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T_Bone
01-19-2008 10:51:17
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Re: cutting torches, Harris or Victor in reply to Don c, 01-18-2008 11:47:35
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Hi Don,
Theres nothing finner than a Victor 100 torch. Small body for great hand control and less hand fatique. A with a 3/16"x25ft hose works well for shop use. The torch is rated for 1-1/2" cutting or brazing 1/2" plate. Great quality and will last a very long time.
Nothing wrong with other brands other than the large mxing body size is like using a club.
Don't confuse Oxy/Gas combinations with a Air/Gas mix. Pure Oxygen greatly increases flame tempature.
Example: Proapne/Air = 2825ºF
Acet/Oxy= 5900ºF
Propane/Oxy= 4580ºF
Propaylene/Oxy= 5900ºF
Mapp/Oxy=5300ºF
Acet/Oxy has a huge welding/cutting advantage as it requires less flame spread for the same BTU reqirement thus will cost less perunit(cft).
For production welding/brazing/cutting then Propaylene would be a consideration to keep costs down. For a small shop that uses 2 cylinders of Acetylene year, buy the Acetylene.
I've included my thoughts on Cutting, Brazing Misconceptions found on the Tool Forum archives:
Original File: 11/10/07
This is probably a great time to clear up some misconceptions on Cutting, Brazing and Rosebuds, that alot of welders have.
All the information can be applied to cutting, brazing, fusion or heating, execpt where noted:
Backfire is 99% caused by to much fuel being supplied for a too small of a orifice size, ie; using the wrong sized rosebud or cutting tip for the amount of output heat required. This is the first indication that the mixing chamber pressures are NOT set correct and the pressures are set too high for the given orifice size.
All cutting/heating orifices have a designed pressure rating that's stated from the mfg as the orifice tip body is cooled by the gases flowing from the orifice while in use.
Exceeding the designed orifice pressure rating will cause the ignited acetylene gas to leave the face of the tip body, thus at the same time the flame will add excessive oxygen (oxygen that is obtained from the surrounding air) to the actylene gas that will cause the flame to momentary extinguish, then as the mixed gas cools it reigintes and causes a small explosion as it reignites thus you here the "bang" or poping noise and this condition is called backfire and can be very dangerous.
When the backfire is not corrected by lowering the fuels pressure or volume, acetylene being the fuel in this case, then another EXTREAMLY DANGEROUS condtion will occur called flashback.
Flashback is where the flame that contains oxygen and fuel, is sucked back inside the mixing chamber and will cause a EXPLOSION if not quickly corrected by shutting off the source of oxygen and then shutting of the fuel. Turn off the cylinders in that order as three conditons are generaly considered to cause a explosion, that being oxygen, fuel and a source of ignition.
I added volume to my descriptions as well as pressure because there are some fuels that can explode under the same conditions without any warnings as I described above.
Weld Fusion: is where two meatls are joined together by melting a equal amount of molten metal from each piece, either with or without the additon of a compatiable filler metal.
Never run Acetylene above 15psi for any reason!
A drip of liquid black goo from the tip, (ie;runny nose), is usually caused by condensastion mixing with the by-products of combustion then dripping from the tip face. This condition is most likely caused by a air leak into the mixing chamber or tip connections.
Fact: Acetone is a combustitable fuel. You will usually smell acetone while using a touch because the acetylene tank is suppling too much volume of gas for a given tank size for the amount of fuel demand of the mixing chamber and tip OR the the cylinder has been layed on it's side and has not been allowed to stabilize after returning the cylinder to the vertical position. Stablize a vertical acetylene cylinder for 12hrs before using the fuel!
Using too much preheat for the thickness of metal your cutting along with a dirty cutting tip will cause problems.
It's most likely your cutting speed is also too slow but without correcting the first two problems, you will not be able to tell.
What happens when you use too much preheat? The molten metal is very liquid in width and when you try to blow the heated molten puddle with oxygen, the puddle runs to the back of the direction your cutting and reforms a weak bond behind your cutting tip. This new molten puddle is high enriched oxygen and carbon making it very hard and brittle thus when your try to reheat this area it takes longer to preheat as well resist being blown out by the oxygen from the hardness of the metal and will cause molten metal too blow out and back onto the cutter.
With the correct preheat flame temperature the molten puddle will not form as wide thus you will achive a narrow cut without any molten puddle run back.
Using a dirty cutting tip, several problems arise. First with the preheat orifices drity you will not achive a even preheat to start the cut. It will take more preheat to start the cut with a dirty tip than with a clean tip. Second once preheat has been established then the if the center tip orifice is not cleaned then slag will collect on the backside of the base metal and the cut face will be ragged.
The above problems will cause a slower forward cutting speed thus once again cause base metal over heating allowing the harden slag to refrom behind the cutting tip.
The cleanest cut comes from a clean tip. After you clean all the orifice bores in the tip, fire up the torch and set flame for cutting, then depress the cutting lever and observe the flame.
There should be a long very "uniform" inner flame cutting cone. If that inner cone is not "very" uniform then your cut will be ragged just like the flame cone is and the back of the metal will have slag. Reclean the center orifice until it's very uniform.
A cut with a clean tip will have a very smooth cut surface with very little (if any) slag on the backside of the cut. If either one of these is not present reclean the tip.
The center bore orifice can get deformed and the tip needs replaced or cut off. It's really important to hold the cleaning file straight in the bore hole and just removing enough material to clean the bore to make the tip last a long
time.
I've never used a new tip that was clean enough for cutting, brazing or heating right out of the box.
Another consideration is as the tip size becomes smaller so does the orifice size and it becomes a bare to clean them ity bity holes. If using an automatic cutting machine then changing tip size would be a production benefit.
Always use a mfg. pressure chart, tip sizing chart and hose sizing chart for setting gas pressures for there brand of mixing chamber and tip combinations.
Setting the proper neutral preheat flame, the orifice holes around the center cutting orifice, can be observed by the tip of the inner flame cone:
A neutral flame has a blue colored flame outer sheild with a light blue to white inner cone flame that is slightly rounded at the cone tip.
A oxidizing flame (too much oxygen) has a sharp pointed very white inner cone.
A reducing flame (not enough oxygen) would have a very round to a ragged third inner cone.
Examples:
I have found 5psi acetylene and 30psi Oxygen while cutting to be a good all around setting for upto 50ft of 1/4" hose. Your final pressure setting is regulated by the needle valve adjustments on the mixing body.
For brazing or welding a size #0 tip works well with 5psi Acetylene and 20psi Oxygen. Again the needle valves on the mixing body sets the final pressure needed at the tip.
I also use the above settings to preheat 2" round bar without any problems using the #0 size tip or the rosebud tip.
The advantage to using a rosebud tip is that it expands the flame temperature over a wider area vs using a #0 size tip. I very seldom use my rosebud tip. Preheating with LP saves some expensive gas then finish heating with Qxy/Acet.
Altough theres many different tip sizes, I have a found a No3 makes for a all around good cutting tip as it will cut upto 1-1/2" or 18ga sheet metal depending on the preheat setting.
I strongly urge you too research more information for your own safety.
T_Bone
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