Rail Systems for Long Travel Applications
While many linear applications are relatively short to moderate in length (12 feet or shorter), there are applications that require travel lengths in the 40 to 50-foot range, and sometimes longer. LEE Linear offers products that fulfill these various long-length requirements, including options that can join rails end to end.
Corrosion resistance and light weights are attractive features for many plain bearing product lines. While they can be great choices for a wide range of applications, they do not lend themselves well for end joining. The simple reason is that the linear plain bearings that are compatible with these products have a precise running clearance for which alignment is critical, and these end joints have a high probability for binding due to misalignment.
Where longer travel requires butting rails end to end, we recommend rolling elements. Generally, these product families contain wheels, rollers, or balls, and are the best candidates to transition a joint along a rail/raceway. Our roller pillow blocks are one of those rolling element products that is well-suited for long-lengths, and we will briefly discuss that below.
Roller Pillow Blocks
Roller Pillow Blocks use round shafting as the raceway. Large cam followers in the roller pillow block deliver industrial strength performance over long travel lengths while excelling in dirty environments. For very long runs, we recommend the hardened steel or hardened stainless steel shaft be supported by an aluminum support rail. The shaft and support rail assembly (SRA) can be butt joined for long runs, and rail joints should be staggered under shaft joints for better joint support. The low-friction rollers easily navigate joined or misaligned shafts, accounting for any shaft deflection.
- Maximum continuous length for one rail: 15 feet (4.57 meters)
- End joining: low-friction rollers will absorb moderate misalignment and shaft deflection.
- Roller pillow block bearings exhibit superior travel over conventional ball bearings.
An example of roller pillow block implementation can be found in a cryogenic storage and retrieval application. In this scenario, a customer needed a 3,200-pound cartesian robot on a welded steel frame to travel lengths between 22 feet and 32 feet. The dimensions of the robot were a sizeable 4 x 6 x 8 feet. The technical challenges for this application included:
- long lengths requiring butt joints
- doweled joints along the shafts
- a welded structure that was neither straight nor square
Our roller pillow block solution included:
- the shimming of fully supported rail for smoother travel
- support rail gaps to allow pass-through
- opened mounting holes
- compliant mount design
To find out if Roller Pillow Block fits your solution, learn more by downloading our Roller Pillow Block catalog.
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