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Welding Notes Transcript
Some hints and tips
Take a welding course
Rule of thumb when starting with an unknown set is 40amps per mm of rod e.g 2.5mm=100amps.
Increase the current slightly when using long extension cables. Try not to have these cables in a coil when welding
The quality of the weld is directly related to the surface preparation. Take a little extra time to prepare and shape the area to weld
Ensure all slag is removed , if necessary by using an angle grinder to gouge out any pin holes, before welding over a run
If your welding rod sticks then clean with an angle grinder the mark especially on critical welds such as pressure vessels. Check the condition of the coating on the rod. If the coating is damaged say with one side of the wire exposed discard the rod or burn it back to good on a non-essential piece
After finishing a run the end of the rod invariably gets a slag coating. When you come to strike again it is difficult so the tendency is to strike harder and harder. The consequence of this is that not only does the slag come off but a good piece of the coating leading to an erratic arc. Penetrate the slag cap by gently rubbing it on a rough surface, or use your fingers to snap it off (as I do)
Keep you glass clean- the fumes tend to coat the glass with a layer of dust. Keep wiping this off. If you cannot see the weld arc properly you have too dark a tint grade of glass. These tend to be supplied suitable for welding maximum amps ( say 300 Amps)
Where the shape of the weld is critical then use two hands. One to hold the holder the other grip the rod a couple of inches back from where the arc is. ( I used to do all boiler tube welding in this way and as I get older most of the vertical welding as well)
Position the piece to avoid as much as possible any other type of weld except horizontal- this is not a cheat but is common sense. Watch a coded welded how he works
Brace yourself against something before starting if possible. Loop the cable over your body so that the weight of the cable does not fall onto you hands
When doing a multi run weld into a narrow groove or right angle join use a small diameter gp rod for the root weld as this is critical and any slag inclusion will cause porosity in the rest of the weld runs
If you get porosity dont mess about putting a thousand runs over the top of it, grind the bugger out and start again
Don't be afraid to use rods. For awkward jobs bend the rod half way down if it helps. I welded an economiser using only the final inch of each rod which was bent to suit due to the position of the hole ( I also had to use a small inspection mirror to see it). Don't be tempted to use old part used rods for critical jobs as they inevitably have a high moisture content in the coating and make for a very porous and/or brittle weld.
When lighting an oxy-acet flame light the acetylene and increase slowly until you see the carbon smoke just disapear. The put on you oxygen.
When using oxy-acet gas cutters make sure you always have a bucket of water nearby incase of blow back.
If you are going to gas weld aluminium - don't. Reach for the TIG welder or if you must MIG. Or if you really, really must, stick weld. If you do not have these and have to gas weld make sure you well remove the oxide layer ( using a non-ferrous wire brush) and weld as soon as possible. Try to make up only the flux you need for the job that day. Get loads of practice.
PRACTICE-that is the main difference between a good and bad welder
Welding faults
Root Faults For deep vee multi run welds the first run or root weld is critical to the quality of the welds laying on top. Typical faults may be caused by too high or low a current of too large a rod .
Fusions Faults The three main causes of this is too low current for rod, too high a travel rate or when too small a rod is used on a cold surface
Bead Edge Defects normally in the form of under cutting or edge craters. The main cause for this is incorrect current setting. Too high will lead to undercutting, too low to edge craters. Similar efects may occur at the correct current due to incorrect arc length. Edge faults are particularly common in vertical welding or 'weave' welding. The general cause for the latter being a failure to pause at the extremes of the weave. Edge defects are stress raisers and lead to premature weld failure.
Porosity May have many causes the most common being moisture in the rod coating or in the weld joint. Poor rod material selection is also a factor
Heat Cracks this is a destuctive fault casued generally due to incompatiblity of the Weld material and weld Rod. Indeed in some cases the material may be deemed unweldable. Heat cracks occur during or just after the cooling off period and are caused byimpurites in the base metal segrateing to form layers in the middle of the weld. The layers prevent fusion of the crystals. The two main substances causing this are Carbon and Sulphur. A switch to 'basic' electrodes may help.
Anouther cause is temsion acroos the weld which , even without segregation in the weld, cause a crack. This occurs during a narrow critical temerpature range as the bead coagulates. During this period the deformation property is small, if the shrinkage of the base material is greater than the allowed stretch of the weld then a crack will result. One method of preventing this is to clamp the piece inducing a compressive force on the weld during the cooling period
Shrinkage Cracks Thes form due to similar effect of allowed weld deformation being less than base metal shrnkage although it is not associated with the critical temerpature rang above and therefore cannot be elleviated by compression. The use of 'basic' electrodes can help
Hydrogen cracks This is generally associated wht either hardened material or material hardened during the welding process. The hydrogen source can be moisture, oil, grease etc. Ensuring that the rod is dry is essential and preheating the weld joint to 50'C will help. The cracking occurs adjacent to the weld pool and allied to the tension created during the welding porcess will generate a through weld crack.
