40 years of reliability for Singleton Birch Limited with Mogensen Sizer machines
Singleton Birch Limited at Melton Ross Quarry in North Lincolnshire has been quarrying and processing Lincolnshire Wolds chalk for almost 200 years, and is the UK's largest independent manufacturer of lime products.
The company has a long-standing relationship with Mogensen UK having installed its first Mogensen machine, a 5-deck Sizer, about 40 years ago. At that time Singleton Birch wished to increase production in a long-established part of the plant, where space was restricted. It was possible to increase crusher and conveyor capacity without great difficulty but screening caused a problem in that there was insufficient space available to accept the much larger conventional screen needed.
The management had earlier read press reports about the Sizer and Dr Fredrik Mogensen's article, published in 1965, explaining the theory and practice of his new screening technique. They were intrigued by the claims that the Sizer could screen about five times the amount of material as could be handled by a conventional screen occupying the same floor space, could at the same time provide a satisfactory screening result in appropriately chosen circumstances and be very resistant to the problem of screen-deck "pegging". They decided to install a machine, and found that the Sizer in that installation did live up to its promises and also reduced maintenance costs in that the mesh panels were smaller and, therefore, easier and quicker to change than the panels in normal screens.
The theory behind the Mogensen Sizer is based on the realisation that the effective aperture of a sloping screen mesh is less than its actual aperture; as seen by a falling particle it is the vertical projection of the aperture. Dr Mogensen started to study this effect in 1947 and found that some scatter occurred, i.e. that the separation achieved was not very sharp. He found that several decks mounted one above the other were necessary to achieve a better result from what he had started to call probability screening, each deck refining the result obtained from the one above.
Following this line of thought during the 1950s he developed a vibratory machine, which comprised seven parallel screen decks arranged vertically one above the other. This improved considerably on the effect obtained from a single deck: further experimentation and mathematical analysis, however, showed that five decks arranged at increasingly steep angles from the top to the bottom of the machine delivered a much sharper separation. This resulted in the "fan" configuration used today. (See image 1, shows the Sizer making two separations, i.e. three products).
It was found, moreover, that the principle would work only if individual particles were free to behave independently, i.e. free from the pressures and interference found, when a bed of material is allowed to build up on a screen deck. The combination of this freedom of movement, the greater particle speed (aided by gravity) and the greater open mesh area available explain the increase in specific capacity in relation to occupied area offered by the Sizer.