US3232378A

US3232378A - Ladder rungs

Info

Publication number: US3232378A
Application number: US333259A
Authority: US
Inventors: Clayton E Larson
Original assignee: White Metal Rolling and Stamping Corp
Current assignee: White Metal Rolling and Stamping Corp
Priority date: 1963-12-19
Filing date: 1963-12-19
Publication date: 1966-02-01
Anticipated expiration: 1983-02-01

Description

Feb, i, 1966 c. E. LARSON 3,232,373

LADDER RUNG'S Original Filed Aug. 11, 1961 2 Sheets-Sheet l ATTORNEYS C. E. LARSON LADDER RUNGS Fen l, 1966 2 Sheets-Sheet 2 Original Filed Aug. 11, 1961 INVENTOR CLAYTON E. LARSON ATTORNEYS United States Patent 3,232,378 LADDER RUNGS Clayton E. Larson, Brooklyn, N.Y., assignor to White Metal Rolling & Stamping Corporation, a corporation of New York Continuation of application Ser. No, 130,805, Aug. 11, 1961. This application Dec. 19, 1963, Ser. No. 333,259

2 Claims. (Cl. 182-194) This application is a continuation of my copending application, Serial Number 130,805 filed August 11, 1961 now abandoned.

This invention relates to ladder rungs and more particularly, it concerns a new and improved ladder rung-tosiderail connection as well as a unique method of assembling ladder rungs and siderails having particular utility in ladders fabricated from light metal such as aluminum or alloys thereof.

Because of the function served by ladder, designers and manufactures thereof have long recognized the need for a ladder construction which is sufficiently strong to carry the weight of a person without danger of the ladder collapsing and thus causing the person to fall from a considerable height as well as a ladder construction which is light in weight to facilitate movement of the ladder from place to place as required. As a result, much use has been made by the ladder industry of light metals such as aluminum, magnesium or alloys of one or both of these metals since they can be fabricated to satisfy both the requirements of strength and lightness. Yet, because of the difiiculties encountered in working with such metals, either relatively heavy sections have been employed in the past, or considerable expenses have been incurred in order to make possible the fabrication or joining of the component parts of the ladder. One of the problems encountered heretofore which is especially troublesome with the use of light metals in the manufacture of ladders is that of providing an adequtae non-skid or traction surface on the ladder rung and at the same time keeping the weight of the rung to a minimum without substantially increasing the costs necessary to effect the rungto-siderail connection. For example, in the use of the well known technique of joining round, tubular-rungs to the ladder siderails by hydraulic expansion or spinning of the rung ends after they have been inserted through an aperture in the siderails, it has been found that the height of flutes or serrations on the exterior of the rungs for traction or non-skid purposes must be kept to within a maximum of 0.010 and'a flat top provided on each flute, so that undesirable rupture of the rung end during the expansion or spinning of process is prevented. To provide a desirable non-skid surface, however, the serrations or flutes for reasonable effectiveness should be at least 0.020 high and be provided at their tops with sharp edges. In order, therefore, to achieve the desirable nonskid surface on the rung while at the same time assure an effective connection of the rung to the siderail by using the technique aforementioned, the ends of the rungs necessarily must be specially formed thereby increasing the overall cost of the ladder.

Further, from the standpoint of economy in ladder manufacture, it has been found desirable to attach a tubular rung to a ladder siderail by forming extending tabs at each end of the rung which tabs extend through corresponding apertures in the siderails and are then bent over to secure the connection. The use of bent over tabs to secure a ladder rung to siderail connection is demonstrated to be quite old by the disclosure of US. Patent No. 901,775, of 1908. While the use of such a joint with steel or iron alloys involves no serious difiiculties, a wholly different situation results when light metals such "ice as aluminum, magnesium or alloys thereof are used. The difficulty referred to is primarily due to the relative brittleness of light metal alloys when a sharp bending thereof is attempted to the extent that there is a tendency for such tabs to break off thereby detracting from the use of this technique in the fabrication of light metal ladders. This problem is rendered more acute by the provision of flutes or serrations on the rung exterior largely because of the increased thickness of material required to provide the necessary depth or height of serrations, which thickness makes more difficult the bending over of tabs extending from such a rung due to the increase in stress placed in the outer fibers of such a thickened section.

Accordingly, a principal object of this invention is to provide a new and improved ladder rung and connection thereof to a ladder siderail as well as a unique method for assembling these components to achieve a ladder construction by which the aforementioned problems are effectively and substantially overcome.

Another object of this invention is the provision of a novel ladder rung formed by extrusion of light metals such as aluminum or alloys thereof, having over that portion normally engaged by a persons foot when in use, sharp pointed serrations or flutes on the order of 0.020" to 0.025" in height while at the same time provided with tabs which may be bent over after insertion through apertures in a ladder siderail to secure the rung-to-siderail connection.

