WO1999048674A1

WO1999048674A1 - A casting model and a method in the manufacture of a casting model

Info

Publication number: WO1999048674A1
Application number: PCT/FI1999/000202
Authority: WO
Inventors: Jalo Pirhonen
Original assignee: Tp-Tools Oy
Priority date: 1998-03-23
Filing date: 1999-03-17
Publication date: 1999-09-30
Also published as: AU2936499A; FI980646A; FI980646A0

Abstract

The invention relates to a casting model for the manufacture of a segment to be fitted into a ring-shaped mould, the casting model (1) comprising at least a pattern surface (2) which is preferably equipped with pattern parts (2a-2d). The pattern surface (2) of the casting model (1) is arranged to be formed by means of at least two model elements (4a-4d), and the casting model (1) is arranged to be used also in the manufacture of another segment by changing the respective order of the model elements (4a-4d), by removing at least one model element (4a-4d), by adding at least one model element (4a-4d), by exchanging at least one model elements (4a-4d), or by performing a combination of any of said alternatives. The invention relates also to a method in the manufacure of the casting model.

Description

1

A casting model and a method in the manufacture of a casting model

The present invention relates to a casting model as will be set forth in the preamble of claim 1. The invention relates also to a method in the manufacture of a casting model as will be set forth in the preamble of claim 7.

In a known way, in the manufacture of tyres, such as automobile tyres, annular moulds of aluminium are used, comprising mould parts to form the pattern of the tread band of the tyre and the side surface of the tyre in connection with vulcanization. One tyre mould is presented in the publication US 4,411 ,175, in which a tyre mould made of metal consists of several arch-like segments to form the surface pattern of the tyre in connection with vulcanizing. In said publication, the different segments of the tyre mould are formed from an annular solid mould by cutting. The different segments are formed to enable vulcanizing, wherein for removing the vulcanized tyre from the tyre mould, the different segments are arranged to be movable in the radial direction of the tyre mould and to be assembled against each other in the closed position of the tyre mould according to publication US 5,290,163. Normally, also air channels are provided in or between the segments to remove gases in connection with vulcanizing. Furthermore, the tyre mould can be provided with two segments dividing the pattern surface of the tyre in its transverse direction in accordance with publication US 5,261 ,804. Thus, the pattern surface is normally divided into two substantially symmetrical parts. These segments are arranged movable in relation to each other both in the radial direction of the tyre mould and in the direction transverse to the radius, to open the tyre mould.

According to publication US 5,290,163, the segment of a tyre mould made of metal is made by means of identical parts substantially transverse to the direction of rotation of the type, the parts being fitted to each other and fixed to a body to form one uniform segment. Publica- tion US 5,261 ,804 presents a segment which is further divided by cuttings parallel to the running direction into smaller parts to arrange air channels between these joined parts, to facilitate the removal of gases 2 from the mould during vulcanizing of the rubber mixture. For the manufacture of one tyre mould, typically 8 to 10 arch-like segments are made. Consequently, one segment corresponds to a section of about 45° (8 pieces) or 36° (10 pieces) of the circumference of the tyre mould. If each segment consists of 4 to 6 separate parts according to the above-mentioned publications, a total of 32 to 60 such parts must be made for one tyre mould. Furthermore, these parts must be fitted to each other and to the body, and fixed to the body to assemble the segments.

A uniform segment for a tyre mould is manufactured in the following way, known as such. For each area corresponding to a segment in the circumferential pattern surface of the tyre to be manufactured, an archlike casting model is made usually of plaster. The casting model is used to make a positive model of substantially natural size, i.e. a model corresponding to the final shape of the pattern surface of the tyre to be manufactured, with its details and markings. The lateral surface of the tyre usually comprises few details and only standardized markings, wherein the mould part forming the pattern for this lateral surface is made simply of a ring-shaped piece. In this ring-shaped piece, the markings are made e.g. by engraving with an engraving machine. For vulcanizing the tyre rubber mixture, the ring-shaped mould parts are arranged to be movable in the direction of the rotation axis of the tyre and to be assembled against said segments.

The pattern surface of the tyre consists of narrow lamella slots, normally of depressions having the width of several millimetres and of wider ridges which further make up pattern elements recurring in the tyre pattern surface in the direction of its circumference. A correspond- ing pattern surface can be formed in the casting model by engraving it entirely manually in accordance with publication US 4,56,737, but normally an engraving machine is used to make the casting model and the pattern surface of the casting model is finished manually. The finishing is necessary e.g. to make sharp edges in the depressions and to finish the inclinations of different planar surfaces in the pattern surface. 3

The fabricated casting model is utilized in the next step to cast a model of silicone-treated rubber, which constitutes a negative model of the tyre surface pattern by means of the casting model. The model of silicone-treated rubber reproduces the details of the pattern surface of the casting model. Depressions in the model of silicone-treated rubber correspond to ridges in the casting model, and the model of silicone- treated rubber constitutes a concave model of the arched and convex pattern surface of the casting model. In connection with the casting, the silicone-treated rubber is normally also equipped with a plastered backing element to support the model of silicone-treated rubber and to facilitate its handling.

