Rear hub shell for bicycles and method of manufacturing same

A hub shell is made in one piece out of plastic and a metal ring is positly connected externally to at least one of its hub heads in such a way that it can neither rotate nor be displaced axially. The metal ring has longitudinal grooves and a continuous annular groove and can easily be provided with fine threading on the outside for attaching a chain wheel. The ring is heated to plasticize the material of the hub head inserted in it until the material can be forced and vibrated into the grooves.

BACKGROUND OF THE INVENTION 
The present invention relates to a one-piece rear hub shell for bicycle 
wheels that consists of a tube with heads on it at the sides and that have 
perforations to accommodate wheel spokes. 
Hub shells of this type now consist in general of metal. Some in particular 
are made in several parts out of steel and some in one piece out of 
aluminum. Both types are expensive to manufacture partly because of 
complicated assembly operations and partly because of the high cost of 
aluminum. 
A multipart hub shell in which the tube and adjacent areas are made in one 
piece out of plastic and function as an external accommodation for the 
bearing while the flanged heads are again made out of metal is also known, 
with the extensive involvement of metal parts and the requisite assembly 
operations again accounting for high manufacturing costs. 
None of the known hub shells involve any problems in attaching the drive 
mechanism, specifically the wheels for the chain drive, each on at least 
one side of the shell and on its own hub head, because a metal component 
is available there in all known designs that provides sufficient strength 
for the fine threading that chain wheels are conventionally supplied with 
to transmit the drive forces. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide both a hub shell of the 
aforesaid type and a method of manufacturing it that will make it 
conceptually simple and very inexpensive to manufacture while fully 
preserving the requisite strength of the threaded area of the drive 
mechanism. 
This object is attained in relation to the hub shell in accordance with the 
invention in that it is made in one piece out of plastic and a metal ring 
is positively connected externally to at least one of the hub heads in 
such a way that it can neither rotate nor be displaced axially. 
A rear hub shell of this type is a plastic component that is inexpensive 
because it is essentially in one piece but that will still be stable if 
the appropriate plastic is selected. The shell, however, does have a metal 
ring, which is in itself simple to manufacture, only where it is necessary 
to strengthen the fine threading. A reliable joint between the hub head 
and the metal ring can be rapidly and simply established in one automatic 
manufacturing step because the head and ring are smoothly and rapidly 
forced together while the appropriate areas of the plastic in the head are 
plasticized and the operation is promoted both with respect to time and to 
reliable filling of the positive seating for the material in the metal 
ring by the simultaneous vibration. 
The metal ring preferably has grooves in its inner surface that are 
parallel to one another and to its longitudinal axis and that are full of 
the hub-head material. The ring can also preferably have a continuous 
annular groove full of the hub-head material around it. 
The ring is preferably shaped by upsetting and can have a continuous upset 
fold full of the hub-head material around it. 
The ring further preferably has a limiting shoulder and fine threading on 
the outside. 
The ring is preferably made of aluminum and the hub shell can be 
thermoplastic, preferably fiberglass-reinforced polyamide. 
In another embodiment, a bushing can be force-fit into the inside surface 
of the hub head that accommodates the metal ring. Moreoever, the hub head 
can taper conically outward where it accommodates the metal ring and the 
inside surface of the the metal ring can have a matching taper. 
The object is attained in relation to the method of manufacturing the hub 
shell in that the material in the area of the hub head that accommodates 
the metal ring is hot-plasticized and forced, while being simultaneously 
vibrated, into a positive seating in the metal ring. 
The metal ring with its conical inside surface can be forced as far as 
possible onto the conical hub head and the metal ring then heated to 
plasticize the hub-head material. 
The pressure needed to completely force the metal ring onto the hub head 
can be generated by applying a weight with the hub shell and metal ring 
positioned vertically. 
A core can be inserted into the interior seat of the hub shell in the 
appropriate area of the hub head while the hub-head material is being 
plasticized and the metal ring forced on. 
