Riverhawk engineers have been working to develop new coating options that will enhance durability and further extend the life of our metal seals used in our high-pressure hydraulic nuts.

A hydraulic nut is a device designed to replace large diameter hex nuts. The hydraulic nut contains its own internal pressure cell and when used in conjunction with a high-pressure pump, it can easily generate and retain very high axial clamping loads in bolted joints. Learn More about Hydraulic Nuts

Riverhawk hydraulic nuts are commonly provided with one of the following sealing methods; Elastomeric/Thermoplastic seals or Riverhawk’s integral metal to metal seal lips.

Elastomeric (or thermoplastic) seals can be preferable in applications when bolted joint members have high misalignment or require frequent (daily) assembly & disassembly. One of the disadvantages of this type of seal is the elastomers inability to function properly when exposed to extreme temperatures and its tendency to wear/degrade over time. This type of seal may need to be periodically replaced to maintain the highest sealing integrity at the pressures used in hydraulic nut applications.

A metal seal can be desirable when the hydraulic nut will experience high service temperatures (exceeding 200°F), long-term service (years) between pressurization cycles, dynamic/cyclic service, or high levels of vibration. These environments have been historically tough on many elastomeric seal types with a high likelihood of experiencing seal leakage during hydraulic nut removal. The metal seals used in Riverhawk hydraulic nuts are designed to address the temperature and wear concerns associated with other seal types. Additionally, Riverhawk’s hydraulic nut seals are capable of higher hydraulic pressure limits which allows for increased preload capacities or a smaller radial footprint when compared with a similar hydraulic nut using elastomeric or thermoplastic seals.  

To further enhance our standard metal seal performance, technical research was performed evaluating a variety of surface coatings ranging from chemical conversion coatings, electrodeposited coatings, PVD coatings, and diffusion coatings. Many factors were considered when narrowing down the potential candidates, such as: wear resistance, corrosion resistance, coatings ability to be applied to different base metals, manufacturing processing impacts, environmental waste impacts, lead time and costs. The top candidates were selected to run through standardized accelerated wear testing to compare the relative performance of each coating versus the baseline uncoated sample. A couple of images are shown below highlighting two standout coatings showing their effectiveness in improving base metals wear properties.

Sample #1 – Uncoated

Sample #2 – Coating 1

Sample #3 – Coating 2

The testing performed simulated the high-pressure metal to metal contact based on the seal interface but over-exaggerated the magnitude of the motion between the sealing surfaces. All tests were performed without any high-pressure lubricants, which further added to the wear that would be expected during normal hydraulic nut operation. Large improvements in the base materials resistance to wear were observed for both coated samples.

Riverhawk’s engineering team continually strives to make improvements that push our products to the forefront of our industry. Contact Riverhawk Company Engineers to see how we can help solve your next demanding bolting challenge!

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Charlie Heysler

Charlie Heysler is Riverhawk Company’s Applications Engineering Director who has been with our organization since 2010. Charlie’s background at Riverhawk includes innovation and customization work for bolt tensioning, hydraulic tooling, and hydraulic pump applications. In addition he has regularly traveled to customer sites to support product applications and share knowledge of Riverhawk’s capabilities. Charlie holds a Bachelors of Science degree in Mechanical Engineering from Clarkson University.