US 3283402 A
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Nov. 8, 1966 c. E. LARSON METHODS FOR FABRICATING LIGHTWEIGHT METAL LADDERS Filed Aug. 23, 1963 2 Sheets-Sheet 1 INVENTOR CLAYTON E. LARSON BY I M JM ATTORNEY i C. E. LARSON Nov. 8, 1966 METHODS FOR FABRICATING LIGHTWEIGHT METAL LADDERS Filed Aug. 25, 1963 2 Sheets-Sheet 2 IE-T 5.
S 8 M H r W O N A/ S R I .,|||1.l g m I m L E A United States Patent 3,283,402 METHODS FOR FABRICATING LIGHTWEIGHT METAL LADDERS Clayton E. Larson, Weston, Conn., assignor to White Metal Rolling & Stamping Corporation, Brooklyn, N.Y.,
a corporation of New York Filed Aug. 23, 1963, Ser. No. 304,196 3 Claims. (Cl. 29-512) This invention relates to a method for fabricating a lightweight metal ladder and particularly to a new and improved method for fabricating and joining metallic tubular rungs for such ladders to metal side rails.
A predominant trend in recent years in the construction of ladders has been the utilization of lightweight metal such as magnesium and aluminum as the construction material. Lightweight metal provides obvious benefits since the resulting ladders are easier to carry, maneuver and store due to their light weight. Also, the low cost and ease of fabrication of these metals allow the ladders to be made at a relatively low cost.
As a result of the advances achieved by the use and the popularity of lightweight metal ladders, there is continuing demand for even less expensive and more durable ladders of this type. Ladders, in general, are subjected to rather severe repetitive strains in use and, for reasons of safety and durability, must be extremely resistant to fatigue and/ or loosening of the components under cyclical loading. The ladders must also be rigid and capable of supporting the heavy loads normally imposed upon them.
It is, therefore, an object of this invention to provide new and improved method of fabricating lightweight metal ladders which are rigid, durable and resist loosening of connected parts under the repetitive loadings normal in a ladder structure. Further objects include:
(1) The provision of a new, simple and inexpensive method of fabricating lightweight metal ladders.
(2) The provision of a new and improved method of joining the rungs of a ladder to the side rails in a manner which, while being simple and inexpensive, is light and durable and serves to improve the rigidity of the side rails and the total ladder structure.
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 detatiled description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
These and other objects will be better understood by those skilled in the art by reference to the following detailed description and the accompanying drawings wherein like numbers indicate like parts and wherein:
FIG. 1 is a perspective view (partly broken away) of a ladder embodying the features of this invention;
FIG. 2 is an enlarged sectional view of a portion of the ladder of FIG. 1 taken along the line 2-2;
FIG. 3 is a still further enlarged and exploded sectional view of a portion of the rung and the side rail of a ladder prior to shaping for assembly;
FIG. 4 is a view similar to FIG. 3 after the components of the ladder have been shaped for assembly;
FIG. 5 is a View similar to FIG. 4 after assembly and joining of the components of the ladder;
FIG. 6 is a sectional view of the structure of FIG. 5 taken along the line 66 thereof; and
FIG. 7 is a sectional view of the rung of FIG. 5 taken along the line 7-7 thereof.
This ladder, in essence, provides a new and improved ladder rung and a method for forming the rung and ladder side rails for assembly and connection thereof. Ladders] fabricated by the method of this invention have an im-' proved joint between the members. This provides in-' creased rigidity in their side rails, rungs and the ladder structure as a whole is more rigid in torsion and compression. This is achieved by extruding tubular ladder rungs through a corrugated die to produce corrugations on both surfaces of the rung. This provides rigidity increasing serrations on both the inner and outer surface of the tubular rung, results in a maximum stiffness of the rung with a minimum amount of metal. The ends of the rung are necked down to provide tapered plug thereon while the side rails are perforated with a die in such a manner as to provide a cupped flange around the perforation with the flange having rung-matching serrations scored on its inner surface. The flange is also formed in such a manner to have an inner diameter equal to the average diameter of the plug ends. This, on full insertion of the plug into the flange side of the aperture causes an interference fit therebetween, tightly holding the rung in the aperture and restraining the rung from rotation with respect to the side rail. The joint is then completed by expanding the plug to conform the end of the plug to the contour of the flange and aperture, thereby permanently fixing the parts together.
