Super Straight Story
Published in Hydraulics & Pneumatics

Brief ideas showing recent system and component applications for industrial and mobile designs

Getting Straight — Tubing, That Is!

It is often assumed that seamless tubing is straight, but a little investigation will show that, while it may be almost straight, it is seldom perfectly straight.

Under these conditions, a cylinder's piston and piston rod must follow the spiraling axis of the cylinder bore. The resulting internal side loading of the cylinder results in excess wear, and in some cases failure.

SCOT Industries, Inc. uses a combination of press straightening and special honing equipment to reduce both camber and spiral wave in tubing when requested.

Deviations from straightness fall into two categories: long radius curvature (camber) and spiral wave.

Most tubing has been roller straightened at the mill. The normal mill straightness tolerance is .015 to .025" per foot. SCOT has extensive press straightening facilities at each plant to improve the straightness of your tubing. Tolerances are negotiated for each job. We are aware that tubes have a certain amount of memory and may move in time. We believe that our process improves the straightness of tubing. There is an extra charge for straightening.

Spiral wave originates when the tube round is pierced at the mill. The piercing point seldom hits exactly in the middle, so that seamless tubing has a heavy side wall and a light side wall.

In addition, the driving rolls twist the steel grain structure so that the heavy wall follows a spiral path down the tube with a pitch equal to about twice the diameter of the tube.

During final roller straightening, the roller straightened tends to make the outside of the tube round. With the outside of the tube round and the wall varying in thickness, the axis of the inside of the tube is not a straight line, but a spiral.