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Molds and castings 2, liquid silicone rubber.

 

The mold is made from liquid silicone with a catalyst, and the casting is done with a two component resin. This process allow for a quick turnaround. The mold will be ready for use in about four hours, and the casting only a few minutes. There is hardly no smell involved with this method, which to me is one of the biggest advantages. Of course the price is higher, but the result is a high quality casting.

The products used in this sample are from "Alumilite." I use the "super casting kit." Click this link for there website.


 

  1. liqued silicone rubber.
  2. catalyst, needed for the silicone rubber.
  3. mixing cup and stir.
  4. resin component A.
  5. resin component B.
  6. synthetic clay.

This method cost a lot more money then the first one, however it is fast and simple to do, with better results. The mold is made with special silicone rubber and catalyst. A mold can be made from just about every part or model. Including the bottom when a two piece mold is made. To make a two piece mold you have to use a synthetic clay. The bottom of the part is placed in the clay on which a mold is made. After the mold has hardened, turn it over and remove the clay, and spray a special coating over the mold, to prevent the second mold to stick onto the first one.

The silicone rubber used in this method will reproduce every detail exactly, even a text written on the bottom of the surface will be visible in the cast. Before the mold can be made the model has to be finished and glued to the bottom of a flat surface. The silicone rubber pours like water and goes anywhere, so there has to be a water tight seal around the model. Excess silicone rubber can be removed with a scissor, when necessarily.

The silicone rubber has to be carefully mixed with the catalyst, before pouring it onto the model. The manufacture will provide the exact mixture to be used. The silicone rubber I use dries in 30 minutes, and can be used for casting after 4 hours. The manufacture recommends to wait 24 hours before casting, to increase the life of the mold. This mold can also be protected with some baby powder, after removing it from the model.

Casting resin is made from a two component resin, liquid as water. The mixture is simple: 1 to 1. As soon as the mixture is made it needs to be poured right away into the mold, since it dries in about 4 minutes. This time depend on the type of resin used and the ambient temperature. When the 2 components are mixed, a chemical reaction starts the hardening process, which will induce heat, until the resin is hard. I usually wait 15 minutes before I remove the cast out of the mold. The cast can be worked right away, like sanding, filing or gluing and painting.

For a better result, it is recommended by the manufacturer to warm the mold for a short time in a microwave, before the resin is added. Also, applying some baby powder, will increase the life time of the mold.

The final product looks a lot like the Artitec models, as it is almost the same material. After the caste has been removed from the mold it have to be sanded and filed a little to remove excess resin. Apply a coat of primer before painting, with any kind of primer and paint of your choice. Gluing more resin parts together or Gluing resin with another material is done with superglue.

Here is a photo session of this method.


The original part is glued on a styrene base and surrounded by styrene walls to keep the liquid silicone in place while poring, and drying.

With a measuring cup with water I can see how much silicone is needed, to make the mold. Now I can mix the exact amount of expensive silicone.


Here I add the catalyst to the silicone in a 1 to 10 solution.

Mix the catalyst and silicone until you have an even yellow color. (Or any other color depending the type of silicone and manufacturer.)


The result after mixing: looks a lot like custard. But I if it taste like custard?

Pour the silicone by starting at one corner and move evenly to the last corner to prevent air bubbles.


After 30 minutes drying time we have two pieces of "cheese".

This is the result after 4 hours drying time. By the way it smells just like lemon dish liquid.


Before pouring the resin, I first place the mold in the microwave for a short time. This will decrease the change of airbubbles.

 

Two component resin. Simply mix part A with the same amount of part B.

 

To safe on measuring cups I pour the two part resin in a different cup where I mix the two and  use this cup for pouring the resin into the mold. After a few uses it can't be used again since the left over resin gets hard quickly.

After 30 seconds mixing the two parts, it has to be poured into the mold, since the resin hardens in 4 minutes. This will give me about 2 minutes to pour the resin, not much time to make up for a mistake. 

 

The color will tell in what state the resin is. From liquid dark yellow to dry light yellow, just like the Artitec models.

The result: These are Fleischmann truck side frames from the plan V train set, which I need to make an plan U diesel train set.

 

This method I like the best. It is not cheap but the result is professional when done right, and this is an easy job. Also a great plus is the lack of bad smell and there are not as many air bubbles.


 


This page is last updated on 15 July 2012

NLMS - Dutch ModelRailroad - www.nlms.info