GB2025886A

GB2025886A - Method and apparatus for shrink wrapping an annular article

Info

Publication number: GB2025886A
Application number: GB7917254A
Authority: GB
Original assignee: Societe des Etablissements Thimon SA
Current assignee: Societe des Etablissements Thimon SA
Priority date: 1978-05-26
Filing date: 1979-05-17
Publication date: 1980-01-30
Also published as: FR2426557A1; SE7904592L; FR2426557B1; NL7904133A; IT7922756A0; IT1166827B

Abstract

A method of covering the outer cylindrical surface and the two ring- shaped sides of an annular article with a heat-shrunk plastics film comprises a first stage, carried out at ambient temperature, of covering said cylindrical surface with heat- shrinkable film which projects laterally beyond said surface, and a second stage of heating from above successive portions of the film to its shrink temperature while rotating the film covered article about an axis (11). During the or each revolution of the article successive parts of each laterally projecting film portion moved below a heater are urged by shrinkage forces and gravity towards a respective side of the article. Gravity subsequently urges said successive parts away from said side but this is of no significance since said parts are below their shrinkage temperature during this time. An apparatus for performing the method comprises a rotatable spindle (8) for carrying the annular article to two stations where respective stages of the method are carried out. <IMAGE>

Description

SPECIFICATION Method and apparatus for packaging an annularly shaped product The invention relates to a method and apparatus for particularly covering a product of a generally annular shape with a film of heatshrinkable plastics material.

Methods and apparatus are already known for completely covering a product of generally annular shape, i.e. its outer and inner cylindrical surfaces and its two ring-shaped sides with a film of heatshrinkable plastics material. The covering of the inner cylindrical surface of the annulus with film requires a specific method and apparatus.

For certain uses, it may be desirable for an annular product to be not completely covered, but only partly covered on its outer cylindrical surface and its two ring-shaped sides. In order to do this previously, the following method has been used:in a first stage carried out at ambient temperature, the outer cylindrical surface and the two sides of the annular product are covered with a film, in which the film is mechanically folded and retained on the sides of the annular product. In a second stage, the film covering the annular product is subjected to a continuous heat treatment causing shrinkage of the film simultaneously over its whole surface. Apparatus for carrying out this method comprises a mechanical unit for covering the outer cylindrical surface and the two sides of the annular product with film and a thermal unit for causing the shrinkage.This method and apparatus have numerous drawbacks. Folding of the film over the two sides of the annular product is a complicated operation which, owing to the fact that it is carried out mechanically, cannot be undertaken in a uniform manner. The mechanical folding means are complicated and their use permits only limited dimensional tolerances of the products to be covered. Therefore, installations of this type are not suitable for dealing with products of different dimensions. The unevenness of the film on the sides of the annular product is still present after the heat treatment and the appearance of the package produced in this way is unsatisfactory owing to the fact that it comprises pockets, folds etc.

The object of the present invention is to obviate or substantially mitigate these drawbacks.

According to a first aspect of the present invention there is provided a method of covering the outer cylindrical surface and the two ring-shaped sides of a product of generally annular shape with a film of heat-shrinkable plastics material, comprising the steps of, in a first stage which is carried out at ambient temperature, covering the outer cylindrical surface of the annular product with a film and leaving projecting from each of two sides of the product a portion of film which is in the form of a cylinder; in a second stage, subjecting the film covering the product and the portion thereof projecting from the sides of the product to at least one and generally several cycles of a discontinuous heat treatment combined with a mechanical treatment; in this cycle or each of these cycles, the projecting portions of film are each subjected to the heat treatment, which comprises an alternate succession over a period of time of short stages during which the film is subject to the action of a source of heat and longer stages during which the film.is not subject to the action of the source of heat and to the mechanical treatment which employs the effect of gravity and in which the film is successively alternately urged first in the direction of the adjacent side of the product and then in the direction away from this side of the product According to a second aspect of the present invention there is provided apparatus for covering the outer cylindrical surface and the two ringshaped sides of a product of generally annular shape with a film of heat-shrinkable plastics material, comprising means for gripping the annular product; drive means for rotating the gripping means; means for guiding the gripping means; drive means for causing longitudinal movement of the gripping means along the guide means; a first station comprising means for covering the outer cylindrical surface of the annular product with film and leaving projecting from each of these two sides a portion of film in the form of a cylinder and a second station comprising means for subjecting the film covering the annular product and the portions projecting from the sides of the product to at least one and generally several cycles of a discontinuous heat treatment combined with a mechanical treatment.

