How Sigma Power ceramic stones are nailed together…

Hello again Faithful Reader,

I apologise for the long delay between posts here, been a tad busy of late…


A question was asked recently about stones and how they’re made, and I said “I’ll ask and find out”. Eventually I got around to that, and today got a reply from Sigma Power as to how their ceramic stones are made.

Do take note that there are no details, nor pictures. As they rightly mentioned, they do have trade secrets they wish to keep so the process is only loosely described, explained and translated here.

I hope it’s of some interest to you all, I know it was to me.

(To me, because I’m at the pointy end of this at the moment. More details on that to follow soon enough.)

A week or three ago, I mentioned that I’d find out how Sigma Power ceramic stuck together by asking the folks who make them.

I just now got word back from them.

(I’ll not be putting up the actual reply, since it also included information relevant to myself that I’m not willing to put under scrutiny just yet, and besides, it’s all in Japanese!)

I asked “How are your ‘ceramic’ type stones made?” and got this reply.

The abrasive and a binder are mixed together, pressed into a block and then fired at very high temperature. This is a higher temperature than ‘regular’ stones (regular are baked at @180*C apparently) and much of the binding material vaporises during the firing process. The specific materials and process can’t be mentioned because they are a trade secret.

Next I asked “How are your ceramic stones different from others?” and they said;

Other types of stones like resinoid (Shapton, Naniwa SS, others), magnesia (Naniwa Chosera, some Suehiro(?)) and conventional (King, etc.) is that when the stone is made, 100% of the binder used remains in place and holds the stone together, so the action of the stone is influenced somewhat by the binder. The ‘ceramic’ stones have less binder material present, so the action of the stone is closer to what the ‘pure abrasive’ alone does. In porous ‘other’ stones, there is a filler material that is removed (burned off?) during manufacture which causes the stone to be able to be water permeable.

(Note, I suspect that some of the ‘binder’ material mentioned here is likely only used to keep the stone in one piece prior to and during firing, and isn’t intended to survive the process at all.)

Lastly, I asked specifically about the Sigma Power ceramic #120, a very coarse stone that uses silicon carbide as it’s abrasive (until now, all information is about their aluminium oxide stones), which is different and was, I think, the original point of the questioning. They said;

As mentioned previously, the binder is vaporised during firing of the stone, but because the abrasive tends to ‘want’ to stick together, we can use less binder initially and more abrasive is present. The binder is still there, but there is very little of the original amount, perhaps less than 50% so we can put a lot of abrasive in the stone and this allows it to grind very strongly.

Now, that kinda sounds disjointed I think, but basically they’re telling me that there is a binder (AlOx won’t stick to itself) but most of it leaves the stone when it’s fired. These would rightly be defined as vitrified.

The #120 ceramic, made with SiC (which will stick to itself, i.e; sinter) does have some of that ‘stick’ but still uses a binder to hold it together ultimately. From what I can work out (remember, they’re protecting their method of manufacture and don’t want to say too much) the ‘coarse’ stone is still vitrified but needs less binder than the AlOx stones, and as such, could rightly be thought of as a semi-sintered stone since an AlOx stone of similar grit/type would need more binder and have a lesser cutting ‘strength’, abrasive not withstanding, just based on how they’d be held together.

Sintering as I understand can be done by several different methods, only one of which is compression and heating at the same time. Another is to use a binder which is completely vaporised during firing, separating the compression and firing steps and giving a porous material with no residual binder.

That’s how I read it from what they’ve given me. I need to get back to them about a few points, specifically the sintered stuff and whether it’s actually done as compression/heat together or separately (nobody’s ever asked, just taken the words of compression and heat and surmised it was at the same time) and a few other details.

Those questions will wait. Still need to send them some information about some things and will add the questions at that time.

I hope that answers the vitrified/sintered question adequately, and I don’t think I can add much to it since they’ve only told me what I’ve put up there, and I’ve elaborated only so far as my own knowledge allows without making assumptions I don’t have the information to back up.

And as a follow up, this information was interspersed with a message that some prototype stones are on their way for evaluation. Some days my job sucks, but today was not one of them. ;)


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