Polyurethane is one of the most diverse materials used to manufacture both small, flexible parts and hard plastic parts. This versatility makes it the perfect material for a wide variety of commercial and industrial molding applications, from automotive products to commercial insulation and consumer goods.

However, polyurethane is both sticky and aggressive, making it challenging to remove cured polyurethane from mold surfaces since it builds up over time. In extreme cases, parts can become stuck inside the mold. Efforts to remove stuck parts can cause irreparable damage to the mold, resulting in lost production and expensive mold replacement.

If you struggle with cured polyurethane buildup in your molding operation, read on for our best tips to remove cured polyurethane and prevent heavy buildup in the future. These methods work best when working with aluminum, steel, or other metal molds and tooling.

If you require a solution to remove cured polyurethane from silicone, plastic, nylon, or vinyl molds, contact Stoner Molding Solutions for recommendations from our experts.

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Removing Cured Polyurethane from Metal Molds & Tooling

Did you know that cured polyurethane buildup can also occur in overflow areas when liquid urethane is injected and the mold is closed? This buildup can cause defects in molded parts, resulting in increased scrap.

Heavy buildup can also make it difficult to remove pieces from the mold, resulting in damage to the part, the mold, or both. Since buildup can range from minor to heavy, here are a few ways our products can help with your level of buildup.

Light Buildup on Molds

Many molding operations find it helpful to clear light buildup from molds after a certain number of molding cycles. The correct number of cycles for your operation will depend on the type of products you manufacture and the details of your molding process.

Using a light cleaning solvent like Stoner’s B510 Light Duty Cleaner softens and loosens the light buildup of cured polyurethane in just a few minutes. Simply apply the solvent with a brush, wait a few minutes, and wipe down the mold with a clean cloth.

After you’ve cleaned the mold, it will be necessary to reapply your mold release agent to prevent parts from sticking so they won’t be as difficult to remove in the future.

Heavy Buildup on Molds

Heavy buildup often requires a more aggressive cleaning method to remove cured polyurethane altogether. There are two ways to remove cured and heavy buildup, and they depend on whether you typically use heat in your molding process or produce parts at room temperature.

In either case, we recommend applying Stoner’s B505 PolyOff Heavy Duty Polyurethane Remover following the steps below.

Heated Molds Procedure

If needed, molds can also be cleaned at room temperature. When possible, mold cleaning can be performed on room temperature molds at the end of the day or during any scheduled downtime.

1. Bring the mold to normal operating temperature.
2. Apply B505 PolyOff cleaner into the mold cavity.
3. Close the mold.
4. Keep the mold heated for 30 minutes to 1 hour or until the cured polyurethane can be scraped from the mold surface with a scraper or brush.
5. Scrape or brush off the cured polyurethane.

Note - Removing cured polyurethane from the mold will also remove your release agent in most cases. Be sure to reapply your release agent before putting the mold back into production.

Room Temperature Procedure

Operations that produce parts at room temperature can schedule mold cleaning for the end of the day (or during any scheduled downtime).

1. Apply B505 PolyOff cleaner and allow the mold to soak overnight (or during multiple days).
2. Scrape off the softened and loosened polyurethane.
3. Reapply release agent as necessary.

Procedures for Heavy or Hard to Move Molds

Molds that are large, heavy, or otherwise difficult to move can be cleaned using a thicker solvent with the ability to cling to vertical surfaces.

Stoner’s B505 PolyOff Mold Cleaner is specifically formulated to cling to vertical mold surfaces, allowing you to soak molds overnight without moving them. Simply brush B506 PolyOff Gel onto the entire mold and use the heated or room temperature procedure described above.

Workspace Areas

Mold manufacturers that rely on pressure chambers to expel all the air from parts can end up with polyurethane spillover on work areas and tools. Stoner’s B510 Light Duty cleaner is perfect to handle cured polyurethane on metal work surface areas. Simply apply, soak, and wipe down the area.

Uncured polyurethane can also be quickly wiped from work surfaces with the same light-duty solvent.

Cleaning/Clearing Injection Equipment

Polyurethane buildup can also create problems with injection equipment. Stoner’s B505 PolyOff can be used to soak metal injection equipment parts to remove cross-linked urethane.

Prevent Future Buildup with the Right Mold Release Agent

While the methods and mold cleaners mentioned above will help you effectively remove cured polyurethane from your molds, if you find you are doing frequent deep cleaning, it may be time to reevaluate your molding process.

Using the right combination of mold sealer and mold release agent is a fundamental step that can prevent buildup, sticking parts, and cracking, while increasing uptime and productivity.

At Stoner Molding Solutions, we offer a full suite of mold release agents for Cast Elastomer, Flexible Foam, and Rigid Foam processes, with formulations designed to optimize your production process and improve your bottom line. Plus, our team is happy to help you find the right solution for your molding operation.

Count On Stoner for All Your Molding Needs

Stoner Molding’s industry-leading experts, chemists, and engineers are here to help you find the right combination of mold releases, sealers, cleaners, rust preventatives, and lubricants to maximize your production and profits. We’ve formulated, distributed, and manufactured our own products for more than 80 years and offer world-class service and same-day shipping. Contact us for a free product sample today.