The typical configuration of a swivel is a round housing and spool. Hot finished seamless tube is used for the housing and ductile iron round for the spool. The housing material machines well and it's weldable, and the spool material is readily machinable. Finding material that's close to size is usually readily available. This allows the material to be purchased at an affordable cost and minimizes the machining.
Recently we've had a number of inquiries on swivel designs that need the housings to be square, rectangular and also irregular in shape. This presents issues that aren't present with the typical swivel. The weight and size of the material available that's close in size to the finished part is difficult to find. This adds to the cost and machine time. Sometimes the material needs to be ordered milled two sides to reduce set up and machine time. There's usually a lot of material removal required. The weight of the finished part can turn out to be a fraction of the weight of the purchased raw material. The machining is a two-step process involving different machine centers. The initial machining is done to remove excess material and to create basic features that are needed in order to aid in the set up for the higher end machine. Here the more intricate external and internal features are done to complete the finished part. The housing bore, seal and flow grooves are machined; along with the surface finishes and radii completed to their specification.
This usually doesn't create an issue for the installation of the seals and the assembly of the swivel. When the housing has ports located on the bottom surface, it creates a problem in the Production Test Stand for performing the pressure test. There's a torque test that is performed and is either accepted or rejected. However, the part needs to be removed to install the port fittings on the bottom for the pressure test. The swivel is then placed back into the test stand and laid on its side to run the pressure test; which is also ran on a pass/fail basis. For more information about hydraulic swivels, check out our “What Questions Should I Ask Before Choosing a Hydraulic Swivel?” blog post.
Thomas Van Veldhuizen