Mold and Method for Molding Double Curved Elements of Elastomeric Material

Abstract

A mold for a longitudinal element of elastomeric material has a housing including at least one longitudinal inner cavity extending between at least two opposing main walls and two opposing edge walls. The main walls of the cavity have elevations extending and sloping both laterally and longitudinally of the cavity, and depressions extending and sloping both laterally and longitudinally of the cavity. Further, an elevation of one wall is opposite to a depression of the other wall.

Claims

1-13. (canceled)

14. A mold for a longitudinal element of elastomeric material, comprising: a housing (1, 2) including at least one longitudinal inner cavity (3) extending between at least a first main wall (4) and an opposing second main wall (5) and between a first edge wall (6) and second edge wall (7), wherein the main walls (4, 5) have elevations (8) wherein each elevation (8) extends and slopes both laterally and longitudinally relative to the cavity (3), and depressions (9) wherein each depression (9) extends and slopes both laterally and longitudinally relative to the cavity (3), the elevations (8) and depressions (9) are arranged alternating along a length of the mold, and an elevation (8) of the first main wall (4) is opposite a depression (9) of the second main wall (5).

15. The mold according to claim 14, wherein the elevations (8) and depressions (9) are arranged adjacent each other.

16. The mold according to claim 15, wherein each of the main walls (4, 5) has one elevation (8) or depression (9) in a lateral direction and multiple elevations (8) and depressions (9) alternating in a longitudinal direction.

17. The mold according to claim 14, wherein each of the main walls (4, 5) has one elevation (8) or depression (9) in a lateral direction and multiple elevations (8) and depressions (9) alternating in a longitudinal direction.

18. The mold according to claim 14, wherein each elevation or each depression or both have a gradual slope and a rounded top.

19. The mold according to claim 14, wherein the elevations (8) and depressions (9) have identical forms and sizes, only extending in opposite directions of the mold from one another.

20. The mold according to claim 14, wherein a distance across the cavity (3) between the opposite edge walls (6, 7) is smaller at a bottom of a depression (9) or at a top of an elevation (8) of the main walls (4, 5), and larger at a transition between an elevation and depression, and the distance between the edge walls (6, 7) along a surface of a main wall is constant.

21. The mold according to claim 15, wherein a distance across the cavity (3) between the opposite edge walls (6, 7) is smaller at a bottom of a depression (9) or at a top of an elevation (8) of the main walls (4, 5), and larger at a transition between an elevation and depression, and the distance between the edge walls (6, 7) along a surface of a main wall is constant.

22. The mold according to claim 17, wherein a distance across the cavity (3) between the opposite edge walls (6, 7) is smaller at a bottom of a depression (9) or at a top of an elevation (8) of the main walls (4, 5), and larger at a transition between an elevation and depression, and the distance between the edge walls (6, 7) along a surface of a main wall is constant.

23. The mold according to claim 14, wherein the housing comprises at least two parts (1, 2) which may be moved in relation to each other to create access to the cavity (3) in the housing.

24. The mold according to claim 17, wherein the housing comprises at least two parts (1, 2) which may be moved in relation to each other to create access to the cavity (3) in the housing.

25. The mold according to claim 14, wherein the longitudinal element (23) is a tire tread.

26. A method for forming a longitudinal element (23) of elastomeric material, comprising (a) providing a mold according to claim 14, wherein the mold comprises at least two parts (1, 2); (b) providing entrance to the cavity (3); (c) placing elastomeric material into the cavity; (d) moving the at least two parts (1, 2) of the mold in relation to each other to provide access to the cavity; and (e) removing the longitudinal element (23) from the cavity (3).

27. The method according to claim 26, further comprising one or more of pressurizing, heating and cooling the mold between steps (c) and (d).

28. The method according to claim 27, wherein step (b) comprises a sub-step of moving the at least two parts (1, 2) of the mold apart from each other, further comprising an additional step of moving the parts (1, 2) of the mold towards each other to close the cavity (3) after step (c).

29. The method according to claim 26, wherein step (b) comprises a sub-step of moving the at least two parts (1, 2) of the mold apart from each other, further comprising an additional step of moving the parts (1, 2) of the mold towards each other to close the cavity (3) after step (c).

30. The method according to claim 26, wherein the method further comprises a delay between steps (d) and (e).

31. A longitudinal elastomeric element (23) having at least one curvature in a longitudinal direction and at least one curvature in a lateral direction, wherein the element is molded in a mold according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The invention will in the following be described with reference to the enclosed illustrative figures that are not necessarily to scale, where

[0064] FIG. 1A shows a part of a mold according to the disclosure,

[0065] FIG. 1B shows a part of another mold according to the disclosure,

[0066] FIG. 2 shows a segment of the mold in FIG. 1A, from above with contour lines, FIG. 3 shows a lateral cross section of another embodiment of a mold according to the disclosure,

[0067] FIG. 4 shows a longitudinal cross section of the mold shown in FIG. 3,

[0068] FIG. 5 shows a cross section of the mold shown in FIGS. 3 and 4, the cross section is parallel to the top and bottom of the mold,

[0069] FIG. 6 shows a segment of an element molded in the mold shown in FIG. 3-5, in perspective,

[0070] FIG. 7 shows a segment of an element molded in the mold shown in FIGS. 1A-5, from a side, and

[0071] FIG. 8 shows a segment of the element in FIG. 7, after depressions are inverted.

