What Type Silicone Pros & Cons

[bruce119]

So I want to make some of my own molds to suet my needs. I want to be able to cast under pressure so maybe a stiffer silicone but need something flexible and durable to hold up to production.

So some of you that make molds what type silicone are you using and why. Also if there is something you tried and didn't like it PLEASE by all means do share.

Just trying to save some time and money instead of trial and error.

Thanks
Bruce

 

[Glass Scratcher]

Oomoo 25 & 30 are very good Tin cure silicones from Smooth-on. They are 25 and 30 on the Shore A scale and are very flexible. They both will stretch/flex 250% before tearing.

I also like the Mold Max series, it is also a Tin cure silicone. I just finished a tub of Mold Max 40. Which has a Duromieter of 40 on the Shore A scale and also will stretch/flex 250% before tearing. The Mold Max series requires vacuum degassing.

The molds made from Oomoo have had hundreds of casts made in them, and are still in use and still have plenty of life left in them. I am slowly replacing them but I still use them for overflow casting.

The ones made with the Mold Max have seen a good amount of use, (10 gal of resin them, roughly 600 blanks) and are showing no real signs of wear.

I will probably move to Smooth-Sil or Mold Star for my next molds. It is a Platinum cure material.

As long as you keep your master plug in your "library" you can always replace a mold that wears out.

http://www.reynoldsam.com/

 

[PTownSubbie]

Bruce,

To me it all depends on the style of mold you are going to construct. I have used OOMOO 25 & 30 along with Mold Max 30.

If you are going to make a strait blank mold like you purchased from me you can use OOMOO 25 or 30.

If you are going to make a resin saver type mold, the OOMOO is not durable enough to be stretched repeatedly without tearing IMO. You need something with greater tear strength. That is where you get to Mold Max from Smooth-On. If you need something more hard to minimize movement then go with some stronger form of Mold Max. I have used the Mold Max 30 and it is fairly hard but still stretchable.

Check out the Smooth-On site (www.smooth-on.com). Here is the Mold Max page: http://www.smooth-on.com/Silicone-Rubber-an/c2_1113_1135/index.html

You want something with higher shore hardness and also has a high tear strength.

 

[Padre]

I have had great success with Mold Max without ever using vacuum.

 

[bruce119]

Now I am leaning toward Mold Max 30. Is the 2 parts by volume or weight I see A is a lot more then B. But is the ration weight or volume I am wondering if I need a good scale. I have just about everything else but a real good scale. I don't work with Alumilite also anything else I mite need so I am ready when it comes. I got a good vacuum pump, pressure pot, ultra sonic and a vibratory table top. Any thing I mite be missing or tips looks like smooth-on mite be the best place to buy. I guess I will get a gal. to start how long is the shelf life. I don't want to get too much but don't want to be short either.

Thanks for the help
Bruce

 

[Glass Scratcher]

It's by weight. 100a:10b. You need a better gram scale than the HF one. I have one and it isn't that accurate and the scale has lag time and it will float on you, right up to the auto-shutoff. Although when you are talking 900g of silicone that +/- 1gram becomes inconsecuential.

 

[bruce119]

I used to have a triple beam I got years ago from a print shop I worked at. But it took about a 10 foot fall onto a concrete floor. I need to get another one of those. Maybe I'll take a look on eBay mite be able to pick up an old one fairly cheap. I know a decent postal scale now a days are a few bucks. Darn I can do volume and even parts but weight. Sounds like I am going to need a good scale for sure.

thanks

 

[Padre]

Now I am leaning toward Mold Max 30. Is the 2 parts by volume or weight I see A is a lot more then B. But is the ration weight or volume I am wondering if I need a good scale. I have just about everything else but a real good scale. I don't work with Alumilite also anything else I mite need so I am ready when it comes. I got a good vacuum pump, pressure pot, ultra sonic and a vibratory table top. Any thing I mite be missing or tips looks like smooth-on mite be the best place to buy. I guess I will get a gal. to start how long is the shelf life. I don't want to get too much but don't want to be short either.

Thanks for the help
Bruce

I use the Mold Max 30 and use a scale I got off of eBay. It is a nice scale, but I only paid about $15.00 for it. It does grams, ounces, kg, pounds, pounds and ounces, kg/g. It works great. This is very similar to the one I got. http://cgi.ebay.com/0-1-x-2000g-Dig...316?pt=LH_DefaultDomain_0&hash=item23079ced9c

 

[PTownSubbie]

Bruce,

Shelf life is probably about 6 months. They sell an aresol can that you can spray into the mold material when storing it for a long time to help it last longer. When I bought my mold material the guy talked to me about it. I don't think you will need it. Just keep the material mixed really well.

It says you need vacuum but I didn't have a container big enough for the expansion so I didn't use vacuum. It turned out alright but I stayed there for a long time popping bubbles as they rose to the top of the mold.....

 

[ctubbs]

I just bought it for 6.80 total. I'll let you know what it really is. Heck, for <$7, how wrong can you go?

 

[PTownSubbie]

I just bought it for 6.80 total. I'll let you know what it really is. Heck, for <$7, how wrong can you go?

Bought what? Mold Max is no where near that cheap!! I gallon is around $100. Even the sample pack is $25.....

