This invention generally relates to belt conveyors and especially concerns such conveyors as are used in air treatment plants for goods or products, for instance refrigerating plants for food. To be more specific, the invention is concerned with a belt conveyor comprising an endless conveyor belt which, along part of its length, travels in a helical path with a first belt edge along the inside of the heli¬ cal path, and with a second belt edge along the outside of the helical path, said conveyor belt comprising trans¬ verse elements, which carry a wire netting extending over essentially the entire width and length of the belt and which are interconnected by links, which are located at the first and second belt edges and which, in the helical path, are so much more spaced apart in the longitudinal direction of the conveyor belt at the second belt edge than at the first belt edge that the conveyor belt fol¬ lows the helical path, said links being pivotable, at each belt edge, in relation to each other about axes extending transversely of the conveyor belt and located essentially in the plane thereof, and the conveyor belt, after leaving the helical path, travelling in a feed-out path up to and partly round a guide roller.

The endless conveyor belt may be self-supporting at one or both of its edges. Such conveyor belts are described in US-A-3,938, 651, US-A-4, 858,750 and US-A- 4,875,343, which are incorporated herein by reference. However, use may also be made of a non-self-supporting conveyor belt, for instance of the type described in US- A-4,450,953, which also is incorporated herein by refe¬ rence.

In the event that the conveyor belt has links that, in the longitudinal direction of the conveyor belt, can be spaced apart to a lesser extent at the first longitu- dinal edge than at the second, the transverse elements

and the wire netting will, in the feed-out path usually extending tangentially from the uppermost or lowermost turn of the helical path, be compressed along the second belt edge, as compared with their state in the helical path. When this happens, parts of the wire netting may project from the otherwise even upper side of the belt. This may cause problems, especially when products have to be removed from the conveyor belt with the aid of e.g. a scraper blade close to the periphery of the guide roller. The object of this invention is to solve the above problem, i.e. to ensure that a scraper blade does not engage individual parts of the wire netting of a conveyor belt in a belt conveyor of the type described by way of introduction. According to the invention, this object is achieved by a belt conveyor, which is characterised in that the guide roller is adapted to keep the links at the second belt edge spaced apart to a greater extent than the links at the first belt edge, such that the wire netting is essentially stretched also closest to the links at the second belt edge as the conveyor belt passes over the guide roller.

The stretching of the wire netting due to the guide roller can be brought about in at least two different ways, or by a combination thereof. First, the axis of rotation of the guide roller may be so inclined essen¬ tially in the plane of the feed-out path that the links at the second belt edge are spaced apart to a greater extent than the links at the first belt edge. Second, the guide roller may comprise a first pulley, which is in contact with the first belt edge, and a second pulley, which has a larger diameter than the first pulley and is in contact with the second belt edge. In the latter case, the axis of rotation of the guide roller need not be ' inclined as indicated above. However, these two ways of stretching the wire netting may be combined.

Advantageously, the greater spacing of the links at the second belt edge is essentially the same round the guide roller as in the helical path.

The wire netting may consist of wires running in zigzag between the first and second belt edges and exhi¬ biting constant dimensions in the longitudinal direction of the conveyor belt. However, the surface of the con¬ veyor belt becomes especially smooth if the wire netting consists of wires running in zigzag between the first and second belt edges and exhibiting dimensions increasing in the longitudinal direction of the conveyor belt from the first belt edge to the second belt edge.

Conveniently, an additional roller is so arranged in contact with the second belt edge before the guide roller that the spacing of the links at the second belt edge is ensured when the belt passes over the guide roller. It is therefore convenient that this additional roller has a slight braking effect.

Thus, the present invention provides reliable unloading of products from the feed-out path of a belt conveyor, i.e. there is no risk of any operational dis¬ turbances caused by inconvenient deformations of the wire netting. The tractive force thus applied to the belt also along the second belt edge results in good belt-guiding performance before and round the guide roller and thus eliminates any tendency towards instability.

The invention will be described in more detail below with reference to the accompanying drawings, in which

Fig. 1 is a perspective view of a prior-art belt conveyor;

Fig. 2A is a cross-section of two belt turns, and Fig. 2B is a top plan view of part of the belt of the belt conveyor in Fig. 1;

Fig. 3 is a top plan view of part of a conveyor belt of another design;

Figs 4A and 4B schematically illustrate guide rol¬ lers arranged in accordance with the invention; and

Fig. 5 is a perspective view showing the guide rol¬ ler in Fig. 4B in more detail.

The belt conveyor illustrated in Fig. 1 comprises a conveyor belt 1 which, along part of its length, travels in a helical path 2 including a plurality of superimposed belt turns. The conveyor belt 1 is endless and travels in a rectilinear feed-in path 3 to the beginning of the helical path 2, which it leaves in a rectilinear feed-out path 4 extending up to and partly round a guide roller 5. From the guide roller 5, the conveyor belt 1 takes a return path over guide rollers 6 back to the feed-in path 3.

The conveyor belt 1 illustrated in Fig. 1 is self- supporting at its two edges, i.e. each belt turn in the helical path 2 supports the superjacent turn. The con¬ veyor belt 1 may be of the type shown in Fig. 2A, which is a cross-section of two belt turns in the helical path 2. More specifically, the conveyor belt 1 consists of transverse elements 8 in the form of rods, which pre- ferably are interconnected in pairs by plate-like links 9. The links 9 of a belt turn carry the superjacent belt turn, the upper edges 10 of the plate-like links 9 engag¬ ing shoulders 11 and flanges 12 provided on the underside of the superjacent turn. The shoulders 11 and the flanges 12 form part of the respective links 9.