The fabricated model of silicone-treated rubber is utilized in the next step to produce a core for casting a segment of the tyre mould. The core is normally made of plaster by casting with the model of silicone- treated rubber. The core reproduces the shape of the pattern surface of the casting model in a positive model, to make it possible to manufacture the part, i.e. segment, of the permanent mould constituting the negative model for the tyre pattern surface by casting in aluminium. Each core for casting the segment is only used once, wherein a new core must be fabricated to cast a similar segment for another tyre mould.

The model of silicone-treated rubber is used for making several seg- ments for the same tyre mould or similar segments for different tyre moulds. If necessary, several models of silicone-treated rubber are made by using the same casting model, if several cores are made for casting a segment and each model of silicone-treated rubber can only be used a limited number of times, due to its wearing.

For example, to reduce noise caused by a vehicle tyre when rotating on a ground, the tyre pattern surface must be provided with an irregular pattern. Moreover, noise is affected by details in the pattern and the rubber mixture used. To reduce noise, it is necessary to e.g. alternate the width of the different pattern parts in the pattern surface and to place these formed alternating pattern parts irregularly on the circumference of the tyre, as presented e.g. in publication US 5,223,065. 4

Regularly alternating patterns of the pattern surface or tyre shapes cause noise at different frequencies. As a result, to manufacture segment parts of a tyre mould for a modern tyre, it is necessary to produce a corresponding number, typically 8 to 10, of casting models engraved of plaster in the way described above, the details of the pattern surfaces varying from each other.

Considering the demands set on the noise properties and behaviour of different tyre models e.g. under snow and water conditions, the pattern parts of the pattern surface become more complex, and the total number of different pattern parts in one tyre increases correspondingly. At present, the total number of pattern parts in a tyre is typically ca. 60. Because different pattern parts do not always occur in the same order in the tyre circumference, also the segments of the tyre mould differ from each other, wherein a separate casting model must be made for each one. Furthermore, a model of silicone-treated rubber is further cast of each casting model in the way presented above, to produce a core for casting each segment and further to produce the segment.

However, there are several considerable drawbacks in the production of a casting model for a segment and particularly in the production of several different casting models. The checking and finishing of casting models made manually or by an engraving machine takes a lot of time, for example to finish the radii of curvature in their depressions and ridges, to form the sharp edges required e.g. in the depressions, to finish the narrow slots formed for lamella plates, to check the diameter dimension of the pattern surface of the casting model, to check the radii of curvature in the pattern surface of the casting model, to rub the surfaces in different directions on the pattern surface, and to check the compatibility of the different casting models, at least with respect to their dimensions and radii of curvature. On the basis of what is presented above, it is obvious that the production of several different casting models for one tyre mould multiplies the required work stages, thereby increasing the time required for the production of the tyre mould and considerably increasing the production costs. Furthermore, it is obvious that in manufacturing of long duration, a deviation in the production conditions, e.g. a change in the settings of the engraving 5 machine or the wear of the working blades, causes quality differences even in the casting models of the same tyre mould.

The tyre pattern surface is normally equipped with also very narrow slots whose width is even less than 1 mm. The production of these slots in the tyre in connection with the vulcanizing is arranged in a way that the core for casting is equipped with straight or bent sheet pieces which are usually made of metal and extend from the pattern surface of the core. Consequently, the protruding parts of these metal lamellae substantially correspond to the lamella slots formed in the finished tyre. The protrusion of the metal lamella from the pattern surface corresponds substantially to the depth of the final lamella slot. Also the casting model must be provided with the lamella slots and equipped with the metal lamellae, which in connection with casting of the model of silicone-treated rubber form a slot in the corresponding location in the model. Before the casting of the core, new lamellae are inserted in these slots, to extend from the pattern surface of the model of silicone- treated rubber and to adhere to the core in connection with its production. When the model of silicone-treated rubber is removed from the finished core for casting, the metal lamellae are detached from the silicone-treated rubber and remain attached to the core.

When several different casting models are produced to form segments, the above-mentioned metal lamellae must be produced and fixed to each casting model and finished, and the lamella slots of each casting model must be sealed to fix the metal lamellae. This increases further the amount of work and the costs caused, as well as the number of metal lamellae needed.

