Molding ceramic parts

Sintec Keramik, Manufacture and supply high temperature ceramics foa all industries including parts for welders.These parts are easily machined and withstand extremely high temperatures, If you would like some information please email me with a sketch. We currently supply an orbital welder with these parts. russell.oliver@sintec-keramik.com

If you would like some information please email me with a sketch. We currently supply an orbital welder with these parts. russell.oliver@sintec-

Thanks but since I only need six pieces to repair one old welder I doubt it makes economic sense. I could probably buy a complete wroking welder for what you would have to charge me for prototyping costs.

We machine from solid material which reuces costs considerably. Until you can supply a sketch you may never know.

Regards

Tafy wrote:

We machine from solid material which reuces costs considerably. Until you can supply a sketch you may never know.

REPLY: Unless you can deliver to my door, quantity 8 pieces for a total cost of $50, including shipping and clearing the border tariff, I can't even consider that option. And since all the pieces are shattered making any kind of sketch with accurate dimensions would be problematic. This is a DIY project in my own time which doesn't require any serious cash outlay.

I used "DEVCON PLASTIC STEEL" for making molds and it worked very well. When I retired and cleaned out the shop I found some molds that were over 20 years old and still in good condition.

http://devcon.com/devconfamilyproduct.cfm?familyid=101&catid=34

Release agent:

http://devcon.com/devconfamilyproduct.cfm?familyid=209&catid=37

I was casting parts of AD-995 Alumina ceramic.

I was casting parts of AD-995 Alumina ceramic.

REPLY: Please tell me more about this ceramic?

The traditional method is a plaster casting.

The pourable liquid will work.

The problems are ceramic parts will shrink 10% or more after firing & which leads to the 2nd problem is do you have the facilities to fire the parts?

Can you make these parts from machinable ceramics?

The problems are ceramic parts will shrink 10% or more after firing. Can you make these parts from machinable ceramics?

Oh well so much for that idea! Neither makes economic sense.

The ceramic pieces act like insulators to support a resistance wire coil so it doesn't touch the supporting metal brackets. Being mounted on an engine driven welder there is a lot of vibration to start with and the expansion and contraction as the resistance wire heats and cools makes for a challenging mechanical mounting problem.

pheneolic, teflon?

Before you give up, take a look in a McMasters catalog of stock materials. There are a number of materials which will take some pretty high temps, the real question is how high and how long you have to withstand. Many items which had been made with ceramic before have now been replaced with some poly-based plastics, even some which have been e-beam radiated to increase their high temp performance. So, get an idea of the temp you need to survive and check out McMasters, if that doesn't work, try doing a material search by the Td (Deflection temp) parameter to get an idea of what may or may not work. I find it hard to believe that a good high temp phenolic or hardened PTFE wouldn't work well for your application.

The wire resistor is mounted in the discharge air stream of a blower to keep it from becoming molten metal. I'm told by the original owner it glows a dull red under normal load conditions. It was only when he noticed it was getting bright like a light bulb that he decided something was broken.

Dull red suggest a temp range of around 1000 - 1100 F and sustained for the duration of a work day. This welder is rated for 200 A at 100% duty cycle. Originally used to weld up broken 3/4" and 1" plate steel on a D12 cat scraper blade and similar sized logging equipment.

OK, so when you say welder, you mean WELDER!

Could you modify something like these ceramic tube holders to work?

http://cgi.ebay.com/_W0QQitemZ330175541250QQcmdZViewItem

Nope! way too small. Gee I haven't seen any of these in 40 years. Not since I first got involved in amateur radio and was building vacuum tube sets.

The WELDER is a Hobart G-213 no longer in production and from what I gather from various user lists and vintage equipment restoring clubs very hard to find parts for. One poster specifically said he had given up trying to find these exact same ceramic supports. The resistive wire coil is 4" in diameter and about 9" long. The resistive element is shaped much like a slinky toy but larger and thicker. Made of a special phosphor bronze alloy that looks very similar to what I use in metering shunts.

This resistor and a selector switch controls the output DC current.

Its more complex than a simple series circuit. A coil (choke) is also wired in serires but this coil(choke?) has a second winding like it was a saturable core reactor. However the welder has a commutator for DC and I thought a saturable core reactor only worked on AC outputs.

The resistor stack carries substantial current and gets very hot. Therefore the individual turns must be seperated and air cooled.

Imbedding the whole in a ceramic cast probably would not dissipate enough heat fast enough. A number of Ohmite resistors are being used elsewhere in the control circuits.

Do you have a picture and some course dimensions of the insulator you are looking for?

Greenshoes wrote:

Do you have a picture and some course dimensions of the insulator you are looking for?

REPLY

No! but I can probably create them over the week-end.

This is kind of rough and ready, dimensions are approximate +/- .005" and nothing is radiused correctly. (Can't seem to upload a .dxf file. Now what?) Its 2.765" long by 0.760 wide and 0.750" high. Ridges number 13 and grooves number 12 plus a half groove at each end. Presumably for stacking multiples. Depth of grooves is approximately 0.150" and width is approximately 0.095" but not 0.100" All told, the resistor block would use 9 of these. Stacked 3 high and arranged on a spyder at 120 degrees apart. The inner slot is designed to let the assembly slide back and forth on the support legs much like a disk brake assembly slides on guide rods. Would probably benefit from some anti seize compound when assembled.

Characteristic failure mode. Cracking as the cadmium plated steel support rods oxidize from heat. The iron oxide expands, causing binding and then the ceramic fails due to internal stresses from heat expansion of the whole assembly. In other words this is a frequent maintenance item requiring application of disk brake anti seize compond in the slide groove. Doubtful if Hobart would have bothered to tell end users of this trick. They probably made a mint selling replacement resistors.

for some reason I cannot upload a CAD file or .dxf formatted copy of the ceramic support piece. What am I doing wrong? The photo uploaded okay.

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