The method and apparatus according to the invention have the advantages of being very simple, of allowing annular products of different dimensions to be packaged, and finally of giving particularly well-finished package devoid of folds and pockets.

The present invention will now be described by way of example with reference to the accompanying drawings in which:~ Figures la, 2a, 3a, and 4a are four diagrammatic elevational views of an annular product, illustrating successive stages of a method for covering the product according to the invention; Figures 1 b, 2b, 3b and 4b are four diagrammatic axial cross-sectional views of an annular product illustrating the four stages corresponding to figures 1 a, 2a, 3a and 4a; Figures 5a, Sb, 5c, Stand 5e are five diagrammatic views, to an enlarged scale, in partial cross-section through an axial plane, illustrating various particular parts of the stages of the method according to the invention; Figure 6 are graphs illustrating aspects of the method according to the invention; and Figure 7 is a diagrammatic perspective view of apparatus for carrying out the method according to the invention.

The method of the invention is for partially covering a product 1 of generally annular shape (figures 1 a, 1 b) with a film 4 of heat-shrinkable plastics material such as a low density polyethylene. More precisely, the method is for covering the outer cylindrical surface 2 and the two ring-shaped sides 3 of the annular product 1.

In a first stage of the method, which stage is carried out at ambient temperature, the outer cylindrical surface 2 of the annular product 1 is covered with the film 4 and from each of its two sides 3 a portion 5 of film is left free in the initial form of a cylinder. The film 4 thus comprises a first part 6 covering the outer cylindrical surface 2 and, on either side, the two end portions 5. In order to do this, the film is of width L, which is greater than the width / of the annular product 1. The direction of shrinkage of the fiirn is transverse or radial, i.e.

corresponding to the circular outline of a plane arranged transversely with respect to the axis 7 of revolution of the annular product 1. This stage is illustrated in figures 2a and 2b.

Unlike the prior art, mechanical folding of the portions 5 of film 4 onto the sides 3 does not take place but a second stage is carried out, in which the film 4 and more particularly the portions 5 are subjected to at least one and more generally several cycles of a discontinuous heat treatment combined with a mechanical treatment.In each cycle, step-by-step, by an angular progression, each successive part of the radial surface of the film 4 is subjected alternately, first to a heat treatment period during which the film 4 is subject to the action of a source of heat and then to a longer period during which the film 4 is not subject to the action of the source of heat.The mechanical treatment in turn uses the effect of gravity in such a way that the film 4, or more precisely each of the portions 5, is successively urged, in the direction of the adjoining side 3, then in a direction away from this side. This second stage is illustrated by figures 3a and 3b, in which the arrows Th and Me respectively symbolise the heat treatment and the mechanical treatment.

The various cycles constituting the second stage of the method are substantially ideritical and it will therefore be sufficient to describe only one cycle in detail. To do this, the development, during the cycle, of the thermal and mechanical conditions along an outline A of the film 4 through a radial plane passing through the axis 7 will be considered. It will be apparent that during a cycle, successive portions of the outline A undergo identical treatments.

The temperature in the immediate vicinity of the outline A will be referred to by t. The angle formed by the outline A of the film with the outline B of the adjacent side 3 of the annular product 1 will be referred to as a (figure 5c). The angle formed by the outline A and a downwards vertical line illustrating the vector g symbolising the action of gravity will be referred to by p. The time will be referred to by 8 and the duration of a cycle by T.

The heat treatment during a cycle has the following characteristics. (figures 3a, 3b, 6). For a relatively short period of time 61, which is very much less than T, the temperature t is equal to t.

This temperature t1 is such that it is able to cause a certain shrinkage of the film 4 without causing actual melting of the film. For example, the temperature t1 is of the order of 2000C.

After the period of time Oi and during a period of time 6, corresponding to the end of the cycle T and thus equal to T-61, the temperature t is equal to t2. The temperature t2 is the ambient temperature or, more generally, a temperature less than t, and not able to cause shrinkage of the film 4. More generally, the temperature t is equal to t2 only during part of the period of time 62, whereas during the remainder of the period of time, the temperature varies between t1 and t2 and conversely between t2 and t,. The period of time 62 is much greater than the period of time 61 and for example the period of time 62 may itself represent more than 80% of the duration T of the cycle.It is also possible that the period of time 62 represents virtually the entire cycle, the period of time 6i being extremely short and corresponding to a temperature peak.

