CN109109574B

CN109109574B - Pneumatic radial tire for load

Info

Publication number: CN109109574B
Application number: CN201810964056.7A
Authority: CN
Inventors: 王红彦; 叶佳蕾; 吴晓东; 王志权
Original assignee: Zhongce Rubber Group Co Ltd
Current assignee: Zhongce Rubber Group Co Ltd
Priority date: 2018-08-23
Filing date: 2018-08-23
Publication date: 2024-08-09
Anticipated expiration: 2038-08-23
Also published as: CN109109574A

Abstract

Aiming at the problem that the durability, the eccentric wear resistance and the handling stability of the tire are difficult to realize good balance on the same tire after the shaping and the vulcanization of the existing belt structure, the invention provides a pneumatic radial tire for loading, wherein the expansion rate of the central area of the innermost belt layer is in the range of 1.2-1.9 percent, the 'tension-elongation' curve of a zero-degree belt steel wire is at a mutation point of curve trend in the area with the elongation of 0.8-1.4 percent, and the mutation point area is positioned in the range of 40-110N of tension; the invention can achieve good balance of the above properties.

Description

Pneumatic radial tire for load

Technical Field

The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire for load.

Background

The belt structure in the schematic cross-sectional view of the tire shown in fig. 1 to 3 is a structure widely used in China at present. These belt structures have the problem that the durability, bias wear resistance and handling stability of the tire after the shaping and curing process are not well balanced on the same tire. This problem becomes particularly pronounced especially with the current trend of increasing groove depth.

Disclosure of Invention

The invention provides a load-carrying pneumatic radial tire capable of inhibiting delamination problem at the edge of a belt layer and improving the stability of operability, which comprises the following technical scheme:

the pneumatic radial tire for load application is characterized in that at least one belt layer formed by steel wires which are arranged in parallel is arranged on the circumference of the tire; the belt layer is provided with steel wires in the two shoulder areas, the 'tension-elongation curve' of the steel wires is provided with abrupt points of curve trend in the area with the elongation of 0.8% -1.4%, the abrupt point area is positioned in the range of 40-110N, and the elongation at break is more than 5%.

Preferably, the central region expansion ratio of the lowermost belt layer of the tension-resistant belt layers of the load-carrying pneumatic radial tire covering the entire crown region is in the range of 1.2% to 1.9% after completion of the molding process and the vulcanization process, calculated according to the following formulas,

Wherein, r _f: belt diameter when applied to the belt building drum; r _f: belt diameter in the mold after curing.

Preferably, the abrupt point of the tension-extension curve of the belt steel wire is controlled between 1.0% and 1.2%.

Preferably, the belt steel wire of the tire has a tensile force of at least 400N at an elongation of 1%.

Preferably, the belt layer is a stack of a plurality of belt layers, the belt layer on the carcass side is narrower than the belt layer on the tread side, and the belt layers on both outer ends of the belt layer on the tread side can cover both ends of the belt layer on the carcass side.

Preferably, the tire has a plurality of belt layers stacked, the belt layer on the carcass side is wider than the belt layer on the tread side, both ends of the belt layer on the tread side are covered with the above-mentioned "tension-elongation curve" so that a sudden change point of the curve trend occurs in a region having an elongation of 0.8% to 1.4%, and the sudden change point region is located in a range of 40 to 110N in tension, and the circumferential belt layer has an elongation at break of 5% or more.

By adopting the technical scheme, the durability reaches or exceeds that of a standard tire, and meanwhile, the eccentric wear resistance and the operability stability are kept unchanged at the original level, so that the durability, the eccentric wear resistance and the operability stability can be obviously improved compared with the tire using the common steel wire with the stretching property.

Drawings

FIGS. 1,2 and 3 show examples of pneumatic radial tires for heavy loads to which the present invention is applied;

fig. 4 is a schematic structural view of embodiment 1;

FIG. 5 is a graph comparing tension-elongation curves of tension-resistant belt steel wire and reinforced belt steel wire;

FIG. 6 is a calculation illustration of belt swell ratio on the carcass side;

FIG. 7 is a calculation illustration of swell ratio of reinforced belts;

FIG. 8 is an illustration of belt swell mode during curing;

FIG. 9 is a graph of tension versus elongation for bare steel and vulcanized steel for a reinforced belt at different expansion rates;

