CH674174A5 - - Google Patents

Description

DESCRIPTION

The subject of the invention is a device for the continuous formation of a tabular envelope from a flexible film, comprising a curved deflecting surface followed by a cylindrical surface through which the tabular envelope is pulled.

Such a device is used, for example, in an installation for packaging in sachets an extrudable product in the hot state such as cheese. Such an installation is described, for example, in US Pat. No. 3,542,570. In this installation, the device for forming the tabular envelope consists of three deflecting surfaces consisting of rounded sheets. It is also known to use deflector plates having approximately the shape of a sailor's neck. All these deflecting surfaces have in common the characteristic of having a large contact surface with the film to be formed into a tube and of carrying out a transformation from a plane surface to a cylindrical surface, with a change of direction, in an entirely approximate manner. . For the packaging of cheese into individual slices, it is known to use a film of Mylar (registered trademark of Dupont de Nemours). With such a material, the known forming surfaces do not pose a problem, but Mylar is an expensive material and, moreover, it is not heat sealable. It would therefore be more advantageous to use an inexpensive and more heat-sealable material, such as, for example, polypropylene. However, already cold, the polypropylene film tends to adhere to a metal surface by electrostatic effect. This disadvantage can be overcome by grounding the formation surface. The fact remains that the film tends to form folds under the effect of traction, due to the geometrically incorrect surface of the forming sheets. However, to condition cheese by extrusion, it is necessary to work at a temperature of approximately 80 ° C. Under these conditions, the softened polypropylene film adheres frankly to the forming surface and the film, generally of a 20 µm thick, tears.

The object of the present invention is to provide a training device which overcomes the drawbacks described above and, more precisely, which makes it possible to use thin films of polypropylene or the like when hot.

5 The device according to the invention is characterized in that the curved deflecting surface is formed by the intersection of a cone and the wall of a cylindrical tube whose internal wall constitutes said cylindrical surface, the apex of the cone being situated on the axis of the cylindrical tube and the axis of the cone being inclined relative to the axis of the cylindrical tube.

Preferably, the axis of the cone forms with the axis of the cylinder an angle such that the developed curve of the intersection of the cone and the interior surface of the cylinder is a parabola, the plane tangent to the cone and containing the generatrix of the cone the most distant from the axis of the cylinder is defining the plane in which the film is brought to the device. In this case, the formation surface obtained is geometrically exact, so that the film does not undergo transverse effects and therefore does not form a fold.

In all cases, this surface is narrow so that the braking of the film by adhesion is acceptable.

The device according to the invention makes it possible not only to use polypropylene films with a thickness of 20 μm when hot, but to use very thin films, for example 10 μm.

According to a particular embodiment of the invention, the cone 25 has an apex angle β of 60 ° and the angle formed by the axes of the cone and of the cylindrical tube is equal to arc sin 2 / ji-30 °.

The choice of a 60 ° cone allows an easy calculation of the angle between the axes of the cone and the cylinder. It also allows machining by simple and usual means.

The accompanying drawing shows, by way of example, an embodiment of the invention.

FIG. 1 schematically represents the main part of a packaging installation comprising a training device.

Figure 2 is a side view of the training device.

Figure 3 is a sectional view along III-III of Figure 2.

Figure 4 is a front view, in direction A, of the training device.

Figure 5 illustrates the reasoning that led to the surface

40 i i> - * •

according to the invention.

The installation shown diagrammatically in FIG. 1 comprises a training device 1 of generally tabular cylindrical shape into which enters a feed tube supplied by a hopper 3 for the product to be packaged. The packaging material consists of a film 4, for example made of polypropylene, unwound from a reel 5. This film passes over a return 6, then over the upper edge of the tube of the forming device 1 in which it is pulled towards the bottom forming a tube, the two edges of the film 4 being superimposed so and welded in the device 1, by means of a heating body, just before filling with the product to be packaged, for example cheese melted at 80 ° C. The tube is therefore welded above the lower end of the feed tube 2. In the case of cheese intended to be packaged in slices, that is to say in 55 wafers, the lower end of the supply tube 2 is flattened and the polypropylene tube 7 follows the shape of the end of this supply tube as illustrated in 8. The tube 7 containing the product to be packaged then passes through a portion former 9 made up of two belts 10 and 11 fitted with cleats and pressers 12 60 and 13 coming to apply against each other to pinch the tube 7 and thus separate the product into portions 14 as described for example in US Patent 3,542,570.

The forming device 1, shown in detail in FIGS. 2 to 4, consists of a thick-walled tube formed more precisely by 65 two half-tubes 15 and 16, the half-tube 15 being fixed is fixed to a support 17 , while the half-tube 16 is integral with a flange 18 articulated at 19, making it possible to open and close the tube, which facilitates the starting of the machine and the maintenance of the device

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674,174

training. The movable part 16 further carries, below the flange 18, a heating body for heat sealing the tube 7.

The upper edge of the tube 1 has a deflecting surface 20 formed by the intersection of a cone whose apex S is located on the axis a of the cylinder 1, whose apex angle ß is 60 ° and whose axis b forms with angle a of cylinder 1 an angle a = arc sin 2 / tc — 30 °, or 39.5402 °, due to the relation a + ß / 2 = arc sin 2 / jt which will be demonstrated more far. The film 4 arrives in a plane containing the generatrix g of the cone located in the same plane as the axes a and b and the most distant from the axis a of the cylinder. Experience confirms that the film 4 progressively passes from the planar form to the cylindrical form, by changing direction on the edge 21 formed by the intersection of the cone and the internal cylindrical surface of the tube 1, without adhering or forming of fold. The film 4 begins by naturally enveloping the conical surface 20 before rolling up on the edge 21 with a minimum of transverse stress.

