JPS5917234B2 - steel cord conveyor belt - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conveyor belt having a core made of a 7×7 steel cord.

In a conveyor belt with a steel cord as the core, the steel cord for the core is 7×7 configuration cord, 7
×19 configuration code, 7XW (19) configuration code, 7×7
There are various types such as ×7 configuration code.

The object of the invention is a conveyor belt having a core of 7x7 construction cord.

FIG. 1 shows a conveyor belt 2 in which 7×7 steel cords 1 are embedded in parallel at a predetermined pitch P.

As shown in FIGS. 2 and 3, the steel cord 1 has six side strands 4 arranged outside one center strand 3, and the center strand 3 and the side strands 4 are composed of one center wire ( Center wire) 5 and 6 side wires (side wire) 6
It is composed of.

Such a steel cord with a 7x7 strand structure is generally indicated by the following structure...(1+6)+6X(1+6) (K J) (-Mushi') (-Original) The diameter is the diameter of the center strand of the center strand... aO-O diameter of the center strand on the side strand... dO- is the diameter of the center strand of the side strand... di- the side element of the 0 side strand Wire diameter: indicated by dl-1.

Steel cords with such a 7x7 twist configuration generally have the following structure in view of strength characteristics, fatigue resistance, etc.

(a) The center strand 3 and the side strands 4 all have the same twist coefficient (the twist coefficient of the strands is 717/m in Figure 4, assuming that the twist length of the center strand 3 is 11 and the diameter is m). It is expressed as

The same applies to the side strand 4).

(b) The twist coefficient of each strand 3 and 4 is 17, code 1
The twist coefficient of is 7, therefore, the multiplier of "twist coefficient of center strand 3" with respect to "cord twist coefficient" is 17/7''=
, 2.4 is considered to be optimal (the twist coefficient of the cord is expressed as L/M in FIG. 4, where the length of twist of cord 1 is L1 and the diameter is M).

(c) The wire diameter of the center strand 3 is larger than the wire diameter of the side strands 4, and in each strand, the wire diameter of the center wire (center wire) 5 is also larger than the side wire (side wire). (This is called central diameter increase,
The diameter of the center wire 5 is increased by about 10 times compared to the side wire 6.)
.

The above-mentioned conventional conveyor belt having a 7x7 steel cord as its core has the following drawbacks.

■ In the production of conventional steel cord conveyor belts, when steel cord and rubber are vulcanized (heated) bonded, the cutting load after vulcanization (hereinafter referred to as "initial cutting load") is lower than the cutting load before vulcanization (hereinafter referred to as "initial cutting load") due to heating. The load decreases.

In particular, when the temperature during vulcanization is 140° C. or higher, the cutting load decreases significantly.

However, the vulcanization temperature in the manufacture of conveyor belts is
Generally, the temperature is 140°C or higher.

Therefore, the strength (breaking strength) of a conveyor belt with a conventional 7x7 cord as its core is lower than the strength designed based on the initial cutting load of the steel cord.
This was a big problem.

Furthermore, the durability of the conveyor belt, as well as its strength, is lower than that designed based on the bending fatigue resistance of the steel cord before heating, which has been a drawback of conventional conveyor belts.

■ Depending on the vulcanization (heating) conditions, the cutting load and bending resistance of the steel cord used as the core may decrease;
As the degree of reduction varies, the strength (rupture resistance) and durability of the conveyor belt also decrease and the reliability of the belt decreases.

■ When designing the strength of a conveyor belt with a 7x7 cord as its core, if a reduction in the cutting load of the steel cord is expected, the amount of steel cord used would have to be larger than if the strength was designed based on the initial cutting load. The price of that conveyor belt increases.

■ In order to prevent the cutting load and bending fatigue resistance of the 7×7 cord, which is the core of the conveyor belt, from decreasing, lowering the vulcanization temperature requires a longer vulcanization time.
This reduces productivity and increases the price of manufactured conveyor belts.

