WO1999054121A1

WO1999054121A1 - Multi-shot process of producing a non-pneumatic tire

Info

Publication number: WO1999054121A1
Application number: PCT/US1999/008651
Authority: WO
Inventors: Roger Fleming
Original assignee: American Tire Corporation
Priority date: 1998-04-20
Filing date: 1999-04-20
Publication date: 1999-10-28
Also published as: AU3656199A

Abstract

A process for producing a product comprising more than one different material is disclosed. More particularly, a method for producing a non-pneumatic tire made of at least two different polymers is disclosed. A spin cast method of producing the tire is disclosed and dependent upon a curing period of the polymer chosen. Additionally, the spinning rate of the tire mold also depends upon the polymer chosen as well as the tire desired.

Description

1

MULTI-SHOT PROCESS OF PRODUCING A NON-PNEUMATIC TIRE

Technical Field

This invention relates to a method for producing a non-pneumatic tire and more particularly to a method for producing a non-pneumatic tire made of at least two different materials. Background Art

The present invention contemplates a new and improved method of manufacturing non-pneumatic tires made of at least two different materials which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results. A great deal of work has been done to develop a non-pneumatic tire that has the same performance characteristics as a pneumatic tire. Pneumatic tires are geometrically torus shaped and are distinguishable from non-pneumatic tires in that they have a flexible membrane pressure container. This pressure container when filled with air under appropriate pressure allows the tire to meet a variety of performance characteristics. These characteristics include load carrying capacity, cushioning ability, noise and vibration reduction and road handling ability.

By definition, pneumatic tires contain pressurized air within a hollow chamber. While there have been many improvements to these tires, one of the greatest disadvantages is that of flat tires and blowouts. Therefore, a great deal of research has gone into producing a pneumatic tire having a run-flat capability. Improvements in this area have allowed tire designers to develop pneumatic tires that are able to adequately perform without pressurized air. Typically, this performance permits the tire, while un-inflated, to adequately operate over a certain distance and for a certain time. This eliminates the need to change the tire immediately. Other improvements have dealt with flat tires that seal themselves when a hole or puncture is acquired, such as driving over a sharp object. These designs place a type of liquid material within the tire, that, upon puncture of the tire, flows to the area surrounding the newly formed hole thereby preventing the air from escaping. In all known cases, overcoming flats and/or blowouts in pneumatic tires has come at the expense of performance characteristics. 2

Non-pneumatic tires eliminate the problem of a flat and/or blowout by eliminating the need for pressurized air. Non-pneumatic tires are typically solid tires having no hollow chambers therein. Thus, the inherent problems within pneumatic tires discussed above are eliminated. However, many of the performance characteristics found with pneumatic tires have not been duplicated in non-pneumatic tires. In particular, the performance characteristics of cushioning ability, noise and vibration reductions have not been equaled. Thus, the pneumatic tire is the standard in virtually all tire and wheel applications.

Initially, non-pneumatic tires were made of natural rubber. As the technology has developed, various other materials have been used. These other materials have greater performance characteristics than rubber. Most of these materials have come from the polymer industry. For example, bicycle tires have been made of polyurethane foam. As the polymer industry has developed, several disadvantageous have surfaced. These disadvantages have included keeping the tire upon the wheel and the cost of the polymer itself.

Some methods for preventing polymer-based tires from rolling or sliding off the wheel rim have led to embedding a member within the tire to acquire stiffness in an appropriate region. Other methods, such as glueing, have been used to hold the tire upon the wheel. Recent designs have included self-skinning the polyurethane foam. However, the use of glue or some type of tension member to keep the tire upon the rim is still needed.

The polymer-based tires, such as polyurethane foam, are manufactured by a molding process. The mold is filled with the polyurethane foam, or like material, while under pressure. The pressure '"pushes" the foam into the cavital areas of the mold.

