Eugh - Plastics!

[Archie]

Now I know this is a (metal) welding forum and so plastic is not the natural material to be making enquiries about but knowing the wealth of technical expertise on here I reckon someone will be able to help!

Got a project on at Uni at the mo. and quite a large chunk of it is to be made from plastics. I, however, have relatively little idea about what plastics to go for; acetal, PVC, acrylic/Perspex, polycarbonate/Lexan, polypropylene etc. etc. ad infinitum.

I have no need of optical clarity or any lubricating properties so I guess I might as well chuck polycarbonate and nylon out the window. Polypropylene is probably too flexible so I'm really left with acetal, PVC, acrylic and any other suggestions. I'm looking to make parts of varying sizes but 100x100x6 would be a good estimate of sizes and I will be wanting to tap into the plastic for threads. So. Anyone got any suggestions as to what plastic might suit my needs?

Ta.

 

[gavuk]

Can u tell us anymore about job?....perspex can be brittle ,we use a lot of nylon and pvc in places i have worked ,will take a thread ok(ish)...Gav

 

[Arsonista]

Just going to say nylon 66 takes a thread well.

 

[Archie]

Most parts will be simple holders for some lenses, mirrors and beamsplitters. Nothing taxing. These parts are the roughly 100x100x6 ones. There are also a few larger parts (about 400mm dia.) and of 10-20mm thickness that will be spinning at anywhere from 300-2000 rpm! The threads are not going to be under any great strain. I've been told Nylon is often used in the department but it's pricier than some of the alternatives.

 

[gavuk]

sorry Arch haven't got a clue about prices,,,,pvc would be worth a look imo pvc

 

[Archie]

Thanks Gav. I'll give it a look.

 

[penfold]

A few points:
-If nylon is regarded as costly, you're not shopping hard enough; it's one of the cheaper engineering polymers.
-I would question the wisdom of mounting lenses etc.(things that need precise alignment) on plastic, which isn't the most dimensionally stable material type. The best polymers would be something with fibre reinforcement to add stability, like Tufnol, glass filled nylon, or glass/CF sheeting. Sandwich if you have deep pockets.
-PVC is really too floppy for this; it's only merit is cheapness, the cost is a bit less than nylon. There's not much between acetal and nylon; acetal is a bit stiffer and easier to machine, nylon is a little cheaper. Acrylic may be pricier, but is relatively stiff and machines well.

 

[scott0031]

From what your describing nylon is the material for your application. Its really considered the mild steel of engineering plastics. It can be a bit pricey considering the amount of plastics that are used in industry in the molding sector and cost pennies compared to buying sheet or rod stock. So yes the price of plastic stock is a rip off, but it doesn't have to be the end of it. There are several grades of nylon on the market at less cost than the most common nylon 66. One you should be looking at is the cast version called nylon 6. It is cheaper and has different properties to the 66 and pretty stable as its cast as apposed to extruded. Sounds like it would be very usable for your application. The one good thing about 6 its available in black as apposed to the 66 being mainly a natural white colour, which is a bit yucky for applications that are seen.


I would recommend you have a word with these guys

http://www.amariplastics.com/amari/default.asp

They are very accommodating and very knowledgeable plus the bonus of being one of the cheapest i have ever found and considerably cheaper than general stockists.

Explain to them what you are doing and the full application, also tell them its a project for uni as i said they are very accommodating. Give them a try and good luck.


Kind regards,


Scott (ward eng)

 

[Wedg1e]

I like black acetal, you can get a beautiful surface finish on it (turned or milled) and can even make close-fitting sliding parts that wear well.

 

[Tigman]

I like black acetal, you can get a beautiful surface finish on it (turned or milled) and can even make close-fitting sliding parts that wear well.

My mate uses acetal to make parts for bottling process plant he drills and taps it mills it no problem

 

[Archie]

Thanks for all the info guys. I'll give Amari a ring as they have a branch in Bristol which is certainly handy. Looks like it's come down to Acetal or Nylon. I think I'm erring towards the Acetal at the moment as I've seen on a couple of sites it is specifically recommended for machining.

In case anyone's interested, this is the sort of thing we're doing though along slightly different lines.

 

[Shox Dr]

Give Locate supplies a call. Good sellection of all sorts really.

 

[weldingscotty803]

what about PE. quite cheap, hardwearing quite strong etc etc, in my album theres a few things ive made using polyetylene, including a boat!

 

[Archie]

I am already using polyethylene for part of it but I'm using it for a part that needs to be flexible. I hadn't thought of looking at it in thicker sheets. I'll have a butchers.