GB2026376A

GB2026376A - Mould segment and method of manufacturing same

Info

Publication number: GB2026376A
Application number: GB7924566A
Authority: GB
Original assignee: HERBERT MASCHBAU KG
Current assignee: HERBERT MASCHBAU KG
Priority date: 1978-07-15
Filing date: 1979-07-13
Publication date: 1980-02-06
Also published as: IT1122152B; LU81504A1; DE2831219A1; BE877705A; YU168279A; DE2831219C2; GB2026376B; FR2430838A1; IT7924296A0; NL7905497A; AT371764B; YU41165B; FR2430838B1; ATA483279A; IT7922089V0

Abstract

The mould segment e.g. for a tyre vulcanising mould is cast from a metal having a relatively low melting point, such as an aluminium alloy, and has integrally cast lamellae (12, 13) which are made from a metal having a relatively high melting point, such as sheet steel, and which pass through the wall of the mould segment (S). The inner surface (4) and the outer surface (3) of the mould segment (S) are interconnected by way of venting gaps located between the regions of the lamellae around which the metal is cast and the adjacent cast surfaces. The inner end (13b) of at least one lamella (13) terminates in an inner shaping surface (4) of the mould segment and its outer end (13f) terminates at the outer surface (3) of the mould segment (S).

Description

SPECIFICATION Mould segment and method of manufacturing same The invention relates to a mould segment, particularly for a tyre-vulcanizing mould, which is of the type which is cast from a metal having a relatively low melting point, particularly an aluminium alloy, and which has integrally cast lamellae which are made from a metal having a relatively high melting point, particularly sheet steel, which pass through the wall of the mould segment, the inner surface and the outer surface of the mould segment being interconnected by way of venting gaps located between the regions of the lamella around which the metal is cast and the adjacent cast surfaces.

In a known mould segment of this kind (German Utility Model 74 11 386), all the lamellae are at the same time shaping parts of the segment which form deep, narrow slots in the tyre to be manufactured. The advantage of such segments resides in the fact that a tyre-vulcanizing mould equipped with segments of this type is vented by way of the said gaps, so that special venting bores are not required. Thus, undesirable protuberances on the tyre are also avoided which otherwise form in the venting bores in tyres provided therewith and which generally have to be removed by expensive manual labour.

However, adequate venting is only ensured when an adequate number of lamellae is suitably distributed round the entire shaping surface of the tyre-vulcanizing mould. This is not the case with all tyre profiles. In order to obtain adequate venting even without venting bores of circular cross section, it has already been proposed (German Offenlegungsschrift 1,965,121) integrally to cast in a complete mould lamellae which serve only for venting purposes and which terminate at the shaping surface of the mould, that is to say, they do not themselves form shaping elements. In this known mould, the lamella project beyond the outside of the mould, the projecting parts acting as holding portions by means of which the lamellae, which are also referred to as "blind lamellae", are inserted into a wall of the mould which incorporates corresponding slot-like recesses or depressions. Blind lamellae constructed in this manner are possible in a complete mould, but not in the case of mould segments which have to be secured to a part of the vulcanizing mould which holds several segments together, since the projecting parts of the lamellae would obstruct the securing of the segments.

An object of the present invention is to provide a mould segment of the type mentioned initially which, irrespective of the tyre profile to be manufactured, permits the mounting of a sufficient number of lamellae required for optimum venting, without the lamellae hindering the mountability of the mould segment.

In accordance with the present invention, there is provided a mould segment, particularly for a tyre-vulcanizing mould, which is cast from a metal having a relatively low melting point, such as an aluminium alloy, which mould segment has integrally cast lamella which are made from a metal having a relatively high melting point, such as sheet steel, which pass through the wall of the mould segment, the inner surface and the outer surface of the mould segment being interconnected by way of venting gaps located between the regions of the lamella around which the metal is cast and the adjacent cast surfaces, the inner end of at least one lamella terminating at an inner shaping surface of the mould segment, and its outer end terminating at the outer surface of the mould segment.

A mould segment constructed in this manner can be mounted in the same way as known mould segments, since the back of the segment has no projecting parts which would hinder the mounting of the segment on a mould. The supporting member can be a closed ring or, alternatively, a displaceable segment on which at least one mould segment in accordance with the invention can be mounted, but preferably, however, a plurality thereof.

Advantageously, at least the regions of the lamellae around which the metal is cast are of an uneven nature so as to enlarge the effective surfaces of the lamella. Thus, one obtains particularly effective venting, since, on the one hand, the unevennesses enlarge the surface of the lamella thus chilling the cast metal more rapidly and consequently enhancing the formation of the gap between the aluminium and the lamella, and, on the other hand, the unevennesses form narrow passages to allow the air to escape.

