CRAB SORTING SCREEN FOR PRAWN FISING

Abstract: Crab sorting screen for prawn fishing, comprising a rotary cylindrical drum formed from a round bar (3) formed into a spiral and with collecting trays (6) disposed between the spiral windings, which are attached by their top edges (10) to opposite spiral parts of the round bar (3), the trays (6) being arranged in a continuous row, with their open side facing the inside of the drum; the trays have an increasing depth in the peripheral direction of the drum and are connected to each other so that each collecting tray is attached by the shallowest end (11) part thereof to the deepest end part (12) of the tray preceding it in the direction of rotation (D) of the drum and to the top edges thereof, so that at that end a sorting aperture (14) is formed.

Description: The invention relates to a crab sorting screen intended for use in prawn or shrimp fishing, comprising a rotary cylindrical drum having at the ends thereof an infeed and discharge opening respectively, and provided with sorting apertures along the entire periphery, which sorting apertures are mainly transverse with respect to the peripheral direction of the drum and are arranged behind each other in a spiral row. Such a crab sorting screen is known from DE-A-3535035. The drum of this screen consists of a curved, plate-like wall, containing local depressions and raised portions which define sorting apertures. This known screen has a disadvantage in that it is difficult to sort out the prawns in a reliable way. In practice it appears that a relatively high percentage of the prawns just slides over the wall, together with the rest of a catch, on their way from the infeed to the discharge opening. The relatively shallow depressions in the wall of the drum are not suitable for reliably collecting the prawns out of the catch. Furthermore, the specifically shaped sorting apertures in the periphery appeared to cause regular blockages in the sorting apertures, necessitating additional actions to eliminate these blockages. The aim of the invention is to provide a prawn sorting screen in which these disadvantages are avoided, and by means of which a reliable operation is ensured. This aim is achieved in that at least one spiral type first round bar is provided with neighbouring windings which are connected by means of elongated generally hollow U-shaped collecting trays, which hollow trays are of increasing depth in the peripheral direction of the drum, have their hollow side facing inwardly with respect to the drum and have a straight bottom running mainly tangentially with respect to the periphery of the drum, whereby the tray is always attached by a shallowest end part to a deepest end part of the tray preceding it to the top edges thereof and in the direction of rotation of the drum, in such a way that between the deepest end of the tray and the shallow end of the following tray attached thereto the sorting aperture is formed. In the screen according to the invention, the prawns first of all tumble between one of the windings formed by the spiral type round bar. These windings operate on the catch in the same way as in a conventional screen, such as known from NL-A-6712469. In the direction of movement of the catch from the infeed tot the discharge opening of the drum, the windings mutually enclose a relatively wide and unobstructed, deep gap. Therefore, there is hardly any chance that the prawns just slide over the inside of the drum. On the contrary, due to the fact that the centre of gravity of a prawns is at their back, it is more likely that they are tipped into one of these gaps, such that a first selection of the catch is obtained. Subsequently, the prawns find themselves on the bottom of a tray, which bottom diverges to the outside with respect to the peripheral direction of the drum. As a result, the prawns very smoothly slide along the bottom to the sorting aperture. The diverging shape of the trays ensures that no blocking will occur. Any other thin objects such as crabs which also tumble into the gaps are rejected by the apertures. Through rotation of the drum, the position of the collecting trays gradually becomes more vertical, with the result that the prawns by the elongated through-shaped trays are conveyed to the sorting aperture located at the end thereof, while the crabs and other catch constituents remain in the collecting trays, and these remaining constituents then fall out of the trays on further rotation thereof. It has been found that an excellent result is obtained with this device, without the risk of blockage of sorting apertures occurring. A very efficient embodiment is obtained through the fact that the side walls of the trough-shaped trays taper in the direction of the bottom thereof. The effect of this measure is that the crabs and other catch constituents left behind fall out of the trays very easily when the trays are at the top of the drum during the rotation thereof. A very efficient embodiment is also obtained by providing the sorting apertures between the collecting trays with an adjustable lip at the top for adjusting the shape and size of the sorting aperture. With this embodiment the crab sorting screen can be adapted in a fairly simple manner for sorting prawns of different desired sizes. A preferred embodiment is obtained if the adjustable lips are each formed by an extended or flattened part of the