Bulk mold release is an affordable and sensible option for high-volume users in a range of molding applications for the thermoplastics, polyurethanes, composites, rotational molding, rubber molding, and investment casting industries. One of the most critical aspects of using bulk liquid mold release is the application to the mold surface. Simple or symmetrical molds can often be coated by brushing or wiping. More complicated, and detailed mold designs however, require a spray application, which provides a thin, even coating for best results while avoiding waste.
Special considerations and procedures:
Spray application of mold release is straightforward, however, there are special considerations, and procedures required to optimize the process. Spay application means atomizing the release into droplets, transporting those droplets onto the mold, while capturing any flyaway particles and vapor. It also differs from paint application as sprayable mold release is less viscous, often does not contain solids, and atomizes very easily.
Users should pay special attention to the commercially available spraying equipment on today’s market. Generally, about 99% of spraying equipment is used for paints and coatings. This type of automotive or commercial painting equipment is often oversized for mold release applications. A typical spray tip for painting is sized at about 0.080mm-in compared to 0.030mm-in for mold release applications. Since mold release liquid is less viscous than paint, manufacturers need to work closely with their suppliers to target their unique needs. Some of the leading U.S. suppliers of spraying equipment made for mold release include Graco, Binks, Spraying Systems, and Unist.
The process of spraying:
Spraying mold release begins by supplying pressurized release to the spray gun. This can be accomplished by gravity or suction, but is more typically accomplished with a pressure vessel (pressure pots) or pump. The spray gun combines the mold release with air to help disperse the release, and propel the particles toward the mold surface. The most common type of spray gun is the high-volume, low-pressure (HVLP) gun, which combines pressurized air with the mold release to atomize the release into a fine mist. A second set of air ports are used to shape the spray pattern from round to a fan-shaped pattern to allow more even coverage. HVLP guns offer broad coverage, high evaporation of carrier solvents, and highly favorable spray patterns. Some of the disadvantages of HVLP spray guns are possible contamination, messy work environments, excessive heat, and potential ventilation problems.
Using a high-pressure pump and a special airless sprayer allows mold release to be applied without the use of any atomizing air. Atomization occurs due to high pressure and a small spray tip. This tends to give a slightly more coarse spray with fewer flyaway particles than HVLP. Other key advantages include reduced vapor, and fewer ventilation concerns. With air-assisted airless spraying, the spray pattern can still be adjusted with a fan adjustment, allowing a round pattern to become more oval shaped.
Leading suppliers of airless systems include Milwaukee Sprayer, which produces the SureShot refillable, rechargeable, portable compressed air sprayer, and Graco, which offers the Merkur air-assist, and airless packages.
An important consideration with HVLP spray guns is the use of supplemental dryers to ensure a moisture-free environment. Most HVLP spray systems utilize refrigerated dryer systems which are not totally efficient. Moisture can react with the mold release or the molded plastic components, resulting in manufacturing problems, lost efficiency, and ultimately poor products. To counteract moisture problems, Beach filters are highly recommended as a supplemental dryer. They are inserted in the gun’s air supply.
Automatic spray guns and efficiency:
Another alternative for high-volume users are micro-scale spray guns which are typically used for hobby or automotive paint repair. These have the advantage of being a smaller size, thus useful for smaller molds. Transfer to molds can be enhanced using electrostatic spray guns, like the Pro XP from Graco. They charge particles to 20,000-40,000 volts. Those particles are then attracted to the grounded mold, helping to improve efficiencies.
Finally, automatic and computerized spray tips are available. This allows for spraying processes to be controlled by pneumatic or electrically triggered controls. Equipment like Spraying Systems Co.’s Precision Spray Control can be used for automated molding lines. They can control pressure, air, and cycle time, thus cutting mold release spraying costs.
High-volume users of mold release can evaluate a range of spray gun systems on the market. However, most important is that users follow important procedures in order to optimize high-volume applications. The system must be right-sized to apply the mold release, any air used must be dried again prior to use, and operators need to be trained on the correct amount to apply. Training on cardboard or paper can help determine the correct amount of release to spray. Proper ventilation and disposal systems must be in place. While Stoner offers tips and recommendations on spraying procedures, users should always consult with an industrial hygienist to ensure compliance with all the necessary regulatory and safety requirements. Once the process is dialed in, users should have years of trouble-free spraying.
Stoner Molding Solutions is a leading supplier of industrial mold release agents in the polyurethane, plastic, rubber and composites fields, based in Quarryville, Pa. For more information, call +1-717-786-7355 or visit www.stonermolding.com