 

[bruce119]

I just bought it for 6.80 total. I'll let you know what it really is. Heck, for <$7, how wrong can you go?

Bought what? Mold Max is no where near that cheap!! I gallon is around $100. Even the sample pack is $25.....

I think he may be talking about the scale. I am looking at eBay I will get a triple beam. Looks like you should be able to pick one up for about $30-40 if you get lucky. I like mechanical you just can't go wrong.

Well I guess now I will start work on my masters. I do have some 5x12x1.5 delrin. Guess I need to come up with a shape and start carving.

I would think you all use a piece of glass. I got a nice piece of 1/4" glass some 1/2 delrin from the sides and I guess Goop to glue it all in place. I use Goop on my hard square molds and it works great. I guess it would be safe on silicone. I read to stay away from model clay.

Thanks for the help

 

[Glass Scratcher]

Snip

I would think you all use a piece of glass. I got a nice piece of 1/4" glass some 1/2 delrin from the sides and I guess Goop to glue it all in place. I use Goop on my hard square molds and it works great. I guess it would be safe on silicone. I read to stay away from model clay.

Thanks for the help

No don't use glass with silicone. Silicone will bond to glass. You can use metal, plexi, plastic, sealed wood..., anything non-porous and not glass. Porous materials you can get and use a product called Super-Seal, if you don't you will get a mechanical bond between the material and the silicone.

The only modelling clays to avoid are clays that contain Sulfer. If you are going to order silicone, the dealer should have Kleen Klay or Plasticene clay.

 

[bruce119]

Snip

I would think you all use a piece of glass. I got a nice piece of 1/4" glass some 1/2 delrin from the sides and I guess Goop to glue it all in place. I use Goop on my hard square molds and it works great. I guess it would be safe on silicone. I read to stay away from model clay.

Thanks for the help

No don't use glass with silicone. Silicone will bond to glass. You can use metal, plexi, plastic, sealed wood..., anything non-porous and not glass. Porous materials you can get and use a product called Super-Seal, if you don't you will get a mechanical bond between the material and the silicone.

The only modelling clays to avoid are clays that contain Sulfer. If you are going to order silicone, the dealer should have Kleen Klay or Plasticene clay.

OK that's good to know perhaps I will use delrin. I have a couple sheets 1/2" thick 12" wide and 4ft long. I could cut a piece of that and use it as my table top to build my form on.

See this is saving me time and money already great info. In the past I would do trial and error and find things out the hard way. It worked but took time and a lot of $$$$.

I know the Goop works good with the delrin bonds and seal it real good drys fast and cleans up real easy afterward. Does it sound like I mite run into any other problems with my plan. I saw on the instructions that it is suggested to post cure at 150 deg. for about 45 minutes. Do any of you guys do that.

thanks for all the info.

 

[Glass Scratcher]

I post cured all my molds, and I preheat them before use.

 

[PTownSubbie]

Bruce,

You may want to save the good materials for your final design and just use wood that you seal with laquer or the same for your trial molds.

Also, remember you need to make your mold negative so it can be taken apart to remove the mold. (It sounded like you were going to make a solid negative that wouldn't come apart)

 

[bruce119]

Bruce,

You may want to save the good materials for your final design and just use wood that you seal with laquer or the same for your trial molds.

Also, remember you need to make your mold negative so it can be taken apart to remove the mold. (It sounded like you were going to make a solid negative that wouldn't come apart)

I follow what you are saying good tip on using wood to practice the delrin is expensive. Silicone is expensive also I mite make a test master in wood and pore with PR to check it's final shape. I know that wouldn't make a mold but it would give me vision of the final shape and I got 5 that's FIVE extra GALLONS of Silmar 249 that was sent to me by mistake and I will not use it to make blanks for sale. I understand about being able to dissemble the mold the Goop is perfect for that. It bonds delrin just enough for a strong hold with a little help of duct tape on the outside then pulls apart fairly easy and cleans off the the delrin real easy. You can just roll it off with your finger and clean any residue with acetone.

Thanks for the help. I just got a triple beam off eBay for $50.00 I will order a Gal. of Mold Max 30 today. So now I got to get to the drawing board and design a mold.

Don't know if I mentioned this yet I got one of ThePenWizard's mold, we did a trade, I like his concept also here's a link
http://www.penturners.org/forum/showthread.php?t=68296
Mine mite be somewhere in-between his and Charlie's R.S. something that can withstand pressure.

Thanks
Bruce

 

[navycop]

Snip

I would think you all use a piece of glass. I got a nice piece of 1/4" glass some 1/2 delrin from the sides and I guess Goop to glue it all in place. I use Goop on my hard square molds and it works great. I guess it would be safe on silicone. I read to stay away from model clay.

Thanks for the help

No don't use glass with silicone. Silicone will bond to glass. You can use metal, plexi, plastic, sealed wood..., anything non-porous and not glass. Porous materials you can get and use a product called Super-Seal, if you don't you will get a mechanical bond between the material and the silicone.

The only modelling clays to avoid are clays that contain Sulfer. If you are going to order silicone, the dealer should have Kleen Klay or Plasticene clay.

Is this the same as polymor clay? The kind used for pens.