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Belt Conveyor Edge-Seal-Support Cradles

While idlers provide an efficient, low-resistance surface over which a conveyor belt can travel, the gaps between idlers also present opportunities for materials to pull the belt away from its sealing system. Edge-sealing-support systems help reduce this danger by providing continuous support for the belt and maintaining a straight belt profile at the belt edges.

“Side rail” cradles are one common form of edge-seal support. These systems rely on low-friction bars along the sides of the conveyor to support the edges of the belt. By placing these side rails directly underneath the skirtboard seal, these systems can help effectively maintain the seal on the belt edge.

Edge-seal supports can help eliminate belt sag and prevent dust and spillage at transfer points.

Aside from aligning these bars with the skirboard seal, designers should also ensure that the top of each bar matches up with the top of the idlers on both the entry and exit sides. This will avoid unnecessary friction and prevent the creation of entrapment points. If a conveyor system makes use of multiple edge-sealing cradles, designers should include an idler between each cradle.

Conveyor systems may require one or more edge-seal cradles depending on several characteristics of the systems, including the length of the transfer point and the speed of the belt among others.

On faster, wider, more heavily loaded belts, the edge-seal cradles may need more than one bar on each side to support the belt edge. Wider belts in particular might require an additional central support roll or further low-friction bars under the middle of the belt to help support the weight.

Edge-support slider bars must provide as little friction as possible to reduce concerns about wear and heat produced by friction. Often these bars are constricted from plastics such as Ultra-High Molecular Weight (UHMW) polyethylene. One proprietary design features bars formed in an “H” or “box” configuration, allowing for the use of both the top and bottom surfaces.

At certain speeds, the performance of even low-friction plastics can begin to deteriorate. As such, many within the industry now advocate for the use of stainless steel support bars for conveyor belts that move faster than 3.8 meters per second, or 750 feet per minute. Stainless steel bars should be incorporated in applications with service temperatures above 82 degrees Celsius, or 180° F.

In certain countries or localities, domestic safety regulations can limit the choice of materials for bar supports. Most nations at least require conveyor belts that go underground to use antistatic and/or fire-resistant materials for any components designed to come in contact with the belt. Other requirements, whether set by local governments or industry standards, may further limit materials choices.

Along with low-friction materials, belt-edge-support systems should also be careful to consider the mounting structure for the bars. This frame should be adjustable to allow for easy installation, alignment and maintenance, and should be able to accommodate various idler combinations and chutewall widths and allow for adjustment due to wear.

In addition, the cradle should be designed to avoid any possible contact between the belt and the frame or fasteners. For example, the bolts holding the bars in place should be installed parallel rather than perpendicular to the belt.

An edge-support cradle may add incrementally to the friction of the belt and to the conveyor’s power requirements. However, this marginal increase in energy consumption is more than offset by the elimination of the expenses for the cleanup of skirt leakage, entrapment-point damage to the belt, and unexpected downtime necessary for idler maintenance or belt replacement.

Topics: Basics of Belt Conveyor Systems, Material Spillage

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