The right roller chain choices can make the difference between 'smooth production' and 'no production' says Robert Young, who examines the use of chains in cement production.
Chains choice can make or break production The right roller chain choices can make the difference between 'smooth production' and 'no production' says Robert Young, who examines the use of chains in cement production. The cement industry represents an extremely tough working environment for roller chain, operating on drag and apron conveyors, bucket elevators, flow conveyors, rotary kilns, stackers and reclaim lines where water ingress and coarse particulate residue can make effective lubrication a challenge and result in accelerated wear. The result is that lower quality chain products suffer heavy wear and can prove to be an extreme exercise in false economy; particularly when they require frequent replacement, excessive maintenance and in some instances cause loss of production.

Cement industry apparatus requires comparatively large pitch chain (over 1.1/2in pitch), and so the results of excessive wear, elongation and stiffness are harder to adjust due to the physical size and weight of the drive system and conveyor attachments such as steel buckets.

Any wear that does occur on heavy chain therefore tends to be accentuated and can quickly result in inefficient or even dangerous plant machinery.

Breakages are rare because advanced wear is easily detectable due to excessive noise and visible slack in the chain drive, but if it does occur then the results can obviously be serious.

The solution is to employ roller and conveyor chain that has been developed specifically for the task, using advanced design, materials technology and improved production techniques to ensure lasting performance.

Tsubaki supplies a range of application specific cement industry chain that matches these requirements, examples of which have doubled wear-life and significantly improved plant reliability at cement plants around the globe.

* Bucket elevator chains - bucket elevators are one of the central processes in any cement mill, and not something that any site engineer or manager can suffer downtime on.

Typically handling cement, clinker and crushed limestone, outdoors and with heavy intermittent loads this application is hard on roller chain.

Large pitch modified conveyor chain can be used in this application, but there is chain available that is designed specifically for extended use and low maintenance on bucket elevators.

Tsubaki BF type chain is a good example, specially designed for centrifugal discharge type bucket elevators it has been developed from the raw material upwards to provide greater fatigue strength and wear resistance.

Unlike the majority of alternatives these chains are manufactured from high-grade 'clean' alloy and carbon steels, have induction-hardened pins, case hardened bushings, and shot peened link plates as standard.

The link plates also go through a specially developed heat treatment process that significantly improves fatigue strength.

Chain attachments are available in five standardised styles to suit the most common bucket designs and Tsubaki will also supply special attachments upon request.

In field trials conducted at working cement mills Tsubaki BF Series chain delivered an averaged 1.1/2 times greater wear life than conventional chain and several times that of cheaper lower-quality chain.

The difference is recognised in the industry with Lafarge, CEMEX, National Cement (USA) and Blue Circle all operate using Tsubaki chain products including BF Series at various locations across the globe, but not every site is aware of what is available.

There is also an RF series derivative that shares many of the BF series features and is designed specifically for continuous discharge type bucket elevators.

RF Series is available with three attachment variations to accommodate high-capacity, slow speed and higher speed elevators.

For heavier applications, there is a reinforced BT version available and a Special Series Bucket Elevator Chain that provides even greater tensile and fatigue strength, and higher wear resistance.

The chain components in Special Series are manufactured using a modified and very precisely controlled heat treatment/hardening process to achieve added strength and ensure consistency in terms of surface hardness and mechanical properties.

* Chain for drive applications - common uses for drive chain in the cement industry also tend to be relatively heavy applications such as turning rotating drums, crushers, fans, hoists, rotary kilns, rotary mills, mixers, and pumps.

While effective lubrication is often physically easier to achieve than on conveyors and bucket elevators, higher temperatures can offset this.

Processes also tend to be continuous; hence high strength and durability are essential.

Again, differences in chain quality lead to substantial differences in wear-life and effective lubrication is absolutely essential in order to reach the expected operating life.

There are different ways of achieving correct lubrication, including 'lube-free' chain that actually lubricates itself from within the roller bushing.

* 'Lube-free' chains - lube free drive and conveyor chain is usually only available up to a 2 inch pitch size and so is not suitable for every application, but where they can be deployed; the need for external lubricant is completely removed.

