Cleaning molds is a key part of running a successful injection molding operation. There are two situations when mold cleaning is required: (1) offline when the mold is on the bench and is cold (room temperature) and (2) online when the mold is warm and still in the press.

Because of temperature differences, the cleaning solvents may have different degrees of effectiveness. Solvents that work well on the bench and evaporate at a convenient rate are usually flashed off very rapidly on a hot mold and aren’t in contact long enough to do much cleaning.

Solvents that work well at higher temperatures are much less aggressive and effective at room temperature. They take longer to evaporate or may even have to be wiped off. Using the wrong cleaner may result in poor cleaning or excessive time to accomplish the job.

The requirements of offline cleaners are primarily to dissolve resins, degrease and remove oil, mold release and sometimes rust. These cleaners generally are required to have a very fast evaporation rate. The best cleaners for this are hydrocarbons and naphthas. They readily dissolve greases and oils by merely flushing the mold with a heavy spray from top to bottom.

Mold releases and resin build-up may require scrubbing the mold with a cloth saturated with the cleaner. Pre-saturated mold cleaning wipes are a great mold cleaning option, especially for medical molding and clean rooms. The advantages of using such a cleaning wipe include the following:

Guaranteed sterile, lint-free and mold cleaning cloth.
Ideal for precision cleaning of your mold
Pre-saturated with the ideal amount of mold cleaning solvent included
Easy-to-use and non-hazardous disposal

A final option for offline cleaning is the use of a metal mold polish and cleaning compound. These products are typically used in paste form and require manual application as well as removal. The typical mold polishing paste contains a combination of cleaning solvents and mild abrasives that are designed to aid with the removal of all contaminants from the mold or die surface.

An added benefit of using such a polishing paste is the resulting sheen or luster that is generally left on the mold surface. Such a finish serves as a natural lubricant and release, thus minimizing the need for a mold release to be used later once the mold is put back into production.

Online cleaners are generally used to remove mold release build up, plate out of resins and light rusting of the mold. Often molds get plate out, which is due to the adhesion of resins [acetals such as Delrin or Celcon have been common offenders in the past] or fire-retardant materials. Such build-ups must be chemically removed from the mold surface in order to minimize potential part deformation. A resin-removing product can chemically work to break down the material and to aid with the removal of the unwanted resin from the mold surface.

As a general rule, cleaning solvents used on a warm or hot mold should be much slower evaporating. This allows for the chemicals to remain on the mold surface for longer periods of time, thus maximizing the cleaning potential.

When your production run is done, as the mold is cooling, apply rust prevention spray to the mold cavity, the plates and mold base to help prevent condensation from causing rust and oxidation. This is a “dirty” step since the hot mold will likely cause the oils in a rust preventive to liquefy and run. It still protects the mold until it is cool enough to pull and take it to the tool room to break it down.

Now that you are in the tool room, break down the entire mold system to look for gas buildup, color stains, water stains, resinous deposits and any other contamination that might have built up on the mold unit during the production run. Use a solvent-based mold cleaner and/or mold polish to remove these contaminants and degrease the metal mold and give you a clean mold that is immediately ready to make parts when it comes out of storage.

Now protect the mold with a long-term rust preventive that is rated for the length of time you need protection while the mold is in storage. The American Society for Testing and Materials (ASTM) testing method for rust prevention designates a long-term rust preventive as being effective for up to 5 years of indoor storage. If you are storing a mold longer than 6 months, we recommend that the entire mold block (cavity as well as mold base) be protected with an oil-based rust preventive.

It is also best practice to crack open and inspect any mold stored for longer than 12 months, looking for any signs of corrosion. You should reapply a rust prevention product following these inspections to ensure all critical surfaces are protected.

Has your mold been running PVC or any other gas-emitting resin? Be sure to use a rust prevention product with protection against not only corrosion due to moisture, but also oxidation caused by the presence of the acidic vapors released by these