Slag Inclusion This common fault is caused by insufficient cleaning of the weld between runs. If necessary as well as using a chipping hammer and brush grind back each weld run with an angle grinder. Once the slag is in the weld it is near impossible to removed it by welding only
Welding Fumes
Welding fumes are generated during the welding operation and consist of a mixture of the filler material and the base material gasses and dust.
The best method of preventing inhalation of these fumes is by forced air extraction. Where this is not possible then the personnel in the area should place themselves away from the general air flow.
Metal Inert Gas (MIG)
Also called Gas Metal Arc Welding (GMAW). Where CO2 is used as the shielding gas the system may also be known as Metal Active Gas (MAG). Generaically the term MIG is applied to the welding sets.
The shield for the arc is formed from a supply of inert gas. Gas stored in a bottle is led via a flow regulator through a tube to the welding torch. When the trigger on th torch is depressed firstly the gas valve is opened and the shield gas emiited from the nozzle. Further depressing the trigger makes an electrical switch and the wire feed is activated and the metal wire electrified.
To start the welding operation the torch is held a set distance-sat 10-15mm, from the work piece, the trigger is pressed and the arc established. Note that the arc is not 'struck' in the same way as stick welding. To improve the arc creation is it advisable to sharpen the wire to a point before starting
Wire Stickout - The amount of wire sticking out of the holder at startup should be controlled. Too long and the weld arc is cool and may not be properly shielded by the gas. Too short and the holder tip can be overheated and weld spatter may enter the nozzle and cause turbulence in the gas flow.
Gouging
This refers to the technique of shaping or cutting metal using specialised electric arc rods. The arc is struck with the rod in the perpendicular position. Oncew the arc is struck the angle is reduced to about 20' ( do not point the rod into the weld. This allows for clean displacement of material. For vertical pieces the rod travel is down.
Air Arc Gouging
This is a system similar in manner to standard gouging but using copper coated graphite rods through which compressed air is pumped. The rod melts the metal and the compressed air displaces it. This system is seen in commmon use for underwater repairs.
Friction Stir Welding
This very modern practice is now becoming increasingly used in shipbuilding particularly for joining aluminium.
Two pieces of material are butted to gether. The FSW head, consisting of a profiled probe rotating at high speed is brought into contact with the join. Heat is generated and the metal softened and forced around the the probe to the rear. In this way material from both pieces are merged and thus the join is main. The weld is made in the semi solid state. There is no sparking, fumes and a reducion in noise. Weld speeds are increase by about 10% over conventional means.
Take a welding course
Rule of thumb when starting with an unknown set is 40amps per mm of rod e.g 2.5mm=100amps.
Increase the current slightly when using long extension cables. Try not to have these cables in a coil when welding
The quality of the weld is directly related to the surface preparation. Take a little extra time to prepare and shape the area to weld
Ensure all slag is removed , if necessary by using an angle grinder to gouge out any pin holes, before welding over a run
If your welding rod sticks then clean with an angle grinder the mark especially on critical welds such as pressure vessels. Check the condition of the coating on the rod. If the coating is damaged say with one side of the wire exposed discard the rod or burn it back to good on a non-essential piece
After finishing a run the end of the rod invariably gets a slag coating. When you come to strike again it is difficult so the tendency is to strike harder and harder. The consequence of this is that not only does the slag come off but a good piece of the coating leading to an erratic arc. Penetrate the slag cap by gently rubbing it on a rough surface, or use your fingers to snap it off (as I do)
Keep you glass clean- the fumes tend to coat the glass with a layer of dust. Keep wiping this off. If you cannot see the weld arc properly you have too dark a tint grade of glass. These tend to be supplied suitable for welding maximum amps ( say 300 Amps)
Where the shape of the weld is critical then use two hands. One to hold the holder the other grip the rod a couple of inches back from where the arc is. ( I used to do all boiler tube welding in this way and as I get older most of the vertical welding as well)
Position the piece to avoid as much as possible any other type of weld except horizontal- this is not a cheat but is common sense. Watch a coded welded how he works
Brace yourself against something before starting if possible. Loop the cable over your body so that the weight of the cable does not fall onto you hands
When doing a multi run weld into a narrow groove or right angle join use a small diameter gp rod for the root weld as this is critical and any slag inclusion will cause porosity in the rest of the weld runs
If you get porosity dont mess about putting a thousand runs over the top of it, grind the bugger out and start again
Don't be afraid to use rods. For awkward jobs bend the rod half way down if it helps. I welded an economiser using only the final inch of each rod which was bent to suit due to the position of the hole ( I also had to use a small inspection mirror to see it). Don't be tempted to use old part used rods for critical jobs as they inevitably have a high moisture content in the coating and make for a very porous and/or brittle weld.
When lighting an oxy-acet flame light the acetylene and increase slowly until you see the carbon smoke just disapear. The put on you oxygen.
When using oxy-acet gas cutters make sure you always have a bucket of water nearby incase of blow back.