Preferably, the lamellae are disposed in recesses in the outer surface of the mould segment. Alternatively, the regions of the lamellae around which the metal is cast are perforated and the openings so formed are at least partially lined. These measures known from German Utility Model 74 11 386, are also advantageous for the blind lamellae in accordance with the invention.

The invention also provides a method of manufacturing a mould segment in which a chill casting mould made from steel is used which has an inner portion provided with narrow depressions for shaping the shaping inner surface of the segment, and an outer portion for shaping the outer surface of the mould segment, lamellae being inserted into depressions in the inner portion of the chill mould when the chill mould is open, the mould is then closed and filled with molten metal in a pressureless manner and, after the metal has solidified, the mould is opened, the cast segment is removed with withdrawal of the lamellae from the inner portion of the chill mould and a holding portion on at least one of the lamella which had been inserted into the inner portion of the chill mould is removed.

Chill moulds for casting mould segments have an outer portion of relatively simple configuration, and an inner portion of complicated configuration. The outer portion only forms the relatively smooth outer surfaces of a segment which can be inexpensively produced by a turning operation. However, the inner portions of the chill mould have the positive shape of the article to be manufactured, that is to say, a tyre profile. Modern tyre profiles have relatively narrow and deep grooves which can be produced in the steel chill mould only by using a spark erosion technique. The spark erosion technique involves a slow operation so that long working times are involved and the workpieces are thus rendered correspondingly expensive. When, in accordance with the aforegoing method, the blind lamella are held on the inner portion of the chill mould instead of the outer portion of the chill mould, there is the advantage that the manufacture of the chill mould involves virtually no additional costs, since the depressions for holding the blind lamella are formed in a single working operation with the formation of other depressions which are also required. Thus, the outer portion of the chilled mould also does not have to be machined by spark erosion. Advantages are obtained even during the equipping of the chill casting mould with lamella, since only the inner portion of the chill mould has to be provided with blind lamella and, possibly, also shaping lamella, while the outer portion of the chill mould is not equipped with them. Compared with these advantages, the removal of the holding parts of the blind lamellae is of less importance with respect to labour, so that overall, substantial savings are achieved compared with mounting the blind lamella in the outer portion of the chill mould.

With respect to chill mould casting in general, it may be mentioned that it is particularly advantageous for the formation of venting gaps between the lamellae and the aluminium, since the aluminium is cooled relatively rapidly in the pressureless state in a steel chill mould. The formation of gaps is not enhanced to the same degree when using the diecasting method, since the hydrostatic pressure in the molten metal opposes the formation of gaps. Advantageously, the lamella can be coated to further enhance the formation of gaps.

Preferably, at least some of the lamella include a means defining a desired fracturing location, disposed between a holding portion and a working portion of a blind lamella which is to be integrally cast.

It is particularly advantageous to use such lamella since, after the segment has been removed from the chill casting mould, the holding portions of the lamella can be removed in a particularly simple manner, namely by breaking them off.

The invention will be further explained hereinafter by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an inner portion of a chill mould; Figure 2 is a perspective view of an outer portion of a chill mould; Figure 3 shows a mould segment, in accordance with the invention, in its state immediately after it has been removed from the chill casting mould; Figure 4 is a vertical section through the inner portion of the chill casting mould, and a mould segment; Figure 5 shows three views of a shaping lamella; Figure 6 shows three views of a blind lamella; and Figure 7shows an enlarged portion of Fig.

6 in the region of the dash-dot circle VII of Fig. 6.

The illustrated mould segment in accordance with the invention is generally designated S and its overall configuration is substantially L-shaped. The long limb 1 of the L serves to shape the tread of a tyre, and the short limb 2 of the L serves to shape a portion of the side wall of the tyre. The long limb of the L extends only up to the equator of a tyre.

The surface of the tyre located beyond the equator is shaped by a mould segment arranged as a mirror image.

The mould segment has an outer surface 3 and an inner surface 4. The outer surface 3 is curved and constitutes a portion of an annular surface. Four recesses 5 to 8 are located in the large limb of the L. A projection 9 is formed at the end of the long limb of the L and, when the segment is mounted in a mould, engages a complementary groove in the supporting portion of the mould.

