High Density Cartridge Heaters

You can possibly use a machinable ceramic material for this application. I have used this material for other high-heat applications, but it has been a long time since. Many of the large industrial suppliers do sell this material. In the U.S.A., it is McMaster-Carr. I don't know whether I helped you, but that is what I can offer. Ing. Robert Forbus

Try http://www.mwswire.com/ for wire. Or if you would rather have a heater made to order try http://www.watlow.com

You're playing catch up with companies which have been making high watt density cartridge heaters for a long time. You can buy ceramic cores and nichrome wire from a number of sources worldwide. If you want to make progress in that business, develop a metal alloy and a ceramic material which can withstand higher temperatures than those now known.

I used to work for Watlow Electric designing heaters as well as manufacturing equipment for them. You have not given us much information as to the type of heater you want to manufacture. "High Density" (assume you mean watt density) and "Cartridge Heater" are both fairly generic terms. Depending on what you plan to place the heater into or next to, you should be concerned about the outside of the heater, its sheath, as well as the core. This is where many heater designs go wrong.

The sheath must be electrically insulated from the heating element, but it must also have very low thermal insulation, or the heat will not transfer and the element will eventually burn out. In practice, there are many insulating materials that work at low-to-medium watt densities, including mica papers, ceramic fibers, ceramic coatings, even silicone rubber. Heater manufacturers get a good compromise between electrical insulation and thermal conduction in cartridge heaters by placing the element in ceramic powder wrapped by a heat resisting metal shell and swaging the shell to compact the powder.

But at very high watt density, if there is insufficent heat conduction away from the heater, core temperatures will rise extremely high and the insulating material will usually break down, and allow current to flow to the sheath, shorting out the elements if it is metallic. Ceramic sheaths may be used, especially in radiant applications, where the sheath has little or no mechanical contact. In this case, the element is often embedded in the soft green ceramic, then fired to hardness. Sometimes these are referred to as "soap dish" heaters because of the resemblence to the ceramic bathroom fixtures. However, be careful in using cermic heaters as they can develop cracks that become "hot spots" as the unprotected heating wire oxidizes at that point.

It sounds like in your application you would be better off having your heater made to your specifications by Watlow or one of its competitors. If you insist on going your own way, get a Watlow catalog anyway. There is lots of good information in there. Often Watlow will work with specialized heating equipment companies who put together the finished product if there is enough Watlow content they can sell to the company, heating elements, sensors, cabling, etc.

Good luck with your effort. You will need it. Working with electric components at high temperatures is much trickier than it might seem at first. Keep a fire extinguisher handy and be sure to "high pot" test your heater for current leakage, or you will kill someone!

You can obtain crushable ceramics from Saxonburg or Duco Ceramics. One of the tricks for high density is to maintain a very thin wall of MGO insulation between the wire and inside the tube. You must reduce the wire to tube delta T. Minimum insulation wall is one way, mixing MGO with other heat transfer materials is another way to reduce wire temperature. Nichrome is good to about 1800F. So as your wire watt density increases it drive your wire temperature and thus the life of the element. There is a lot of technology behind a "simple" cartridge heat. It gets into swage die design, mesh of MGO, resulting wire damage during swaging, ect. Yes, thermocouples can be placed internal to a heater, just about anywhere you want. Both grounded and ungrounded. We use to make elements with 15-30 T/C's for simulation studies where the element would be used instead of nuclear fuel rods.

Hi Sir

I just read your comment on high watt cartridge heaters, it was really useful, actually we are a mnufacturing firm in mumbai for electrci heaters.

We have a good name in the local market, which we are now looking to expand with setting up a bigger unit, so we were looking for some consultant who could guide and help us on the same.

Sir would you be interested and help us, we would surely pay your fees.

Regards

Rakesh

You could mail me on vke.ent@gmail.com