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Silicone RTV for molds?

General engine tech -- Drag Racing to Circle Track

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dannobee
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Silicone RTV for molds?

Post by dannobee » Wed Feb 05, 2020 10:37 am

There seems to be quite a selection of pourable silicone RTV's available now for making molds for ports and chambers. Anyone have a preference?

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Re: Silicone RTV for molds?

Post by Ken_Parkman » Wed Feb 05, 2020 12:59 pm

I find the silicones not the greatest. Have had very good luck with a 2 part urethane molding compound, durometer 20. Less expensive and easier to work with. A few tricks to know, one being it is very important to mix it well as it is not easy to tell, and not mixed well enough does not work. And best to remove it almost exactly 24 hours later.

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Re: Silicone RTV for molds?

Post by hoodeng » Wed Feb 05, 2020 5:29 pm

There are two that i have used, one is called ' White condensation cure RTV-2 Silicone M4503/T35' [also known as Elastosil M4503] in a 1kg kit, the other is 'Flexivinyl 1kg Red'.

The Flexivinyl red is a one part semi rigid molding, that is melted in a saucepan then poured into the shape required, i found with this one that the job had to be preheated to keep the pour consistent. This stuff works fine for plunge molds.

The other M4503/T35 is a two part silicon + catalyst material that gives about 30+ minutes work time, but needs to be left in-situ for 20/24 hrs before de-mounting and has only .5% linear shrinkage. I found this one a bit messier to work with but gave better results when doing combustion chambers and ports. I have used this when submitting chamber shapes to custom piston manufacturers.

Both need the surfaces being molded to be lightly oiled before pouring.

Cheers.
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Momus
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Re: Silicone RTV for molds?

Post by Momus » Thu Feb 06, 2020 1:49 am

The pink, 2 part stuff they sell in the sex shops works well for ports. :D
You do have to work quickly and not over catalyse.

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Re: Silicone RTV for molds?

Post by mag2555 » Thu Feb 06, 2020 6:34 am

I use 2 part prosetic foam.

It expands a big rate so you use only a little and you can remove it from the port in 20 minutes and is very flexible just like foam pads on crutches and such.

Sorry, not home now to look at what the last brand of it was I ordered!

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Re: Silicone RTV for molds?

Post by Truckedup » Thu Feb 06, 2020 8:18 am

For combustion chamber molds I have used Plaster of Paris with a popsicle stick molded in for easy removal,cheap and easy....But don't drop it on the floor... :D
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

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Re: Silicone RTV for molds?

Post by David Redszus » Thu Feb 06, 2020 11:05 am

For the last 25 years we have developed, sold, and used a product called FlexiPort.

It is a one component latex liquid, which when heated in a sauce pan, becomes a pourable gel.

After being poured into port, combustion chamber (with piston in place) or any crevice and allowed to
cool, it forms an easily removable rubber-like mold. It can be sliced and measured to obtain cross section areas
or lengthwise to obtain port curvature.

Afterwards, the mold can be heated to a liquid and reused as often as necessary.

dannobee
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Re: Silicone RTV for molds?

Post by dannobee » Thu Feb 06, 2020 11:35 am

Do you have a link? Or how can I get more info about Flexiport?

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Re: Silicone RTV for molds?

Post by Kevin Johnson » Sat Feb 08, 2020 12:48 pm

dannobee wrote:
Thu Feb 06, 2020 11:35 am
Do you have a link? Or how can I get more info about Flexiport?
http://www.precisionautoresearch.com/GE ... e/PAR8.htm

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