In order to make a Urethane Molding, there are 2 main processes
Safety First:
Since we are going to work with the chemicals which are irritable to the skin, safety equipment such as gogles, lab coats, gloves, and respirator should be worn before working. Some of the chemicals we will are vaporized, the working room should also be well ventilated.
Procedure for casting a mold
The first step in casting a mold is to make a mold box. A mold box can be anything that will hold the liquid chemicals during the pouring. For our mold box, we used a plastic cup cutting the bottom off.
Since a mold box required one side of contact. The smooth surface board layered with a contact paper will be used to place the mold box on. Kleen Klay Regular will also be used to hold the box in place.
The master piece will be placed in the cup (at the center) and secured to the contact paper with double sided tape. In order to prevent the master piece from stuck in the mold, the Synlube - 1711 Release Agent must be sprayed on the piece before pouring the chemicals.
To make a mold, we will use Por-A-Mold S 111 (silicone-polyuretain compound) which comes out separately as a curative and a prepolymer. Before using, we have to re-mix these two chemicals first. The ratio by volume for the curative and prepolymer recommended by company is 1:1. Since the mixture will take 15 minutes to harden, do not take too much time mixing the chemicals.
Be careful not to have a bubble in the mold while pouring the chemicals.
After pouring the chemicals into the box, leave it overnight (the mold will take around 24 hours to cure). When the mold is cured, separate the mold from the box by using a knife.
Procedure for casting parts
Placing a sheet of contact paper on a smooth table surface and have all your materials (chemicals, spatula, beakers, etc) in proximity of your work. The mold we had done from the first part should be placed on the contact paper and is ready for work.
Before pouring the casting parts chemicals into a mold, make sure that there is nothing left inside the mold crevices. To prevent the parts we cast stuck in the mold, spraying some Synlube -1711 Release Agent into the mold crevices as well.
To make parts, this time we will use Por-A-Kast Mark I (another silicone-polyuretain compound) which come out separately as a curative and a prepolymer. As same as what we did in the first part, remixing these two components with 1:1 ratio of volume. Mixing the compound immediately with a stir for about 30 seconds.
Pouring the chemicals into the crevices until the voids are all filled up. Since this compound chemical harden so quick, the time allowed for mixing and pouring is just about 1 min. After pouring, use a flat spatula to even out the top of the mold.
It will take around 30-45 minutes for the parts to harden. Taking the parts out of the mold by simply bending the mold.