The invention relates to an apparatus for form¬ ing a shoulder in a ladder rung, the apparatus compris- ing a forcing means for forcing the material of the tubular rung from the centre line of the rung outwards, support means for keeping the rung in place and the forcing means being connected to be driven by a power unit. Traditionally, a ladder rung is secured to a ladder rail either by a bolt-nut joint or by welding, which makes the joints stable. However, when ageing, the joints get easily rusty and are oxidized under the in¬ fluence of outdoor air, which makes the ladder very dangerous. Correspondingly, the ladder as a whole will be very heavy.

German Publication 2 549 505 discloses an equipment, in which a tube having a small diameter is provided with a shoulder to be used as soldering mate- rial when the tube is joined to a tube having a greater diameter. In this equipment, a guide tube 9 is posi¬ tioned in a shoulder tool 6, the outer diameter of the guide tube being substantially equal to the inner dia¬ meter of the tube. Further, the guide tube 9 is long enough to support the tube at the place which is pro¬ vided with a shoulder. The tube is positioned on the guide tube 9 and in the tool 6 according to the guide tube 9, respectively. Subsequently, another tool 7 is fastened at a distance from the tool 6, but in such a way that the guide tube 9 supports the tube 5. The tube 5 is forced towards the tool 6 by pressing the tool 7, due to which an aperture 8 in the tool 6 is filled with the material of the tube 5 and forms thus a shoulder. Subsequently, the tube 5 is positioned in the tube 12, whereby the shoulder acts as soldering material and

joins the tubes 5 and 12 together, when the tube 5 is heated. However, said joining method is intended for tubes having a very small diameter, the like of which are usually used in cold machines and equipments. Fur- ther, said equipment does not comprise an automatic line for producing said shoulder, but the equipment in ques¬ tion is primarily intended for individual measures. Cor¬ respondingly, a tube used in cold machines and equip¬ ments is usually very soft, which makes it easy to machine in the manner shown in the publication.

European Patent Application 0040971 discloses a method and an apparatus for connecting a tube to a flange. The flange is provided with a bore, the diameter of which is along a distance equal to the outer diameter of the tube. Correspondingly, the flange bore is provid¬ ed with grooves, into which the outer surface of the tube is forced by means of a separate tool, which is pushed into the tube at the end thereof. The tool ex¬ pands the tube and forces it simultaneously into the grooves in the flange bore, due to which the tube and the flange are connected to each other by means of a compression joint. The flange to be joined to the tube acts as a counterpart of the expansion tool of the in¬ vention according to the publication. However, a problem with said method and apparatus is that a separate flange part has to be used for forming a shoulder in the tube, whereby at least two parts are used for providing a whole. On the other hand, the tube is subjected to a very high stress due to the joint between the flange and the tube, and therefore, it also breaks easily.

German Publication 2 825 538 discloses an equipment for securing a ladder rung to a ladder rail, a tube or the like acting as the rail. The ladder rung is mounted in a hole in the rail, and then a device is pushed into the ladder rail to expand the rung inside

the rail, which makes the rung immovable with respect to the rail. Subsequently, the end of the rung is bent against the rail. However, said arrangement does not provide a stable attachment between the rail and the rung. Since it is necessary to use a tube as a rail, the consumption of material increases high. Respectively, when the end of the rung is bent against the rail, the rail sinks easily inwards and the result is an unesthet¬ ic whole. Swedish Publication 415 736 discloses an equipment for securing a ladder rung to a rail. As the ladder rail is used a rail having an I-shaped cross- section and provided with holes for the rung to be posi¬ tioned in place. For positioning the rung in place, a forcing edge of a tool moves from the end of the rung inside, after which the rung is expanded in such a way that shoulders are formed on both sides of the rail wall. Subsequently, another tool is placed inside the rung, by which tool the rung is compressed on both sides of the rail so much that broader shoulders are formed against the rail. The equipment according to the inven¬ tion is, however, very difficult to accomplish and very sensitive to failure because of its complicated struc¬ ture. Similarly, the surface of the rung is easily torn at the compression stage, which makes the whole ladder blank unusable.

U.S. Patent 3,500,956 discloses a method for securing a ladder rung to a ladder rail, in which method additional sleeves are positioned at the end of the lad- der rung on both sides of the rail, which sleeves are fastened to the rung by means of separate press tools simultaneously causing an attachment to the rail. How¬ ever, a problem with the ladder solution according to the invention is that several different additional parts have to be used to provide the joint. Accordingly, it

is a very expensive solution for the manufacturer, since many kinds of mounting sleeves must be kept in stock.

The object of the present invention is to pro¬ vide an apparatus for forming a shoulder in a ladder rung.

