By Robert A. Sladky, Vice President, Tube Mill Engineering, Roll-Kraft Nebraska U.S.A.

ROLL-KRAFT makes and reworks its tooling to very close tolerances and high standards. This fact places a large responsibility on a mill since the tooling will only be as good as the mill on which it is installed. If the mill alignment is not held to the same close tolerances to which the rolls are manufactured, problems may result. Therefore, alignment checks must be scheduled on a regular basis. It is important that you set your own standards, and then follow them. Waiting to align the mill until tubing can no longer be run results in premature tooling wear and possible customer rejection. This article is written to cover the important areas on the mill so as to insure proper alignment and therefore high quality tubing, as well as longer life out of the tooling.

All of these focus on the center point of the mill thus insuring it is level and “straight” in line.

 

CHECK POINT 1
Checking Integrity of Guide Rolls

It is very important that the entry guide system is mechanically tight. If the strip is allowed to drift off to one side or the other, the strip is not formed evenly by the tooling and camber may be introduced into the strip. This may cause twist, roll over or weld problems. Make sure guide rolls are in good order. Worn guide rolls can damage strip edges which affect weld.

The Driven Stands

CHECK POINT 2
Checking O.D. of Driven Shafts

Look for worn spots, rings and grooves. Check the shaft especially in the area where the roll rides. If under specification by more than .002" (depending
on shaft diameter) the shaft needs to be repaired. Undersized shafts can cause out-of-roundness, line surge, varied O.D.-of-tube, chatter or ripple marks and ultimately increased roll and shaft wear. Shafts can be repaired by chroming and then grinding them back to their original size. When Roll-Kraft reworks your tooling, the bore of each roll is checked, and if worn, is chromed
to original tolerances.

CHECK POINT 3
Checking Bearing Play

First check to see if bearings are tight or if they need to be replaced. If the bearings are taper roller design, as most are, they must be pre-loaded to manufacturer’s specs. Check bearing blocks and their end plates to see if the end plates fit tightly against the machined gib surface of inboard and outboard stands. If bearings are tight and you try to move the shaft up and down and the
entire gearing block moves, you need to tighten the assembly.

CHECK POINT 4
Checking for Bent Shafts

If a shaft is out of concentricity more than .002" (depending on shaft diameter) it needs to be replaced, but not thrown away. These shafts can be chromed and ground-to-size at a fraction of the cost of a new shaft. A chromed shaft will last longer, in most cases, than a new uncoated shaft due to the hard chrome layer resisting
wear from the pressure of the rolls.

CHECK POINT 5
Checking Back Shoulder Alignment

Insure that the shoulder of the shaft is in the correct relationship to the machined gib surface of the inboard stand and that the shoulders are consistent
in measurement with one another, stand to stand, top and bottom. Most mills have specs for this measurement.

CHECK POINT 6
Checking Driven Stands Alignment

Make sure all stands are aligned with each other, horizontally, vertically, and diagonally.

CHECK POINT 7
Checking that Driven Shafts are Parallel

Check to see if the driven shafts are parallel, base to bottom shaft, bottom shaft to top shaft, stand to stand.

CHECK POINT 8
Checking that Rolls are Parallel

When the rolls are on the mill, make additional checks for alignment with a straight edge and bridge levels.
 

CHECK POINT 9
Checking Side Roll Passes

Weld Box Assemblies

The weld box forges the prepared edges from the fin section to a welded tube. In order to do this, perfect alignment and good mechanical integrity are required. Therefore:

Failure to do so will result in out-of-round tubing, weld roll marks, and poor weld with problems showing up in the sizing section.

Ironing Passes

Aligning and checking this unit should be done the same as driven passes, including “back line” settings.

Turks Head Units

The turks head units’ primary function is to straighten the tube after final sizing.
Make sure the inside faces of the clevis and washers are not scored or chewed up. Check the O.D. of the shafts as well as the bore of the clevis where the shafts are mounted. The lead screws that adjust the rolls in and out must not have excessive play. The clevis, yokes, and gib plates must be tight. All rolls must be parallel to their opposing mates, forming a perfect square.

Tube Mill

CHECK POINT 10
Checking Alignment with Tooling Installed

Final alignment check of the mill can now be performed to insure proper alignment with rolls installed. Use a transit, laser beam or common piano wire to confirm proper alignment of the entire mill. Systematic application of these check points will assure proper alignment resulting in efficient operation and higher quality tubing.

Quality is our number one priority. American Industry, in the global environment, has found itself in an arena where there are not just more players, but some of them are every bit as good as many of us here in the U.S. The quality of the product reflects the commitment to excellence. Regardless of nationality, today, quality sells. American companies have been the pioneers and innovators for many years. The free enterprise system is the most popular in the world. In order to maintain a competitive edge everyone must continually strive to improve and perfect their manufacturing and production processes. ROLL-KRAFT PROFIT POINTERS is a continuation of a series of technical tips designed to help you perform at your very best, every day. We will offer advice and recommend procedures on how you can get optimum performance from our rolls and your mill to produce the highest quality tubing.

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