It is an aim of the present invention to eliminate the above-mentioned drawbacks in the process of manufacturing the tyre mould, as well as to speed up the production time and to reduce the production costs. It is a particular aim of the invention to present a casting model of a novel principle to manufacture a segment for a tyre mould. The casting model of the invention is characterized in what will be presented in the characterizing part of the appended claim 1. The method of the invention in the manufacture of a casting model is characterized in what will be pre- 6 sented in the characterizing part of the appended claim 7. It is an essential principle in the casting model of the invention that the casting model is formed by means of attachable and exchangeable model elements, which make up the pattern surface of the casting model.

Several considerable advantages are achieved when using the casting model according to the invention. The number of pattern parts of the pattern surface to be produced and finished is decreased considerably, when each model element makes up one pattern part. In an advantageous embodiment of the invention, to form a total of 60 pattern parts of the entire pattern surface, only about 15 different model elements must be produced in order to take e.g. the irregularity of the pattern surface sufficiently into account to prevent noise. Thus, according to the invention, considerably fewer pattern parts must be finished than in prior art, i.e. only 15 different model elements with the details involved. In this case, according to prior art, a total of about 9 different casting models must be produced, and a total of 60 pattern parts in them must be engraved and finished each one separately, even though the same pattern part would alternate in another location in the pattern surface of the tyre.

In a known manner, casting models with their pattern parts are designed graphically by using 3D modeling and a computer. It is an advantage of the invention that also the work in designing the casting models is accelerated. In one case, the costs on design work were found to decrease by as much as 40 %.

Another advantage of the invention is that the costs on the design and production of tyre prototypes are reduced and the manufacture of proto- types e.g. for testing is accelerated considerably. A further considerable advantage of the invention is that it is easy to produce casting models with varying orders of pattern parts, for example to check the properties of tyre prototypes. Also, the order of the model elements can be changed without redesigning and production of a casting model, even by selecting the order of the model elements randomly. Another advantage is that it is possible in the manufacturing process to change the order of the pattern parts in a desired manner at a considerably later 7 stage than by using a casting model of prior art, wherein it is no longer possible to change the pattern parts after the casting model has been made. Furthermore, it is a considerable advantage that the same casting model according to the invention can be utilized in the production of both prototypes and actual production models.

The invention has also the advantage that if the casting model is partly damaged or broken, only the damaged or worn-out model elements need to be changed to new ones. Furthermore, it is easy to make changes in a detail of the casting model, such as in a pattern part, because the changes are preferably made by changing only one model element.

Furthermore, it is also a considerable advantage of the invention that the introduction of the casting model is very easy, because the use of the casting model of the invention does not require substantial changes in the work methods of prior art to produce the model of silicone-treated rubber, the core for casting, and the segment. Consequently, the invention can be introduced easily, and in the production of the segment, it is possible to flexibly use both casting models of prior art and the casting model of the invention. This has the considerable advantage that the invention can be introduced without significant investments e.g. in redesigning of the operation or the process of manufacturing tyre models, and that it is still possible to use old casting models.

Another advantage of the invention is that the number of metal lamellae to be manufactured can be reduced substantially in the same order as the number of pattern parts to be made is reduced. Thus, it is obvious that also the work on placing the metal lamellae and the need for finish- ing is reduced considerably in comparison with the casting model of prior art.

A particular advantage of the invention is also that the finishing of the different details in the model elements is easier than the finishing of the details in the casting model of prior art. When the partition of the model elements follows depressions in the pattern parts of the pattern surface and the model elements are relatively narrow, access to the details of 8 the model elements is thus easier with finishing tools from different directions. Furthermore, the model elements are easier to handle than a whole casting model.

In the following, the present invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a casting model of prior art in a perspective view,

Fig. 2 shows three model elements of a casting model according to an advantageous embodiment of the invention in a perspective view,

Fig. 3 shows a model element of a casting model according to an advantageous embodiment of the invention in a lateral view,

Fig. 4 shows three model elements of a casting model according to an advantageous embodiment of the invention in a lateral view and fastened to a fixing element for the casting model,

Fig. 5 shows a fixing element for the casting model according to an advantageous embodiment of the invention seen in a cross-sectional view at location A — A of Fig. 4,

Fig. 6 shows a fixing element for the casting model according to an advantageous embodiment of the invention seen in a cross-sectional view at location B — B of Fig. 4 and with the model element fixed to the same, and

Fig. 7 is a reduced chart illustrating the use of a casting model according to an advantageous embodiment of the invention in the manufacture of the segment of a ring-shaped model.

As presented above, casting models are made by engraving in plaster by using an engraving machine. Naturally, it is obvious that casting models can also be made of other workable materials, such as metal and plastic. However, in the selection of the material, one must take 9 into account the behaviour of the material in connection with casting of a model of silicone-treated rubber by the effect of heat, and the applicability of the material to be worked for finishing the pattern surface. For example, the preparation of very narrow slots by working in metal and their finishing with manual tools is difficult because of the hardness of the material.

