Classifying – separating – and assorting solids – Sifting – Elements
Patent
1996-01-17
1999-12-07
Bollinger, David H.
Classifying, separating, and assorting solids
Sifting
Elements
B07B 149
Patent
active
059968079
DESCRIPTION:
BRIEF SUMMARY
The invention is directed to a screening device with a gauze or screen fabric having two groups of threads, the threads of one group running substantially orthagonal to the threads of the other group.
Screening devices, also referred to in the following as screens for the sake of brevity, are needed in a great many applications for sorting out particles from a product which do not exceed a determined size. Such screens are also used, among other things, for obtaining a starting product which is free of foreign bodies. The foodstuffs industry and pharmaceutical industry are especially important fields of use. In this case, products intended for human consumption must be prepared. For instance, flour must be screened so that it is free from foreign bodies such as stones. In nut grinding, it must be ensured that no nut shells are contained in the end product. Such stones or nut shells, if bitten, can cause injury to the consumer.
The screen fabric is relatively highly stressed, among other things by vibrations which occur when the material to be screened is moved across the screen fabric. Without such movement, however, satisfactory screening cannot be ensured in practice. The stresses can result in damage to the screen fabric. In this case, a hole is made in the screen fabric which is larger than the mesh width so that particles of a size which should be sorted out, per se, reach the starting product. Even if the defect is detected, a relatively large amount of the starting product must generally be reprocessed to ensure that no unwanted foreign bodies have been introduced into the starting product accidentally since the occurrence of the defect. As this is very expensive and also involves a relatively high liability for the producer, the screen fabrics are changed periodically at intervals which are so selected that the probability that no defect has yet occurred in the screen fabric is very high. Consequently, the intervals must be very short. Many screen fabrics are still completely intact when exchanged so that the premature exchange, in principle, represents a waste of material. Moreover, the amount of labor involved in exchanging the screen fabric is relatively high because the screening device must be at least partially disassembled. On the other hand, it is not possible to rule out every defect with certainty.
For this reason, various suggestions have been made in the past for monitoring the screen fabric by means of auxiliary devices. For example, a device for monitoring wear in material webs exposed to operating stresses is known from DE 24 43 548 A1. In this device, at least one electrically conducting control thread is introduced at intervals in the material web to be monitored. This electrically conducting control thread is connected with a measuring device for determining the increase in its electrical resistance in order to detect the cross-sectional reduction of the control thread which is concomitant with wear. However, this results in the problem of additionally introducing a control thread in the material web. This control thread causes local changes in the movability of the screen fabric which becomes harder in the region of the control thread. This also changes the vibrating behavior of the screen fabric which leads to the risk of increased susceptibility of the screen fabric to breakage in the vicinity of the control thread. Further, a control thread of this kind allows only a relatively crude monitoring of the screen fabric. Generally, damage confining itself to the size of a few meshes cannot be detected.
A similar design is known from DE 28 47 153 A1. In this case, another electrically insulated wire system is woven into the wire gauze. This wire system runs axially along the entire circumference of the screening drum with laterally closely spaced hairpin windings and is connected to a power source.
DE 31 43 779 A1 shows a device on sifting devices or screening devices for monitoring sifting cloths or screening cloths for crushing and sorting installations in the metallurgical and st
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patent: 3620368 (1971-11-01), Comis et al.
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patent: 4491517 (1985-01-01), Janovac
patent: 5039412 (1991-08-01), Marsh
Dellmann Paul Gerhard
Rumpf Wolfhard
Bollinger David H.
Dietrich Reimelt KG
Kueffner Friedrich
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