US3621936A

US3621936A - Ladder structure

Info

Publication number: US3621936A
Application number: US29507A
Authority: US
Inventors: Alfred E O Andreassen
Original assignee: Chamberlain Manufacturing Corp
Current assignee: Chamberlain Group Inc
Priority date: 1970-04-17
Filing date: 1970-04-17
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23
Also published as: CA923092A

Abstract

Ladder structure for incorporation in metallic ladders of various types including stepladders and extension ladders among others, staging, bus ducts, etc., and embodying side rail structure, step or rung structure, and connecting means to join the rungs to the side rails.

Description

United States Patent lnventor Alfred E. O. Andreassen Waterloo, Iowa Appl. No. 29,507 Filed Apr. 17, 1970 Patented Nov. 23, 1971 Assignee Chamberlain Manufacturing Corporation Elmhurst, Ill.

LADDER STRUCTURE 9 Claims, 10 Drawing Figs.

[1.8. CI 182/194, 182/228 Int. Cl. E06c 7/08 Fieldotsearch 182/228,

[56] References Cited UNITED STATES PATENTS 1,045,957 12/1912 Dicks 182/228 2,013,964 9/1935 Knight 285/158 3,354,987 1 H1967 Werner 182/228 3,472,340 [0/1969 Dahlquist 182/207 3,481,026 12/1969 Lindesmith.. 182/228 3,491,853 l/l970 Stillman 182/46 FOREIGN PATENTS 822,698 10/1959 Great Britain 182/228 Primary Examiner- Reinaldo P. Machado Attorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT: Ladder structure for incorporation in metallic ladders of various types including stepladders and extension ladders among others, staging, bus ducts, etc., and embodying side rail structure, step or rung structure, and connecting means tojoin the rungs to the side rails.

SUMMARY OF THE INVENTION In the past, in every instance of which I am aware, metal ladders, especially those made of aluminum, aluminum alloys or equivalently light and ductile metal, have embodied channeled side rails in which the marginal flanges projected outwardly with respect to the ladder rungs or steps. The webs of such channeled side rails connected the inside edges of the flanges. As such, the side rails were subject to bending or distortion where the rungs were connected, and subject as a whole to torsion. Consequently, such ladders frequently became somewhat wobbly when in use. Also, heretofore, the rungs have been attached to the side rail web in some instances by placing a sleeve over the ends of each rung, centering the sleeves within openings in the siderails, and then swagging the sleeves both directions into tight engagement with the web of the side rail and the rung. Consequently, extra care was necessary to properly center the sleeves, and there was danger of bending or otherwise distorting the side rail web. In other instances, portions of a rung at each end thereof were removed leaving integral projections extending, which entered the side rail web through suitable openings and were then riveted to the outside of the web or bent laterally into close proximity with the outside of the web. The cutting away of portions of the rung was an added expensive step in the ladder construction, and there was also danger of distorting the side rail web. In many cases, metal ladders made heretofore were objectionably expensive, especially in view of the high amount of competition in this field. In general, the weakest points in ladders made heretofore were at the joints between the rungs and side rails.

The present invention overcomes the aforesaid disadvantages of the prior art by providing a ladder embodying side rails, each of which may be so shaped that the marginal flanges thereof extend away from the web in opposite directions, and the web is so shaped as to provide deeper engagement and interlocking with an extension ladder section. Also, the shear center of the web is disposed in the exact center of the entire rail extending between the flanges at an intermediate point rather than totally to one side of the rail. The rungs are also of a reinforced construction and are engaged with the side rail web in an economical manner that substantially eliminates bending or distortion of the web in normal use. As a consequence, the resultant ladder is extremely rigid, effectively resists torsion, provides better and positive engagement with an extension section, has extremely little tendency to side sway when in use, and is economically manufactured.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary side view of a metal ladder embodying the principles of the instant invention;

FIG. 2 is a fragmentary front view of the ladder;

FIG. 3 is an enlarged fragmentary sectional view taken substantially as indicated by the line IlI-III of FIG. 1, looking in the direction of the arrows;

FIG. 4 is an enlarged fragmentary sectional view taken substantially as indicated by the line IV-IV of FIG. 1;