Lube-free chain can provide huge advances in wear life in the right conditions; examples of Tsubaki Lambda lube-free chain are still in operation four years later where poorly lubricated standard chain lasted only six months.

The lube-free feature is particularly advantageous in areas where the chain is easy to neglect or difficult to reach and maintain.

There is a cost premium for lube-free chain, but the difference is normally recouped quickly by avoiding replacement costs and reduced maintenance requirements.

The technical aspect of Lambda chain involves a sintering (oil impregnation) process of the roller bushes during manufacture.

The steel bushings are forged with lubricant actually included within the material structure of the steel.

During operation, the lubricant forms a micro thin layer between the pin and internal roller surfaces.

Meanwhile, the exterior of the chain is totally dry to the touch, a condition that stops it acting as a surface receptor for harmful contaminant particles.

As chain passes over a sprocket, particularly a driven one, it is the internal bearing surfaces that have to articulate under load.

Given inadequate lubrication, these are the main areas of wear.

Using a sintered bush the motion of the lubricant within the rollers under load is from the centre outwards, the opposite direction to conventionally lubricated chains that draw lubricant in from the exterior.

As a result of this, any debris from the atmosphere that does settle on the surface of the chain is mostly excluded from the load bearing surfaces of the rollers and deters the acceleration of wear * 'Super chain' - larger pitch sizes require specialist heavy duty drive chain offering a higher load capacity, greater resistance to shock loads, together with the fatigue strength needed to sustain reliable operation for long periods of time.

Depending on application requirements there are at least five types of Tsubaki's Heavy Series and Super Series chain in each pitch size, up to six strand, and all share a characteristic link plate form.

Designed from the raw material up as a large pitch, heavy duty chain, the design is significantly different to conventional drive chains that are usually engineered to work at their optimum under 2in pitch size - Super series is available as standard up to a 3in size.

Super series chains are also more resistant to contaminants such as mud, sand, metal particles, and other abrasives.

In addition, they handle intermittent shock loading, and operate with minimal maintenance and lubrication.

A particular differentiator for these chains is a patented ring coining process applied to the connecting link, most chains effective load capacity is limited by the kW rating of the connecting link, which is often lower than the rest of the chain, Tsubaki's ring coining process increasing the kW rating of the connecting link by 25% exceeding that of the chain.

As a result, chains are more compact and reliability is higher.

* There are four main categories of chain beyond the standard RS80 series.

These are as follows.

1 - RS-HT Series chains, which offer greater ultimate tensile strength (19% higher) than Tsubaki's ANSI standard roller chains as a result of using through hardened pins and link plates of the next larger chain size, plus seamless rollers.

These chains also have a 9% higher allowable load capacity, making them entirely suited to applications on such equipment as motor graders, small agricultural vehicles, vertical parking towers and skid steer loaders.

2 - Super Series chains with link plates of a special design and pitch holes that are critically formed (ball drifted) to improve their allowable load by 32%.

The pins of this chain are through hardened for greater shock load resistance and seamless rollers are employed.

3 - Super-H Series chains with link plates, whose thickness is the same as that of the next larger size of Super Series chain, and pins that are quad riveted and through hardened.

As a result, the chains have greater ultimate tensile strength and allowable load than Super Series Chains.

4 - The Ultra Super Series, which in field tests has demonstrated greater ultimate tensile strength and allowable load than any other roller chain manufactured.

As the allowable load is 62% higher than ANSI RS standard roller chain, using Ultra Super Series allows selection of a chain of up to two sizes smaller than the suitable standard chain.

Ultra Super Series is excellent for applications where heavy shock loads or space limitations pose problems, such as drilling or mining applications.

* Specification and distribution - good chain suppliers and distributors should be willing to work with Cement Mills and processing sites to find the ideal chain product for a specific site application, and as stated earlier, quality is paramount while proper care and maintenance are also essential in order to maximise wear life, limit the amount of maintenance required and prevent unscheduled halts in production.

(Even if this means not lubricating the chain at all).

Tsubaki claim that a chain that has been specified correctly for the task and is maintained correctly can be 100% reliable.

Chain products are being developed all the time and with the cement industry employing such a large number of chains, the industry can expect to be well served into the future.

* About the author - Robert Young is with Tsubaki chain.