PEEK Corrosion Resistant Coating? Here's A 'PEEK' At This New Engineered Thermplastic

PEEK corrosion resistant coating, you say? What's PEEK? This comparatively new engineered family of thermoplastics: PEEK (polyether etherketone), PEK (polyether ketone), and PAEK (polyaryl etherketone) are partially crystalline engineering thermoplastics (plastic polymers) that can be used at high temperatures. These resins have excellent chemical resistance. Their high thermal stability comes from rigid ketone and phenyl groups, while their high strength and thermoplastic state below the decomposition temperatures come from the ether groups.

These compounds can have melting temperatures in excess of 650 degrees Fahrenheit, with mechanical properties retained to about 500 degrees Fahrenheit.

Tensile properties are comparable to most engineering thermoplastics. Creep resistance is outstanding and may sustain large stresses over a useful service life without measurable strain.

Wear rates and friction are becoming increasingly important against metals. Corrosion protection, too, is often an integral part. For these reasons, PEEK (and related polymers) are becoming increasingly important, as demands on them for their structural properties grow, particularly at elevated temperature.

Friction from composites of thermoplastic vary in a unique way from metals in that their asperities (surface irregularity) will deform much more under load. Consequently, friction between a thermoplastic and metal surface is typically characterized by adhesion deformation disproportionally lower to load. The primary mechanism is adhesive wear, which is characterized by fine particles of polymer removed from the surface. This is a good illustration that the surfaces are wearing properly. (Large gouges or corrugations in a polymer surface would suggest not adhesion wear, but abrasion wear or the material's pressure velocity limit was violated.

Wear factors of PEEK plastics, PEK or PAEK appear much less affected by load and speed components, independent of PV. Wear performance seems to be better at low pressures and high speeds, rather than high pressures and intermediate speeds. All display excellent resistance to wear over wide ranges of pressure, velocity, temperature, and counterface roughness.

Properties of some of the PEEK coating or PEEK plastic plastic are now characteristic of PTFE, PFA, and other corrosion resistant compounds. The advantage is in markets demanding greater resistance to abrasion, higher temperature environments, too. Next time consider PEEK corrosion resistant coating.

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Anodizing Wear Resistant Coatings Instead of Hardened Tool Steel?

Today, anodizing wear resistant coatings for aluminum surfaces can be made harder than tool steel. How? Through modifications of anodize, a process common in the finishing industry for electrolytic treatment of metals to form stable films or coatings on the metal surface. Anodized aluminum or magnesium, for example, are typically associated with functional coatings like hard anodize, also known as 'hardcoat'.

And they can be made so much more.

In the anodic coating process, unlike electroplating, the work is made the anode, and its surface is converted to a form of its oxide that is integral with the metal substrate.

Generally, it's agreed that the ceramic oxide coating consists of two layers:

The initial layer, which forms right at the surface, is called the barrier layer. It is a comparatively thin, dense, and nonporous form of aluminum oxide.

Next form the outer, heavier layers of the anodic coating. They are more porous and are stacked somewhat like parallel tubes extending through the layer, from the outermost surface down nearly to the barrier layer.

It's important to recognize that, unlike plating, whose thickness accumulates by depositing more and more onto the outermost surface, the anodic layers form by oxygen transfer from the underlying aluminum surface and force existing layers outward.

This means that oxides newest forming are always located between the metal surface and the last, most recently formed alumina oxide. Consequently, the greater the thickness, the lower the density of coating at the outermost surfaces, based on longer solvent action of the electrolyte. Consequently, for maximum wear resistance, more is not always better.

A factor to consider in your design, such as close tolerance bores, bearing diameters, dowel holes or threads, is that the resultant growth portion of the coating is a fractional percentage of the total coating thickness. Hard anodize, for example, will typically result in 50% penetration and 50% buildup.

Keep in mind that buildup is normal or perpendicular to the surface and sharp corners should be rounded to avoid chipping.

To anodize aluminum, one of the most important factors influencing oxide formation is composition of alloy. Reaction of all the various possible alloying or impurity constituents can result in coating voids or disruptions, while other constituents may themselves oxidize in the conditions of anodizing and lessen the intended properties.

Depending on electrolyte, a wide range of thickness can be obtained. Coatings produced in sulfuric acid electrolyte, for example, can be as low as 0.0001 inch (2.5 um) to as high as 0.003 inch (75 um).

Anodic coatings have a definite cellular structure. Imagine individual cells with pores down their centers totaling millions per square inch. This makes for excellent dyeing and sealing. Sealing processes make the coatings non-absorptive and include, immersion in boiling de-ionized water, steam, or nickel acetate.

De-ionized water is often preferred as a sealing solution for its ability to react with anhydrous aluminum in the outer layers of the film. A mono-hydrate of the oxide is formed, which occupies greater volume than the alumina from which it was formed. The result is a reaction to close down and plug the pore structure.

Structures of hard anodizing can be supplemented with a variety of materials, including Teflon (PTFE) waxes, oils and other compounds, to lower friction or add release. And because these compounds penetrate the ceramic with negligible surface growth, making their wear resistance simply exceptional.

So, next time, reduce the weight in your design. Instead of steel, think hard anodizing wear resistant coatings for aluminum.

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