EP0064596B1 - Granulating mill for comminuting runners, moulded parts, blown hollow bodies, etc. - Google Patents

Description

The invention relates to a cutting mill for crushing sprues with a roller-shaped, driven rotor mounted in a housing, over the circumference of which several cutting element groups are arranged offset from one another, which interact with at least one knife provided in the housing, with an additional device in front of the knife in the feed direction is provided for increasing the throughput, and with a sieve extending over part of the circumference of the rotor for separating the ground material.

Such a cutting mill is known from DE-B-1 168220. However, this document contains no information about the speed of the machine. It must be assumed that the machine works at a normal speed of 1,500 rpm, for example. If this were not the case, the sharp-edged cams 3 would not be able to develop the mode of operation mentioned in the description of this publication, as described, for example, in column 4, lines 13 to 21. The centrifugal effect of the rotating knives, which is expressly mentioned at this point, by means of which the material is controlled against the accumulation surfaces and cutting edges of the cams, so that the regrind is split by the force of the impact or impact, actually occurs only in the known high-speed mills. In the shredding machine known from the aforementioned publication, the focus is on improving the throughput. The open rotor construction for the cutting knives used in the known mill would require a collection of pre-broken and depending on the size of not yet broken sprues in the cavity of the open rotor at low speeds, so that in this way a blockage of the screen space occurs, which further Use of such a facility would make impossible.

DE-A-2 216 640 describes a cutting mill rotor in the form of a roller runner for comminuting large compact lumps of plastic. The rotor carries groups of knives with axially parallel blades, these knives being divided into several sections over the length of the rotor and the axially adjacent sections being circumferentially offset from one another in order that, when the cutting mill is in operation, individual cutting knives on the cutting mill rotor engage the standing knife in succession allow.

The known cutting mills usually work at speeds of rotation between about 1,000 and 1,500 rpm. Such cutting speeds are acceptable for shredding large, compact chunks of plastic. Such high cutting speeds are unfavorable for crushing sprues and injection molded parts, since the less compact, varied material of sprues springs back from injection molding machines, eludes the cutting process and sprays out of the cutting gap again, so that protective covers have to be provided over the cutting mills in order to cut the material catch, to reduce noise and also to avoid unwanted dust.

It was therefore necessary to additionally provide cutting mills of the known type for the comminution of sprues with the protective devices mentioned, as a result of which their overall height became greater. With the advancing development of plastic injection molding technology and in the context of the automation of the operation of injection molding machines, there was a desire to reprocess the sprues per cycle, if possible without manual intervention, in the injection molding machine after appropriate comminution.

In the field of automation of injection molding machines for mass production of mass parts, there is therefore a need to immediately process repeated sprues. This processing is currently carried out in such a way that the sprues are crushed, i.e. be reduced in size so that they roughly correspond to the usual granules in their grain size and are added to the granules as regrind depending on the attack. In the case of certain injection molded parts, the proportion of regrind can make up a high percentage of the total amount of plastic fed to the injection molding machine.

In the known granulators for the preparation of the sprues, it was previously done so that the sprues were conveyed from the site of their attack by means of a large screw laterally to the granulator or by means of a type of inclined elevator that grips the sprue and transports it upwards, where it is laterally arranged cutting mill can be fed. Pneumatic devices for conveying sprues into the area of the cutting mill have also become known. The use of compressed air, however, undesirably promotes the development of dust, which, as already mentioned, is unavoidable in high-speed cutting mills during gate processing.

The described devices for crushing sprues of injection molding machines for their re-supply as regrind in the injection cycle have the disadvantages described of a relatively large noise and dust development. These disadvantages can only be countered by appropriate insulation of the housing, dust caps and the like. The overall height of the known granulators is so great that it is usually not possible to accommodate them under an injection molding machine because the space available there (approx. 500 to 600 mm) in most cases it is not sufficient to position the granulator at this point.

