Casting resin in aluminium?

[Munty Scruntfundle]

Hi folks. There isn't a resin section, for some reason I thought wood people might have more experience with resin than the metal people. No idea if that assumption is correct!

Anyway, I need to resin cast a number of clear tubes, around 60mm outer diameter with a 10mm wall thickness, approx 80mm in height. I need to make quite a few so I don't want to mess around cutting up water bottles.

I thought I'd take two short aluminium tubes, seal them at the bottom, cast the resin then press the inner tube and resin slug out. The question being, is the resin going to let go of the aluminium for pressing? I've seen a few release agents, but have no idea what would be best. I can polish the aluminium to a reasonable finish on the lathe, hopefully that would help?

Anyone with any experience?
Many thanks.

 

[ChaiLatte]

Whatever you do, the inner will be a lot more trouble than the outer. If you had to, you could heat the outer one with a hairdryer and the expansion might help it to let go. Maybe the opposite, freezing the inner, would work. Give it a through hole and squirt it with some pipe freezing spray.

Does your cast tube absolutely, unequivocally have to be seamless? A single seam on the outside with a clamp would give more confidence of easy release. Think through how you would make this such that only a single line is visible on the finished part. A two part mould with two seams is a lot easier.

You could make a collapsible mandrel for the inside but it would need a flexible liner of some sort to make the finished tube bore totally smooth. The liner would have to be tubular for zero seam but could be sheet for a single seam.

 

[Simon89]

A taper on the tube would also help significantly.

 

[MARK.B.]

Instead of ally could you use plastic tubing used for plumbing etc ,use something like petroleum jelly as a release agent .Maybe cast your tube in longer sections and then cut to size rather than individual smaller ones, if you have a router then you could cut two end caps by cutting circles into a piece of flat timber for your tubes to sit in spacing them 10mm apart ,put your tubes into the wood and if a tight fit you should not need to seal the end .Pour in your resin and then place on the top end cap to keep the two tubes correctly spaced while it cures.Leave a couple of inches empty at the top so you can get a grip on the inner tube and with a little luck it will slip out,then push the resin cast out of the outer tube . warming slightly with a hairdryer or heat gun might help things along if it gets stuck or if needed the outer plastic tube could be cut away from the casting.
I would do a practice run first on a short length to see how it goes and avoid wasting resin if it does not go as planned.

 

[Inspector]

Before answering I'd like to know a few things.
#1) Is the casting going to be used as cast or worked later, further shaping? Polishing?
#2) What type of resin are you planning to use? Polyester casting resin? Epoxy Casting resin? Urethane casting resin?
#3) Do you need these to be bubble free?
#4) When you said a number of tubes how many did you actually mean? A one time project or will it be an ongoing thing you want to do? How many at a time?
#5) Are you prepared you invest in equipment? Compressor? Pressure pot/vessel? Respirator?
#6) Do you have a warm place to work that is away from living areas to keep fumes isolated?

Pete

 

[ChaiLatte]

Instead of ally could you use plastic tubing used for plumbing etc

The plastic tube is a very good idea. Pressure rated pipe is available in ABS. It generally has a thickish wall so can be turned to the required diameter if a stock size does not work.

As you say, at worst, you could cut through it to release the cast item.

A variation on this theme which might work for the inside former is to cut semi-circular grooves into it leaving a very thin wall and then use the thinness of the wall to flex it smaller when removing. This has the advantage that it will be perfectly smooth.

 

[Droogs]

Have you thought about using wax candles for the inner which can be melted out or the metal spinners trick of creating the form in ice for complex shapes, which after spinning the metal plate, is then left to melt away

 

[RobTy]

Have you thought about using wax candles for the inner which can be melted out or the metal spinners trick of creating the form in ice for complex shapes, which after spinning the metal plate, is then left to melt away

Given most curing is exothermic.... not sure this is a good idea.

 

[Jones]

You could buy clear perspex ( acrylic) pipe and cut to length.