An experimental classification of energies necessary to crimp seal copper and stainless steel tubing

Abstract

Crimping by means of deformation is a process commonly performed which restricts the flow of a substance through a tube. This process is unique by requiring large amounts of deformation between the inner tube walls which must lock and seal together allowing no flow to occur. This research studies how much energy is required to seal tubes constructed of copper or stainless steel between 0.125" and 0.25" encompassing all wall thicknesses available. Each cross section of tubing was cut, tightened into the end of a compression fitting, and plumbed through an integral vacuum sensor via plastic tubing running back to an oil-filled vacuum pump. This setup was mounted into a crimping fixture with interchangeable die sets within an Instron 5882 load frame and compressed at a quasi-static rate while monitoring load, displacement and vacuum level through a LabVIEW data acquisition program. All testing was analyzed to identify which die set produced the most efficient seal and required the least amount of input energy. Several sets of crimped samples were laid on their sides, mounted within epoxy and ground down to expose the sealing interface of the inside walls. From all acquired information, a new die set was constructed in an optimizing attempt to minimize both the leak rate and the energy required in creating the seal. The shape and contours of the optimized die set were the parameters changed from the 3 original sets. Final results showed that a shear shaped die set required the least amount of energy to establish a seal. The flat die created the best seal having the lowest resulting leak rate. The optimized die set created did not minimize the energy, but did produce a comparable leak rate to the flat set. This research develops a strict testing regimen to be followed when crimping a tube using a quasi-static deformation technique.