WO2000021727A1

WO2000021727A1 - Method and apparatus for molding a tire

Info

Publication number: WO2000021727A1
Application number: PCT/US1998/021410
Authority: WO
Inventors: Gregory Lee Loney; David Chester Robek; Joseph Paul Verderico
Original assignee: The Goodyear Tire & Rubber Company
Priority date: 1998-10-09
Filing date: 1998-10-09
Publication date: 2000-04-20
Also published as: AU1187199A

Abstract

A tire mold (10) is provided which includes an upper mold section (12), a lower mold section (14) and a plurality of segments (22) pivotally and slidably connected to a plurality of mounting blocks (18) that are fixedly attached to the lower mold section. The upper mold section includes a pressure ring (13) having an upper register surface (20) that selectively engages segment register surfaces (21) of the segments (22) as the tire mold is closed. Slide biasing means (34), such as a first plunger/spring assembly biases the segments to slide toward an open, radially outward position and tilt biasing means (40), such as a second plunger/spring assembly biases the segments to tilt toward an open position. To close the tire mold, a green tire (50) is placed on the lower mold section (14) and the upper mold section (12) is lowered onto the lower mold section. As the upper mold section is lowered, the segment register surfaces (21) are engaged by the upper register surface (20) of the upper mold section (12). This engagement causes the segments (22) to move radially inward toward the green tire (50) and to both tilt and slide toward a closed position. The second plunger/spring assembly (40) is fully depressed before the segments (22) contact the green tire (50). Thus, all tilting movement is stopped before the segments (22) contact the green tire (50). Subsequently, the segments (22) slide into engagement with the green tire (50). During opening of the mold, the segments (22) are moved radially outward and then tilted away from the tire to avoid wiping damage to the tire.

Description

METHOD AND APPARATUS FOR MOLDING A TIRE

Technical Field

This invention relates to methods and apparatuses for molding tires and more specifically to a tire mold having tiltable and slidable segments and a method for using the same to mold tires.

Background Art

A mold for molding tires having an upper mold section, a lower mold section and a plurality of segments that are used in forming the tread portion of the tire is shown in U.S. Patent No. 5,190,767. Such a mold is typically referred to as a segmented mold. Typically, the segments are hinged for pivotal motion relative to the lower mold section. The upper mold section may have an upper register surface that selectively engages segment register surfaces on the segments as the tire mold is closed.

The operation of a segmented mold, in particular to close such a segmented mold, typically includes the steps of (1) placing a green (uncured or unvulcanized) tire onto the lower mold section, (2) lowering the upper mold section toward the lower mold section, (3) engaging the segment register surfaces of the segments with the upper register surface of the upper mold section, (4) pivoting the segments about pivoting means operatively connected to the mold, and (5) moving the segments into engagement with the green tire. Once the tire is fully molded (typically this means the tire has been cured) the upper mold section is raised from the lower mold section and the tire is then removed from the tire mold.

One problem known in the art is called "wiping." Wiping occurs when tread forming portions attached to the segments contact the tread portion of the green tire while the segments pivot. Wiping can create unwanted non-uniformities in the cured tire.

Another problem known in the art is the expense and complexity of systems used to close molds. It is known to use hydraulic systems (typically mounted on or near an associated curing press) to slide segments toward the green tire. Though generally effective, such systems are expensive and complex and are therefore undesirable.

Another problem known in the art is the use of elaborate guiding systems to guide segments toward the green tire. British Patent No. 1,176,162, for example, discloses segments having slots that receive guide members as the segments slide into the molding position. Special materials are used in an attempt to minimize friction as the segments slide. This patent also discloses segments having levers that come into contact with compression springs to bias the segments in an outward, or open position. Thus, the compression springs provide only indirect spring action with no contact of the springs and the segments. This indirect contact requires additional parts (such as a lever) and thus is more cumbersome and complex and is therefore undesirable.

What is needed then, is a tire mold that reduces or eliminates wiping without the use of expensive and complex mold closing systems and further without the use of elaborate guiding systems.

