METHOD OF PRODUCING A LADDER

Abstract

 The present invention relates to a method of manufacturing a ladder comprising the steps of cutting away defined sections (12, 16) in a plane plate (10) of metal to form longitudinally extending sections (14) and transversally extending sections (18) between the longitudinally extending sections, forming the transversally extending sections (18) to generally tubular rungs; and forming the longitudinally extending sections (14) to profiled side profiles.

Description

TECHNICAL AREA

[0001] The present application relates to a method for producing a ladder in an effective way, providing a sturdy ladder.

BACKGROUND OF INVENTION

[0002] Ladders have many uses and in particular ladders are used on roof instalments in order to access certain areas and elements placed on roofs such as ventilation units and chimneys. In this regard, these types of ladders are also used for securing points for personal fall protection. Thus, such a ladder must be properly anchored to the roof or components thereof as well as being sturdy enough to withstand forces from both climbing personnel as well as if someone slips and is prevented from falling off the roof by the personal fall protection.

[0003] Regarding manufacturing of ladders, there is always a strive to reach as few production steps and yet provide a sturdy and safe product. One example is disclosed in the document WO 2006/011843. It describes a method of producing a ladder from a one piece of metal-plate material. Here a workpiece is cut from a metal plate. The method comprises steps of deep-drawing of portions to form the rungs to trough-shape together with perforation and press-up for forming friction-increasing elements. A subsequent step is then to bend, for example by rolling, the side elements to profile shape. Then the ladder is preferably corrosion treated in order to withstand the environment on a roof. The rungs are preferably provided with areas with different inclination so that the same ladder may be used on roofs with different inclination by orienting the ladder in one or an opposite direction. The treads work well in most instances but for heavy loads, the deep-drawing into rungs may not provide enough sturdiness.

[0004] Another solution is disclosed in US 1,196,667 with a method of forming a ladder from a sheet metal piece in two steps. The upper die of the second step is arranged as a large cavity that as such does not form the rungs. Instead two formers are placed in the cavity that are pivotally mounted. The inner ends of the followers are then pressed towards each other such that a rung is formed. Moreover, the upper die is arranged with a projection that engages the metal and bends the ends or edges inwards. The second die thus provides a rather complicated solution with moving parts that might be prone to wear and malfunction during extended use. Thus, there is a constant need for improvement in the manufacture of ladders from sheet metal.

BRIEF DESCRIPTION OF INVENTION

[0005] The aim of the invention is to provide an improved method for producing a ladder. The aim is solved by a method characterised by the features of the independent patent claim. Preferable embodiments form the subject of the dependent patent claims.

[0006] According to one aspect of the invention, it comprises a method of manufacturing a ladder comprising the steps of cutting away defined sections in a plane plate of metal to form longitudinally extending sections and transversally extending sections between the longitudinally extending sections. Thereafter, the method comprises forming the transversally extending sections to generally tubular rungs and forming the longitudinally extending sections to profiled side profiles.

[0007] With such a method, a very sturdy and stable ladder is produced from a single piece of material. No assembly is thus required and no welds, screws or rivets are necessary.

[0008] Preferably, the edges of the transversally extending sections are substantially in contact with each other after forming to rungs. Also, the formed rungs preferably have a generally circular cross-section. This provides sturdy rungs that can withstand high loads without the use of joining means such as welds.

[0009] According to one aspect, the method may comprise the sub-steps of pressing the transversally extending sections in a first die, forming a generally U-shape in cross-section, and placing the lower part of the U-shape in a lower die section of a second die and pressing on the upper part of the U-shape with an upper die section of the second die to form the tubular rungs. Thus, the rungs of the ladder according to the method may be formed in two steps in order to obtain the tubular cross-section.

[0010] In this regard, the first die may comprise a lower die section and an upper die section, where the lower and upper die sections may have complementary shape in cross-section. In particular, the lower die section of the second die may have a shape corresponding to the shape of the lower die section of the first die and the upper die section of the second die may have a shape corresponding to the lower die section of the second die but with an opposite orientation such that the two die halves when put together form a circular cross-section and a tubular cavity.

[0011] Moreover, the side profiles may be formed to generally rectangular C-shape in cross-section. This shape has several advantages. The shape provides a sturdiness and strength in directions generally transversal to the longitudinal direction of the ladder, preventing sagging of the ladder at midpoint if the ladder is mounted for instance on an inclined roof resting on support structures at each end if a person is climbing on the ladder. The shape is also fairly easy to produce by folding the longitudinally extending sections three times, either simultaneously or in subsequent folding steps.

[0012] Further, the method may comprise the step of providing friction enhancing elements in the transversally extending sections and the friction enhancing elements may comprise protrusions formed during the cutting step. These friction enhancing elements will reduce the risk of a person slipping off a rung when climbing or descending the ladder.

[0013] Further, the ladder may comprise the step of providing a number of attachment holes along the extension of the longitudinally extending sections. These attachment holes may be used for different purposes such as attaching treads or steps to the ladder in order to have a larger stepping area than just the rungs. Further, safety equipment such as rails for the anchoring of personal fall protections may be attached to the ladder by the holes. Further, the ladder may comprise attachment holes in the transversally extending sections. These holes may be used for attaching treads or steps to the rungs. In order to provide a weather-resistant ladder, surfaces of the manufactured ladder may be treated with anti-corrosion material.

