- September 01, 2007, By Timothy J. Walker Contributing Editor
Most of us like to feel we are well-supported, i.e., secure and stable. A roller isn’t that different.
How should a roller be supported or attached to your equipment? To answer this question, let’s review your roller support needs and your options to meet these needs.
- Aligned | Rollers should be parallel to each other. Each roller must be installed and measured to be level (perpendicular to gravity) and trammed (perpendicular to a machine’s centerline), usually to less than 2 mils/ft error. (Stretchier, thicker, and narrower webs are less sensitive to misalignment than this.) Even rollers that will be intentionally misaligned should begin with a known parallel reference position.
- Rigid | Rollers should hold their position and alignment through tension and process changes and over the life of the equipment.
- Serviceable | Rollers should be designed so they can be removed for maintenance and reinstalled back into their alignment position with reasonable ease.
To mount a series of rollers between two side frames, the builder will clamp the two plates together and bore all the roller positioning holes as a set. When the side frames are separated and spanned by rollers, in theory, the rollers should automatically be parallel since the holes are spaced identically in each frame.
The bored holes may be quite accurate, but in all bored side frame cases, something must be press fit into the holes that then holds the shaft. This is what will make or break this approach.
Shaft-holding options include: 1) bearings, 2) shoulder bolts, or 3) engineered plugs that function as large shoulder bolts. In inexpensive equipment or wrinkle-insensitive products, this method is good enough. The engineered plug approach can work quite well, especially if it includes split caps and some minor alignability.
When you don’t have bored side frames, there are two other options to connect rollers to any horizontal or vertical surface: flange mounts (where the shaft holder bolts to the side frames parallel to the roller shaft) and pillow block mounts (where the shaft holder is bolted down in a direction perpendicular to the roller shaft). Flange and pillow block mounts can be well or poorly executed, depending on the details of their execution.
Flange and pillow block mounts may be an all-in-one design with an integrated standard bearing and a Zerk fitting. Though these are great for many shaft applications, overly greased bearings often have higher rotational drag than I’d like to see in my idler rollers.
If the live shaft roller has an exceptionally long shaft or journal (something that should be avoided), having spherical bushings to capture the bearing can avoid detrimental torsional bearing loads from shaft bending.
I’m a fan of split cap pillow block mounts. The pillow block mount is the easiest to level and tram in independent steps. The split cap feature is the best for easy removal and reinstallation of a roller without losing alignment.
And one last point on alignment of these shaft holders: If you’d like to keep your alignment over time, don’t rely on the bolt friction to hold things in place; take the time to drill and pin the roller mounts securely in place.
If you are a person who enjoys living on the edge, you may find roller support options a boring topic. For you thrill seekers, I have two words: cantilevered rollers. But that will have to wait for a future column.
Timothy J. Walker has 20+ years of experience in web handling processes. He specializes in web handling education, process development, and production problem solving. Contact him at 651/686-5400; firstname.lastname@example.org; tjwa.com.