Strange resin sought 4

[Theophilus]

I'm looking for a sort of thermoset, such as unfilled polyester casting resin. At least that's what I think it is.

A client of mine is getting some parts machined from what I believe is a pre-cast resin in rod form (from a vendor in England, I believe). This seems to be because of the nature of the appearance and water resistance of the part.

I need a nice opaque white part, able to put a polished finish on it. I've looked at the thermoplastics available and cannot seem to find quite the right look/feel. (Tried Delrin--nice white, but somewhat translucent.) Normally, injection molded high-volume production stuff is my niche, but this part cannot be feasibly molded while retaining the aesthetic characteristics I need (very thick sections--over 1" in areas--with thin sections in other areas, bad undercuts to be machined in, etc.)

This part will work as part of a premium-line bathing accessory, so it will get plenty of soap and hot water over time. It doesn't need to be terribly accurate (+/-0.015" tolerance is fine) when machined, but needs to be able to sustain decent drops onto the floor without damage.

Can anyone recommend a resin that may work for this machining process, even if somewhat complicated?

One more thing--if it's a cast thermoset, we can cast the rods ourselves, but cannot use the material if there is a significant risk of air bubbles within the rod to be machined.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe trumps reason.

 

[Demon3]

It sounds like you are trying to make something like cultured marble, as used for sinks, countertops etc. I am no expert on that but I know someone who is. He said they are made from methylmethacrylate filled with ATH (aluminium trihydrtae or aluminium hyroxide). The methylmethacrylate is then cured to give PMMA. This gives the right look and enables you to polish out scratches during use with a mild abrasive. If you need to know more I can try to ask him directly as he spent years developing such formulations.

 

[Demon3]

I just remembered a tradename for such materials is Corian from DuPont, see for example

http://www2.dupont.com/Corian/en_GB/index.html

 

[dwightdixon]

Thermal sets do not normally have good drop resistance if they are not reinforced. The reinforcement usually means they can not achieve a high polish. Thermoplastic rods can be bought from many distributors like Caddilac Plastics. Try a Goggle search or Thomas register. Delrin is slightly translucent in its natural color but can easily obtained in white. It would be my choise.

 

[patprimmer]

Filled thermoset methyl methacrylate or filled thermoset polyester can be used, I think the methyl methacrylate is superior.

Acetal, PET or PMMA rod coloured white could be used.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Theophilus]

Wow--thanks for the quick tips.

I've checked into acetals (Delrin, POM [Acetron GP]) and PET, and those aren't quite what I need in this case (yeah, very picky about the final finish/aesthetic qualities). However, methyl methacrylate I've not checked on (isn't that sort of a brittle acrylic?). Corian I've heard of, but haven't checked that either--does it come in rods instead of only sheets?

I'll do some research in those areas and see how well they pan out for this application. For the filled polyester, what would be the fill? What I've got could be talc-filled, but nothing like glass fiber. If I can polish the final part, I can put a gloss coat over it if necessary, but the surface finish does need to be extremely smooth when complete.

Thanks again! I'll report back if I need some tweaked material suggestions.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[patprimmer]

Methyl methacrylate is acrylic.

It actually has fairly high energy at break, but very low elongation.

Corian is filled methyl methacrylate.

The filler you need will depend on the appearance you want.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Theophilus]

Thanks again.

I'd like a pure white, but if I could also get a very white pearlescent sort of color, that would be great to check out--maybe a Corian (or variant) would be available like that. I imagine it would machine well, judging by the countertops I've seen.

By the way, this is an industrial design/product design project. I'm creating a women's razor design and some other things that will use the same material I need for the razor handle. Normally I wouldn't have something like this machined, but molded, but for technical reasons (like the huge, solid sections coupled with thin sections I mentioned) this really won't work out well while keeping a stellar aesthetic. Plus, we'd like to keep up-front tooling costs to a minimum.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Pud]

Jeff,

PMMA can be solvent polished to a very high gloss.

Not sure if it's still available, but Cellulose Acetate (Propionate or Butyrate - CAP or CAB) machines well, polishes excellently and easily - very tough (used to be used for screwdriver/chisel handles) - and self-polishes with handling.