For fast production of prototypes for different products, a rapid prototyping (RP) technique has been developed, whereby the pieces to be made are typically composed by one layer after another, often without machining by cutting. A 3D model of the piece is stored in a computer and processed to give instructions to the process of manufacturing the piece.

RP techniques include e.g. stereolitography (SL) using photopolymers, i.e. plastic materials to be hardened by light, and sintering. RP techniques also include ballistic particle manufacturing (BPM), three-dimensional printing (TDP), fused deposition modeling (FDM), multi-jet modeling (MJM), laminated object manufacturing (LOM), and solid ground curing (SGC). In stereolitography, a laser beam is typically used to harden fluid photopolymers, and in sintering, thermoplastic powders are used, such as polystyrene, polycarbonate, and polyamide. Sintering is typically performed by means of a laser beam, e.g. by selective laser sintering (SLS). In sintering, it is also known to use elastomers and metal or ceramic powders admixed with binders. Above-mentioned powders include e.g. plastic coated sand and plastic coated metal powder.

In the BPM technique, a material, such as wax, plastic, photopolymer, ceramic, or metal, is sprayed in layers to the cross-section of the piece. In the TDP technique, a fluid binder is sprayed into a powder material. In the FDM technique, a thermoplastic material is heated and compressed through a nozzle onto an area in layers, after which it sets solid. In the FDM technique, also wax materials and ABS plastic are used. In the MJM technique, a nozzle head moving in an XY plane is used to spray layers of a thermoplastic material, and the operation of the device resembles that of an ink-jet printer. In the LOM technique, 10 several material layers cut by a laser beam are joined to form an entire model. In the LOM technique, sheet-like paper, plastic, metal and ceramic materials are used. In the SGC technique, a fluid photosensitive polymer material is exposed through a mask layer, to polymerize it in layers.

The RP technique, known as such, is described e.g. in publications US 4,863,538 and US 5,014,207. The production tolerances achieved with the RP technique are normally even 0.01 mm, and the pieces to be formed can also be provided with chambers which are difficult to manufacture by conventional methods. Furthermore, after manufacturing, the pieces can be worked and joined to each other also to test the functionality of the products.

When RP technique is used in the manufacture of model elements for a casting model according to the invention, several considerable further advantages are achieved. It becomes easier to make the details in the surface pattern of the casting model, because thanks to the 3D model of the model element stored in a computer, it is possible to make even complicated pattern parts and constructions. Thus, e.g. properties of the tools or changes in the settings of the engraving machine do not restrict the design of the pattern surface, and even complicated patterns can be reproduced identical from one casting model to another, which is not possible when the casting model is made and finished manually. Furthermore, the narrow lamella slots of the model elements can be also provided with structures having sharp edges by the RP technique, which is not possible in the case of drills and broaching bits with circular diameters in an engraving machine. Narrow tools of the engraving machine bend due to forces present in working, and the preparation of slots, walls or the like to be made is thus inexact.

A detail in the casting model that should be mentioned are the narrow slots, or lamella slots, made for bent metal lamellae, the directions of the planar parts and the different bends being preferably parallel. Thus, the corresponding metal lamellae can be easily placed in the lamella slots. When the longitudinal lamella slots are made with a drill-like tool, these tools are bent by the working forces, and thus the bent walls of 11 the lamella slots and the corners therebetween deviate from each other in their directions. Therefore, these lamella slots must be widened or fixed for the metal lamellae in connection with the finishing. These problems can be avoided by making the lamella slots by the RP technique.

Using the casting model of the invention has also the further advantage in that smaller parts, or model elements, must be made by the RP technique than in prior art. The production is thus faster than the pro- duction of entire casting models, wherein e.g. 9 casting models need to be made for the segments of one tyre mould. In one case, the manufacturing costs have decreased by even 50 %. Advantages are achieved also in that defects in manufacture do not require that the whole casting model is made again.

