Description

Gravitational pressure device for wrapping pallets machines

Technical Field

The present invention relates to a gravitational pressure device for pallet wrapping machines.

In the design of machines for wrapping palletised loads, a collateral, but essential requirement for packaging correctly is the need to apply a predetermined pressure, which can be changed according to the various contingent requirements, on the top of the load to be wrapped.

Background Art The devices currently used to perform this function, called pressure devices, are of various types and have several disadvantages.

There are pneumatic cylinder pressure devices, in which the plate which makes contact with the load is at the end of a rod which slides in the cylinder, which is rigidly connected to the upper part of the machine structure. When the load to be packaged is transported to the wrapping position, the rod comes out of the cylinder until it reaches the top of the load. Considering the dimensions of machines of this type, never less than 4 metres tall, and the variability of the height of the loads to be packaged, usually between 1 and 3 metres, it is easy to conclude that the overall dimensions are such that a machine with that design can only be housed in factories at least 6 or 7 metres high. In addition, the device is deformable: since the rod must perform strokes of at least a couple of metres and its diameter is just a few centimetres, it may bend, compromising its primary function which consists of making the load more stable during wrapping. Finally, electric controls are required, which control the movement of the rod and adjustable pressure switches for modifying as required the pressure on the load to be wrapped.

Pantograph pressure devices are also used, in which the plate which presses on

the top of the load to be packaged is fixed to the lower end of a pantograph, whose fixed part is connected to the machine frame. These may be operated either by a pneumatic cylinder or a motor-driven belt. In the former case, the sliding cylinder is connected to the pair of pantograph arms at the opposite end to the plate, so that its movements cause the whole pantograph to open and close and, consequently, it determines the height of the plate, according to the height of the load. In the latter case, the two ends of the belt are respectively connected to a pulley, driven by a variable speed motor, and to the plate. Since the free ends of the upper arms of the pantograph are connected to the machine frame, starting the variable speed motor causes the pulley to rotate, winding (or unwinding) the belt by the amount necessary to bring the plate to the desired height. Although the dimensions are contained within the profile, this solution has the disadvantage of possible pantograph oscillations relative to the vertical line, most likely increasing with wear on the whole of the machinery. Moreover, the need to use electric controls makes the whole mechanism very expensive and difficult to assemble. Finally, if the pneumatic cylinder is used, the pressure which the plate applies on the load varies according to both the height of the load and the degree of cylinder opening, which is in turn determined by the height of the load, making it difficult for the operator to control said parameter. Finally, telescopic pressure devices with a motor-driven belt are also used, in which the plate is at the lower end of a set of tubes which slide inside one another. Their operation is similar to that of the pantograph pressure device with motor- driven belt and they have the same defects. Moreover, the structure is less stable, due to the gradual reduction in the plate supporting surface, and the pressure applied on the load is greatly influenced by the height of the load. Whilst the weight of almost all of the plate supporting structure is applied on a "high" load, only the weight of the smallest telescopic elements is applied on a "low" load.

Disclosure of the Invention The aim of the present invention is, therefore, to eliminate the above-

mentioned disadvantages. The invention described in the claims achieves said aim with a suitably guided pressure device which moves due to the effect of gravity.

The main advantage of the present invention is basically the elimination of all electric and electronic components for controlling pressure device movement. Also, the pressure device reaches its operating position more rapidly and maintains it more precisely, since it is not subject to any stress other than the force of gravity. In this way, it guarantees maximum stability of the load to be wrapped. Finally, maintenance is minimised, being restricted to regularly changing some accessories due to wear.

Brief Description of the Drawings

Further advantages and features of the invention are more apparent in the detailed description which follows, with reference to the accompanying drawings, which illustrate an example embodiment without limiting the scope of the invention, in which:

Figure 1 is a perspective assembly view of the invention in the home position;

Figure 2 is an enlarged perspective view of the invention in use;

Figures 3 and 4 are perspective views of details relative to parts of the invention.

Detailed Description of the Preferred Embodiments of the Invention

The invention relates to a gravitational pressure device for pallet wrapping machines, comprising a weight (1) able to move freely in a vertical direction, a supporting element (2), able to move in the same direction, designed to support the weight (1) during its movement from the home position to the operating position, and guide means (3), integral with the weight (1), designed to guide its movements relative to the machine (10).

In the drawings, the invention is shown on a ring machine with a quadrangular plan. In this case, the supporting element (2) prevents the weight (1)

from moving when the latter is in the home position.

The guide means (3) shown in Figures 3 and 4 comprise at least one pair of elements (3a, 3b) able to slide relative to fixed guides (11). Of these, at least one sliding element (3a) comprises means (4) for adjusting its radial position. In turn, the adjusting means (4) may be made in various ways, which are alternative or complementary. For example, the accompanying drawings show an elastic element (41), designed to automatically compensate for any size play, and a telescopic arm (42), whose length can be adjusted to compensate for any variations relative to the machine (10) nominal dimensions. In the specific case, the adjusting means (4) described may both be present in the invention, although there could only be one of them.

The fixed guides (11) are made on pallet (P) wrapping machine (10) load- bearing elements (12).

Use of the pressure device (20) can be inferred from Figures 1 and 2. When the machine (10) is in the home position, the pressure device (20) is in the raised position and is supported by the supporting element (2). When pallet (P) wrapping is started, the supporting element (2), which also supports the reels of plastic film to be unwound, starts to descend together with the weight (1). While the supporting element (2) continues to descend to complete pallet (P) wrapping, the weight (1) stops as soon as it reaches the top of the pallet (P), resting on it. When wrapping is complete, the supporting element (2) returns upwards and when it intercepts the weight (1), which at this point has completed its task, it carries the weight back to the home starting position above the pallet (P) in the upper part of the machine (10). The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept. Moreover, all details of the invention may be substituted by technically equivalent elements.

Obviously, in practice modifications and/or improvements are possible, all covered by the claims herein.