[0014] These and other advantages and features of the present invention will become apparent from the following detailed description of the invention and from the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0015] In the following detailed description of the invention, reference will be made to the accompanying drawings, of which

Fig. 1 shows a perspective view of a plane sheet of metal with different stages of forming rungs of a ladder,

Figs. 2a-d show the steps of forming the rungs of the ladder,

Fig. 3 shows an end view of a manufactured ladder and the steps of forming profiled side sections, and

Fig. 4 shows a perspective view of a ladder manufactured according to the method of the invention, and

Fig. 5 shows a step that may be attached to the ladder of Fig. 4.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The method for producing a ladder according to the present application comprises starting with a plane plate of metal 10, preferably steel. The plate may be discrete items or be a reel of sheet metal that is cut into the length of the ladder to be produced. The plate 10 is placed in a stamp and certain areas are cut away. If a reel of sheet metal is used, the stamp may cut the sheet to appropriate length of the ladder. As seen in Fig. 1, side areas 12 are first cut away adjacent side sections 14 that are to be the side profiles. Then a square area 16 is cut away leaving transversal areas 18 that are to be the rungs. Further, a row of holes 20 may be stamped in the side profile sections 14 and friction enhancing elements 22 like corrugations or protrusions are made in the rungs sections 18. The rungs sections 18 may also be provided with a number of holes 24.

[0017] The cut plate is then placed in a forming machine wherein the outer sides 18a of the rungs sections are first bent upwards with a bottom curvature, forming a generally U-shaped profile as seen in Fig. 1. The forming machine may in this regard have a lower die section 26, Fig. 2, having a general U-shape open upwards as seen in cross-section as well as an upper die section 28 with a shape corresponding to the lower die section as seen in Fig. 2a. As an alternative, the lower die may be made of sections along its length that are movable in order to support the plate section of the rung when forming the U-shape.

[0018] The U-shaped rungs section 18 is then placed in a second die where it is bent so that the opposite edges 18b meet each other to form a tubular and generally circular rung as seen in a cross-sectional view. For doing this, the forming machine may have a lower die section 30 in which the formed rung section is placed and an upper die section 32 having a general U-shape open downwards as seen in a cross-sectional view, Fig. 2c. When the upper die section 32 contacts the upper edges 18b of the upper die section 32, Fig. 2c, the upper sections are bent inwards until the edges 18b are in contact with each other, Fig. 2d. as seen in Fig. 2d the two die halves form a generally circular cross-section and a tubular cavity when brought together.

[0019] The next step is to form the side profiles 14. They may be formed by bending, such as by rolling or by folding, to a generally rectangular C-shape in cross-section as seen in Figs. 3 and 4, where the folding is performed in three steps. The holes 20 along the side profiles may then be arranged generally in the center of the C. As seen in Fig. 3, the rungs and the side profiles may preferably be formed so that the rungs are positioned inside and between the side profiles, providing a better force distribution.

[0020] Even if the manufacture of the ladder is described as being done by several machines, a single press may be used wherein the cutting is performed in a first section, the bending of the rungs section to a U-shape is made in a subsequent section and the forming of the U-shaped rungs section to tubular rungs in yet a subsequent section. The plate of sheet metal is moved in steps through the subsequent sections until all the rungs have been formed. Further, lubrication may be used in some of the steps in order to facilitate the forming of the rungs and the side profiles as desired.

[0021] The design makes the ladder very sturdy with the tubular rungs and the shaped side profiles. The finished ladder is then treated by anti-corrosion layers such as zinc and paint. Further, the ladder may be provided with separate treads 40, Fig. 5, that may be secured with bolts going through the holes 20 in the side profiles 14 and possibly through the holes 24 of the rungs 18.

[0022] It is to be understood that the embodiment described above and shown in the drawings is to be regarded only as a non-limiting example of the invention and that it may be modified in many ways within the scope of the patent claims.

Claims

1. Method of manufacturing a ladder comprising the steps of:

- cutting away defined sections (12, 16) in a plane plate (10) of metal to form longitudinally extending sections (14) and transversally extending sections (18) between the longitudinally extending sections;

- forming the transversally extending sections (18) to generally tubular rungs by;

- pressing the transversally extending sections in a first die (26, 28), forming a generally U-shape in cross-section, wherein the first die comprises a lower die section (26) and an upper die section (28), where the lower and upper die sections have complementary shape in cross-section;

- placing the lower part of the U-shape in a lower die section (30) of a second die and pressing on the upper part of the U-shape with an upper die section (32) of the second die; wherein the lower die section (30) of the second die has a shape corresponding to the shape of the lower die section (26) of the first die and wherein the upper die section (32) of the second die has a shape corresponding to the lower die section (30) of the second die but with an opposite orientation to form tubular rungs, wherein the edges of the transversally extending sections are brought in contact with each other;
and

- forming the longitudinally extending sections (14) to profiled side profiles.

2. Method according to claim 1, wherein the formed rungs have a generally circular cross-section.

3. Method according to claim 1, wherein the die sections (30, 32) of the second die have shapes forming a generally circular cross-section when brought together, forming a tubular cavity.

4. Method according to any of the preceding claims, wherein the side profiles (14) are formed to generally rectangular C-shape in cross-section.

5. Method according to any of the preceding claims further comprising the step of providing friction enhancing elements (22) in the transversally extending sections.

6. Method according to claim 5, wherein the friction enhancing elements comprise protrusions formed during the cutting step.

7. Method according to any of the preceding claims, further comprising the step of providing a number of attachment holes (20) along the extension of the longitudinally extending sections (14).

8. Method according to any of the preceding claims, further comprising providing attachment holes (24) in the transversally extending sections (18).

9. Method according to any of the preceding claims, further comprising the step of treating surfaces of the manufactured ladder with anti-corrosion material.

10. Ladder manufactured according to any of the claims 1 to 9.

11. Ladder according to claim 10, further comprising treads (40) attachable to said rungs.

12. Ladder according to claim 11 when dependent on claims 7 or 8, wherein said treads are attached to said rungs with bolts through the attachment holes (24) of the rungs and/or the attachment holes (20) of the side profiles.

Drawing