[larry lee]

Multiplaz-3500 Evaluation, Part 07: Testing the Cutting Torch (conclusion)

DISCLAIMER!
Let me emphasize that I will not be able to tell you whether the Multiplaz-3500, or any other piece of equipment, will be a good investment for you. Only you can decide that. My intent is to provide as much factual information as I can about the Multiplaz-3500 so that others in our company can make an informed decision about that. The company has no objection to my sharing the information with you as long as I leave their name out of it and make it clear that I am not endorsing any particular product.
DISCLAIMER!

This is a continuation of the testing of the Multiplaz-3500 cutting torch that was started in Part 04 of this Evaluation. Two additional sets of measurements were carried out:

1. The effect of cutting mild steel sheet of various thicknesses with the sheet mounted vertically and the torch mounted horizontally. Cutting was done moving left, right, up, and down.

As stated in Part 04 of this Evaluation for the cutting tests in the traditional flat position:
“As with an oxy-fuel cutting torch, the steel reacted with the oxygen in the “cutting flame” (plasma) once the steel started to get hot. At this point the heat into the metal is noticeably more (as determined by the color change) and the rate of melting the metal also is noticeably more. The force of the plasma gas to blow the melted metal out of the cut (kerf) is then not enough to keep up with the rate of melting and so the melted metal hangs as a large drop(s) under the kerf due to surface tension. Then a layer of cooling metal tends to fuse the bottom edge of the kerf back together as the plasma moves forward. The thickness of the fused layer (~1/32”) seems to be almost independent of the thickness of the steel, at least for the thicknesses tested (1/16” to 1/4”).” Thus it was not possible to get cutoff in one pass for any thickness or cutting speed in the flat position once the steel started to get hot.

The idea of trying to cut with the steel sheet mounted vertically was that perhaps gravity would assist in removing the hanging drops of melted metal. In actuality, the thickness of the fused layer was least for cutting in the traditional flat position. It was somewhat surprising to see the drop of melted metal always behind the plasma, regardless of the direction of travel of the torch. Even when cutting vertically down, the drop formed above the plasma (not below it) and did a very good job of rewelding the kerf as the plasma moved down. Apparently the surface tension is highest to the hotter metal behind the plasma.

2. A test of the ability of the torch to cut “up to 1 mm per second (3 IPM) for (low-alloyed steel) thicknesses of 10 mm (3/8”)” as stated in the Multiplaz manual.

We tested the cutting torch by cutting in the traditional flat position using 3/8”-thick by 3”-wide bars of 6061-T6 aluminum, 304 stainless steel, and 1018 mild steel to determine whether the torch could really cut that thickness at 3 IPM. Several measurements were made on each piece, varying the speed of the welding positioner between 2 IPM and 3 IPM. For the aluminum and the stainless steel, 2 IPM gave a single-pass cutoff, albeit with a ragged cut and lots of dross. At 3 IPM the torch could not quite cut through. So for aluminum and stainless steel under our test conditions, the torch did indeed cut at “UP TO 3 IPM”, as claimed. For the mild steel, the same problem occurred with the fusing of the melted metal behind the plasma. The plasma could penetrate the metal thickness easily enough and one could see the “hole” around the plasma all the way through the metal, but the momentum of the gas stream was not sufficient to blow the melted metal away. (The issue of low gas mass flow rate in the Multiplaz cutting torch is discussed more in Part 05 of this Evaluation).

In one of the Multiplaz videos about using the cutting torch on their website
http://www.multiplaz.com/video
it is suggested that one can direct the dross to one side or the other of the kerf by tilting the torch (essentially making a bevel cut). Our experience is that this does have some effect, but it doesn’t much affect the bridging that occurs behind the plasma.

I looked carefully at the two videos about cutting on the Multiplaz website. The first one is called “Cutting in Mode II”. If you look closely at the inside of the steel pipe as the plasma moves in from the end (1:23 to 1:27), you can see the rather large melted metal drops start to form and move around each side of the plasma towards the cut behind the plasma. At thist point there is a change of view to the top of the pipe. At the next view of the end of the pipe (1:32 to 1:35), note that you cannot see any clear cut at the starting end.

In the second video, called “Cutting characteristics”, when the cut circle drops out of the pipe (1:35), you can see the typical roughness of the cut and typical dross on the top and bottom edges. On the straight cut (2:09 to 2:12), you can see the bridging of the cut and the dross. The video does not go all the way to the end of the cut, so you cannot tell whether it drops off.

My conclusion from all of this is that the bridging of the melted metal across the kerf in mild steel is a regular feature of this cutting torch. It can usually be overcome by making multiple passes, but the cut is certainly not a “quality cut”. For just severing it might be fine. But if one wants to use the cut edge for further work (joining, threading, or mating to another surface), a good deal of machining (grinding, drilling, or milling) will be required. I would say that the overall quality of the cut is comparable to (certainly no better than) a typical manual cut using an oxy-fuel torch. There is no comparing it to the quality of the cut produced by a compressed-air plasma cutter, not even a small self-contained unit such as the Miller Spectrum 125C.

In closing, let me list a few PERSONAL observations and comments.
a. Although the idea of using water instead of compressed air as the plasma gas is interesting, the actual mechanics of filling, starting, adjusting, using, and cooling the Multiplaz-3500 cutting torch become very tedious if you have to do it many times in a row (as in doing all of the tests in this evaluation). The main nuisance is that the cathode to nozzle spacing must be made small for starting and then increased as the torch warms up. If the current is increased above position 4 (the default starting current), additional adjustment of the cathode to nozzle spacing is required to keep the cathode to nozzle voltage within the recommended range. Watch the first video listed above (“Cutting in Mode II”) and note how many turns (about 7) are required on the back knob before the torch is ready for use. After use, the torch must be cooled and refilled. The cathode to nozzle distance must then be reduced by the same number of turns, the arc started, and then the distance increased again.
b. Drops of liquid water sometimes get in the plasma chamber and cause the arc to sputter and/or go out. This is particularly true when first pointing the plasma down. Restarting is easy enough, but it is one more nuisance. The problem can be minimized by letting the torch warm up longer (2 to 3 minutes) before pointing it down.
c. The power cable to the torch is a little stiffer than I would prefer. In our tests with the torch position fixed and the workpiece moved by the variable-speed welding positioner, this was not an issue. For manual cutting (we did try some), it makes turning the torch more difficult.
d. The devices provided for maintaining the nozzle-to-workpiece spacing and for circle cutting do work, but they are awkward. To cut a circle, the whole torch must be turned 360 degrees, and the cord with it.

This concludes the planned testing of the cutting torch. We now proceed to the testing of the welding torch.

to be continued

larry lee

[WerkSpace]

Larry, I must agree with your findings. The cutting ability of the MultiPlaz is not very good. It will cut without an air compressor or compressed gas cylinders but it doesn't do it anywhere near as good as a traditional Plasma cutter.

[Billbong]

Hi, this is a worry, although it doesn't bother me as I bought the outfit purely for the welding function.

It would appear that there is not enough volume or steam exiting the nozzle at enough velocity to blow the melted metal away, so it just melts and hangs there.....a possible solution would be to have a higher steam pressure (how?) or a supplementary compressed air supply pipe with a fine nozzle placed just in front of the cutting nozzle to blow the metal away.....posible room to experiment.
Ian.