It is therefore the object of the invention to avoid the disadvantages described and, starting from a cutting mill of the type described at the outset, to create a device which has a relatively low level of noise and dust during operation, can be arranged under the injection molding machine and is efficient for comminuting Sprues, injection molded parts, but also blown hollow bodies that are to be reprocessed as regrind are used.

This goal is achieved with a cutting mill of the type mentioned at the outset by means of claim 1. The fact that the roller-shaped cutting knife rotor can be rotated at a relatively low speed means that the problem of undesirable noise and dust development can be handled in a simple manner. The essential improvement according to the invention of previously known cutting mills for the stated purpose, however, consists in the additional arrangement for holding before crushing and drawing in the sprues and injection molded parts in the drawing-in direction in front of the knife. This device preferably consists of plate-shaped elements which are arranged orthogonally to the axis of the cutting knife rotor in the housing. These plates lie with their feed edges slightly outside the path of the cutting edges of the cutting knives on the rotor and, thanks to their arrangement, ensure a more even and effective insertion of the sprues and injection molded parts into the area of the knife. The plates are preferably arranged equidistantly and in a number which corresponds approximately to the number of cutting knife arrangements lying next to one another on the roller-shaped rotor. However, the number of plates of the feed device can also be somewhat less. The angular position of the plates, which are preferably orthogonal to the axis of the rotor, can also be arranged obliquely in order to better prevent the parts to be shredded from springing back.

For the crushing of particularly difficult-to-grasp injection molded parts, such as hollow articles blown from rejects and the like, the feed device can be provided with special baffles, for example in the form of teeth, on the feed edge of the plates. Such teeth can be replaced or supported by ribs which are formed on the roller-shaped rotor with the cutting blades themselves, for example by removing the outer surface of the rotor and replacing it with ribs which are parallel to the axis. These ribs can work together or together with the toothing on the leading edges of the plates of the feed device and thus ensure a particularly efficient comminution or feeding of hollow bodies into the area of the knife of the cutting mill.

Depending on the material that is preferably to be shredded, the curve shape of the plates of the feed device can be designed differently: In general, a tapering gap will be aimed at the knife, the insertion plates gently springing back from the beginning of the feed area and running back against the housing. However, these feed elements can also be designed so that a more or less sharp-edged configuration of the plate is provided in the area of the first interaction between the material to be shredded and the tool, by means of which a shredding is already carried out here. The gap between the sharp edge and the knife can converge. However, it can also expand somewhat at first, only to then converge in the area of the level meter.

Because of the relatively low number of revolutions of the driven rotor, it is possible to derive the drive of a conveyor belt from the rotor itself, through which the injection-molded parts to be shredded are transported from the point of their occurrence into the housing inlet for the cutting mill. For this purpose, the stub axle of the rotor can be extended along the rotor axis beyond the front end face of the housing (not shown in FIG. 1) and there carry a V-belt wheel for direct drive of the conveyor belt.

Particularly low-dust regrind has been achieved with a cutting mill in which the sieve for separating the regrind is provided with openings which are both against the interior, i.e. towards the knife rotor and outside, i.e. to the collection container in the housing.

• Fig. 1 eine perspektivische Darstellung der neuen Schneidmühle, wobei zum besseren Verständnis der Konstruktion der vordere Gehäusedeckel weggebrochen ist;
• Fig. 2 eine Seitenansicht der Schneidmühle nach Fig. 1 bei weggebrochenem Gehäusedeckel;
• Fig. 3 die gleiche Darstellung wie Fig. 2, jedoch mit gegenüber dem Ausführungsbeispiel nach den Fig. 1 und 2 modifizierten Einführplatten;
• Fig. 4 die gleiche Ansicht wie die Fig. 2 und 3 auf ein Ausführungsbeispiel der Schneidmühle mit gezahnten Einführungsplatten;
• Fig. 5 die gleiche Darstellung wie die Fig. 2, 3 und 4, wobei der Messerrotor mit zusätzlichen Rippen versehen ist und die Einführungsplatten die gleiche Konfiguration wie bei dem Ausführungsbeispiel der Fig. 1 und 2 zeigen;
• Fig. 6 einen Schnitt durch das Sieb der erfindungsgemäßen Schneidmühle.

