Improper urethane molding practices can lead to less-than-desirable results, but there are a few tips that may help improve the process. All urethane resin components should be mixed thoroughly before they are poured into the mold. Air bubbles must be completely removed from the mixture before the curing process begins. Use a screen sieve funnel and begin at the lowest point of the mold when pouring the mixture. Allow sufficient curing time and remove the finished product carefully to avoid damage.
Urethane molding requires careful preparation to produce a good finished product. Most resins contain fillers that can sink to the bottom of the container over time, and it is important to mix the material thoroughly before pouring it into the mold. A paint can shaker is the best way to mix the resin, but an electric drill also works well. The drill should be fitted with an impeller blade and held at a slight angle to prevent air bubbles from forming during the mixing process. Remember to mix the individual components before combining them.
The presence of unwanted air bubbles is one of the most common problems encountered during urethane molding. As a result, certain precautions must be taken during every phase of the preparation process. After the materials have been thoroughly mixed, it is best to pour the mixture through a wire sieve to further eliminate air bubbles. The sieve should be funnel-shaped to narrow the flow of the mixture into the mold. Begin pouring at the lowest point of the mold, and complete the process within a few minutes of mixing the individual components.
Another good way to remove unwanted air bubbles during urethane molding is to vibrate the mold during the entire pouring process. There are a couple of different ways to accomplish this. A portable hand vibrator usually does a good job with the help of an assistant. A bench-mounted vibrator also works well if an assistant is not available. Placing rubber pads beneath the bench legs may help to increase the amount of vibration produced.
Although the mixing and pouring portion of urethane molding must be accomplished quickly, the curing process should always be allowed to progress slowly. Read the product manufacturer’s curing-time recommendations carefully to avoid premature demolding. Great care must be taken when demolding the finished product to avoid damage. Forcing compressed air around the edges of the mold usually works best. Wedge-shaped shims may also be inserted along the mold’s edges if compressed air cannot be used.