[larry lee]

Multiplaz-3500 Evaluation, Part 02:
The Multiplaz Technology Co., Ltd. and the Multiplaz Technology

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!

A great deal can be learned from visiting the company’s website at
http://www.multiplaz.com
and the websites of those who are in the business of reporting the organizational and financial aspects of companies, such as
http://multiplaz.en.alibaba.com/company_profile.html.
Multiplaz is a registered trademark of the International Plasma Corporation Ltd. (Hong Kong), who claims to hold the worldwide patent rights to what is often referred to as the Multiplaz technology (water/alcohol plasma). The Multiplaz Technology Company Ltd. claims to be the exclusive licensee of the Multiplaz technology and has three main locations: Russia (R&D Center), China (Headquarters, Manufacturing, Sales), and USA (North American Sales). Administratively, it would probably be considered a Russian Company, with a Russian CEO headquartered in China. (The China operation is technically a “Foreign-Invested Enterprise” and was established in 2006.) The Multiplaz-3500 plasma cutter/welder is their best known product at the moment, having evolved from the original Multiplaz in 1998 to the Multiplaz-2500 in 2003 to the Multiplaz-3500 in 2008. You can see photos of the three models at
http://www.multiplaz.com/history.
The company reports total annual sales of between 2.5 million and 5 million USDollars with about 25% of production sold in China and about 75% of production exported.

The exact relationship between the International Plasma Corporation and the Multiplaz Technology Company is not clear. The Multiplaz-3500 that we received has a label on the back of the inverter power supply that says:
“International Plasma Corporation Ltd.”
3rd floor Jonsin Place, 228 Queens Road
East, HK-Wanchai, Hong Kong, E326983
Multiplaz-3500 Arc Welder, Serial N: xxxxx
(The label also gives other information, such as voltage/current/power in and out for cutting and welding. See later parts of this evaluation for more details.)
Each of the torches (cutting and welding) says “IPC Ltd Plasma Tool” on it.

The Multiplaz trademark is also used for several other related products. These are the Multiplaz-4000 (a 180 amp AC/DC welder similar to the Everlast PowerTIG), the Multiplaz-7500 (a compressed-air plasma cutter - capacity 1” steel) and the Multiplaz-15000 (a high power compressed-air plasma cutter - capacity 2” steel). As far as I know, these products are not marketed in the USA at present. (Incidentally, the number after the Multiplaz trademark is the maximum volt-amperes into the inverter power supply for that unit.)

According to the company literature, the original Multiplaz technology was developed by Alexandr Apunevich and Evgeny Titarenko in the Russian Federation in the 1990s for use in space capsules. Worldwide patent applications were filed in 1997/1998. The first patent was granted in Russia in 1998 and sales started soon after. (According to the company, more than 20,000 units of the Multiplaz-2500 and Multiplaz-3500 have been sold in Russia since 2003.) The USA patent for the Multiplaz technology is #6,156,994, and was issued in 2000. You can get a free copy of the patent at
http://www.patentlens.net/patentlens/pa ... nguage=en&.
The North American Sales office in the USA (Multiplaz LLC) did not open until 2011, so the product is not as well known in the USA as it is in Europe and Asia. Searches of the Internet (mostly in English) turned up no serious complaints by customers. Most customers were quite pleased with the Multiplaz products.

My PERSONAL OPINION of the company is that it is well structured, that it uses well-established and well-protected technology, and that it has products and service that are well regarded by the vast majority of its customers. All of these characteristics are important because they increase the probability that the company will be in business well into the future. Unless you buy a product with the understanding that it is a disposable commodity, the most important characteristic of a company to you as a customer is that the company is there when you need it - for information, for a replacement part, or for a repair.

The Multiplaz Technology

Having worked on plasma torches back in the 1960s, I am very impressed with the science and engineering that is incorporated in the Multiplaz technology. (The Russians have a long history of developing welding equipment and procedures for use in space. The first record of welding in space was in the Russian spacecraft Soyuz 6 in 1969.)

