Field of the Invention

The present invention relates to a grating roller, especially intended for grating potatoes and manioc roots, which along its periphery is provided with a plu- rality of axial grooves for holding strip-shaped grater tools, which are axially inserted into the grooves, which have an undercut with a width increasing radially inwards from the mouth of the grooves, the grooves being spaced apart by axial partitions with a predetermined minimum wall width, seen in the circumferential direction, and having a radial depth.

Background Art

Grating rollers are used in grating machines for producing starch from raw products, such as potatoes or manioc roots. In the production of starch, starch grains in the cells of the raw product are to be released by grating, separated, washed and dried. When the starch grains are to be released, the raw product is disinte- grated by means of a grating machine.

Fig. 1 illustrates a known grating machine 5 for grating potatoes or manioc roots . The machine has a grating roller 100 which is driven by a motor 7. The grating roller 100, which is shown in a partial end view in Fig. 2, has axial grater tools 3 along its periphery. Potatoes or manioc roots are introduced through an open¬ ing 6 and bounce against the grater tools on the rotating grating roller 100. During grating, the cell walls are destroyed and the starch grains are released. The grating roller 100 has axial grooves 200 uni¬ formly distributed along its periphery. A grater tool 3 is arranged in each groove 200. A grater tool 3 is here shown in the form of a grating strip 3a which is sur-

rounded by two locking strips 3b. The grater tools 3 are axially inserted into the grooves 200 and are fixed radially outwards therein. Each groove has an undercut with a width increasing radially inwards from the mouth of the groove to hold a grater tool in the radial direc¬ tion. A groove should not be formed with pointed corners since they could constitute indications of fracture. The grating roller 100 shown in Fig. 2 therefore has grooves 200 which in cross-section are substantially drop-shaped. The grooves 200 are spaced apart by axial partitions 400 with a predetermined minimum width b _m i _n seen in the circumferential direction. Said minimum width b _m i _n is determined by the strength of the roller material in com¬ bination with a given grater tool. A grater tool can be symmetrical or unsymmetrical and the shape of the groove is, of course, adjusted accordingly.

On rotation of the grating roller 100, the grater tools 3 will be pressed outwards by centrifugal force and wedged against the groove walls. The grater tools 3 in Fig. 2 are shown in this position.

The grating strips 3a are quickly worn down and must frequently be exchanged. For instance, when grating pota¬ toes, the grating strips are exchanged after 48 h, each exchange causing expensive stoppage. It is known to use reversible grating strips, which certainly doubles their life but still causes stoppage when reversing the blades .

There is a need to increase the production capacity of the described grating machine. One way of increasing the capacity is to increase the roller speed, that is make each grating strip 3a more often hit the raw product that is to be grated. However, this results in quicker wearing down of the grating strips 3a and, thus, more frequent exchanges. In the further development of a grating machine it is above all important to increase the time between exchanges and design grater tools that allow quick exchanges. Since grating strips and locking

strips are parts that are quickly worn, they must also be designed so as to be easy and inexpensive to manufacture.

The object of the invention is to provide a grating roller for the grating machine illustrated in Fig. 1 and generally described above, which grating roller allows grater tools to be arranged more closely together and, consequently, an increased production capacity compared with the grating roller shown in Fig. 2.

Furthermore with more closely arranged grater tools, finer grating and thus a higher yield are obtained, which results in a reduced loss of starch.

Summary of the Invention

This object is achieved by a grating roller of the type stated by way of introduction, which is character¬ ised in that the partitions have said predetermined mini¬ mum width (br _a i _n ) in a portion which is positioned less than 50% of the groove depth (D) from the periphery of the grating roller. This portion is advantageously arranged at such a distance from the periphery of the grating roller that the undercut of each groove extends radially inwards substantially only over the surface of the partitions, which define the groove, against which surface a grater tool abuts. For easy handling in connection with exchange, each groove is preferably symmetrical with respect to a radius which extends through the groove, and each grater tool is symmetrical with respect to a plane which is perpendicu¬ lar to said radius. As a result, two identical reversible locking strips can be used to fix the grating strip. Two locking strips make it possible to use a wider and thus more durable grating strip.

The grater tool is preferably formed with cavities, which reduces the weight of the tool and thus makes, it possible to reduce the predetermined minimum width b _m i _n .

Brief Description of the Drawings

The invention will in the following be described in more detail by way of a preferred but not limiting embo¬ diment and with reference to the accompanying drawings . Fig. 1 is a perspective view of the above-described prior-art grating machine, its protective cover being removed for the sake of clarity.

Fig. 2 is a partial end view and illustrates the above-described prior-art grating roller with grater tools inserted into some of the grooves.

Fig. 3 corresponds to Fig. 2 but illustrates a grat¬ ing roller according to the invention.

Description of Preferred Embodiments Fig. 3 shows a grating roller 1 according to the invention. This grating roller is intended to replace the grating roller 100 in a grating machine as shown in Fig. 1.

