Double-toothed Roller Crushers Double-toothed Roller Crushers for difficult Materials
In recent year, mainly as a result of environmental problems, the raw material crushing sector has often had to use quarries in which the materials are imperfect or mixed with soil. This has made work difficult to traditional crushers, such as impact or jaw crushers, because they are often required to process materials for which they have not been designed.
Bedeschi machines have been installed in difficult location worldwide. The company promotes the spread and development of double-toothed roller crushers, which are employed in many different fields: cement plants, mining firms, brick and tile factories and company specialized in waste processing scrap material. They are basically very simply machines; they consist of two toothed rollers turning in opposite directions and the material to be crushed is made pass between them. The material is not crushed through compression but through a combination of shear and tensile stresses.
The processing system of the double-toothed roller crusher makes it possible to crush any type of raw material from hard (limestone and rock) to soft (clay, soil and mud) or even elastic-like wood or rubber tyres. The rotation speed, especially if compared to traditional crushers, is very low; so low, in fact, that tip speed is under 3 m/s.
These crushers have turned out to be particularly effective in situations where other crushers experience problems. They are ideal for processing wet, sticky materials, and blocks of hard material mixed with soil, in addition to crushing ordinary hard materials. Under these conditions, traditional crushers clog. Double-toothed roller crushers are equipped with scrapers, which keep the grooves and the work surface perfectly clean.
These crushers are invaluable for crushing clay, soil and sticky materials containing up to 30 % moisture content or rocks covered with a layer of soil, a situation that, as mentioned earlier, is often encountered due to environmental restrictions imposed on quarries. The majority of cement plants set up in the 1990s in the Far East where, because of the frequent rain, raw materials are very moist, are equipped with clay crushing systems with double roller crushers; most of them supplied by Bedeschi. These machines allow a maximum reduction ratio of ten at each crushing stage.
They can act as primary or secondary crushers and can be installed to suit any required arrangement, even one on top of the other, with the primary crusher discharging directly onto the secondary crusher.
In double roller crushers, the outlet size depends on:
- the gap between the two rollers and
- the size, shape and number of teeth.
The gap is adjusted in the factory according to project requirements but can be easily changed after the machine has been put into service, to improve or change crushing parameters. The roller gap of Bedeschi crushers can easily be adjusted to individual preferences.
The study and dimensioning of teeth is particularly important. Bedeschi technical staff, thanks to their calculation models defined over many years of experience, establish the characteristics and shapes that most suit the material to be crushed and the customer’s outlet size requirements. The most important and qualifying tooth characteristics are:
- number of teeth on each roller,
- tooth shape, and
- tooth thickness.
These crushers, due to their special crushing method, are characterized by their relatively low power consumption compared to traditional crushers. Many applications and tests confirm an average power absorption of 0.3 to 0.4 kWh/t.
Their special design, featuring an external reduction unit, allows compact sized machines to be made, which can be installed where space is at a premium; installations in tunnels are a particularly significant example.
Another important characteristic of double roller crushers is that, since the material is crushed by applying shear stress, not compression, they produce low levels of fines.