GB1581480A

GB1581480A - Ladder construction

Info

Publication number: GB1581480A
Application number: GB20990/77A
Authority: GB
Original assignee: Raufoss Ammunisjonsfabrikker AS
Current assignee: Raufoss Ammunisjonsfabrikker AS
Priority date: 1976-05-18
Filing date: 1977-05-18
Publication date: 1980-12-17
Also published as: DK144686B; NO761689L; NO138541C; DE2722597C2; NO138541B; DK219377A; SE7705748L; DK144686C; DE2722597A1

Description

(54) LADDER CONSTRUCTION (71) We, A/S RAUFOSS AMbtUNISJONS- FABRIKKER, a Norwegian Company, of P. O.

Box','831 Raufoss, Norway, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be par ti. ularly described in and by the following statement :- This invention relates to a ladder construction and is particularly related to joints between the rungs and the side rails of metal ladders, particularly, but not exclusively made of aluminium and its alloys.

1nl P i n a rP X. t ; n s. interposed therebetween, wherein at least one annular groove is provided in the outer surface of each rung end prior to the positioning in the parts together and the sleeve is positioned to cover said groove or grooves, whereafter the sleeve is pressed axially so that sleeve material is caused to flow into said groove or grooves during the pressing of the sleeve.

The provision of one or more grooves adjacent each rung end has been shown to give a substantially increased stability. The metal pressed into a preferably sharp-edged groove

PATENTS ACT 1949 SPECIFICATION NO. 1581480 The following amendments were allowed under Section 29 on 19 March 1987.

Page 1 Delete Lines 34 to 37 Insert Stresses may occur during Page 1 Line 41 Delete The known joints tend to grad Page 1 Delete Line 42 THE PATENT OFFICE 13 April 1987 Tests have shown that this known joint may be deficient. The joint has shown to be insufficiently durable when the ladder is exposed to certain stresses. Such stresses may occur during normal use of the ladder, due to the loading of the rungs and impacts against the ends of the side rails when placing the ladder on a supporting base. The known joints tend to gradually lose their rigidity. it is an object ot the present invention to provide a ladder joint that provides a durable stability and an improvement of the previously known joint.

The present invention consists in a method of forming a joint between ladder rungs and ladder side rails which comprises providing a hole in each side rail for each rung end and positioning a rung end in a hole with a sleeve @@@@@@ @@@@@ @@ @@@@ @@@ what is necessary to achieve the required bending stiffness of the rung.

Where the rung has a polygonal outer cross-section, the depth of the groove or grooves may be such that the groove or grooves is/are principally cut in the apex areas of the rung, substantially without protruding into the rung material in the areas between the apex areas.

In an embodiment of the invention employing a rung having a polygonal outer crosssection, a sleeve of polygonal cross-section is also used, the number of projecting edges corresponding to the number of ribs on the rung, whereby the ribs are located immediately inside the edges of the sleeve.

The invention will now be further described by way of example, with reference to the accompanying drawings, showing embodiments (54) LADDER CONSTRUCTION (71) We, A/S RAUFOSS AMMUNISJONS- I ABRnCKER, a Norwegian Company, of P. O.

Box'2831 Raufoss, Norway, do hereby declare the invention for which we pray that a patent mav he granted to us and the method by which it is to be performed to be par timlarly described in and by the following statement : This invention relates to a ladder construction and is particularly related to joints between the rungs and the side rails of metal ladders, particularly, but not exclusively made of aluminium and its alloys.

The invention pertains to such joints wherein the ends of the rungs project through holes in the side walls of the rails, the rungs being joined to the rails in a perpendicular relationship.

Various types of rung and side rail assemblies are known, one example of which is disclosed in U. S. Patent No. 3,039,186.

According to the above patent a sleeve is provided between the rung end and the hole in the side rail. By use of a pressing tool the sleeve is pressed axially, thereby causing the metal in the sleeve to flow radially outwardly into engagement with the edge of the hole and sim ultaneously to flow radially inwardly to be pressed against the rung and thereby to form an annular latching valley in the rung end, the rung itself being a hollow tube. This deformation and the friction between the sleeve and the rung provides a joint therebetween.