FIG. 10 is a graph of bare steel wire at a break point of 2% versus 1% and a graph of vulcanized steel wire at a break point of 1%;

FIGS. 11 to 13 are graphs showing the relationship between the intersection angle and the stability of the wear resistance and handling properties

Symbol description

1. A pneumatic radial tire for load;

2. a tread;

3.4, a tension-resistant belt layer;

5. a protective belt;

6. reinforcing the belt layer;

7. And (3) a carcass.

Detailed Description

Example 1

The belt structure shown in fig. 1 is taken as an example for illustration (refer to the reference sign of fig. 4). In this structure, tension-resistant belt layers 3, 4 are overlapped with each other at an angle of 10 DEG to 45 DEG with respect to the tire circumferential direction, a protection belt layer 5 having a narrow width is provided at the center of the crown and covers the tension-resistant belt layer, and 2 or 3 reinforcing belt layers 6 are arranged in the circumferential direction and parallel to each other at both ends of the protection belt layer 5 and above the tension-resistant belt layer 4. The outer end point of the reinforcing belt layer 6 is closer to the tread center line than the wider one of the tension-resistant belt layers 3, 4.

Since the reinforcing belt layers 6 in the above-described structure are arranged in parallel in the circumferential direction, the increase in the belt circumferential length cannot be compensated for by the angular change in the molding and vulcanization steps like the other tension-resistant belt layers 3, 4 or the protection belt layer 5, and therefore the reinforcing belt layer 6 solves the problem of the circumferential length change by utilizing the "tension-elongation curve" characteristic as shown in fig. 5. Since this elongation characteristic is a structural elongation function of a steel wire by adjusting the lay length of the steel wire, such a steel wire is also called a high elongation steel wire.

In the tire forming step, the belt layer is bonded to a belt bonding drum having a predetermined circumference, and a green tire is formed. The green tire is then placed into a designated mold, and pressure and heat are applied to the inner surface of the green tire to complete the hot vulcanization. In this process, radial expansion of each belt occurs, and the ratio of the vulcanized belt diameter to the belt diameter at the time of molding becomes the expansion ratio.

Fig. 6 and 7 are schematic diagrams showing calculation references of the expansion ratios of the belt layers on the tire at the time of molding and after vulcanization, respectively. The calculation formula of the expansion ratio can be summarized as:

For the reinforcing belt layers 6 arranged in parallel in the circumferential direction, if two layers are arranged, the central position of the width and thickness may be taken for convenience to calculate the expansion ratio thereof.

As described above, radial expansion of each belt layer occurs in the vulcanization process. At this time, since the tension-resistant belt layers 3, 4 must use a steel wire material without structural stretch for functional factors, expansion in the radial direction by an angular change occurs as shown in fig. 8. But such angular variations do not occur uniformly across the belt. During vulcanization, the expansion in the radial direction is realized by means of the expansion of the wire spacing without basically changing the angle near the end points of the two sides of the belt layer. The angle of the crown center region of the vulcanized cross-laminated tension-resistant belts 3, 4 is smaller than that of the molding, while the angles of the both ends are kept substantially unchanged.

We have focused on investigation and study of the effect of varying belt angles at different belt expansion rates and different elongation characteristics of the reinforcing belt 6 on tire performance. The test object was 315/80R22.5, a longitudinal and transverse pattern, and a mold groove depth of 18mm, and 7 test tires with different expansion rates were designed and evaluated.

TABLE 1

TABLE 2

The left side in table 1 is the expansion ratio of the tensile force resistant belt layer 3 and the reinforcing belt layer 6 of 7 test schemes calculated according to the expansion ratio calculation formula. Test tires of 7 different expansion ratios were produced according to this table and their properties were tested. Wherein the tension-resistant belt layers 3, 4 are made of a belt material of 3+8×0.33ST, the reinforcing belt layer 6 is made of a material of 3×4×0.22HE, and the abrupt point of the tension-extension curve thereof occurs at 2% elongation. The fitting angles (relative to the circumferential direction) of the tension-resistant belt layers 3 and 4 were 25 ° and 15 °, respectively, and the reinforcing belt layer 6 was 0 °. The belt structure is shown in fig. 1, and is a very common belt design in China, both in terms of steel wire characteristics and belt structure.

