How the Right Techniques and Mold Release Prevents Bubbles in Your Cast

Oct 4, 2021, 10:33 AM by The Stoner Molding Solutions Team
Industrial molders who employ cast molding to create various parts know that one of the most frustrating aspects of the process is when there are bubbles in the finished casting.

Rows of polyurethane seal rings with tiny bubbles in them.Industrial molders who employ cast molding to create various parts know that one of the most frustrating aspects of the process is when there are bubbles in the finished casting. Not only does this defect frequently lead to scrapping the part, but it also wastes time, money, and materials in having to make the part again. Savvy industrial molders use a high-quality mold release and cleaner to prevent bubbles in polyurethane applications.

At Stoner Molding Solutions, we are experts at providing mold solutions that improve efficiency, reduce scrap parts, and produce high-quality products. We know how to get your products to release with fewer defects like bubbles and which of our products will work best for your needs.

Read on to discover how we’ll help you reduce the number of bubbles in your finished casting through our products and general casting tips.

What Causes Bubbles in Your Cast?

Before learning how to create a bubble-free cast product, you first need to understand what causes bubbles in your casting.

Most frequently, bubbles are either trapped air or moisture. You can introduce these problematic air bubbles into your mold by whipping air into the polyurethane, pouring the resin into the mold too quickly, or molding at improper temperatures. Additionally, moisture can get trapped in the polyurethane by using a water-based mold release or excess particles in the resin.

For Bubble-Free Castings, Follow These Tips

Whether air or water causes the bubbles in your cast, there are some general tips to follow to ensure your finished casting comes out with fewer or no bubbles.

A bottle of Stoner’s 93234 CUT Mold Cleaner1. Start with a Clean Mold

By using a solvent-based mold cleaner, like Stoner’s 93234 CUT Mold Cleaner, to clean the mold surface, you’ll remove possible contaminants and build-up that could cause bubbles in your mold. In addition, this cleaner is designed to displace moisture and evaporate quickly, leaving little chance for water to get on your casting materials.

When you start with a clean molding surface, you can ensure your mold release agent adheres properly, releasing your parts with fewer defects.

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A bottle of Stoner’s G402 Nix Stix X-9032A Mold release2. Be Aware of Water Contamination

After you clean the mold, you need to use a mold release that dries quickly and does not contain water. Our G402 Nix Stix X-9032A Mold Release is an aerosol, silicone-based release agent specifically formulated for cast elastomers. It features a precision spray pattern for lower transfer risk.

A light coating on the mold ensures that your parts have fewer defects, like bubbles. However, choosing the best mold release agent for your product depends on the materials and type of cast you’re performing. Contact our experts for advice on the right product for you.

3. Protect Molds When Not in Use

If your production facility is closed for weekends where molds aren’t in use, or you need to store your molds for an extended amount of time, you need to protect them from excess moisture during the storage process. A high-quality rust preventative will form a protective barrier between your production mold and outside contaminants, like moisture and oxidation.

This barrier will help reduce the possibility of contaminates getting on the mold and casting materials when used again. Our A612 Short Term Rust Preventative is perfect for overnight and weekend protection.

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A bottle of Stoner’s A612 Rust Preventative4. Avoid Introducing Air Bubbles when Mixing or Pouring

Besides using the right products that protect your molds and form a protective barrier, you also need to use the correct techniques when handling the polyurethane mixture, especially in its liquid form.

When mixing a resin and hardener, don’t overmix and introduce air into the formulation. When pouring into the mold, ensure you pour slowly enough to minimize the number of air bubbles that get into the mold. You can also vacuum de-gas the mixture to remove any air bubbles.

5. Use the Correct Temperature to Cure

Another cause of bubbles in your finished casting is not allowing the polyurethane resin to have the proper temperature to cure. The wrong temperature to cure the polyurethane resin will not allow any remaining air pockets to expand and pop during the curing process, leaving bubbles in your final casting. Warming the resin before casting can help avoid air bubbles.

6. Provide Adequate Curing Time

Besides the right temperature to cure, you also need to allow the product to cure for the proper length of time. You can increase the holding pressure time for adequate cooling and curing to reduce air bubbles in the final product.

Request A Sample Today to See How Our Products Can Help Your Cast Molding

When casting polyurethane products, you need to ensure you’re using the right products and techniques to reduce the possibility of air or moisture bubbles in the finished product. You can remove air by not introducing air when mixing or pouring and using the correct temperature and time to cure. Also, eliminate moisture from the mold by using high-quality sealers, cleaners, and rust preventatives.

Request a sample today if you’d like to see how well our products can help your casting process! Stop wasting time and money throwing away scrap parts due to bubbles. Instead, trust our products to help you improve the quality of your finished pieces!

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