Referring now to FIGS. 1 and 2 of the drawings, for a more complete understanding of the invention, the ladder is composed of rungs 2 disposed between side rails 4. The rung and side rail of the ladder are preferably formed from an extruded lightweight metal, such, for example, as aluminum, magnesium and the like.
Referring to FIG. 3, rung 2 and side rail 4 are shown in their extruded form prior to shaping thereof for assembly. Side rail 4, in this embodiment, is in the form of an I beam and comprises web member 6 and cross members 8. Rung 2 in this embodiment, extruded in the form of a cylindrical tube, is provided with longitudinally disposed serrations 10 and 12 on the external and internal surfaces thereof respectively. Referring to FIG. 7, serrations 10 and 12 are disposed alternatively around the periphery of the cross section of the rung to form an essentially corrugated wall therefor. The alternating disposition of these serrations produces a corrugated wall configuration which provides a unique advantage in that,
structurally, a maximum stiffness of the rung under lateral loading is achieved with a minimum volume of metal. In other words, a maximum strength-weight ratio is provided since the corrugations act as a plurality of small, integral stilfeners for the lateral wall.
In an embodiment of the invention utilizing extruded members, the serrations are preferably incorporated in the rung during the extruding operation through the use of a serrated or corrugated extruding die. If the rung were formed of rolled sheet metal or the like, the corrugations could be rolled in the metal sheet in the usual manner prior to formation of the tube member.
Obviously the cross sectional geometry of the rung and related structure is not limited to circular form but could consist of rectangularly or triangularly configured tubing if so desired.
Returning now to FIG. 3, side rails 4 are cut to suitable length and the required number of rungs 2 are provided, the rungs being slightly excess, in length, of the 'desired spacing between side rail web members 6.
FIG. 4 is a view similar to FIG. 3 showing an end of rung 2 and the web member of the side rail formed and prior to assembly thereof. Rung 2 has been compressed by a suitable tool to form inwardly tapering plug 14 on the end thereof, the plug also being of reduced darneter to form angular shoulder 16 between the plug portion and the cylindrical portion of the rung. Web 6 3 has been punctured by a suitable tool to form aperture 18 therethrough. The perforation operation also displaces metal from web 6 to provide inwardly extending flange 20 around the periphery of the aperture. Also,
,- during the perforation operation, serrations 22, matching serrations 10 on rung 2, are formed on the inner surface of flange 20 by scoring or any suitable means. These serrations may be formed by flutes on one of the aperture and flange-forming tools or may be performed separately as desired. The resulting inner mean diameter is preferably substantially equal to the average diameter be tween the mean major and mean minor diameter of plug 14. In preferred form of the ladders, the transverse face of flange 20 is provided with tapered surface 24, substantially equal to the angle of shoulder 16. This arrangement creates an extra tight connection between the side rails and the rungs.
provides a springing and nesting action against the interior of the flange. After insertion of plug 14 into flange 20, the end of the plug projecting through aperture 18 is flared outwardly until the .plug end conforms to the inner configuration of aperture 18 and flange 20 as shown. The resulting joint provides a tight, strong connection between rung 2 and side rail 4, which, due to the spring quality of the nesting action, is durable and resists permanent deformation and resulting loosening of the joint under repetitive loading. The depth of the resulting joint also provides a connection which resists angular displacement between the rung and side rails and thereby increases the rigidity of the rungs and the torsional ladder stiffness in a unique and simple manner.
Referring to FIG. 6, a sectional view through the complete joint shows the nesting action between serrations 10 and 22 of the components of the structure. This nesting action provides, in addition to the benefits enumerated above,rotational resistance between the rung and side rail structure which is not vulnerable to weakening under repeated cyclical loadings thereof.
