Designing conveyor systems with safety in mind

Unfortunately, conveyor systems are rarely a pristine environment and, in most operations, some bulk material leaves the belt as dust and spillage, building up on the rollers and conveyor structure below the belt. This fugitive material rapidly adheres to the generator wheel, causing a host of problems such as vibration, excessive rolling inertia and high shaft loads.

In most conveyor designs, the belt runs on a set of rollers that provides support and guides the belt. Product designers theorized that they could draw power from a moving belt by attaching an independent generator directly to one of the rollers.

Product engineers developed a design to accomplish this through the use of a magnetic coupling that attaches to the end of an existing roller. The outside diameter of the generator matches the diameter of the roll but places the generator outside the material path to avoid the heavy loads and fugitive material that tends to damage existing design attempts. The roll generator is held in a fixed position by the roll-support system, but it is not normally required to bear any of the material load.

Conveyor roll loads are carried by a large support shaft in the generator, which does not rotate and is rigidly mounted to the idler support structure. The generator forms a lightweight driven unit that does not affect the existing roll in any way, except to be rotationally engaged via the magnets and draw a small amount of mechanical power to generate electrical energy. The generator is sealed from fugitive material and forms an integral unit independent of the conveyor roll.

Low-bid process versus life cycle cost

The low-bid process is generally not explicitly stated, yet it’s an implied rule baked into a company’s culture.

The process encourages bidders to follow a belt conveyor design methodology based on getting the maximum load on the belt and the minimum compliance with regulations while using the lowest-priced materials, components and manufacturing processes available.

Maximizing cargo volume and minimizing the price of a system usually means selecting the narrowest possible belt while operating at the highest speed possible. This, in many cases, results in chute plugging, excessive spillage and reduced equipment life.

When companies buy on price, the benefits are often short-lived and costs increase over time, eventually resulting in losses. In contrast, when purchases are made based on lowest long-term cost, the benefits usually continue to accrue and costs are lower. This results in a net savings over time.

Design hierarchy

To safely maximize production, designers and engineers should approach projects with specific priorities.

Rather than meeting minimum compliance standards, a conveyor system should exceed all code, safety and regulatory requirements using global best practices. By designing the system to minimize risk and the escape and accumulation of fugitive material, the workplace is made safer and the equipment is easier to maintain.

Life cycle costing should play into all component decisions. Be aware of specifications on project components that state “specific manufacturer’s name/or equal.” Vaguely written “or equal” specifications exist for competitive reasons and allow contractors to purchase on price without adequate consideration for construction or performance.

Finally

Engineering safer conveyors is a long-term strategy. Although design absorbs less than 10 percent of the total budget of a project, the engineering, procurement and construction management services can account for as much as 15 percent of the installation cost of a major project.

By encouraging the use of the hierarchy of controls at the planning stage, as well as the design hierarchy at the design stage, the installation of an evolved basic conveyor can be achieved. The system will likely meet the demands of modern production and safety regulations, with a longer operational life, fewer stoppages and a lower cost of operation.

Todd Swinderman is CEO emeritus of Martin Engineering.

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