Classifying – separating – and assorting solids – Sifting – Drum sifters
Patent
1997-09-03
1999-11-16
Terrell, William E.
Classifying, separating, and assorting solids
Sifting
Drum sifters
209290, B07B 122
Patent
active
059841060
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a machine for sorting solid objects comprising a horizontal or slightly inclined rotary drum through which the objects to be sorted pass longitudinally and the wall of which is riddled with calibrated sorting holes, in which machine the drum consists, in the longitudinal direction, of various sections, the size of the sorting holes increasing from one section to the next in the direction of progression of the objects to be sorted.
Although not being limited thereto, the invention more specifically targets a machine for sorting the grinding bodies which form the grinding charge of a horizontal mill, such as those used in cement making or in the mining industry for grinding and crushing ores.
It is well known that the composition of the grinding charge, that is to say the quantity, the size of the grinding bodies and their distribution greatly influences the yield and quality of the grinding.
The wear of the grinding bodies constantly alters the ideal starting conditions throughout the service life, and this is why it is attractive to be able rapidly to sort the grinding charge in order to allow it to be returned to optimum conditions.
It is envisageable to carry out this sorting operation frequently only if it can be done quickly, without increasing the normal down-time of the mill.
The consequence of this is that the sorting machine has to have a high sort rate.
Various types of machines for sorting the grinding bodies are known. The machine described in document BE-834187 essentially includes two cylinders which are slightly inclined with respect to the horizontal and which define between them a sorting slot the width of which increases from one side to the other. These two cylinders turn in opposite direction, each turning outwards. The grinding bodies are tipped out into the sorting slot on the minimum width side thereof. The bodies progress under the effect of the rotation and of the inclination of the cylinders and drop through the slot into various collecting hoppers as soon as the width of the slot exceeds the minimum cross-section of a body to be sorted.
This machine gives good sorting provided that the grinding bodies progress in a string one at a time along the cylinders. Under these conditions, the sorting rate is, however, very low.
Another machine is the one described in the preamble and which forms the subject-matter of French Patent Application No. 2248884. The shape of the sorting holes generally corresponds to that of the grinding bodies. To favour the longitudinal movement of the bodies to be sorted the drum is preferably inclined upwards in the direction of progression. As the bodies to be sorted advance through the drum and find a passage larger than their minimum cross-section they pass through this sorting hole to drop into a collecting hopper placed under the drum.
This machine suffers from the handicap that the bodies to be sorted easily become jammed in the sorting holes which thus become obstructed, a phenomenon which not only reduces the surface-area for sorting and therefore the rate but also reduces the sorting accuracy because the bodies to be sorted progress too rapidly towards the outlet since the holes of their size are obstructed.
The object of the present invention is to provide an improved sorting machine which does not have the aforementioned drawbacks; in other words a machine which is endowed with good sorting accuracy and which operates at a high sorting rate.
In order to achieve this objective, the invention proposes a sorting machine of the kind defined in the preamble which is characterized in that each section includes a frustoconical wall converging in the direction of progression of the objects and in that the sorting holes are in the form of slots which widen in the direction of progression through the drum.
The fact that the various sections have a frustoconical profile contributes to favouring the grading of the grinding bodies in superimposed layers, the large bodies as a preference occupying the upper layers and the smaller
REFERENCES:
patent: 107994 (1870-10-01), Allonas
patent: 182693 (1876-09-01), Neuerburg
patent: 772331 (1904-10-01), Baxter
patent: 1617688 (1927-02-01), Toole
Crawford Gene O.
Magotteaux International
Terrell William E.
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