Looking for Plastic Casting Advice

More info needed!

For example, polycarbonate is a high strength plastic, but the alkalinity of wet concrete will affect it .

I considered polycarbonate but changed my mind, basically it doesn't need to be any really special, essentially I'm just going to be making a block of plastic 1 inch and a half wide and about 10 inches long, the weight I'm aiming for is about 10 oz, it's just going to be making repeated motion thru wet concrete, and since there are so many different mixes of concrete, it would need to be a type of plastic that is fairly inert, as far as chemical reactions are concerned I guess, above all it just needs to be tough fairly heavy and pretty tough, not indestructible lol, just tough. Just any thoughts or suggestions would be great, thanks.

OOPS! It helps to read all the responses.

They make many thermoplastic sheets in 1" thicknesses.

First blush, try polyethylene, it's slick and chemically resistant.

Next up polypropylene, but I'd try PE first. It's easy to cut with a circular saw and a fine tooth blade. Remember, it's like cutting wet sandpaper, no matter what you use.

Forget everything I said about injection molding.

See Lyn's note on PE & PP- I would suggest you might be best with UHMW instead of standard PE.

Teflon (PTFE) is the most inert of course, and quite abrasion resistant but it has poor flex properties if that matters. Nylon is another option that would be the strongest of the bunch and tougher as well- and more dense than PE or PP for weight purposes.

I agree about UHMW, but polyamide (Nylon is Du Pont's tradename) seems to me to be too brittle and less abrasion resistant. It also has a high moisture absorption rate.

Best thing for the OP to do is order some from McMaster-Carr and try them.

You might look at using Delrin. It's a hard plastic with fairly high strength, and is somewhat slippery which might be an advantage for use in wet concrete.

Here's a video that talks about casting delrin:

http://www.youtube.com/watch?v=hTrRM82YOrY

Thank you, most of what I found myself was like abs or high impact, or fiberglass style resins, and I really don't have any knowledge of this kind of thing, figured I'd ask the experts lol.

Let's talk terms.

"Casting" is pouring a liquid resin (usually a two part liquid such as epoxy) into a mold and letting it harden, then removing the mold.

Forming thermoplastics into a shape using a mold is referred to as injection molding. IM tooling is usually high strength steel. Can be aluminum for short runs.

Describe the form of the part. Is it used to separate, smooth or otherwise work the concrete.

You have two enemies.

#1 is sand and rocks that will abrade the material away. There is no plastic that will not be "eaten away by the abrasive action of the sand/aggregate ABC whatever.

#2 is chemical attack which is much less a worry.

So, what are you trying to do?

You might want to try this page at McMaster Carr. They have a wide variety of plastic bars of all different types.

They give pretty good descriptions of the properties of each and you can order a sample of the most likely candidates for evaluation.

If you are wanting to melt and "CAST" the object, then you need to get one that has no filler materials. Often talc or other materials are used to bulk up plastics. Often glass fibre and other stranded materials are used to give added strenght or other properies. If you melt and then try to cast such materials, the fillers will separate and you get a real mess.

Delrin/Acetal/Nylon would all seem suitable. Density and such are prety good. Polypropylene at that thickness might be OK but lack of stiffness would be my concern with that material.

Stay away from Acrylic and Polycarbonate. While they have good stiffness, as they abrade away it is likely that a brittle failure will happen and you will end up with a large sharp shard in your mix. (Google "crystaline" plastics to see why.)

Remember that in casting the pieces, there will be significant shrinkage relative to the mould size and the surfaces will not be flat regardless of how good your mould is.

I like the earlier suggestions about getting slab/rod/bar material already formed (extrusion usually) as this would probably be cheaper that sourcing small quantity of raw pellets from the suppliers.

An engineering grade of Nylon (example Nylon 6) or HDPE both have good abrasion characteristics and can be cast and machined.

10" x 1½" x ?. Unless this object is especially intricate or curved, machining an extrusion would probably be be better than casting for one off or a small quantity. Casting requires precise temperatures and cooling rates to achieve good results. If is will be used in production quantities then buying in from a specialist plastic casting supplier would be more cost effective than setting up your own casting plant.

HDPE is what they make cutting boards out of. So it should wear well. A little more rigid and stronger then UHMW. Not as costly as the other plastics. So replacing it as it wears will not cost so much.

Some of the other respondents here have mentioned that finding a plastic that is abrasion resistant may be a tall ask.

Concrete, wet or dry, is abrasive.

That block of plastic material will wear away quick smart.

Why does this block need to be plastic? Why can't it be steel?

The reason I'm trying plastic first is, weight and hopefully ease of manufacturing, if all goes well, we will probably be building on a large scale for commercial purposes, thank you for all the great suggestions I went ahead and got a few small blocks of several different types of plastic that were suggested, if nothing else, it will be an interesting experiment!