Figure 1 shows a casting model 1 of prior art, comprising also a fixing element 1b attached to the casting model 1 and usually made of metal. The fixing element 1b is fixed to the casting model 1 e.g. with screws (not shown in the figure). The fixing element 1b is used as a support for the casting model 1 , made of plaster or plastic, du ng the finishing of the casting model 1 and the casting of the model of silicone-treated rubber. The arch-like pattern surface 2 of the casting model 1 corresponds in its details to the pattern of the finished tyre. The pattern surface 2 shown in Fig. 1 corresponds to a pattern used in an automobile tyre, but it is obvious that the invention can be also applied in the manufacture of other tyres having a varying pattern surface as well as tyres for other vehicles, such as bicycles and motorcycles. The invention can also be applied in the manufacture of tyres for different machines and apparatuses. The pattern surface 2 is typically provided with pattern parts 2a — 2d which differ from each other in detail and consist further of ridges 3a and depressions 3b formed therein as well as of lamella slots 3c formed for metal lamellae. In Fig. 1 , the area of the pattern part 2a is marked by separating it more clearly with a broken line. The area of the pattern part 2a can also be formed in another way, wherein the pattern part 2a does not extend across the whole pattern surface 2 in its transverse direction. For example, pattern part 2c is formed of a smaller area which is also reproduced in a mirror image on 12 the other side of the pattern surface 2. In the lamella slots 3c are inserted metal lamellae, as described above, which extend from the pattern surface 2 of the casting model 1 when inserted in position. The pattern parts 2a — 2d consist advantageously of areas limited by the depressions 3b, but it is obvious that the pattern parts 2a — 2d can also be formed by another suitable way, depending on e.g. the details of the pattern surface 2 and particularly the recurrence, or distribution, of the pattern parts 2a — 2d on the pattern surface 2.

Figure 2 shows model elements 4a — 4c of the casting model 1 according to an advantageous embodiment of the invention. The model element 4a is shown separately from the other model elements 4t> — 4c, and the model elements 4b — 4c are shown as joined to each other. The model elements 4b and 4c are joined to each other in a corresponding way when they are installed in a fixing element 15 to be described below and shown e.g. in Fig. 4. The model element 4a is designed to extend across the pattern surface 2 in its transverse direction, and the model elements 4b and 4c are designed to have a substantially identical shape in relation to the model element 4a and to follow the shape of the area formed by their pattern parts. The model elements 4a — 4c are designed by following, in principle, the area formed by the pattern part 2a of the casting model 1 shown in Fig. 1. However, it is obvious that the invention is not limited to model elements 4a — 4c with a substantially identical shape, but preferably the adjoining surfaces 5a and 5b of these model elements 4a — 4c are arranged to have a similar design and to be placed tightly against each other, to allow changing of the order of the model elements 4a — 4c or adding of new model elements in the casting model 1 without restrictions. The width in the direction of the circumference (arrow Z) of the model elements 4a — 4c can be changed, even though the adjacent surfaces 5a and 5b had the same shape in different model elements. By arranging the adjacent surfaces 5a and 5b compatible, different casting models 1 can be arranged to have a different length in the direction of the pattern surface 2, i.e. in the direction of the circumference of the casting model 1. At the same time, the model elements 4a — 4c make up a series of model elements with a substantially identical shape. The model elements 4b and 4c are supported to each other also in the 13 transverse direction of the pattern surface 2 by arranging the model elements 4b and 4c substantially to have a V-shape and to extend across the pattern surface 2 in its transverse direction, as shown in Fig. 2. This will prevent their respective movement during the casting of the model of silicone-treated rubber. Furthermore, the model elements 4a — 4c can be divided in the transverse direction of the pattern surface 2 into two elements to be joined to each other, wherein the surface pattern of the pattern surface 2 varies also in the transverse direction of the pattern surface 2.

Figure 3 shows a model element 4d of a casting model according to an advantageous embodiment of the invention, seen from the side, and the pattern surface 2 is shown as a simplified smooth surface in the transverse direction of the tyre (arrow Y). The tyre, whose part the casting model 1 represents, is arranged to rotate around an axis PA which is perpendicular in relation to the plane perpendicular to the drawing plane of Fig. 3 and extending via the arrow R. The arrow X refers to a straight line directed towards the rotation axis PA, and in the presented figure, the adjoining surfaces of the model element 4d, of which the surface 5a is visible, are substantially parallel with respect to the straight line X, which can be seen also from the lines X and adjoining surfaces 5a and 5b shown in Fig. 2. A curved arrow Y refers to the diametral plane of the tyre which extends via said rotation axis PA and simultaneously defines the transverse direction for the casting model 1 and the pattern surface 2 of the model element 4d. A line P1 refers to the bottom of the depression of the pattern surface 2, the depression extending across the model element 4d in its transverse direction Y. It should be noted that in the transverse direction Y, the curvature of the pattern surface 2 varies, and the pattern surface 2 is preferably symmetric in relation to the straight line R set in the middle of the pattern surface 2.

With reference to Fig. 2, the model elements 4a — 4c are arranged to be fitted to each other by means of the adjoining surfaces 5a and 5b. The packing surfaces formed by the adjoining surfaces 5a and 5b are finished e.g. by manual rubbing, when the model elements 4a — 4c placed in the fixing element 15 of Fig. 4 are fitted to each other. This step in- 14 volves also checking of the compatibility of the pattern parts in the model elements 4a — 4c, checking of the curvature of the pattern surface 2 in the transverse direction (arrow Y), and checking of the curvature of the pattern surface 2 in the direction of its circumference, i.e. the dimension corresponding to the radius of the tyre to be produced.

