Productivity Fundamentals: Kiln Lubrication - Part II

This is the second post in a two-part series about kiln lubrication – specifically less-often discussed components. Last week, we covered trunnion wheel support bearings and the trunnion wheel riding ring interface. This week, we’ll cover the riding ring and the thrust roller.

Riding Ring

Riding Ring

The kiln riding ring, also called the rotary kiln tire, supports the weight of the kiln and helps to increase the rigidity of the shell. During kiln operation, the inner-diameter of the riding ring must be lubricated as the kiln shell and riding ring rotate at different rates. This rotational difference is called “creep” and results in sliding contact between the shell and riding ring.

The sliding motion that predominates during creep creates friction, and may result in increased heat and wear, causing weld fractures. Lubricants used to reduce this possibility include:

  • Colloidal bars are composed of a solid carrier and a graphite, molybdenum, copper and aluminum mix. These bars are placed between the riding ring and kiln shell filler bars, where the carrier melts at (50⁰C) and leaves behind a colloidal mix behind to provide lubrication.
  • The spray contains the same colloidal mix but the carrier is a liquid. It is applied in the same location, with the carrier evaporating, leaving the colloidal lubricant behind.

The residual colloid has an auto-ignition point of up to 530⁰C, so it can withstand most kiln shell temperatures and has proven effective in reducing friction related heat and wear. Typically four colloidal bars are required per kiln riding ring and are applied once a week. The spray requires several gallons per application and is reapplied every two days.

One word of caution: kilns operate in a contaminant rich environment. It is advisable to clean the area between the riding ring and the shell during each shutdown. Removing the old colloid prevents contaminated lubricant from becoming impregnated with debris, resulting in lapping wear. Fresh lubricant should be applied once the cleaning process is complete.

The Thrust Roller

The Thrust Roller

Kilns are installed at an incline, and as a result are subjected to a downward or thrust movement. This movement must be limited and is controlled by a thrust roller. Though applied separately, the thrust roller uses the same lubricants as the trunnion wheel roller and support bearings.

The thrust roller bearing requires either grease or oil:

  • An NLGI 3 grease with a grade of 320 or 460 cSt. An NLGI 3 is preferred as the bearing is vertically mounted and the grease tends to bleed away from the bearing load zone.  
  • Oil - Typically bath lubricated, a PAO or PAG synthetic with a viscosity between 680 and 1000 cSt @ 40⁰C is used. The most critical lubrication traits include maximum viscosity at operating temperature, resistance to oxidation and the ability to handle moisture.
  • The thrust roller face contacts the side of the riding ring at a 90⁰ angle. A graphite bar is needed to lubricate this interface. This bar contains colloidal graphite of the same type used to lubricate the trunnion wheel and riding ring interface. It is held in place via a mounting screen and replenished as needed.
  • One last lubricant required for a modern thrust roller is hydraulic oil. In newer thrust roller configurations, hydraulic pressure maintains the desired thrust angle between the thrust roller and the kiln riding ring. An ISO 68, anti-wear and oxidation inhibited hydraulic oil is preferred.

To summarize, in this tip series, we have covered lubrication of the riding ring, trunnion wheel, trunnion support bearings and the thrust bearing. Thanks for the opportunity to provide a little bit of knowledge. I hope you enjoyed this tip, and “Like” this post if you found it useful!