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    • April 12, 2017 2:53 PM EDT
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      Casting resins and molds

         I have been doing some resin casting the last few months. I am using resins from Moldputty.com  Amazing resin. What I was wondering if there is any other resin out there that is thinner in viscosity when mixed together. I would like to find something that will pour into the mold cavity easier and prevent air pockets occurring. I thought somewhere I read that you could heat up the resin, however I haven't tried this. I would think it would speed up the curing and setting process of the resin being cast. Anyone have thoughts on any of this?......

    • April 12, 2017 4:30 PM EDT
      • Pittsburgh, Pennsylvania
         
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      Yes, heating the resin usually speeds up its setting time, but it can also make it thinner, or less viscous. So its a trade off.

       

      I know some people use vibrators (shut up Rooster) to vibrate the molds to get the air bubbles to move to the top of the mold, out of the casting.

       

      I used an el cheepo paintbrush to paint the resin on the mold face, before I slowly poured in the resin. That way, any air bubbles I did trap, weren't on the surface, where they would ruin the part. But the casting resin I was using was very thin, and my mold was an open cavity mold, since the parts were to have a flat back to them. So YMMV.

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    • April 12, 2017 4:48 PM EDT

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      Raw Material Suppliers sells a wide variety of ATR for molds and resins for parts. They have many formulations for different setting times, viscosity, and hardness. They package in small quantities for the hobbiest. I have used them for many years on many projects both for club members and commercial use. 

    • April 12, 2017 5:57 PM EDT
      • Farmington, New Mexico
         
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      Travis,  I have found that there seems to be a difference in product quality in the " Hobby " brands of castings resins.  I have changed over to using Professional grade products.  The quality of the pro products is top grade,  the trade off is that they seem to be less forgiving, but much higher grade.

       

      I use the products from Aeromarine, out of San Diego CA.  Top notch.  They have started to sell on e-bay, in smaller quantity. They also sell a "Thinner" agent that is added to reduce the viscosity if needed.

       

      Their standard resin has a pot life of 3 minutes @ 70 deg.   Yes Heating does decrease viscosity,  but you had better get in the mold within 10-15 sec.  Which will drastically reduce the time that you have to mix the two parts together properly.

       

      https://www.aeromarineproducts.com

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    • April 12, 2017 6:29 PM EDT
      • Burke, Virginia
         
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      guess I don't do enough casting.   I usually make a mold and then by the time I'm ready to cast something else the mold jar is already solid.   Are there any mold making materials that have a LONG shelf life?

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      Bruce

      http://jbrr.com/

       

    • April 12, 2017 7:07 PM EDT
      • Port Orchard, Washington
         
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      Bruce,
      Are you talking RTV or resin not lasting? I find that when I have "fresh" RTV I'm more willing to make molds, and I find my self casting a lot. When it runs out or goes bad, I tend to stop for a while.
    • April 12, 2017 7:16 PM EDT
      • Burke, Virginia
         
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      Craig Townsend said:
      Bruce, Are you talking RTV or resin not lasting? I find that when I have "fresh" RTV I'm more willing to make molds, and I find my self casting a lot. When it runs out or goes bad, I tend to stop for a while.

      Hehe...I never know how long the resin really lasts.   I build a master, then go to use the RTV to make the mold - and it's a tad solid.  I never seem to get to pouring the resin into the mold.  

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      http://jbrr.com/

       

    • April 12, 2017 7:59 PM EDT
      • Sparta, TN
         
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      On molds that are too big to pressure cast, I tease the surface bubbles (bottom of the mold) out with a bamboo skewer.  Usually the same one I mixed the resin with. 

       

      Your resin should come with a spec sheet that states the viscosity in centipoise (cps).  The lower the value, the thinner the resin in liquid form.  You can compare that to the major hobby resin makers' specs, like Alumilite, Smooth-on, etc.

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    • April 12, 2017 8:11 PM EDT
      • Farmington, New Mexico
         
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      Again Check Aeromarine's web site,  for additives that can slow the "set" time, and decrease the viscosity.   I would highly recommend checking with the manufactures recommendations before cross using different brands of additives.

       

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    • April 12, 2017 8:46 PM EDT
      • Lewiston, NY
         
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       Sometimes the mold itself is to blame for trapping air bubbles. I can only guess that injection molding is different. Maybe the use of sprue holes in the right place would help the resin pouring process to release trapped air?