FIG. 5 is a fragmentary sectional view taken substantially as indicated by the line V-V of FIG. 4;

FIG. 6 is a fragmentary vertical sectional view taken substantially as indicated by the line Vl-VI of FIG. 2 illustrating the inside appearance of the connection between the rung and side rail;

FIG. 7 is a perspective view of the end of an extruded piece from which a rung end cap is made;

FIG. 8 is an enlarged inside view of the finished end cap;

FIG. 9 is a vertical sectional view of the end cap taken substantially as indicated by the line IXIX of FIG. 8; and

FIG. 10 is an enlarged vertical sectional view through the rung or step of the ladder taken substantially as indicated by the line XX ofFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Metal ladders and related structures are made with various shapes of rungs and side rails, and such various shapes may be used in the instant invention, depending upon the size and type of structure made and specifications furnished by the customer. The rungs may be round, rectangular, inverted channels, or D-shaped, among other shapes. The side rails may be in the form of I-beams, channels, modified I-beams, modified channels, offset 2, sigma in cross section, among other shapes. By way of example, therefore, and not by way of limitation, the invention is herein illustrated and described with a rung or step that is substantially rectangular in cross section and with side rails of the shape of a modified Z in cross section. Both the rungs and side rails of the ladder may be extrusions of aluminum or equivalently ductile metal or alloy.

The instant ladder is made up of a pair of confronting side rails, generally indicated by numerals l and 2, a series of rungs or steps generally indicated by numeral 3, and a series of end caps collars generally indicated by numeral 4, there being two end caps for each rung.

The side rails l and 2 are identical pieces of extrusion, but one is turned end for end with respect to the other to provide the proper left and right-hand confrontation. In the illustrated embodiment each side rail has a modified Z-shape in cross section, and comprises a web 5 having marginal or

side edge flanges

6 and 7 extending in opposite directions away from the web. On one side, the web turns inwardly as at 8 to join with the flange 6, while at the opposite side the web turns outwardly as at 9 (FIG. 3) to join with the flange 7. With this arrangement, the flange 7 projects inwardly beyond the flange 6, and the flange 6 projects outwardly beyond the flange 7. Each

flange

6 and 7 has an inwardly turned lip 10 on its free edge extending lengthwise of the flange opposite a groove I l at the junction between the flange and web. The web is further strengthened with two or more longitudinally extending ribs l212 in the central portion of the web.

This shaping and structure of the side rail provides a side rail with a strong web extending intermediately between the flanges of the side rail thereby placing the shear point at the exact center of the rail. The rail is therefore highly resistant to torsion and the flange construction is such as to provide a deeper and interlocking engagement with an extension ladder section.

With reference to FIG. 10, it will be seen that each rung 3 has a general cross-sectional shape of a rectangle with rounded comers. Centrally thereof the rung is preferably provided with an interior crossbar 13, which can be integral with the rung. The crossbar extends substantially perpendicularly to the upper and lower rung surfaces 14-14 and materially strengthens the rung. The surfaces 14-14 are provided with spaced ribs 15 extending lengthwise of the rung and which further strengthen the rung as well as provide a suitable tread surface for contact by the foot of the user regardless of which side of the rung is uppermost. From the disclosure in FIG. 10 particularly, it will be seen that the rung is slightly wider at the rib 13 or centrally thereof than at the front and rear edges of the rung. Thus, the tread faces l4l4 are slightly concave interiorly as indicated at 16, and naturally slightly convex exteriorly, the ribs 15 being graduated in height to compensate for the convex outer face and maintain a level tread surface regardless of which side of the rung is uppermost. The external convexity and rounded corners of the rung transfers the stress of the load around the rung in the manner of an arch support for a bridge or viaduct, rather than have the load concentrated in a small area. It will be noted that the rung 3 is an exceedingly strong rung and will not sag under the weight of a very heavy user, and has a high strength-to-weight ratio that permits economies in design to meet specified performance standards.