shallow end of a collecting tray, said extended part being bent back along the bottom side of the collecting tray in question. An embodiment which is relatively simple to produce is obtained if the cylindrical drum comprises a round bar formed into a spiral, while the collecting trays are disposed between the spiral windings and are attached by their top edges in each case to spiral parts of the round bar lying opposite each other. Here the round bar formed into a spiral also forms the spiral-type round bar disposed between the collecting trays for guiding the catch in the crosswise direction along the inner periphery of the drum. The effect of guiding the prawns in the crosswise direction and taking them into the correct position for good sorting is further improved by providing a second round bar formed into a spiral on the inside of the first round bar formed into a spiral. It is also preferable to provide at the discharge opening of the crab sorting drum along the inside in circular form one or more round bars placed on each other, which have the effect that the discharge of the catch conveyed in the drum is delayed until full sorting has taken place. The crab sorting screen according to the invention can form part of an existing rinsing prawn sorting machine, the crab sorting screen drum then being fastened to the screen drum at the discharge side of the known rinsing prawn sorting machine and being driven in common therewith. It is, however, also possible to design the crab sorting screen drum according to the invention as a separate unit, provided with its own drive system. The invention will now be explained in greater detail with reference to the drawing, in which by way of example a number of embodiments of a crab sorting screen according to the invention are shown. Fig. 1 shows a side view of a known rinsing prawn sorting drum with a crab sorting screen according to the invention attached thereto, part of the side wall of the device being omitted in order to show the inside of the device. Fig. 2 shows a side view of the crab sorting screen according to the invention, designed as an independently driven unit. Fig. 3 shows a perspective view of two connecting collecting trays and the way in which they are disposed on the round bars formed into a spiral from which the crab sorting screen drum is made. Fig. 1 shows a crab sorting screen drum 1 which is fastened in a manner indicated in further detail below to a rinsing prawn sorting screen which is known per se and is indicated in general by the reference number 2. The crab sorting drum 1 comprises a round bar 3 formed into a spiral (see Fig. 3), which is fixed by means of fixing elements 4 to the inner drum 5 of the prawn sorting drum 2. The round bar 3 formed into a spiral is wound in such a way that the distance (a) between the spiral windings is constant. Collecting trays 6, which are shown in detail in Fig. 3, are disposed along the entire periphery of the drum between the spiral windings of the round bar 3 formed into a spiral. Each collecting tray 6 is trough-shaped (respectively U-shaped) and has side walls 7 and 8 which are fastened by their top edges 9 and 10 to the peripheral faces facing each other of the adjacent spiral windings of the round bar 3. The side walls 7 and 8 taper towards the bottom of the trough-shaped tray 6. As can be seen clearly in Fig. 3, the trays 6 have a varying depth, the trays being arranged in such a way that a tray 6 is connected by its shallow end 11 to the deep end 12 of the preceding tray 6, viewed in the direction in which the drum is rotated during the working of the device, said direction of rotation being indicated by the arrow P in Fig. 3. As can also be seen from Fig. 3, the shallow end 11 of each tray 6 is extended by a lip 13 which is bent back on itself and is formed in such a way that said lip 13 forms the top side of a sorting aperture 14 formed in the deep end 12 of a tray 6. The lip 13 can be bent in such a way that the shape and size of the sorting aperture 14 can be changed. The lip 13 is fixed by its side edges to the side walls 7 and 8 of the preceding tray 6. The spiral bar 3 also has attached on the inside thereof a further spiral bar 15 which is of smaller diameter than the bar 3. Provision is also made on the discharge side of the crab sorting drum 1 for a set of round bars 16 and 17 in circular form, the object of which is to delay the discharge sufficiently until the complete sorting has taken place. Via the fixing elements (f) the drum 1 is driven by the drum 5 of the prawn sorting device 2, drum 5 being connected in a manner known per se to the outer drum 18, which is driven in a manner known per se by the schematically indicated drive unit 19. The above-described crab sorting drum works as follows. The prawn catch to be sorted is fed into the inner drum 5 at side A (Fig. 1). Prawns, crabs, undersize fish and additional small catch are then separated from the rest of the catch in the drums 5 and 18 and conveyed to the crab sorting drum 1. By means of the spiral bar 15 (Fig. 3), the prawns, crabs and undersize fish are guided in the crosswise direction until they go between the spiral bar 3. This guidance of the prawns and other catch produced by the spiral bars 15 and 3 is necessary to permit the commencement of the sorting process. Due to their elongated shape, and due to the fact that their centre of gravity lies at