2–26.
Figure 2–26Bell-mouthed cut
When the cut is not smooth, how can you determine what corrective action to take?
Compare the defective edge with the drawings in Figure 2–27 to diagnose the problem.
Figure 2–27Cutting Problems and their causes
Air Carbon Arc Cutting
What is the AWS abbreviation for Air Carbon Arc cutting?
The American Welding Society acronym is CAC-A
How does the CAC-A cutting process work?
This process uses an electric arc to melt the metal which is blown away by a high-velocity jet of compress air. See a CAC-A torch in Figure 2–28.
Figure 2–28Air Carbon Arc Torch
Why was this process developed?
Myron D. Stepath originated the process during WW II, while working as a welding engineer with the U. S. Navy, where he conceived the idea to solve the problem of removing defective stainless steel welds in armor plate on warships; the conventional methods, at the time, were chipping and grinding, which had proved infeasible due to time and cost factors.
How is the CAC-A process used?
Today this process is used to rapidly remove defects in welds and base metal.
What are the electrodes made of?
The electrodes are rods made from a mixture of graphite and carbon and most are coated with copper to increase their current-carrying capacity. Manufacturers make both DC and AC rods for this process. See Figure 2–29.
Figure 2–29Carbon electrode air stream and travel direction
What type of power source is required for CAC-A?
Standard constant current welding power sources are used to provide current.
What is the required source of air for this process?
A jet of ordinary compressed shop air is all that is required.
What are the amperage requirements for this cutting or gouging process?
Depending on the electrode diameter and job requirements the amperage ranges can be as low as 60 amperes or as high as 2200 amperes. See Table 2–3.
Table 2–3 Matching electrode diameter to current
Can we calculate electrode consumption?
When used correctly every inch of carbon consumed by the user will get approximately eight inches of groove when making a gouge that is equal in depth to the diameter of the carbon electrode; the gouge should be
What are the advantages of the CAC-A process?
•The primary advantage of this process is the rapid removal of defects so repairs may be made in a timely manner.
•The CAC-A torches are relatively inexpensive.
Are there disadvantages to the use of this process?
•Operator can leave carbon deposits in the area that will be re-welded.
•Carbon deposits must be ground or brushed away before re-welding.
•This process requires compressed air.
Safety for CAC-A
What considerations should be made when using this equipment?
All of the electrical safety considerations covered in Chapter 13 should be followed. The minimum shade lens requirements are the same as those found in Chapter 5, Table 5–7. All of the clothing requirements covered in Chapter 4, Figure 4–26.
Safety
What precautions in handling oxygen and fuel gas cylinders and related equipment apply to OFC?
In addition to the safety precaution covered in this chapter beginning on the next page, all precautions listed in the Safety section of Oxyacetylene Welding, Chapter 1 must be followed.
What are the main hazards of OFC and what safety equipment can prevent these injuries?
•External eye injuries from cutting sparks prevented by safety glasses, or safety shields.
•Internal eye (retinal) damage from viewing hot metal and the radiation coming off it prevented by using a number 5 tinted lens while cutting or oxyfuel welding.
•Burns from weld sparks and hot metal prevented by leather gloves, nonflammable clothing, leather skins when working overhead, cuffless pants, pocketless shirts, a welding cap, and high-top shoes.
•Fires from the welding process are prevented by moving flammables away from the weld zone and having water or fire extinguishers close at hand.
•Fumes from paint or plating vaporized by the cutting process prevented by good ventilation and keeping out of the cutting plume.
What fire safety considerations are important in OFC?
•When cutting near materials that will burn, make sure that flame, sparks, hot slag, and hot metal do not reach them. Cutting creates more sparks than OAW.
•If the work to be cut
