Wear tire preparation method and tire grinding machine

Abstract

The present invention relates to a method for preparing a worn tire and a tire grinding machine. The method uses a rotating grinding wheel to reciprocate on the tread to achieve tread grinding when the tire rotates, and sprays a carbon dioxide jet to the tread to cool it down. The temperature of the carbon dioxide jet at the tread is -30 to -50°C, and the average flow rate of the carbon dioxide jet is 0.25 to 0.75kg / min. The carbon dioxide jet can be sprayed at intervals. The present invention uses a carbon dioxide jet to cool the contact surface during grinding. Since the temperature of carbon dioxide is low, it can take away the heat generated by the friction process during sublimation and evaporation, so the effect of controlling the temperature rise is obvious; on the other hand, carbon dioxide quickly evaporates into the air in the form of sublimated carbon dioxide gas, and will not remain and accumulate at the grinding interface, so it has almost no effect on the surface effect after grinding.

Description

Technical Field

[0001] The invention relates to the technical field of tire testing and grinding, and in particular to a method for preparing a worn tire and a tire grinding machine. Background Art

[0002] The ECE R117 certification, which was issued and took effect on December 16, 2019, introduced the requirements for wet grip test limits for C1 category worn tires and announced the effective date:

[0003] (1) For newly developed tread patterns, it is planned that after July 7, 2024, the ECE R117 certification will add a worn tire wet grip test, and the logo will change from "S2WR2→S2WR2B";

[0004] (2) For existing tread patterns, on July 7, 2026, the ECE R117 certification will add a worn tire wet grip test, and the logo will be changed from "S2WR2→S2WR2B".

[0005] The preparation of worn tires becomes the first step in applying for ECE R117 certification. At present, the vast majority of worn tires in this industry in China are prepared by grinding the tread using a tire profile simulation grinder. The grinding process grinds the tread according to the set grinding procedure and is based on the control of the groove depth. Attention is paid to whether the groove depth after grinding meets the tolerance requirements and whether the surface roughness after grinding meets the regulations. However, due to the friction between the grinding wheel and the tire during the grinding process, the tread temperature rises. In addition, due to the pre-pressure during grinding, the tire rubber will soften and form adhesive, resulting in the surface roughness of the tire after grinding failing to meet the experimental requirements. The adhesive will also adhere to the grinding wheel, reducing the grinding efficiency. At present, there is no good solution to the adhesive problem that occurs during the grinding process.

[0006] Regarding the adhesive problem during the grinding process, there are two main technical difficulties that need to be optimized:

[0007] (1) The friction temperature rise between the tread and the grinding wheel is too high:

[0008] During the grinding process, the grinding wheel and the tire rotate relative to each other, the speeds are superimposed, and contact friction is used to achieve the grinding purpose; during the contact friction process, the temperature of the contact point will rise rapidly, and the tread formula is greatly affected by the temperature. If the temperature rise is too high, it will affect the performance of the tire, but the temperature rise during the friction process is unavoidable.

[0009] (2) Cumulative deformation of tread due to circumferential force:

[0010] The grinding principle of the grinding machine: the control system calculates the coordinate position that is tangent to the target contour arc during the operation of the grinding wheel according to the set target contour data and the equipment's own system data, and then automatically controls the grinding wheel to perform radial positioning, feeding and lateral swing according to the coordinate position data, and performs grinding through cyclic feeding.

[0011] During the cyclic feeding process, the tread always keeps in contact with the tread, the force is continuously accumulated and superimposed, the tread is always in a stressed state, the stress distribution of the tread after vulcanization is destroyed, and new stress concentration points appear, which will affect the tire performance. However, force transmission during the grinding process is unavoidable.

[0012] Therefore, it is necessary to minimize the temperature rise of the tread while ensuring the grinding target as much as possible, and reduce the cumulative force during the grinding feed process to solve the problem of tread rubber melting and sticking to the guide wheel and grinding wheel during the grinding process.

[0013] A Chinese invention patent application entitled “New Tire Retreading and Grinding Machine” with publication number CN101148020A provides a device for tire retreading and grinding, which provides a technical solution of using a spray device to spray water for cooling to prevent tread burning and carbonization. However, when using water spray cooling, liquid water will produce a water film on the friction interface between the grinding wheel and the tire, reducing the friction between the grinding wheel and the tread, resulting in reduced grinding efficiency. Summary of the invention

[0014] In view of the sticky problem existing in the existing tire testing and grinding process, the present invention provides a method for preparing a worn tire using carbon dioxide for cooling and a tire grinding machine.

[0015] The technical solution of the present invention provides a method for preparing a worn tire, wherein a rotating grinding wheel is used to reciprocate on the tread to achieve tread grinding when the tire rotates, and a carbon dioxide jet is sprayed onto the tread to cool it down. The temperature of the carbon dioxide jet at the tread is -30 to -50°C, and the average flow rate of the carbon dioxide jet is 0.25 to 0.75 kg / min.