The tires of the 7 test schemes are subjected to an indoor machine tool endurance test, a whole vehicle eccentric wear test and a whole vehicle operability stability test. Wherein the endurance test method of the indoor machine tool refers to the certification test standard of the United states department of transportation; the eccentric wear test is to measure the wear difference between the center of the crown and the shoulder of a tested tire which is arranged at the front wheel position of a vehicle and runs for 4 ten thousand kilometers; the handling stability test method is quoted from the ISO evaluation standard. The test results of the former two are shown by indexes, and the higher the index is, the better the performance is represented. The latter adopts scoring system, and more than 10 points are fully scored, and more than 7 points are qualified, so that a trained test driver can feel a difference of 1 point, and an ordinary driver can feel a difference of 2 points.

The tire of the scheme 7 exhibited significant defects due to insufficient stretching of the reinforcing belt layer 6, and could not be used for performance testing, and was therefore excluded from the comparison results. The tire of scheme 4 is a specification that i company is currently producing normally.

The results of the above performance tests are listed on the right side of Table 1. As can be seen from the results, durability is improved after the belt expansion ratio becomes large, but at the same time, the eccentric wear resistance and handling stability are deteriorated; when the expansion ratio is small, the wear resistance and handling stability are improved, but the durability is greatly reduced.

To find out the reasons for the above results, we measured the steel wire alignment angles of the center and both ends of the belt layer after the test tire was vulcanized, as shown in table 2. The results showed that as the belt expansion ratio became larger, the arrangement angle α in the central region of the crown became smaller in order, and the arrangement angle β in the vicinity of the both end points also showed the same trend, but the change width was much smaller than the central region α, and it was considered that the influence of the expansion ratio was hardly affected. Further, it was found that the performance of the uneven wear resistance and the steering stability was related to the crossing angle of the tension belt layers 3 and 4 from a review of the relationship between the angle change and the test result. The intersection angle here means the sum α1+α2 of the arrangement angle α1 of the tension-resistant belt layer 3 and the arrangement angle α2 of the tension-resistant belt layer 4.

The crossing angle of the tensile belt has a great influence on the radial bending stiffness of the tread, which affects the wear resistance and steering stability. The relationship between the crossing angle and the results of the eccentric wear resistance and the stability of the operability is shown in fig. 11 to 13, and it can be seen that when the crossing angle is about 36 degrees, the two performances have good and bad boundary points.

In terms of durability, since the angular variation at the belt ends is less pronounced than in the central region, we put the focus on the pre-tension level before curing of the reinforced belt 6. The reinforced belt steel wire was peeled from the above test tire to prepare a sample, and the tensile-elongation curve was tested for the test object of the case 1 (reinforced belt expansion ratio 0.1%) and the case 4 (reinforced belt expansion ratio 0.9%). Meanwhile, the steel wire is directly coated with glue in a laboratory without applying any tensile force, and then vulcanized, so that a steel wire sample with a pretension of 0 is manufactured, and compared with a bare steel wire without the glue, as shown in fig. 9. It can be seen that the wire tension-stretch curve of the solution 1 tire with 0.1% expansion of the reinforcing belt 6 substantially corresponds to the curve of the wire without pretension in the laboratory.

The radial expansion of the tread cap can be estimated to be in the range of 0.5% to 1.5% at standard air pressure, in which case the belt modulus of the tire of scheme 1 is only 30% to 40% of the belt modulus of scheme 4, that is, for such tires having a relatively small belt expansion ratio, the reinforcing belt thereof is not sufficiently stretched throughout the production process, so that the reinforcing effect of the reinforcing belt is not exerted, resulting in deterioration of durability.

Based on the above reasoning, we performed a second round of tests on durability, eccentric wear performance, and handling stability by adjusting the lay length of 3×4×0.225HE so that the point of mutation of the tension-extension curve is advanced to around 1.1%, and then combining this wire according to the following scheme.

TABLE 3 Table 3

TABLE 4 Table 4

No.	Durable indoor machine tool	Wear resistance against offset wear	Stability of handling
				1-A	108	135	8
2-A	105	134	8
				3-A	100	128	8
4	100	100	7
				8	90	135	8

TABLE 5

Table 3 shows the construction scheme of the second-round test tire, and the schemes 1-A, 2-A and 3-A are test tires prepared by advancing the reinforced belt steel wires of the original schemes 1,2 and 3 to the steel wires around 1.1% of extension by using the abrupt points of the tension-extension curve. The case 4 is a standard tire, and the case 8 is a comparative tire in which the belt bonding angle at the time of molding is adjusted so that the belt crossing angle after vulcanization is ensured to be 36 ° or more.

