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
- Pre-release
- 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. If applying by hand, always use a fresh, clean set of cloths for each coat of release. A 100% bleached, white cotton cloth is preferred. As you continue to use the cloth, it can become loaded with dust, start to breakdown or the release agent can begin to gel in the cloth. All of these flaws can cause streaking on the surface, which is a tell-tale sign that it’s time to replace the applicator cloths with clean ones. Some releases’ production processes lend themselves to spray application of the release agent. When using these products, high-quality spray guns are the best choice of equipment. High-quality spray guns provide a better spray pattern/adjustability, controlled throughout and good atomization. Plastic spray bottles should be avoided. Because many solvent-based, semi-permanent mold releases are sensitive to moisture, it is important to use a dry air source when spraying; this is easily accomplished by equipping air lines with moisture traps.
- Know your product
There are many different types of semi-permanent mold releases available. Information about the product’s benefits, limitations, cure times, proper uses and more should be documented and well understood by the workforce. Key instructions from the supplier of the release system regarding use, handling, storage, etc. should be easily seen and/or available to workers and supervisors. It sounds simple, but the majority of composites manufacturing shops have no visible procedures for mold cleaners, sealers, releases, etc. How are operators and supervisors to perform their job adequately when procedures and data sheets are in an office drawer?
- Treat it right
Properly preparing and storing your products for future use will extend their lifespan. A tightly closed container can make all the difference with products sensitive to air and moisture. Also, semi-permanents need to be properly rotated while stored according to the mold release manufacturer’s recommendations to prevent old, out-of-shelf-life product from accidentally being used. Using products beyond their shelf life can lead to poor performance, as well as damage the parts or the molds. Solvent-based semi-permanent mold releases are often very sensitive to moisture. Leaving these products open or repeatedly exposing them to the atmosphere can cause polymerization in the can. This degradation may be invisible, but can compromise the performance. One way to reduce risks when using moisture-sensitive mold releases is to dispense the release into heavy duty HDPE bottles with flip-top caps. Siphon-type bottles are not suitable, as they draw in air each time they are squeezed. Low density or other plastics should be avoided. Open cans, (paint) trays, buckets, etc. of release should definitely be avoided. Large containers of release can be conserved with a desiccant drum drier or by purging with nitrogen after dispensing. Remember that these are general guidelines. Each molder should assess the materials they are working with and decide which combination of mold strippers, cleaners, sealers and release agents are most appropriate in their situation. Contact your supplier if you have any questions about your mold release programs. Your supplier should work with you to establish the right care and handling procedures. Scott Waterman is director of global sales at AXEL Plastics. Email comments to
swaterman@axelplastics.com. Disclaimer: Opinions, statements and technical information within the Tech Talk column are that of the authors. ACMA makes no warranty of any kinds, expressed or implied, with respect to information in the column, including fitness for a particular purpose. Persons using the information within the column assume all risk and liability for any losses, damages, claims or expenses resulting from such use.