[0016] Specifically, the carbon dioxide jet follows the contact point between the tire and the grinding wheel.

[0017] Specifically, the distance between the contact point and the outlet of the carbon dioxide jet is 0.5-0.9 m.

[0018] Specifically, the carbon dioxide jet is injected at intervals, and the ratio of the interval time to the injection time in one working cycle is 3.5 to 14.5.

[0019] Specifically, the injection time of the carbon dioxide jet in one working cycle is 75 to 135 seconds.

[0020] Preferably, during the tread grinding process, the grinding profile is composed of three tangent arcs, and the ratios of the radii of the tangent arcs from the tread centerline to the sidewall are 1000:(250-300):(30-45) respectively.

[0021] Preferably, the single-side arc length ratio of the tangent arc from the tread centerline to the sidewall is 55:30:15.

[0022] The present invention also provides a tire grinding machine for preparing worn tires using the above-mentioned worn tire preparation method, comprising a mounting seat for mounting and driving the tire and a grinding wheel for grinding the tread, and is characterized in that it also includes a carbon dioxide injection system for injecting carbon dioxide into the tread.

[0023] Specifically, the carbon dioxide nozzle of the carbon dioxide injection system follows and points to the contact point between the tire and the grinding wheel.

[0024] Specifically, the carbon dioxide nozzle is arranged on the side of the rotating surface of the grinding wheel and is arranged perpendicular to the rotating surface of the grinding wheel.

[0025] The present invention uses a carbon dioxide jet to cool the contact surface during grinding. Since the temperature of carbon dioxide is low, it can take away the heat generated by the friction process when it sublimates into gas, so the effect of controlling the temperature rise is obvious. On the other hand, the carbon dioxide quickly evaporates into the air in the form of sublimated carbon dioxide gas, and will not remain and accumulate on the grinding interface, so it has almost no effect on the surface effect after grinding. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the movement of the tire and the grinding wheel of the present invention;

[0027] Figure 2 It is a schematic diagram of the grinding profile of the present invention;

[0028] Figure 3 It is a schematic diagram of Comparative Example 7;

[0029] Figure 4 It is a schematic diagram of Comparative Example 8;

[0030] Figure 5 is a schematic diagram of Example 5;

[0031] Figure 6 It is a schematic diagram of Comparative Example 9;

[0032] Figure 7 The following is a photograph of the tread of a buffed tire according to the present invention.

[0033] In the figure:

[0034] 1 Tire; 2 Grinding wheel; C Contact point; A Tread. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. In this specification, the size ratios in the drawings do not represent the actual size ratios, but are only used to reflect the relative position relationship and connection relationship between the components. Components with the same name or the same number represent similar or identical structures and are only for illustrative purposes.

[0036] The tire grinding equipment used in the present invention is a PCR<R tire profile simulation grinding machine. The PCR<R tire profile simulation grinding machine used in the following experimental process is manufactured by Shantou Haoda Tire Testing Equipment Co., Ltd. Figure 1 The schematic diagram of tire grinding is shown in Figure 1. The grinding wheel 2 of the grinding machine is pre-pressed on the tread of the tire 1. The various parts of the tire move during the grinding process. Figure 1 The tire 1 rotates in a direction T perpendicular to the paper surface, and the grinding wheel 2 rotates in a rotation direction G within the paper surface. The grinding wheel 2 and the tread of the tire 1 are pre-pressed at the contact point C. At the same time, the grinding wheel 2 reciprocates from one sidewall to the other on the tread A between the two sidewalls (in the direction indicated by the arrow M), thereby achieving the tread grinding operation.

[0037] In order to avoid the tire rubber softening and forming sticky glue due to the increase of tread temperature during tire grinding, the present invention adopts a method of spraying carbon dioxide to the tread during grinding to cool it down. The method of spraying carbon dioxide liquid to the contact point of the tread / grinding to cool down the temperature during the grinding process reduces the temperature rise during the grinding process, and at the same time, the environment is kept ventilated to avoid oxygen deficiency for the operator.

[0038] The temperature of the coexistence point of solid, liquid and gas phases of carbon dioxide is -56.6℃. After carbon dioxide is sprayed out, the temperature is relatively different at a certain distance. Therefore, it is necessary to avoid the effect of too low temperature on rubber performance, especially to avoid the tread becoming hard and unable to be polished after the temperature is lower than the glass transition temperature of the tire, or the temperature is too low, resulting in insufficient tread elasticity. Of course, on this basis, the lower the temperature, the more conducive it is to control the temperature rise during the polishing process. For this reason, the relationship between the distance of liquid carbon dioxide from the carbon dioxide nozzle and its temperature was first experimented as shown in the following table:

[0039]

[0040]

