A tube expander is a device that is used to increase the diameter of a piece of metal tubing. The tube expander is comprised of several individual sections of steel placed around a threaded shaft with wedge-shaped nuts on each end. The entire assembly is held together by a spring encircling each end. The assembly is slid into the end of a piece of tubing, and the tube expander is tightened, drawing the wedge nuts inside of the steel sections. As the wedges are drawn into the sections, they are forced outward, expanding the tubing.
Most tube expanders come in a set of two or more different sizes. The sizes are small to large in most cases, with the small size fitting small copper tubing and the large size working with the exhaust pipe. The benefit of using a tube expander with a small copper tube is found mostly in plumbing applications. When plumbing, long, straight lengths of tubing can be used and then sized with a tube expander to fit nicely around another piece before soldering it tight. This requires no fittings or couplings, and the joints are tight.
Automotive exhaust systems are readily created from lengths of straight pipe with the aid of a tube expander and a pipe-bending machine. The vast array of automobile types make it nearly impossible for repair shops to stock systems for all types of vehicles. Most automotive exhaust repair shops use a template to bend an exhaust system for a particular vehicle and use a tube expander to create joints for the sections to fit together. Once the system is completely fit together, the joints can be held tight by installing a clamp around the joint flange or by welding the two pieces of tubing together.
When using an expander on a large or thick piece of tubing, it is often necessary to heat the tube to aid in the expansion. By applying heat to the tube, it becomes more pliable and the expander does not need to work as hard in order to expand the tube. When deciding to use heat, it is imperative that the expander be removed from the tube before heating. The application of heat while the expander is inside of the pipe can cause the expander to seize and break. It is also a good idea to spray the inside of the tube with a lubricant, such as an all-purpose oil, to aid the tube expander in sliding inside the tube as it opens.