 3 types of flame, namely neutral flame, reduction and oxidation. The neutral flame is shown in the picture below:
Figure: Neutral flame and temperature reached on the burner tip
In the internal flame of the flame internal cone at the tip of the flame requires a ratio of oxygen and acetylene approximately 1: 1 with the reaction of the certi fi cation which can be seen in the figure. The bluish outer sheath is the reaction of CO or H2 gas with oxygen taken from the air.
b. Oxyhydrogen welding
The flame of oxyhydrogen welding reaches 2000 ° C lower than oxygen-acetyline. This welding is used in welding thin sheets and alloys with low melting points.
c. Air-Acetylene Welding
The flame in this welding is similar to
Bunsen burners. To be needed, the air that is sucked according to needs is needed. The welding temperature is lower than the others, so its usefulness is very limited, that is only for tin solder and low temperature solder
d. Pressurized Gas Welding
The connection to be welded heated with a gas flame using oxygen acetylene to 1200C is then emphasized. There are two ways of connecting, the connection is closed and the connection is open. On a closed connection, the two surfaces to be connected are pressed together during the heating process. Flame uses double flame with cooling water. During the heating process, the flame is swung for
prevent excessive heat on welded connections. When the right temperature has been obtained, objects are treated. For carbon steel the initial pressure is less than 10MPa and the pressure up is between 28MPa
e. Oksiasetilen flame cutting
Flame cutting is also a production process. The flame for cutting is different from flame for welding where around the main hole the oxygen source is a small opening for heating. The initial heating function is to warm up the steel before cutting. Because the material to be cut becomes hot so the steel will burn and melt when oxygen is flowed.
Tools and materials
One unit of oxy-acetylene gas equipment, consisting of:
oxygen gas cylinders and regulators
acetylene gas cylinders and their regulators
hose
brander (torch)Filling material (wire)
Safety devices (gloves, welding glasses)
Matches and oncor
Stopwatch
Brush steel
Bench work tools when needed.
Implementation method
a. Prepare all equipment that will be used.
b. Checking brander must be closed.
c. Open the oxygen and acetylene gas cylinders by loosening the closing bolt with the opening key.
d. Check the contents of the gas cylinder by looking at the pressure indicator manometer attached to the regulator.
e. Adjust the work pressure by turning the handle on the regulator (turn to the right to increase gas pressure).
f. Open a little acetylene gas in brander and turn it on with fire.
g. Open and simultaneously regulate the size of oxygen gas in the brander until neutral flame is obtained.
h. Start welding by directing the brander flame on the parent metal.
i. If the parent metal has started to melt, then directs the filler metal to the parent metal that melts and swings the brander until the desired welding ridges are formed.
j. Repeating number h to number i until good welds are obtained.
k. Exercise connecting various forms of workpieces.
l. Carry out practical work seriously and be careful so that things that are not desirable do not occur.
m. After the practicum is complete, clean up the practicum place and equipment and return it to its original place.