The mechanical treatment is as follows during a cycle. At the instant 6=0, the angle is equal to +900, i.e. the portions 5 are urged in the corresponding direction of the sides 3. At the time approximately 6=-T 2 the angle 3 is equal to --900, which signifies that the portions 5 of film 4 are urged in the corresponding direction away from the sides 3. At the end of the period T, the angle /3 has returned to its value +900.

The cycies of period T relating to the heat treatment correspond to the cycles of the same period relating to the mechanical treatment. This correspondence is such that at the instant 0, the temperature is equal to t1 and the angle /3 to +900, whereas at the instant T 6=-, 2 the temperature t is equal to t2 and the angle P to ~90 , as illustrated in figure 6. However, it can be understood that the cycles corresponding respectiyely to the heat treatment and to the mechanical treatment are staggered one with respect to the other.

As aforementioned, the second stage of the method comprises one cycle or more generally several cycles. In practice, it was found that a succession of the order of six cycles was satisfactory.

Naturally, the various successive portions of the outline of the film undergo progressively, by degrees and by an angular progression, the treatment which has been described.

Figures 5a, Sb, 5c, Stand 5e illustrate diagrammatically the same portion of the outline of the film at the beginning of each cycle of the treatment. Initially, and as has been seen previously, on leaving the first stage of the method, the portion 5 of film is arranged as an extension of the outer cylindrical surface 2 of the product 1. The application during the period of time 61 of the temperature t1 causes temporary shrinkage of the film without melting. The relative value of shrinkage depends on the stresses to which the film is subjected. This is why shrinkage occurs more towards the free edge of the portion 5 than towards the first part 6.Since this shrinkage occurs when the angle /3 is equal to +900, it follows that the portion 5 is urged in the direction of the corresponding side 3 as illustrated by figure Sb. Subsequently, the outline A is subject to the temperature t2 and it follows that the shrinkage is "stopped" at the degree obtained previously. However, successive outlines adjacent to A undergo the same treatment as that which has been described.The fact that the outline A passes through a point where the angle is equal to 900 is of no significance in view of the fact that at this instant, the temperature is equal to t2 and that consequently shrinkage is "stopped." During the subsequent cycle, a phenomenon of the same type occurs, thus producing subsequent second partial shrinkage which is added to the first partial shrinkage already obtained so that the portion 5 moves closer to the side 3 (figure 5c).

The same phenomenon occurs during subsequent cycles and thus for each of the outlines of the film.

It thus appears that the angle a between the outline A and the corresponding outline of the side 3 varies by steps of 900 to O at the end of the last cycle where the portion 5 is applied against said side 3.

As may be noted, at the end of each cycle, the film 4 and more particularly the portions 5 are in the same state whatever the angular position in which they are located.

Naturally, it is possible to conceive of numerous possibilities for carrying out the heat treatment and mechanical treatment cycles which have been described.

As regards the heat treatment, by way of example, one may proceed with a relative movement of a source of heat corresponding to the temperature t, about the axis 7. As regards the mechanical treatment, a convenient solution is to cause the rotation of the annular product 1 and of its film 4 about the axis 7 at a constant speed. The combination of the two treatments may consequently be achieved very simply by keeping a source of heat stationary and by causing the annular product 1 covered with its film 4 to pivot about the axis 7 so that successive regions of the film pass in front of said source of heat; In order to achieve the desired correspondence between the heat treatment cycles and mechanical treatment cycles, it is sufficient to locate the source of heat with a desired angular spacing from an ascending vertical line passing through the axis 7.If one retains the correspondence described previously and illustrated by figure 6 as desirable, it is sufficient that the source of heat is located substantially above the annular product 1.

The final result obtained by carrying out the method which has been described is an annular product 1 whose outer cylindrical surface 2 and two ring shaped sides 3 are covered by the film 4.

More specifically, as regards the portions 5, the film 4 is applied perfectly to the sides 3, in a uniform manner and without pockets, folds or the like.

