NZ212514A - Two piece axially split tyre vulcanising mould:sipe insert extraction wedge - Google Patents

Description

Priority Date{s(': ..

Complete Specification Filed; X.',\k,KK Class: &?.?. f}. ?/W.... %A3. £ Publication Date: .. B2.NWJSM P.O. Journal, No: 8^ 212514 Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "TWO-PIECE MOLD FOR CURING TIRES" -I-WE SUMITOMO RUBBER INDUSTRIES, LTD., of 1-1, Tsutsui-cho, 1-chome, Chuo-ku, Kobe, Japan, a Japanese company hereby declare the invention, for Which-t-/we pray that a patent may be granted to-roe-/us, and the method by Which it is to be performed, to be particularly described in and by the following statement (foffowed by page TA.) 2125 1 $ - !flr TWO-PIECE MOLD FOR CURING TIRES 1 The present invention relates to an improved two-piece mold for curing tires provided with a number of knife blades on the internal circumferential surface of a tread ring.

In general, a number of "knife blades" 2, which are obtain-5 ed by punching a thin stainless sheet having a predetermined uniform thickness into a desired shape and bending the punched stainless sheet into a desired shape, have been mounted on the internal circumferential surface of a tread ring 1 of a mold, as shown in Fig. 1, in order to form a number of fine cuts 10 (knife cuts or siping) on the surface of a tread to mainly improve the wet grip performance of tire.

However, a problem has occurred in that, when the upper mold is moved and separated from the lower mold 4 in the direction of an arrow to open the mold after completion of the 15 vulcanizing of the tire 5 by the use of a two-piece mold consisting of the tread ring 1, 1', the upper mold 3 and the lower mold 4, as shown in Figs. 2 and 3, and the knife blade 2 mounted on the tread rings 1, 1' comes out of the tread rubber in the direction of an arrow, the surface portion (as shown by a 20 circle mark in Fig. 3) of a tread rubber 6 of the knife cut is excessively rubbed by the side 7 of the knife blade 2, the side being in or facing the direction in which the knife blade 2 is pulled out of the tread rubber, in particular by the lower portion of said side, to produce worm-eaten-like damage to ill 25 . affect the tire appearance and further give rise to cracks thereby having also a bad influence upon the performance of tire.

It is an object of the present invention to solve the above described problems thereby providing a two-piece mold for curing tires whose damage of tread by knife blades is remarkably reduc-30 ed and which is in no danger of having a bad external appearance In order to achieve the above described object, the 212514 2 present invention comprises a two-piece mold for curing tires provided with a number of knife blades fixed to an internal tread moulding surface of the mould, characterized in that each knife blade is provided with a tapered thickened portion formed on at least a part of its one side facing the direction in which said knife blade is pulled out of the tread rubber when the mold is opened, thereof.

The present invention will be below described in more detail with reference to the drawings.

The drawings are summarized as follows.

Fig. 1 is a partial perspective view showing a mold having knife blades therein, Fig. 2 is a partial.sectional view showing a two-piece mold, Fig. 3 is a partial sectional view showing the state of a knife blade of the conventional mold being pulled out of the tread rubber, Fig. 4 is a partial sectional view showing a mold having knife blades therein according to the present invention, Fig.-5 is a partial sectional view showing a method of forming a tapered padding portion on one side of the knife blade shown in Fig. 4, Fig. 6 is a diagram showing a knife blade shown in Fig. 4 seen from the direction X-X, Fig. 7 is a partial sectional view showing another preferred embodiment of the present invention, and Fig. 8 is a partial sectional view showing the state of a knife blade of a mold according to the present invention being pulled out of the tread rubber.

Referring now to Fig. 4, a padding portion 14 having a taper 13 is formed integrally with the tread ring in the casting proces of the tread ring 10 (for example, made of aluminium of a two-piece mold at the position of the internal circumferential surfac of the tread ring 10, wherein a knife blade 11 is to be embedded, so as to directly engage with at least a part of the side 12 (shown by an arrow) of the knife blade facing the direction in 2 115 1 < which the knife blade 11 pulled out of the tread rubber when the mold is opened. The padding portion 14 has preferably the size (a) 1.0 to 2.0 times the thickness t of a knife blade and the size (b) 0.3 to 1.0 times the height h of a knife blade.