Further details of the invention will become apparent from the following description of the drawing. Four exemplary embodiments of the invention are shown schematically in the drawing. Show it:

• Figure 1 is a perspective view of the new cutting mill, with the front housing cover broken away for a better understanding of the construction.
• FIG. 2 shows a side view of the cutting mill according to FIG. 1 with the housing cover broken away;
• 3 shows the same representation as FIG. 2, but with insertion plates modified compared to the embodiment according to FIGS. 1 and 2;
• 4 shows the same view as FIGS. 2 and 3 of an embodiment of the cutting mill with toothed insertion plates;
• 5 shows the same representation as FIGS. 2, 3 and 4, the knife rotor being provided with additional ribs and the insertion plates showing the same configuration as in the embodiment of FIGS. 1 and 2;
• Fig. 6 shows a section through the sieve of the cutting mill according to the invention.

As can be seen from the perspective view of the cutting mill shown in FIG. 1, it consists of a roller-shaped driven rotor 1, which is mounted in the housing 2 in a known manner. The housing, which is rectangular in cross section, consists of the front wall 3, the rear wall 4, the rear left end face 5, a corresponding front end face which has been broken away for a better view, the flat inclined bottom 6 with the oblique side walls 7 and 8 and one in the drawing Not shown attachment in the form of a funnel or the like. For feeding the material to be shredded. The roller-shaped rotor is driven by a drive motor, also not shown in the drawing, preferably with the interposition of a corresponding reduction gear, in order to achieve the desired low number of revolutions of about 100 rpm. The bearing of the rotor is also not shown. The rotor rotates about the axis 9 and is mounted in corresponding bearings with the stub shaft shown in the drawing.

The rotor shown in Fig. 1 has four cutting element groups 10, 11, 12 and 13. Each group consists of three knife plates 10a, 10b, 10c, 11a, 11b, 11c, 12a, 12b, 12c and 13a, 13b, 13c, evenly distributed over the circumference of the rotor. Due to the equidistant arrangement of the knife plates of a cutting element group and the uniform angular offset between adjacent cutting element groups, in the exemplary embodiment of the cutting mill according to the invention shown in FIGS. 1 and 2, there is an angular offset of 30 ° between successive knife plates in their cutting process on the stationary knife, as can be seen from FIG 2 can recognize. This angular offset follows directly from the number of knives in a cutting element group multiplied by the number of cutting element groups (3 x 4 = 12.360 °: 12 = 30 °). If the number of knives in the individual cutting element groups were increased to four and the cutting element groups from four to five, the total number of 20 knives would reduce the angular spacing between successive knives on the knife 14 from 30 ° to 18 °.

The housing 2 is divided into two housing halves by the standing knife 14 and the opposite sieve carrier web 16: in a lower collecting space 37, which is located under the sieve 15 and by parts of the side walls 3, 4, 5, the inclined bottom 6 and the likewise inclined Side walls of the bottom 7 and 8 is limited. In this collecting space 37, the shredded material which has passed through the openings 32 of the sieve 15 is collected and discharged through a process not shown in the drawing. This process can be connected to a mechanical, pneumatic or other suitable conveying device which feeds the shredded material back into the specification or mixing funnel for the injection molding machine.

The upper housing part is delimited by the rotor part, which protrudes above the level of the leveling knife 14 and the sieve carrier web 16, by the end faces of the housing and the guide plates 18 and 19 and the protruding part of the front wall 3 and the rear guide plates 21 and 22, whereby the upper diagonally inclined downward baffle feeds the material to be shredded to the rotor and the lower cylindrical baffle in the feed area of the material to be shredded is approximately opposite the roller surface of the rotor and is adapted to the cylinder shape. From this guide plate combination 21, 22, which is supported by the tubular support 23, guide plates 24, 24 'protrude, which lie in orthogonal planes to the rotor axis 9.

