With any tool, understanding how to use it will optimize the performance. Mold release is no different. Regardless of what you’re molding, there are five general guidelines to keep in mind that will ensure you get the most from your product.
- Keep it clean
Starting with a clean mold is the foundation for a perfectly working mold release system. When molds haven’t been properly stripped and cleaned, many problems can occur, including the following:
- Poor cosmetics
- Difficult demolds
- The need for more frequent touch-ups
- Ensuing stripping/cleaning occurring more often
It is often assumed that because a mold surface looks clean, then it is clean. Many polishes and cleaners may leave a mold looking shiny, but can leave waxes, oils, silicone or animal fats on the mold surface that are not compatible with semi-permanent mold release agents.
There are two parts to consider related to stripping and cleaning. First, there’s stripping and cleaning a mold (whether composite or metallic) that has build-up on the surface. Once any repairs have been made, the mold is then usually buffed and polished with a buffing tool to a high shine. Most shops perform a visual, qualitative measure of gloss, while some use a gloss meter to measure the surface and obtain empirical data.
The second part – stripping and cleaning of the polish from the mold surface – is most critical to a successful semi-permanent program. For the most difficult to remove polishes (those containing animal fats and silicones) a stripper should be used. The concept is analogous to paint stripper; you can clean up a surface, but to remove the paint, you need to strip it from the surface. Strippers can be chemical, mechanical or a combination of both. Water-based strippers are readily available to remove these fats, silicones, oils and other contaminants.
The next step is usually a tap water wash and drying of the mold (for water-soluble compounds and strippers) with cotton cloths, microfiber clothes or industrial paper towels, followed by a final proper cleaning with a solvent-based mold cleaner. Low-grade or recycled solvents shouldn’t be used for this step.
For easily removed polishes, usually a quick water-wash and then solvent clean are all that are needed. This eliminates the need for the stripping step. Soap is generally not recommended for the water wash. A clean mold should be streak-free, and masking tape should adhere well to the surface. When tape adheres well to the mold, it provides a non-scientific, but good guideline that the mold was properly cleaned.
There are numerous benefits for all that work:
- More parts between reapplication of the mold release
- More parts before build-up occurs
- Easier demolds (less force)
- Quicker demolds
- Mold re-conditioning/stripping is easier and takes less time
- Less mold wear/damage
- Better molded part cosmetics
- Fewer defects
Proper stripping and cleaning pays for itself many times over.
- Pay attention to cure time
Not following proper cure times for mold sealer and mold release agents can result in diminished release performance, a dull mold surface and other issues. Dedicating the time for the mold to cure properly will enable an optimal release.
To determine the best cure times, follow the mold release supplier’s recommendations for your molding conditions and the specific release you are using. For semi-permanent releases that cure at ambient temperature, 15 to 30 minutes between coatings is generally enough, however, the longer you can wait, the better the cure will be. (Semi-permanent releases allow for the production of multiple parts before re-application is required, thereby decreasing labor and increasing productivity.)
Temperature, humidity and airflow will all impact the cure of the mold release. Therefore, it is always recommended to allow for longer cure times at low temperatures. (The specific cure time is dependent on the chemistry and environment, but a general industry guideline is to double the cure times for every 10 degrees below ambient temperatures.) In high humidity environments, air flow is necessary to allow the semi-permanent sealers and release agents to cure.
- Avoid over-applying of release agents
On big molds with hard-to-reach surfaces, dripping, running or puddling is likely to occur if a release agent is over applied. Poor mold release application will prove particularly troublesome for parts with complex geometries.