"Alternative Mold Materials for Organic Black Rubber Molds" Topic

I need to make up some new molds so went to Contenti to purchase some 700 Series Black Organic Rubber 9" mold blanks only to discover that such is no longer available. A call to Romanoff provided the info that the only manufacturer of black rubber for molds had shut down last year. Silicon rubber seems to be the only alternative. My question for you professional casters is what material are you using? From what source (USA)? I am casting 94-6 Tin alloy running it at about 610F. Any help would be appreciated. Thanks.

Jeff

Having the same issue and after doing homework realized the chance for U.S. moldmakers to get organic rubber are slim to none, I used pink silicone from Omar's Workshop in CA. Omarsworkshopllc@outlook.com

We have the same problem!!
We use 100s of molds a week !!
Silicone tears much quicker and does not last
Russ Dunaway

Well, I may have gotten the last of their stock when I ordered in January, as I only got 70% of my order.

I've used silicone molds in the past and they retain heat longer, get brittle quicker and tear easily. Another factor that will eventualy increase the cost of doing business.

Dave

I suspect that the profit margin on silicone is much better than on black rubber?

martin

Well it does not sound as if there is a really good answer. I tried a silicon mold once and did not like the results as it warped and ended up curling badly. I was told that I had probably abused it by running it too hot. The info I was given was that you only allow the metal to spin in the mold for about 20 to 30 seconds then de-mnold the sprue, lay the mold open on a flat surface with a fan blowing air over it to cool it back to near room temp before you spin it again. I guess I'll try a few types and see what works.
Thanks everyone for your comments.

I tried a silicon mold once and did not like the results as it warped and ended up curling badly. I was told that I had probably abused it by running it too hot.

Silicone moulds curl if the outsides are cooler than the insides. It's down to expansion/contraction at different temperatures (the cold surfaces of casting machine plates will cool down the outside of the mould). Organic rubber tends to keep its heat better and is less prone to the curling effect than silicone; because it retains heat, it also tends to overheat faster.

By prewarming silicone moulds and operating using a warm stack of four to five-plus moulds, you can in effect reheat the outsides of a freshly cast mould while you de-mould and cast from the others (the warmth from the other moulds reheats the outer surfaces). Running silicone moulds from cold will give a more pronounced curling effect. I always cast with prewarmed silicone moulds. They cast better, and they expand to nearer what was their original size in the can, reducing the effects of shrinkage.

All rubber tears easily. Undercuts will kill black rubber moulds as readily as they do silicone. And if you want to see brittle, cracked moulds, you should see some of the black rubber ones that I have retired from the Gladiator Miniatures line. :-)

It will effect prices!
Our molds went up $11 USD per.
Now, multiply that by 60- 100 molds a month?

Regards
Russ Dunaway

I learned about this happening several months ago and believe me it came out of the blue. Conley Casting in Rhode Island closed without notice apparently. I had be a customer of theirs since the 1970's and I did not receive any pre-notice. Simply put, Conley made, by far, the raw black rubber sets used by those in the jewelry and while metal casting trade. Contenti – also in Rhode Island and also a huge supplier to the trade took over all aspects and stock of Conley's including their phone numbers, but not the black rubber making operation. I believe Conquest Industries in California also used the black rubbers manufactured by Conley – but now I believe they have gone out of business or have stopped for some reason. (Conley made the rubber sets on their premises in Warwick RI on a large machine which I once saw in operation. We called it the million dollar machine.)
Now – and until who knows when – no more black rubber is available for open purchase. There are silicone based sets appropriate for ‘some' white metal casting, but I disagree strongly with anyone professing they are an adequate substitute for black rubber sets. Silicone costs more – WAY more in some cases – is not as tough and flexible in use as black rubber vulcanized sets, and will go far to change things dramatically in this hobby.
I'm certain there will be more coming down the road about all this and how it will ultimately affect our great hobby.
Toby Barrett
Thoroughbred Figures

Sure silicone is readily available, but at 2 – 3 times the cost of black rubber. I would be willing to pay the price, but the real problem is undercuts.

Wargaming figures often have deep undercuts, especially horses and humans with weapons. Armored vehicles with bogey wheels, ships with tripod masts, you get the picture. A large dragon's head with big rows of teeth would be hopeless. Silicone just can't handle them like black rubber.

Contenti took over the black rubber trade of Tekcast and Conley, became the sole supplier of said rubber, then discontinued it. Thanks a lot, guys.

And to make matters worse, if anyone has a large supply of black rubber, be sure to use it all in a timely manner because it starts to go bad after a few months.

Can anyone in Nottingham (or anywhere else) offer any assistance or advice? Who is the biggest seller of black rubber in the UK?

That all sounds a bit grim.
Im in the UK and I get my moulds from Coker and excellent they are to.
j-coker.co.uk/casting-discs

L
Adler Miniatures

I sent them an email this morning and received a reasonable quote for black rubber sets within the hour. Even with a hefty shipping fee, the total price was still much better than Contenti's best price for silicone.

Thanks Leon!

All I can add since my posting five days ago is that the problem is being ‘worked' – from reliable sources – here in the states. No idea of when or how. When and if I hear more I will post again but I'm only in intermittent internet capability.
Toby Barrett

Tumbleweed, your welcome.
L