Consider the objectives in the development of a cutting/welding torch to use in a space capsule in outer space. Because of size, weight, energy, pollution, and distance considerations, the objectives are:
a. No compressed gas or other hazardous components
b. No auxiliary water cooling unit
c. No evacuation of fumes and vapors to the outside
d. Low electrical and magnetic interference (EMI)
e. High duty cycle and limited DC electrical power
f. Torch must work in all positions
g. Low weight
h. High reliability.
So, what can you do?

Given that you want to use electrical energy to heat a workpiece (metallic or non-metallic) in order to cut it or to solder, braze, or melt (weld) it, the most efficient general transfer mechanism is to convert the electrical energy to a plasma and then use the plasma to heat the workpiece. One must therefore have a suitable plasma gas, but not from a compressed gas cylinder. One solution is to evaporate a liquid that is suitable for the plasma and that is also non-polluting to the atmosphere. Water was chosen and it also has the additional advantages that it is low in cost, readily available, non-flammable, and produces a slightly oxidizing plasma that helps cut through some materials. The Multiplaz-3500 cutting torch uses about 250 mL/hr of liquid water when cutting at maximum power. If we assume that this is vaporized to an average temperature of about 1000 degrees Celsius in the plasma and shielding gas, this results in about 400 cubic centimeters of water vapor per second (50 cubic feet per hour ) through the cutting torch nozzle. The gas pressure in the inner plasma chamber ranges from 6 psig to 17 psig (0.4 to 1.2 atmospheres gauge pressure). The orifice in the cutting nozzle has a diameter of 1.1 millimeters (0.044”) and a cross-sectional area of 0.95 square mm (0.0095 square cm). The calculated gas velocity out of the nozzle orifice is thus about 42,000 centimeters per second (1380 feet per second), which is greater than the speed of sound. (Because of the gas dynamics, the actual velocity is probably close to the speed of sound.) This is desirable because it provides maximum momentum for blowing the melted material out of the cut. We will be measuring the actual maximum cutting rates of the Multiplaz-3500 cutting torch as a function of thickness and quality of cut for several metals, so I will be able to report those results later.

With a plasma temperature of 8000 degrees Celsius (14,000 degrees Fahrenheit), a power input of up to several kilowatts, and a duty cycle of 100%, how do you keep this torch, and especially the copper constricting nozzle, from melting without using water cooling? The answer is threefold:

1. The water or water/alcohol mixture can be passed over the copper nozzle (and some other parts) and the heat required to vaporize the liquid is removed from the copper, thus cooling it and keeping it well below its melting point (1084 degrees Celsius).
2. High temperature insulation (air spacing, quartz, etc.) can be used between some components to limit the thermal energy transfer rate. One consequence of this is that the torch is physically larger than a typical water-cooled plasma cutting/welding torch.
3. Heat can be transferred to the ambient air and to the workpiece.

When used in the non-transferred arc mode (called MODE I), the electrical current flows only inside the torch from cathode to nozzle and the electrical power input to the plasma (and hence the cutting/welding speed) is limited by how much heat can be dissipated by the torch itself. When used in the transferred arc mode (called MODE II), some electrical current flows inside the torch (to maintain a pilot arc) but most of the electrical current to the torch is transferred to the workpiece. Under this condition, the power input and the cutting/welding speed can be greatly increased.

Using just water vapor for the plasma gas works fine for plasma cutting. But, as mentioned earlier, water vapor alone gives a slightly oxidizing gas output. For soldering, brazing, and welding, one wants a neutral or slightly reducing shielding gas to minimize the oxidation of the workpiece (think in terms of an oxyfuel torch). In the Multiplaz torch, the plasma gas and the shielding gas are the same. The gas can be made more reducing by changing the composition of the fluid that is evaporated. Using the analogy of the oxyfuel torch, one can make the gas more reducing by increasing the amount of carbon in the fluid. But again, there are several constraints:

1. Solubility of the additive in water - the additive must be stable and must not separate out over a wide range of temperatures.
2. The additive itself must not be hazardous, and it must not produce hazardous fumes when injected into the plasma.
3. The additive must not react in undesirable ways with the torch components, nor with the workpiece.