A further object of this invention is that of providing a new and improved ladder incorporating a rung of the type referred to and having a rung-to-siderail connection which is resistant to loading stresses imposed on the rung and transmitted to the siderail connection thereof, while at the same time being adapted to an extremely economical and eflicient method of assembly.

Another object of this invention is the provision of a ladder having an extruded, light metal rung of semiround cross section and which is formed having an etfective non-skid or traction surface thereon without in any way impairing connection of the rung to the ladder siderail.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since it will become apparent to those skilled in the art from this description, that various changes and modifications can be made without departing from the true spirit and scope of this invention.

in general, the aforementioned objects are accomplished by extruding a tubular length of light metal such as aluminum or alloys thereof, to provide a rung cross-section defining a plurality of peripherally spaced, substantially flat wall portions integrally connected by intermediate wall portions having on the exterior thereof serrations or flutes toprovide the necessary non-skid or traction surface. The intermediate wall portions are cut back at the ends of the rung to leave extending the flat wall portions as siderail connecting tabs. A pair of ladder siderails are provided, each formed having sets of apertures therein which apertures are arranged to correspond with crosssection defined by the connecting tabs or the flat wall portions so that the tabs may be inserted through the apertures and bent over on the outside of the siderails to secure the rung to siderail connection. Preferably, the rungs are attached to the siderails in such a manner that the flat wail portions are positioned at the top, bottom and sides of the rung when the ladder is in a vertical position and further, it is preferred that the tabs extending from .the top and .bottom flat wall portions are bent downwardly on the outside of the siderail to enhance the strength of the connection.

A more complete understanding of the new and improved ladder of this invention as well as its method of assembly will be had by reference to the accompanying drawings in which:

FIG. 1 is a perspective view illustrating one end and the upper portion of the new and improved rung of this invention;

FIG. 2 is an enlarged fragmentary side elevation of the ladder of this invention partially in cross-section and showing the position of the ladder in use;

FIG. 3 is an enlarged fragmentary cross-sectional view taken along lines 33 of FIG. 2;

FIG. 4 is a perspective view of the ladder of this invention showing details of the method of fabrication thereof;

FIG. 5 is an enlarged cross-sectional view taken along the lines 55 of FIG. 4; and

FIG. 6 is a view similar to FIG. 5 taken at a later step in the process.

As shown in the drawings, the ladder of this invention includes a tubular rung of an extruded, light metal alloy generally designated by the numeral 10. Preferably, the metal from which the rung is made is an aluminum alloy of the group known commercially as the 60 Series Aluminum Alloys though it is contemplated that other materials having similar physical characteristics might be used. The rung is formed having peripherally spaced, substantially flat top, bottom and

side wall portions

12, 14, and 16, respectively, extending longitudinally of the rung and integrally interconnected by a plurality of intermediate wall portions 18. The intermediate wall portions 18, preferably, are of generally arcuate cross-section and formed having on the exterior thereof a plurality of longitudinally extending flutes or serrations 20. The serrations 20, as shown, are sharp pointed to assure a good non-skid or traction surface and further, are preferably 0.020" to 0.025" in height. The

fiat wall portions

12, 14, 15 and 16, on the other hand, are devoid of such serrations, though if desired, a plurality of relatively small ribs 22 may be provided on the upper and

lower wall portions

12 and 14 respectively. The ribs 22 are of insuificient height to afford a good non-skid surface and are provided solely to avoid a perfectly smooth surface on the upwardly facing portion of the rung as well as for appearance purposes. The height of the ribs 22, however, is desirably kept at a minimum so as not to increase the thickness of the upper and lower wall portions 14 on which they are formed.

As shown in FIG. 1, the intermediate wall portions 18 at each end of the rung 1d are cut back to leave the

fiat wall portions

12, 14, 15 and 16 extending as

siderail connecting tabs

24, 26, 28 and 30. The connecting tabs thus formed on each end of the rung provide means for effecting the joint between the rung and ladder siderails in the assembly of the ladder of this invention as will be clearly understood from the description which follows below.

Referring now to FIGS. 2 and 3 of the drawings, fragmentary portions of the ladder of this invention are shown including a pair of

siderails

32 and 34, each preferably, though not necessarily, formed having a central web portion 36 and a pair of flange portions 33. In each of the webs are formed sets of apertures 40 at points spaced longitudinally thereof as desired for establishing the proper spacing between rungs, the apertures 40 in each set being arranged to conform with the cross-sectional configuration defined by the connecting

tabs

24, 26, 28 and 30 or by the

flat wall portions

12, 14, 15 and 16.