With reference now to FIGS. 7, 8 and 9 it will be seen that the cap 4 for each end of the rung is formed from an initially tubular piece of stock 17, FIG. 7, having the same general shape as the rung, and sized for intimate telescopic engagement over the end of the rung. This piece of stock 17 is then compressed into a tight annular fold to provide a flange 18 which is made abnormally or extra wide, as indicated at 19, along the longer sides of the tube 17, corresponding to the top and bottom faces l414 of the rung. Forming the flange 18 with the extra width as indicated at 19 by folding the tubular piece of stock 17, work hardens the material thereby materially increasing the rigidity of the flange. While the width of the flange can be varied in accord with available space on the web of the side rail, it is preferable that the wide part 19 of the flange is at least five times the thickness of the material in the stock piece 17. In the illustrated showing with a rung generally rectangular in cross section, the wide portions of the flange are above and below the rung, the available space not permitting equal width at the sides ofthe rung. On the other hand, if a round rung were utilized and the side rail web was of the same width, the flange could be made extra wide entirely around the rung, The open end of the tubular member 17 adjacent the flange 18 is turned or flanged inwardly as indicated at 20 to form a seat for the end ofa rung. The remainder ofthe tube 17 remains as it was originally until after the cap has been placed over a rung end.

In assembling the ladder, a cap is inserted through a suitable aperture in the web of the side rail, and as seen in FIGS. 1 and 6 the aperture is on an angle to the median line of the side rail so that when the side rail is angled properly against a support, the upper face of each rung will be parallel to the floor or the ground, thereby providing a level step. The cap is positioned so that the flange 18 is against the outer face of the side rail web, while the tubular portion on the other side of the flange 18 from the seat 20 extends through the aperture. Then the end of a rung is inserted into the cap until the rung end contacts the cap seat, as seen in FIGS. 4 and 5. Thereafter, the portion of the cap on the inside of the web is upset or swagged to provide a flange 21 on the inside of the web, the web being pinched tightly between the

flanges

18 and 21 and the rung is firmly bonded to the side rail. During the upsetting operation, backup means in the form of a tapered plug hold the cap in position with the flange l8 tightly against the outer face of the web. It will be noted that the inside and outside flanges extend the full width of the web between the

bends

8 and 9 adjacent the side rail flanges. The extra wide parts 19 by the flange 18, aided by the flange 21 makes an extremely rigid structure preventing the side rail web from bending which also materially adds to the stability of the ladder by greatly resisting torsional bending and swaying.

When the upsetting or swagging operation is perfonned on the cap, the rung is automatically indented or bowed inwardly beneath the flange 21, as indicated at 22. It will be noted that this indentation occurs on each side of the center bar of the rung but not in the vicinity of the center bar. Without the center bar in the rung, the indentation would be entirely around the rung and a weaker joint between the rung and web of the side rail would result.

Also, during the swagging operation, the tapered backup plug is forced a little way into the outer end of the rung thereby flaring the rung outwardly along with the adjacent part of the end cap, as indicated at 23 in FIGS. 4 and 5. At the same time the plug in effect irons the flange seat intimately over the end of the rung and into tight engagement therewith. The flare 23 coupled with the indentation 22 securely locks the end of the rung to the side rail. The joint formed as above described between the end of the rung and the side rail is an exceedingly strong and rigid joint. The strength of the joint is further enhanced by the fact that the end of the rung extends through the hole in the web of the side rail approximately onehalfinch in locked engagement with the end cap, a materially greater distance than is the case with ladders as made heretofore.

The assembly ofthe ladder is simple, and the preforming of the rung cap 4, leaving only the portion inside the side rail to be swagged after the rung end is inserted in the cap, hastens the assembly operation and eliminates the need for careful adjustments of the cap relatively to the web of the side rail. The resultant ladder is entirely stable, strong, and long lived, besides being capable ofsupporting a heavy load.

I claim as my invention:

1. A metallic ladder structure including a pair of confronting side rails each having a web and side edge flanges, and spaced hollow rungs secured to said side rails, wherein the improvement comprises a preformed tubular cap extending through an aperture in the respective side rail web and telescopically engaged over each end portion of each rung, an integral flange on said cap spaced inwardly from the outer end thereof for engaging the outer face of the web,

an annular flange on the outer end of said cap extending toward the axis of the cap and forming a seat for the end of the rung,

the inner portion of each cap being swagged into a flange engaging the inner face ofthe web,

the end of each said rung projecting through the web being outwardly flared along with the surrounding portion of said cap, and

said cap flange being in tight engagement with and turned over and turned inwardly inside the flared end of the rung.