The best additives were found to be “oxygen-containing hydrocarbon compounds, in particular, alcohols”. The Operating Manual for the Multiplaz-3500 specifies ethanol (also called ethyl alcohol or ethyl hydrate). The use of methanol (methyl alcohol, methyl hydrate, wood alcohol) is specifically warned against, because of the greater flammability and because of the hazardous fumes produced in the plasma. Isopropyl alcohol can also be used. The longer the carbon chain in the alcohol, the more reducing the shield gas would be expected to become, based upon the chemistry in the plasma. Also, the longer the carbon chain in the alcohol, the lower the solubility in water, especially at lower temperatures. We will be measuring the actual maximum welding rates and weld quality of the Multiplaz-3500 welding torch as a function of the composition of the starting solution, so I will be able to report those results later.

Incidentally, in the Fronius TransCut plasma cutter mentioned in Part 01 of this evaluation, the fluid used for cutting is a water solution containing from 10% to 25% ethanol. The ethanol makes the plasma gas less oxidizing and this reduces the amount of oxide on the cut surface. Fronius claims that this makes for a cleaner cut and can often eliminate the need for further cleaning/grinding of the cut surface before welding it.

Another difference between cutting and welding is that when cutting one wants a high velocity gas stream to help blow the melted metal out of the cut; when welding one wants a lower velocity gas stream to prevent blowing the melted metal out the puddle and to minimize the turbulence in the shielding gas so as to avoid drawing air in. (Some gas force is desirable to help agitate the puddle.) Hence, the copper constricting nozzle used in the Multiplaz-3500 welding torch has a larger orifice (twice the diameter, 4 times the area, and approximately one-fourth the gas velocity of the cutting torch).

Although some electrical and magnetic emissions (EMI) are given off by the plasma itself, the major source of EMI in conventional welding machines is the high frequency (HF) current used for non-contact arc starting and for AC arc stabilization. The HF current is generated by a high-voltage arc across a tuned spark gap. The HF current that results has a broad frequency range, with a fundamental frequency of about 2 MHz and harmonics up to about 20 MHz. As most of you know, many electronic devices do not function correctly in the presence of such EMI. One way to eliminate this source of EMI is to use momentary contact to start the plasma arc. This is the method used in the Multiplaz torches. It is also being used more and more in other commercial compressed-air plasma cutters (for example, Miller Spectrum 125C). One of the things that makes this practical is the use of a hafnium insert, rather than a tungsten rod, as the electron-emissive material for the cathode. The use of hafnium as the cathode in a plasma arc was patented by David Bykhovsky and Alexandr Medvedev in the Russian Federation (USA Patent #3,597,649, filed 1969, issued 1971). You can get a free copy of the patent at
http://www.ptodirect.com/Results/Patent ... PN/3597649.

Most of us will not be using the Multiplaz-3500 in outer space, but rather under conditions that we call normal here on Earth. How many of the constraints in outer space are important on Earth? The constraints in outer space given above, i.e.,
a. No compressed gas or other hazardous components
b. No auxiliary water cooling unit
c. No evacuation of fumes and vapors to the outside
d. Low electrical and magnetic interference (EMI)
e. High duty cycle and limited DC electrical power
f. Torch must work in all positions
g. Low weight
h. High reliability.
all translate into cost and environmental advantages down here on Earth. Some also translate into disadvantages, including lower cutting/welding rates, larger torch size and weight, frequent fluid refills, more oxidation of the work piece than with inert shielding gas, and possibly higher initial cost. Whether the advantages outweigh the disadvantages, or visa-versa, depends upon the relative importance of each advantage and disadvantage to you.

To be continued

larry lee

[Otto Nobedder]

The history is fascinating.

One question your description rased for me is this:

When a water-vapor plasma cools and returns to "normal" matter, what proportion reconstitutes as water vapor (humidity to be dealt with in a space capsule), and what proportion is free H2 and O2 (an explosive mixture, as H2 is combustible in standard atmosphere from 4% to 96%)?