Disclosure of Invention

This invention is directed to a tire mold for use in molding a green or uncured tire. The tire mold includes a upper mold section, a lower mold section and a plurality of segments pivotally and slidably connected to pins mounted to a plurality of mounting blocks. The mounting blocks are fixedly attached to the lower mold section. The upper mold section includes a pressure ring having an upper register surface that selectively engages segment register surfaces of the segments as the tire mold is closed.

In accordance with one aspect of the invention, a tire mold includes an upper mold section, a lower mold section and a plurality of circumferentially positioned segments pivotally connected to a plurality of mounting blocks. The mounting blocks are attached to the lower mold section. The upper mold section having an upper register surface that selectively engages segment register surfaces on the segments to close the tire mold. The tire mold is characterized by having slide biasing means for biasing the segments to slide toward an open, radially outward position. The slide biasing means has direct contact with the segments. The tire mold is also characterized by having tilt biasing means for biasing the segments to tilt toward an open position. The tilt biasing means biasing the segments to rotate about the mounting blocks.

In accordance with another aspect of the invention, a method of closing a tire mold that includes an upper mold section, a lower mold section and a plurality of segments pivotally connected to a plurality of mounting blocks is provided. The mounting blocks are attached to the lower mold section and the upper mold section has an upper register surface that selectively engages segment register surfaces on the segments to close the tire mold. The method includes the steps of placing a green tire onto the lower mold section, lowering the upper mold section toward the lower mold section, engaging the segment register surfaces of the segments with the upper register surface of the upper mold section, and moving the segments toward the green tire to a position radially spaced from the green tire. The method is characterized by the additional steps of overcoming tilt biasing means for biasing the segments to tilt toward an open position thereby stopping tilting motion of the segments and sliding the segments radially into engagement with the green tire.

Thus, the tire mold of this invention provides full segmented mold construction yet eliminates the need for any hydraulic systems. No elaborate guiding systems are required yet, the segments of this invention engage the green tire without wiping.

Brief Description of Drawings

The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: Fig. 1 is a cross-section elevation view of this invention taken along the line 1-1 of Fig.

3 showing one of the segments in the retracted position between the upper and lower mold sections.

Fig. 2 is another cross-section elevation view taken along line 2-2 of Fig. 4.

Fig. 3 is a fragmentary plan view of the lower mold section with one of the segments removed showing the mounting block pins in the slots of the connecting arms.

Fig. 4 is a cross-section elevation view of the tire mold of Figs. 1 and 2 showing the segments fully tilted downward yet radially spaced from the green tire.

Fig. 5 is a cross-section elevation view like Fig. 4 showing the mold in a closed condition. Detailed Description of the Invention Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the invention only, and not for purposes of limiting the same, Figs. 1-5 illustrate a tire mold 10 for use in molding green or uncured tires 50. The tire mold 10 includes an upper mold section 12, a lower mold section 14 and a plurality of segments 16 pivotally and slidably connected to a plurality of mounting blocks 18. The mounting blocks 18 are fixedly attached to the lower mold section 14.

With reference to Fig. 1, the upper mold section 12 includes an integral pressure ring 13 having an upper register surface 20 that selectively engages segment register surfaces 22 of the segments 16 as the tire mold 12 is closed. The pressure ring 13 is concentric for 360° contact with the segments 16 thereby providing full surface pressure to the segments 16. A bronze weld 21 may be added to the surface of the pressure ring 13 to assure minimal friction during closure of the tire mold 10. As shown, the upper register surface 20 has a surface angle B with respect to the axis 46 of the upper mold section 12. This is illustrated by showing angle B with respect to a line 47 that is parallel to the axis 46. It should be noted that since it is preferred that the lower mold section 14 be positioned coaxial with the upper mold section 12, the axis line 46 also represents the axis of the lower mold section 14. Surface angle B may be an acute angle and is preferably within the range of 10° to 40°. Before significant pressure is exerted on the segments 16 by the upper mold section 12