The inside of the segment S incorporates aluminium ribs 10, 11 of zig-zag configuration which are integrally formed with the mould segment, as well as shaping steel lamellae 1 2 and blind lamellae 1 3 which do not participate in the shaping of the tyre. The blind lamella 1 3 are disposed in the region of the recesses 5 and 6, and the shaping lamella are disposed in the region of the recesses 7 and 8. One edge of each of the shaping lamella 1 2 engages the rib 11, while the blind lamella 1 3 do not project beyond the inner surface 5 of the segment when the segment is in its finished state, in that, when the segment is in its finished state, the region 1 3a referred to as a "holding portion", of the blind lamella is removed, so that the inner edge 1 3b of the blind lamellae is flush with the inner surface 4. The lifter portion 14 is also removed when the segment is in its finished state. The removal of the portion 1 3a is facilitated by means defining a desired fracturing location which is formed by a notch 13c(see also Figs. 6 and 7 in this connection).

A blind lamella is illustrated in Fig. 6. The blind lamella includes the holding portion 1 3a already mentioned, and a working portion 1 3 d The working portion 1 3 d is curved in a roof-like manner, as is shown by the view on the left hand side of Fig. 6. An opening 13e is located in the central region 1 3'dof the working portion. The notch 13calready mentioned extends in line with the edge 1 3b. This notch weakens the lamella 13, which, in any case, is only thin, to a cross section 1 3g which is otherwise approximately half the thickness of the lamella and which can be, for example, 0.5 mm. After the mould segment has been removed from the chill casting mould, the holding portion 1 3a can be removed rapidly by breaking it off, it only being necessary to bend it for this purpose, whereupon it breaks off in the region of the weakened cross section 1 3g. The end edge parallel to the edge 1 3 b is designated 1 3 f.

The working lamella 1 2 is bent at an acute angle at the bending edge 1 2a It incorporates an opening 1 2 b which corresponds to the opening 13ein the blind lamella 13. A weakening location is not provided on the shaping lamella 12.

The inner portion 1 5 and the outer portion 1 6 of the chill casting mould are illustrated.

Side walls (not shown in the drawing) form part of the chill mould and close the casting chamber laterally and abut against the side walls of the portions 1 5 and 16 of the chill mould.

The inner portion of the chill mould has the negative shape of the shaping inner surface 4 of the segment S. Relatively narrow and deep grooves 1 7 and 1 8 are provided for forming the ribs 10 and 11. For the purpose of inserting the shaping lamella 12, two narrow, deep slots 1 9 and 20 originate from the groove 1 8 and their width is such that the lamella 1 2 fit therein. The width is, for example, approximately 1 mm. The depth is equal to the freely projecting height of the lamella 1 2 from the aluminium casting of the segment.

Grooves 21 and 22 branch from the groove 1 7 and form corresponding rib extensions on the mould segment S, although the rib extensions are not visible in the perspective illustration. A critical region for venting is the location at which the ribs formed by the passages 21 join the ribs formed by the passage 17.

Slots 23 and 24 are provided in this region for receiving the blind lamellae 1 3.

For the rest, the inner portion 1 5 of the chill mould incorporates a wide recess 25 which serves to form a pouring-in funnel.

A turning operation is performed in the first instance when ,manufacturing the inner portion 1 5 of the chill-mould, whereby the convex surface of the tyre to be manufactured is formed. The deep grooves 17, 18, 21, 22 and the deep slots 19, 23 and 24 are then formed using the spark erosion technique. The formation of the depressions 23 and 24 involves scarcely any additional cost, since these slots can be eroded at the same time as the other slots.

The outer portion 1 6 of the chill mould has an inner shaping surface 26 which constitutes the negative of the outer surface 3 of the segment. This surface is produced by a turning operation and so is relatively inexpensive.

The shaping surface 26 is partially formed by four blocks 27 which constitute the negative of the recesses 5 to 8 in the segment S.

These blocks are secured by means of bolts 28.

During manufacture of a segment S, the chill mould is taken apart and the inner portion 1 5 of the chill mould is first equipped with shaping lamella 1 2 and blind lamellae 1 3. The shaping lamella are inserted into the slots 19, 20, the slot receiving the portion which is exposed on the finished segment, while the region of the finished segment around which metal is cast projects from the inner portion 1 5 of the chill mould. The holding portions 1 3a of the blind lamella project from the portion 1 5 of the chill mould.

The chill mould is closed after the inner portion 1 5 of the chill mould has been equipped with the lamella, the outer portion 1 6 of the chill mould being applied to the inner portion 1 5 of the chill mould such that the outer edge 29 of the outer portion of the chill mould abuts against the inner edge 30 of the inner portion of the chill mould. Furthermore, a first end wall is applied to the side faces 31, 32 and a second end wall is applied to the oppositely located side faces 33, 34.

