Pros and cons of current open gear lubricants are discussed in the article.
Open gears are most often used for drive units in the raw materials industry. Among this are tube mills and rotary kilns in cement and gypsum production. Production equipment using open gear drives units usually occupies a key position in the production process.
Operational safety and therefore also the lubrication of these units thus acquire a special significance. For the lubrication of open gears, there is a variety of lubricants in the market. Depending on design of the open gear as well as concerning the method of application today’s lubricants all have certain restrictions.
The selection of the correct open gear lubricant has three main aspects:
-The suitability of the lubricant for the existing gear design
-Suitability for the production equipment and process
-The suitability of the lubricant for the existing application unit
Design criteria
By design one distinguishes between DIN/ISO designed gears and open gears according to AGMA design. AGMA designed gears mainly have helical teeth, pinion and shaft is one unit. Pinion diameter and module is, compared to DIN/ISO designed gears mostly much smaller.
Lubricants for AGMA designed gears are specified in ANSI/AGMA 9005-E02. In this standard (Annex D) open gear lubricants with high and extreme high viscosities are specified. Therefore, either high viscous, synthetic oils or asphaltic containing oils with volatile solvents are used for AGMA designed gears. For DIN/ISO designed gears mainly grease based, graphite containing greases are used.
Production equipment
Within the cement industry one distinguishes in mill and kiln applications. The main difference concerning lubrication is the rotational speed and the environmental conditions. Kilns gears are running rather slow but are exposed to higher radiation temperature. Mill gears are running comparatively fast but lower gear tooth temperatures.
The majority of kilns and mills is lubricated with graphite containing greases, some with synthetic, high viscose oils.
Method of application
Still the majority of open gears is lubricated by intermittent spray units. Some equipment manufacturers recently install circulation systems which provide continuous lubrication via an enclosed circulation unit.
Some minor open gear equipment is lubricated with splash lubrication, where the girth gear is submerging into the lubricant and transfer the so collected lubricant onto the pinion teeth. For all above mentioned application methods graphite greases and high viscose oils are suitable. Solvent containing asphaltic lubricants are restricted to intermittent spray systems which are adjusted to the gear-rim.
General aspects of today’s open gear lubricants
Bitumen and solvent containing lubricants, so called asphaltics have been mostly replaced by graphite containing greases. Because of their volatile solvent and bitumen content their use has been restricted by many users in order to prevent any environmental or health hazards.
As mentioned before they are not suitable for circulation, dip or pinion-spray application and are thus restricted to gear-rim spray application only. Some of these lubricant-types can built-up hard residues at the tooth root which can lead to serious mechanical problems.
Graphite containing greases are still the most used open gear lubricants. They are approved by all major gear and machine manufacturers within the cement industry. They provide optimum wear and damage protection for all kind of kiln and mill gears. Suitable grades for spray, dip and circulation applications are available.
Unfavourable is their limited drainability from the gear housing. The black colour of the graphite containing lubricants is seen as a disadvantage by some users. High viscose fluids are a clean and technically sound solution for fast running mill gears. Most of these fluids meet the AGMA criteria. They provide excellent drainability but demand a good sealing arrangement of the gear housing.
High viscose fluids have shown significant disadvantages if used on slow running kiln gears. On such gears a sufficient lubricant layer cannot be built up with pure oils. To separate the meshing gear flanks, additional solid lubricants are missing. As a consequence, many kiln gears developed severe damages within a relatively short period of time.
As most sealing arrangements of kilns are not designed for oils, the lubricant can creep onto the hot kiln shell which results in the risk of ignition.
This clearly shows that all today’s open gear lubricants have certain restrictions. FUCHS LUBRITECH as the leading manufacturer of modern open gear lubricants thus decided to develop a new lubricant which combines all advantages of above mentioned products.
The new evolution in open gear lubrication
The new CEPLATTYN GT Range combines all benefits of commonly used graphite products and high-viscosity fluids. It is free of asphaltics and volatile solvents. CEPLATTYN GT is based on a high viscose synthetic oil with white solid lubricants. This combination provides a save lubrication film and an optimum protection against metal to metal contact on slow and hot running kiln gears and high-powered mill gears. The formulation includes flame retarding additives, which guarantees a safe use on kiln gears, it is designed for spray, dip and circulation application.
The special flowability behaviour of CEPLATTYN GT guaranties a remaining thick lubrication layer even after several weeks of shut-down but excellent drainability to the gear sump at the same time. The milky appearance of CEPLATTYN GT warrants a clean gear set and its environment. In addition, the product provides a self-sealing effect which makes it a perfect solution for gears which are not perfectly sealed by design.
Experiences on mills and kilns over the last few years have shown excellent results. The tooth flank temperatures and vibrations could be reduced even though the sprayed-on consumption was reduced substantially. With significantly reduced volumes the running conditions like vibrations and gear tooth.
About the author:
Klaus Holz, Head of Technical Service, FUCHS LUBRITECH GmbH, Germany
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