The grating roller 1 according to the invention has, like the grating roller 100 shown in Fig. 2, axial grooves 2 which are uniformly distributed along its peri¬ phery. A grater tool 3 is arranged in each groove 2. Each grater tool 3 comprises a reversible grating strip 3a, which is surrounded by two locking strips 3b which are also reversible, that is each grater tool is symmetrical with respect to a plane which is perpendicular to a radius extending through the centre of the grater tool. The grater tools 3 are axially inserted into the grooves 2 and are radially outwards fixed in the grooves . The grooves 2 are spaced apart by axial partitions 4 with a predetermined minimum width b _m i _n , seen in the cir¬ cumferential direction. Said minimum width b _m i _n is deter¬ mined by the strength of the roller material in combi¬ nation with the shape of the grooves 2 and the shape and weight of the grater tools 3. A higher tool weight implies, for example, a greater minimum width b _m i _n . Both

the grating roller 1 and the grater tools 3 are suitably made of steel.

What distinguishes the grating roller 1 according to the invention from the grating roller 100 in Fig. 2 is the design of the grooves. Each groove 2 has an undercut with a width increasing radially inwards from the mouth of the groove. The groove 2 must, as mentioned above, be undercut to hold a grater tool 3 in the radial direction outwards• The undercut of the groove 2 has the same inclina¬ tion as the undercut of the groove 200 but not the same extent. In the grating roller 1 in Fig. 3, the undercut of the grooves 2 extends radially inwards only over the surface of the partitions 4, which define the groove 2, against which surface a grater tool 3 abuts. Then the two side faces of the grooves 2 are radially inwards substan¬ tially parallel or slightly converging. The undercut of the grating roller 100 extends basically radially inwards along the entire depth D of the groove 200. The predetermined minimum width b _m i _n is generally positioned on a circular arc at a radial distance r from the centre of the grating roller. The groove has a width varying along the depth and its maximum width B _max is also positioned along a circular arc at the same radial dis- tance r from the centre of grating roller. The greatest possible number of grooves in a grating roller is deter¬ mined by the circumference O of a circle with the radius r since (number of grooves) x (b _m i _n + B _max ) = O.

It will thus be possible to increase the number of grooves in the grating roller 1 according to the inven¬ tion owing to the limited undercut, which means that the distance decreases between the periphery of the grating roller 1 and the portion where the predetermined minimum wall width b _m i _n is positioned. Said minimum wall width b _m i _n is in the preferred embodiment positioned on the line where the abutment surface between the side face of a groove 2 and a grater tool ceases radially inwards.

According to the invention, said distance is about 60% at most, or preferably 50% at the most, of the depth D. In the preferred embodiment shown in Fig. 3, the minimum width b _m i _n is positioned in a portion which is located about 40% of the depth D from the periphery of the grat¬ ing roller.

To maximise the number of grooves per grating roller, the radius r is thus selected to be as close as possible to the radius of the grating roller with regard to the abutment surface that is necessary for the fixing of the grater tool radially outwards. This abutment sur¬ face is due to the degree of undercut and the shape and weight of the grater tool.

With a diameter of 1000 mm, a minimum wall width b _m i _n of about 5 mm and a grater tool of the type shown, the number of grooves per grating roller 1 according to the invention is 187 and per grating roller 100 according to Fig. 2 only 160. For an adequate comparison of the signi¬ ficance of the design of the groove between the grating roller 1 in Fig. 3 according to the invention and the prior-art grating roller 100 in Fig. 2, both rollers are illustrated with the same type of grater tools.

The two locking strips 3b in the grater tool 3 are suitably identical and symmetrical with respect to a plane which extends perpendicular to a radius passing through the grater tool. As a result, they can be insert¬ ed into the grooves turned up or down. If the grating strips 3b are to be reversed but not exchanged, the entire grater tool 3 is thus turned without time-consum- ing removal of the locking strips from the grating strip, turning and reassembling. When exchanging a grating strip 3a, the operation of checking in which direction the locking strips 3b are turned is omitted. The grating strip 3a and the locking strips 3b further have pins and holes (not shown) to hold each other in the longitudinal direction.

The grating strip 3a and/or locking strips 3b of the grater tool 3 is/are further provided with recesses (not shown) . This reduces the weight of the strips 3a and 3b, which in turn means that either the predetermined minimum length b _m i _n can be reduced, or the rotating mass and thus the stop and start time of the grating roller 1 can be reduced.

On rotation of the grating roller 1, the grater tools 3 will be pressed outwards by centrifugal force and wedged against the groove walls, with the grating strips 3a projecting beyond the surface of the grating roller 1. The grater tools 3 are shown in this position in Fig. 3. It is important for wear to occur on the easily exchange¬ able parts, that is on the grating strips 3a and locking strips 3b, and not on the grating roller 1. Also the locking strips 3b, which surround a grating strip 3a, should therefore project beyond the outer surface of the ^" grating roller as the grating roller rotates.

With a given roller radius and a minimum wall width bmin _/ it is possible to achieve a higher production capa¬ city while maintaining the speed of the roller with a grating roller according to the invention, compared with a grating roller according to Fig. 2.

Alternatively, it is possible, with maintained pro- duction capacity, to reduce the speed of the roller and thus reduce the energy consumption with a grating roller according to the invention, compared with a grating roller according to Fig. 2.

Even if the invention has been described in connec- tion with a grater tool with two symmetrical locking strips, it will be appreciated that the inventive idea of optimising the number of tools per grating roller based on a given minimum wall width b _m i _n is applicable also to a grating roller whose grater tools have only one locking strip and/or unsymmetrical locking strips.