I need to replace the bolts holding together the boiler of an espresso machine.
The top part is aluminium, or something similar, and I think the bottom is chromed brass.
The original bolts are galvanised. Will it be OK to replace them with stainless steel ones?
Thanks,
Daniele
So, you managed to get them out.
The original screws may have been cadmium plated, rather than galvanised (zinc plated) if they were in contact with aluminium.
There are different types of stainless steel and martensitic stainless steel fasteners are most definitely not recommended for use in contact with aluminium. Fortunately, the easiest to buy are austentic stainless steel, which are acceptable for use with both aluminium and brass, although, in a wet environment, they can marginally increase the rate of corrosion of both of the other metals. Look for the descriptions A2, A4,
304 or 316. A plastic or fibre washer under the head of the bolt will help reduce the risk of galvanic corrosion between the dissimilar metals.If you don't need the strength of steel, you could be sure of avoiding galvanic corrosion between the fastening and the metals by using a nylon or polypropylene bolt instead. Nylon is stronger, but should not be used if the operating temperature is likely to exceed 100C, while polypropylene can operate up to 135C.
Colin Bignell
Eventually. One had to be chiselled out.
According to the parts list, they are 6X16 GALV. SCREW.
They shouldn't get wet; I'd hope not, anyway.
They are holding together the two halves of a boiler that has to hold in water at 15 bars, so I think it's going to need to be steel.
Anyway thanks - got some. I no longer have a handy local hardware store, but eBay's good enough if you don't need the things now.
Daniele
Serious question, Does that sort of boiler need a regular insurance inspection? That is quite a high pressure. I appreciate it is only a smallish one in a drinks machine and in a private home it probably isn't regulated, but what if the machine is used in a commercial premises. Those small boilers you see on miniature traction engines and steam locomotives need periodic inspection and testing if they are used in public. I think they are around 6 to 7 bar pressures.
G.Harman
Assuming it is classified as a steam generator, if the capacity is under
2 litres, the only requirement under the Pressure Equipment Regulations 1999 is that it is designed and manufactured in accordance with good manufacturing practice.Colin Bignell
It's down to the product of bar x litres with some exemptions. Making your own boiler or having a homebuilt one certified for insurance purposes is apparently a regulatory PITA now.
But for professionally engineered steam generators 15 bar is below the limit for regular inspections if the volume is less than 2 litres (which it almost certainly is)
...
Possibly why you had trouble getting them out. Cadmium is virtually neutral to aluminium and close to neutral to brass, so would have provided longer lasting corrosion protection.
Colin Bignell
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