Cold casting with resin and Ali powder

[cardiffrob]

Not strictly suited to a welding site, but I've been looking into this method of making something.

I have a cast Ali rocker cover for an old car that I need to copy. I looked first at making an Ali casting from a sand mould but shrinkage is an issue. Next, I looked at forming it from bent sheet Ali and TIG welding the features onto it. Hard work! This led me to look at Cold Casting it in some sort of resin with a dusting of Ali powder on the silicone female mould and then Ali dust in th resin itself. I'm told (by Google) that it should be viable.

Does anyone have any experience of this idea and does anyone know which resins would be heat and fuel resistant enough for a small 50hp water-cooled engine? Polyester, polyurethane, Epoxy???

Thanks

Rob

 

[mart13]

Loads materials and info on this site http://www.mbfg.co.uk/
Use silicone to make a mould and epoxy or polyurethane with filler to cast.
Other suppliers are available.....

 

[Fergus]

I use polyester to cast items, it doesn't stand up to heat terribly well. Whilst I wouldn't expect it to fail completely I suspect you'd lose clamping power as it deformed around stress points.

 

[cardiffrob]

Lots of stuff on that MB website but it doesn't say much about how the finished part would stand up to the temp/fuel/sealing. Any ideas, Mart?

 

[The_Yellow_Ardvark]

Find your local Alloy casting specialist.

Place near me would scan the Alloy part and make a mould from it. They did move into early 3D printing to make a mould.
Could cost a penny, but if they could be tempted to make a few for a club or owners club. That may make worth a look into.

 

[Rocketman]

I can't see this working particularly well in use being from resin also what makes you thing that won't shrink as it cures. Just out of interest why can't you repair the original?

What's the expected shrinkage on casting it in ali - 2% max? You could fettle the original casting add a bit of material to the edges with resin, fill in the holes and slightly oval then with some resin. Then use that to make the sand cast.

 

[cardiffrob]

There isn't one going spare to finish off somebody else's engine. I have one to use as a template but it will need to go back. It is down to cost and as there will never be any call for another one it will be a single item for me to make.

What do they use on modern rocker boxes?

 

[oddbob]

I've been cold casting bronze, copper, nickle/brass, slate and all sorts for more than forty years. You'd use polyester for a metal filled resin ...just dusting the mould wouldn't really work ...but I wouldn't bother. The surface finish would deteriorate fairly quickly, and without glass or fibre reinforcement the finished piece would be very brittle and frail. Coldcast metals are really only suitable for decorative applications.

 

[cardiffrob]

Oh poop. Thanks for the input...it looks like that plan is a no-go. Best option looks to be to roll a piece of 5mm ali sheet into the approximate profile and then TIG away for a bit to form all the fancy curves on the back edge to clear the head studs.

 

[Wendelspanswick]

What about a fibreglass cover and then spray with aluminium paint?

 

[bigegg]

Take a look at lost foam casting.
Might be easier to shape a piece of blue/pink insulating foam to the correct size?
Failing that, if you pour a thin (3mm?) layer of wax over the cover, you can make up for the shrinkage?
You will have to fill the mounting holes, and redrill in the correct location using the original as a template.

 

[Kram]

It doesnt look like a complicated part, just sand cast it. Only the gasket face is important to make it functional and that would be machined or finished after.

If you were fabricating it you could bend some 12mm bar to the dimensions of the gasket face and weld a bit of 5mm sheet ontop.

 

[cardiffrob]

I'll get some photos when the swelling in my shoulder goes down.
I've been bending 6082 8mm with a suitable BFH to produce the curvy sides to the Mk1 version of the rocker cover.

 

[cardiffrob]

On reflection, 8mm 6082 was maybe a bit adventurous. Anneal, bend, hammer, TIG.

 

[cardiffrob]

So far it has cost 10 quid for the 6082 ali and a little gas/leccy plus the destruction of a couple of Dremel bits.

 

[cardiffrob]

To put the lid on this, should I cut the lid a bit smaller or keep it the same outer size and bevel the mating faces so they fill with weld? I've tried stacking the pennies but they ended up looking a bit like chocolate coins left in the sun too long.

I've got to say that welding 8mm plate has been a lot easier than the normal 1.2mm that I've been learning on. Much more forgiving and fewer puddles on the floor.

 

[cardiffrob]

Getting there. Even with pre-heating I was having trouble getting the weld pool to open up until I had the arc going for a while. Is 8mm too much for a 160 amp machine? I tried smaller rod to stop the weld pool cooling but it made little difference. Worked fine after it was all red hot and the ceramic cup was glowing. More cutting and grinding today.

 

[arther dailey]

the skill set of members on this forum never ceases to amaze me ! so with 8mm do you reckon it will sound quieter as a bonus?

 

[cardiffrob]

No rattles in MY engines, Arther! The original cast cover was about 8mm so it shouldn't make much difference.

As to skills, I've never had a lesson (apart from an hour with Wyn about a decade ago) so I'm no expert. All the stuff I've learnt is from watching Youtube, asking questions on here and then going into the workshop and having a go. Looking at things that Langy made was always going to inspire me to have a try, what with the stunning quality of his work. I could never get that good but I can always dream and keep practising!

Found a nice Monza filler cap to go on. Just need to form a welded lip round a piece of tube to thicken it out to the right size and cut out the threads from the cap.

 

[cardiffrob]