Further, with reference to Fig. 3, the model element 4d is provided with three support legs 6a to 6c for the purpose of supporting the model element 4d to the fixing element 15 shown in Fig. 4. Supporting sur- faces 8a — 8c of support legs 6a — 6c are supported against the mounting face 14 of the fixing element 15. The support legs 6a and 6b are equipped with shoulders 7a and 7b directed towards each other and arranged to be placed in links 12a and 12b in the fixing element 15, shown in Fig. 5. The links 12a and 12b are formed in the fixing element 15 by means of L-shaped link parts 13a and 13b. The links 12a and 12b are arranged in such a way that the model elements glide along the curved mounting face 14 of the fixing element 15 in a direction perpendicular to the transverse direction (arrow Y) of the pattern surface 2, marked also in Fig. 2 with an arrow Z, and which is simultaneously the direction of the circumference of the tyre. It is the purpose of the shoulders 7a and 7b to position the model element 4d and to prevent its displacement in the transverse direction Y when the model element 4d is mounted in the fixing element 15. The support leg 6c, which has the function of preventing the bending of the pattern surface 2 e.g. during finishing and casting, is equipped with a shoulder 7c, which is arranged to be placed in a link 12c formed in the fixing element 15. The link 12c is formed in the mounting face 14 by means of a link part 13c. The shoulders 7a — 7c prevent the detachment of the model element 4d from the fixing element 15 in the direction X, in the direction R and in the direction Y. Shoulders 7d and 7e are used in connection with the casting of the model of silicone-treated rubber, wherein the side walls of the trough-shaped casting vessel are supported to these shoulders.

Via curved holes 9a, 9b and 9c formed in the model elements 4a — 4c, it is possible to insert a fixing means, preferably a curved locking rod (not shown in the figure) to fix two or more model elements to each other to 15 form a uniform casting model. Typically, 8 to 10 of these model elements are fixed to each other, depending on the size of the casting model and the distribution of the pattern parts of the pattern surface. It is a particular advantage of the RP technique that the curved holes 9a — 9c can be easily made in the model elements 4a — 4c. It is not possible to make the curved holes 9a — 9c by means of a conventional straight drill. With reference to Fig. 2, the model elements 4a — 4c are also equipped with holes 9d — 9f, through which a second curved locking means can be placed, for example a binding bolt. The distance of the central line of each hole 9a — 9f from the mounting face 14 is arranged to be substantially constant.

Further, with reference to Fig. 3, the thickness T1 at different locations of the model element 4d may vary e.g. according to the strength of the material to be used. The distance between the pattern surface 2 and the fixing element 15, i.e. distances H1 , H2 and H3, can be changed by changing the length of the support legs 7a — 7c of the model element. This has the advantage that the same fixing element 15 can be used also in connection with model elements formed for the manufacture of different tyre sizes, wherein the respective diameter dimensions of the tyre sizes vary. Thus, there is no need for a large number of fixing elements with a varying radius of curvature in the mounting face 14.

Figure 4 is a side view showing the fixing element 15 of a casting model according to an advantageous embodiment of the invention, and also model elements 4a — 4c placed in position on top of the fixing element. The fixing element 15 is designed to have a mounting face 14 with the shape of a circular arc; that is, the mounting face 14 constitutes a cylindrical surface or a part of the same. The length L1 of the fixing ele- ment 15 may vary, and it is preferably at least the total length of the 8 to 10 model elements to be placed on top of the fixing element 15. The fixing element 15 is arranged to be fixed, in a way known as such, e.g. on top of a bench for finishing. Furthermore, it is obvious that the fixing element 15 can be arranged as a closed annular structure, or that the arch-like fixing element 15 corresponds in its dimensions to e.g. a portion of 45 to 90 degrees of the structure of the tyre mould. 16

Figure 5 shows the fixing element 15 as a cross-section at the location A — A of Fig. 4. The fixing element 15 of e.g. metal is provided, by turning, with the above-mentioned links 12a — 12c which are fitted to cooperate e.g. with the shoulders 7a — 7c formed in the support legs 6a — 6c of the model element 4d, as shown in Fig. 6. With reference to Fig. 2, also the model elements 4a — 4c are provided with corresponding shoulders. It is obvious that the links 12a — 12c can also be formed by fixing separately made arch-like link parts 13a — 13c to the mounting face 14 of the fixing element 15. If necessary, the fixing element 15 can also be equipped with more link parts, if e.g. the length of the model element 4d in the transverse direction (arrow Y) is greater than that shown in Fig. 3, or if the model element 4d is equipped with more than three support legs. In particular, the same fixing element 15 is arranged to be used with casting models of different width by standardizing the placement of the link parts and the respective distances of the support legs in the model element. The links 12a — 12c can be formed in the fixing element 15 also in the direction transverse to the example shown in Fig. 5, wherein the links 12a — 12c are substantially straight and, correspondingly, e.g. the supporting surfaces 8a — 8c of the model element 4d must be fitted to correspond to the shape of the cylindrical mounting face 14. Thus, for example the model element 4d is placed on the mounting face 14 in such a way that the transverse direction (arrow Y) of the pattern surface 2 is substantially parallel to the circumference of the fixing element 15.

