Functional Coatings and Tight Tolerances: No Need to Worry About a Costly Redesign

It is understood that a component designed to need a functional coating would have its tolerances accordingly compensated. However, if the component you’re dealing with already has tight tolerances to begin with and a functional coating is determined to be a need after the fact, there should not be a stack up issue in the vast majority of instances.

For example, a typical “tight” tolerance is +/- 0.1mm. Converted to inches, this is about four thousandths of an inch, or .0039” (we will round up to .004” for simplicity’s sake).

In the coating industry, the most universal form of measuring a coating’s thickness is microns.

One thousandth of an inch is equal to 25.4 µm (microns). So four thousandths of an inch would be equal to 101.6 µm. Tighten the tolerance even further, let’s say +/- 0.05mm, and it would be 48.26 µm if you were to equate it to a coating thickness.

If it is assumed that the manufacturer of the component is not taking up the entire tolerance on the high side, a functional coating should not present any issues at all in terms of stack up, regardless of which type of coating you apply.

Fluoropolymer coatings, such as Whitford’s Xylan series, Henkel’s Emralon 333, or Chemours’ PTFE resins, provide dry film lubrication and non-stick release and are applied in film thicknesses of 15 to 25 microns in order to be functional.

Magni and Doerken zinc-flake coatings, which provide salt spray corrosion resistance in excess of 1000 to 1500hrs, are typically applied in thicknesses of 12 to 24 microns depending on the OEM specification.

Dow Corning’s Molykote D-708 anti-friction coating provides lubricity and corrosion protection in as little as 11 microns.

Although any coating applicator cannot center their process (read about that here), there should be enough “wiggle room” within the tolerance where coating peaks should not pose a problem. If coating thickness is extremely critical, a rack-spray process should be utilized.