Roller alignment costs money. It takes a couple of technicians something like an hour to move a typical roller into alignment. This is not a large cost if the machine is already down because it is being installed or rebuilt, or it is not fully utilized. Thus, there is absolutely no excuse not to align to precision ingoing standards in those situations. Economics change when we take a running machine down specifically for alignment. We only do what we have to do; only the specific rollers that exceed outgoing tolerances in order to improve specific aspects of quality and runnability that are alignment-sensitive.

There are three or four events in a machine's life that would require alignment. The first, after assembly at the machine builder's shop, is to make sure that there is sufficient clearance between the bolts and their holes to allow a roller to be brought into the 0.002-in. precision ingoing alignment discussed last month. It's not unusual to have a few things that have to be tweaked a bit. The principle exception: Some parts bolted to match-drilled side-frame plates are not intended to be moved into alignment. There is some truth to that “side-plates-are-good-enough” philosophy.

The next alignment takes place during reassembly on your plant floor. Every single roller is moved into square and level again if it is out more than the ingoing tolerance specification. There are at least two reasons. The first is that even with the best stress relaxation of framework, it will continue to warp slightly during the truck ride out. The frame is full of residual stresses due to machining and particularly welding. If you do not relieve them by “baking” in an oven or by vibration, the assembly will relieve itself (warp) with time. The other reason is that the frame may get distorted due to lifting and setting onto its pads which causes a micro-slip of bolted joints.

The third alignment takes place 1-2 years after installation. Now is when you find out how good your foundation work was. You'll find that the typical 6-in. slab floor on gravel is often not stable enough on which to mount precision machines. This is why we specify mounting on sills and other sturdy elements. It keeps the inevitable motion of the earth, which is primarily seasonal wetting and drying, from shifting machinery so much. If you have a good frame and foundation, very little will have moved and thus little will need to be realigned.

Several events might prompt a fourth or additional outgoing-toleranced alignment. One is if the machine moved a great deal in the first year. If so, we will be back into alignment regularly, forever. Another is if we had an accident which caused a large impact. Another is if we changed grades to a much more demanding (usually thinner) material. And another is if we do maintenance on a part of the machine, we may need to recheck the rollers that were moved.

Finally, and most importantly, you would realign based on alignment-sensitive waste and delay such as wrinkling, web breaks, uneven forming/converting, etc. Here, however, we would use a targeted approach. To take a rifle instead of a shotgun approach, you need careful observation of your process as well as web-handling literacy.

920/312-8466 drroisum@aol.com, www.roisum.com