4 min

Wear resistance: surface roughness is key

Inside stories
Wear resistance: surface roughness is key

Wear resistance of a coating is the result of combined hardness and toughness. A homogenous surface roughness is key in this aspect, especially in situations where piston rods are used 24/7 under severe circumstances.

Prevention of slip-stick

Surface roughness plays a key role in the combined action of coating and seal set. If the surface roughness of the coating is suboptimal there is a realistic possibility of the infamous slip-stick phenomenon. This is caused by a friction coefficient that is too high or (too) heterogeneous. Slip-stick not only leads to increased wear of the seals but also produces extremely annoying sounds. The people who can tell from experience are the crew aboard large drilling vessels, where long piston rods move up and down all day long. As we do with all our coatings, during the development of TOPCOAT 107 we have also paid a lot of attention to the wear resistance of the coating surface, its homogeneity and to the stability of the grinding and polishing process.

Keeping out dirt

The joint forces of coating, seals, wiper and oil have to be reviewed meticulously, anyway, when it comes to wear resistance and reliability. When contaminants enter the cylinder through the wiper there is an instant effect on wear, regardless of the quality of the coating. Grains of sand, salt crystals, and other contaminants lead to abrasive wear. Water, especially in combination with salt, affects the friction coefficient, contaminates oil and increases the likelihood of corrosion. Performance reliability and correct functioning of the cylinder are greatly reduced by these effects. As an experienced coating supplier we collaborate with our customers’ engineers on a regular basis to achieve the best possible reliability of the entire cylinder system.

Seal wear tests

Coating and seals have to be viewed as one system. Because it is of essential importance to know the influencing variables when engineering a cylinder, we have joined forces with two major seal suppliers. At the moment TOPCOAT 107 is being tested in several different seal setups to measure wear of coating and seals. One important variable is surface roughness. The final results will have to wait but for now we can tell that the wear of our durable, hexavalent-chrome-free TOPCOAT 107 is so small that it cannot be measured after 1.000km of distance travelled over the seals. Moreover, the seals are also not affected.

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