The additional device 20 for holding and pre-shredding in front of the leveling knife 14 is thus essentially formed by the tubular support 23 which supports the guide plates 21 and 22 and a plurality of guide plates 24, 24 ', preferably evenly distributed over the length of the housing 2, the guide plates preferably lying in planes perpendicular to the rotor axis 9. However, they can also converge somewhat in the direction of the stationary knife 14, in particular in the central region of the housing, in order to prevent the material to be comminuted from accumulating in the lateral regions in the vicinity of the end walls 5 of the housing 2.

The number of guide plates 24, 24 'depends on the type of injection molded parts to be shredded, on the width of the individual knife plates on the rotor 1 and will expediently be equal to or less than the number of knife groups lying side by side on the rotor. In the embodiment shown in FIGS. 1 and 2, two guide plates 24, 24 'face the four groups of cutting elements 10, 11, 12, 13. If the rotor 1 is made longer and provided with 5 or 6 cutting element groups, the number of guide plates 24 can be increased to 3 or 4 in the embodiment shown. The essence of the additional device 20 is the holding and pre-shredding of the sometimes very tough and bulky sprues that are fed to the shredding on the knife 14.

The guide plates 24, 24 'extend from the upper edge of the housing 2 and initially run over a straight, obliquely downwardly inclined region 24a, then merge into an inwardly inclined curvature 24b and finally extend concavely over an region 24c which is adjacent to the rotor , wherein the curve of section 24c is designed such that it converges against the cutting edge 14a of the knife 14, as shown in FIGS. 1 and 2, or first diverges and then converges, as shown by curve 25c in the embodiment of FIG. 3 or concentric to the rotor axis 9 as in the embodiment of FIG. 5 based on of the curve 27c shown.

3, 4 and 5 further exemplary embodiments of the cutting mill according to the invention are shown, with all parts except the guide plates being the same in FIGS. 3 and 4 and therefore not requiring further explanation, and additionally the shape in FIG. 5 of the rotor is modified.

The guide plates 25, 25 'in FIG. 3 differ from the guide plates of the exemplary embodiment according to FIG. 2 in that a sharp guide plate corner or a tooth 25b adjoins the edge part 25a of the guide plates, which is particularly useful for pre-crushing the material to be shredded is then suitable if it projects into the path of the knives of the rotor 1 as far as the stationary knife 14 or in any case up to the cutting path of the knives 10a, 10b, 10c. As already mentioned, the course of the further plate edge 25c is designed in such a way that the space between the rotor and the edge initially widens and then tapers again to the level knife 14.

For the shredding of hollow bodies, as indicated by the hollow body 28, the embodiment of a cutting mill according to FIG. 4 is particularly suitable. Here, the guide plates 26, 26 '.... in addition to the edges 26b, 26'b ... are included provided with a toothing directed against the edge 14a of the leveling knife 14 to increase the holding force in the feed direction. When the rotor 1 rotates in the direction of the arrow 17, the subsequent knife 10a pushes the hollow body 28 into the gap between the toothed edge 26c and the surface of the rotor 1 until the hollow body 28 is clamped in this area and then by the subsequent cutting edges of the knives 10a, 10b, 10c are reduced to the necessary particle size which is desired for the regenerate.

In the embodiment of FIG. 5, the cylinder of the rotor 1 is flattened between adjacent knives of each cutting element group and provided with additional ribs 29a, 30a, 31a. These ribs improve the conveying action of the roller of the rotor for the material to be shredded against the stationary knife 14. The associated guide plates can be smooth, as shown in FIG. 5, wherein the concavely curved edge 27c opposite the rotor can run concentrically to the axis 9. However, like the edge 24c in the exemplary embodiment according to FIG. 2, this edge can also widen outwards, the configuration of the exemplary embodiment according to FIG. 3 with edge 25b and a widening interior space, or else the configuration according to FIG. 4 with an additional toothing and edge Have 26b.