(the condition shown in Fig. 1), the segment register surface 22 has a surface angle C with respect to the axis line 46 (shown with respect to line 47). This surface angle C is greater than the surface angle B and for this reason the segments 16 rotate about later to be described pins 30 as the upper mold section 12 closes. The greater the difference between surface angles B and C, the greater the rotation of the segments 16 about the pins 30 for any given amount of downward travel of the upper mold section 12. Preferably surface angle C is at least 3 ° greater than surface angle B. The segments 16 also slide toward a closed, radially inward position (shown by arrow 27 in Figs. 1 and 3) as the upper mold section 12 closes. The maximum radially inward distance that a segment 16 can travel is the length of later to be described slot 62. The upper register surface 20 preferably has a length equal to the length of the segment register surface 22 which permits the segments 16 to move the full travel length inwardly before the upper mold half 12 fully closes. Thus, the segments 16 are moved in two stages. During the first stage, the segments 16 both tilt (rotate) about the pins 30 and slide inwardly. Due to the surface angles B and C described above, the segments 16 complete the tilting before they complete the sliding. Thus during the second stage, the segments 16 only slide inwardly toward the tire. In this way wiping is eliminated.

With reference now to Fig. 1, the tire mold 10 includes slide biasing means, such as first plunger/spring assembly 34, for biasing the segments 16 to slide toward an open, radially outward position, that is toward outward direction 26. Similarly, as shown in Fig. 2, tilt biasing means, such as second plunger/spring assembly 40, biases the segments 16 to tilt toward an open position, that is to pivot about pins 30 in a clockwise direction 32 as shown in Fig. 2. The first and second plunger/spring assemblies 34, 40 assist the unloading of cured tires and hold the segments 16 in a specified angle for loading of a green tire 50 as will be discussed further below. The first plunger/spring assembly 34 includes at least one first plunger 36 that receives a first spring 38 preferably within a first bore 48 in the lower mold section 14 as shown. As shown in

Fig. 2, the second plunger/spring assembly 40 is similarly constructed having at least one second plunger 42 that receives a second spring 44 within a second bore 52. Preferably the first plunger/spring assembly 34 includes one first plunger 36 that receive one first spring 38 within one first bore 48 respectively. The second plunger/spring assembly 40 includes two second plungers 42,42 that receive two second springs 44,44 within two second bores 52,52 respectively. Although the first and second plungers 36,42 can be made of any material chosen with sound engineering judgement, it is preferred that they be formed having bronze coatings to allow smooth, non-friction sliding of the segments 16 as will be discussed further below.

With continuing reference to Figs. 1-2, the first and second springs 38,44 have predetermined spring rates chosen to properly bias the segments 16 depending on the size of the tire mold 10 and thus also depending on the size of the segments 16. It should be noted that the first and second plunger/spring assemblies 34, 40 have direct contact with the segments 16. In other words, the first plunger 36 directly contacts a later to be described biasing surface 64, and the second plunger 42 directly contacts a later to be described bottom slide surface 58.

Still referring to Figs 1, 2 and 3, each of the segments 16 preferably includes a main body 54 and a pair of connecting arms 56,56. The main body 54 includes a segment register surface 22 and a bottom slide surface 58 for selective sliding engagement with the second plungers 42,42.

The bottom slide surface 58 is substantially perpendicular to the axis 46 just before the tire mold 10 is fully closed. This will be discussed further below. The main body 54 selectively receives tread inserts 60 that are used to form a particular tread pattern on the green tire 50. The tread inserts 60 are well known in the art and thus will not be discussed in detail here. The connecting arms 56,56 are preferably integral parts of each segment 16. Each of the connecting arms 56 has a slot 62 for rotatably and slidably receiving the pin 30. Each connecting arm 56 may also have a stop region 70 (called "a stop") that contacts the lower mold section 14 and prevents further rotation of the segments 16 about the pins 30. The connecting arms 56,56 also have biasing surfaces 64,64 for selective contact with the first plungers 36,36. Preferably, each biasing surface 64 is substantially parallel with the upper register surface 20 when the segment 16 is fully tilted down.

