Wear-resistant ceramic coatings

Reactive maintenance procedures force the plant to make quick fixes where parts are reinforced, patched, rebuilt, or completely replaced to get back up and running as soon as possible. If repaired or replaced parts are put back into service without somehow protecting the parts against recurrent damage, the service life of that equipment will be less predictable.

04/08/2015


The performance and longevity of industrial piping that can be protected using ceramic coatings. Courtesy: HenkelReliability and predictability are pivotal to the operational success of industrial equipment. In aggressive industrial applications, preventive and scheduled maintenance maximize the life and structural integrity of large and small metal components such as mixing vessels, pumps, hoppers, housings, tanks, chutes, pipes, and centrifuges. These heavy-duty parts are often exposed to aggressive slurries, sand aggregates, particulates, and large stones that can damage and abrade even the hardest reinforced steel substrates.

Damage to components can be caused by mechanical attack, chemical attack, corrosion, or by a combination of these three modes. Mechanical attack involves dry particulates or slurries dropping onto and traveling through chutes, pipes, pumps, and other components. Over time, even soft flowing materials can abrade and wear away at hard alloys such as AR400 steel. As the surface metal weakens, thin layers are gradually stripped away from the parent substrate, reducing its thickness and structural integrity.

Chemical attack and corrosion physically change substrates through chemical reactions. For example, corrosion occurs when iron oxidizes, leaving a very weak and loose layer of oxide on metal surfaces. Corrosion can be concentrated locally, forming a pit or crack, or can extend across a wide area, uniformly corroding an entire surface. If left untreated, active corrosion below the surface of a high build coating can cause the substrate beneath to weaken, ultimately causing a critical failure in the structure.

In chemical attacks, damaging chemicals passing through metal equipment can react with and eat away at the surface of the metal, causing layer-by-layer damage. Courtesy of HenkelIn chemical attacks, damaging chemicals passing through metal equipment can react with and eat away at the surface of the metal, causing layer-by-layer damage. As damaged layers are continuously stripped from the parent substrate, the thickness and structural integrity of the metal part gradually decrease. 

Examples of wear are easy to find in any industrial facility. Pump casings and impellers wear as a result of abrasive slurries and solids, cavitation, and chemical attack, wearing down internal sections of the equipment. Some of the common wear areas include the cutwater, wear ring seats, impeller vane tips, and inside the volute. In the case of pipes and ducts, most wear occurs at elbow bends where fluid flow changes direction. Some plants are forced to repair or replace duct elbows every three months, adding significantly to labor and material costs. In quarries and mines, iron ore can severely abrade reclaimer buckets due to the continuous sliding caused by the digging and reclaiming action.

Many facilities only conduct maintenance on large components once damage becomes extremely apparent or a catastrophic failure occurs, such as a hole in a sidewall or a part dropping off of equipment. When critical failure occurs, equipment must be shut down for an unscheduled, costly, and time-consuming repair. Reactive maintenance procedures force the plant to make quick fixes where parts are reinforced, patched, rebuilt, or completely replaced to get back up and running as soon as possible. If repaired or replaced parts are put back into service without somehow protecting the parts against recurrent damage, the service life of that equipment will be less predictable and the chances of another unscheduled critical failure increase.

To deliver long-term protection from wear, abrasion, chemical attack, and corrosion, epoxy-based wear-resistant coatings containing ceramic fillers can be applied to vulnerable metal surfaces to protect them and minimize planned and unplanned downtime. These coatings act as a sacrificial and renewable working surface preserving the structural integrity of the base substrate and preventing mechanical attack, chemical degradation, and corrosion caused by abrasive particles, slurries, and chemical exposure. These engineered coatings can be applied to worn equipment for restoration or to new equipment before it is placed into service.

How does a wear-resistant coating work?

Ultra-smooth and high gloss, epoxy-based wear-resistant ceramic coatings increase equipment efficiency and life expectancy. These coatings can be a quick and cost-effective remedy to damage because parts are returned to service with little interruption or process downtime.

Wearing compounds are two-part epoxy systems containing ceramic beads or ceramic powder, and silicon carbide. The epoxy-base polymer that adheres the ceramic material to the substrate is formulated to be extremely robust, offering excellent performance under high-compression and high-impact loads. These coatings cure in temperatures between 55 F and 90 F, with cure time dependent on mass and temperature—the larger the mass, the faster the cure. This is a result of the exothermic heat generated by the epoxy reaction during the cure process. Higher substrate and air temperatures will also result in accelerated cure.

Because ceramic is inert, it does not react with most materials that come in contact with metal components. Ceramic coatings resist harsh chemicals and withstand temperatures to 450 F. The size of the ceramic material—powder or bead—used in the wear-resistant coating directly corresponds to the size of the particulate that will ultimately damage metal components. For large particulates and stones, maintenance professionals should use coatings with the largest available ceramic beads. For fine slurries or wastewater, fine powder ceramics are sufficient to inhibit damage.

Designed for a wide variety of operating environments, wear-resistant coatings fall into seven distinct categories: putties with beads, high-temperature formulations, ultra-high-temperature formulations, fast-set materials, brush-on formulations, sprayable formulations, and impact-resistant materials.

Putties are thick pastes best applied using a trowel or a gloved hand on surfaces within arm’s reach. These wearing compounds withstand abrasion from fine to coarse particles in locations including elbows, cyclones, and other areas where fluid changes direction and causes turbulence. Various sized bead fillers incorporated into different putty formulations give them distinct strength and hardness characteristics to resist wear based on the fluids or solids running through the system.

High-temperature formulations that resist up to 350 F are standard performers. Ultra-high-temperature wearing compounds resist temperatures to 450 F, commonly found in ovens and hot water or hot fluid slurries. These wearing compounds are often used to protect the substrate from elevated temperature chemical attack.

Fast-set materials are used when equipment and parts need to return quickly to the production line. These compounds cure to functional strength in as little as three hours.

Brush-on coatings are self-leveling, low viscosity materials that can be applied with brushes or rollers, or simply poured onto a substrate and allowed to coat the desired area. At just 1/8- to 1/4-in. thick, brushable coatings work best on equipment carrying slurries with very fine particles such as sand, metal chips, shells, or seeds. They can easily be applied to areas that are out of arm’s reach, like the inside of pipes, and will reduce friction caused by moving fluids in applications like fluid pumps.

Sprayable coatings are low-viscosity materials similar to brush-on materials, but achieving just 0.020-in. thickness. When applied with a spray gun equipped with an atomizing mix tip, these ultra-thin coatings can be applied overhead, used on large application areas and on hard-to reach, intricate, and small-diameter parts like curved components and elbows. Because these coatings are so thin, they should not be exposed to high turbulence or impact.

Impact-resistant coatings are specially formulated to absorb shock and withstand damage from medium to large sized aggregate such as rocks, coal, and other substances falling onto or otherwise striking a substrate. These materials are often found protecting chutes at the end of conveyor belts in mining and construction.


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