When choosing plating for your mold or mold components, you must first identify the problem to be solved or the problem to be prevented. The first question you should ask is “What is the cause of this problem? Is this problem the result of corrosion or wear?” If the component has previously been plated, this may be difficult to determine. Have your plating vendor look at the component to determine if it has been plated and if so, what type of plating was used.

Abrasive wear can occur on compression molds that use mineral or glass-filled materials. These materials can cause a scouring action on the mold surface. In transfer and injection molding of thermosetting materials, wear often is detected in the high flow areas such as in the sprues, runners, gates and portions of the cavities and cores that are directly opposite the gates. In injection molds for thermoplastics, wear most commonly appears on the surface opposite the gate.

Most damage results from continuing to run the mold after flashing occurs. However, there are other sources of damage of which to be wary. These sources can include water contacting unplated surfaces, causing corrosion; water condensing in the molds; seepage through porous metals; and leaky pipe fittings and “O” rings.

Where chillers are used for mold temperature control, condensation of moisture on the mold surfaces can sometimes occur even while they are in full operation. Careless handling of hoses and feed lines during hookup can leave water on the mold surface. Corrosion is progressive and even if the molds are stored after being sprayed with an antioxidant, a few drops of water or condensation can cause tremendous and costly damage.

Another source of damage is attacks from acids. These acids may form after exposure to corrosive materials generated by thermoplastics decomposition (often due to overheating). Overheating can occur in the platicizing cylinder, the hot runner system or in the mold cavities as the result of too small gates, or inadequate venting or cooling systems. During the molding of PVC, a small amount of hydrochloric acid is formed, which is extremely corrosive to the mold cavity.

Electroless nickel, by its very nature, is an excellent corrosion barrier for most mineral acids, whereas these acids will attack chrome. Stainless steels also can be susceptible to attack by chlorine or fluorine containing plastic, leading to pitting or stress corrosion cracking. This can be eliminated with a high phosphorous electroless nickel deposit over the stainless steel.

With so many different types of molding and even more types of materials available, there is no easy answer as to which coating will best enhance performance. An investigation into these coatings is worthwhile because if your molding operation is left unprotected, it can create corrosion, erosion, materials flow or release problem. The proper plating can make all the difference. Before you make that critical decision, call your plating vendor of choice and ask which coating will work best for your application.