In this way, the strength and durability of conveyor belts using conventional 7x7 cords are significantly lower than those designed based on the cutting load and bending fatigue resistance of unheated steel cords.
Furthermore, there were problems in terms of quality and cost due to lack of reliability.

In order to understand the cause of the large decrease in cutting load due to heating in the conveyor belt using the conventional steel cord with the above-mentioned 7 x 7 twisted configuration, the present inventors investigated the following relationship between the wire diameters: d > d : dt-o>dt-t O-0-0-1 and the ratio of the twist coefficient of the center strand to the twist coefficient of the cord is 2.4. A tensile test was conducted on the steel cord before and after heating (heated at 160°C for 30 minutes and left to cool), and the cutting conditions of the steel cord were examined.

This consideration was made by photographing the steel cord with a high-speed camera at 120 frames per second and observing the image, and by observing the tensile load at the point when the wire starts cutting (the point at which the cutting sound of the wire first occurs). is removed, and the steel core V at that time is
This was done by observing.

As a result, we compared and examined data such as elongation and load obtained from tensile tests, and observed the state of cutting the strands, and found that the elongation of the steel cord before heating was greater than that after heating. It was a dog, and there was an indentation at the cut end that was thought to be caused by the interlocking action between the strands and between the strands.

This revealed that when conventional steel cords are heated, the elongation rate of the steel cords is significantly reduced.

In addition, in the film taken with a high-speed camera, the state of each strand of the various steel cords before heating is photographed in the same frame of the film at the time of cutting, whereas the various steel cords after heating are photographed in the center strand. A few frames after the frame in which the condition of the side strand when it was cut was photographed, the condition of the side strand when it was cut was photographed.

As a result, it was found that in the steel cord before heating, each strand was cut almost simultaneously, whereas in the steel cord after heating, the center strand was cut first, and then the side strands were cut.

Furthermore, at the time when the strands started cutting, uncut strands and cut strands were mixed, and the number of uncut strands was different in the center strand.

As a result, in the steel cord after heating, the entire cord does not break instantly, but several strands begin to break first, and during the cutting process, the number of cuts in the center strand strand is greater than that of the side strand strands. It was found that the number of cuts was greater than the number of cuts, resulting in the side strands being cut after the center strand was cut as described above.

As mentioned above, the reason why the elongation rate during cutting drastically decreases when the steel cord is heated is because it is made of high carbon steel (each strand of the steel cord is made of high carbon steel).

) occurs even below 150°C (i.e., the general vulcanization temperature for rubber) (see, for example, Journal of the Japan Institute of Metals, Vol. 24, No. 8, 1960, p. 515). This is thought to be due to a decrease in ductility due to aging, that is, embrittlement.

In addition, when heating a conventional steel cord, the center strand breaks and then the side strands break.The reason why the side strands break after the center strand breaks is because when a tensile load is applied to a steel cord, the center strand generally receives the largest load, and after heating, the steel cord becomes ductile due to strain aging. It is thought that the center strand cannot withstand the load that it could withstand before heating and breaks off before the side strands.

From this, the reason why the cutting load after heating is much lower than the initial cutting load in the conventional steel cord with a 7 x 7 twisted configuration is that the ductility of each strand is reduced and the This is thought to be due to the fact that the maximum load is applied to the center strand and the center strand breaks first, and then the side strands break, even though the tensile stress is reduced due to the indentation caused by the interlocking of the strands. .

Based on the above considerations, the present inventors conducted various experiments and research, and found that when the ratio of the twist coefficient of the cord to the twist coefficient of the center strand is set to a predetermined value, the cutting load due to heating is reduced. The present invention has been completed based on the discovery that this can be significantly improved.

The present invention uses a steel cord with a 7x7 strand structure as the core material, which does not significantly reduce the cutting load when a tensile load is applied even when vulcanized at normal temperatures. The purpose of the present invention is to provide a conveyor belt with increased breakage resistance and durability compared to conveyor belts, and with improved reliability.

