Avoiding common pitfalls with shaft-mounted gearboxes

TRADITIONAL GEARBOXES with solid shafts are a well-recognised feature in automotive transmissions, industrial machinery and heavy-duty equipment. Yet these mechanical power generating stalwarts have several drawbacks; including limited flexibility due to rigid design, increased weight and susceptibility to vibration or wear - all of which can lead to higher maintenance costs and decreased efficiency.

Overcoming these shortcomings is where shaft-mounted gearboxes, otherwise known as direct drive gearboxes, come in. Unlike traditional gearboxes with solid shafts, these gearboxes slide over the shaft, so the shaft supports the weight and torque. There are numerous advantages to this design.

The benefits of direct drive gearboxes

First, shaft-mounted gearboxes eliminate the need for extra mounting components like couplings or belts. Not only does this make the designs of the gearboxes less complex, it eases the assembly and alignment process and makes the systems ideal for space-constrained environments. Known for strong performance in tight spaces, shaft-mounted gearboxes efficiently convert high-speed, low-torque motor output into low-speed, high-torque motion, reducing misalignment and maintenance needs.

That’s why shaft-mounted gearboxes are favoured in critical applications like conveyors, mixers and pumps. Nevertheless, despite their advantages, shaft-mounted gearboxes come with their own set of installation challenges and can experience premature failure and operational inefficiencies if they are improperly mounted.

Here are some tips for how installers can prevent these mistakes and, in doing so, get the most efficiency and cost savings.

1. Ensure proper alignment

Many operators make the mistake of bolting the gearbox down to a solid plate or mounting surface. While bolting the gearbox down may seem like a solid solution, bolting down the gearbox prevents it from adjusting to shaft movements, causing misalignment, vibration and damage to components like bearings and gears. Over time, even slight shaft imperfections can lead to premature failure.

Instead, proper alignment is essential for the smooth operation and longevity of a shaft-mounted gearbox. A reaction bracket, torque arm or reaction bolt kit should be used to allow the gearbox to move with the shaft. These flexible mounting solutions help accommodate misalignments, reduce radial loads and minimise wear on the gearbox bearings. In large machinery, such as mixers or conveyors, the reaction bracket helps redistribute torque and protect the gearbox from damage.

Additionally, the anchor point for the reaction device must be strong enough to handle high reactive forces, especially during direct-on-line (DOL) starting, when torque can spike up to three times its nominal rating. Operators should also schedule regular inspections both during the installation and for ongoing maintenance.

2. Choose the right components for the application

Selecting the right components is critical when designing a gearbox system. It’s essential that the shaft and bearings are properly sized to support the gearbox’s weight and torque. The chosen parts must help the system withstand operational loads without premature wear or failure.

For instance, Technidrive recently assisted a customer in the asphalt industry, which faced repeated gearbox failures on its mixers. The issue arose from two gearboxes that were bolted down solidly on misaligned shafts. The bending of the shafts under the weight of the gearboxes caused excessive strain, leading to frequent breakdowns and costly downtime. The system used a 37-kilowatt motor, which contributed significant power and was crucial in ensuring that the gearboxes could handle the torque demands.

To solve the problem, Technidrive designed a new system using a reaction bracket and flexible mounting along with Bonfiglioli hollow bore gearboxes. These are favoured in quarry and mine applications where absolute reliability and low maintenance are key factors.

This solution allowed the gearboxes to shift with the shaft movement, alleviating the stress that was causing premature gearbox failure. As a result, the customer experienced a significant reduction in failures. Whereas the previous system was prone to failures two or three times a year, it has since run smoothly for years without further issues.

3. Consult technical experts

This example shows us that selecting the right gearbox components is only part of the equation - it’s just as important to consult an expert and understand how to best configure these parts to your specific application. This helps avoid installation mistakes - like bolting the gearbox solidly or using incorrectly sized shafts — which cause significant issues further down the line. It’s also why Technidrive leverages over 25 years of experience, providing expert consultation from component selection to installation.

While the advantages of shaft-mounted gearboxes over traditional gearboxes are clear in some applications, their efficiency and longevity utterly depends on proper installation. By seeking expert advice and using the right solutions, such as flexible mounting and precise alignment, costly mistakes can be avoided so operators can ensure long-term system performance, efficiency and cost savings.

David Strain is technical director at Technidrive

For more information:

www.technidrive.co.uk

Tel: +44 (0) 28 37 518111