Homemade boiler gaskets? - Page 2

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
Sw1ssdude
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#11: Post by Sw1ssdude »

Viton is a brand name for a technical elastomere, that keeps its properties in different surroundings (doesn't get softened when hot, or exposed to chemicals, except acetone) and a lot of applications for sealants also involve friction, like piston gaskets in lever espresso machines. there you want a specific gasket thats up for the task, made from a specific material. this is why some gaskets cost a load of money, even if it is 'only a ring'....

a sealing gasket, that just closes a gap between two mating surfaces is (mostly) not exposed to friction, hopefully not in your Pristina...
So what you want is something that deforms and therefore fills flaws in the surface, like scratches. It should not creep and lead to relaxation in your screws, or worse, fail to seal (again a lesson learned from bikes: sometimes fiber gaskets leak at first, until they absorb some oil and expand, filling the tiniest scratch). But elastic gaskets should seal instantly.

So i'd go for silicone (which is the name of a material, not a brand) or Teflon ( = PTFE). Since your surfaces are not flawless, or just rough from the casting, i'd tend to silicone, which mostly is softer, also because its laser-able.

I just ordered some at a swiss company called VULKATEC, they have all kinds of vulcanized (= non-thermoplastic) elastomeres. a sheet of 1.2x0.5 Meter costs about 40 Swiss francs.

A colleague of mine used for a functional prototype of a device a 'reusable parchment paper' from a supermarket, which was silicone with a glass fiber inlet. that cost like 5 bucks and was the size of a baking pan.

.....i just checked online; those come in all colors, and most of those are about a millimeter thick, and most dont have the fiber inlet. they are most likely foodsafe (as they touch your cake/cookies/turkey) and withstand an oven (250°C). (like this: https://www.westfalia-versand.ch/shops/ ... kfolie.htm) also, you can get them faster than order-by-mail.

With something like this you can even match the color of the gasket to the housing of your machine....
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DaveC
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#12: Post by DaveC »

Use a high temp food safe Silicone RTV sealant. You have to get one that is firm, but flexible, you will also have to experiment with bead size based on the flange or element seal construction. The other key thing is to let them cure for 3 or 4 days....regardless of what the instructions say.

If you don't use food grade, some of them will taint the water and it never goes away, it's also the reason for an extended 3-4 day cure...I know because a manufacturer used one on their machines and had a huge problem!

As long as the bead isn't to proud, or you might go for a flatter profile depending on the fitting, they should last a long time....just don't use too much.

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CoffeeBeetle (original poster)
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#13: Post by CoffeeBeetle (original poster) »

So the strength of viton is amongst others its suitability as gaskets that are sealing on moving parts? Since that isn't the case here i guess i will go with silicone. The UK shop i linked offers 1.2mX1m of 1.5mm for 43 euros, which i think is a decent offer. It gives me the chance to mess up the first try without having to wait for more to be shipped and i hope to be able to use it for some of the other gasket needs i will have with this machine and others.
The silicone paper seems like an interesting thing to try but i would be a bit nervous about using it since i plan on laser cutting the silicone in a machine i don't own. I'm also a bit worried about how it might hold up over time since it's not designed for such tasks.

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CoffeeBeetle (original poster)
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#14: Post by CoffeeBeetle (original poster) »

Dave, wouldn't it be easier to cut a seal out of silicone instead of experimenting with liquid sealant? I can get sheets of silicone and i have access to a laser cutter, which i would trust more than my own ability to properly use liquid silicone.

DaveC
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#15: Post by DaveC replying to CoffeeBeetle »

I have not seen a photo of the area you want to gasket and it was more general advice to cover you and others. If you can get the right hardness silicone sheet, and have access to a laser cutter plus the ability to program the shape you need....then of course....go for it. Usually for most people RTV is the easier solution, but for you, I think you have a good solution.

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CoffeeBeetle (original poster)
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#16: Post by CoffeeBeetle (original poster) »

I sometimes forget when writing that of course not everyone has seen the boiler of a conti prestina. Here are some pictures i took when i cleaned it up.

Sw1ssdude
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#17: Post by Sw1ssdude »

Huaa, that brim looks nasty!

Can you see that groove that runs along the brim, between the lip and the holes of the lid? This is there on purpose, so that the gasket can creep into it when appropriate tension is applied, making it extra tight.

i would advise against any liquid sealant: the screws are very short and thick, they need to relay on some spring tension to stay in place. long screws use the elasticity of steel and slightly stretch their long shaft. most short screws have a spring washer under their head (but thats not the appropriate way), and a lid like this provides some springiness with the gasket that gets compressed, and counteracts to the compression.

A screw always needs a part of their shaft free, free as in not engaged-thread, or bare shaft.

In other words: a thin sheetmetal, that you screw onto a massive block with an m6 screw, will come loose very easily, as it is just held with the friction in the thread, but not the tension, as the free shaft is only as long as the thin sheet metal.

My opinion and experience: liquid sealant, in combination with short and stout screws, is more to be considered glue.

Dont worry too much about different silicones and laserplotters. PVC is the one you mustnt lasercut, as it contains chloride (pvc = polyvinylchloride), which causes very unhealthy fumes.
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CoffeeBeetle (original poster)
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#18: Post by CoffeeBeetle (original poster) »

Yeah, the flanges were cleaned up after those pictures and now there is mostly just discoloration from the gasket left. It's not "machine flat" but I do believe that it will work as long as the gasket is compressible.
My "introduction course" in laser plotter is set for next week and unless they have an explicit "no silicone"-rule I should be able to get that done soon enough.

Nino, thanks for that info. Without formal training in such a field details like that isn't something I would even consider, but when explained it makes complete sense.

Now, since I've already got you guys here...perhaps some of you could help with assessing what kind of O-rings I should get?
The place where I plan on buying the silicone: https://www.polymax.co.uk/o-rings/rubber-o-ring-kits/ also sells a lot of different sets of o-rings, but they aren't exactly as cheap as I thought o-rings could be. I originally had my eyes on a simple set from a local plumbing shop, much like the cheaper one they sell on that site, but looking at the specifications I can see that they are rated for max 120C, which seems like it would be a bit too optimistic with such a machine.
This worry is only strengthened when looking at the quote from Dough that Gary posted since that cheap set is labeled NBR.

The shop also sells a set of Viton or EPDM O-rings, at a considerably higher price and a silicone set priced in between.
Are those cheap, generic o-ring sets you can get everywhere out of the question for such a project? I would like to keep the cost of restoration down, but I would rather pay a bit more now, than risk having to clean melted plastic off every small part of this machine after getting it warmed up.

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drgary
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#19: Post by drgary »

I would get cheap o-ring sets that are Viton, and you'll be set. Silicone will also work if it's hard enough. These are listed on sites like eBay.

Maybe you can post photos here of what the flange looks like now.
Gary
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yakster
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#20: Post by yakster »

Harbor Freight has Viton O Ring sets.
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