This apparatus is characterized in that the apparatus comprises swivel plates arranged to be turned around axes by the operation of the power unit, that the swivel plates are connected to each other by means of a substantially unelastic beam and that the forcing means are connected to move by the operation of the swivel plates in such a way that they force the material of the rung from the centre line outwards to form a shoulder at both ends of the rung essentially simulta- neously.

An essential idea of the invention is that shoulders are formed in a rung by pressing both ends of the rung simultaneously against each other. Another es¬ sential idea is that the rung is supported at its mid- part in such a way that a shoulder formed at both ends of the rung is supported on the ends of a centre sup¬ port, due to which the length of the rung is determined very accurately. A further essential idea is that a forcing tool is formed so as to comprise a centre, which supports the rung inside, and respectively, that there is a groove around the centre, on which groove the end of the rung is supported. Accordingly, when forcing tools are pressed at the both ends simultaneously against each other, the structure of the rung is sup- ported by centre supports, while the forcing tools at both ends force the rung material to be pressed from the centre line of the rung outwards, and when the forcing tools are pressed sufficiently, a shoulder is formed between the centre supports and the forcing tools. Still another essential idea is that the forcing tools receive

the force via swivel plates from a hydraulic or a pneu¬ matic cylinder, respectively. In addition, since the swivel plates are joined together by an unelastic beam, the forcing takes place on both sides very evenly. An essential advantage of the invention is that a ladder rung can be provided with shoulders by means of said apparatus without additional sleeves. Another essential advantage is that the apparatus is very simple, due to which its maintenance and repair costs are very low. Respectively, the forcing tools are very resistant to stress, due to which the tool costs remain very low. Still another essential advantage is that, with the rung supported at its midpart and shoulders being forced simultaneously at both ends of the rung, the rung cannot move in the lateral direction, and therefore, its surface remains unscratched and tidy- looking. Respectively, the centre support presses the rung sufficiently so that the rung cannot loose its shape when forced. The invention will be described in more detail in the following drawings, in which

Figure 1 shows a side view of a ladder rung forcing device according to the invention simplified, Figure 2 shows a side view of a similar device, Figure 3a shows how a forcing tool is posi¬ tioned with respect to the ladder rung and

Figure 3b shows how a shoulder is formed in the ladder rung.

Figure 1 shows a ladder rung forcing device 1. The forcing device 1 is illustrated in the simplest pos¬ sible manner in Figure 1 and only the most essential de¬ tails are illustrated therein. The forcing device 1 com¬ prises swivel plates 2a and 2b connected to be turned around axes 3a and 3b. Respectively, the swivel plates 2a and 2b are connected to each other by means of a

substantially unelastic beam 4. To the swivel plates 2a and 2b are connected power units 5a and 5b, which may be hydraulic cylinders, pneumatic cylinders or other similar power units. The purpose of the power units 5a and 5b is to turn the swivel plates 2a and 2b around the axes 3a and 3b. Simultaneously, forcing tools 7a and 7b are moved via arms 6a and 6b, also connected to the swivel plates 2a and 2b, in cylinders 8a and 8b control¬ ling the motion. The term forcing tool means in this application generally at least forcing means by which the material of a rung 13 can be forced from the centre line of the rung 13 outwards. The cross-sectional shape of the cylinders 8a and 8b may be whichever, if only it matches the opposite surfaces of the forcing tools 7a and 7b, whereby the forcing tools 7a and 7b move in opposite directions with respect to each other. The cylinders 8a and 8b are attached to a frame portion of the forcing device 1, which frame portion is not shown more accurately in Figure 1. Since the swivel plates 2a and 2b are joined to each other by means of the unelas¬ tic beam 4, the motion of the compression tools 7a and 7b via the power units 5a and 5b occurs very evenly, and accordingly, differences in the operation of the power units 5a and 5b do not cause problems when the swivel plates 2a and 2b are turned. Further, Figure 1 shows centre supports 9a and 9b as well as an actuator 10 for the centre support 9a, which actuator may be a hydraulic cylinder or the like. The centre support is also called support means. The purpose of the actuator 10 is to press the centre support 9a against the centre support 9b, which is fastened to the frame of the forcing device 1. Accordingly, a ladder rung to be positioned in a groove of the centre supports 9a and 9b is pressed even¬ ly on all sides. After the rung has been compressed in the groove of the centre supports 9a and 9b, the power

units 5a and 5b turn the swivel plates 2a and 2b around the axes 3a and 3b, whereby the arms 6a and 6b connected to the swivel plates 2a and 2b move the forcing tools 7a and 7b in the cylinders 8a and 8b against each other, until a shoulder is formed in the ladder rung on both sides thereof. Subsequently, the ladder rung is removed from between the centre supports 9a and 9b and a new rung is inserted between them.

