Metal on metal: General Industry Coverage

A pump on a waterjet machine generates the high-pressure water needed for cutting by taking low-pressure water into a cylinder, compressing the water with a plunger and then pushing the high-pressure water out of the cylinder. During a pressure cycle of intake, compression and expulsion, high-pressure components and polymer seals see the water pressure jump from two-digit inlet pressures to outlet pressures in the tens of thousands of psi.

According to Michael Wheeler, R&D engineer for waterjet machine builder Jet Edge Inc., there are 40 to 60 pressure cycles per minute in an intensifier waterjet pump and 800 to 1,000 per minute in a direct-drive waterjet pump. “These constant, frequent and dramatic changes in pressure are the reason most waterjet components eventually fail from fatigue,” he said.

To extend seal life, Wheeler designed a metal-on-metal, high-pressure, fluid sealing mechanism for static pressures up to 130,000 psi and received a patent for it. He noted the concept was initially tested using finite element analysis, and once the R&D group was confident the concept was viable, they built a prototype and validated the FEA results.

The seal is created by two convex curved surfaces, which contact each other tangentially along a single circular line, Wheeler explained. The curves minimize contact between the mating components of the seal and eliminate the surface damage typically associated with traditional metal-on-metal, high-pressure seals. He noted a traditional metal-on-metal seal usually consists of two cones. To create the seal, a convex cone is forced into a concave cone. The two cones slide against one another as the load is applied. About a third of each cone’s surface is in contact with the other cone, which can lead to cold welding and damage to the surfaces. “This damage can make the seal a one-time use item or require more force to create a seal on subsequent assemblies,” he said.

Courtesy of Jet Edge