High temp rtv

[bryanmc]

Does anyone have a decent source for tin sil 70-60 or some other high temp rtv to make a lead mold out of?  I looked at a couple places but they want $35 to ship 1lb of rtv.

[Jig Man]

I don't know much about that stuff but I got some at Auto Zone to use in one of my jig molds for some modification.  It was very reasonably priced.  You might check it out and see if it will work.

[CNC Molds N Stuff]

From what I have read at lead temperatures all silicons degrade over a number of usage cycles.  RTVs, catalyst kicked, and heat vulcanized alike.  The difference is how many cycles, and it seems the better stuff costs more.  The highest safe temperature rating I have seen on silicon products is around 390F.  That's why some grades work fine as bakeware, oven mits, and trivets.  You usually bake under 390 (not always I know).  I think the only reason lead works in silicone at all is that the area of over temperature is small and it drops quickly as heat is dissipated through the block of silicone so no energy is being added to the lead at that point. 

I'm not sure looking for a cheaper product is going to get you one that handles heat better.  I know "I want both cheaper and better" is a common refrain, but its one often fraught with frustration.  Silicone is a cheaper alternative to a cut aluminum mold, but its not really much cheaper than a cast aluminum mold and in either case it just doesn't perfom as well.  For a custom product or for doing knock-off its certainly cheaper though.   Yes the spin casters use silicon molds, but they also use heat vulcanized silicon rubber and they plan to remake them every so many cycles.  If they are good they guard and catalog their masters so they do not get product drift over time. 

[bryanmc]

I'm not looking for a cheaper product Bob, I'm talking about not paying  $25 for 1lb of silicone and then $35 to ship it.  The mold I'm looking to make will be single cavity (approx 1.5" x .5" x .5" and probably see 10 castings at the most.

Edited June 15, 2017 by bryanmc

[CNC Molds N Stuff]

Get ahold of Smooth-On then.  I've bought silicone from them in the past, and I don't recall the shipping being onerous.  They have a variety of good products.  If you aren't sure which one then ask them.  They will not say any particular one is "good" for lead casting as lead melts way above the degradation temperature of cured silicone, but they may say which ones handle heat the best.  I like the Sorta-Clear 37 for its 4hr cure time, but there may be others that are better or less expensive with a longer cure time.  If you get the 37 you only have a 25 minute pot life. 

 

 

 

 

Edited June 15, 2017 by CNC Molds N Stuff

[Anglinarcher]

For the amount and number of cycles you are doing, a silicon mold putty will work.  Go to hobby lobby and get some Alumilite mold putty and be done with it. 

I have poured larger and more then you are doing with them and it came out very well.

[psilvers]

2 hours ago, Anglinarcher said:

For the amount and number of cycles you are doing, a silicon mold putty will work.  Go to hobby lobby and get some Alumilite mold putty and be done with it. 

I have poured larger and more then you are doing with them and it came out very well.

 

That is some great info - will Alumalite hold up to 10 castings or so? I am looking to make some models from which CNC molds can be made.

 

Pete

[bryanmc]

5 hours ago, Anglinarcher said:

For the amount and number of cycles you are doing, a silicon mold putty will work.  Go to hobby lobby and get some Alumilite mold putty and be done with it. 

I have poured larger and more then you are doing with them and it came out very well.

 

Can you make a 2 piece mold with it?

[Anglinarcher]

Sorry it took so long to get back.  Yes, it will take 10 castings or so.  You should be able to get a couple of dozen or more if you let it cool a little between pours.

Yes, you can do a 2 piece mold.  Press the item into one side first, let it cure.  Then do the second side. 

For the 2 piece I did, I used a small box to hold it and quickly mixed the putty, forced it into the box, then pressed the lead spoon mold into it about half way.  I then quickly used a knife to flatten the mating surface/top like you would level butter in a cup when mixing it for baking.  15 minutes or so later I pulled the silicone out of the box and coated the mating surface with petroleum jelly.  I then mixed more putty, forced it into the box, pressed the box over the part to form the 2nd half.  Once cured, I separated the 2 pieces and used a craft razor knife to cut pouring channels and air escape paths. 

I actually saw Larry Dahlberg do this on his TV show "Hunt for Big Fish" some years ago, so I only wish I could take credit.  LOL  It was his idea.

I should have that mold still, but it is lost in a move.  It is in my back log of projects to perfect so if I get to it soon I will do a short video and post it somewhere.

Hope this helps.  When I get my project perfected, I have access to other molding materials that handle the heat just fine but do not require machining, but that is another subject and another day.

[bladesandbaits]

Why not try Bondo? I make all of my prototypes from Bondo which eventually wind up as a master then sent to Cast Industries for mastering baits for a vulcanized mold. 

I average getting several thousand spin cast baits from one mold. And Cast can spin me up a couple thousand pretty quick.

Regards,

Blades 

 

 

[jcool3]

On 6/14/2017 at 5:49 PM, bryanmc said:

Does anyone have a decent source for tin sil 70-60 or some other high temp rtv to make a lead mold out of?  I looked at a couple places but they want $35 to ship 1lb of rtv.

Alumilite's Plat 55  buy direct from alumilite https://www.alumilite.com/store/p/927-Plat-55.aspx

$27.50 for 1 lb plus less than $7.50  for shipping.  Platinum cure should work fine for pouring lead.