In 1989, MMD were invited to Sac-Tun mine in Mexico to investigate how a Sizer could assist with the processing of coral limestone for use in the cement industry. The mine’s existing primary jaw crusher was failing to break the limestone with the material either stalling or being ejected from the machine. MMD believed the Sizer could meet the customer’s requirements, and what followed was a partnership which has continued for over 30 years, where together MMD and the mine operators discovered that when it comes to crushing, the hardness of a material isn’t necessarily its most important attribute.
All the limestone at Sac-Tun passes through one primary crushing station, so everything downstream relies on this one machine. In replacing the jaw crusher, the requirements of the Sizer were to reduce the limestone down from 1200mm lumps to 300mm, achieve a throughput average of 2,000tph, and remain reliable whilst being efficient to run.
Coral limestone features a honeycomb-like structure, which compresses under pressure. This elasticity means the limestone resists breaking in compression and absorbs power, making it a particularly difficult material for a traditional crusher to handle. However, because the Sizer breaks rock under tension and sheer rather than just compression, it is able to effectively cut through the limestone and avoid its natural resistance to compression. The Sizer is unique in this regard and may be the only machine capable of effectively crushing this kind of material.
Once installed the Sizer was successful in breaking the limestone, however, in the early days, the materials ability to absorb power meant the machine would occasionally stall. Working with the customer and following some initial variations and experiments, MMD designed a bespoke drive train and spur gearbox arrangement which timed the Sizer shafts together. This resulted in double the torque now being delivered to the shafts, whilst drawing even less power from smaller motors. This proved to be an ideal solution, simultaneously being more energy efficient and eliminating any stalls. Consequently, the mine’s production rate has increased significantly and annual targets are consistently met and surpassed.
Carlos Lesser, the mine’s Operations Manager of 32 years said: “We’ve worked with MMD from the very beginning with a targeted production of 2,000tph. Today, we’re producing 3,000tph with an even smaller Sizer than what we started with. [MMD] made an important effort to modify their technology to our specific needs and thanks to the Sizer,we’ve enjoyed huge company success.”
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