I haven't yet done the equations to speculate on the products of ethanol reverting from a plasma state, and do not have the skills to calculate the "consumption" of plasma components during the acts of welding and cutting, i.e. the ions bonding with the parent metal producing dross, and the compounds formed from the remaining conponents.

I assume these have been considered and answered, or it would never have been on a man-rated space flight, but I'm curious, none the less.

I'm enjoying this in-depth analysis, and look forward to the next installment.

Steve S.

[rjm]

<snip>
Multiplaz-3500 cutting torch uses about 250 mL/hr of liquid water when cutting at maximum power. If we assume that this is vaporized to an average temperature of about 1000 degrees Celsius in the plasma and shielding gas, this results in about 400 cubic centimeters of water vapor per second (50 cubic feet per hour ) through the cutting torch nozzle. The gas pressure in the inner plasma chamber ranges from 6 psig to 17 psig (0.4 to 1.2 atmospheres gauge pressure).
<snip>
With a plasma temperature of 8000 degrees Celsius (14,000 degrees Fahrenheit), a power input of up to several kilowatts, and a duty cycle of 100%, how do you keep this torch, and especially the copper constricting nozzle, from melting without using water cooling? The answer is threefold:
<snip>
larry lee

I don't follow the assumption of 1000° C--is it for calculation of gas volumes and flows _into_ the ionization chamber, as opposed to exit temps and pressures? Obviously there's no plasma at that temp, and as you note later we're talking 8000° C in the plasma.

Interesting article. I look forward to more.

Best regards,

Riley

[Otto Nobedder]

Great question, Riley,

I had read that as the temerature of the pre-plasma vapor entering the arc, as the inlet stream is described as the cooling medium, but after reading your question, that seems an impractical value, as it is above the melting point of some of the components.

A flow diagram through the torch head would be a useful visual aid.

I may have to look at the patents, and related referenced sites, but that is time-dependent (and time-consuming), so I'm looking forward to Mr. Lee's further input.

Steve S.

[larry lee]

With regard to the questions about the composition and temperatures of the plasma;

The central core of the plasma is, according to the Multiplaz literature, at a temperature of about 8,000 degrees Celsius. But the central core (the brightest point in the plasma) is surrounded by gas at lower temperatures, and the temperature of the gas at the copper nozzle must be much less than 1084 degrees Celsius, or the nozzle would melt at the orifice. The estimate of 1000 degrees Celsius as the AVERAGE temperature of the gas exiting the plasma chamber was intended to show that water heated to such a temperature could produce enough volume that the gas velocity through the orifice would be about the speed of sound. Don't take it as any more than an estimate.

As to the composition of the plasma gas as it condenses, there is essentially zero probability that it would ever become separated hydrogen gas and separated oxygen gas. It takes great care to keep a mixture of hydrogen gas and oxygen gas from reacting to form water, and in the presence of the temperature and energetic electrons of the plasma, hydrogen atoms and oxygen atoms will always combine to form the compound with the lowest possible energy state, which would be the water molecule in this case.

larry lee

[Otto Nobedder]

...As to the composition of the plasma gas as it condenses, there is essentially zero probability that it would ever become separated hydrogen gas and separated oxygen gas. It takes great care to keep a mixture of hydrogen gas and oxygen gas from reacting to form water, and in the presence of the temperature and energetic electrons of the plasma, hydrogen atoms and oxygen atoms will always combine to form the compound with the lowest possible energy state, which would be the water molecule in this case.

larry lee

This much I had assumed. Regarding the components lost to the process, i.e. free oxygen ions in the plasma combining with the parent metal forming ferric oxide, ferrous oxide, etc., or the comparable compounds for other weldments, what happens to the excess hydrogen ions? I assume they are in low quantity, and combine with free O2 in the air, forming H2O and H2O2. I'm just curious to what proportion this happens, particularly in space, where the O2 supply is limited.

Thanks for your reply,

Steve S.