the back, the prawns are then tipped into the collecting trays 6, in which they come to rest on their backs in the lengthwise direction. Through rotation of the drum 1, the position of the collecting trays 6 gradually becomes increasingly vertical, as a result of which the prawns in the collecting trays 6 are moved through the sorting apertures 14, while the crabs, which are generally slightly rounded in shape, and the other catch are left behind in the collecting trays 6, or even remain lying on the bars 15. During further rotation of the drum in the direction of the arrow P, and due to the fact that the side walls 7 and 8 taper towards the bottom of the trays 6, the crabs and any other constituents in the trays are conveyed back to the inner periphery of the drum 1 and then discharged at the discharge side B (Fig. 1). The prawns sorted by the drum 1 are collected in the tray C. It was found that no blockages occurred. The lips 13 can be bent to change the size and shape of the sorting apertures 14, for example with a gauge. This means that the device can be adapted to different sizes of the prawns to be sorted. Fig. 2 shows a view of a crab sorting screen drum according to the invention, the dimensions of which are much greater in the lengthwise direction than that shown in Fig. 1, and which is of a size which practically corresponds to the size of an ordinary rinsing prawn screen unit of the type shown in Fig. 1 by reference number 2. This extended crab sorting screen device, indicated by the reference number 1a in Fig. 2, can be driven by the same type of drive unit 19a as that shown in Fig. 1 with the reference number 19. This separate crab sorting screen device 1a can be provided at the infeed end with catch already sorted by a separate rinsing prawn screen unit of the type shown in Figs. 1 and 2, via the infeed opening indicated by A in Fig. 2. The extended crab sorting screen unit according to Fig. 2 is also in principle designed in the same way as the crab sorting screen indicated by reference number 1 in Fig. 1.

Claims: 1. Crab sorting screen intended for use in prawn or shrimp fishing, comprising a rotary cylindrical drum (1) having at the ends thereof an infeed (A) and discharge (B) opening respectively, and provided with sorting apertures (14) along the entire periphery, which sorting apertures (14) are mainly transverse with respect to the peripheral direction of the drum (1) and are arranged behind each other in a spiral row characterized in that at least one spiral type first round bar (3) is provided with neighbouring windings which are connected by means of elongated generally hollow U-shaped collecting trays (6), which hollow trays (6) are of increasing depth in the peripheral direction of the drum (1), have their hollow side facing inwardly with repect to the drum (1) and have a straight bottom running mainly tangentially with respect to the periphery of the drum (1), whereby the tray (6) is always attached by a shallowest end part (11) to a deepest end part (12) of the tray (6) preceding it to the top edges (9, 10) thereof and in the direction of rotation of the drum (1) in such a way that between the deepest end (12) of the tray (6) and the shallow end (11) of the following tray (6) attached thereto the sorting aperture (14) is formed. 2. Crab sorting screen according to Claim 1, characterized in that the side walls (7, 8) of the trays (6) taper towards the bottom thereof. 3. Crab sorting screen according to Claim 1 or 2, characterized in that the sorting apertures between the collecting trays (6) are provided with an adjustable lip (13) at hte top for adjusting the shape and size of the sorting aperture (14). 4. Crab sorting screen according to Claim 3, characterized in that the adjustable lips (13) are each formed by an extended or flattened part of the shallow end (11) of a collecting tray (6), said extended part being bent back along the bottom side of the collecting tray (6) in question. 5. Crab sorting screen according to one of the preceding claims, characterized in that the cylindrical drum (1) comprises a first round bar (3) formed into a spiral, while the collecting trays (6) are disposed between the spiral windings and are attached by their top edges (9, 10) to spiral parts of the round bar (3) always lying opposite each other. 6. Crab sorting screen according to Claim 5, characterized in that a second round bar (15) formed into a spiral is provided on the inside of the first round bar (3) formed into a spiral. 7. Crab sorting screen according to one of the preceding claims, characterized in that one or more round bars (3, 15, 16, 17) placed on each other are provided at the discharge opening (B) of the crab sorting drum (1) along the inside in circular form. 8. Rinsing prawn sorting unit, characterized in that it is provided with a crab sorting screen (1a) according to one of the preceding claims. 9. Rinsing prawn sorting unit according to Claim 8, characterized in that the crab sorting screen drum (1) is fastened to the discharge side of the rinsing prawn sorting machine (2, 5, 18). 10. Rinsing prawn sorting unit according to Claim 8, characterized in that the crab sorting screen drum (1) is designed as a separate unit, provided with its own drive system.

Inventors: VERBURG, ABRAHAM LEENDERT
Applicants: VERBURG, ABRAHAM LEENDERT
Application year: 1988
Main classification: A22C29
IPC codes: A22C29, A22C25