The above object, according to the invention, is such that the ratio of the twist coefficient s of the central strand to the twist coefficient a of the cord (b/a) is 1.
This is achieved by using a 7x7 construction steel cord with a diameter of 1.8 to 1.8 as the core material.

If a steel cord with the ratio (b/a) exceeds 1.8 is used, the cutting load will be greatly reduced due to heating, unlike conventional conveyor belts using steel cords, and the ratio (b/a) If a steel cord with a diameter of less than 1 is used, the twisting loss of the mechanical strength of the cord itself will be large, resulting in a small initial cutting load, which is not sufficient as a cord for the core of a conveyor belt.

The reason why the ratio of the twist coefficient of the center strand to the twist coefficient of the cord from 1 to 1.8 can prevent a large decrease in the cutting load after heating with respect to the tensile load is that the twist coefficient of the center strand is Since it approximates the twist coefficient of the cord, it is possible to prevent the center strand from breaking earlier than the side strands when a tensile load is applied (premature breakage of the center strand), i.e. each strand is This is thought to be because they are cut at the same time.

In fact, on the film in which the cutting state was photographed with the aforementioned high-speed camera, the state of the steel cord used in the present invention at the time of cutting was photographed in the same frame.

Experiments have shown that not only should the ratio of the twist coefficient of the center strand to the twist coefficient of the cord be 1 to 1.8, but also that all the strands of the side strands have the same wire diameter or that all the strands of the center strand have the same diameter. Equivalent (wire diameter is JISG-3521
It has been found that the deterioration of cutting load and bending fatigue resistance due to heating can be further improved by using a wire diameter of 3522 (considered to be equivalent within the same tolerance within the same 3522).

The reason for this is thought to be that, in addition to being able to prevent early breakage of the center strand, by making the diameters of each strand in the strand the same, the effect of the interlocking effect due to interlocking between the strands is reduced.

In particular, the improvement in the bending fatigue resistance of the improved steel cord is thought to be mainly due to the reduction in internal wear of the cord due to the reduction in the meshing action caused by the meshing between the strands.

The strength (rupture resistance) and durability of a conveyor belt using the above-mentioned improved 7×7 steel cord as a core are significantly improved under any vulcanization conditions compared to belts using conventional steel cords.

Next, the present invention will be specifically explained based on examples.

Example 1 ■-1 The twisting length of the center strand was changed in steel cords with the configurations shown below, and the respective cutting load change rates after heating at (a) 160°C for 30 minutes and (b) 180°C for 30 minutes. ((Cutting load after heating X 100/Initial cutting load) -10
0) was investigated.

The results are shown in FIG.

From this result, when the twist coefficient of the center strand is 12.8 or more and the magnification of the "center strand twist coefficient" to the cord twist coefficient J (7,0) is 1.8 or more, the cutting load after heating decreases significantly. It turns out that it does.

Steel cord 7 -17)
=732kg *Representative strand diameter [diameter of the most common strands (at-t' in this example) constituting the cord],
same as below.

-2 A prototype conveyor belt with the following specifications using each of the steel cords shown in -1 as a core was fabricated, and its breakage resistance and durability were investigated.

As shown in Table 1, the results show that compared to the conveyor belt using conventional cords (belt symbol f),
The strength per unit (lcrfL) of a conveyor belt (belt symbol a r b + Cr d ) using a cord with L/M = 1 to 1.8 increases by about 6 to 8 coefficients and 5
The strength will also improve after 1,000,000 runs.

Conveyor belt specifications Belt width L (tomo) 500 (S
T-670) Belt length (m) 30 Pitch P (71!7K) 10 Thickness T (mm) 14.6 Vulcanization conditions 160°C x 30 minutes φ Belt running conditions Pulley diameter 5001m.

