Monday, May 25, 2009

Product Review: Barnes Pinkysil moulding silicon and Barnes Easycast casting resin

Moulding and casting have been around for thousands of years but only in the 20th century and the advent of synthetic resins did they move out of the hands of foundrymen and the most gifted artisans, and into those of hobbyists and enthusiasts for engineering in miniature. The theory of three dimensional reproduction is far from rocket science and some basic arithmetic and a steady hand are all it really takes to generate copies of objects.

My previous experience includes learning the art at the Palaeontology laboratory of Flinders University of South Australia many years ago, where as an after-classes project I reproduced the skull of a Tasmanian devil in fibre-reinforced epoxy, out of plaster-backed two-part skin moulds. That was a complex job which took me weeks at an hour or two per session. More recently, I’ve worked in high-definition Alumilite resin out of Dow HS-III moulds for repetitive components needed for scratchbuild projects. Difficulty in obtaining these supplies in Australia at this time lead me to look for alternatives, and I came across the following excellent supplies.

Barnes Pinkysil is an addition-cure silicon mouldmaking rubber with a mixing ratio of 1:1 by weight. It has a short working time, only six minutes pot-life before it begins to gel, so from adding part B to the part A already in the mixing cup, you’ll be finished making your mould in six minutes or never, less if the weather is against you! It was a hot day when I did my mould-making, so I cooled the chemistry for ten minutes in the fridge, which got me around eight minutes. It also has a rapid demould time, as little as twenty minutes, though leaving it an hour will help ensure maximum mould life -- anywhere up to a hundred pulls, even more, which is excellent value. The rubber catches extremely fine detail and cures to a solid consistency, with 400% elastic distortion at the tear. The colour is of course bubble-gum pink.

Hand in hand goes Barnes Easycast, aptly named as it is truly free of mess and fiddling. No pre-heating the mould, no talcum-powdering the mould to encourage bubbles to move away from the surface, in fact very few bubbles in evidence at all. Mix by volume in a measuring cup, stir with any old thing (a popsicle stick is just fine), and after about forty seconds the exothermic property makes itself felt. When the container is getting warm you know it’s time to stop stirring and pour. You have a nominal pot life of two minutes, I try to have the castings poured in a count of 90 to 100 seconds from commencing stirring, as the mixture gels and changes to white rapidly after that point. Demould the castings in twenty minutes or less, again depending on the heat of the day and the thickness of your castings: thin sections and edges cure last.

The cured resin, snow-white in colour, has a slightly flexible character, not an issue with chunky castings but it might be a problem with thin, fine shapes. The material is then workable with all standard techniques: it can be sanded, ground, sawed, drilled, and accepts all regular paints and primers. One word of caution if bonding separate castings to make a whole structure: superglue bonds Easycast instantly -- no slippage time at all, so if your parts accidentally flop together while you’re still applying the glue, it’s adios muchachos. Ask me how I know... It’s a good job it’s so easy to mix a couple of drams more and pour it into the moulds, you can have replacement parts while you’re thinking about it with other systems.

I took the shot above while making the parts for the Arrowhead project, posted last week. Note another casting curing at the same time. The darker chemistry is the resin, the lighter the catalyst. Below is the pattern, the mould, a pair of fresh castings and a completed structure made from the previous pull.

Pinkysil is not rated a hazardous substance according to national standards, Easycast is. Normal safety precautions apply, hand and eye protection, general cleanliness of the work area, and wash up before eating or drinking. The chemistry is flammable, so appropriate cautions apply with regard to sources of ignition.

Another recommended product is F-720 Dry Air Blanket by Chemlube, an inexpensive way to extend the life of your chemistry. It’s just what is sounds like – a liquefied gas which expresses from the can as 100% moisture free and inert. A two-second squirt into your resin bottles when capping them for the last time at the end of a session ensures zero moisture in the airspace of the containers, therefore nothing to contaminate the resin over time.

Between these products, you can be turning out excellent mouldings the same day you set up your pattern. At a current cost of around Aus twenty-something dollars each for a half-kilo (1 lb) pack, it’s extremely good value, and the small quantity ensures you can use up your supplies within their shelf life. If you’re working with bigger quantities, package sizes increase up to industrial volumes, but the general hobbyist will probably find the small packs more than adequate.

I bought mine from:

Adelaide Moulding and Casting Supplies
735B Marion Rd
Ascot Park, South Australia 5043

Ph: (08) 8277 7278

AMCS offer online discounts, which guarantee your savings against larger quantities of other chemistry coming longer distances from industry-oriented suppliers.

Double thumbs-up, superb products which I’ll be using in future.

1 comment:

petra said...

many thanx from greece for the wonderful review... very helpful!!!