Fig. 2B is a top plan view showing part of the con¬ veyor belt 1 travelling in a curved path, such as the helical path 2 in Fig. 1. To be more precise, the links 9 are spaced apart to a lesser extent at a first edge 13 of the conveyor belt 1, the first edge 13 corresponding to an inside 14 of the helical path 2, than at a second edge 15 of the conveyor belt 1, the second edge 15 correspond¬ ing to an outside 16 of the helical path 2. Although this is not shown, the conveyor belt 1 in Figs 2A and 2B may ^■ ,be provided with a wire netting which extends essentially over the entire width and length of the conveyor belt 1 and may be composed of zigzag wires, each enclosing at

least two of the rods 8 and exhibiting constant dimen¬ sions in the longitudinal direction of the conveyor belt 1 or exhibiting dimensions increasing in the longitudinal direction of the conveyor belt 1 from the edge 13 towards the edge 15.

Fig. 3 is a top plan view of another conveyor belt 1' , which also can be used in a belt conveyor according to the invention. The conveyor belt 1' is of non-self- supporting type and thus requires separate guide means at its two edges.

The transverse rods 8 ' of the belt 1 ' are, at the first edge 13' , interconnected by U-shaped links 9' that do not permit any substantial displacement of the rods 8' away from each other in the longitudinal direction of the conveyor belt 1 ' .

However, the transverse rods 8 ' of the belt 1 ' are, at the second edge 15', interconnected by links 9" that can be displaced away from each other in the longitudinal direction of the conveyor belt 1. Each pair of adjacent rods 8' is enclosed by a zigzag wire 17 extending over essentially the entire width of the conveyor belt 1 and exhibiting dimensions increasing in the longitudinal direction of the conveyor belt 1 from the first belt edge 13' to the second belt edge 15'. When conveyor belts of the types illustrated in Figs 2A, 2B and 3 travel round the guide roller 5 in Fig. 1, there is a considerable risk that the zigzag wires or any similar wires in the wire netting forming the upper side of the conveyor belt 1 or 1' will project from the cylindrical surface otherwise formed by the rods 8 or 8 ' . The inventive concept for eliminating this prob¬ lem is schematically illustrated in the form of two alternatives in Figs 4A and 4B. These alternatives may be used separately or together. According to the invention, use is made of a guide roller 18 or 19, which is adapted to keep the links 9 or 9" at the second belt edge 15 or 15' spaced apart to a

greater extent than the links 9 or 9 ' at the first belt edge 13 or 13' , such that the wire netting is essentially stretched also closest to the links 9 or 9" at the second belt edge 15 or 15' when the conveyor belt 1 travels round the guide roller 18 or 19.

According to the alternative illustrated in Fig. 4A, this is achieved by the axis of rotation of the guide roller 18 being so inclined essentially in the plane of the feed-out path 4 that the links 9 or 9" at the second belt edge 15 or 15' are spaced apart to a greater extent than the links 9 or 9' at the first belt edge 13 or 13' .

According to the alternative illustrated in Fig. 4B, the guide roller 19 comprises a first pulley 20, which is in contact with the first belt edge 13 or 13' , and a second pulley 21, which has a larger diameter than the first pulley 20 and is in contact with the second belt edge 15 or 15'. According to this second alternative, the pulleys 20 and 21 may either be mechanically intercon¬ nected or rotate independently of each other. Naturally, the alternatives of Figs 4A and 4B may be combined by selecting a suitable inclination of the axis of rotation of the guide roller, as well as a suitable diametrical relationship between the pulleys 20 and 21. Advantageously, the greater spacing of the links 9 or 9" at the second belt edge 15 or 15' is essentially the same round the guide roller 18 or 19 as in the heli¬ cal path 2. Furthermore, the links 9 or 9 ' at the first belt edge 13 or 13' are preferably only pivotable in relation to each other, and not displaceable in relation to each other in the longitudinal direction of the con¬ veyor belt 1.

There are many known ways of driving the conveyor belt 1 along the helical path 2. As a rule, the guide roller 5 shown in Fig. 1 is used for supplementary driv- ing of the conveyor belt 1, and the same goes for the guide rollers 18 and 19 in the belt conveyor according to the invention.

The alternative of Fig. 4B is also illustrated in the perspective view of Fig. 5. As is evident from Fig. 5, the axes of rotation of the first and the second pulleys 20 and 21 may be offset in parallel in a plane essentially transverse to the plane of the feed-out path 4, such that the upper side of the belt 1 is horizontal up to the guide roller 19. On the side where the conveyor belt 1 leaves the larger-diameter pulley 21, there may be provided a rail 22 adapted to cause the conveyor belt 1 to be applied properly against the pulley 21.

As indicated in Figs 4A and 5, a roller 23 or 24 is conveniently provided before the guide roller 18 or 19 so as normally to brake the belt 1 at the second belt edge 15, thereby ensuring that the belt 1 is properly stretch- ed before and round the guide roller 18 or 19.

It goes without saying that several modifications of the above embodiments of the belt conveyor are conceiv¬ able within the scope of the invention as defined in the appended claims. Thus, the wire netting may be of diffe- rent design. Naturally, the belt conveyor may be used for other purposes than refrigeration, as well as in associa¬ tion with other products than food.