Figure 6 shows the fixing element 15 in a cross-section at location B — B of Fig. 4 and the model element 4d mounted in its position in the fixing element 15. The different model elements are slid along curved links 12a — 12c into their position on the mounting face 14. The model elements are placed in the links 12a — 12c from the end of the fixing element 15 or e.g. by means of a discontinuity in the link part 13a (not shown in the figure). The link parts 13a — 13c are arranged in such a way that they support the model elements, e.g. the model element 4d, also in the radial direction of the tyre, so that the transverse distance of the model element 4d from the rotation axis of the tyre (arrow PA in Fig. 3) in relation to the pattern surface 2, i.e. the distance of the pattern surface 2 from the mounting surface 14, would not vary more than 17 the allowed tolerance. Thus, the shoulders 7a — 7c of the model element 4d are advantageously arranged to comply in their shape with the curved shape of the links 12a — 12c and in their thickness substantially with the height of the link 12a— 12c.

Figure 7 is a simplified chart illustrating the use of the casting model according to the invention in the manufacture of segments in a ring- shaped mould, i.e. a tyre mould. The model elements 101 for making a casting model 102 according to the invention comprise 17 different model elements, of which eight, i.e. the model elements A1 — A8, are selected in this case and assembled in the next phase 110 into the casting model 102 which thus corresponds to a desired casting model A in a set 107 of casting models according to prior art. By using another combination B1 — B8 of the model elements 101 , it is also pos- sible to form a casting model 102 corresponding to a casting model B of the set 107. The selection of the model elements 101 depends on the distribution of pattern parts related to the model elements 101 on the circumference of the complete tyre. Moreover, the model elements 101 can be formed further of two model elements, such as model elements 101a — 101f, wherein the combination possibilities are increased and wherein several series of model elements are formed. By using two smaller model elements 101a — 101f, it is possible to make nine larger model elements of different pattern surfaces, wherein the number of required model elements can be further reduced. It should be noted that each casting model A — H in the set 107 according to prior art must be separately made of e.g. plaster, but the casting model 102 corresponding to the casting models A — H according to the invention can be formed by combining the model elements 101 , e.g. by disassembling the casting model 102 at least partly and combining a new casting model 102 of the model elements 101.

At the next stage 112, a model 103 of silicone-treated rubber is formed of each casting model 102 by casting, which is performed also by using a casting model 107 according to prior art (stage 109). At the next stage 113, a core 104 is made of each model 103 of silicone-treated rubber for casting normally with plaster. At the next stage 114, each core 104 is used to make a segment 105, normally of aluminium, which 18 is placed in the final tyre mould 108 at the next stage 111. In the case of the example, eight such segments 105 are required for one tyre mould 108. At the different stages of manufacturing, the tyre pattern surface is in a positive model in the casting model 102 and in the core 104 for casting, and in a negative model in the model 103 of silicone- treated rubber and in the segment 105. The tyre mould 108 comprises also the segments required for forming the patterns of the lateral surface of the tyre (not shown in the figure) and the mould elements required for forming the inner surface (not shown in the figure).

The present invention is not restricted solely to the above-presented examples, but it can be modified within the scope of the appended claims. For example, it is obvious that the total number of model elements required may vary from that presented, as well as the number of various casting models to be made for the tyre mould. Furthermore, it is obvious that the design of the model element may vary to a great extent from that presented, because the pattern of the pattern surface varies between different tyre models. In the above-presented example, the model element extends across the pattern surface in the transverse direction, but it is obvious that for example a pattern surface which is wider than that presented can be divided into model elements according to the invention also in the transverse direction of the pattern surface.

Moreover, it is obvious for a man skilled in the art that the invention can be applied also in the case that the pattern of the pattern surface varies only to a small extent between different casting models, e.g. only with respect to text markings. Also in this case considerable advantages can be achieved with the invention, because e.g. with the RP technique, parts that are smaller than in prior art need to be made, and because it is considerably faster and easier to make changes and to add patterns in the pattern surface, if necessary, than in prior art.