The recess 25 is closed by the surface 35 of the outer portion 1 6 of the chill mould, so that a pouring-in channel closed on all sides is formed.

Molten aluminium is poured in a pressureless manner by way of the pouring-in passage 25 after the mould has been closed, the cavity in the casting chill mould being filled.

The molten aluminium thereby surrounds those regions of the lamellae 1 2 and 1 3 which project from the inner portion 1 5 of the chill mould. The aluminium cools very rapidly in the steel chill mould. Narrow gaps are thereby formed between the aluminium and the surfaces of the lamella 12, 1 3 around which the metal is cast. However, this does not prevent the lamellae from being securely held in the casting. The hold is further enhanced by virtue of the fact that molten aluminium flows into the openings 1 3e and 12bin the lamellae, thus resulting in positive anchoring.

The height of those regions of the lamellae 12 and 1 3 which project from the inner portion 1 5 of the chill mould is such that the lamellae extend up to the end faces of the blocks 27, so that the end edges of the lamella are flush with the bottoms of the depressions 5 to 8.

After the aluminium has solidified, the portions of the chill mould are taken apart, for example into the position shown in its entirety in Figs. 1 to 3, whereupon the segment can be removed. The lifter 14 is still located on the segment in the first instance. The holding portions 13aare still located on the blind lamellae 13. The holding portions 13a are then removed by bending. The lifter is removed by knocking or sawing it off. The segment is then trimmed or finished.

A large number of segments can be cast by means of one chill mould, generally several thousand pieces.

In accordance with a variant (not illustrated), at least those regions of the lamellae around which metal is cast can be provided with corrugations which extend preferably approximately at right angles to the surface 3.

This results in the effects already stated in the introduction. As already mentioned initially, before or after the lamellae have been inserted into the interior portion of the chill mould, they can be provided with a coating which enhances the formation of the gaps. Advantageously, if the lamellae are only to be coated in places, they are coated after they have been inserted. When the lamella are coated before insertion, the lamellae will generally be coated in their entirety.

Claims

CLAIMS,

1. A mould segment, particularly for a tyre-vulcanizing mould, which is cast from a metal having a relatively low melting point, such as an alluminium alloy, which mould segment has integrally cast lamella which are made from a metal having a relatively high melting point, such as sheet steel, which pass through the wall of the mould segment, the inner surface and the outer surface of the mould segment being interconnected by way of venting gaps located between the regions of the lamella around which the metal is cast and the adjacent cast surfaces, the inner end of at least one lamella terminating at an inner shaping surface of the mold segment, and its outer end terminating at the outer surface of the mould segment.

2. A mould segment as claimed in claim 1, in which at least the regions of the lamella around which the metal is cast are of an uneven nature so as to enlarge the effective surfaces of the lamellae.

3. A mould segment as claimed in claim 2, in which the unevenness of the laminae is provided by the formation of grooves therein, which extend from the inner surface to the outer surface of the mould segment.

4. A mould segment as claimed in any of the preceding claims, in which the lamella are disposed in recesses in the outer surface of the mould segment.

5. A mould segment as claimed in any of the preceding claims, in which the regions of the lamella around which the metal is cast are perforated and that the openings so formed are at least partially lined.

6. A method of manufacturing a mould segment as claimed in claim 1 in which a chill casting mould made from steel is used which has an inner portion provided with narrow depressions for shaping the inner surface of the segment, and an outer portion for shaping the outer surface of the mould segment, lamellae being inserted into depressions in the inner portion of the chill mould when the chill mould is open, the mould is then closed and filled with molten metal in a pressureless manner and, after the metal has solidified, the mould is opened, the cast segment is removed with withdrawal of the lamella from the inner portion of the chill mould and a holding portion on at least one of the lamella which had been inserted into the inner portion of the chill mould is removed.

7. A method as claimed in claim 6, in which at least those regions of the lamellae around which metal is to be cast are coated with a material, preferably a plastics material, which decomposes at least after the cast metal has solidified.

8. A lamella for performing the method as claimed in claim 6 or 7 in which a means defining a desired fracturing location is disposed between a holding portion and a working portion of a blind lamella which is to be integrally cast.

9. A mould segment substantially as hereinbefore described with reference to and as illustrated in Figs. 3 to 6 of the accompanying drawings.

10. A method of manufacturing a mould segment substantially as hereinbefore described with reference to the accompanying drawings.