In all crushing applications, the end user experiences wear on their crushing elements, whether it be jaw dies, Cone Crusher liners, Horizontal Shaft Impact Crusher blow bars or the rolls in Roll Crushers.
If one was able to extend the life of these elements, this would equate to increased production due to less downtime required for maintenance and lower cost per ton by increased wear life, which ultimately equals more sellable product and profitability, not to mention the safety aspect and less exposure for possible injury to your workforce because of less wear parts being replaced.
Introduction of weld-on crusher teeth
In 2003, McLanahan Corporation initiated the development of a weld-on tooth for our roll elements with a focus on two key elements: first and foremost, the tooth must offer a substantial increase to wear life, which ultimately reduces downtime and maintenance costs; second, the tooth must be replaceable so the life of roll elements can be maximized.
Feeding from earlier successes using carbide tooth caps, we recognized a need for carbide in more than one plane to further protect a tooth’s leading edge.
To achieve these objectives, several issues had to be overcome, including the use of dissimilar materials, as well as the casting process that would allow for carbide to be evenly distributed on two planes of the crushing surface. The end result was a casting (shown below) impregnated with carbide particles of varying sizes in the front and top that could be successfully welded to base elements specific for a Roll Crusher design.
Field trials
Once developed and our internal testing complete, the focus shifted to field trials. A select mine in the Powder River Basin was chosen due to the amount of tons processed and because they were already using McLanahan roll elements with teeth having carbide tooth caps.
Prior to the development of these teeth, mines utilizing our roll segments were processing approximately 20 million tons of coal before having to address wear or replace with new. With the implementation of this design, the carbide impregnated teeth were an instant success. The mines were able to process approximately 40 million tons before needing to address the segments.
After additional meetings, it was discovered that it wasn’t wear on the teeth that was forcing the mines to change the roll segments, but wear on the segment body as well as missing teeth. Therefore, we determined that the weld securing the teeth was most prone to wear, so we began to cover the weld joint with hard-surfacing.
In addition, we began applying hard-surfacing to the segment body radially (with the direction of rotation) rather than the standard cross-hatch pattern. These simple changes have allowed these mines to process in excess of 60 million tons over a set of our roll segments equipped with carbide impregnated teeth.
Success stories
Since the success in the Powder River Basin, roll elements with carbide-impregnated teeth have proven successful in many different applications, including: ROM coal with high percentage of ash (rock), bauxite ore, polymetallic ore (zinc/silver/lead), salt and most recently, phosphate ore. No matter the application mentioned, all installations have reduced maintenance time, which obviously increases operating time.
Other examples of how carbide-impregnated teeth have increased operating time include the following:
For ROM coal
A prep plant in Utah that was processing ROM coal from their underground mine would install a set of roll shells rebuilt by a local shop into their machine. The machine would operate for approximately six weeks before the customer would spend 36 hours every weekend welding on and building up the teeth and adding hard-surfacing in preparation to operate the next week. After repeating this process for six months, the shells would be removed and replaced with another set.
After installing a rebuilt set of roll using carbide-impregnated weld-on teeth, the customer addressed some minor wear on the roll shell bodies after six months of operation. After 12 months of operation, some missing teeth were replaced (the crushers will occasionally receive some uncrushable material from the underground mine). At 16 months, the customer removed the shells and installed another set.
For phosphate ore
At another mine in Utah, a McLanahan Heavy-Duty Double Roll Crusher was processing phosphate ore using hardened steel segments with each tooth hard-surfaced. Due to the speed at which the roll assemblies were turning, combined with a high feed rate and large feed size, the customer was forced to address wear on the segment teeth at least two shifts per week. One segment equipped with carbide-impregnated weld-on teeth was installed among a balance of the existing cast steel segments with hard-surfaced teeth.
The customer continued to hard-surface teeth on the existing segments; however, the customer did not need to address the segment equipped with carbide-impregnated teeth for approximately nine months.
Since then, the customer has equipped one roll assembly with carbide tooth segments while consuming stock of the original cast steel segments. The last report is that the segments have been in operation for more than a year with no additional maintenance required.
Other successes
There are certainly other successes; we have not witnessed one installation where carbide-impregnated teeth have not met or exceeded the customer’s expectations. Although impossible to predict or guarantee their duration, many applications that have been converted to carbide-impregnated teeth have improved wear life a minimum of three to four times.
In addition, the teeth are also sold separately for the support of existing roll elements. Therefore, if teeth wear or one is broken off due to uncrushable material, new teeth can be welded in position for continued operation.
For more information on how carbide-impregnated weld-on teeth can help you reduce downtime and increase productivity, contact McLanahan.
