Tube and Pipe Manufacturing Case Study

Raising the Bar on Tube and Pipe Manufacturing Throughput

Tube and pipe manufacturing is all about maximizing the number of feet per minute. Tube mills using older technology may produce only 200 feet per minute while some mills using newer technology run up to 800 feet per minute or more. The shears that cut tubes to length need to cut very quickly, and the effects of that cutting (burrs and dimples at the tube ends) need to be removed or repaired just as quickly to keep up with the shear. Another in-line process, I.D. flash removal typically results in additional material handling and labor to remove the cut scarf from the inside diameter of the tube in an off-line process. Buckeye Manufacturing of East Palestine, OH has developed a new in-line tube processing, that supports the functions of scarf flushout, dedimpling and deburring at processing speeds up to 80 tubes/minute, with headroom to run even faster in the future.

One of the key factors that enables the new machine to reach such high performance levels is its extensive use of hydraulic motion, controlled by a new programmable 8-axis motion controller, the RMC100 from Delta Computer Systems, Inc. (Vancouver, WA).

There are several unique elements to Buckeye's motion control system design, including extensive use of absolute rotary position control. An example of this is the control of the ball valve that turns on and off the aggressive water blast that flushes the interior of the tubes as part of the scarf removal step. The rotation speed of the hydraulic motor that operates the ball valve must be coordinated with the speed with which tubes are transferred to the blowout station. The ball valve and the sprocket drives that move cut tubes through the burr-removal process are all driven by hydraulic motors that only turn in one direction, as opposed to typical hydraulically controlled motion which is back-and-forth. To keep all these motors in synch, the RMC100 motion controller relies on its ability to do "electronic gearing," whereby the rate of motion of one system element is regulated by motion elsewhere in a system, like the speed of a camshaft being related to the velocity of the crankshaft in an internal combustion engine. Just as with internal combustion engines, well-tuned motion control systems can be run at higher speeds using the proper control systems.

Use of a sophisticated hydraulic motion controller also makes machine setup and maintenance much easier for tube mill operators. In older machines, tube transfer has been coordinated by a set of mechanical cams and rotating rods that required regular maintenance and skilled maintenance people to sustain maximum throughput, risking human error in machine setup. With the new hydraulic systems, the motion elements are electronically synchronized, and power is delivered by smoother, more forgiving means (i.e., hydraulic fluid). "Recipes" for processing different types of tubing can be stored electronically, and when processing is interrupted, the "smart" hydraulic system can be restarted without requiring in-process material to be removed from the machine.

"The precision, speed, velocity and acceleration control available by using an electronic motion controller allows us to explore new capabilities that wouldn't have been possible before," said Buckeye engineer Keith Webster.

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