Tests have shown that this known joint may be deficient. The joint has shown to be insuf ficiently durable when the ladder is exposed to certain stresses. Such stresses may occur during normal use of the ladder, due to the loading of the rungs and impacts against the ends of the side rails when placing the ladder on a supporting base. The known joints tend to gradually lose their rigidity.

It is an object ot the present invention to provide a ladder joint that provides a durable stability and an improvement of the previously known joint.

The present invention consists in a method of forming a joint between ladder rungs and ladder side rails which cornprises providing a hole in each side rail for each rung end and positioning a rung end in a hole with a sleeve interposed therebetween, wherein at least one annular groove is provided in the outer surface of each rung end prior to the positioning in the parts together and the sleeve is positioned to cover said groove or grooves, whereafter the sleeve is pressed axially so that sleeve material is caused to flow into said groove or grooves during the pressing of the sleeve.

The provision of one or more grooves adjacent each rung end has been shown to give a substantially increased stability. The metal pressed into a preferably sharp-edged groove will provide a joint of a different character htan previously known joints. The essential difference lies in the connection between the sleeve and the rung. A considerable deformation of the sleeve material will be necessary to loosen this connection in a joint according to the invention, while the previously known type of joint is mainly based on friction.

In a preferred embodiment of the invention the annular groove or grooves are provided substantially only in protuberances or ribs extending longitudinally of and on the outer surface of the rungs. This is advantageous compared to a more simple solution consisting of using a thicker walled rung of circular crosssection and forming one or more grooves in the wall. This requires a rather thick wall to prevent an unaceeptabie weakening of the rung due to the groove or grooves, and the material consumption would be more than what is necessary to achieve the required bending stiffness of the rung.

The invention will now be further described by way of example, with reference to the accompanying drawings, showing embodiments of the invention, and in which: Figure I is a cross-sectional view through a ladder side rail taken through the middle of a rung, Figure 2 shows a preferred embodiments of a rung profile to be used, and Figure 3 shows another embodiment of the rung and an associated sleeve.

Figure 1 shows a rung I joined to the ladder side rail 2 by means of an intermediate sleeve 3.

The sleeve 3 is located between the end of the rung I and the edge of a hole 4 in the side rail and has been deformed by pressing, mainly axially of the sleeve. Adjacent the end of the rung 1 are provided circumferential annular grooves 5, and by pressing of the sleeve 3, seleve material has flowed into the grooves 5.

In Figure 2 is shown an end view of a rung I provided with longitudinal ribs 6 spaced around the periphery. One or more circumferential annular grooves are provided adjacent the end of the rung, the grooves having a depth substantially corresponding to the height of the ribs.

Thus, the provision of the grooves causes less weakening of the rung compared to grooves formed in a rung of even wall thickness. Nevertheless, the sleeve 3 will be sufficiently anchored in the grooves which are cut in the ribs 6 of the rung.

Figure 3 shows an embodiment wherein the rung I has a polygonal outer cross section, and wherein the groove or grooves 5 are cut in the apex areas or protuberances 7 of the rung, without protruding into the rung material in the areas 8 between the apex areas. There is also shown a polygonal sleeve 3 surrounding the rung 1, some of the sleeve material having flowed under pressure into the groove or grooves 5 in the area of the sleeve apices 9.

Claims

WHAT WE CLAIM IS :- I. A method of forming a joint between ladder rungs and ladder side rails which comprises providing a hole in each side rail for each rung end and positioning a rung end in a hole with a sleeve interposed therebetween, wherein at least one annular groove is provided in the outer surface of each rung end prior to the positioning of the parts together and the sleeve is positioned to cover said groove or grooves, whereafter the sleeve is pressed axially so that sleeve material is caused to flow into said groove or grooves during the pressing of the sleeve.
2. A method as claimed in claim 1, wherein the rungs are formed with longitudinal ribs and the groove or grooves are provided substantially only in the ribs.
3. A method as claimed in claims I or 2, wherein the rung has a polygonal outer crosssection and the groove or grooves are cut in the apex areas of the rung substantially without protruding into the rung material in the between the apex areas.
4. A method of forming a joint as claimed in claim I and substantially as hereinbefore described with reference to Figure I and 2 or Figure 3 of the accompanying drawings.
5. A ladder construction produced by the method according to any of the preceding claims.