14.3 Operation of a PAC System
Karl Fulton
Making Cuts
Before you start, make sure you have all your PPE on. The following chart shows the recommended shade (ANSI Z49.1) you will need to protect your eyes.
|
Amperage |
Minimum Shade |
Recommended Shade |
|---|---|---|
|
Less than 20 |
4 |
4 |
|
20-40 |
5 |
5 |
|
40-60 |
6 |
6 |
|
60-80 |
8 |
8 |
|
80-300 |
8 |
8 |
|
300-400 |
9 |
12 |
Note: Table reprinted from ANSI Z49.1 (“Guide For Shade Numbers” pp. 9)
Once you are wearing the needed PPE to safely complete your cut, follow this process:
- Hold the touch perpendicular to the metal being cut.
- Pull the trigger and drag the torch across the metal.
- If you do not have a drag tip or shield you will want to hover about ⅛ inch for the material.
- Just like welding you will always want to practice on a similar piece of material before starting on your actual project. This way you can troubleshoot your settings.
- If you are not cutting all the way through you need to slow down and turn up your amperage.
If you find that you have excessive dross on the bottom of your cuts. This can be caused by going too slow. Increase your speed a little. It can also be caused by excessive travel speed so do not go too fast either. If you are not cutting all the way through your material you run the risk of the molten metal blowing back into your torch and at you.
If you are experiencing a negative kerf angle (the sharp part of the metal is at the top and drifts away at the bottom) you are too close. If you have a positive kerf angel (the part looks like it has a bevel on it) you are holding the torch too far away. If you are getting a square edge on your cut this is outstanding, keep it up.
Direction of your cut masters. This matters because of the swirl that is produced inside the torch. When cutting a part where you want to keep the inside of the cut, the travel direction should be clockwise. When cutting out the interior of a part (so you will keep the outside of the cut) you will want to travel counter clockwise. This will give you the best end product.
After you have made your cut it will be hot. You will want to be cautious when handling metal after it has been cut. Most of the dross should break off very easily with a chipping hammer.
Maintaining the System
Maintenance for a Plasma cutter is quite simple. Check all electrical connections before and after use. Replace the consumables in the torch when needed and the occasional blow down with compressed air. As always check the owner’s manual for detailed instructions.
Special Safety Considerations
Safety is paramount when plasma arc cutting (PAC).
Electrical shock is a possibility. Always wear your PPE and do not operate if you are wet or have sweat through your gloves. Whenever possible, reduce the probability of being shocked. If using an extension cord concert the machine to the cord then the power and when disconnecting disconnect the power then the machine from the cord.
Fire is another hazard to be aware of. As you can see in most of the pictures there are lots of sparks. Make sure to check your surroundings before you start cutting and make sure you know where the nearest fire extinguisher is.
Compressed air is another safety concern when plasma arc cutting. It can puncture the skin and create debris that can get in your eyes. Be careful when using compressed air.
Both outside the visible light spectrum of the human eye, ultraviolet and infrared light can be hazardous and burn your eyes. Always wear the appropriate safety shade for your eyes. Please be sure to check the shade recommended by ANSI Z49.1 and presented earlier in this chapter to ensure you have proper protection for your eyes.
Machined torches and CNC machines have their own safety concerns the you will want to pay close attention to. Be sure to ask for specific safety guidelines and read the manufacturer’s warnings carefully before operating these machines.
Attributions
- Figure 14.15: US Navy 111128-N-OY799-092 Hull Maintenance Technician Fireman Tom Fields, from Brinnon, Wash., uses a plasma cutter in the sheet metal shop aboard by Mass Communication Specialist 3rd Class Kenneth Abbate in the Public Domain; United States government work
- Figure 14.16: US Air Force (USAF) Technical Sergeant (TSGT) Jeffrey Wright, Aircraft Metal Technician, 52nd Equipment Maintenance Squadron (EMS), uses plasma arc cutting torch to destroy a 30mm gun barrel, inside the welding shop at Spangdahlem Air Base (AB), Germany. The weapon was removed from an aircraft and set for destruction after reaching its serviceability date by Department of Defense. American Forces Information Service. Defense Visual Information Center. in the Public Domain; United States government work
Unwanted byproduct of molten metal, this material can stick to the bottom the metal being cut.
the cleanliness and squareness of a cut.