In the assembly of the ladder, the rungs 10 are first arranged between the

siderails

32 and 34 with the connecting

tabs

24, 26, 28 and 30 extending through the apertures 40. The loosely connected assembly thus established is then fed between rollers which engage the outside surfaces of the siderail webs 36 such that upon the advance of the rollers over the siderails from top to bottom of thereof (as the ladder is ultimately to be used), both the upper and lower connecting

tabs

24 and 26 are bent downwardly over the exterior surface of the siderail webs 36. The

tabs

28 and 30 extending from the

wall portions

15 and 16, on the other hand, are bent outwardly over the siderail web 36 as shown in FIG. 2 preferably by progressive rollers as is well known in the art. Use of progressive rollers for such bending is illustrated in prior US. patents such, .for example, as US. 2,493,415 to Navin and US. 2,825,384 to Goldsmith. As an example of progressive rolling as applied to this invention, and with specific reference to FIGURES 4, 5 and 6 of the drawings, the loosely assembled ladder having the rungs 10 arranged between the

siderails

32 and 34 and the connecting

tabs

24, 26, 28 and 30 extending through the apertures 40 in the siderails, is rolled in th direction of the arrow in FIGURE 4 between oppositely disposed pairs of

rollers

46 and 48. Roller 46 is provided with a central cylindrical surface, tapering off in beveled edges at the radial faces thereof, so that

tabs

24 and 26 are fully bent down on passage under the roller while

tabs

28 and 30 are bent away from each other at an angle dictated by the angle of the roller bevel. In FIGURE 6, the second roller 48 having a fully cylindrical peripheral surface flattens the

tabs

28 and 30 against the

siderails

32 and 34 to complete the connection with the rung 10. It should be obvious that, if it is required that the bending process be more gradual, roller sets comprising three or more step rollers could be used in lieu of the two-step rolling process shown. It will be noted, therefore, that the downward bending of the upper and

lower tabs

24 and 26, as well as the outward bending of the

side tabs

28 and 30, not only enable an extremely economical and simple method of attaching the rungs 10 to the

siderails

32 and 34, but also results in a substantially stronger joint. This result is achieved, as will b seen particularly in FIG. 3 of the drawings, because the

tabs

24 and 26 being bent downwardly over the outside of the siderail web, both operate to effect a maximum resistance to separation of the rung and siderail as might be caused by vertical loads applied to the upper portion of the rung.

In use, the ladder thus assembled will, in the usual fashion, be inclined against the wall of a building or other supporting structure at an angle of the vertical approximating 15. While this angle may vary in different circumstances, it has been found through experience that the aforesaid angle of inclination is desirable both from the standpoint of comfort to one using the ladder and development of maximum strength in the ladder siderails. Since in the assembly of the ladder the upper and

lower tabs

24 and 26 and thus the upper and

lower wall portions

12 and 14 are arranged on the longitudinal center lin of the siderails 32 and 34, the rung also, in use, assumes a canted or inclined position along with the siderail so that the pointed flutes or serrations 20 are presented upwardly to be engaged by the users foot illustrated in phantom lines at 42 in FIG. 2. Because of the positioning and size of the serrations 20, a substantial traction or non-skid surface is atforded the user on those portions of the rung where such a traction surface is essential. However, because of the arrangement of the serrations 20 on the intermediate wall portions between the flat wall portions, the serrations in no way interfere with attachment of the rung to the siderail nor do they sacrifice in any respect the desirable qualities of an extruded rung of continuous crosssection. The difficulties encountered with the use of light metals for ladder rungs of this type, as aforementioned, are that when the rung Wall cross-section is increased sufficiently in thickness to permit a non-skid exterior surface in which serrations are provided in the range of 0.020" to 0.025 in height, bending or otherwise upsetting such a wall portion is for all practical purposes prevented because the increased stresses placed in the Outer fibers of the wall result in rupture thereof and particularly along the lines defined by the bottoms of the serrations. In the present invention, however, the

flat wall portions

12, 14, and 16 may be kept at the maximum thickness permitted for abrupt 90 bending without in any manner weakening the rung since the serrations or flutes required to provide the necessary traction surface are omitted from these portions. Thus, the tabs which form extensions of these wall portions may be bent over in the manner described Without in any manner weakening the metal and thereby afford an extremely strong and eifective manner of attaching the rung to the ladder siderails. Further, it is to be noted that not all types of light metals or alloys thereof can be used in this manner because of the brittle characteristics thereof and tendency to break off when bended. For this reason, it has been found that certain alloys of aluminum are particularly desirable in the formation of rungs of the type to which this invention relates. Specifically, it is preferred that aluminum alloys known as the 60 Series Aluminum Alloys are used though it will be understood that other alloys having the same or similar characteristics may be used.

