MMD (Mining Machinery Developments), the inventor and patent holder of the twin shaft mineral sizer, is playing an ever-increasing role in the world’s cement industry.

The MMD mineral sizer was originally designed in 1978 to meet the requirements of the British underground coal mining industry. Having successfully achieved this in the demanding underground coal mining environment, it became evident that the unique attributes and advantages of the MMD twin shaft mineral sizer could be applied to other underground and surface applications and industries. Today, MMD can process over 65 different minerals worldwide, in many varied process industries.

The first unit in to the cement industry was delivered to Cauldon cement works in the UK, (then part of Blue Circle Cement, now Lafarge), in the early 1980s. In contrast to the smaller 500mm centres machines supplied to the underground coal mines, this was a larger unit with 1000mm shaft centres, designed to handle large pieces of shale. This 1000 Series sizer rapidly proved its capabilities as a primary crusher and after providing years of valuable service at the cement plant has been sold to an opencast mine in the Philippines, where it is still working today. This machine was soon followed by another, this time to size sticky clay containing hard material within it. Despite there being specialist clay machines on the market, the issue of sizing this mix of materials was a universal problem, and again the MMD machine proved to be an instant success, and very quickly the industry came to appreciate the unique capabilities of the MMD twin shaft mineral sizer. The MMD 750 Series twin shaft sizer has also been successfully employed in a secondary role at the Cauldon Cement Works for many years and has recently undergone an upgrade to bring its capacity to 1200tph.

Although the major portion of MMD’s interface with the cement industry is still in hard rock quarries and clay, it is by no means confined to these areas, MMD having gone on to increase their product range to include equipment such as their heavy- duty plate feeder, and adapt existing products to meet the requirements of the cement industry.

Against many odds

In the current economic climate of rapidly rising fuel costs and with environmental pressures being felt across all industries around the world, the importance of the cement industry taking a new look at the significant progress being made regarding these issues in the allied mining industry, cannot be underrated.

Although the volume of the raw materials required by the cement industry is low compared with mining, it is a highly visible and therefore potentially contentious element in the production chain, as cement plants tend to be developed close to the markets, and hence in more sensitive areas. A situation which makes the growing use of In-Pit Crushing and Conveying (IPCC) rather than truck haulage, an area of particular significance. Not only does IPCC allow for a reduction in the dependence on expensive oil based fuel, it is seen as being eco-friendly due to the potential reduction (or elimination) of green-house gasses in exhaust fumes as well as the noise and dust generated by trucks.

Mobile crushers and IPCC are not new concepts and their benefits are well established within quarrying. However, the vast majority of these quarries produce at a lower rate than is generally required by cement plants. But this scenario is changing, due to both the unprecedented boom in the commodities market and rapid urbanisation. New IPCC installations in mining and articles and conferences dedicated to this technology, have resulted in a proliferation of the number of companies which are developing or attempting to develop high capacity equipment for the burgeoning IPCC market. This is a field where MMD, who have championed the use of mobile sizing equipment in both the mining and cement industries, can justifiably lay claim to being world leaders, having consistently been involved in this market for over 25 years. During this time, they have installed a host of semi-mobile units, as well as a significant number of low (under 1000tph), medium (2-3000tph), and high capacity (over 5000tph) fully mobile sizers around the world. The unique know-how and experience gained has allowed them to be able to offer the best possible unit, with all the inherent benefits of mobility to the cement industry. However, for the cement industry especially, it is not enough for a potential supplier to be capable of providing high capacity units. The demands for flexibility, consistency in product size and chemistry are onerous. The real need being for equipment which is capable of handling a range of material having very different physical characteristics, as the requirement for a chemically consistent product usually involves blending the core limestone with different often sticky materials.

Breaking and mixing

A prime example of this is the use of the sizer to not only break, but mix the material too; the MMD twin shaft sizer’s contra-rotating shafts and scroll action are ideal for blending the different materials, even those with very different constituencies and moisture content. An increasing number of cement plants are using the MMD sizer in this breaking-cum-blending role. A cross- belt analyser is linked to the variable speed drive of the apron plate feeders, feeding limestone, clay and additives into the sizer, thus ensuring a consistent mix of material to the stockpile and eliminating the need for separate stockpiles and the problems associated with the stockpiling of sticky clay material.

MMD’s existing record within the cement industry and the established features and benefits of the mineral sizer, will hopefully lead to an increased use of this now well established technology. The MMD twin shaft mineral sizer is not limited to a high capacity primary sizing role, there have been numerous examples of cases where the installation of an MMD sizer has either replaced or supplemented the existing equipment when problems have been encountered. For example, in Belgium an MMD sizer was installed in a plant that had been running for many years, where the ever- increasing stickiness was causing problems for the existing roll crusher. The compact size and low profile allowed MMD to install the sizer over an existing conveyor line, involving minimal expense and complication.

Similarly, this new cement plant designed and installed by one the world`s leading cement manufacturers suffered severe production hold-ups due to the amount of clay in the system. The problem was put to MMD, who quickly resolved the situation with a simple installation of a 500 Series sizer within the existing plan, successfully allowing the plant to run at full production.

Some of the most recent orders won by MMD to supply equipment to the cement industry include: A 500 Series twin shaft sizer to process 200tph of clay, from an in-feed size of 350mm to a product size of 80mm, for an Ital Cement plant in Italy. For Volsk Cement in Russia, an apron plate feeder and two 500 Series Twin shaft sizers to reduce gypsum slag (additives) from 350mm in-feed down to 75mm at a rate of 150tph. Plus, for the same plant; a 350 Series machine to reduce gypsum from a feed size of 75mm to a 25mm product at 22tph.

Having supplied their technology worldwide to a variety of cement producers such as Holcim, Cemex, Lafarge, Heidelberg, Italcementi, CRH, Buzzi and Titan Cement as well as to leading cement plant designers such as FLS and Polysius, MMD can justifiably lay claim to a position amongst the leading suppliers to the cement industry.