A typical method of producing bicycle tires is known as spin casting. This method involves filling the mold with a pre-blended polymer material while the mold is rotated about its axis. The rotation of the mold produces a centrifugal force effecting movement of the material radially outwardly. The material thus collects in the form of an annulus within the mold. The rotation of the mold continues until the material has gelled sufficiently. The mold is thereafter stopped from rotation and the material is allowed to fully cure. 3

The known prior art methods of producing a non-pneumatic tire have comprised a single polymer-based tire. Certain polymers having distinct advantages over other polymers. For example, one polymer may exhibit superior vibration and noise characteristics in comparison to another polymer, however, its load-carrying capacity may be inferior. Thus, a non-pneumatic tire is desired having performance characteristics similar to a pneumatic tire and also having the option of being comprised of several different materials. Disclosure of the Invention

In accordance with the present invention, a new and improved method for producing a non-pneumatic tire made of at least two different materials PI, P2 is provided which produces a non-pneumatic tire able to be comprised of several different materials.

A method for producing a non-pneumatic tire made of at least two different materials PI, P2 is comprised of (a) spinning an annular tire mold at a first spin rate Rl. The spinning rate of the tire mold is dependent upon the material chosen and the type of tire desired. The next step (b) is to pour a material PI into the annular tire mold that has an opening. The next step of the process comprises (c) waiting a predetermined curing period Tl . The predetermined curing period Tl is the time that the material PI has begun to cure to the point where the material PI has sufficient structural integrity able to withstand the penetration of a second material P2.

Where the non-pneumatic tire is made of more than one material the method further comprises the steps of (d) spirining the annular tire mold at a second spin rate R2 and (e) waiting a predetermined curing period T2. The predetermined curing period T2 can be equal to the predetermined curing period Tl or different than the curing period Tl . The curing T2 is the time that the material P2 has begun to cure to the point where the material P2 has sufficient structural integrity to withstand the penetration of a material P3.

The non-pneumatic tire produced from the method described herein is also disclosed and is shown in the accompanying figures.

Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed 4 specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement of parts. A preferred embodiment of these parts will be described in detail in the specification and illustrated in the accompanying drawings, which form a part of this disclosure and wherein:

Figure 1 is a perspective view of a bicycle;

Figure 2 is a profile view of a cross-section of a wheel and tire assembly;

Figure 3 is a cross-section of a typical bicycle tire mold initially filled with a material that has not yet cured;

Figure 4 is a profile view of a cross-section of another wheel and tire assembly;

Figure 5 is a cross-sectional view of a tire mold cavity;

Figure 6 is a cross-sectional view of another tire mold cavity;

Figure 7 is a profile view of a cross-section of a wheel and tire assembly;

Figure 8 is a profile view of a cross-section of another wheel and tire assembly;

Figure 9 is a profile view of a cross-section of yet another wheel and tire assembly; and,

Figure 10 is a profile view of a cross-section of still another wheel and tire assembly. 5

DESCRIPTION OF THE PREFERRED EMBODIMENT

This invention relates to a process to produce a non-pneumatic tire comprised of more than one material. The process described herein will be used to form a bicycle tire, however, this process can also be used to form a variety of different tires such as for golf carts, lawn mowers, wheelchairs, automobiles and trucks. This process will also work for numerous other material-molded non-tire articles.

The process described herein generally comprises a two-shot process. However, using more than two-shots is within the scope of this invention and such a multi-shot process essentially requires repeating the same two-shot process described herein. The non-pneumatic tire produced from this two-shot process will comprise two differing materials wherein that of a multi-shot process may have multiple layers comprising the same or different materials. The process will also be described with reference to spin casting the molded tire. However, in producing other molded articles spin casting may not be the preferred method. As such, this invention is not limited to a spin cast method but can also be applied to any pressure-dependent process for molding articles.

Referring now to the drawings, which are for purposes of illustrating a preferred embodiment of the invention only, and not for purposes of limiting the invention, Figure 1 shows a typical bicycle 10 having front and rear tires 12, 14. The tires 12, 14 are mounted upon front and rear rims 20, 22 on front and rear wheels 16, 18, respectively. The front and rear tires 12, 14 are non-pneumatic tires and may be solid or may have a non-pressurized chamber produced by the process described below. Figure 2 shows a prior art solid non-pneumatic tire 24 mounted upon a rim

26. The tire 24 comprises only one material. Producing such a solid non- pneumatic tire made of one substance is well known within the prior art. Typically, the tire 24 is produced by utilizing a spin cast method.