Thus, it will be seen that by the present invention the aforementioned objectives are fully attained. The construction of the rung 10 as described above not only brings about an extremely strong and safe rung construction but also the method by which it is attached to the ladder siderails enables an eifective and economical assembly of the ladder without in any manner sacrificing the strength and safety thereof. The foregoing description, however, is to be understood as being illustrative only and not limiting since it will now be apparent to those skilled in the art that other modifications and embodiments of the invention may be used without in any way departing from the true spirit and scope thereof as defined by the appended claims:

I claim:

1. A light metal ladder comprising:

a pair of siderails extruded from light metal comprising a flat central web portion and a pair of end flange portions;

a plurality of tubular rungs each extruded from light metal alloy to have;

(a) peripherally spaced, substantially flat top, bottom and side wall portions extending longitudinally of the rung, and

(b) four intermediate arcuate wall portions integrally connected to said flat wall portions, and

(0) four tabs on each end thereof that are straight extensions of said flat wall portions formed by 6 removal of the arcuat wall portions from therebetween to the depth of said tabs;

sets of four slots through the central web portions of said siderails arranged to conform with the cross-sectional configuration of the four tabs of said tubular run-gs, the slots corresponding to the tabs constituting straight extensions of said top and bottom Wall portions of the rungs being disposed in spaced relationship along and perpendicular to the longitudinal centerline of the side rails;

said rungs being spaced substantially equidistant along said siderails and being fixed normal to the siderails with the ends of the arcuate wall portions of the rungs abutting the inner surfaces of the flat central web portions of the siderails and with the rung tabs extending through said siderail slots, the tabs being bent over the outer surfaces of the flat central Web portion of the siderails securing the rung to the siderail, the tabs which constitute straight extensions of the Wall portions of the rungs being bent over onto the outer sunfaces of the siderail web portion, the tabs constituting straight extensions of said top and bottom Wall portions of the rungs, because of their disposition, absorbing the major portion of bending stresses imposed on the rungs.

2. A ladder in accordance with claim 1 wherein at least two of the opposed arcuate wall portions have longitudinal serrations at least 0.020 inch deep formed in the exterior surface thereof.

References Cited by the Examiner UNITED STATES PATENTS 518,767 4/ 1894 Plecker.

901,755 10/1908 Tiepolt 182-194 1,450,961 4/ 1923 Otterbeing 29513 2,113,403 4/ 1938 Harmon 182-228 X 2,857,665 10/1958 Cohen 29513 2,871,556 2/1959 Chisholm 29-513 2,957,543 10/ 1960 Larson 182228 X 3,002,582 10/ 1961 Marcelis 182194 3,016,976 1/1962 Munson 182-194 3,142,356 7/ 1964 Rich 182-194 FOREIGN PATENTS 561,625 10/ 1957 Belgium.

HARRISON R. MOSELEY, Primary Examiner.

REINALDO P. MACHADO, Examiner.

Claims

1. ALIGHT METAL LADDER COMPRISING: A PAIR OF SIDERAILS EXTRUDED FROM THE LIGHT METAL COMPRISING A FLAT CENTRAL WEB PORTION AND A PAIR OF END FLANGE PORTIONS; A PLURALITY OF TUBULAR RUNGS EACH EXTRUDED FROM LIGHT METAL ALLOY TO HAVE; (A) PERIPHERALLY SPACED, SUBSTANTIALLY FLAT TOP, BOTTOM AND SIDE WALL PORTIONS EXTENDING LONGITUDINALLY OF THE RUNG, AND (B) FOUR INTERMEDIATE ARCUATE WALL PORTION INTEGRALLY CONNECTED TO SAID FLAT WALL PORTIONS, AND (C) FOUR TABS ON EACH END THEREOF THAT ARE STRAIGHT EXTENSIONS OF SAID FLAT WALL PORTIONS FORMED BY REMOVAL OF THE ARCUATE WALL PORTIONS FROM THEREBETWEEN TO THE DEPTH OF SAID TABS; SETS OF FOUR SLOTS THROUGH THE CENTRAL WEB PORTION OF SAID SIDERAILS ARRANGED TO CONFORM WITH THE CROSS-SECTIONAL CONFIGURATION OF THE FOUR TABS OF SAID TUBULAR RUNGS, THE SLOTS CORRESPONDING TO THE TABS CONSTITUTING STRAIGHT EXTENSIONS OF SAID TOP AND BOTTOM WALL PORTIONS OF THE RUNGS BEING DISPOSED IN SPACED RELATIONSHIP ALONG AND PERPENDICULAR TO THE LONGITUDINAL CENTERLINE OF THE SIDE RAILS; SAID RUNGS BEING SPACED SUBSTANTIALLY EQUIDISTANT ALONG