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What is the difference in a resin kit and let's say just a model you'd buy at say Walmart?

Thanks

Edited by Arbatron

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I am not a expert and I'm sure you will get some precise answers but for a quick rundown I will try and help.

So it is a different compound or material used to make models in smaller production runs. Mostly from vendors who make models or kits per order in their home as a side business.

I only own two different resin makers kits and both happen to be at the top of the resin world ( modelhaus and Morgan automotive detail) and they are very similar to plastic and far as feel and smoothness.

Since resin is hand made and made to order kits can well exceed $75 for a quality piece.

On the flip side their are some crude castings that will be body only for as little as $10 and than it is up to the builder to make or finesse it into a presentable model.

Also a lot of resin production is in the form of parts for adding on to plastic kits to add detail or correct issues with accuracy.

I've yet to build a resin kit so I can't comment on approach to building and in my research the only info I've gathered is you can only use super glue (ca glue) and wash well before applying paint.

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That's a good general answer from Greg.

Part of the rest of the story is that typical "just-a-model" kits are mass produced by large machines, made of poly-styrene plastic, using a process called "injection molding", under extreme temperature (to melt the plastic) and pressure (to force the molten plastic into molds). The development of the tools to make these models may cost hundreds of thousands of dollars.

"Resin" kits or parts are made by hand, one at a time as Greg notes, usually by pouring a 2-part liquid plastic compound (that hardens as it cures) at room temperature, into a silicone mold. After curing, which takes from a few minutes to a few hours depending on the exact material used, the hardened part is removed by dis-assembling the mold. The cost to produce these 'soft' molds is far far lower (under $100 if someone does all the work themselves) but it takes a high degree of skill and a lot of labor time to do a quality job.

Edited by Ace-Garageguy

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Mass-produced model kits are manufactured by a process called "injection molding," in which liquid (molten) styrene plastic is injected under pressure into hollow molds. Once the plastic has cooled and hardened, the resulting parts are popped out of the molds. An injection molding machine is a big investment... the cost to manufacture an injection molded kit can run into the hundreds of thousands of dollars, not to mention the physical space needed for the machines.

Resin is a completely different material than styrene. Resin kits (or parts) are made by the casting process... pouring liquid resin into molds. Once the resin sets, the parts can be removed from the mold. Resin casting doesn't require the huge injection molding machines or the huge upfront $$$ investment... that's why the aftermarket guys use resin instead of injection molded styrene.

The molds for injection molded kits are cut from tool steel and can cost many thousands of $$$ for just one mold. In resin casting, generally a "master" of the desired part is made, than a rubber mold of that master is made to use to cast resin copies of the master. The quality of the master (and thus the quality of the resulting resin parts) can vary among aftermarket vendors from nearly perfect to junk.

The resin casting process is relatively inexpensive and lends itself to small runs, so it's the perfect way for aftermarket guys to make parts. Injection molding is used for large runs–many thousands of models are made from one mold.

Resin is more brittle than styrene, and regular "model glue" won't work on it (you need to use either CA glue or epoxy)... but other than that, as far as building a model, resin and styrene parts are pretty similar.

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Pretty cool! Thank you all for the I depth answers. I've seen some ads for resin bodies that look pretty cool and I thought I would like to build one in the future. I think I will now. Lol

Thanks again

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If you do buy one do yourself a favor and make sure you read the instruction about cleaning/ degreasing the body before you attempt to lay down some paint.

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Most points were well covered but I wish to add a few. Styrene is injected under pressure. The heat is a byproduct of the pressure and many modern molds have liquid cooling to prevent them from overheating. Heat will degrade the styrene to the point of ruining it completely. No heat is applied during injection molding.

Most resins used in the hobby are urethane. They have two parts and produce a chemical reaction produces heats which cures the mixture. Most of these resins have agents in them which promote de-molding. If you use spray cans to paint, some of the chemicals in the paint will react with the release agents and produce fisheyes. That is why most people use degreasers to clean them up. If you airbrush your paint the cleanup is much less critical.

I have been pouring resin and rubber for over 30 years now and I can say the materials have vastly improved and fortunately my techniques have too! I think resin casting is one of the greatest things to happen to this hobby. It opens up the choices a builder has to an unprecedented degree.

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This is all new to me. And I mean everything. I built models as a kid. Painting them out of the box never prepping the body, using Testors glue in the orange tubes and getting glue finger prints all over it. Then I ended blowing them up with firecrackers. Now that I'm all grown up I thought I'd take a grown up approach to this hobby. If every question I ask gets answered the way this one has been this is going to be so much easier then I had thought. I'll have the knowledge. So it will only be my lack of skill holding me back. Lol. Thanks guys.

Edited by Arbatron

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... Styrene is injected under pressure. The heat is a byproduct of the pressure and many modern molds have liquid cooling to prevent them from overheating. Heat will degrade the styrene to the point of ruining it completely. No heat is applied during injection molding.

Heat IS routinely applied to facilitate melting of the feedstock pellets (in the processes I'm familiar with, anyway), and the amount of heat is dependent on the specific thermoplastic material being injected. It is true that the screw-compression process adds heat the the molten mix, lessening the amount of external heat necessary. It is also true that the temperature of the molten material must be controlled VERY closely to achieve correct cavity-filling without degradation of the thermoplastic.

From engineeronadisk.com, 46.2 INJECTION MOLDING

Basic process - Heat a thermoplastic material until it melts. Force it into a hollow (cooled) cavity under pressure to fill the mold. When cool remove the finished part.

Typical materials are,

- nylon
- styrene
- ethylene

A typical injection moulding machine is seen below with the covers removed. Plastic pellets are poured in the hopper, and finished parts emerge from the dies.

molding13.gif

Edited by Ace-Garageguy

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Having some 15 years of resin casting in my background, allow me please to offer some observations:

Bill, Harry, Andy and others have laid it out pretty well, especially regarding the upfront costs of injection-molding anything, particularly model kits.

In the general scheme of things, however, when injection molding is applied over large quantities of any product thus manufactured, the costs of producing that particular product, per piece, come way, WAY down. With resin casting, on the other hand, there's very little "up-front" investment to be made--the mastering is a lot simpler, making the molds is, while not cheap, VASTLY less than cutting steel dies for injection molding.

However, with resin casting, the "upfront" costs while low, are actually added back into the equation constantly, for as long as any item is thus produced, in that silicone RTV rubber molds have a definite, and short useful life--often as few as 25-30 castings before the rubber surfaces degrade to the point of producing what modelers would consider to be unsatisfactory qualit. RTV rubber itself is quite expensive. While I've not priced it lately, I suspect that this material now runs in the neighborhood of $17-$20 per pound--and it can take upwards of 5-lbs of RTV rubber to make a mold for a 1/25 scale car body. The polyurethane resin isn't inexpensive either--in fact it's several times more costly than the equivalent volume of polystyrene contained in a model car kit body shell. Add to these considerations the factor of human labor--resin casting is far more labor intensive than any injection molding process--and there you have the basis for the much higher price for a resin body or transkit. On the flip side, of course, most resin cast items are of subjects that pretty much don't have nearly the market potential needed in order to justify the really significant upfront investment.

Art

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