DETAILED DESCRIPTION

[0072] FIGS. 1A-5 show different embodiments of a mold for molding a longitudinal double curved element of elastomeric material, such as a tire tread. FIG. 1B shows an embodiment for molding several longitudinal double curved elements simultaneously. FIGS. 6-8 show a tire tread being molded in a mold such as shown in FIGS. 1A and 1B. For clarity reasons, identical or similar parts of the mold are given the same reference number in all embodiments.

[0073] All embodiments of the mold comprise a housing of two parts 1, 2, wherein the two parts may be removed from each other. The housing has a flat base and top, and includes a longitudinal cavity 3 extending between two opposing main walls 4, 5 and two opposing edge walls 6, 7, wherein one main wall 4, 5 is arranged on each part 1, 2 of the housing, and thereby access to the cavity 3 is created by moving the parts 1, 2 away from each other. The main walls 4, 5 have elevations 8 and depressions 9 extending both laterally and longitudinally of the cavity 3, wherein one elevation 8 or depression 9 is arranged in lateral direction, and several elevations and depressions are arranged alternating adjacent to each other in longitudinal direction. The elevations 8 and depressions 9 of one main wall 3 is opposite to the elevations 8 and depressions 9 of the other wall 4, giving the cavity 3 between the main walls a wavy shape in longitudinal direction.

[0074] In the shown embodiments, one of the main walls 4 have recesses and holes 10 to create a pattern 30 on a tire tread 23 being molded therein, wherein the pattern 30 will improve the grip once the tire tread 23 is mounted on a wheel.

[0075] FIG. 1A and b shows a part 2 of the housing of the mold, removed from the other part 1. The part is shown in perspective, with the main wall 4 facing upwards. The main wall 4 of the shown part 2 includes protrusions and recesses, and will give the element a pattern 30 of grooves and sipes on one side, for a good grip once the element is mounted on a tire. The shown part in FIG. 1A has one cavity with three elevations 8 and three depressions 9 in longitudinal direction, each elevation and depression extends along the whole lateral direction of the cavity.

[0076] The shown part in FIG. 1B have three cavities, each having four elevations 8 and four depressions 9 in longitudinal direction, each elevation and depression extends along the whole lateral direction of the cavity. The cavities are separated from each other by edge walls 6, the height of the edge walls 6 correspond in the shown embodiment with the height of the cavity, and any elements formed therein will be removed from the mold as separate elements.

[0077] FIG. 2 shows a section of the mold in FIGS. 1A and 1B, from above, and contour lines are added to indicate the gradient of the slope of the elevation 8 and depression 9. As can be seen from the contour lines, each elevation and depression has a slope in the lateral direction as well as in the longitudinal direction. Depressions and elevations are arranged alternating and adjacent to each other in longitudinal direction, and in the transition from elevation to depression and vice versa, there will be a transition line with no elevation in either direction. A transition line is indicated in FIG. 2 as C-C.

[0078] Further, in any longitudinal plane taken through a mold shown in the Figures, such as indicated by A-A in FIG. 2, each elevation and depression is symmetrical about a line running through its highest or lowest point. Each elevation and depression is also symmetrical about a line running through its highest or lowest point, in any lateral plane taken through the mold, for instance as indicated by B-B in FIG. 2. The average gradient of the elevations and depressions is not identical in the longitudinal and lateral direction, as the lateral and longitudinal curvature of the element to be molded are not identical.

[0079] In the shown embodiment, the opposing edge walls 6, 7 of the cavity are closer to each other at the bottom of a depression or at the top of an elevation of the main walls, and further from each other at the transition between elevation and depression. This is shown in FIGS. 1A and 1B as the walls 6, 7 curves along the longitudinal direction. This is also shown in FIG. 2, wherein the edges of the section are closer along line B-B which is at the top/bottom of an elevation/depression than along line C-C which is at a transition between an elevation/depression. As the distance between the edge walls 6, 7 varies, the distance between the edge walls along the surface of the main wall will be constant.

[0080] FIG. 3 shows a lateral cross section of a mold, wherein the two parts 1, 2 of the housing are arranged in relation to each other and encloses the cavity 3. A lateral cross section is also referred to as a cross section in XY plane. Each elevation 8 or depression 9 extends along the whole lateral direction of the cavity, that is from edge wall 6 to edge wall 7, and thus the lateral cross section has the form of an arc. In FIG. 3 it is shown that the main wall 4 of part 2 has a number of recesses and holes 10, to create a pattern on the tire tread.