A typical spin cast procedure will now be described. Figure 3 shows a typical tire mold 30 used in a spin cast process. The tire mold 30 comprises upper and lower annular halves 32, 34. A liquid material (or materials) 44 is introduced into an opening 36 located substantially at a center 38 of the tire mold 30. Top and 6 bottom plates 40, 42 hold the upper and lower annular halves 32, 34 together. The plates 40, 42 apply pressure to the annular halves 32, 34 to ensure that the liquid material will not be lost due to leakage from insufficient compression. The materials 44 are introduced through the opening 36 and thereafter flow outwardly to a periphery 50 (shown in Figure 5) of the tire mold 30. This outward flow occurs because of the centrifugal force caused by the rotation of the tire mold 30 along with the plates 40, 42. This centrifugal force forces the material 44 into the cavity 46. The material 44 is poured in the direction of arrow A until it substantially fills the cavity 46. Then, the pouring of the liquid 44 is stopped and the tire mold 30 continues to spin. Thus, the material 44 collects at the outermost periphery 50 and fills the entire cavity 46. This process produces a non-pneumatic tire 24 comprising only one material as shown in Figure 2.

The process that is the subject of this invention involves pouring an initial material into the spinning mold, waiting a desired period of time, and then pouring a second material into the spinning mold. Preferably, the second material is different from the initial material to take advantage of the second material's characteristics.

More particularly, the process involves pouring a first material PI, such as a polyurethane elastomer formulation, into a spinning mold and waiting a desired period of time Tl before pouring a second material P2 within the same mold. The period of time Tl between material pours is of paramount importance. The time Tl must allow the first material PI to partially cure. However, where the only difference between materials is for aesthetic purposes, such as differing colors of material, then the first material may be allowed to fully cure. The time Tl permits the first material PI to develop structural integrity in order to withstand the penetration of the second material P2 as it is added. The second material P2 is poured into the opening 36 of the annular tire mold 30 as was the first material PI . The spinning of the tire mold 30 is at a predetermined rate R, that is dependent upon the materials PI, P2 chosen and the type of non-pneumatic tire being formed. The first spinning rate required for the first material PI is denoted as Rl. The second spinning rate required for the second material P2 is denoted as R2. The second spinning R2 can be the same as the first spinning rate Rl or it may be 7 different. The only material restriction is that the second material P2 must be different than the first material PI. The difference in material is that of a property or chemical basis. This invention allows the designer to choose among materials having differing chemical structures. These chemical differences allow the designer to choose one material, for example, that exhibits superior wear characteristic, and also to incorporate a second material that exhibits superior shock- absorbing ability.

If the second, material P2 is poured too early (that is, if time Tl is too short) the second material P2 will penetrate the initial elastomer layer formed by the first material PI thereby leaving streaks of the second material P2 within the first material P. Pouring the second material P2 too soon may also cause one or both materials PI, P2 to have a non-uniform thickness. Figure 4 shows a non- pneumatic tire 25 produced by such a process where the second material P2 was poured before the first material PI attained the critical curing time Tl . In other words, the time Tl was insufficient for the first material PI to develop the appropriate structural integrity. As shown in Figure 4, the second material P2 penetrated the first material PI layer thereby leading to a non-uniform thickness of the first material PI layer around the periphery 48 of the tire 25. The non- pneumatic tire 25 produced is thus non-uniform and cannot properly take advantage of the properties of the materials PI , P2.

Preferably, at the outer periphery 48 of the tire 25 the first material PI is chosen, for example, such that it exhibits superior characteristics for wear, gripping ability and other characteristics. The second material P2, on the other hand, may be chosen for its vibration absorbing characteristics or other favorable characteristics that one may prefer for a specific design requirement. In the preferred embodiment, the materials PI, P2 are polymer-based materials.