Claims

19Claims:

1. A casting model for the manufacture of a segment to be fitted into a ring-shaped mould, the casting model (1) comprising at least a pattern surface (2) which is preferably equipped with pattern parts (2a ΓÇö 2d), characterized in that:

ΓÇö the pattern surface (2) of the casting model (1) is arranged to be formed by means of at least two model elements (4a ΓÇö 4d), and ΓÇö the casting model (1) is arranged to be used also in the manufacture of another segment by changing the respective order of the model elements (4a ΓÇö 4d), by removing at least one model element (╬¢a ΓÇö 4d), by adding at least one model element (4a ΓÇö 4d), by exchanging at least one model element (4a ΓÇö 4d), or by performing a combination of any of said alternatives.

2. A casting model according to claim 1 , characterized in that the shape of at least one model element (4a ΓÇö 4d) is fitted to comply at least partly with the shape of an area formed by one or several pattern parts (2aΓÇö 2d) of the pattern surface (2).

3. A casting model according to claim 1 or 2, characterized in that the casting model (1) is, seen from the direction perpendicular (arrow R) to the pattern surface (2), formed of at least one set of model elements (4a ΓÇö 4d) joined to each other and having a substantially identical shape.

4. A casting model according to any of the claims 1 to 3, characterized in that the casting model (1) is formed of at least two model ele- ments (4a ΓÇö 4d) which extend across the pattern surface (2) in its transverse direction (arrow Y), are joined to each other with adjoining surfaces (5a, 5b) substantially perpendicular to the pattern surface (2), and having substantially a V-shape when seen from a direction (arrow R) perpendicular to the pattern surface (2).

5. A casting model according to any of the claims 1 to 4, characterized in that: 20

ΓÇö the casting model (1) comprises a fixing element (15) provided with a mounting face (14) forming a cylindrical surface or part of a cylindrical surface, ΓÇö the model element (4a ΓÇö 4d) is equipped with at least two shoulders (7a ΓÇö 7c) which are fitted to be placed in substantially parallel links (12a ΓÇö 12c) formed in the mounting face (14), wherein the model element (4a ΓÇö 4d) is arranged to slide along the mounting face (14), and wherein the disengagement of the model element (4a ΓÇö 4d) from the fixing element (15) is prevented at least in the transverse direction (arrow Y) of the links (12a ΓÇö 12c) and in the perpendicular direction (arrow R) of the mounting face (14), and

ΓÇö the model element (4a ΓÇö 4d) is equipped with at least one hole (9a ΓÇö 9f) preferably parallel to the mounting face (14), to fix the model elements (4a ΓÇö 4d) to each other by means of a fixing means placed through the hole (9a ΓÇö 9f).

6. A casting model according to any of the claims 1 to 5, characterized in that at least one model element (4a ΓÇö 4d) is made by using a rapid prototyping technique.

7. A method in the manufacture of a casting model, which casting model (1) is made to manufacture a segment to be fitted into a ring- shaped mould, and which casting model (1) comprises at least a pat- tern surface (2) which is preferably equipped with pattern parts (2a ΓÇö 2d), characterized in that:

ΓÇö the pattern surface (2) of the casting model (1) is arranged to be formed by means of at least two model elements (4a ΓÇö 4d), and ΓÇö the casting model (1) is arranged to be used also in the manufacture of another segment by changing the respective order of the model elements (4a ΓÇö 4d), by removing at least one model element (4a ΓÇö 4d), by adding at least one model element (4a ΓÇö 4d), by exchanging at least one model element (4a ΓÇö 4d), or by performing a combination of any of said alternatives. 21

8. A method according to claim 7, characterized in that the shape of at least one model element (4a ΓÇö 4d) is fitted to comply at least partly with the shape of an area formed by one or several pattern parts (2aΓÇö 2d) of the pattern surface (2).

9. A method according to claim 7 or 8, characterized in that the casting model (1) is, seen from the direction perpendicular (arrow R) to the pattern surface (2), formed of at least one set of model elements (4a ΓÇö 4d) joined to each other and having a substantially identical shape.

10. A method according to any of the claims 7 to 9, characterized in that the casting model (1) is formed of at least two model elements (4a ΓÇö 4d) which extend across the pattern surface (2) in its transverse direction (arrow Y), are joined to each other with adjoining surfaces (5a, 5b) substantially perpendicular to the pattern surface (2), and having substantially a V-shape when seen from a direction (arrow R) perpendicular to the pattern surface (2).

11. A method according to any of the claims 7 to 10, characterized in that:

ΓÇö the model element (4a ΓÇö 4d) is equipped with at least one hole (9a ΓÇö 9f) preferably parallel to the mounting face (14), to fix the model elements (4a ΓÇö 4d) to each other by means of a fixing means placed through the hole (9a ΓÇö 9f). 22

12. A method according to any of the claims 7 to 11 , characterized in that at least one model element (4a ΓÇö 4d) is made by using a rapid prototyping technique.