Switching element type on kilns

[cpdean86]

Hi everyone

First time poster. I have a large kiln that is currently using spiral SiC elements. These are being degraded rapidly due to firing of PZT ceramics which are giving off lead and fluxing the silicon in the elements.

The degradation only subtle but the spiral element runs into large problem because I end up with a conductive path between the positive and the negative terminal - shorting it all.

Besides that the kiln is quite good. 

My question is: has anyone had any experience changing the element types in the kiln? I want to move from a spiral type to a U bar. I recognise that the spaces for the elements will require readjustment. in terms or power draw etc will the U bar design require more elements etc? to achieve the same heating rates?

 

Thankyou for any assistance here.

 

Regards

Chris

[Hulk]

Hi Chris!

My reading indicates that PZT parts are sealed "...in high purity alumina crucibles..." to prevent lead from escaping during sintering, as the process requires temperatures well over lead's volatilization threshold. 

That (probably) doesn't help. You might identify the kiln in question, and/or post a picture?

Be careful with that lead!

 

[cpdean86]

Hello 

Thankyou for the response. I have attached a photo of a similar kiln and the same element type. Ideally I want to move to U shaped SiC elements (attached). 

My question is really concerning the power draw required. Both elements have a positive and negative terminal from the top end of the element however I am unsure if any of my existing wiring would be suitable for the new elements as it may require a higher power to drive? any feedback here is appreciated. I also recognise I will have to replace the roof with correctly spaced holes to accommodate the new elements.

From a safety perspective we are very careful with the lead (extraction etc is all in place) but it certainly burns through the elements at a fast rate.

Regards

Chris

[Hulk]

Interesting!

Given the kiln's amperage (or watt) draw, looks like eighteen elements, from there, calculate the draw per rod? My guess, your replacements should draw about the same in order to provide the heat and not overheat the wiring harness; the wire gauge should be discernable via inspection.

The kiln and element vendors may be helpful, else the specifications.

Perhaps the pics will generate some helpful response for you.

[Bill Kielb]

On 6/14/2021 at 4:52 PM, cpdean86 said:

. Ideally I want to move to U shaped SiC elements (attached). 

Element loading is dependent on surface area so equivalent wattage is important but available surface area is important also. Your spirals likely result in increase surface area. My best thought is Kanthal may be able to suggest an equivalent form for you. I am not convinced that they would not short out quicker though unless your intention is to periodically remove them and remove the lead ………. Which likely could be done with the present elements as well I suppose. Since you basically have lead anodes electrolytically dissolving the lead is probably possible but as all things lead, need to know what you are doing for sure for safety. 
Sheathed elements could be a a great solution as well and eliminate the conductive effect of the buildup.  Definitely something for an industrial engineer / chemist IMO. The Kanthal folks likely could help and very well may have products more suitable for your use that simply don’t short and could be disposed of properly at the end of their life. 
 

What temperature are you sintering or firing to?