Likley to be expensive if you can get it....

Cheers

Harry

 

[Demon3]

Yes you can still get those cellulosics from Eastman. As you mentioned the CAP is used for screwdriver handles due to a special feel it has. Also you can polish out scratches or anneal them out with a heat gun or hairdrier. CAP is around the 3 Euro per kilo mark or it was last time I checked. You can find the material properties and links to suppliers at

http://www.matweb.com

(free)

 

[Theophilus]

OK, I've contacted Eastman and DuPont for Corian samples. The Corian rep says I can only get Corian 1/2" thick and will have to laminate to thickness (would like to start machining with 2" diameter rods) and then machine--we'll see if that works well--certainly will add to the cost.

Still waiting to hear back from Eastman.

Thanks, again, everyone for the input on this. I'm hoping one of these materials will work out.

Does anyone have any other creative materials ideas? I don't know about the CAB/CAP materials yet, but the Corian will probably fulfill the aesthetic requirements very well--but will be a bit of a bear to machine.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[dwightdixon]

Howmany do you intend to make per year? If it is alot then a molding operation will be cheaper. If it is less than 5,000 per year machining will be less since you will not have to pay for tools.

 

[Theophilus]

Since we're just launching this as a new product, we don't expect high sales from the start. Maybe 10,000 units the first year, depending how well things take off.

I just received some samples of the butyrate (Tenite) from someone who uses this stuff to make--you guessed it--screwdrivers. This stuff looks great for this purpose, and although most of the samples are clear, they sent a white chip that looks great--excellent finishing capabilities and good color and opacity.

We may still machine this stuff even if volumes get high because of some strange undercut features we need for assembly. However, I could mold some solid plugs of inexpensive resin, let those plugs shrink/sink like crazy, and then mold a much thinner, even-walled coat of Tenite over the plug. (The plug could even be machined to give me my undercuts, but that would still involve additional cost.) The guys that sent the samples to me suggested this molding option, and it may prove to be the viable link we need. This stuff vapor-polishes great, so we could probably erase the parting line for a perfect finish if we go that way.

At this point, starting with machining is probably the best idea, and we can transition to molding later if that becomes more feasible.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Demon3]

I see that you are deliberating machining versus injection molding. You also mentioned that the appearance of the part is critical. It could be important to consider that a filled part will show flow lines if you injection mold it due to the way the filler / pigment flows. This is likely to detract significantly from the appearance. In contrast an extruded rod or thermoset part can be made without flow lines and give the natural marble appearance you seem to be looking for.

 

[Theophilus]

Good point. Because this is a "premium" item, we're planning to stick with machining, at least through the launch and into production. If we can get identical quality in molding, and if molding becomes more feasible otherwise, we'll consider doing that.

It's nice to have options.

Thanks everyone for all the input so far!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[Pud]

Theophilus:

Jeff, how is the project going? Much joy or gloom, doom and despondency?


Merry Christmas

Harry

 

[philwarren11]

I'd like to bump this thread as i'm kinda in a similar situation, high end bathroom accessories requiring material with similar spec.

Thanks.

 

[patprimmer]

Why not start your own thread instead of hijacking this one.

You could start it with a post that is a clear and concise question. That is normally the best way to encourage a positive response.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[philwarren11]

I'd just be making a thread the same as this one, which i dont see the point of.

I was more interested in his outcome and not hijacking.

 

[Theophilus]

Just got back into the office after quite a while out (nice vacation). It seems I wasn't the only one out, since my prime contact for the butyrate material hadn't responded for a while either.

So--I'm meeting with my client today on this to get a quantity estimate, to look over our rapid prototype, and to otherwise begin moving toward production. My client likes the butyrate sample my source gave (found through Eastman--very helpful people there).

Everything is moving along about as fast as I can move things along, considering all my projects. So the help you've provided has been extraordinary! I really appreciate it. A similar hardness to the samples I received will probably meet our needs exactly, though the material is entirely different in chemical make-up from my original search. The properties, however, and not the chemical recipe, is what we need.

More to report after receiving a machined sample in the right material to run through paces.

Thanks again!



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.