As seen in Figs. 1 and 3, an axis 29 of the second plunger/ spring assembly 40 is aligned substantially parallel to the axis of the lower mold section 14 and thus with the axis line 46. In this way the second spring and plunger 44, 42 provide maximum tilt bias (the axis 29 of the second plunger/spring assembly 40 is also aligned substantially perpendicular to an axis 31 of the pin 30) to the segment 16 while simultaneously providing the desired sliding friction surface (the bronze coated tip of the second plunger 42) for the segment 16. As shown in Fig. 1, the first plunger/spring assembly 34 has an axis 25 that is aligned at a slide angle A with respect to the axis line 46 (and thus also with respect to the axis 29 of the second plunger/spring assembly 40 which is parallel to the axis 46). The slide angle A should be within the range of 0° and 90°. If, however, the slide angle A is 0°, then the first plunger/spring assembly 34 would not provide any slide biasing force (that is, in radially outward direction 26) to the segment 16. Furthermore, if the slide angle A is 90°, then the first plunger/spring assembly 34 would provide only a slide biasing force in radially outward direction 26. It is preferred that the first plunger/spring assembly 34 provide a significant slide biasing force in an outward direction 26 as well as a significant tilting force (that is a force that biases the segment 16 to tilt or rotate about the pin 30) to the segment 16. Thus, it is preferred that the slide angle A be within the range of 5° and 85°.

With reference now to Figs. 1, 2 and 3, each mounting block 18 has an opening 66 for rotatably receiving a pin 30. The opening 66 therefore permits each segment 16 to tilt or rotate about the pin 30. The slot 62 in each connecting arm permits each segment 16 to tilt or rotate about the pin 30 and also permits each segment 16 to be moved in the radially inward direction 27 and in the radially outward direction 26. The slot 62 has a centerline 68 that is positioned substantially perpendicular to the axis line 46. Therefore, the segments 16 can only slide in the inward and outward directions 27,26.

In an alternate use of this invention, the tire mold 12 may be used in an upside-down configuration. This has shown to have an advantage for large tires requiring segments 16 that are too long to allow an unloader mechanism (not shown) to come in to remove the cured tire.

In this case, a combination of the pins 30, the slots 62 and the stops 70 keep the segments 16 from opening past the center of gravity.

With reference now to Figs. 1, 2, 3, 4 and 5, the operation of the inventive tire mold 10 will now be discussed. To close the tire mold 10, a green tire 50 is placed onto the lower mold section 14. The upper mold section 12 is then lowered toward the lower mold section 14. As the upper mold section 12 is lowered, each of the segment register surfaces 22 is engaged by the upper register surface 20 of the pressure ring 13. This engagement causes each segment 16 to move toward the green tire 50. As the segments 16 are moved, they tilt radially inward toward a closed position (that is they rotate or pivot in counter-clockwise direction 33 about the pins 30) and they slide toward a closed, radially inward position in the inward direction 27.

Fig. 4 shows that the second plunger/spring assembly 40 is fully depressed before the tread inserts 60 contact the green tire 50. Thus, all tilting movement (that is rotative or pivotal movement about the pins 30) is stopped before the segments 16 contact the green tire 50. Subsequently, the segments 16 slide radially in the inward direction 27 only, into engagement with the green tire 50. During this sliding, the bottom slide surface 58 slides against the depressed second plunger 42 which is preferably coated with bronze to prevent damage to the plunger. It should be noted that each segment 16 of this invention is properly positioned with respect to its neighboring segments such that all the segments are movable toward the green tire 50 simultaneously and in proper alignment. With this positioning no gaps between segments 16 are created. Thus, no "flash" is produced on the finished or cured tire. Once the tire mold 12 is fully closed the green tire 50 is cured or vulcanized. With reference to Figs. 1-5, once the green tire 50 is cured, the tire mold 12 is opened.

In particular, the upper mold section 12 is raised away from the lower mold section 14. As the upper mold section 12 is lifted, the upper register surface 20 of the pressure ring 13 comes out of engagement with the segment register surfaces 22 of the segments 16. This frees the segments 16 to be moved as forced by the first and second plunger/spring assemblies 34, 40. Generally, however, the now cured tire is sufficiently attached (though the tread) to the segments 16 so that the segments 16 remain unmoved by the first and second plunger/spring assemblies 34, 40. Next, tire lift means (not shown) are used to lift the now cured tire away from the lower mold section 14 and away from the segments 16. As the cured tire 50 is being removed, the segments 16 tilt in clockwise direction 32. Once the cured tire 50 is fully removed from the tire mold 10, the segments 16 rebound (that is, they are tilted or pivoted by gravity in counter clockwise direction

33). The segments 16 then contact the first and second plunger/spring assemblies 34, 40 which act as rebound protection for the segments 16. In this way, the segments 16 are protected from damage.