By means of simple experiments, the material generated can be used to optimize the guide plates in the direction of the desired holding and pre-shredding effect.

If required, the cutting mill according to the invention can also be constructed in such a way that the guide plates 24, 25, 26 and 27 are designed to be interchangeable by providing them with corresponding cutouts or guides and plugging them onto the tubular support and into corresponding slots in the guide plates 21 and 22 and corresponding guides on the rear wall 4 and also in the knife 14.

The screen 15 is expediently provided with chamfered extensions 33, 34 both on the side 35 facing the rotor 1 and on the side 36 facing away from the collecting space 37, as shown in FIG. 6.

Claims (10)

1. Cutting mill for the comminution of sprues comprising a drum-shaped driven rotor (1) mounted in a housing (2), around whose periphery a plurality of mutually offset cutting element groups (10 to 13) are arranged which cooperate with at least one stationary blade (14) in the housing, an additional arrangement (20) being provided, for increasing the throughput, in front of the stationary blade (14) in the intake direction, and comprising a sieve (15) extending over a portion of the periphery of the rotor for separating the material to be milled, characterised in that the additional arrangement (20) for increasing the throughput consists of a plurality of guide plates (24, 24') preferably distributed uniformly along the length of the housing, which plates extend perpendicularly to the rotor axis and towards the stationary blade (14) for improvement of the intake, and in that the rotor (1) is driven with a low rotational speed of below 500 rpm, preferably about 100 rpm.

2. Cutting mill according to claim 1 characterised in that the drum-shaped rotor (1) carries three to five adjacent cutting element groups (10 to 13) in the form of blade plates secured on the rotor, each individual group consisting of two to four blade plates (10a, 10b, 10c) and neighboring cutting element groups (eg. 10, 11) being angularly mutually offset in such manner that an equidistant cutting sequence of the rotating blade plates (10 to 13) relative to the fixed stationary blade (14) results.

3. Cutting mill according to claim 1 or 2 characterised in that the additional arrangement (20) for increasing the throughput further comprises guide plates (21, 22) supported by a tubular carrier (23).

4. Cutting mill according to one or more of claims 1 to 3 characterised in that the intake region converges slightly towards the stationary blade (14).

5. Cutting mill according to one or more of claims 1 to 4 characterised in that the number of plates (24, 24') is equal to or less than the number of cutting element groups (10 to 13) on the rotor (1).

6. Cutting mill according to one or more of claims 1 to 5 characterised in that the guide plate edge (24c, 24'c or 26c, 26'c) in the vicinity of the rotor (1) is constructed to converge to the cutting edge (14a) of the stationary blade (14). (Figure 2 or Figure 4).

7. Cutting mill according to one or more of claims 1 to 5 characterised in that the edge of the guide plates (25, 25') extends downwardly in the upper region from the edge of the housing (2) firstly through a gently curved region (25a, 25'a), then extends through teeth (25b, 25'b) in the neighborhood of the cutting blade path into a region (25c, 25'c) which first widens and then narrows again towards the cutting edge (14).

8. Cutting mill according to one or more of claims 1 to 6, in particular for comminuting blown hollow bodies and the like, characterised in that the guide plates (26, 26') have an edge (26b, 26'b) and have on their edges (26c, 26'c) in the vicinity of the rotor (1) a toothed region directed towards the edge (14a) of the stationary blade (14) for increasing the holding strength in the intake direction.

9. Cutting mill according to one or more of claims 1 to 8 characterised in that the cylinder of the rotor (1) is flattened between neighboring blades (e.g. 10a, 10b, 10c) of each cutting element group (10, 11, 12, 13) and is provided with additional ribs (e.g. 29a, 30a, 31a). (Figure 5).

10. Cutting mill according to one or more of claims 1 to 9 characterised in that the bores (32) in the sieve (15) have contiguous widened portions (33, 34) both on the side (35) facing the rotor (1) and also on the side (36) directed away from the collecting chamber (37).

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