Figure 2 shows a procedure in which a ladder rung 13 is moved from above a conveyor belt 11, bringing rungs 13, between the centre supports 9a and 9b. The numerals of Figure 2 correspond to the numerals of Fig¬ ure 1. The ladder rung 13 is brought to the forcing device 1 by using a conveyor belt solution known per se, in which the conveyor belt 11 rotates around a roller 12 and the motion of the conveyor belt 11 can be regu¬ lated for instance by means of a photocell or the like. Then the ladder rung 13 is in a suitable position so that a transferring arm 14 shown in Figure 2 can turn the rung 13 gripped by a gripping apparatus 15 around an axis 16, whereby it is positioned on a surface 17' of a hook-like holding lever 17. The gripping apparatus 15 may be whichever apparatus operating for instance by pneumatics, by which apparatus it is possible to fasten the rung 13 to the transferring arm 14. Figure 2 shows only one 17 holding lever. There is a corresponding holding lever also on the other side of the centre sup¬ port 9b. The holding lever 17 is connected to be turned around an axis 19 by an actuator 18. The actuator 18 can be operated pneumatically as well as hydraulically or it may operate by means of a separate electromechanical device. When the conveyor belt 11 moves the rung 13 on the belt forward, until a photocell or another detecting means stops the motion of the belt 11, the transferring arm 14 turns in such a way that the gripping device 15

grips the rung 13. Subsequently, the transferring arm 14 turns according to arrow A around the axis 16 and places the rung 13 on the surface 17' of the holding levers 17 on both sides of the centre support 9b. Then the actuator 10 moves the centre support 9a towards the other centre support 9b, whereby the rung 13 supported by the holding levers 17 is positioned in grooves 9' and 9" of the centre supports 9a and 9b. When the centre support 9a meets the centre support 9b fastened to the frame of the forcing device 1 and presses simultaneously the rung 13 sufficiently in the grooves 9' and 9", the actuator 18 turns the holding levers 17 around the axis 19, upon which the forcing tools 7a and 7b may force shoulders at the ends of the rung 13 without impediment. After the forcing procedure has taken place, the centre support 9a is moved away from the centre support 9b by the actuator 10, after which the rung 13 remained in the groove 9" is pushed away by a pushing device 20. The pushing device 20 may be for instance a member operating by means of a bar, in which case the axis pushes the rung 13 out of the groove 9" by means of a hole arranged in the centre support 9b. Subsequently, the holding lever 17 is returned in place by means of the actuator 18 to wait for a new ladder rung 13. Figure 3a shows a situation, when a ladder rung

13 is compressed between the centre supports 9a and 9b in such a way that part of the rung remains outside the centre supports 9a and 9b. Figures 3a and 3b show the forcing procedure of one rung only, but this procedure takes place simultaneously at both ends of the rung 13. Figure 3a shows further the forcing tool 7a, which moves in the cylinder 8a. The forcing tool 7a also comprises a guide 21 leading the forcing tool 7a into the tubular rung 13. Respectively, the forcing tool 7a comprises a groove 22, on which the end of the rung 13 is supported.

Since the forcing procedure takes place at both ends of the rung simultaneously, the rung 13 is not able to move in the grooves 9' and 9" of the centre supports 9a and 9b in the direction of the grooves. Further, the guide 21 supports the rung 13 when its end is pressed against the centre supports 9a and 9b. Accordingly, the rung material bends from the centre line of the rung 13 out¬ wards while the groove 22 presses the end of the rung 13. Figure 3b shows a situation when a shoulder 23 is forced at the end of the rung 13. While the material of the rung 13 bends between the centre supports 9a and 9b and the forcing tool 7a from the centre line of the rung 13 outwards, the outwards bending material of the rung 13 is supported on a surface 7' of the forcing tool 7a and on surfaces 9a' and 9b' of the centre supports 9a and 9b, respectively. Accordingly, the outwards bend¬ ing material constitutes the shoulder 23 between the surfaces 7', 9a' and 9b' . Since the material of the rung 13 is supported by the guide 21 from inside the rung, the material of the rung 13 is not able to sink inwards and the shoulder 23 is formed from the material of the rung 13 by forcing outwards. Because the forcing takes place at both ends of the rung 13 simultaneously, the rung 13 is not able to move between the centre supports 9a and 9b in the direction of the grooves 9' and 9". The surface of the rung 13 thus remains unscratched and tidy-looking.

The figures and the description relating to them are only intended to illustrate the inventive idea. As to the details, the apparatus according to the inven¬ tion may vary within the scope of the claims.