Safety factor 7.0. Example 2-1 In order to examine whether the combination of steel cord strand diameters affects the cutting load after heating, the presence or absence of an increase in the center diameter of the side strands and the twist coefficient of the center strand ( The following A, A', and B are combinations of large and small twist length)
, B' experimental code (the number of samples was 5 in each case) was created, and the rate of change in cutting load due to heating was investigated.

For A and A', the magnification of the center strand twist coefficient against the cord twist coefficient is 2.43, and the magnification of code B and blur is 1.36. Furthermore, A and B are the center strand twist coefficients. With diameter increase (dl, = 0.2 c+ri,
A′l E3/ is without diameter increase (dl-o-φ 0.26771771).

The test results are shown in Table 2.

As is clear from the table, codes A' and B/, which do not have an increase in the center diameter of the side strands, are better than codes A and B, which have an increase in the center diameter.
The reduction in the cutting load is smaller than that of the ``center strand twist coefficient'' and the ``cord twist coefficient'' is
It can be seen that the cords B and B', which have a magnification of 8 or less, have a smaller reduction in cutting load than the cords A and A, which have a magnification of 1.8 or more.

Steel cord-7X7 (0,26) O wire chemical composition (%) CO, 73, MnO, 50, So, 010°SiO,
23, Po, 013. Cu0.020 cord twist coefficient = 7.0 Twist coefficient of 0 side strand -17 0 each strand (it) dl -1 = 0.26do-t
-〇, 29 do-o=0.31 -2 Conveyor belts t-g, g', h, h' with the following specifications using A, A', B, B' were prototyped and their breaking strength and durability were investigated. We investigated gender.

Conveyor belt specifications...Bell) width (xi)
)500 (ST-570) Belt length m)3
0 pitch (dragon) 10 belt thickness) 14.4 Vulcanization conditions 160℃ x 30 minutes (press vulcanization) φ Belt running conditions Pulley diameter (mm) 500 Safety factor 70 Pulley 500 passes 10,000 times The test results are shown in Table 3.

As is clear from the table, compared to the conventional conveyor belt g, the belt h having the improved cord as a core has an improved breaking strength at 22 before running and after running 14115 million times.

Furthermore, as a result of observing the surface of each of the reinforcing steel cords of belts g and h' after 5 million running tests, no broken wires were found in the improved steel cord h', and there was little deterioration in the quality of the conveyor belt. There was found.

Example 3-1 In Example 1 above, the heating conditions were 160°C x 30 minutes and 180°C.
Although only in the case of 30 minutes at ℃, the influence of heating conditions on cutting load reduction was tested for the following two codes CD.

Code C has a configuration in which the multiplier of the "center strand twist coefficient" to the "cord twist coefficient" is 1.50, which is within the range of 1 to 1.8, and the diameters of the side strands are all the same. , and code D has the above magnification factor of 2.43.
A structure in which the diameter of the center wire of the side strands was increased was used.

The test results are shown in FIG.

As is clear from the drawings, for code C, there is almost no decrease in the cutting load due to variations in heating conditions, but for code D, it was found that the cutting load decreases rapidly depending on the heating conditions.

D Center strand twist coefficient 10.5 17 (multiplying factor for cord twist coefficient) (1,50) (2,43
)CD side strand twist coefficient 17 17 Cord twist coefficient (L/M) 7.0 7.0φ Element wire diameter (mm) cl+-10,430,43at-o
O,430,47 do-s O,470,47 do, 0.51 0.51 -2 A bending fatigue test was conducted on the above code CD.

As shown in Table 4, the results are as follows: Code C has an even higher cutting load after heating, and the number of bending breaks is greater than Code D.

Bending fatigue test method JISG-3535 pulley diameter
6.0crIL Tension 34.5kgZ-3 A conveyor belt with the following specifications having the code CD shown in 3-1 as a core was manufactured as a prototype, and its breaking strength and durability were investigated.