A preferred embodiment of the invention and of the method of manufacturing 
it will now be described with reference to the attached drawing, wherein:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, a hub shell 1 is in one piece and consists of 
thermoplastic, of fiberglass-reinforced impact-resistant polyamide for 
example. It can be high-pressure injection molded. In the center is a tube 
2. Tube 2 is connected to two hub heads 3, 13 that have flanges 4 with 
perforations 5 to accommodate wheel spokes. 
In the embodiment illustrated, a metal ring 6 is positively connected 
externally to one of the hub heads 3, specifically to the one that the 
chain drive will be attached to, in such a way that it can neither rotate 
nor be displaced axially. Optionally, head 13 can be configured identical 
to head 3 for receiving ring 6. 
Hub head 3 tapers conically outward where it accommodates the metal ring 6 
and the inside surface of the metal ring 6 also tapers conically outward 
to match. Metal ring 6 has a number of grooves 7 in its inner surface that 
are conically parallel to one another and to its longitudinal axis. Ring 6 
also has a continuous annular groove 8 around its inner surface at what 
will later be the outer end. 
Parallel longitudinal grooves 7 and annular groove 8 are completely filled 
with the material of the corresponding hub head 3 once hub shell 1 and 
metal ring 6 are joined, resulting in a highly non-rotating positive 
connection that will transmit the driving forces as a result of engagement 
between the material of hub head 3 and longitudinal grooves 7. The 
material in continuous annular groove 8 prevents ring 6 from sliding off 
head 3 axially. 
Metal ring 6 consists in a practical way of aluminum and can be 
manufactured very simply by upsetting. Upsetting can be carried out in 
such a way as to produce a small, annular second groove or fold 9 inside 
the ring along the ridges between longitudinal grooves 7. Material from 
hub head 3 can also enter groove or fold 9 to provide optimal 
reinforcement against axial displacement. 
Metal ring 6 can easily be provided with fine outer threading to accept the 
chain wheel. Ring 6 also has a limiting shoulder 10 on the outside of its 
inner end for the chain wheel to be screwed against. 
The inside of hub head 3 on hub shell 1 accepts either an outer bushing 11 
or a complete bearing. The bushing or complete bearing is 
overdimensionally forced in a practical way into hub head 3, which 
additionally permanently secures the inner positive connection between the 
material of hub head 3 and the corresponding seating in ring 6 provided 
for that connection. 
One example of a method of manufacturing a rear hub shell of the aforesaid 
type will now be described. 
The hub head 3 of a hub shell 1, itself high-pressure injection molded in 
one piece out of thermoplastic, that is to be covered with a ring 6 is 
brought into contact with the ring. The conical taper of the parts in 
question or of the areas in question produces a certain amount of loose 
engagement between hub head 3 and metal ring 6. The material of the outer 
wall of hub head 3 can accordingly now be very easily plasticized by 
heating ring 6 until it begins to flow. Pressure that is directed to force 
metal ring 6 completely onto head 3 is now exerted and both parts 
simultaneously vibrated. This can easily be done by positioning both parts 
vertically on a vibrator and applying a weight. It is also of course 
possible to mount the parts in a vibrating vise. The plasticizing in 
connection with the aforesaid weighting and with facilitating the flow of 
the plasticizing material by means of vibration ensures that the 
longitudinal grooves 7, the continuous annular groove 8, and if necessary 
the continuous upset fold 9 in metal ring 6 will fill up. 
The diametrical ratios at the outer surface of hub head 3 are selected in 
relation to the accommodation bore in metal ring 6 to provide enough 
excess material to ensure the desired complete filling of longitudinal 
grooves 7, annular groove 8, and if necessary upset fold 9. 
A core is inserted inside hub shell 1 while the aforesaid joint is being 
established to prevent the hub-head material from escaping into the 
interior space. 
It will be appreciated that the instant specification and claims are set 
forth by way of illustration and not limitation, and that various 
modifications and changes may be made without departing from the spirit 
and scope of the present invention.