If you are going to gas weld aluminium - don't. Reach for the TIG welder or if you must MIG. Or if you really, really must, stick weld. If you do not have these and have to gas weld make sure you well remove the oxide layer ( using a non-ferrous wire brush) and weld as soon as possible. Try to make up only the flux you need for the job that day. Get loads of practice.
PRACTICE-that is the main difference between a good and bad welder
Welding faults
Root Faults For deep vee multi run welds the first run or root weld is critical to the quality of the welds laying on top. Typical faults may be caused by too high or low a current of too large a rod .
Fusions Faults The three main causes of this is too low current for rod, too high a travel rate or when too small a rod is used on a cold surface
Bead Edge Defects normally in the form of under cutting or edge craters. The main cause for this is incorrect current setting. Too high will lead to undercutting, too low to edge craters. Similar efects may occur at the correct current due to incorrect arc length. Edge faults are particularly common in vertical welding or 'weave' welding. The general cause for the latter being a failure to pause at the extremes of the weave. Edge defects are stress raisers and lead to premature weld failure.
Porosity May have many causes the most common being moisture in the rod coating or in the weld joint. Poor rod material selection is also a factor
Heat Cracks this is a destuctive fault casued generally due to incompatiblity of the Weld material and weld Rod. Indeed in some cases the material may be deemed unweldable. Heat cracks occur during or just after the cooling off period and are caused byimpurites in the base metal segrateing to form layers in the middle of the weld. The layers prevent fusion of the crystals. The two main substances causing this are Carbon and Sulphur. A switch to 'basic' electrodes may help.
Anouther cause is temsion acroos the weld which , even without segregation in the weld, cause a crack. This occurs during a narrow critical temerpature range as the bead coagulates. During this period the deformation property is small, if the shrinkage of the base material is greater than the allowed stretch of the weld then a crack will result. One method of preventing this is to clamp the piece inducing a compressive force on the weld during the cooling period
Shrinkage Cracks Thes form due to similar effect of allowed weld deformation being less than base metal shrnkage although it is not associated with the critical temerpature rang above and therefore cannot be elleviated by compression. The use of 'basic' electrodes can help
Hydrogen cracks This is generally associated wht either hardened material or material hardened during the welding process. The hydrogen source can be moisture, oil, grease etc. Ensuring that the rod is dry is essential and preheating the weld joint to 50'C will help. The cracking occurs adjacent to the weld pool and allied to the tension created during the welding porcess will generate a through weld crack.
Slag Inclusion This common fault is caused by insufficient cleaning of the weld between runs. If necessary as well as using a chipping hammer and brush grind back each weld run with an angle grinder. Once the slag is in the weld it is near impossible to removed it by welding only
Welding Fumes
Welding fumes are generated during the welding operation and consist of a mixture of the filler material and the base material gasses and dust.
The best method of preventing inhalation of these fumes is by forced air extraction. Where this is not possible then the personnel in the area should place themselves away from the general air flow.
Metal Inert Gas (MIG)
Also called Gas Metal Arc Welding (GMAW). Where CO2 is used as the shielding gas the system may also be known as Metal Active Gas (MAG). Generaically the term MIG is applied to the welding sets.
The shield for the arc is formed from a supply of inert gas. Gas stored in a bottle is led via a flow regulator through a tube to the welding torch. When the trigger on th torch is depressed firstly the gas valve is opened and the shield gas emiited from the nozzle. Further depressing the trigger makes an electrical switch and the wire feed is activated and the metal wire electrified.
To start the welding operation the torch is held a set distance-sat 10-15mm, from the work piece, the trigger is pressed and the arc established. Note that the arc is not 'struck' in the same way as stick welding. To improve the arc creation is it advisable to sharpen the wire to a point before starting
Wire Stickout - The amount of wire sticking out of the holder at startup should be controlled. Too long and the weld arc is cool and may not be properly shielded by the gas. Too short and the holder tip can be overheated and weld spatter may enter the nozzle and cause turbulence in the gas flow.
Gouging
This refers to the technique of shaping or cutting metal using specialised electric arc rods. The arc is struck with the rod in the perpendicular position. Oncew the arc is struck the angle is reduced to about 20' ( do not point the rod into the weld. This allows for clean displacement of material. For vertical pieces the rod travel is down.
Air Arc Gouging
This is a system similar in manner to standard gouging but using copper coated graphite rods through which compressed air is pumped. The rod melts the metal and the compressed air displaces it. This system is seen in commmon use for underwater repairs.
Friction Stir Welding
This very modern practice is now becoming increasingly used in shipbuilding particularly for joining aluminium.
Two pieces of material are butted to gether. The FSW head, consisting of a profiled probe rotating at high speed is brought into contact with the join. Heat is generated and the metal softened and forced around the the probe to the rear. In this way material from both pieces are merged and thus the join is main. The weld is made in the semi solid state. There is no sparking, fumes and a reducion in noise. Weld speeds are increase by about 10% over conventional means.
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