The results are shown in Table 5. As is clear from the table, the improved belt i has a greater breaking strength of 50% than the conventional belt j.
The remaining strength after running 00,000 times is also large.

Furthermore, after running 5 million times, C shows a smaller degree of decrease in the strength of the wire and a smaller decrease in the number of twists (according to JIS G-3522) than D, indicating that fretting due to internal wear is small.

Conveyor belt specifications: Heald width (m71
1) 400 (ST-1100) Belt length Co., Ltd. 30 pitch (mi) 14 Belt thickness C → 16.1 Vulcanization conditions 160°C x 30 minutes Press vulcanization belt running conditions Pulley diameter Safety factor φ 600mm 7・0 Passage through the pulley 500 times 10,000 times Example 4-1 The following cases where the twist coefficient of the center strand is multiplied by the "cord twist coefficient" are 1.13 and 2.06, and the wire diameter is different from that of Example 3. A bending fatigue test was conducted for cords E and F.

Steel cord 7X7 (0,37) F Center strand twist coefficient 9.6 17.5 (multiplying factor for Cor equivalent coefficient) (1,13) (2
,06) Side strand twist coefficient 17.5 17
．． 5E F Cord twist coefficient 8.5 8.5 Wire diameter dl, 0.37 0.37d, ,
0.37 0.41do,
0.41 0.41do, 0.41
0.45 The results are shown in Table 6.

As is clear from the table, the "twist coefficient of the central strand"
Cord E, whose magnification for the "cord twist coefficient" is in the range of 1 to 1.8, has a higher cutting load change rate after heating and bending fatigue resistance than cord F, which is outside the range. .

Bending test method JIS G-3535 Pulley diameter 38mm Tension 5.8kg/piece-2 A conveyor belt with the following specifications using the cords E and F shown in 4-1 as the core was prototyped and its breaking strength and durability were evaluated. investigated.

The results are shown in Table 7. As is clear from the table, the conveyor belt according to the present invention has the conventional conveyor belt L-L.
It has higher breakage resistance and improved durability compared to other types.

Conveyor belt specifications: Belt width (mm)
400 (ST-990) Belt length (m) 3'0 pitch (m) 11 Belt thickness (m) 13.5 Vulcanization conditions 160°C x 30 minutes Belt running conditions Pulley diameter φ 500 (Tomo) Safety factor 7.0 Pulley passing 5 x 106 times As explained above, in a conveyor belt with a steel cord as a core, the magnification of the "center strand twist coefficient" to the "cord twist coefficient" is set to 1 to 1.8 for the steel cord. By using a 7x7 construction cord, the breakage resistance of the belt is improved and the deterioration of belt performance after long-term use is also reduced.

In addition to this condition, if the diameters of all the strands of the side strands are made equal, the effect will be further improved, and there will also be an advantage that the restrictions on the vulcanization conditions during the production of the conveyor belt will be relaxed.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conveyor belt with a steel cord as the core, Figures 2 to 4 show steel cords with a 7x7 configuration, Figure 2 is a perspective view, and Figure 3 is a cross-sectional view. , Fig. 4 is an explanatory diagram of the twisting structure, Fig. 5 is a graph showing the relationship between the magnification of the center strand twist coefficient to the cord twist coefficient and the rate of change in cutting load, and Fig. 6 is the heating temperature and cutting. There is a graph showing the relationship with load change rate. 1...Steel cord, 2...Conveyor belt, 3...Center strand, 4...
... Side strand, 5 ... Center wire (strand)
, 6... side wire (strand wire).

Claims (1)

[Claims] 1. A steel cord conveyor, characterized in that the core is a 7×7 steel cord in which the "twisting coefficient of the center strand" is multiplied by the "twisting coefficient of the cord" from 1 to 1.8. belt. 2. The steel cord conveyor belt according to claim 1, wherein all the wires of the side strands of the steel cord have the same wire diameter.