Castor structure

Abstract: The self-orientatable twin castor (1) has a support (2) made of plastics for a pair of coaxial wheels (3,4). The support (2) is constituted by a tubular hub (5) with which a substantially semicircular wall (10), arranged in the median plane of the castor (1), is rigidly associated in a perpendicular manner. A semi-cylindrical casing (26) made of metal is associated with the edge of the wall (10) and has wings (30) for positioning and retaining it on the edge of the semi-circular wall (10).

Description: The present invention relates to a castor structure, and in particular to a self-orientatable twin castor of the type which comprises a pair of coaxial wheels. Twin castors are constituted by a pair of wheels 5rotatably mounted on a pivot. The pivot is horizontally supported by a tubular hub of a support which comprises a semi-cylindrical wall defining a casing or fairing-like structure which covers the upper part of the castor. A blind hole is defined in the semi-cylindrical wall, is open upward and acts as rotation seat for a vertical self-orientatable pivot intended to be inserted and fixed in an accommodation of the piece of furniture to which the castor is to be applied. The hub is internally provided with coupling elements for a collar provided externally on a hollow tang which protrudes coaxially from the respective wheel. In conventional twin castors, the support is made of plastics or metal. When it is desired to give the castor a metallic appearance, a Metal cover is applied onto the casing. Castors of this Rind are disclosed in GB-A-2025220 and FR-A-2 325 281 Castors in which the support is made of plastics are more economical than metallic ones. However, metallic supports are stronger and are used when the castor is designed to have a particular aesthetic appearance, such as chromium plating, brass coating, etc. The technical aim of the present invention is to provide a twin castor which obviates the shortcomings of known castors. Within the scope of this aim, an object of the invention is to provide a twin castor structure which offers greater resistance to wear and impacts, so as to comply with safety rules, and is at the same time more economical than conventional castors. A further object of the invention is to provide a twin 5castor structure with a visible surface having a metallic appearance, which is more appreciated by users. This aim and this object are achieved according to the invention by the present self-orientatable twin castor according to the invention as defined in the appended claims. Further details of the invention will become apparent from the following detailed description of a preferred embodiment, illustrated only by way of non-limitative example in the accompanying drawings, wherein: figure 1 is an exploded perspective view of the elements which constitute the twin castor structure according to the invention; figure 2 is a side view of the castor having a wheel removed therefrom; figure 3 is a sectional view, taken along the plane III-III of figure 2, of the twin castor according to the invention; figure 4 is a side view of a further embodiment of the invention. With reference to the above figures, the reference numeral 1 generally indicates the self-orientatable twin castor, which comprises a support 2 for supporting the pair of wheels 3, 4 which is manufactured by molding plastics and is symmetrical with respect to the median plane A. The support 2 is formed by a horizontal hub 5 composed of a central enlarged portion 6 from which two coaxial tubular portions 7, 8 extend in opposite directions. A through hole 9 is defined in the enlarged portion 6 and is coaxial to the tubular portions 7,8. A substantially semi-circular wall 10 is rigidly associated in the plane A externally with respect to the hub 5; said wall rises vertically and has, along its edge, a semi-cylindrical wall, referred to hereinafter as a half-ring 11, which protrudes on both sides of the median plane A. The half-ring 11 is coaxial to the hub 5 and has, along its lower edges, chamfers 12, 13 and tapers 12a, 13a at its terminal portions. Semicircular teeth 14, 15 are defined inside the tubular portions 7, 8 and have a saw-tooth cross section; said teeth define shoulders for preventing the escape of the wheels 3, 4 as will become apparent hereinafter. A slot 17 is defined in the tubular portions 7, 8, between each tooth 14, 15 and the enlarged portion 6. The slot 17 allows the extraction of an insert which, during the molding of the support 2, determines the forming of the teeth 14, 15. A pivot 16 is inserted in the hole 9 and has respective grooves 18, 19 at its opposite ends. One of the wheels 3, 4 is applied to each end of the pivot 16; said wheels have a cambered lateral surface 20 and a cylindrical rolling surface 21. A tubular portion 22 extends internally from the cambered surface 20 of each wheel and has, at its end, an external collar 23; said tubular portion encloses a blind hole 24, the bottom whereof is constituted by the central portion of said cambered surface. An annular ridge 25 is defined proximate to the