Thus, the tire mold 10 of this invention provides full segmented mold construction yet eliminates the need for any hydraulic systems. No elaborate guiding systems are required yet the segments 16 of this invention engage the green tire 50 without wiping. It should also be noted that generally speaking, when it comes to tire molds, "the smaller the better" due to limited press sizes available. The simplicity of the tire mold 12 of this invention allows for the smallest possible diameter for the tire mold 12. The invention has been described with reference to preferred embodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alternations in so far as they come within the scope of the appended claims or the equivalence thereof. Having thus described the invention, it is now claimed:

Claims

1. A tire mold including an upper mold section, a lower mold section and a plurality of circumferentially positioned segments pivotally connected to a plurality of mounting blocks, the mounting blocks being attached to the lower mold section, the upper mold section having an upper register surface that selectively engages segment register surfaces on the segments to close the tire mold, the tire mold being characterized by: slide biasing means for biasing the segments to slide toward an open, radially outward position, the slide biasing means having direct contact with the segments; and, tilt biasing means for biasing the segments to tilt toward an open position, the tilt biasing means biasing the segments to rotate about the mounting blocks.

2. The tire mold of claim 1 wherein said tilt biasing means has direct contact with said segments.

3. The tire mold of claim 2 wherein said slide biasing means comprises a first plunger/spring assembly and said tilt biasing means comprises a second plunger/spring assembly.

4. The tire mold of claim 3 wherein said first and second plunger/spring assemblies are positioned within first and second bores in said lower mold section.

5. The tire mold of claim 1 wherein said tilt biasing means is aligned substantially parallel with the axis of the lower mold section and said slide biasing means is aligned at a slide angle A with respect to the axis of the lower mold section, said slide angle A being within the range of 5 degrees and 85 degrees.

6. The tire mold of claim 5 wherein each segment has a main body and a pair of connecting arms, said main body having a bottom slide surface for selective sliding contact with said tilt biasing means, said connecting arms each having a biasing surface for selective contact with said slide biasing means, said bottom slide surface being substantially perpendicular to said axis of said lower mold section before said mold is closed, said biasing surface being substantially parallel with said upper register surface of said upper mold section.

7. The tire mold of claim 6 wherein said slide biasing means and said tilt biasing means selectively contact said segments thereby providing rebound protection for said segments.

8. The tire mold of claim 1 wherein said mounting blocks have pins disposed in slots in said segments and said segments being selectively slidable on said pins.

9. The tire mold of claim 8 wherein said slots have center lines positioned substantially perpendicular to the axis of the lower mold section.

10. The tire mold of claim 1 wherein the upper register surface has a surface angle B with respect to the axis of the upper mold section and the segment register surface has a surface angle C with respect to the axis of the upper mold section, the surface angle C being greater than the surface angle B.

11. A method of closing a tire mold that includes an upper mold section, a lower mold section and a plurality of segments pivotally connected to a plurality of mounting blocks, the mounting blocks being attached to the lower mold section, the upper mold section having an upper register surface that selectively engages segment register surfaces on the segments to close the tire mold, the method including the steps of placing a green tire onto the lower mold section, lowering the upper mold section toward the lower mold section, engaging the segment register surfaces of the segments with the upper register surface of the upper mold section, and moving the segments toward the green tire to a position radially spaced from the green tire, the method being characterized by the additional steps of: overcoming tilt biasing means for biasing the segments to tilt toward an open position thereby stopping tilting motion of the segments; and, sliding the segments radially into engagement with the green tire.

12. The method of claim 11 wherein, before the step of overcoming tilt biasing means for biasing the segments to tilt toward an open position thereby stopping tilting motion of the segments, the method comprises the step of: pivoting the segments about pins mounted on the mounting blocks.

13. The method of claim 11 wherein the segments have slots for rotatably receiving pins that rotatably receive the segments, the step of sliding the segments radially into engagement with the green tire, comprises the step of: sliding the segments within the slots.

14. The method of claim 11 wherein the segments have main bodies with bottom slide surfaces, the step of sliding the segments radially into engagement with the green tire, comprises the step of: sliding the bottom slide surfaces across said tilt biasing means.