Ceramic Bandsaw Guides

[custard]

I was reading a sobering post about a near miss fire in a dust extraction system.

Made me think, I've got ceramic guides fitted to a bandsaw and occasionally (especially if I do something daft like cut timber without fully tensioning the blade) they will spark, although the "sparks" are red and seem confined to the surface of the ceramic plate rather than the blue, jumping sparks you get from an electrical arc. These are the guides,

https://www.youtube.com/watch?v=bTu0nY5Hn5c

Does anyone know, are these sparks the genuine high temperature version, or is it just a lower temperature feature of ceramic guides?

 

[Peter Sefton]

A little off topic, but are the ceramic side guides any good?

I have a ceramic thrust wheel which seems fine, I have been using it for a couple of years.

Cheers Peter

 

[custard]

Peter, it's the ceramic thrust wheel that sparks, I guess I'll just have to be more diligent about blade tensioning.

Are ceramic guides any good? Well, I'm regularly cutting 200mm deep, 2mm thick veneers with them, however I was cutting exactly the same veneers with the old, standard guides. The only difference was that with the old guides I didn't worry that the workshop would burn down!

 

[AJB Temple]

My understanding (based on partially remembered explanation from my brother when he was teaching me about metallurgy in forging processes) is that minute steel particles (or rather the carbon within them) will burn in air. It is, from dim recollection to do with the enthalpy of the metal (enthalpy being the energy inherent in a thermodynamic system). The surface area of the freshly exposed hot particles enables combustion to occur.

As ceramic is harder than steel, and presumably with the guides / bearings in contact with the steel, the steel from the blade must be being ground away microscopically. The heat generated is presumably causing the carbon within the microscopic steel particles to burn off (what you are seeing as sparks). I can no longer remember what the temperature requirement is for steel to "burn" but I seem to recall that the melting point of iron oxide is somewhere around 1500 degrees C.

I have never used ceramic bearings but if carbon is igniting in steel I would have thought it is plenty hot enough to combust wood dust, though the combustion of the carbon in the steel must be exhausted very quickly. I would be interested to know if this is a risk in extraction systems. No doubt there are some engineers here who will know this.

The factory where my brother is a design engineer has some sort of special extraction system that deals with sparks. It is an issue for them because of the wooden tooling formers they make I think. I don't know how the fire prevention works though. I do know that they don't buy bandsaw blades like we do: it comes on a massive reel and they weld the blades themselves with a special machine.

 

[AJB Temple]

My understanding (based on partially remembered explanation from my brother when he was teaching me about metallurgy in forging processes) is that minute steel particles (or rather the carbon within them) will burn in air. It is, from dim recollection to do with the enthalpy of the metal (enthalpy being the energy inherent in a thermodynamic system). The surface area of the freshly exposed hot particles enables combustion to occur.

As ceramic is harder than steel, and presumably with the guides / bearings in contact with the steel, the steel from the blade must be being ground away microscopically. The heat generated is presumably causing the carbon within the microscopic steel particles to burn off (what you are seeing as sparks). I can no longer remember what the temperature requirement is for steel to "burn" but I seem to recall that the melting point of iron oxide is somewhere around 1500 degrees C.

I have never used ceramic bearings but if carbon is igniting in steel I would have thought it is plenty hot enough to combust wood dust, though the combustion of the carbon in the steel must be exhausted very quickly. I would be interested to know if this is a risk in extraction systems. No doubt there are some engineers here who will know this.

The factory where my brother is a design engineer has some sort of special extraction system that deals with sparks. It is an issue for them because of the wooden tooling formers they make I think. I don't know how the fire prevention works though. I do know that they don't buy bandsaw blades like we do: it comes on a massive reel and they weld the blades themselves with a special machine.

 

[PeteHB]

Whether it's the ceramic or steel and it's likely to be the ceramic, the sparks will be above 750 degrees C and could conceivably ignite some very dry fine sawdust that will initially smoulder then provide the source for a larger scale fire. It's exactly what fire making kits do for backpackers. The problem is that the spark may land somewhere you don't notice and by the time you do or worse you may have left the shop and the real fire starts. The only real answer is not to get any sparks by remembering to tighten the blade.