[0081] FIG. 4 shows a longitudinal cross section of a part of a mold, wherein the two parts 1, 2 of the housing are arranged exploded, that is in distance to each other. A longitudinal cross section is also referred to as a cross section in YZ plane. As several elevation 8 and depression 9 are arranged alternating and adjacent to each other along the longitudinal direction of the cavity, the cross section has the form of an wave.

[0082] Further on FIG. 4, it is shown that the edge wall 6 is a part of a side wall 11 of one part 2 of the housing. The other part 1 has a protruding flange 12, to be supported by the side wall 11 once the mold is mounted. The height of the edge wall 6, and thus the thickness of the cavity 3, will be given by the design of the side wall 11 and flange 12, as will be obvious to a skilled person. When a tire tread should be molded in the mold, upper part 1 is removed, elastomeric material is added, part 1 is replaced, and pressure is added on top of part 1, until the flange 12 rest upon the side wall 11.

[0083] FIG. 5 shows a cross section along a 0 plane for the cavity, also referred to as the xz plane. As the cavity has the form of an arc in lateral section, and a wave in the longitudinal section, a cross section in the xz plane shows an elevation 8 of one part 1 of the mold, (the upper part in FIG. 5) as well as a depression 9 of the other part of the mold 2, wherein the elevation 8 is arranged above, and partly in, the depression 9.

[0084] A tire tread 23 molded in the cavity 3 of a mold according to FIG. 1A, 1B or 2 is shown in FIGS. 6 and 7, wherein FIG. 6 shows a section of the tire tread 23 in perspective from above, and FIG. 7 shows the tire tread from one side. The tire tread 23 will have a wavy form with elevations 28 and depressions 29 in longitudinal direction, and a pattern 30 on one side.

[0085] When the tire tread is to be used, the depressions 29 should be pressed from the lower side and upwards, as indicated by an arrow in FIG. 7, until they are inverted. Due to elastic properties of the material of the tire tread, this inverting procedure is possible. A small amount of strain energy may still be persistent after inverting, mainly due to the fact that the article does not have zero thickness. Then the tire tread will curve as shown in FIG. 8. For clarity reasons, the tire tread 23 in FIG. 8 is shown with an even surface, that is without pattern 30.

[0086] Once the depressions 29 of the tire tread 23 are inverted, it will be double curved, having a radius r in lateral direction, and radius R in longitudinal direction. The radii r and R are determined among other things by the slope of the elevations and depressions in lateral direction and longitudinal direction of the cavity. The gradient of the slopes are indicated by the contour lines in FIG. 2. As the distance between the edge walls across the cavity varies, but the distance between the edge walls along the surface of the main walls is constant, the lateral distance from one edge of the element to the other, once the depressions are inverted, is constant. This is shown as a constant side edge 27, 27 in FIG. 8.

[0087] As shown in FIGS. 7 and 8, any segment Ax with longitudinal length Z of the element yields a corresponding segment Bx of the double curved element with angle W after any depressions are inverted, where angle W and length Z is proportional.

[0088] In the shown figures, the shape of the elevations are identical to the depressions. However, in an alternative embodiment, the shapes may be different, but the shape of any elevation or depression may be such as to yield a segment of the desired double curved shape, meaning that if a segment Ax is defined as between the transition into an elevation or depression and the transition out of the same elevation or depression, the segment would correspond to any segment Bx of a double curved shape with Angle W proportional to longitudinal length Z of Ax.

[0089] A double curved shape with radius R can as such be obtained with elevations and depressions of varying amplitudes and wavelengths by adjusting the number of elevations and depression on the element in total.

[0090] When a mold as shown in FIGS. 1A-5 should be used to mold a tire tread as shown in FIG. 6-8, a part 1 of the housing is removed from part 2, to provide entrance to the cavity 3. A suitable amount of elastomeric material is then be added to the cavity, before the first part 1 is replaced, closing the access to the cavity. Once the cavity is closed, pressure should be added, preferably on top of part 1, until the flange 12 of part 1 is resting against the side wall 11 of the lower part 12. The pressure may be about 16 MPa, preferably exerted by a hydraulic force. After a predetermined time, part 1 is removed again to provide access to the cavity, and the molded tire tread may be removed. The curing or hardening time may for instance be about 5-15 minutes, depending on the elastomeric material. Even if the method is described above with reference to one cavity, the same applies if the housing comprises more cavities.

[0091] The example above is given to illustrate the invention and should not be used to interpret the following claims limiting. The scope of the invention is not limited by the example give above, but the following claims. Modifications and amendments of the invention, being obvious to a person skilled in the art, should also be included in the scope of the invention.