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Casey

A History of Pyro & The First Modern Injection Molding Machine

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11 hours ago, Snake45 said:

I believe this also explains where the term "high-impact styrene" (not seen that much anymore, but common in the '60s) comes from. 

Yes, high-impact-polystyrene is stronger and less brittle than plain polystyrene.  ABS is just another type of polystyrene Coplymer.

A good info on polystyrene is at https://en.wikipedia.org/wiki/High_impact_polystyrene  Here is a quote

Pure polystyrene is brittle, but hard enough that a fairly high-performance product can be made by giving it some of the properties of a stretchier material, such as polybutadiene rubber. The two such materials can never normally be mixed because of the small mixing entropy of polymers (see Flory-Huggins solution theory), but if polybutadiene is added during polymerisation it can become chemically bonded to the polystyrene, forming a graft copolymer,[citation needed] which helps to incorporate normal polybutadiene into the final mix, resulting in high-impact polystyrene or HIPS, often called "high-impact plastic" in advertisements. One commercial name for HIPS is Bextrene. Common applications of HIPS include toys and product casings. HIPS is usually injection molded in production.

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12 hours ago, Art Anderson said:

As for that 1/10 scale hollow Ranchero body, that would have been an acrylic (think polyester resin here) casting made by closing up the prototype hand-carved basswood mold patterns, ...

Art

Which is it?  Acrylic or Polyester?  Those are distinctively different types of resins.  Acrylic is not Polyester, and vice versa.

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On 3/20/2013 at 2:44 PM, Casey said:

There's a nice pic of the Revell USS Missouri mold in the Revell article, too:

missour-molds.JPG

 

Now that many of the vintage Revell molds are in the possession of Atlantis Toy & Hobby, they aren't wasting any time putting some of them to use. These pics were on Atlantis' facebook page, showing the Revell(?) USS Iowa molds set up in the injection molding machine, getting ready to be run:

atlantisussiowa1.jpg.d6c2bd2cc0d0185da59ee72605e8a002.jpg

atlantisussiowa2.jpg.2fe0bbb58e70069d0051c76809be62ff.jpg

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An interesting sidelight to the story of Pyro:  Years ago, at one of the annual Hobby Industry Association of America trade shows I attended in Chicago, I met the man who owned the company.  I had to ask just how he came to name the model company.   He replied that he was the president and principal stockholder of the Pyrometer Corporation (pyrometers are instruments used for measuring the temperature of surfaces, such as the grille at say, McDonald's).  He started Pyro the model company,  just to have something to get away from the stress and everyday grind at Pyrometer,  and simply drew on that corporate name for his new venture. 

Kind of a strange "hobby"--more like a second job, but he said he really liked being able to go to the Pyro factory, and just be able to enjoy something else for a respite--a second job that to him was very like having a hobby that also made him a little bit more money.

Art

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A good look at ejector pins, and an insert for what appear to be 1/16 scale valve covers:

RevellMoldEjectorPins.jpg

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On 10/11/2018 at 12:17 AM, peteski said:

Which is it?  Acrylic or Polyester?  Those are distinctively different types of resins.  Acrylic is not Polyester, and vice versa.

Thanks for pointing that out. Saved me the trouble.  :D

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Good reference for the various terms involved with injection molded parts: http://www.nttd-es.co.jp/products/e-learning/e-trainer/trial/en/mold/kiso/sample/step3/runner.htm

 

The below top image shows:

1) The sprue is only the channel into which molten plastic flows and enters the mold

2) The runners are what distributes the molten plastic to each individual part after it enters the mold

3) The gate is the entry point from a runner to each individual part

D2-02.gif

 

Below you can see what remains of the sprue, circled in red:

Blitz2.thumb.jpg.2540e279461323f0bd03c760b60689d1.jpg

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Kind of amazing how much clean plastic can get through those tiny gates connecting the part to the sprue

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You can even buy a 1/20 scale model of a plastic injection molding machine!

 

Nissei_Injection_Molding_Machine_Model_Kit.jpg

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3 hours ago, Mike999 said:

You can even buy a 1/20 scale model of a plastic injection molding machine!

Was that kit actually molded using that injection molding machine? :D

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On 2/19/2019 at 7:48 PM, Lunajammer said:

Kind of amazing how much clean plastic can get through those tiny gates connecting the part to the sprue

Yes, it is. From what I was reading earlier today, something about shear forces increasing as the molten plastic passes from the runners through the gates, increasing fill rate, etc. Pretty amazing stuff, really.

Here are are a few images of both the cavity and core sides of two different molds, all shared by Atlantis models vie either their blog or facebook pages. While they are molds for ships (USS Iowa is the one set up in the molding machine) one can still find many details common to injection molded model kit molds:

atlantisship1.jpg.b4d0e27d24cd860caa4f902746b376a5.jpg

atlantisship2.jpg.11b5533dc6b8abd64d5d9006cb2e0751.jpg

atlantisussiowa1.jpg.13bb1c676a2c59694a369de439974629.jpg

atlantisussiowa2.jpg.09463dd0e233b7252c72b8556cfe1729.jpg

 

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Interesting, top mold set looks like the cavity sides of each insert set were copper plated or made from a copper alloy.  They probably have been electroformed instead of machine carved.  

Any other toomakers on this forum??

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On 2/25/2019 at 3:05 AM, Flat32 said:

Interesting, top mold set looks like the cavity sides of each insert set were copper plated or made from a copper alloy.  They probably have been electroformed instead of machine carved.  

I figured it was heat tinting with some new or refurbished blocks added.

With it just metal against metal, it makes me wonder how they can even make make a part without flash oozing everywhere, but still get clean, tiny detail parts just fine.

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Those are copper-beryllium mold inserts. Read about copper alloys for injection molding HERE.

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10 hours ago, Lunajammer said:

I figured it was heat tinting with some new or refurbished blocks added.

With it just metal against metal, it makes me wonder how they can even make make a part without flash oozing everywhere, but still get clean, tiny detail parts just fine.

The surfaces are machined flat, and there are tons and tons of pressure holing the mold halves together.  The liquid plastic is also injected under very high pressure, so it fills all the cavities in the mold. As the molds wear out, the flat surfaces are not so flat, and that is where flash on parts comes from - the plastic starts to ooze in between the mold halves.

Edited by peteski

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