The follow is a string that I have been carry off line with Mark Schanze.
The information is very helpful. I was sure that others on the list would
find it useful and Mark has graciously agreed to let me share it with the
At 10:28 AM 3/26/98 -0600, you wrote:
>I use Ciba RP 4036 Aluminum Filled Epoxy for my molds. When I make a mold
from a rigid master I usually lay up a print layer of a high temp. laminate
material. This does not work on silicone. The 4036 material is hard to
deair and needs 2% of PTM&W's PA0550 Bubble Breaker (213 946 4511) added
before deairing. Then partially fill the mold and deair the material again
in the mold. Finish filling the mold and cure for 24 hours @ 30 psi. The
Epoxy shrinks .03% by the third day of cure. For high temp. applications
you will need to postcure the epoxy mold as per Ciba instructions. This
appears not to induce more shrink. Use RP 1500 hardener (your mold is
small, right?) Deair this material a full 29 in. hg. and hold it there for
a while. You'll see what I mean. If the material doesn't collapse you
haven't deaired it. There are lots of other epoxies to use. Call Ciba
for some help. If it gets confusing use the 4036. Should we post these
conversations on the RP ML?
>>>> Kelly Hand <firstname.lastname@example.org> 03/25 8:56 PM >>>
>I'm leaning now towards making the delrin mold first, only because I don't
>have much time or budget for a learning curve, and then if it shuts off
>well and appears to work I will make a couple of silicone molds of the
>delrin molds. Then I can make epoxy molds, like the delrin molds, from the
>silicon molds. Then for my multiple molds I'll use the epoxy molds rather
>than delrin molds because it's faster to mold a mold than machine a mold.
>What epoxy would you recommend and how do you ensure that you get a good
>fill on your important surfaces, no air trapped in the corners and such,
>you know, the kind of things that spoil your day?
>At 11:08 AM 3/25/98 -0600, you wrote:
>>Cutting aluminum is easy. Use sharp cutters (new) low RPM and a maximum
>cut of .050. If you go slow you don't need coolant. If you get in a hurry
>use motor oil in an oil can and apply when necessary, you don't need a
>bath. Have you thought of pouring epoxy molds? Epoxy takes release agents
>well. They are permanent molds too. Machine your master, pour epoxy
>mold, make silicone mold of epoxy mold, pour multiple copies, your there!
>I wish it were that easy, don't you? Hope this helps, let me know.
>>>>> Kelly Hand <email@example.com> 03/24 10:05 PM >>>
>>Very helpful information Mark, Thanks.
>>Originally I thought about a silicone for this project but the client wants
>>to get about 500 parts in short time frame (go figure), and I've been told
>>that I could only expect about 15 parts per mold as well as the fact that I
>>have to capture an existing part in the mold with very little room to shut
>>I figured machine something easy to cut and make a half dozen of them. The
>>only reason I'm thinking Delrin is because we are a model shop, we cut
>>plastic and that's about it. Aluminum sounds better but we are not set up
>>to cut metals, no coolant or expertise for that matter. Thoughts?
>>At 09:52 PM 3/24/98 -0600, you wrote:
>>>We in the industry use silicone to mold because it naturally self-releases.
>>> Machinable plastics such as polypropylene also have self-releasing
>>>characteristics. Polypropylene is not easy to machine due to it's low melt
>>>temperature. Delrin is easier to machine but certain grades still create
>>>lots of "hair" or melt build up on the cutter. The easier the material is
>>>to cut and the better the cutting finish the less natural release
>>>characteristics the material will have. Polypropylene will have an
>>>unlimited mold life. Delrin will have a limited mold life. Therefore the
>>>release agent one uses will determine the life of the mold. Delrin will
>>>not take most release agents well. Since you are trying to mold from a
>>>material that will ultimately be dependant upon the release agent used,
>>>maybe a material that handles release agents well should be considered,
>>>like aluminum. Machining aluminum versus delrin and expecting to hold
>>>tolerances is a no brainer. Finishing delrin is a bitch! Freekote 700
>>>from Dextor Hysol is a great release agent for aluminum. Depending on the
>>>tolerances required I would prefer silicone. At the most I would build a
>>>hybrid mold of machined aluminum for high toleranced features and encompass
>>>the fixtures in silicone. Obviously I could go on for a while so I will
>>>Molding Technology Manager
>>>CIVCO Medical Instruments
>>> 319 656 4447
>>>For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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