Screw conveyor for the transport of flowable substances and/or lumps of material

A screw conveyor for the transport of flowable substances and/or lumps of material comprises a rotatable first screw (1) provided with helical windings (2) arranged in a housing (3) with an inlet opening and an outlet opening. The housing (3) comprises an inlet chamber (4) and a pumping chamber (5) between said inlet and outlet openings and at least in the pumping chamber (5) a second screw (6) is provided with helical windings (7) and arranged for rotation in the opposite direction of the first screw (1), said screws (1, 6) in said pumping chamber (5) providing a positive displacement pumping function by mutual engagement between the two screws (1, 6). By having the parts of the two screws (1, 6) in mutual engagement extending a distance corresponding to at least one half winding out of the pumping chamber (5) and into the inlet chamber (4), overfilling of the pumping chamber (5) and accordingly, the subsequent increased friction in the pumping chamber (5) is avoided.

TECHNICAL FIELD

The present invention relates to a screw conveyor for the transport of flowable substances and/or lumps of material of the kind set forth in the preamble of claim1.

BACKGROUND ART

In conveyors of this kind, it is known to reduce the friction between the walls of the pump housing, the pump screw and the material being handled by constructing the parts of the two screws in mutual engagement with an increasing pitch, i.e. increasing distance between the windings, in the pumping chamber. In this way, it is possible to handle very lumpy and very viscous materials. A construction of this kind is e.g. known from WO 98/35135.

U.S. Pat. No. 4,043,002 describes a construction in which the pumping screw may extend into the charging chamber. The purpose of this extension of the pumping screw into the charging chamber is to capture material and carry it into the pumping chamber. In connection with very lumpy and very viscous materials this may lead to increased friction in the pumping chamber due to overfilling.

DISCLOSURE OF THE INVENTION

Based on this prior art, it is an object of the present invention to provide a screw conveyor in which overfilling of the pumping chamber and accordingly, the subsequent increased friction in the pumping chamber is avoided, With this invention, the mutual engagement between the pumping screws in the inlet chamber results in a displacement of excess material out of the screws before entry into the pumping chamber, whereby overfilling of the pumping chamber and consequent increased friction in the pumping chamber is avoided.

Preferred embodiments of the screw conveyor, and the advantages thereof are explained in the following detailed description.

DESCRIPITON OF THE PREFERRED EMBODIMENTS

The apparatus shown inFIGS. 1 and 2is a meat-mincing machine incorporating a screw conveyor in accordance with the present invention. This apparatus comprises an inlet chamber4into which the material to be handled is introduced through an inlet opening24, and in the bottom of which two transport screws8are mounted to move the material towards a set of pumping screws1,6provided with inter-engaging helical windings2,7. The pumping screws1,6are mounted in a pumping chamber5, whereby said screws1,6and pumping chamber5provides a positive displacement pumping function by the mutual engagement between the two screws1,6inside the pumping chamber5. The first screw1, the second screw6and the transport screws8are mounted on common axles9for rotation by the drive gear19driven by a drive motor20. The axles9are rotated in opposite directions and so are the screws1,6,8mounted on the axles9. As can be seen inFIGS. 1 and 2, the pumping screws1,6extend approximately one and a half winding out of the pumping chamber5and into the inlet chamber4. By this feature it is secured that the pumping chamber5is not overfilled with material due to the fact that the mutual engagement29between the two screws1,6in the inlet chamber4will remove superfluous material from the screws1,6. It is suggested that approximately one half winding of the mutual engaging screws1,6inside the inlet chamber4will be sufficient to avoid overfilling of the pumping chamber5.

A vacuum connection17is provided at the upstream end of the transport screws8, said connection comprising a twin-screw pump18providing a pumping function for pumping material sucked towards the vacuum connection17back into the inlet chamber4. This vacuum facility will improve down feed of the material into the screw and ensure the filling of the pump chamber. Furthermore, it will facilitate removal of air from the material in the feed screws1,6. If the whole inlet chamber is to be under vacuum, it will naturally be necessary to have a lid on top of the inlet opening24of the inlet chamber4in order to vacuumize the material inside this inlet chamber4.

