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View our video or read the article below for tips to properly set up weld boxes for tube and pipe mills.
It is imperative to properly set up and plug your multi-roll weld box to ensure an efficient and dependable changeover to your next size on your tube/pipe mill. However, for a successful setup, you need to first ensure that you have proper integrity of the weld box and all its components before you start your setup.
Inspect the O.D. of the weld roll shafts for wear, and also to see if anyone did any grinding on the shafts as the example shows in the picture above. Inspect the end cap washers and fasteners as well. Replace worn or damage components as required.
Inspect all components of your weld box. In this example of a three-roll weld box with clevises mounted on a three jaw chuck, ensure that the scroll of the chuck is cleaned and lubricated on a regular basis, and all internal working parts are within tolerance. Inspect the clevises and their reference/alignment bushings for wear and/or damage from a previously failed bearing. Repair and/or replace as necessary.
Ensure that the open side of the bearings is to the inside of the weld rolls, and the sealed/shielded side is to the outside of the weld rolls so they can accept grease when lubricated. If using double-side sealed or shielded bearings, simply remove the seal/shield from one side of the bearing.
It is imperative that you use a sleeve between the two bearings used in the weld rolls. As the end cap washer and fastener are tightened up, it pulls up tight the weld roll pin shaft shoulder to the inside races of the bearings to the reference/alignment bushing of the clevis. Failure to have this sleeve between the bearings will result in binding up of the bearings, which causes excessive drag and misalignment of the weld rolls.
Ensure that the end of the weld roll pins are just below “flush” with the surface of the clevis. Check with a scale as illustrated in the picture above. In this way, when the end cap washers are installed and tightened, the pin pulls tight the bearing assembly (bearing and spacer) to the alignment bushing on the clevis, thus aligning the weld rolls within the clevis. Too long of a pin, and the weld roll assembly will float within the clevis. Next, ensure the clevises are at the proper angle so the weld seam will be on center. Most weld boxes, such as the one illustrated below, have a rack/pinion adjustment behind the face plate that will rotate the chuck and weld rolls.
It is very important to install the correct weld roll in the correct location. In this example of a three-roll weld box, the top rolls will be labeled, WR-T (Top) this side up, and the bottom weld roll, WR-B (Bottom). It is imperative to install the top weld rolls in the top clevises; make sure the side that states “top side” is installed to the top side of the top clevises. The reason for this is because the contour/rim of the “top side” of the rolls has more clearance allowance for the weld bead to be forged. Failure to install these rolls properly (i.e., upside down) will result in a narrower rim clearance and a crowded weld forge zone between the top weld rolls.
Many operators set up their weld rolls in their weld boxes by just checking the gaps between the rims of the weld rolls. While the equal gap between these rolls is important, using a plug gage is by far the more accurate and faster method of setup. Why? When you adjust the clevises in on the solid setup plug gage, you eliminate all of the backlash in the leadscrews in the clevises and/or scroll in the chuck style weld box. Once the tube is threaded into the mill, little or no adjustment will be required, as the rolls will have been preset/preloaded against the setup plug, imitating the pressures of the tube.
In the example of a three-roll “Y” configuration weld box, or four-roll weld box, the top rolls will be hanging down from the force of gravity when setting up by rim gap only, (not using a plug gage). Then, once the material is fed into the weld box, these top weld rolls/clevises/etc. will move upward, taking up the backlash in the lead screws, and further adjustments will be required to get everything back to a symmetrical setup, and welded tube size, resulting in longer changeover times and scrap.
Time studies have proven that an operator can save up to 85% in setup time using the setup plug method of presetting the weld rolls.
Position a light behind the weld box (see photo above) for an easy view of the clearance between the weld roll contours and the setup plug.
Adjust the chuck and/or individual clevis adjustments (see photo below) until you get a proper symmetrical fit to the weld plug gage, and there is no light between the rolls and the plug gage.
We used a typical three roll, chuck-mounted weld box for this article for illustration purposes only. The same common sense application of checking the integrity and using a plug gage would apply to any design type of weld box unit.
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Robert A. Sladky
Vice President Tube Mill Engineering
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