Proper care and feeding of your pet molds

[Hiflt4@juno.com]

Was looking for tips and tricks for maxamizing the number of casts avalable from a given mold.

Mainly the idea of bakeing a mold. However I seem to be missing any sort of tutorial on the subject.

Equipment used
Time and tempature
Silicone oil? and where you buy yours.

Any info or a full tutorial would be great if not ill post one in a month or two after i work the bugs out.

[paulson games]

Mold baking can be done in your oven or using a toaster oven.

I haven't bothered with it myself but from what I understand they are heated somewhere around 400 degrees? They are heated for 4-6 hours. You are supposed to do this every ten or so casts, which is why I haven't ever bothered as it takes a lot of extra time.

Assuming I cast full time it'd be very easy to get 10 casts from a set of molds in an afternoon, so I'd be baking the molds every night. I'd be looking at 8 hours casting and 6 hours baking molds, which is not a very good time trade off.

The main purpose of baking and oiling molds is to increase the shelf life of when they are being stored. If you have a set of molds that are going to be sitting for months without use that's when you should consider baking. Most basic tin cure silicons are only good for 6months to a year as they dry out on their own, others (like platinum basesed) have a shelf life of several years.

[Lane]

I did a quick search and found 160-250 F for a couple of hours. Some sources say every ten casts others 20+ casts. Use whatever oven you have available but I personally would avoid one used to kook food in.

You can generally get silicone oil from the same company you get the RTV from. In the US you can also get it from http://sculpt.com/ though probably best to use silicone oil from the same manufacturer as the RTV.

[mangozac]

I don't think anybody on here has bothered with the mould baking. Like Jon says it's kind of hard to justify for the relatively small moulds we're working with. Certainly larger moulds with hundreds of dollars worth of silicone you would want to maximise the lifespan as much as possible, but when it only costs $10 and 15 minutes to make a new mould why bother mucking around with several hours baking?

I wouldn't go much past 250°F (125°C) and have heard that even without adding a silicone oil it will be advantageous...

[Lane]

When you run a business reducing material cost by 20% is huge. Say you make 100 molds a year and get 30 casts out of each. If baking the mold gets an extra 6 castings (20%) you save roughly 20 molds. At $10 each that's $200 saved. Also consider time, that 20 molds is another 5 hours of labor saved.

[paulson games]

But what type of costs are you incurring for paying for the gas/electric for baking as well as buying the silicon oils? It may be fairly inexpensive for one or two molds, but you're running that oven for hundreds of hours if you're baking 100+ molds multiple times.

For my production molds on simple parts I'm usually getting upwards to 200 pulls from each mold, so with mold release they tend to last way longer than a few dozen pulls. Assuming it's all new material my average mold takes about 12oz so it's not quite $20, I find it easier to run it without baking and just recycle chunks of the old mold. (recycling has cut my silicone costs by about 50-60%)

Most of the wear and dry out will be at the outer surfaces so if you recycle the inner core you can stretch that silicon a long way. Each time you bake it it pulls the oils from the core out to the faces. I would suspect that you probably wouldn't want to recycle old baked molds as their internal oil level will have been significantly depleated.


Edit:
I found this on the tekcast site

10. Mold Life ExtensionBarrier Coating. The use of a barrier coat when casting polyurethanes can greatly extend mold life, in some cases up to 200 percent. The barrier coat should be sprayed into the silicone mold prior to each casting. When the cast part is removed from the mold, the barrier coat becomes the outer skin of the casting. The barrier coat can then be stained or painted, an important feature. Note that this type of barrier coat is different than the barrier coat mentioned in “Techniques to Prevent Inhibition.”
Reconditioning. Reconditioning can be accomplished by burnishing a low viscosity 200 Fluid into the surface. When the mold is to be put back in use, any excess fluid should be removed from the surface. This is necessary to ensure the cast parts will be paintable. Non-wetting or fisheyes can occur on the surface of the cast parts if all excess 200 Fluid is not removed.

Bake-Out. A bake-out is recommended to remove the hardeners, plasticizers and other materials that leech out of the casting materials and are gradually absorbed into silicone molds. A slow, gradual bake-out at 93°C (200°F) for eight hours or a rapid bake-out at 204°C (400°F) for two hours can be used.