Kiln Maintenance for Machine Longevity 

“The kiln turns fine. We do not need to lubricate the tire.” 

“We throw a little lube in there every once in a while.” 

Do these statements reflect how your company approaches kiln tire lubrication? If so, skimping on this crucial component of kiln maintenance may end up costing you a lot of money in the long run.

In a market where demand for cement generally exceeds supply, cement plants routinely run at full capacity. The importance of keeping the kiln ‘turning’ is paramount, and maintenance managers struggle to stretch the interval between maintenance shutdowns. Ironically, however, the importance of kiln tire lubrication is often minimized or overlooked entirely — although the benefits of properly lubricating kiln tires are well-known and have been documented for over 25 years!

In this blog post we will be discussing the importance of kiln maintenance and how something as simple as tire lubrication can make a world of a difference for your machine. 

Is Tire Lubrication for Kiln Maintenance Necessary?

In 1979, Donald P. Giencke, an engineer with Allis-Chalmers Corporation (now A.C. Services), stated in an article that ‘if the riding ring bores are not lubricated properly, an accelerated wear condition will occur. This will eventually cause excessive clearance and will result in a cyclic deformation of the shell’. In a later article in World Cement, Walter Gebhart, Vice President of Phillips Kiln Service, concluded that ‘lubrication [between the tire and the kiln shell] with appropriate solid lubricants is one step contributing to a well-maintained kiln’.

As you know, the heavy loads associated with cement kilns result in extreme metal-to-metal stresses, including sliding and rolling friction. These stresses can cause damage that is expensive to repair, including scoring, galling, and cold welding of the kiln tires, wear pads, and stop blocks.

Even under ideal conditions, the kiln tire and wear pads are subject to extreme pressures and temperatures. Add the likelihood of tire wobble, which is present in many kilns, and suddenly the inside of the tire bore, the sides of the tire, stop blocks, and wear pads can all experience wear and damage. Repairs cost upwards of tens or hundreds of thousands of dollars. Fortunately, a high quality tire lubricant will help prevent damage from all of these conditions.

Rotary Kiln Maintenance Basics

As the kiln rotates, its tires cradle the free moving shell. Thus resulting in immense pressures, severe friction, and metallic wear. Designers mitigate potential kiln damage with sacrificial wear pads which are designed to protect the kiln shell from direct contact with the tire bore.

The fact is, systematic application of proper lubrication to the tire bore is a major factor in avoiding kiln downtime since it extends the life of wear pads and delays the need to replace them.

Avoiding Creep

In simple terms, creep can be defined as the difference between the distances travelled by the tire and the kiln shell during a single revolution of the kiln. Preventing creep is vital and necessary to proper kiln operations. Although not conclusive by itself, the amount of creep that a kiln is experiencing can be an important indicator of the need for tire lubrication. Appropriate tire lubrication will ensure that creep is maintained by preventing the wear pads and shell from “sticking” to the tire. 

Types of Tire Lubrication

Various approaches can be used to lubricate kiln tires, keep in mind some better than others. Below are the most common methods of tire lubrication and why each does, or doesn’t, work.

Graphite Blocks

Traditionally, solid blocks of graphite mixed with water, oil or diesel, or bagged inside cotton bags are often used in an attempt to introduce graphite to the mating surfaces of the kiln. Although these antiquated concepts were well intentioned, they are now generally thought of as difficult to implement and extremely inefficient. 

For example, one operator explained how he tried to “un-stick” his tire by filling cotton bags with graphite and placing them under the tire. Unfortunately, the bags caught fire and ignited the residue left over by a grease product he had used previously. 

In another instance, a different operator tried to lubricate his tire by inserting large “chunks” of solid graphite between his kiln’s tire and shell. After three years, and almost no reduction in the size of the graphite chunks, he realized the blocks weren’t dispersing enough graphite to lubricate the kiln tires properly.

These examples are just a handful of issues one may come across when trying to use graphite blocks for kiln maintenance. 

Greases

Once thought of as an ideal solution, the application of greases has been shown to be anything but! In fact, some experts agree that applying grease lubricants to a tire bore actually causes wear, rather than preventing it. In his 1979 article in Pulp & Paper, Giencke explained that grease lubricants actually attract dust and other particles, which act as a grinding compound and accelerate wear.

Many grease lubricants are petroleum-based and have a relatively low auto-ignition point, which can result in kiln fires. In response, the lubrication industry has developed synthetic greases that are temperature tolerant and can overcome this problem. 

Additionally, both petroleum and synthetic greases contain 90 – 98% liquids. When exposed to the extreme temperature of the kiln, these fluids oxidize and leave a residue of carbon and other tacky deposits. In turn, that residue attracts dust and debris, which further contaminates the grease. Hence the conclusion that grease may accelerate wear, rather than retard it, when used for kiln maintenance lubrication. 

Lubrication Bars

In response to the problems of applying straight graphite or grease, the lubrication industry developed the lubrication (lube) bar. Lube bars, such as Easy Bar, are safe and easy to apply. Depending on the type that is used, these bars offer all of the lubrication qualities that are needed for this type of application.

A lube bar is essentially a supply of solid, dry lubricants encased within a carrier agent. The carrying agent can be a wax, polymer, or another compound. The carrier agent generally has a melting point of less than 93 °C (200 °F). When placed adjacent to the heated kiln shell the agent melts and evaporates, gradually releasing the lubricants. The turning of the kiln causes the lubricants to spread across the wear bars and inside of the tire bore, coating the mating surfaces in need of protection against wear.

The application of lube bars to the tire bore is relatively easy. While the kiln rotates, the operator simply inserts the recommended number of lube bars between the tire and the shell. Some lube bar suppliers recommend eight to 25 lube bars per week/per tire. Therefore, several revolutions of the kiln may be required to apply these lube bars correctly. Other suppliers recommend as few as 3 or 4 lube bars per week/per tire, which can be easily inserted in a single revolution of the kiln.

Not all Lube Bars are Created Equal

While lube bars would seem to meet all the lubrication requirements, not all are of sufficient quality to do so. Some lube bar manufacturers substitute carbon black for graphite lubricant. Others may use halogen-based fire retardants, which can be harmful to humans at high temperatures.

The Easy Bar Difference

A patented blend of graphite, mineral, and mineral lubricants work together to lubricate a kiln’s tires and lower maintenance costs. What’s more, only three to four bars per pier are needed per week. 

In addition to easy application, Easy Bar lowers kiln maintenance costs and downtime by:

  • Increasing the life of stop blocks and wear pads by at least 50%
  • Minimizing or eliminating weld fractures
  • Minimizing shell ovality and maintaining creep
  • Reducing tire lubrication time to less than one minute per week
  • Extending refractory life

There is no other lubricant in the industry that works as well as Easy Bar. With over 15-years of proven field performance, we can proudly guarantee these benefits. Contact us if you would like to try Easy Bar — your rotary kiln will thank you in advance. 

 

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