|Title of Invention||
"SIEVE FRAME FOR PLAN SIFTERS"
|Abstract||'Sieve frame' for plan sifters which can be inserted into or applied to a sieve box (6) consisting of a frame with a base (7) and a fine material outlet, the sieve frame (1) being covered with a sieve cloth (4) and comprising at least one batten (2), characterized in that sieve frame (1) and sieve batten (2) consist of a plastics material and in that the sieve cloth (4) is surrounded with material in the region of the surfaces of sieve frame (1) and batten facing the sieve cloth, the sieve cloth being surrounded by foaming in said regions.|
|Full Text||The present invention relates to a method of producing a sieve frame for plan sifters and a sieve frame.
The invention relates to a sieve frame for plan sifters, in particular an insertable sieve frame which is inserted into a sieve box of a sieve and a method of producing such sieve frames,
A plan sifter, in particular a large plan sifter or square plan sifter is a cubic shape with large flat elements and is used for the sieving of corn, grit-like and floury products in milling and for sorting various types of cereal grains and the like.
With many separation procedures, for example in processing, it is known to reduce the product humidity, where necessary, so the separating devices do not clog. On the other hand, optimum moisture is desired for the processing of ground cereal products to flour, grit, shot etc. However, as repeated grinding and sieving has to be carried out in a cereal mill, the humidity is adjusted according to comminution and not according to the best possible sifting effect.
It is known that many ground fractions have poor flow behaviour .sifting behaviour owing to their moisture content. ...
All possible sizes of sieve mesh widths are used in a plan sifter, from about 80 urn upwards. Maximum sifting, performance is to be achieved similarly for all, without clogging of the sieve mesh. The sieve cloth is tensioned over a sieve frame which, in turn, is inserted in a sieve box comprising a base plate and a fine material outlet as well as freely movable cleaning elements as described , for example, in EP-B-584302, EP-A-330846 or US-PS 3565251 etc.
The maximum possible throughput and the highest possible quality of ground products must be attainable. In contrast to conventional sieving, a closed layer of product up to several centimetres is maintained over the sieve covering when sifting in mills. As a result, a greater pressure acts downward on the finer heavier particles against the sieve covering, resulting in a higher throughput or a higher sieving performance. Flat husks (coarse material), on the other hand, should float to the top with the layer as sieve reject. With moist products, this method of thick layer sifting leads to frequent clogging of the sieve cloth and caking of product on the sieve box or the base plate.
More powerful plan sifters have been developed systematically in the past and the sieve cleaning has been continuously improved without basically overcoming the aforementioned (product-induced) problems. Numerous variations of forms and materials have been tested, some of which have been used in practice. Only a few forms have been retained in large plan sifters.
As already mentioned, keeping the base plate completely free is a further problem in plan sifters. The fine material passing through the sieve meshes (sifted matter) should be removed from the base plate in the shortest possible time and should be discharged through lateral slits. A variety of base cleaners has been developed for this purpose.
Several factors influence the mode of operation of plan sifters. Thus, a freshly covered sieve frame usually operates better as not only the wear of the cloth but also the tensioning of the sieve cloth are important. It is known from experience that plan sifters are subject to natural limits of performance, for example the intensity of the oscillating
movement (maximum acceleration) owing to the maximum permitted forces in the plan sifter housing and on the other hand due to the movement of the product. Excessive accelerating forces obstruct the free passage of the product. The performance is determined by the specific quality of the individual sifted fractions.
It is proposed in DE-A-2506981 that the base plate be given a sawtooth-shaped surface so the product can be discharged intermittently and in a short period. Advantages can be imagined in specific cases but fine ground fractions are also expected to quickly clog the base plates and sieve boxes. A main requirement, however, is that a key machine of this type operates as far as possible in a self cleaning mode and can be cleaned easily and with minimum expenditure if necessary.
EP-A-330846 and WO 93/16815 disclose devices for plan sifters consisting of a plan sifter sieve comprising a sieve housing with fine material outlet , an insertable sieve frame and freely movable cleaning elements, the sieve frame being provided with a cover only on one side and batten subdivisions at least in one direction for forming an appropriate number of cleaning fields and base plate and wherein, furthermore, cleaning elements rest on the base plate and can be inserted into the cleaning fields. Support grids are not required with these solutions. According to EP-B-584302, the sieve frame is designed as an insertable frame without connecting elements, but consists of assembled individual parts, preferably of metal or a metal/wood composite. The sieve frame is advantageously produced from light metal profiles as a welded or adhered unit. The inherent rigidity is sufficiently high to absorb the forces occurring with a one-sided sieve covering without significant deformation. A light metal frame of this type, in particular of aluminium, may be subject to problems of authorization
specific to the country, the production costs are comparatively high (though significantly lower than with conventional screw fittings or the like) and problems with the strength of the joints (in particular adhered points) are possible owing to the dynamic stress. The sieve box is designed in a known manner as a wooden frame which is stable in shape and size,- and product carrying surfaces can be coated with plastics material. Sieve frame and sieve box are adapted to one another such that the former can be inserted alackly on or in the sieve box. The base plate of the sieve box can consist of both metal and plastics material, the latter being adapted to specific cases. It is also known from EP-A-330849 to provide the internal surfaces of the aluminium sifter casing with a wear-resistant lining of foamed plastics material which is compatible with foods, also for sound insulation and sealing purposes.
Accordingly, there is provided a 'Sieve frame' for plan sifters which can be
inserted into or applied to a sieve box consisting of a frame with a base and
a fine material outlet, the sieve frame being covered with a sieve cloth and
comprising at least one batten, characterized in that sieve frame and sieve
batten consist of a plastics material and in that the sieve cloth is arranged
so as to be surrounded with material in the region of the surfaces of sieve
frame and batten facing the sieve cloth, the sieve cloth being
surrounded by foaming in said regions.
