Confined Spaces: Eliminating Chute Entry with an External Wear Liner

By: Daniel Marshall, Contributor

Confined space entry requires a permit, because it is deceptively dangerous and has injured several workers in the past.

The wear liner on a belt conveyor transfer point is essentially considered a sacrificial layer. Removal and replacement is a grueling job that could require multiple workers and days of scheduled downtime. Conventional wear liners have historically been installed inside the chute, but modern designs are placed on the outside—improving skirtboard sealing and preventing spillage.

OSHA considers most transfer chutes to be “permit-requiring confined spaces,” mandating that an “authorized entrant” perform the work inside the chute. An attendant must also stand outside, monitoring the safety of the person inside, while assisting in the removal of material from the chute. In some cases, a supervisor further oversees this procedure.

The goal of the external design is to significantly cut the installation and service time while reducing risk and improving safety. The result is excellent performance with fewer labor hours, no required certification for maintenance and a lower cost of operation.

Rethinking Chute Design

Previous designs securely welded the wear liner to the inside of the chute, with only the skirt seal located on the outside. The logic behind the conventional design is for the wear liner to protect the skirtboard, which is typically ¼-inch sheet metal and not strong enough to withstand the sustained force and abrasion from bulk material.

A recent design from Martin Engineering has raised the chute work about 4 inches above the belt, out of the way of the material, then putting the wear liner on the outside. Using this approach, the material still hits the liner and doesn’t damage the chute. To engineers, it was a real light-bulb moment. The team was surprised no one had tried it before, as it had some obvious benefits.

After elevating the chute box above the material flow, a 3/8-inch or ½-inch thick abrasion-resistant liner plate is mounted on the outside of the chute, followed by the skirt seal. Mounting brackets with jackscrews provide a tight hold, with precision adjustment of the wear liner to reduce spillage. This system closes the gap between the liner and the sealer, thus eliminating abrasion from trapped material without interfering with existing supports. When accompanied by skirting and clamps, the system forms a tight belt seal, delivering outstanding fugitive material control.

The external wear liner and skirting system improve safety, maintenance costs and equipment life. (Copyright © Martin Engineering 2024)

Safer By Design

When a conventional wear liner loses its edge, the replacement procedure is what operators describe as an undesirable maintenance assignment. The authorized entrant would go into the chute with a grinder to remove the welds and take off the sacrificial liner, which may have required a torch to cut away the existing material.

This can be extremely dangerous, for two reasons. First, the liner can weigh several hundred pounds, and when a worker cuts it loose, it can fall and endanger the personnel inside the confined space of the chute. Second, nearly any dust can be explosive under the right conditions, and having to grind or torch-cut the old liner introduces a spark or open flame.

Some companies thoroughly wash out the chute prior to entry to avoid any chance of combustible particulates, making the job even more time-consuming. Once the old liner had been removed, the new wear liner was positioned to keep it as close to the belt as possible and welded into place.

Installing an External Wear Liner

An external liner can be installed and adjusted faster and more easily, without the need for a grinder or torch, through the use of special mounting tabs. Clips for bolting the liner are initially welded in place but do not require removal when the liner wears out. Since the work is done from the outside, without any grinding sparks or torch flame, the hazard of explosive dust from tool usage is greatly reduced. Replacement liners come in a standard length of 72 inches, and laser-cutting technology is used to create the complex geometries necessary for a custom fit.

The new liner is easily retrofitted onto existing equipment. Installers simply cut back the chute wall on existing chute boxes to accommodate the external wear liner. On new installations, the chute is easily engineered to work with the new liner design, as well as other components, such as dust curtains, track-mounted idlers and cradles.

Safety in Design

An external wear liner could be considered a safety device, since it eliminates the need to expose maintenance staff to a potentially hazardous activity like confined space entry. Moreover, the external wear liner and skirting configuration extend the life of the equipment and the chute, while reducing spillage and dust. Retrofitting the transfer chute with updated equipment improves system performance with no required certification for maintenance—which reduces the number of workers and hours to replace and service—thus lowering the cost of operation. IHW

About the Author:

Daniel Marshall, Process Engineer, Martin Engineering, received his BS in Mechanical Engineering from Northern Arizona University. With 20 years at Martin Engineering, Dan has been instrumental in the development and promotion of multiple belt conveyor products. He is known for his work in dust suppression and is a leading expert in this area. A prolific writer, he is one of the principal authors of Martin’s FOUNDATIONS™ The Practical Resource for Cleaner, Safer, and More Productive Dust & Material Control, Fourth Edition, widely used as one of the main learning textbooks for conveyor operation and maintenance. For more information: info@martin-eng.com, www.martin-eng.com, 800-544-2947.