# Turning Polyester resin



## ed4copies (Jan 25, 2013)

In this thread:  Plastic?

the question was asked, how are the numerous types of plastic blanks  different from each other.  I gave a short (possibly terse) answer and I  was surprised how much interest the thread got.

Our new librarian (and one of my good friends), Wayne suggested that we  try to get answers that were "library-worthy" and incorporate this as an  article.  Honestly, I think that is such a good idea that I am starting  a few of these threads and I will incorporate the information into an  article for Exotics and make it available to the IAP Library.

Polyester Resin:
Also known as Silmar 41 and other "trade names", including "Castin Craft", and a product from US Composits---someone may have that name and add it here, please.

Polyester resin is "poured in the kitchen or garage", it is a resin that is mixed with a catalyst (usually MEpK).  This causes a chemical reaction that is exothermic (gives off heat).  The amount of catalyst used will effect the turning characteristics of the final product.  The more catalyst, the higher the temp during curing and the more "glass-like" the final product becomes.

Polyester resin can be clear or dyed one or several colors.

When very little catalyst is used, the resulting pen blank is easy to turn and will "peel off in ribbons" with a sharp turning tool.  It is very easy to sand and polish, using Micromesh or Novus or buffing.  

When a great deal of catalyst is used, one such product is called "Inlace acrylester".  This is extremely "chippy", and takes a fair amount of tool control to achieve the "ribbons" turning off.  I consider Inlace Acylester one of the most difficult of the plastics to turn successfully, but it does polish EXTREMELY well and the available colors are striking---because the resin sets very quickly, so the colors do not blend, they remain intense.

Again, please contribute YOUR thoughts and experience with polyester resins.


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## InvisibleMan (Jan 25, 2013)

I'll run a test soon on the effects of different amounts of catalyst.  I'm a skeptic that more (within reason) equals more brittle.  But, I've never tested the exact recipe under the exact same conditions with different amounts.  

I'll do it without pressure on clear blanks.  I'll turn, drill and thread a barrel with single start 12mm die and 9mm tap.

4 drops/oz, 12 drops/oz.  

Good?  Changes?


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## BRobbins629 (Jan 25, 2013)

The use of liquid colorants such as Mixol brand can significantly increase curing time, but offer a different look than powder pigments.  It may increase cure time to days or longer but can always be accelerated in a warm toaster oven.   In my experience powder pigments have little effect on cure time.  

The viscosity of uncured polyester resin changes with temperature.  Warming the resin slightly before casting often helps the inevitable bubbles rise to the top.  As these resins are actually blends of polyester polymer and styrene monomer, the later can be used to thin the resin for even lower viscosity.


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## LagniappeRob (Jan 25, 2013)

> Silmar 41  ... and a product from US Composits



I'm sure you already know this, but Silmar 41 is from US Composites.
They also make 435 - "Standard" PR  & Silmar 249

IIRC, the 435 isn't "water clear", I don't remember about 249. I know they say it's clear, but not sure about "water clear"

Edit 
They make some others too... that I'm pretty sure would not be very good for pens - like their "EB" product.


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## ed4copies (Jan 25, 2013)

This is GREAT input!!!   Thank you all and let's have some more!!!!


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## Ed McDonnell (Jan 25, 2013)

US Composites = Silmar 41  = Interplastics SIL95BA-41  Good for thicker casts

US Composities = Silmar 249 = Good for very thin surface casting.  Not ideal for thick casts.  Resin is greenish tinted, but cures water clear.

Styrene is the solvent for PR.  Silmar can be thinned by adding up to 10% styrene.  This will increase shrinkage in the final product as it cures, but greatly reduces the viscosity for casting objects with small openings.

Eye protection, gloves and a chemical mask should be used when working with PR.  It should not be used indoors without adequate ventilation to the exterior.  

Silmar 41 recommends 10 drops MEKP per ounce.  Plus or minus depending on temperature and the type of additives being used for color / texture.  

Here are links to Silmar 41 mixing instructions, MEKP MSDS and Silmar 41 MSDS:

http://uscomposites.com/pdf/MEKPDirections.pdf

http://uscomposites.com/pdf/plyst/mekp.pdf

http://uscomposites.com/pdf/plyst/silmar41.pdf

Any exterior tackiness on cured PR can be eliminated by either warming the cured resin or by applying a thin coat of wax to the cured tacky surface.  Alternatively, "surfacing wax" can be added to the resin when poured and this will eliminate all tackiness on the cured resin.  It will also prevent any additional coats from adhering so should only be used on the final cast.  This is sometimes useful for rotocasting.

Ed


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## ed4copies (Jan 25, 2013)

EXCELLENT information, Ed!!

Do you have the MSDS for the other plastics?  If so, please post and I will add to the article---- if not, I will find them----THANKS for that input!!


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## Ed McDonnell (Jan 25, 2013)

Hi Ed - Here's the MSDS for Silmar 249:

http://uscomposites.com/pdf/plyst/silmar249.pdf

Ed


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## Ed McDonnell (Jan 25, 2013)

Powerdered (atomized) metal powders can be mixed with PR to give the look and luster of metal without losing any of the machinability of PR.  The end product looks like cast metal.

Do not mix copper metal powder with PR.  It will supercharge the curing and set up before you can pour it.  Bronze and brass (copper alloys) seem to work without any problem.  

Ed


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