Where the size (a) is less than 1.0 times the thickness t of a knife blade, the casting process is difficult to carry out while where the size of a exceeds t x 2.0, an image of knife cut is lost in respect of design. In addition, where the size b is less than 0.3 times the height h of a knife blade, a knife blade can not be smoothly pulled out of a rubber. The padding portion 14 is smoothly tapered from the root of the knife blade 11 toward the pointed head of the knife blade "11 to reduce the resistance of the knife blade 11 when the knife blade is pulled out of the tread rubber in Fig. 4.

The above described casting process is carried out as follows, as shown in Fig. 5. That is to say, at first a groove 21 for the knife blade is dug at the position previously marked-off of a master model (made of gypsum) of the tread ring and then a tapered notch 23 having the above described predetermined sizes (a), (b) is formed on the groove wall portion in or facing the direction (shown by an arrow) in which the knife blade 22 is pulled out of the tread rubber. Subsequently, after the knife blade 22 was inserted into said groove 21 with the pointed head thereof toward the direction of the groove, a casting material (for example, aluminium) is cast to form a tapered padding portion 24 together and integrally with a tread ring in such a manner that the tapered padding portion 24 is directly engaged with the knife blade 22. In addition, in this casting process, the knife blade is previously provided with a small hole 25 (having a diameter of 1.0 to 1.5 mm) so that the knife blade can surely be held by the tread ring, as shown in Fig. 6.

In another preferred embodiment, in the casting or forging process of a knife blade 30 itself, a padding portion 32 provided with a taper 31 is formed on at least a part of its one side in the direction (shown by an arrow) in which the knife blade 30 213514 4 is pulled out of the tread rubber when a mold is opened. This padding portion has the same sizes (a), (b) as those of the i padding portion 14 In the above described first preferred embodiment to form a tapered thick portion of the knife blade.

"The side in the direction in which the knife blade is pulled out of the tread rubber" in each of the above described preferred embodiments is a side facing to the moving direction of the upper mold 3 when the mold is opened after completion of the vulcanizing in Fig. 2, in other words, a side portion of the knife blade rubbing the tread rubber when the knife blade Is pulled out of the tread rubber with an opening action of the mold, as described above. Accordingly, for the knife blade which is mounted in a parallel or biased relation to the circumferential direction of a tread ring, the tapered padding portion Is formed all over the width of one side surface of the knife blade while for the knife blade which is mounted at an angle of 90° to the circumferential direction of the tread ring, the tapered padding portion Is formed on one end edge portion of the knife blade. ; In the present invention, as described above, a knife blade, itself is provided with a tapered padding portion having a j described size on its one side in the direction in which the knife blade is pulled out of the tread rubber, or the padding portion is formed integrally with the tread ring using a mold casting method, so that a smooth taper 42 is formed on the wall ! i portion of the knife cut groove in the direction in which a j knife blade 41 is pulled out of the tread rubber when the mold is opened, as shown in Fig. 8, thereby the rigidity of the j tread rubber at such a portion is increased, the knife blade 41 being smoothly slid along the tapered surface 42 when pulled out of the tread rubber in the direction of an arrow, and worm-eaten-like damages and the like of the tread rubber being remarkably j reduced to prevent a tire having a bad external appearance -' being produced. Furthermore, the volume of a knife cut is increased in comparison with that of the conventional one due to the padding portion, so that the wet grip of tire can 1 improved. 212514

Claims (4)

WHAT WE CLAIM IS;

1. A two-piece mold for curing tires provided with a number of knife blades fixed to an internal tread moulding surface of the mould, characterized in that each knife blade is provided with a tapered thickened portion formed on at least a part of its one side facing the direction in which said knife blade is pulled out of the tread rubber when the mold is opened, thereof.

2. A two-piece mold for curing tires as set forth in Claim 1, in which said thickened portion is formed when the mould is formed by casting.

3. A two-piece mold for curing tires as set forth in Claim 1, in which said thickened portion is a thickened portion of the knife blade itself.

4. A two-piece mold for curing tires substantially as herein described with reference to Figures 4 to 6 and 8 or Figure 7 of the accompanying drawings. BALDWIN, SON & CAREY iMzd ATTO^KEVS FOR THE APPLICANTS