A tube mill is a type of mill that uses belts to feed large amounts of raw materials into a shop. Because the belts are so large, it takes less space than a lathe or a table. Tube mills make both pipe and sheet metal by taking a flat strip of material from a bulkhead and repeatedly roll shaping the strip until the end of the strip meets with a weld puddle at a weld pore. Then the welding process fuses and melts the exposed ends of the tube to form a welded tube, and the melted material exits the arc pore as welded tube. There are several types of these machines and each has its own benefits. In this article, we’ll look at some common types of tube mills, how they operate, and their general design.
Most common is the roller type of mill. It consists of a series of concentric rolls that are fed by belt tension into a spindle. As the rolls pass through the spindle, they continue to be rolled without abrasion as they reach the corners of the ring. When they reach the center of the ring, they are struck by a counter-rotating wedge that forces the entire strip to be drawn into a weld puddle. The resulting welds are very strong and often require fewer filler rods to complete the same diameter range as an untreated strip. They have less wear resistance than treated strips, and because of the close proximity of the centers of the rolls, they have fewer cold welds than treated rolls.
A similar tube mill is the rotary vane type. Like the roller mill, it also feeds rolls of flat steel but rotates on two vertically positioned wheels. The difference lies in the way the rolls are directed. In the rotary vane style, the innermost roll is fed first and turned by a solenoid. The outermost roll, which is usually a coil or a rod, follows and is turned by an arc that is powered electrically via welding electrodes.
Arc tube mills utilize a variety of different shapes. Some are designed for use with wire sizes ranging from a twin wire to 16 gauges, while other tube mills can be designed to weld thinner alloys of different shapes. Some can even weld three different shapes at once, which increases the ability to bond more shapes together in one process.
An important part of working with tube mill blanks is the selection of electrode material. Gas tungsten electrodes are typically used in these mills because they are a good match with the unique properties of flat steel and allow for a more efficient energy transfer. Merely pre-ground electrodes are not as effective because a working plasma comes with the metal when the electrode material cools after welding.
After welding, the electrode material needs to be shielded from all heat and gas flow. This shielding is achieved through a specially designed attachment to the work area. Shielding also minimizes the chances that the arc will spill or leave a black mark on the sheet metal. One other option is to allow the workers to perform final testing prior to welding begins. By doing so, any possible problems with electrode performance will be found out before the start of the welding process and any changes can be made without having to disturb the welded sheet.