Apparatus for carrying out the method is illustrated diagrammatically in figure 7 and comprises the following parts:~ ~means 8 for gripping the annular produce a via its central hole 9: these gripping means 8 are constituted by an expansion spindle which can be adapted to fit annular products 1 with differently sized central holes 9; ~drive means 10 for producing the rotation of the gripping means 8 about their axis of revolution 1 these drive means 10 are constituted for example by a motor; ~means 12 for guiding the gripping means over a certain distance, on which two stations of the apparatus are located; ~drive means 13 for bringing about the longitudinal movement of the gripping means 8 along the guide means 12; and - a first station 14 for carrying out the first stage of the method and a second station 15 for carrying out the second stage of the method.

The first station 14 comprises means 1 6 for the storage and supply of film and means 17 for cutting and welding the film coming from the means 1 6, in order to achieve covering of the outer cylindrical surface 2 of the annular product 1 with film. Naturally, when the annular product 1 to be treated is located at the first station 14, the rotary drive means 10 are inoperative, as are the drive means 13 for longitudinal motion.

The second station 15 comprises heating means 18 such as a nozzle device for emitting pulses of hot air. These heating means 18 naturally occupy a position which is preferably above the position of the product 1 at the second station 1 5. If necessary, means are also provided controlling the operation of the heating means 18 and the rotary drive means 10 which operate when the ann#ular product 1 is at the second station 15.

Claims

1. A method of covering the outer cylindrical surface and the two ring-shaped sides of a product of generally annular shape with a film of heatshrinkable plastics material, comprising the steps# of, in a first stage which is carried out at ambient temperature, covering the outer cylindrical surface of the annular product with a film and leaving projecting from each of the two sides of the product a portion of film which is in the form of a cylinder; in a second stage, subjecting the film covering the product and the portion thereof projecting from the sides of the product to at least one and generally several cycles of a discontinuous heat treatment combined with a mechanical treatment; in this cycle or each of these cycles, the projecting portions of film are each subjected to the heat treatment, which comprises an alternate succession over a period of time of short stages during which the film is subject to the action of a source of heat and longer stages during which the film is not subject to the action of the source of heat, and to the mechanical, treatment which employs the effect of gravity and in which the film is successively alternately urged first in the direction of the adjacent side of the product and then in the direction away from this side of the product.

2. A method as claimed in claim 1, in which the temperature of the source of heat and the duration of the shorter stage during which the film is subject to the action of the source of heat are such that the film is heated in order to be shrunk without reaching melting point.

3. A method as claimed in claim 1 or 2, in which during the shorter stage in which the film is subject to the action of the source of heat in the heat treatment the film is urged in the direction of the adjacent side of the annular product in the mechanical, treatment.

4. A method as claimed in any one of claims 1 to 3, in which the heat treatment is carried out whilst the source of heat is moved relative to the annular product such that the source of heat passes progressively over successive areas of the film.

5. A method as claimed in any one of claims 1 to 4, in which the mechanical treatment is carried out by rotating the annular product about its axis of revolution.

6. Apparatus for covering the outer cylindrical surface and the two ring-shaped sides of a product of generally annular shape with a film of heatshrinkable plastics material, comprising means for gripping the annular product; drive means for rotating the gripping means; means for guiding the gripping means; drive means for causing longitudinal movement of the gripping means along the guide means; a first station comprising means for covering the outer cylindrical surface of the annular product with film and leaving projecting from each of these two sides a portion of film in the form of a cylinder and a second station comprising means for subjecting the film covering the annular product and the portions projecting from the sides of the product to at least one and generally several cycles of a discontinuous heat treatment combined with a mechanical treatment.

7. Apparatus as claimed in claim 6, in which the first station comprises means for the supply and storage of the film and cutting and welding means.

8. Apparatus as claimed in claim 6 or 7, in which the second station comprises localised heating means and means for governing the operation of the heating means by the operation ot the rotary drive means.

9. A method of covering the outer cylindrical surface and the two ring-shaped sides of a product of generally annular shape with a film of heat shrinkable plastics material, substantially as hereinbefore described with reference to the accompanying drawings.

10. Apparatus for covering the outer cylindrical surface and the two ring-shaped sides of a product of generally annular shape with a film of heat shrinkable plastics material substantially as hereinbefore described with reference to Fig. 7 of the accompanying drawings.