The most common method of support in plastic carrier applications where unsupported spans are exceeded is to install a guide trough to prevent lateral movement during travel. In a center mounted application, the trough consists of two sections: deep and shallow. As the carrier begins to travel from the retracted position, it initially sags and rides on itself. When the gliding section passes the center point, it transitions to the shallow trough segment.
An important consideration for applications requiring plastic carriers in a guide trough is the bending moment that occurs at the moving end as the carrier is pushing, particularly when high velocities/accelerations and heavy fill weights are introduced.
A potential solution for this problem is lowering the mounting height of the carrier, thereby reducing the bending moment. In a lowered mounting height design, the moving end begins gliding immediately as it begins to push.
The lowered mounting height is achieved by adding reverse bend links, extending the ‘K’ dimension of the carrier.
Dynatect can run tow force calculations on an application to determine whether a lowered mounting height is advisable.
In cases where the moving end cannot be lowered due to application restrictions, a “push plate” may be utlilized. If the moving end cannot be mounted at the recommended mounting height, a push plate provides additional support to the carrier system at the bending moment that occurs at the moving end as the carrier is pushing.
When the carrier performs under normal operation without sag, force is applied is a straight trajectory along the moving section:
As sag is introduced, the mass of the carrier falls below the force plane, creating a bending moment on the links at the moving end:
In a long travel carrier system configured for a lowered mounting height, the sag is eliminated, redirecting the force vector back to a straight trajectory. Furthermore, the loading that the carrier introduces as it is dragged over the bottom carrier section is replaced with a more even wear pattern. The force is distributed over the entire system instead of just the first few links at the moving end: