13.2 CAC-A Equipment and Setup
Stephanie Oostman
Components
The information included in this section is generalized, and you should check with the operating manual and/or manufacture of your specific equipment on set up procedures, limitations, and safety considerations.
In section 13.2.1 Basics of the Process we read what CAC-A does, and a few notes on specifications on the equipment. Most welding machines that are capable of SMAW can also be used to perform CAC-A with a few additional pieces of equipment. To set up a welding machine for manual CAC-A you will need the following:
- A constant current (CC) welding machine capable of at least 28V output.
- A CAC-A Electrode holder. See image above
- A ground clamp.
- Carbon arc electrodes capable of the polarity you need.
- compressed air that can be supplied at at least 80-100 psi.
- Air Hose for compressed air.
The power source can be either AC or DCEP, however the carbon arc cutting process requires higher output than some welding machines produce, making them an ineffective choice for this process. Running a machine at the higher output needed for CAC may cause the machine to over extend its duty cycle unless the machine is a heavy industrial type capable of 100% duty cycle, to avoid overloading your welding machine take breaks and consult the manufacturer for the machine’s duty cycle.
The electrode type and diameter, and the material to be cut, may also impact which polarity to select. Minimum electrode diameters, polarity, amperage and air pressure settings will all be dictated by what the material is and how thick. This is no different than most welding procedures. A ¼” electrode on DCEP has a range of 200-400 amps for example, and can be used to cut carbon steel, stainless, copper and nickel alloys, aluminum and cast iron.
Air supplied should be 80-100 psi nominal. While you can use higher than 100 psi, it does not make the removal of molten metal more effective. The air line needs to have at least an inner diameter of ⅜”, and the air compressor must meet the needed capacity to adequately produce a clean effective cut. For lighter duty work, these recommendations can vary with air pressure as low as 40 psi and an airline inner diameter of ¼”. If the air pressure is not sufficient, the operator will not be able to produce a smooth, uniform cut. This can also happen if the diameter of the air hose used is too small, as it will create a constriction of air flow to the electrode holder.
Note: Oxygen should never be used in place of compressed air in the CAC-A process.
The modern day CAC-A torch is designed to bring both the electrical cutting power of the process together with the blasting power for compressed air.
Refer to the pictures in this section. Both the upper and lower jaws are insulted and the lower jaw has a head with holes to allow compressed air through. The head can be rotated allowing for different angles or positions and both jaws only have one groove that can accept multitude of electrode sizes. Not all torches are created equal. Just like different electrodes are designed for different amperages, torches are also rated for amperage. Using a lower amperage rated holder may be dangerous or cause damage to the holder and other equipment.
Setting up the System
Look at your welding machine, it may have a setting for CAC-A already available.
If that’s true, select that program on the machine.
For carbon steel applications, connect the ground clamp to the negative terminal of a CAC-A capable welder, and the end of the CAC-A electrode holder to the positive terminal.
This is now set up for DCEP (reverse polarity). As mentioned previously in this text, DCEN should not be used in the carbon arc cutting process.
Next connect compressed air to the CAC-A via an air hose with at least an inside diameter of ⅜” The air pressure will need to reach 40-80 psi for general applications, but may require upwards of 100 psi for heavier duty needs.
Don’t forget to connect your ground clamp to your cutting table to complete the electrical circuit.
Next select a carbon arc rod. When placing the electrode in the holder, the end should be within 6” of the air holes, but not closer than 2” to prevent damage to the equipment.
The holder must be held so that the air holes are positioned on the bottom in order for the air to effectively blow the molten dross away from the area being worked.
Next set the voltage output on your welding machine.
Electrodes
Electrodes may be copper coated or plain graphite. The copper coating on the electrodes keep the electrode from overheating, and increases its conductivity and arc stability when using higher amperages. It can also make the electrode slightly more durable. Both types of carbon arc rods are fragile, and should not be left in the rain or out in moisture. If you are using alternating current (AC), then a special electrode type must be chosen. These AC electrodes contain other elemental additives which aid in their stability.
Carbon electrodes come in a multitude of sizes, each rated to withstand more or less amperage, and come in round, rectangular or diamond shaped.
Some Electrodes can be joined together to reduce waste, and also to increase productivity in robotic and semi-automatic operations.
Attributions
- Figure 13.1: CAC-A Electrode Holder by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 13.2: Compressed Air Line by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 13.3: A carbon arc electrode in the electrode holder by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 13.4: CAC-A setting selection by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 13.5: The electrode holder is connected to the positive by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 13.6: Air hose connection into the CAC-A electrode holder by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 13.7: Connect the group clamp by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 13.8: Carbon arc electrodes by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0
Compressed air is air that has been pressurized to a pressure greater than the atmosphere. Compressed air is made up of the same gasses in the atmosphere, so it shouldn't be confused with oxygen or other pressurized gasses.