Among the advantages afforded by the method of fabcricating the ladder are the relative simplicity of tooling :and speed of assembly afforded thereby as well as the strong, lightweight and durable resulting article. Formation of cups in the web portion of side rail 4, aswell as providing depth for the resulting joint as described above, also increases the web stiffness of the side rail members by increasing the structural depth thereof. Flange 20 further provides a greater load bearing surface between rung 2 and web 6 avoiding concentrated loading of the web itself. The concentrated loading generally results in wear and loosening of the rung-side rail joint under repeated cyclical loading. The formation steps provided for by this invention also provide advantages in that, since severe form-ing operation such as the necking down of rung 2 and the perforation and flange forming of web 6 may be performed prior'to aging of the metal, the final Rockwell hardness of the material may be higher than heretofore possible. For example, an extruded aluminum rung having a T4 temper, solution heat-treated but not aged, may be subjected to the severe operation of necking down the ends of the rung without failure. After the severe operations are performed on the rung, and prior to assembling the side rail, the material may be heat-treated to a T6 temper. Similarly, the side rail may also be punctured and 4 flanged prior to the aging process. The final flaring step of the assembly is not as severe a working of the material as that imposed by spinning, beading or other similar operations. The flaring may be performed on the hardened material without fracture or other failure of the metal during assembly. As was pointed out for the rung member illustrated in this embodiment of the invention, the various components of the ladder may, of course, be fabricated by methods-otherithan extruding within the scope of the invention. For example, the side rail could, if desired, be formed of sheet metal bent into any desired channel configuration and thereafter formed in accordance with the steps outlined above What is claimed as new and desired to be secured by Letters Patent of the United States is: I claim: 1. The method of making a lightweight metal ladder comprising the steps of:
(A) providing a hollow corrugated ladder rung by:
(a) extruding a metal tube through a corrugated annular die; (b) necking the ends of said tube to form shoulders between the tubular portion and the necked portions thereof, and tapering the neck portions out-. wardly to provide frusto conical plugs of decreas-- ing diameter outward of said shoulders; (B) providing ladder side rails by:
(a) forming thin metal channels having flatweb portions thereto;
(b) puncturing the web of said rails to form aperr' tures at equally-spaced intervals therealong;
(c) simultaneously cupping the periphery of said apertures to form normally extending flanges substantially equal in inner diameter to the average diameter of said plugs;
(d) simultaneously forming rung-serration matching serrations on the inner surface of said flanges; and (C) assembling said ladder by:
' (a) forcing the plugs of said rung into the flanged sides of the apertures, on said side rails until said shoulders bottom-against the ends of said flanges to elastically deform said flanges and said plugs and thereby forming tight interference fits therebetween; and
(b) expanding the outer ends of said plugs to conform to the surfaces of said flange and said web portion to fix said rungs and said side rails firmly together.
2. The method of making a lightweight metal ladder comprising the steps of:
(A) providing a hollow ladder rung by:
(a) forming a metal tube having axially disposed serrations thereon;
(b) forming the ends of said tube to have reduced and outwardly tapering plugs thereon of decreasing diameter, toward the end of said tube;
(B) providing ladder side rails by:
(a) forming metal channels having flat web p01.-
(b) forming apertures in the web of said rails at equally spaced intervals therealong; (c) forming the periphery of said apertures to define normally disposed flanges therearound substantially equal in internal diameter to the. average diameter of said plugs;
(d) forming rung serration matching serrations on the inner surface of said flanges; and
(C) assembling said ladder by:
(a) inserting the plugs of saidrungs fully into. the flanged sides of the apertures in said side rails to form a tight interference fit therebetween; and
(b) deforming the outer, ends of said plugs to conform to the surface of said flange and said aperture to fix said rungs and said side rails firmly together.
3. In a method of making lightweight metal ladders having tubular rungs and channel metal side rails, the improvement which comprises:
(A) providing a section of metal tube having axially disposed serrations thereon;
(B) forming the metal tube to have reduced and outwardly tapering plugs thereon of decreasing diameter toward the end of said tube;
(C) providing metal channels having fiat web portions thereon;
(D) forming apertures in the web of said metal channels at equally spaced intervals therealong;
(E) forming the periphery of said apertures to define normally disposed flanges therearound substantially equal in internal diameter to the average diameter of said plugs;
(F) forming serrations on the inner surface of said flanges matching the serrations on said metal tube;
(G) inserting said plug formed in step B into a flanged side of one of said serrated apertures resulting from step F to form a tight interference fit therebetween; and
(H) deforming the outer end of said inserted plug of stepf G to conform to the surface of said flange and one of said Web portions to fix said tube to said metal channel.
References Cited by the Examiner UNITED STATES PATENTS 909,024 l/ 1909 Reach 182-194 1,737,780 12/ 1929 Wagenhorst. 2,356,901 8/1944 Wackman 29512 2,511,077 6/1950 Race. 1 2,550,070 4/1951 La Brecque et al 29-512 2,552,630 5/ 1951 Hutchinson 182194 2,951,550 9/1960 Rich 182194 3,037,276 6/1962 Woods 29512 3,119,435 1/1964 Greenman 29512 XR CHARLIE T. MOON, Primary Examiner.