With the introduction of coiled steel approximately 100 years ago, welded tube and pipe mills became popular. A tube mill begins with an uncoiler, straightener, and shear end welder at the entry of the line. The "forming" part of the mill is made of a breakdown section and forming section that takes 3 to 6 passes. Each pass is made up of a lower and upper arbor containing roller die tooling which gradually forms the steel into a tube shape.

Several more passes are made to get the new tube ready to weld. The seam on the tube is welded by a solid state welder or high frequency welder. Sometimes the inner and outer bead are removed before the sizing section. There, the tube is made to conform to the desired dimensions. Finally the new pipe is cut to length.

Like it does with other metal forming lines, a coil end joiner shears ends of strips, butts them, and then makes a smooth weld so that the joined coil can proceed through the metal forming line. Maintaining continuous flow of stock coil metal through a processing line can cause productivity gains of up to 70% and reduce scrap production and tooling wear. There are several things to consider in choosing a coil joiner for a given processing line.

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For one thing, the joiner must do its shearing, butting, and welding before the accumulated coil is used up. With a strip accumulator between the coil joiner and the processing line, the minimum accumulator storage time will determine that upper limit to the coil end joiner's cycle time. Calculate the time required for shearing, fitting, and welding for the widest strip and heaviest gauge and add strip feed time to it to learn if a particular coil end joiner is appropriate for a given tube or pipe mill.

Another important consideration is the coil end joiner's duty cycle. When a power source halts during a welding operation, it usually follows too-frequent use near or at its maximum output. This causes enough heat to build up to trip a thermostat that shuts down the unit automatically to prevent permanent damage. Usually, variable displacement hydraulic units that shut down between cycles are enough to prevent overheating, however. But choosing water-cooled weld torches and choosing torches whose ratings exceed maximum requirements are an added buffer against overheating.

The material properties of the metals being processed, and their width and gauge ranges will determine the size and features necessary in a coil joiner. The carbon content in particular will determine whether weld normalizing is necessary. In some cases, joined coils are simply transport welds and are discarded as scrap, but in other cases, the joined coil ends can be used as part of the end product. For this to be the case, the weld has to pass through the mill both unbroken and without causing any mill damage. Welds should be flat with parent material thickness and strength if they are to be processed through to the final product.

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The gauge range for the application will determine the shear blade clearances and tonnage capacity. Shear force necessary to cut the heaviest gauge determines tonnage because then the strip width at the maximum gauge does not affect the shear force necessary. On some designs, shear blades are made with four way reversibility. This extends blade life and cuts back on necessary maintenance.

Coil joiners may be stationary or portable, and may be fully automatic or welder operated. Much depends on the particular application, the speed needed, and the type of material to be processed. But whether partly or fully automated, coil end joiners have the effect of boosting productivity and reducing wear on machinery that would result from it having to be frequently started and stopped to thread a new coil of metal in.