Glide castors
Glide castors comprises a two-part body assembly consisting of lower and upper mouldings fitted together. The lower moulding has a convex bottom ground-engaging surface and an integral upstanding boss with a bore for a mounting spindle. The upper moulding is of cap-like form and seats on a peripheral seating on the lower moulding. An integral inwardly projecting lip of the upper moulding provides snap-on engagement with said boss, thereby to hold the two mouldings together as an assembly.
Description
This invention relates to non-rolling castors of the so-called glide or “slipper” type, having a body with a convex ground-engaging surface offset from a vertical pivot axis.
It is known for castors of this type to have a castor body formed as an assembly of two plastics mouldings, namely a lower base member moulding and an upper cover member moulding. The lower moulding has an upstanding boss to receive a mountingspindle and around which the upper moulding is fitted and the upper moulding has an internal peripheral lip providing a snap-on fixing on engagement with an annular outer peripheral seating around the top surface of the lower moulding.
This prior construction of castors suffer from two main disadvantages: firstly the peripheral rim of the upper moulding is of varying thickness which results in differential shrinkage and thus makes it difficult to hold close fixing tolerances; andsecondly the lower moulding is of solid form and hence is expensive in terms of moulding material. The invention has for its object to provide a construction which materially reduces, or substantially eliminates, the fixing tolerance and shrinkageproblems referred to and which, moreover, can be designed so as to effect a considerable economy in moulding material.
SUMMARY
According to the invention a glide castor comprises a lower moulding with a convex bottom ground-engaging surface and an integral upstanding boss with a bore for a mounting spindle, and an upper cap-like moulding which seats on a peripheralseating on the lower moulding and which is formed for snap-on engagement with said boss thereby to hold the two mouldings together as a two-part body assembly.
As a result of the invention the upper moulding can be a shell of substantially uniform thickness, apart from the region surrounding and which snaps on to the boss, and this region can be formed as an internal boss which is of annular form andconstant thickness. Thus the shrinkage and fixing tolerance problems of the prior construction can be obviated.
As the lower moulding of the invention merely has to provide a simple seating for the upper moulding this is provided around the periphery of the lower moulding which is conveniently of circular plan form, whereas in the prior construction acircular seating was required eccentric with respect to that periphery. The result is that the lower moulding can also be formed as a dished shell of more or less constant wall thickness, thereby effecting considerable economy in the moulding materialused. Both mouldings may be of nylon or like plastics material, and the two mouldings may be of contrasting colours to provide a decorative effect.
The lower moulding of the castors may include strengthening webs between the boss and the wall of the moulding, thereby allowing a yet thinner shell to be used. A ring of such webs may be provided, for example twelve in number, each extending radially from theboss to the peripheral rim of the lower moulding.
The bore of the boss is preferably moulded with an internal projection or projections providing for retaining engagement with a grooved mounting spindle which thus has a snap-in fixing within the body assembly, thereby obviating the need for afixing circlip or other separate fixing means as has previously been used. The fit of the spindle in the bore is preferably such that the body can pivot on the spindle, thereby allowing direct spindle fixing of the castor if desired, although ifpreferred a flanged or other fixing member can be mounted on the spindle according to the requirements of the user.
When a separate fixing member is employed this may also be pivotable on the spindle and the latter may have a second groove providing for snap-on fitting on the one hand into the castor body and, on the other hand, into the fixing member. Thespindle grooving is then desirably symmetrical, rendering the spindle reversible so that it can be fitted either way round thereby facilitating mechanical handling and assembly.
It will be appreciated that other forms of fixing means can be used which actually turn on the spindle, in which case the castors spindle may be reversible with two grooves for snap-in fixing, respectively, with the castor body and the fixing means. Alternatively, the fixing means may be omitted entirely when the user desires to employ direct spindle fixing of the castor.