Do you wonder formed wheel tires and ways?
The present invention is related to a combination of a wheel and tire. It finds particular usage on bicycles, but the same can be used on numerous other vehicles not the least of which is a rickshaw, small carriage, and related vehicles.
The traditional tire for use on a bicycle is an inflatable tube. It may be with or without an inner tube. Normally such tires are secured in a U-shaped rim on the periphery of the wheel. They rely on the tensile strength of the tire to maintain the same in the rim. Molded tires have also been employed. A highly successful type is exemplified in Canadian Patent No. 1,185,641.
Molded urethane tires for mounting on ordinary bicycle wheels suffer some of the following disadvantages:
1. The tension members have to be placed in molds before the tires are cast. It is time consuming and expensive.
2. Since the tension member is the critical to obtain the best result, the location of the tension members has to be optimized. This is a difficult task. If the tension members are set in the mold in a slightly larger diameter than the desired, the tires may be rolled off from the rims during riding. If diameters of the tension members are slightly smaller than the optimum, it will be difficult to mount the tires on the wheelshttps://www.pufoamwheel.com.
3. Since the wheel structure is designed for pneumatic tires, when the wheels are equipped with the solid tires, their shock absorption and load bearing capacity are seriously affected. Consequently, the dynamic load acts on the bicycle frame, which results in shorter bicycle life.
4. The edges of the rims in a typical configuration also act as a cutting device and can split the foam tire under normal stress.
5. Above all, the rim channel structure of the conventional wheels is specifically designed for mounting and holding the pneumatic tires with bead wires. Obviously, this structure does not have any special consideration in accommodating the solid tire structure. For the tires directly molded on the ordinary wheels, the problems 3 and 4 remain. In addition, the following issues need to be considered:
A. Extra materials have to fill the rim channels.
B. Shock absorption only relies on the tires, which might not be enough.
C. Because of removal of tension members, it is possible that the tires are rolled off from the rim during riding with the rim channel structure. This imposes a serious safety problem.
Also, tires made of an elastomer or polyurethane foam require some method of preventing them from elongating and rolling off the rim in use, as elastomers soft enough to provide a cushioning effect have relatively low tensile modulii. Such methods normally involve embedding into the tire a flexible tension member constructed of a material with the appropriate tensile stiffness. The objective is to have the resulting tensile stiffness of the composite tire such that the load required to stretch the tire on and off the rim is higher than the loads encountered in use. This allows the tire to be mounted, yet prevents it from inadvertently rolling off in normal usage.
Materials used as tension members include natural and synthetic fiber and cord such as nylon, polyester and cellulose, and metal wires or coils. A more recent innovation was to manufacture the tire from self-skinning flexible microcelular polyurethane foam. In this concept the foam interior provides the flexibility for the shock absorption characteristics, while the unfoamed skin on the outer surface provides the wear resistant riding surface. Various means can be used to hold the tire on the rim including tension members and gluing of the tire on to the rim. Polyurethane foam products of this type are molded. In order to mold a tire shaped object the mold should be filled under some pressure to prevent surface defects caused by air pockets. This pressure can be obtained by injecting the preblended liquid urethane components into a sealed and pressurized mold, or else by rotating the mold while pouring in the preblended liquid urethane components. Both of these methods are used extensively in casting products from various materials.
The preferred version of the prior art is to produce a polyurethane foam tire with an embedded tension member. The preferred location of the tension member is near the inside diameter of the tire. Current practice has tension members located at or about he center of the tire cross-section near the inside diameter of the tire. However, current methods of producing polyurethane foam tires suffer from difficulties in economically mass producing the tires. A particularly troublesome aspect is to ensure full coverage of the tension member by the urethane foam.
Preblended liquid urethane components expand as they react to form urethane foam. Thus to completely fill the mold cavity with unfoamed material is extremely wasteful as a volume of foam equal to the degree of expansion would be forced out of the mold. However, when only enough material to form the tire is introduced into the mold, the liquid congregates at the outside diameter of the mold, especially if the mold is being rotated. As a result, tension members near the inside of the mold are not immersed in the liquid material. Instead the tension members must be engulfed by the expanding urethane foam which is already in a state best described as semi-solid, so molding flaws result. The difficulty of covering the tension member by this expanding semi-solid foam is increased if the tension member is located near a wall of the mold.
The main distinctive feature of the new design is that the rim has an O-shape of cross-section instead of the conventional U-shape (channel) of cross-section to hold a solid of filled tire. The rim assembly or disc type of wheels, for example as one shown in FIG. 2, consists of two half pieces, separating along a central plane. The half pieces are first molded and then are bonded to form a light, hollow and strong rim and wheel assembly. A wheel assembly having a solid tire is made by pouring formed polymer materials such as polyurethane into a rotating mold in which the rim assembly is used as an insert. Use of rotating/reaction casting method can achieve a very high productivity. Optionally a double shot molding may be employed to concentrate strong rigid material such as glass filled nylon in the flat cone and softer polypropylene in the rim.
The wheel assembly created by the present invention has many objects and advantages over the conventional pneumatic wheels, some of which are the following:
1. Conventional wheels are designed to accommodate the mounting of a pneumatic tube and tire, and bead wires on the tire hold the tire on the wheel when inflated. As those wheels are used for solid tires, tension members are imbedded in the tire to hold the tires on the wheels. The new wheels designed by the present invention eliminate the need for such tension members.
2. Placing tension members in the mold prior to casting a solid tire is the most time consuming labor expensive in the entire process. The elimination of tension members results in eliminating that function.
3. The elimination of tension members avoids many difficulties both in design and manufacturing such as accurate determination of location of tension members.
4. The new wheel structure increases the capability of bearing side loads for a solid tire.
5. Using conventional rims to make a solid tire requires filling of the rim channel with formed polymers in order to bond the tire to the rim. It wastes expensive materials and increases the weight. In the present invention, the U channel is replaced by a formed convex rim, so this problem is avoided.
6. Conventional wheels rely on tires for shock absorption. The new structure provides additional flexibility and shock absorption. It also reduces the risk of rim and wheel damage which is caused by sudden or severe impacts.
7. The new wheel significantly simplifies the manufacturing process which results in saving the labor costs.
8. A solid disc wheel offers good aerodynamic property and great potential for visual graphics.
9. The new wheel reduces heat build-up in the tire which in turn reduces rolling resistance.
10. When a solid tire is used in a conventional rim assembly, the tire sits on the edges of the rim. These edges act as cutting devices, and also cause high stress concentrations around the shoulders. Therefore, the crack failure of tires often occurs. The new wheel structure eliminates such a problem.