It’s often stated that form follows function. This is no truer than in the specification and design of a tube mill line.

Customers need to firstly specify what tube size or tube size range will be produced. And it’s what production volume, quality level, and any particular characteristics such as tube end condition, tube length tolerance, welding seam position, etc.

Generally, tube raw material decides welder type. And required welder output is determined by tube diameter, wall, and milling speed. If customers don’t choose the speed, the mill builder can determine it based on annual production requirements, estimated uptime, number of shifts, and expected changeover frequency. With this information, the mill builder can also calculate horsepower requirements.

Roller stand size and number and roller shaft diameter is determined by tube diameter, wall thickness, and material being formed. The ratio of thickness to diameter, the surface finish, and tube shape also directly affect roller stand number. And other factors, such as the need to preserve existing rollers or specific welding seam position, may also affect the design.

After roller stand number and required horsepower are finalized, the number and placement of motors can be determined.

Most customers want the mill that is large and sturdy, and they often choose oversize machine. But the mill must be large enough to do the job, shafts heavy enough to withstand bending, and castings large enough to house shafts and bearings. And the mill must be small enough to minimize distance between points where roller contact steel strip.

Shaft diameter and its effect on the throat diameter of rollers must also be considered. A larger shaft diameter requires a larger throat. That means more roller cost, and a greater number of possible regrinds.