It is accordingly the object of the invention to develop a generic insertable sieve frame so as to improve its functionality and simplify production. A further object is to develop an improved method of producing the sieve frame.
The object according to the invention is achieved in that the sieve frame, including battens, consists of a plastics material and preferably contains a reinforcing skeleton. In the simplest case, the skeleton is a welded metal profile frame. The plastics material is preferably a foamed plastics material, in particular a polyurethane.
Sealing elements can also be incorporated by foaming as a substitute for conventional felt seals. The sieve cloth is also foamed in.
With respect to the production process, the object is achieved in that the skeleton and the sieve cloth are inserted into a
mould and the complete frame is then foamed in in one operation with simultaneous tensioning of the sieve cloth/ to different extents according to cloth thickness. In the region of the sieve frame and the battens, the sieve cloth is surrounded by plastics material and is embedded therein.
The insertable sieve frame basically has the advantages
described in EP-B-584302, i.e. it can easily be removed from a
sieve box and the sieve cloth can be cleaned on both sides with minimum expenditure, including a treatment with water, hot steam or the like. Sieves can also advantageously be stacked in the plan sifter compartment. The advantageous formation of the base plate from plastics material considerably reduces the adhesion of product and contributes to noise reduction, when sieve cleaners made of plastics material are also used.
An embodiment of the invention is described in more detail
, hereinafter with reference to accompanying drawings,
Figure 1 shows a sieve frame.
Figure 2 shows a detail of the sieve frame according to Figure
Figure 3 shows a sieve box with a partially applied sieve frame.
A sieve frame 1 often has 6 to 12 cleaning fields of rectangular shape. Figure 1 shows a subdivision into only 4 cleaning fields by means of battens 2 for the sake of clarity. Reference is made, for example, to EP-B-584302 for a detailed description of the known sieve box 6. As a freely exchangeable insertable sieve frame, the sieve frame 1 has only a small height, of which the inherent rigidity is sufficiently high
owing to a continuous metal core 3. This metal core 3 is surrounded by foamed polyurethane and therefore forms an integral sieve frame 1. The sieve cloth 4 lies taut on the sieve frame 1 and the battens 2 and is positively surrounded at these points by foaming so slackening of the cloth tension is prevented. The sieve box 6 has foamed-in seals 5', just like the sieve frame 1 can have such seals 5 instead of the conventional felt seals.
The base 7 of the sieve box 6 is also a foamed polyurethane part on which known sieve cleaners 8, 8' are freely movably arranged (with respect to cleaning field).
The sieve frame 1 seals the sieve box 6 flush at the top with the sieve cloth 4.
The sieve frame 1 is produced by initially inserting the metal
core 3 in the form of a welded assembly of round steel profile
parts or the like into a mould, not shown. The
sieve cloth 4 is then arranged in the mould in such a way that it is completely surrounded by foaming in the sieve frame 1 and the battens 2 with simultaneously tensioning. The latter can be carried out in various ways. For example, the sieve cloth 4 can be placed flat on the sieve frame 1, any projections being removed after foaming. Or the sieve cloth 4 is surrounded by foaming completely or partially to the height of the sieve frame 1, or a combination of the two variations is possible.
The polyurethane foam is then introduced and the finished sieve frame can be removed after curing. The polyurethane is preferably compatible with foods.
The invention is not restricted to this example.
List of reference numerals
1 sieve frame
3 metal core
4 sieve cloth
5, 5' seal
6 sieve box
7, 7' base
8, 8' sieve cleaner
1. 'Sieve frame' for plan sifters which can be inserted into or applied to a
sieve box (6) consisting of a frame with a base (7) and a fine material
outlet, the sieve frame (1) being covered with a sieve cloth (4) and
comprising at least one batten (2), characterized in that sieve frame (1)
and sieve batten (2) consist of a plastics material and in that the sieve
cloth (4) is surrounded with material in the region of the surfaces of
sieve frame (1) and batten facing the sieve cloth, the sieve cloth being
surrounded by foaming in said regions.
2. Sieve frame as claimed in claim 1, wherein the sieve frame and sieve
batten(s) additionally contain a continuous skeleton.
3. Sieve frame as claimed in claim 2, wherein the skeleton is a metal
4. Sieve frame as claimed in claims 1 and 2, wherein plastics material is
5. Sieve frame as claimed in claim 1, wherein the entire sieve box and
including the base consists of foamed polyurethane.
6. A sieve frame comprising a sieve mesh (4) having a number of
peripheral frame elements (1) extending along the edges of the sieve
mesh (4), wherein the frame elements are formed from plastics
material and the edge region of the sieve mesh is embedded into the plastics material.
7. A sieve frame as claimed in claim 6, wherein a transverse frame
element or batten (2) extends across the sieve mesh (4) to divide the
sieve frame into two regions, the batten being formed from plastics
material and a portion of the sieve mesh (4) adjacent the batten (2)
being embedded therein.
8. A sieve frame as claimed in claim 6 or claim 7, wherein the frame
elements (1,2) contain a reinforcing skeleton (3).
9. A Sieve frame as claimed in claim 8, wherein the skeleton is a metallic
reinforcing core (3).
10. A sieve frame substantially as herein before described with reference
to and as illustrated in the accompanying drawings.
|Indian Patent Application Number||642/DEL/1998|
|PG Journal Number||13/2009|
|Date of Filing||12-Mar-1998|
|Name of Patentee||BUHLER AG|
|Applicant Address||CH-9240 UZWIL,SWITZERLAND|
|PCT International Classification Number||B07B 1/42|
|PCT International Application Number||N/A|
|PCT International Filing date|