As we saw in part 1 of this series, bearings, gears, rollers, and other precision components can experience excessive wear in applications with metal-to-metal interaction, repetitive friction at high speeds, or where little to no lubrication is present. To address this problem, product engineers and component manufacturers often turn to specialized PVD (physical vapor deposition) coatings, and in this month’s conclusion, we’ll take a closer look at how specialized PVD coatings increase surface hardness and durability for potential applications such as bearings, gears, and rollers to significantly increase lifespan under high load conditions.
POTENTIAL APPLICATIONS: BEARINGS
Bearings often suffer from severe and disproportionately distributed abrasive wear. A coating such as BALINIT C is particularly suitable for case-hardening as well as ball- and roller-bearing steels because it can be applied at temperatures under 392 degrees Fahrenheit (200 degrees Celsius).
The PVD coating can be applied not only to inner and outer races and cylinders but also to the balls in ball bearings in a highly uniform coating thickness of 0.5-1 μm. The slight increase in roughness is offset by the good burnishing qualities of the coating, which smoothes the raceway of the inner and outer rings, providing additional protection against scuffing and pitting.
Bearings in the soft calendar rolls of paper machines frequently experience smearing. Not only does PVD coating reduce the possibility of smearing, but by making the bearings harder with coating, it has been shown that the life of these parts can be increased by a factor of three or four. As a result, paper mills are able to hold off on bearing replacement until the calendar roll needs regrinding, significantly reducing costly production downtime.
Similarly, cylindrical roller bearings in compressors are often exposed to low loads and vibrations, causing potential smearing. Applying PVD coating to the bearings removes any such possibility.
POTENTIAL APPLICATIONS: GEARS
Gears experience similar wear conditions. The PVD coating significantly reduces scuffing and pitting in gear as well. In fact, BALINIT C has been shown to quadruple the service life of high-speed gears.
The standard FZG C test shows that the fatigue strength is increased by 10-15 percent over case-hardened but uncoated gears. In the test, the failure criterion for gear service life was defined as single-tooth wear of 4 percent due to pitting.
The main factors in these improved figures were the lower local surface pressure (Hertzian pressure), which resulted from reduced friction in the rolling contact, and the superior running-in behavior of BALINIT C.
Coatings can also benefit worm gears, where lubrication is not always enough to protect helical-gear transmissions against friction and wear.
The sliding motion and the force between the worm and gear faces make it difficult for a lubricant film to form. For this reason, the gear is most often made of bronze in order to avoid scuffing.
In service, however, the teeth of the bronze gear wear away quickly and the gear must be realigned or replaced. Coating the steel worm with a carbon-based coating can improve reliability and performance by reducing wear on both the worm and the bronze gear.
POTENTIAL APPLICATIONS: PUMPS AND COMPRESSORS
Screw spindle-, vane-, gear-, lobe-, and centrifugal pumps often function in abrasive and poorly lubricating media. This may be cooling media in grinding machines such as screw pumps and internal gear pumps. BALINIT coated screws provide the ideal combination of hardness and low friction for preventing wear in such poorly lubricated conditions.
Similarly, industrial compressor components, such as reciprocating pistons, screws or valve plates can undergo extensive wear when oil-free operation, dry gases, refrigerants, high or low temperature limit the use of lubricants.
In addition to designing and manufacturing PVD coating equipment, Oerlikon Balzers offers coating services at more than 140 coating centers worldwide, including sixteen locations throughout the United States.
According to Dr. Florian Rovere, director of sales for precision components in North America, companies like Oerlikon Balzers also have the R&D capabilities to tailor coating solutions to meet unique requirements. In addition to coating thickness and hardness, properties such as structure, chemical and temperature resistance, and adhesion can be precisely controlled.
In most cases, no alteration of the formula for the coatings is required, as it is already optimized for high load, high friction environments.
“I find engineers are most surprised about two factors when learning about these specialized PVD coatings,” says Berger. “First, that the coating can be applied in a thickness as low as .5 or 1 micrometers. The other is that these coatings can last the lifetime of the machine or systems it is in, despite the difficult operating conditions.” ◆
Oerlikon Balzers is one of the world’s leading suppliers of surface technologies that significantly improve the performance and durability of precision components and tools for the metal and plastics processing industries. For more information, call 408.375.4408, email firstname.lastname@example.org, or visit www.oerlikon.com/balzers.
MODERN PUMPING TODAY, February 2018
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