Plasma Burning Distortion

Date 05-11-2009 15:42

Not an expert but have the following question:
Are they using a torch rated for the material capacity that they are cutting?

I ask this because we all know that heat input is the main problem with the distortion and slow travel speeds due to an undersized torch can input more heat than one that is properly sized.

By defaced (**)

Date 05-11-2009 16:26

Good question. I'll add that to the list of questions I'm going to ask. From looking through some other people's notes, they're having this issue on three different plasma machines, all different makes and models. Some cutting is being done on water, others being done dry, but none being done underwater.

By leterburn (**)

Date 05-11-2009 17:38

If you're experiencing it on all machines - I would be inclined to question the integrity of material from last shipment?? We attempt to utilize only quality first material - try to never use seconds - also P&O seems to work much better than just hotroll - and grade 50 and above normally cuts superbly in 1/2" and thicker. DL

By defaced (**)

Date 05-12-2009 15:43

This is all HSLA (80 and 100 ksi) material, and the mill is involved. I'm too far removed from the front lines to know if it's a recent shipment or if this has been an ongoing problem. We're looking at everything that we can think of: mill material processing issue, a storage issue, a cutting procedure issue, like cut sequencing, using/not using tabs, cut parameter, etc.

By CHGuilford (****)

Date 05-11-2009 16:28

defaced,
John has a good point. A properly sized tip and the faster cutting speed resulting from the proper tip will put less heat into the material.

Another trick is to use a water table. Many automated plasma torches are designed to operate underwater so the water will keep the material cool as it is cut. On our table, we normally bring the water level to slghtly more than the bottom ot the plate- so the operator can see is the tip is running into an edge, but water still cools the plate.

If a water table is out of the question, perhaps an air/water siphon could be rigged to travel with the torch and that can keep the material cooled?

I'll bet the equipment manufacturer has already designed something for the systems they sell.

By welderbrent (*****)

Date 05-11-2009 17:13

Defaced,

I would also be curious as to rather they are cutting a hole or pattern of any kind out of the center which would cause a build up of extra heat in the center and weaken the part as well. And along with that, is it properly supported under the center as they are cutting. If it is only supported at the ends it would give it a chance to sag as it was cut.

I agree with the assessment of the others also as to speed of cutting operation and amount of heat being put into the part as it is cut. But at 1/2 to 1" I would think it would still need the contributing factor of not enough support in the center or an additional cut through that area that pushes it out of flatness.

Have a Great Day, Brent

By defaced (**)

Date 05-12-2009 15:44

Thank you for the suggestions. I'll run them up the flagpole and see what shakes out.

By DaveBoyer (*****)

Date 05-12-2009 03:49

Brent makes a good piont about table support. The flame cutting machine at the plant had verticle steel pins on 4" centers to support the entire 10' x 20' plate. The pins were replaced when they got too carved up from use.