    • April 12, 2017 9:30 PM EDT

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      The resins and RTV from Raw materials is professional quality. they sell from "test kits" of about 100 mls to 55 gallon drums. their major customers are commercial craft casters. They are very helpful  with advice.  I am sure their are other vendors. I just found them to be the most helpful and price as I usually purchase 2.5 gallons of each part A and B. I often am able to remove bubbles by stoutly rapping table the mold is on (resins) The RTV is too viscous for this so I use a hand held body/muscle vibrator. I find that trying to heat resins results in poor uniformity of polymerization either too soft or brittle. Perhaps others have a better technique here.

    • April 12, 2017 10:03 PM EDT
      • Port Orchard, Washington
         
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      Bruce Chandler said:
      Craig Townsend said:
      Bruce, Are you talking RTV or resin not lasting? I find that when I have "fresh" RTV I'm more willing to make molds, and I find my self casting a lot. When it runs out or goes bad, I tend to stop for a while.

      Hehe...I never know how long the resin really lasts.   I build a master, then go to use the RTV to make the mold - and it's a tad solid.  I never seem to get to pouring the resin into the mold.  


      Well I had resin sit for 4 years in storage, along with RTV. The RTV was dead when I went to make my first casting last year, but the resin still worked much to my shock The color wasn't quite the same, but it cast just fine. I was expecting to have to throw out both. Lesson learned, if you by RTV in 2.5 gallon sizes use it up asap. The resin I bought was 1 gallon of each part. Now that types this up, I'm sure my resin just decided to kick... I am planning on casting a mold tomorrow.
    • April 13, 2017 2:59 AM EDT
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      Thanks for all the info and input guys...  

       

    • April 13, 2017 11:10 AM EDT
      • KENILWORTH, WARWICKSHIRE UK. (Just up the road from Stratford-Upon-Avon)
         
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      .It def does go off after 6 months depending on how stored.  I just dumped a 1 litre can of resin (it WAS  6 yrs old!!) which was  kept in a warm room.... but the hardener seems to be still very liquid (unopened).  I must get around to do the jobs I buy stuff for!! but I will be buying in smaller quantity from now on unless a big job is on the stocks.....might cost a bit more over time..but cheaper than throwing it away! 

      This post was edited by Ross Mansell at April 13, 2017 11:12 AM EDT
    • April 14, 2017 12:58 AM EDT
      • Ohio
         
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      Thanks again for all the input guys. The reason I was looking for a thin type of resin is I am trying to cast one of those reflectors or whatever they are called that goes around the lens on a switch lantern for railroad switch stands. I am having no luck getting he resin in the thin space it needs to go into. I was thinking if it was thinner it would flow better.....

    • April 14, 2017 1:15 AM EDT
      • Farmington, New Mexico
         
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      Travis,  Try this... If it is a two part mold..  Fill the cupped shape half with resin, and then press the other half into the cupped side, forcing out the excess between the halves.   This will leave excessive flash, but will ensure a full mold..

       

      One more thing.... Manufactures set their pot life and de-mould times based on a minimum amount of resin mixed.  It is exothermic ( generates its own heat as it cures )  very small mixed quantiles do not have enough chemical reaction to generate enough heat to provide proper curing.  In which case, heating the mold up ( <150 deg.) after pouring will help it to properly catalyze.

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    • April 14, 2017 6:47 AM EDT
      • Sparta, TN
         
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      Travis: If you could post a picture, it might help.

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    • April 14, 2017 9:08 AM EDT
      • romeoville, illinois
         
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        Lots of good info here already . I'll just add that Alumalite White resin is very thin and has a 3 minute set time. Alumalite Regular resin is thicker and has a 90 second set time. Start counting as soon as the two parts touch each other.

    • April 16, 2017 11:05 AM EDT
      • Ohio
         
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      What do you guys use to pour the resin out into the mold with?. I am not getting good results with just pouring out of the mixing cups. I was thinking of something that had a spout ?... Any pictures of what ya'll use?

       

    • April 16, 2017 12:17 PM EDT
      • romeoville, illinois
         
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          I used the mixing cup to pour directly into the mold. When you pour start with the cup high and try to get a ribbon of resin to flow into the mold . That helps eliminate most of the air bubbles . Don't forget to work fast as time is the enemy.

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