bottom of said blind hole 24. The opposite ends of the pivot 16 are inserted by being force-fitted into the blind holes 24, so that the grooves 18, 19 are engaged by the ridges 25 so as to rotatably retain the wheels 3, 4 on the pivot 16. The axial retention of the wheels is ensured by the engagement of the collars 23 behind the teeth 15, without compromising the rotational action of the wheels 3, 4. The half-ring 11 supports a semi-cylindrical casing 26 made of metal, for example by pressure die-casting a Zn + Al + Mg alloy, which is coaxial to the hub 5. Two mutually parallel ridges 27 extend along the internal surface of the casing 26 and are arranged in planes which are perpendicular to the pivot 16. Said ridges 27 delimit a seat 27a the width whereof corresponds to that of the half-ring 11. In order to secure the casing 26 onto the half-ring 11, a series of vertical notches 28, 29 is defined in the ridges 27; the notches indicated by the reference numeral 28 run along the line which connects the ridges 27 to the internal surface of the casing 26, whereas the notches indicated by the reference numeral 29 cut said ridges radially. The notches 28, 29 define pairs of wings 30 and 31 which are bent against one another. More precisely, the wings 30 are bent onto the tapers 12a, 13a and the wings 31 are bent onto the chamfers 12, 13, so as to ensure the fixing of the casing 26 to the support 2. A collar 32 is advantageously defined in the casing 26 and protrudes vertically therefrom. A sleeve 32a protrudes from the half-ring 11 and is integral therewith. The sleeve 32a is inserted into said collar and defines a seat for the rotatable support of a pivot (not illustrated) and allows to fix the castor 1 to a piece of furniture. An essential prerogative of the present invention is constituted by the fact that it allows to manufacture twin castors which are economical and strong, using two types of material. In particular, the wheels 3, 4 and the support 2 can be manufactured from polypropylene, which ensures silent rolling, whereas the load stresses are supplied by the metallic casing 26, which furthermore ensures a pleasant appearance. It should be noted that by means of the invention, with respect to castors with a fully metallic support, one achieves a considerable saving in metal and therefore a considerable reduction in costs, since the plastics with which the support is manufactured has a significantly lower cost. It should be noted that the casing 26 can be manufactured by pressure die-casting with conventional opening dies, without having to resort to slides or the like. Since the notches 28, 29 can be orientated in the opening direction of the mold, they in fact do not lead to undercuts capable of preventing the removal of the part from the die. In a further embodiment of the invention, illustrated in figure 4, instead of the notches 28, notches 33 are provided forming wings 34 which are bent onto the chamfers 12, 13 and 12a, 13a of the half-ring. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: Castor of the type comprising a support (2) for a pair of coaxial wheels (3,4), constituted by a tubular hub (5), a substantially semicircular wall (10), arranged in the median plane of the castor and substantially perpendicular to said hub, a half-ring (11) extending along the edge of said semicircular wall (10) and protruding on both sides thereof, said hub (5), said semicircular wall (10) and said half-ring (11) having a monolithic structure of plastic material, a semicylindrical casing (26) made of metal and extending on said half ring (11) characterized in that it comprises a vertical collar (32) protruding from the casing (26) and monolithic therewith and defining a seat for the rotatable support of the vertical pivot for the application of the castor to a piece of furniture and means for positioning and retaining the casing (26) on said half-ring (11), said means comprising two parallel ridges (27) which are defined inside the casing (26) and arranged in planes perpendicular to the axis of said hub (5) at such a mutual distance as to delimit a seat (27a) for the accommodation of said half-ring (11), notches (28,29,33) being formed in said ridges (27), said notches defining wings (30,31,34) which can be bent over the edges of said half ring (11) for retaining the casing thereon. Castor according to claim 1 characterized in that said half ring (11) has internal edges provided with chamfers (12,13) and opposite ends provided with tapers (12a,13a) and that at the opposite ends of the casing (26), along the line with connects the ridges (27) to the internal surface of the casing (26), notches (28) are provided adapted to be bent against the tapers (12a,13a). Castor according to claim 1 characterized in that said half ring (11) is provided with a vertically protruding sleeve (32a) inserted into said collar (32) to define a seat for the rotatable vertical pivot of the castor.

Inventors: MELARA FRANCESCANTONIO, MELARA, FRANCESCANTONIO
Applicants: EMILSIDER MECCANICA, EMILSIDER MECCANICA S.P.A.
Application year: 1991
Main classification: B60B33
IPC codes: B60B33