Using High-Hardness and Low-Friction Coatings to Increase Mold Durability

Used to protect mold components and molds from corrosion and wear, two of the most popular low-friction coatings include electroless nickel plating and hard chrome. Coating technologies, already being highly engineered, must continue to evolve in response to several things:

  • The aim of improving part release and polymer flow
  • Between tool components, the need to avoid galling
  • Tighter dimensional requirements on more complex tooling geometries

Low-Friction Coatings Being Used on Molds

For the last couple of decades, numerous low-friction coatings for molds have been available and based on a range of metals. In just recent years, no fewer than five more have made an appearance. Making high-end coatings worth a second look is the growing use of any number of things including the following:

  • Flame retardants
  • Wood fibers
  • Metal powders
  • Higher percentages of mineral and glass fillers contained within high-performance resins
  • Other potentially corrosive or abrasive materials

While raising release performance, low-friction and high-hardness coatings can impart significantly higher resistance to corrosion and wear. Reducing maintenance, the thin metal films can also extend tool life.

The Trouble with Molds

What causes tool corrosion? The following can have a detrimental effect on tools:

  • Spillage from hoses during hook-up or ill-fitting pipe fittings and O-rings.
  • Perhaps due to too-cold chillers, condensing in the mold.
  • Seepage through micro cracks.
  • The contact of untreated mold surfaces by water leaks.
  • Trapped gases scoring tool components through accelerated corrosion due to inadequate venting.
  • Due to overheating, bromine- or chlorine- containing additives and resins becoming corrosive.

The realization by molders and die makers that their components need the proper coating in order to achieve higher quality parts and productivity gains is a step in the right direction. Because of this realization, materials with lubricious surface characteristics, low friction, and low energy characteristics, were developed.

Steadfast and True

While being old standbys, electroless nickel and hard chrome are, for some time to come, likely to remain major players. You know what they say, “If it ain’t broke – don’t fix it!”

Even from high glass-containing plastic compounds, a proven defender against wear is hard chrome. The coating can, however, wear down due to the presence of micro cracks and the non-uniformity of the plating. Maintenance and visual inspection are required.

On the other hand, with a lower hardness level than chrome, electroless nickel is still a viable plating material. In thin deposits, it can be coated uniformly and used on components having dimension tolerances that are more critical, as well as the precise sizing of cavities and cores. Under flash chrome coatings, it can also be used for dimensional buildup.

In a nutshell, corrosion resistance is offered by nickel, whereas wear protection is offered by chrome.

Today’s new and improved high-hardness and low-friction coatings are specially designed and engineered to provide the best of both worlds to the mold maker – lubricity is added as a bonus, in some cases.

Mold Coatings

Mold coatings come in seven categories which are as follows:

  • Impregnated polymers
  • Thin-film hard coatings
  • Surface-hardening treatments
  • Metallic plating
  • Metallic/PTFE co-depositions
  • PTFE-infused metallic
  • Thin inter-metallic

To metal substrates, these can be applied in a number of manners including PACVD, CVD, PVD, and more. Depending on the process, coating thicknesses can be more or less uniform, and generally range from as high as 8 µm down to 0.5 µm.

Low-Friction Coatings from A&A Coatings

For more than 70 years, A&A Coatings has been supplying thermal sprayed coatings for numerous industries. We use the newest techniques and materials and are capable of tailoring a coating to precisely suit your needs. Our research and development team is constantly striving to improve and advance our industry as a whole. If you’d like to find out more about our low-friction and high-hardness coatings, contact one of our knowledgeable representatives today.

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