The present invention relates to a protective bellows and a method for making the same. More specifically, the invention concerns a protective bellows for enclosing mov¬ able parts of a tool, such as a scissors-type lifting table, and a method for making such a bellows.

Protective bellows have long been used for widely different purposes. One important application concerns the enclosure of movable mechanical devices, such as the underframe of a scissors-type lifting table and piston and cylinder units in vehicles or workshop machinery, for protecting these devices from dirt and/or protecting the operator from injuries. In general, prior-art protective bellows are compos¬ ed of two or more layers of material, of which one has a stiffening function and the other or others serve to keep the bellows structure together so as to form the finished bellows. Alternatively, use is made of stiffening elements in the form of springs or steel rings arranged in the folds of the bellows. One instance of the prior art is disclosed in DE 12 51 650, which relates to a bellows composed of three layers of material. One layer has a stiffening function and comprises four sheets which are interconnected at the upper and lower edges by a narrow strip of material, whereby to form a coherent piece. Each sheet has slits extending across almost the entire sheet width. The slits constitute weakened portions where the material is folded when an inner and an outer layer of flexible material have been glued on to the stiffening layer.

The prior art suffers from several drawbacks. Using several layers of material is complicated, time-consuming as well as costly. Also, it involves a large consumption of material and many working operations. Since the sheets in the stiffening layer are only interconnected by two narrow strips, the finished bellows will have fairly weak

corners, these being formed of but the flexible and compa¬ ratively thin layers.

The object of the present invention is to obviate the above drawbacks in the manufacture of the protective bellows, as well as those associated with the finished bellows.

This object is achieved by a bellows and a method for making the same having the features recited in the charac¬ terising clauses of, respectively, appended claim 1 and appended claim 5.

One thus obtains a protective bellows which differs from prior-art bellows by being much simpler, self-sup¬ porting without any additional stiffening -layers or stif¬ fening elements, as well as time- and cost-effective in terms of production, owing to a reduced number of working operations and a substantially enhanced economy of mate¬ rial. A further advantage is that the bellows according to the invention has essentially the same strength all over. The present invention will be described in more detail below with the aid of embodiments illustrated in the accompanying drawing, in which like reference numbers indicate like parts. In the drawings,

Fig. 1 is a schematic perspective view from above of a bellows according to the invention; Fig. 2 is a schematic perspective view from below of the bellows in Fig. 1;

Fig. 3 is a schematic plan view of a blank forming part of the bellows in Fig. 1;

Fig. 4 is a schematic perspective view of the blank in Fig. 3 when folded together; and

Fig. 5 is a schematic perspective view of two inter¬ connected blanks.

Fig. 1 shows a preferred embodiment of a bellows 1 according to the invention. This bellows is designed to enclose the underframe of a scissors-type lifting table, and is composed of four sheet-like blanks 2 interconnected along the edges 3 of their long sides. The resulting con-

necting portions 4 thus constitute the corners of the bellows 1. The blanks 2 consist of substantially rectangu¬ lar fabrics of a synthetic material, preferably PVC. The edges 3 of the long sides of the blanks 2 have a saw-tooth shape, as shown in Fig. 5, which enables two blanks 2 that are interconnected along their long-side edges at an angle to fold. Further, the blanks 2 have a first set of fold lines 5, shown in Figs 3 and 5, extending between opposite crests 6 of the saw-tooth long-side edges 3, as well as a second set of fold lines 7 extending between opposite troughs 8 of the saw-tooth long-side edges 3. The first set of fold lines 5 is provided on the inside of the blank, i.e. on the side that forms the inside of the bellows, and the second set of fold lines 7 is provided on the outside of the blank. By the fold lines 5, 7, the blank 2 is divided into fold portions 9. Also, the fold lines 5, 7 make the material fold at precisely these lines and in a predetermined direction. Further, the fold lines impart stability to the material, resulting in pliable folding of the bellows 1. In the preferred embodiment, the fold lines 5, 7 are provided by means of a high-frequency welding machine, but also other tools and methods may, of course, be used. At the upper end, the bellows 1 is equip¬ ped with an upright circumferential flange 10 formed from an upper end portion 11 of each blank 2, the end portion 11 being twice as wide as a fold portion 9 and being fold¬ ed into the shape of a T turned upside-down. The web of the end portion thus constitutes the flange, and the branches of the end portion are high-frequency welded to the fold portion 9 adjoining the end portion 11. This gives both the flange 10 and the fold portion 9 a double thickness of material, which is of importance, since the flange 10 is fixed to a corresponding flange of the scis¬ sors-type lifting table and thus carries the entire weight of the bellows 1.

As shown in Fig. 2, a circumferential channel 12 hav¬ ing openings 13 at each corner is provided at the lower end of the bellows 1. The channel 12 is formed of the two lowermost fold portions 9 of each blank 2 by high-frequen- cy welding of the lower short-side edge 14 of the blank 2 to the lowermost but one fold portion 9. Flat irons, for instance, are introduced in the channel 12 which, with its contents, is fixed to the floor.

The preferred embodiment of the bellows 1 according to the invention is manufactured as follows.

Four rectangular equally-sized blanks 2 are cut from a roll of fabric of a high-frequency weldable synthetic material, preferably PVC. Each of the blanks 2 is provided with a first set of fold lines 5 on the inside, and a second set of fold lines 7 on the outside, as shown in

Fig. 3. In doing this, every other fold line 5 is provided on the inside and every other fold line 7 is provided on the outside by high-frequency welding, a positive elec¬ trode being placed on the side of the blank 2 where the fold line 5, 7 is to be provided, and a negative electrode being placed on the other side of the blank 2. High-fre¬ quency voltage is generated between the electrodes, and the material in the blank is heated and deformed so as to form a fold line 5, 7. Then, the blank 2 is folded along the fold lines 5, 7, resulting in a body 15, i.e. a folded blank, as shown in Fig. 4. The body 15 is cut at both ends at an angle of 45° to the short sides, as illustrated by the dashed lines in Fig. 4, thereby forming a trapezium. The blank 2 is extended and now presents saw-tooth long- side edges 3, where the first set of fold lines 5 extend between opposite crests 6 of the saw-tooth long-side edges 3, and the second set of fold lines 7 extend between oppo¬ site troughs 8 of the saw-tooth long-side edges 3. All the blanks 2 are interconnected as shown in Fig. 5 so as to form a tubular unit, i.e. a bellows. The blanks then are arranged in pairs, applied against one another and inter¬ connected by high-frequency welding along one long-side edge 3.

It goes without saying that various modifications of the inventive bellows and the inventive method are conceivable within the scope of the invention as defined i the appended claims. Thus, the fold lines may be provided by any optional method. Apart from PVC, polyurethane or some other suitable material may be used, depending, inter alia, on the interconnecting technique. The flange at the upper end of the bellows may be optionally positioned on the uppermost fold portion, e.g. at the outer or the inne periphery. Both the flange and the channel may be provide at one or both ends of each blank. Further, the blanks ma have optional shape, such as triangular, ellipsoidal or irregular. The term "saw-tooth" relates not only to the symmetrical shape in the illustrated embodiment, but also to any regular or irregular shape presenting crests and troughs.