2. The structure ofclaim 1, wherein each said rung includes an integral center bar extending lengthwise of the rung to strengthen the same, and

said rung being indented beneath the inside swagged flange except in the region ofsaid center bar.

3. The structure of claim 1, wherein the cap flange of each cap for engaging the outer face of the web is a reverse fold in the metal ofthe cap and work hardened for added rigidity.

4. The structure of claim 1, wherein said integral flange engaging the outer face of the web is abnormally wide at least above and below the end portion of the rung to bear against a relatively wide area of the web and prevent bending of the web.

5. The structure of claim 1, wherein said integral flange engaging the outer face of the web is approximately five times the thickness of the metal of the cap at least above and below the end portion of the rung.

6, The structure of claim 1, wherein the end portion of the rung within the end cap extends approximately one-half inch beyond the outer face of the side rail web.

7. The structure ofclaim I, wherein each prises an extruded tubular member, and

an integral center bar extruded along with said member and extending lengthwise of said member to strengthen the same by providing a solid uniform structure.

8. In a metallic ladder,

a pair of confronting side rails each of a modified Z-shape and comprising a web and side edge flanges,

said flanges extending at right angles to and in opposite directions from said web, and a plurality of rungs extending secured to the webs thereof,

said web having the margins thereofturned obliquely in opposite directions to connect with said flanges to place the shear point at the center of the rail.

9. A preformed ladder rung cap having an outer and an inner end, comprising a tubular element sized and shaped for telescopic reception ofthe end portion ofa ladder rung,

an integral flange on said element for contact with the outer face of a ladder rail web and ofa width of approximately ofsaid rungs combetween said side rails and five times the thickness of the metal of said cap at least above and below a received rung end portion,

an inwardly turned peripheral flange at the outer end of said cap to act as a seat for the end of a rung, and

said cap being of sufficiently ductile metal for the inner por- 5 tion thereof to be swagged against the inside face of the ladder rail web.

Claims

1. A metallic ladder structure including a pair of confronting side rails each having a web and side edge flanges, and spaced hollow rungs secured to said side rails, wherein the improvement comprises a preformed tubular cap extending through an aperture in the respective side rail web and telescopically engaged over each end portion of each rung, an integral flange on said cap spaced inwardly from the outer end thereof for engaging the outer face of the web, an annular flange on the outer end of said cap extending toward the axis of the cap and forming a seat for the end of the rung, the inner portion of each cap being swagged into a flange engaging the inner face of the web, the end of each said rung projecting through the web being outwardly flared along with the surrounding portion of said cap, and said cap flange being in tight engagement with and turned over and turned inwardly inside the flared end of the rung.

2. The structure of claim 1, wherein each said rung includes an integral center bar extending lengthwise of the rung to strengthen the same, and said rung being indented beneath the inside swagged flange except in the region of said center bar.

3. The structure of claim 1, wherein the cap flange of each cap for engaging the outer face of the web is a reverse fold in the metal of the cap and work hardened for added rigidity.

6. The structure of claim 1, wherein the end portion of the rung within the end cap extends approximately one-half inch beyond the outer face of the side rail web.

7. The structure of claim 1, wherein each of said rungs comprises an extruded tubular member, and an integral center bar extruded along with said member and extending lengthwise of said member to strengthen the same by providing a solid uniform structure.

8. In a metallic ladder, a pair of confronting side rails each of a modified Z-shape and comprising a web and side edge flanges, said flanges extending at right angles to and in opposite directions from said web, and a plurality of rungs extending between said side rails and secured to the webs thereof, said web having the margins thereof turned obliquely in opposite directions to connect with said flanges to place the shear point at the center of the rail.

9. A preformed ladder rung cap having an outer and an inner end, comprising a tubular element sized and shaped for telescopic reception of the end portion of a ladder rung, an integral flange on said element for contact with the outer face of a ladder rail web and of a width of approximately five times the thickness of the metal of said cap at least above and below a received rung end portion, an inwardly turned peripheral flange at the outer end of said cap to act as a seat for the end of a rung, and said cap being of sufficiently ductile metal for the inner portion thereof to be swagged against the inside face of the ladder rail web.