Metso Insights Blog Mining and metals blog Is your rotary kiln gearing system ready for an upgrade?
Metals refining
Feb 19, 2020

Is your rotary kiln gearing system ready for an upgrade?

The gearing components for kilns can be maintained to extend their life. However, after many years, even with proper maintenance, rotary kiln gearing can exhibit signs of progressive decline, and can even succumb to sudden failure due to a variety of chronic issues. In these scenarios, the strategic replacement of gearing components or scheduled upgrades are essential. “But how will I know when?” you ask. In this blog article, our experts share some valuable industry tips.

Steady gearset wear vs. sudden failure

Take a closer look at your gearset when it begins to show signs of significant wear. Without a doubt, the most common issues contributing to the wear and gradual decline of your kiln gearing include the following:

  • Lubrication Issues: Examples include inadequate or excessive applications, the loss of lubricant, the wrong type of lubricant, and situations where the lubrication becomes contaminated.
  • Alignment Issues: Examples include poor pier-to-pier or axial alignment of the kiln. You might also experience poor alignment of the gear set (radial/axial), or the unwanted offset of components.
  • Kiln Shell Issues: Your kiln shell might become warped (out-of-round) or exhibit signs of a condition known as kiln shell crank.
  • Other Issues: A host of other issues can result from inferior workmanship or materials, inadequate maintenance, or design flaws.

As if steady wear-and-tear weren’t enough, sudden failures can and do occur. Upon examination, these failures are almost always the result of chronic conditions that were permitted to worsen over time including poor quality supply, extreme misalignment of components, or the complete loss of lubrication.

TIP: To minimize your risk exposure to sudden equipment failure and lost productivity, don’t let your equipment age to the point of exhaustion and failure.

Upgrade older kiln gearing based on legacy designs

If your equipment was based on one of the following outdated design standards, it is likely time to upgrade:

Flange-mounted gearing: The origins of this traditional-style date back to the 1900s. Flange-mounted gearset designs involve the attachment of the bull gear directly to the kiln shell via a rigid mounting ring, making it very difficult to align this type of gearing on an active kiln. Radial misalignment from gear expansion can often occur with this design, as the gear is directly mounted to the shell, which expands from heat

Split flanges with 2 or 4 pieces: On large gearsets of 20 or more feet, supplying 2-piece or even 4-piece gears is difficult. Few shops around the world can handle the size, schedule the delivery, estimate the lead time, manage the shipping constraints, and still provide quality.

V-belt drive motors/reducers: If your kiln still does not have a modern drive system that incorporates a direct coupled motor to the reducer, an inching auxiliary drive, and a rollback brake with a clutch system, you have a potential safety risk undermining the reliability of your old components.

Upgrades are often more economical than replacement

When you fully weigh the costs of a direct replacement of a traditional gear set versus a full upgrade, often times the supply costs a direct replacement are higher than upgrading!

For example, you might be able to convert from a spur gear to a helical gear set. The reduced face width on helical gears will reduce costs.

Even better, if you can convert to a multi-segmented gearset, your total supply costs including shipping tend to be significantly cheaper. The manufacturing costs for older 2-piece or 4-piece designs of larger gears with diameters of 20 feet or more are much higher. In fact, for gearsets of any size (typically 3 meters or more), multi-segmented main ring gearing has several advantages over traditional 2-piece or 4-piece gears.

Upgrades Provide Superior Gear Quality

The design and manufacturing process for multi-segmented gearsets provides these distinct advantages:

  • Quality control: The production process increases the number of segments for smaller casting pours. Other improvements result from the smaller size of the patterns, machining precision, and heat treating.
  • Improved materials: Current designs can offer superior mechanical properties over traditional materials including exceptional wear resistance and performance. The smaller segments are more maneuverable during installation and eliminate spatial constraints.
  • Design enhancements: Replacing flange-mounted gearing with newer tangent/spring plate designs can yield better alignment especially on kiln shells where expansion has major effect on gear radial or axial alignment.
  • Lower shipping costs: Shipping can take place in a standard cargo container (no more special over-size loads). Delivery timeframes are typically reduced.

TIP: With a multi-segmented gear set, it is recommended to have a spare segment on hand. That way, if damage occurs to a segment, rather than continuing to operate with the defect and potentially cause further damage, it can be easily replaced.

Don’t forget to upgrade the drive systems

Another area where upgrades are often a better choice than making costly repairs is in the drive systems. Replacing outdated drive systems with hydraulics provides a much more compact design that allows operation over a wide range of torque/speed ratios. Directly coupled to the pinion shaft,  no alignment is required (no more separate motor, gearbox, auxiliary drive, low-speed coupling, or other traditional components).

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