Diamond discs for dry cutting

[fuegos]

My local hardware shop has some Bosch Diamond disco on offer at about half the usual price but which type for hard refractory brick ?
turbo , standard or expert for hard ceramic? segmented or continuous rim ? this is for use with an angle grinder.any recommendations about other brands would be welcome. 

[josephcrawley]

I have had the best luck with segmented rims. The continuous rim is better for tile where you need a smooth cut. The gullets in the segmented rim make for a faster cut.

If dry cutting soaking the bricks will reduce the dust a bit but there's really no substitute for a wet saw. Good thing there's N95 masks aplenty these days

[fuegos]

Thanks Joseph, I wear a mask when cutting.I bought some no name cheap discs for a job a few years ago , cutting stone & was amazed by how they performed but im looking forwards to the next build with some "proper" refractory bricks.I live way out in the sticks so hiring a wet tablesaw just isn't pactical.

[josephcrawley]

Those cheap 14 inch metal chop saws do a decent job for the price with a diamond blade. I think you could rig water on there with some rubber tubing and some zip ties. Any water is better than nothing. And of course the mask plus hearing protection.

[fuegos]

" plus hearing protection" what ? :-) thanks for the H&S advice .i have years of experience in Metalwork , forestry & construction but for anyone else reading this please take the advice seriously.

[Forsythe]

You might be able to rent a wet tile saw for making the cuts you need. I completely agree with josephcrawley on the "any water is better than nothing" sentiment. The heat from friction of cutting through bricks like that will wear out the blades faster than you can batt an eye, and the water really helps to cool everything down — and seems to help get a cleaner cut, too.

[Forsythe]

oops. just read the note about living too far out in the sticks to hire a wet tile saw. whelp. disregard my last post/suggestion, then.

[Forsythe]

Might be worth mentioning for anybody who's following along, though, and is new to working with [wet] firebrick:

If you do soak the bricks, it's important to allow them to dry before firing the stove at its highest heat, as the pockets of trapped steam building up within the wet brick can cause explosive spalling.

Most people who build masonry heaters will do several rounds of very small "drying" fires over the course of a couple days to allow the entrained water to evaporate relatively slowly. Then, once everything is dry internally, the heater is ready for a full-scale firing.

Edit: some people also dry out wet brick using a high-heat-output incandescent lightbulb, left switched-on in the firebox for a day or two.

[josephcrawley]

Mar 28, 2022 9:50:53 GMT -8 Forsythe said:

Might be worth mentioning for anybody who's following along, though, and is new to working with [wet] firebrick:

If you do soak the bricks, it's important to allow them to dry before firing the stove at its highest heat, as the pockets of trapped steam building up within the wet brick can cause explosive spalling.

Most people who build masonry heaters will do several rounds of very small "drying" fires over the course of a couple days to allow the entrained water to evaporate relatively slowly. Then, once everything is dry internally, the heater is ready for a full-scale firing.

Edit: some people also dry out wet brick using a high-heat-output incandescent lightbulb, left switched-on in the firebox for a day or two.

I too have read the cautions about slowly firing a wet stove. Over the years my partner and I have built about ten stoves. We always end the build with a fire that we keep going till stove is completely dry. We start small and build it up over a few hours. By the end it is going full bore. Never had any issues with spalling. A note of caution none of the stoves contained castable refractory just fire brick and house brick. So if you're as impatient as we are I say go for it.

[Forsythe]

Mar 28, 2022 15:19:14 GMT -8 josephcrawley said:

We always end the build with a fire that we keep going till stove is completely dry. We start small and build it up over a few hours. By the end it is going full bore. Never had any issues with spalling.

That's fair. Starting with a small fire and building it up gradually may be sufficient to dry out any wet spots.

FWIW, the modern ASTM standard test for brick spalling in the refractory industry is: spraying the brick surface with water and then returning it to a heating oven — with more severe spalling resulting sooner from the older test which involved dunking the bricks into a water bath to quench them, which [it was/is assumed] allowed more water into the pores and crevices of the brick's interior, and caused spalling not just from the thermal quenching, but from entrapped steam explosively blowing chunks off of the side(s) of the brick.

A note of caution none of the stoves contained castable refractory just fire brick and house brick.

True that. A castable will definitely have higher potential for remaining internal water content, absorbed into the un-vitrifed refractory mix than an already-"burned" and vitrified brick will.

[martyn]

Most refractory products are very prone to absorbing water and I think it is very important to pay attention to that fact.
Any steam that forms inside a brick or casting can very easily crack the component and therefor shorten the overall lifespan.

I build and sell refractory products namely pizza ovens and fire place inserts plus associated one off pieces.
Regardless of my advice to carefully and gradually heat the refractory people are regularly causing damage by overheating to quickly!

Re the best blades … there is no doubt that some blades are far better quality and longer lasting than others however in recent years the price has dropped to a fraction of what they cost 20 years ago and I tend to buy packs of five of mid range blades and they seem to last very well.

[ronyon]

I have a small harbor freight wet saw, it was very cheap.
So far it's mostly used for tile, but it uses the same cheap HF blades as my angle grinder, and they eat through firebrick dry.