Figure 5 shows a cross-sectional view of the cavity 46 of the spinning tire mold 30. As the first material PI is introduced in the direction of arrow B, due to centrifugal forces, the first material PI collects at the outer periphery of the cavity 46. As the first material PI begins to cure, a second material P2 is introduced as shown in Figure 6. At the introduction of material P2, PI has begun to cure along the outer periphery 50 of the cavity 46 and is in a more stable state than that of P2. 8

Thus, the introduction of P2 into cavity 46 is unable to penetrate PI . The material P2 exhibits a force upon PI. This force of P2 against PI allows PI to further elongate and flow further along the outer periphery 48 of the cavity 46 as shown in Figure 6. Thus, as shown in Figure 7, PI forms an outer layer of uniform thickness t along the outer periphery 50 of the cavity 46. Where it is desired to have PI form an outer layer along the periphery 40 of the tire, the non-pneumatic tire 52 produced will be similar to that as shown in Figure 7. The thickness t of the material PI is uniform throughout the cross section of the tire 52. With this process, the thickness t of the layer of first material PI can be controlled. Thus, where it is desired to have a greater thickness t along the periphery 48 of the tire 52 more of the material PI would be shot into the mold 30. Additionally, the thickness t is controlled by the spinning rate R, the curing time Tl and the chemical properties of the material chosen.

As noted above, the spinning rate R of the mold is also critical feature of this invention since in a spin cast procedure the spinning produces the pressure against the polymers. Where the second spinning rate R2 of the mold is too great, the material P2 penetrates the elastomer layer PI producing the unequal distribution of material similar to the tire shown in Figure 4. Conversely, when the first spurning rate Rl of the mold is too slow the material PI is unable to flow around the mold 30. A tire produced when the first spinning rate Rl is too slow is shown in Figure 6. Thus, the bicycle tire 52 shown in Figure 7 was formed using proper spinning rates Rl, R2. For that reason, the tire 52 has a uniform thickness PI along the outer periphery 48 of the tire 52.

Figure 8 shows a bicycle tire 54 where it is desired to use the polyurethane elastomer, or other first material PI, only for the tread region 56. To produce a non-pneumatic tire 56, the material PI must have fully cured within the mold 30 and/or the first spinning rate Rl of the mold 30 must have been slow enough so that the material PI does not extend along the sidewalls 58 of the tire 54. The spinning rate R of the mold 30 is also dependent upon the density of the material chosen. Thus, for thicker materials the first spinning rate Rl must be greater than that for a thinner material if the material is to flow along the sidewalls 58 of the tire 54. 9

The multi-shot process comprises utilizing a number of materials. More specifically, the method comprises following the identical procedure as with the two-shot process described above but having the additional steps of waiting a predetermined second curing time T2 for the second material P2 to cure or partially cure, and thereafter, utilizing a third material P3 different from the previous material P2. Upon waiting the predetermined time T2 for the curing of material P2, the third material P3 is poured within the tire mold 30. Thereafter, if it is desired a fourth material P4 could also be used. Again, prior to pouring material P4 a predetermined curing time T3 for material P3 must have elapsed. Material P4 will thereafter be poured. Utilizing four materials in the manner described above could yield the non-pneumatic tire 60 shown within Figure 10 and would depend upon the preference of the design criteria chosen for the tire 60. The tire 60 shown within Figure 9 was formed by a process which allowed PI to extend along a portion of the outer periphery 48 of the tire 60 and is described in further detail below. With reference to Figure 10, a tire 62 is shown whereby it was preferred to have different thicknesses of each layer of the tire 62.

Figure 9 shows a non-pneumatic tire 60 that utilized three materials PI, P2, P3. Initially, the mold 30 is spinning and the first material PI is poured. In order to achieve the flow of the material PI around the outer periphery 50 of the mold 30 the spin rate Rl must be great enough to force the flow of the material along the outer periphery 50. The determination of the spin rate Rl lies with the material PI chosen. Properties such as viscosity, density and flow will greatly determine the spin rate Rl. However, the spin rate Rl alone may not satisfy the flow of material PI around the entire outer circumference of the mold 30. The introduction of the second material P2, after the appropriate curing time Tl, will also aid in forcing the material PI along the outer periphery 50 of the mold 30.