Table 4 shows the test results of tires constructed according to the protocol of Table 3, the test methods being identical to the first round test methods. From the results, the scheme 1-A, 2-A and 3-A, which are used for advancing the abrupt change point of the tension-extension curve of the reinforced belt layer steel wire from 2% to 1.1%, all realize that the durability reaches or exceeds that of a standard tire, and meanwhile, the eccentric wear resistance and the operability stability are kept unchanged at the original level, and the overall performance is more comprehensively superior to that of the standard tire. It can also be seen that the durability is also deteriorated in case 8, although the eccentric wear resistance and handling stability are improved.

Table 5 shows the angle change of the tensile belt layers 3 and 4 of the test tire of table 3. The angles of schemes 1-A, 2-A, 3-A, 4, while slightly different from the first round of testing, were substantially uniform. Scheme 8, which exhibits poor durability, has a crown tension belt 3, 4 crossing angle of 36.5 ° close to scheme 2-a, but a crossing angle near both ends of 41.3 °, which is higher than all other schemes. It is well known in the industry that an intersection angle near the end points of a tension-resistant belt layer if exceeding 40 ° causes a drastic decrease in the durability of the belt layer, and therefore, it is inevitable that the intersection angle of the end regions exceeds the limit value to reduce the durability by adjusting the belt layer fitting angle to a relatively proper level in the crown center region.

From the above results, it can be concluded that if the intersection angle of the tension-resistant belt of the crown is 36 ° or more and the intersection angle in the vicinity of both end points is not more than 40 °, it is necessary to control the expansion ratio of the tension-resistant belt against the carcass to 1.9% or less. The problem of insufficient tension after the belt is vulcanized can be solved by changing the tension-elongation curve of the steel wire according to the required expansion rate. Fig. 10 is a tension-elongation plot of the bare steel wire of scenario 3-a versus the post-vulcanized steel wire, which can be seen to be substantially identical to the post-vulcanized plot of standard tire scenario 4. To sum up:

① When the expansion ratio of the belt layer close to the carcass in the tension-resistant belt layer is controlled within the range of 1.2% -1.9%, the belt layer crossing angle of the central region of the crown part can be more than 36 degrees, and the belt layer crossing angle near the two ends can be controlled below 40 degrees, and most desirably below 39 degrees.

② When the abrupt change point of the tension-extension curve of the steel wire of the reinforced belt layer 6 is controlled to be 0.8% -1.4%, and most desirably 1.0% -1.2%, the reinforced belt layer can still exert the due reinforcing effect under the expansion rate of ①.

By implementing the above 2 measures simultaneously, durability, eccentric wear resistance and handling stability can be remarkably improved as compared with a tire using a conventional tensile property steel wire.

Claims

1. The pneumatic radial tire for load application is characterized in that at least one belt layer formed by steel wires which are arranged in parallel is arranged on the circumference of the tire; the belted layer has steel wire at both shoulders region, its characterized in that: the 'tension-elongation curve' of the steel wire has a curve trend mutation point in a region with the elongation of 1.0% -1.2%, the mutation point region is positioned in the range of 40-110N, and the elongation at break is above 5%;

The central area expansion ratio of the lowest belt layer in the tension-resistant belt layer of the load-carrying pneumatic radial tire covering the whole crown area is in the range of 1.2% -1.9% after the completion of the molding process and the vulcanization process, calculated according to the following formulas,

Formula (VI)

Wherein, r _t: belt diameter when applied to the belt building drum; r _f: belt diameter in the mold after curing.

2. The pneumatic radial tire for load carrying according to claim 1, wherein: the belt steel wire of the tire has a tensile force of at least 400N at an elongation of 1%.

3. The pneumatic radial tire for load carrying according to claim 1 or 2, wherein: the belt layers are stacked by a plurality of layers, the belt layer on the side close to the tire body is narrower than the belt layer on the side close to the tire tread, and the belt layers at the two ends of the outer side of the belt layer on the side close to the tire tread can cover the two ends of the belt layer on the side close to the tire body.

4. The pneumatic radial tire for load carrying according to claim 1 or 2, wherein: the tire has a plurality of superimposed belt layers, the belt layer on the carcass side is wider than the belt layer on the tread side, and circumferential belt layers are covered at both outer ends of the belt layer on the tread side.