Its disadvantage is cost. They are only needed when large gas volumes are needed as with multiple stations or rosebud tips.
Figure 1–14Two-stage regulator
Torches, Tips, and Hoses
What are the major parts of an oxyacetylene torch?
Shown below is the most common oxyacetylene torch design. Other designs are available. Some have very small flames for jewelry and instrument work, while others take no accessories and are much lighter in weight than standard torch designs to reduce operator fatigue.
Figure 1–15Oxyacetylene torch and tip
Besides a selection of tip sizes for different sized jobs, what other devices can be put on the torch handle and what are they used for?
•Cutting heads also called cutting attachments (see Chapter 2).
•Multi-flames for heating metals prior to bending, brazing, or heat-treating.
Figure 1–16Oxyacetylene torch attachments: cutting head (left), welding tips (center) and multi-flame tip (right)
Why are there different size torch tips?
Matching the size of the flame and the resulting volume of gas to the thickness of the metal in the weld is important. Too much flame and the base metal around the weld may be damaged, too little and there is inadequate heat to melt metal for full penetration.
How are torch tip sizes designated?
There is no industry standard; each torch manufacturer has its own numbering system. Cross-reference tables compare each manufacturer’s tip sizes with numbered drill sizes.
The American Welding Society (AWS) has been urging tip manufacturers to stamp tips with the material thickness size to eliminate the confusion of tip size numbers. The AWS C4.5M Uniform Designation System for Oxy-Fuel Nozzles calls for tips to be stamped with the name of the manufacturer, a symbol to identify the fuel gas, the maximum material thickness, and a code or part number to reference the manufacturer’s operating data; many manufacturers are not in compliance. Most companies making welding tips do provide information booklets available to cross reference their tip sizes to tip drill sizes. See Table 1-2 tip drill size to material thickness.
Table 1-2Matching welding tip size to weld material thickness
How can the drill size of a tip be determined?
Using a tip cleaner find the round file which fits into the tip easily but snuggly then check the drill size of that file listed on the body of the tip cleaner cover.
When should the torch tip be cleaned and how is it performed?
When sparks from the weld puddle deposit carbon inside the nozzle and on the tip face. These act as spark plugs and cause premature ignition of the gas mixture. Torch tips should be cleaned at the start of each day’s welding and whenever flashback occurs, the flame splits, or when the sharp inner cone no longer exists. To clean, select the largest torch tip cleaning wire file that fits easily into the nozzle and use the serrated portion to remove any foreign material. Be careful not to bend the tip cleaner file into the tip which can cause the cleaning file to break inside the tip; if the file breaks inside the tip it is nearly impossible to remove. Also be sure not to enlarge the existing hole. Then touch up the face of the tip with a file or emery cloth to remove any adhering dirt. Use compressed air or oxygen to blow out the tip. Never use a twist drill to clean the tip; it will cause bell-mouthing.
Why is it important to purge each gas hose separately and not simultaneously?
All possibility of permitting gas to enter the wrong hose and regulator must be prevented as it can lead to a deadly explosion.
How are gas hoses color coded?
Hoses for oxygen and acetylene welding and cutting are coded red for acetylene and green or black for oxygen.
What is flashback and what hazards does it present?
Flashback occurs when a mixture of fuel and oxygen burns inside the mixing chamber in the torch handle and reaches the hoses to the regulators or cylinders. Such burning in the hoses, regulators, or cylinders is likely to cause an accident with burns, a major fire, explosion, shrapnel injuries, and fatalities. If either through operator horseplay (like turning on both the acetylene and the oxygen with the torch tip blocked), or through regulator failure, an explosive mixture of acetylene and oxygen is forced back toward the cylinders. This explosive mixture may enter:
•One hose, or
•One hose and one regulator, or
•One hose, one regulator, and one cylinder.
The stage has been set for a catastrophic explosion. When the torch is lit, this explosive mixture will go off. See Figure 1–17.
Figure 1–17How flashback can occur
How can flashback be prevented?
Flashback is easily prevented by installation of flashback arrestors consisting of both a check valve and a flame arrestor. One flashback arrestor fits between each hose and the torch handle hose fitting. The check valves prevent the gas from one hose from entering the torch handle and then crossing to the other gas hose inside the back of the mixing chamber. Without the mixing of gases into an explosive mixture in the hoses, there can be no explosion in the hoses, regulator, or cylinder. The flame arrestor consists of a compressed stainless steel or sintered metal cylinder. The flame arrestor cylinder tends to stop fire from passing through it by both lowering the temperature of the flame front by absorbing its heat and by forcing the flame through small passages.
These devices are about the diameter of the gas hoses and about 1
Figure 1–18Reverse-flow check valve flashback arrestor cross section
What