The non-pneumatic tire 60 shown within Figure 10 utilized four materials PI, P2, P3, and P4. The curing time T for the process used to produce tire 60 is not as critical as the time T for producing the tires shown in Figures 7 and 9. The curing time T for the tire 60 shown within Figure 10 must be long enough to ensure that the material has cured and thus not allow penetration of the next material being introduced. Thus, the time T has only one limitation, a lower limit, 10 in that it must be long enough to ensure the material has cured. The time T for the tire 60 in Figure 10 can be distinguished from the tires depicted within Figures 7 and 9. The tires within Figures 7 and 9 have an upper and lower limitations with respect to time T. The time T must not be too long and must also not be too short, for the reasons mentioned earlier (discussed with respect to Figure 4). The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of the specification. It is intended by applicant to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Having thus described the invention, it is now claimed: Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.

Claims

11 CLAIM

1. A method for producing a non-pneumatic tire, said method comprising the steps of: (a) spinning an annular tire mold at a first spin rate Rl ;

(b) pouring a first material PI into said spinning annular tire mold having an opening;

(c) waiting a predetermined curing period Tl, said curing period Tl being the time that said material PI has begun to cure to the point where said material PI has sufficient structural integrity to withstand penetration of a second material P2;

(d) spinning said annular tire mold at a second spin rate R2;

(e) pouring said material P2 into said opening of said annular tire mold.

2. A method as recited in claim 1 further comprising the steps of: (f) waiting a predetermined curing period T2, said curing period T2 being the time that said material P2 has begun to cure to the point where said material P2 has sufficient structural integrity to withstand penetration of a material P3.

3. The method as recited in claim 1 further comprising the steps of: (g) spinning said annular tire mold at a third spin rate R3;

(h) pouring said material P3 into said opening of said annular tire mold;

(i) waiting a predetermined curing period T3 , said curing period T3 being the time that said material P3 has begun to cure to the point where said material P3 has sufficient structural integrity to withstand penetration of a material P4

4. The method as recited in claim 3 further comprising the steps of:

(j) spinning said annular tire mold at a fourth spin rate R4;

(k) pouring said material P4 into said opening of said annular tire mold;

(1) waiting a predetermined curing period T4, said predetermined curing period T4 being the time that said material P4 has begun to cure to the point where said material P4 has sufficient structural integrity to withstand penetration of a material P5. 12

5. The method as recited in claim 4 wherein said predetermined rate of revolutions Rl, R2, R3, and R4, are dependent upon relative reaction rates of said respective materials' PI, P2, P3, and P4.

6. A method for producing a non-pneumatic tire made of at least two materials, said method comprising:

(a) spinning the tire mold at a predetermined rate of revolution;

(b) pouring a material into an annular tire mold having an opening; (c) waiting a predetermined curing period, said curing period being the time said material has begun to cure to the point where said material has sufficient structural integrity to withstand penetration of another material;

(d) repeating steps (a) - (c) using another material until said tire mold is filled.

7. The method as recited in claim 5 wherein said predetermined rate of revolution is dependent upon said material's relative reaction rate.

8. The method as recited in claim 5 wherein said material in step (b) is a polyurethane elastomer.

9. The method as recited in claim 8 wherein the second material used in the first repetition of steps (a) - (c) is polyurethane foam.

10. The method as recited in claim 8 wherein said mold is a bicycle tire mold.

11. The method as recited in claim 13 wherein said step (d) is repeated only one time.

12. The method as recited in claim 14 wherein said step (d) is repeated more than one time. 13

13. The non-pneumatic tire produced according to the process of claim 1.

14. The non-pneumatic tire produced according to the process of claim 3.

15. The non-pneumatic tire produced according to the process of claim 4.

16. The non-pneumatic tire produced according to the process of claim 6.

17. The non-pneumatic tire produced according to the process of claim 8.

18. The non-pneumatic tire produced according to the process of claim 9.

19. The non-pneumatic tire produced according to the process of claim 11.

20. The non-pneumatic tire produced according to the process of claim 12.