In the embodiment shown inFIGS. 1 and 2, a cutting device22comprising a perforated disc10co-operating with sets of rotating knives11is provided, the rotating knives11being rotated by the axle9for rotating the first screw1and the corresponding transport screw8. The outlet opening25from the pumping chamber5is connected to this cutting device by a relatively small volume channel26in order to reduce the amount of material left inside this volume when stopping the machine for cleaning/changing handled material.

FIG. 3shows an alternative cutting device, in which the rotating knives11are rotated by a separate drive13. This provides a possibility of driving the pumping screws1,6independently of the rotating knives11, whereby the rotational speeds of these elements can be controlled individually, e.g. in dependence of a measured pressure in the material in front of the cutting device, e.g. the higher pressure, the higher rotational speed of the rotating knives. Furthermore, a low speed of the knives will perform a non-smear cool clean cut minced meat, whereas high speed of the knives will perform an emulsion. Thus, the function of the machine can be changed by changing knife speed.

FIG. 4shows an alternative embodiment of the pumping screws1,6, in which the first screw1comprises relatively thin helical windings2and the second screw6comprises relatively thick helical windings7, whereby material is predominantly transported by the first screw1. In the embodiment shown inFIG. 4, a cutting device similar to the one shown inFIGS. 1 and 2is driven by the axle9for the first screw1and accordingly the main stream of material out of the pumping housing3is delivered in line with the cutting device.

As an alternative, as shown inFIG. 5, the first screw1and second screw2are provided with substantially identical helical windings2,7. This provides a mainly equal delivery of material from the two screws1,6. Accordingly, a cutting device comprising a double-perforated disc12of a “figure-of-eight” shape is provided and the corresponding rotating knives11are rotated by the axles9for rotating the screws1,6, thus rotating in opposite directions and in mutual “engagement”.

As can be seen from the drawings, the apparatus is of a modular construction comprising separate exchangeable components, i.e. cutting device10,11mounted in a corresponding housing and connected to the pumping chamber5by means of corresponding mounting fittings, pumping chamber5containing pumping screws1,6and mounted on the housing3by means of corresponding fittings, the pumping screws1,6, transport screws8and twin-screw pump for the vacuum connection18being mounted on the axles9to be rotated thereby.

FIG. 6shows a bearing construction for the downstream ends27,28of the pumping screws1,6, said bearing construction comprising pilot bearings14for said screws1,6or the corresponding axles9and a first rod connection15between said bearings14providing a fixation of the ends of the two screws1,6relative to one another (i.e., a floating connection), thereby primarily providing a bearing counteracting the tendency of those two screws to move away from one another due to the displacement of the material inside the pumping chamber5provided by the mutual engagement29between the two screws1,6. This bearing construction primarily reduces the wear on the outwards sides of the pumping chamber5which would otherwise have to withstand the above-mentioned tendency of pressing the two screws1,6away from one another.

InFIG. 7, the bearing construction inFIG. 6is supplemented by a second rod connection16connecting the first rod connection15to the pumping chamber5, whereby the fixation of the two screws1,6relative to the pumping chamber5is provided, said fixation primarily lifting the screws6,1away from the walls of the pumping chamber5. This is a prerequisite for avoiding metal to metal contact.

As can be seen fromFIGS. 6 and 7, the rod connections15,16are primarily positioned in the area of mutual engagement between the two pumping screws1,6, in which substantially no flow of material out of the pumping chamber5is present. In this way, the bearing construction will substantially not interfere with the flow of material out of the pumping chamber5.

In the embodiment shown, an interspace23is provided between the drive gear19and the screws18,8,6,1where product is present, thereby providing a secure separation between product and gear oil preventing mutual mixing/contamination thereof.

Above, the present invention has been explained in connection with preferred embodiments relating to a meat-mincing machine, which is specially suited for mincing frozen or partially frozen meat containing lumps of material to be transported by the pumping screws1,6. In this connection, the extension of the pumping screws1,6into the inlet chamber4provides a displacement of material out from the helical windings2,7on the two screws1,6, thereby avoiding overfilling of the pumping chamber5. However, the present invention is not restricted to such meat-mincing machine but could be used in other constructions, in which flowable substances and/or lumps of material are to be pumped by a positive displacement pumping function and in which similar problems are met.