The cone could have a vertex angle ß other than 60 ° and the angle a could have a different value of arc sin 2 / tc — 30 °. The angle a could be determined experimentally or using a computer.

The choice of a conical surface is not due to chance, but to an inventive approach, at the same time empirical, experimental and mathematical. This approach will be explained in relation to FIG. 5. We consider the end of the film 4 when it is introduced into the tube 1. During this introduction, the film 4 suddenly changes direction. However, if one grasps the corners A and B of the end of the film 4 and folds them symmetrically in the direction of the center, one notes that two folds 22 and 23 are formed and that each of these folds forms with the edge of the film an angle 8 equal to 45 °.

It has also appeared that the winding of a flat sheet on a cone makes it possible to wind this sheet easily. On the other hand, a cone of angle at the top of 60 ° has the particularity in the developed state of forming a semicircle, in particular a semicircle 24 whose diameter is equal to the width L of the film 4. When the cone is reformed, the ends C and E of the diameter of the semicircle 24 meet. During the winding of the film 24, the same points C and E located on the edges of the film also come to coincide.

By carrying out a test of winding of the film 4 on a cone followed by a cusp in a cylindrical shape, by noting the points of the curve of the cuspid edge obtained and by entering these points noted in a computer, one obtains a curve developed in the plane very close to a parabola.

Considering therefore that this developed curve is indeed a parabola, and returning to Figure 5, we see that the angle 5 = 45 ° is equal to the angle of the tangents at points C and E to a particular parabola whose focus is the point S and whose focal surface f is 5 equal to L / 4.

If the cone is formed again and this cone is placed on the tube 1, the apex P of the parabola is placed on the upper edge of the tube 1 on the generator situated in the plane of the film 4, as shown in the lower part of FIG. 5. The points C and E also meet on the edge of the tube 1, on a generatrix of the coplanar cone with the axis b of the cone and the axis a of the tube 1. The axis b of the cone is inclined relative to the axis a of the tube 1. If we designate the angle at the top of the cone by ß and the angle formed by the axes a and b by a, we see in Figure 5 that sin (a + ß / 2) = D / 2f where D is the diameter of tube 1.

By replacing f by L / 4, we get sin (a + ß / 2) = 2 / jt and therefore a + ß / 2 = arc sin 2/71 = 39.5402 °

For the machining of tubes 1, it suffices to know the angle y = 90 ° - (a + ß / 2).

Tests performed with a part machined in this way demonstrate that the film is wound up perfectly.

It is obvious that it would be possible to arrive at the same result with a cone having an angle at the apex different from 60 °, but in this case the angle a would have another value than the value calculated above.

In its upper part, the half-tube 16 is cut by a plane parallel to the axis of the tube and tangent to the interior surface of this tube. In the area thus cut, the half-tube 16 also has a wide vertical slot 25. This slot is covered by two sheets 26 and 27 which partially overlap on the slot 25, the end of the sheet 26 being bent so to match the curvature of the inner cylindrical face of the tube 1. These sheets 26 and 27 are used to superimpose the two edges of the film 4 which are welded below by the heating body fixed to the lower part of the tube 1. In the considerations presented in relation to FIG. 5, it has of course been disregarded these two welding edges of the film 4.

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3 sheets of drawings

Claims (6)

674174 1. Device for the continuous formation of a tabular envelope from a flexible film (4), comprising a curved deflecting surface (20) followed by a cylindrical surface through which the tabular envelope (7) is drawn, characterized in that said curved deflecting surface (20) is constituted by the intersection of a cone and the wall of a cylindrical tube (1) whose inner wall constitutes said cylindrical surface, the apex (S ) of the cone being located on the axis (a) of the cylindrical tube (1) and the axis of the cone (b) being oblique relative to the axis of the cylindrical tube. 2. Device according to claim 1, characterized in that the axis of the cone (b) forms with the axis (a) of the cylindrical tube an angle a such that the developed curve of the intersection of the cone and the surface inside of the cylindrical tube is a parabola, the plane tangent to the cone and containing the generatrix (g) of the coplanar cone to the axes of the cone and of the cylindrical tube farthest from the axis of the cylindrical tube defining the plane in which the film is brought (4) to the device. 2 3. Device according to claim 2, characterized in that the cone has an angle at the top ß of 60 ° and that the angle a formed by the axes of the cone and of the cylindrical tube is equal to arc sin 2 / n — 30 °. 4. Device according to one of claims 1 to 3, characterized in that the tube (1) consists of two parts (15,16) hinged together around an axis parallel to the axis of the tube. 5. Device according to claim 4, characterized in that the cylindrical tube is cut in its upper part by a plane tangent to the inner surface of the cylinder and containing the generator diametrically opposite to the generator passing through the highest point of the tube cylindrical in vertical position, the cylindrical tube having a vertical slot (25) in this tangent plane. 6. Device according to claim 5, characterized in that the cylindrical tube has two deflecting sheets (26, 27) crossed above said slot (25).