[0041] By sublimating or evaporating carbon dioxide into a gas to absorb heat and cool the tread, it is only necessary to ensure that the carbon dioxide contacts and covers the tread. Since the tire is rotating, it is possible to set the carbon dioxide nozzle at a fixed position to spray carbon dioxide onto the tread. However, it is preferred to set the carbon dioxide jet to follow the reciprocating movement of the grinding wheel. It is preferred to set the carbon dioxide nozzle on one side / both sides of the rotating surface of the grinding wheel directly opposite the rotating surface of the grinding wheel, so that the impact position of the carbon dioxide jet always follows and points to the contact point, thereby ensuring the contact point, that is, the rapid cooling of the relative friction position. On this basis, the grinding wheel reciprocates in one direction on the tread for about 60 seconds. The use of spraying carbon dioxide for cooling requires cooling the entire tire surface, so the minimum injection time should be set to be greater than the time of one reciprocating movement.

[0042] In order to save the amount of carbon dioxide used, the method of interval injection can be used, that is, after a short injection, start again after a period of time. At this time, since the temperature of the entire tread has been reduced by the rapid cooling effect of the carbon dioxide jet during the injection stage, it can be maintained for a period of time. The interval time is 3.5 to 14.5 times the injection time. Whether it is interval injection or continuous injection, the appropriate average flow rate of carbon dioxide is 0.25 to 0.75 kg / min (kilograms per minute). The average flow rate here refers to the ratio of the mass of carbon dioxide consumed to the total working time used in a working cycle from injection to interval.

[0043] According to the above content, the present invention provides Example 1 and Example 4, and also provides corresponding comparative examples.

[0044] Among them, Comparative Examples 1 and 2 are benchmark experiments conducted on the same tire grinder without taking any measures. Comparative Example 3 is the experimental data of reducing the initial temperature and the ambient temperature, and Comparative Examples 4 and 5 are comparative experimental data of using coolant for spraying and cooling.

[0045] Among them, in Comparative Examples 4 and 5, the coolant is used to continuously spray and cool the polishing contact parts, and the specific design is:

[0046] Nozzle: 2mm metal sprayer

[0047] Water pressure: 0.8MPa (low pressure); 1.6MPa (medium pressure); 2.5MPa (high pressure)

[0048] Cooling fluid: Use 10% cutting fluid emulsified oil, which has low corrosion resistance and no lubrication requirements;

[0049] Nozzle position: always on both sides of the grinding position where the grinding wheel contacts the tire, and moves back and forth with the grinding wheel;

[0050] The following are experimental data of the present invention:

[0051]

[0052]

[0053] Continuation table:

[0054]

[0055] Obviously, from Comparative Examples 1-5, it can be seen that whether it is the benchmark experiment or the grinding process by lowering the initial grinding temperature or by cooling treatment with coolant / water in the prior art, the problem of tire softening and sticking exists to varying degrees. Even in Comparative Example 6, due to the unreasonable design of the parameters of carbon dioxide cooling, there is also the problem of not being able to achieve good grinding, but the timing of sticking is relatively late.

[0056] On the basis of solving the problem of grinding temperature rise, this application also studies the influence of grinding profile on tire softening.

[0057] The setting of the grinding profile has a great impact on the entire grinding process. In order to ensure that the groove depth target is achieved within 75% of the tread center, the adjustable space of the main groove part is very small, and the adjustable part is locked in the part outside 75% of the tread, that is, the shoulder profile position; the smoother the grinding profile (the deeper the depth of point D), the larger the second arc and the smaller the third arc, the more uniform the force during the grinding process, and the less heat is generated. Figure 2 As shown, we have drawn up the profile when the tire is worn to a groove depth of 2mm according to the following method of drawing up the profile. After sweeping the outer contour, the tread profile P is obtained by rounding. A perpendicular line is drawn to the rounded tread profile P at the depth of the groove. A distance of 2mm from the tread profile P is selected to obtain points A and B in the figure. At the mid-surface of the tread, there is no groove. The tread profile P is offset downward to -2mm after rounding or by offsetting the tread profile to the position that most coincides with points A / B. Point D is taken from 15 to 25mm from the shoulder transverse groove (avoiding the bulge), and a perpendicular line is drawn to the shoulder contour after rounding, and it is taken at ≤2mm.

[0058] Based on comparative example 1, we set up four crown radius ratios with changes mainly in the shoulder position according to the four points A, B, C, and D. The schematic diagram is shown in Figure 3-6 , the crown arc radius ratio and polishing phenomenon are as follows:

[0059]

[0060]

[0061] From the above, it can be seen that only on the basis of Example 5, a good grinding effect is achieved. Under the crown arc radius ratio of Comparative Example 9, although the grinding can be completed as scheduled, the size after grinding does not meet the requirements and cannot be used for subsequent experiments. The above method for adjusting the crown arc radius ratio is applicable to semi-steel radial tires with a nominal section width of 205mm to 305mm. For tires with different nominal section widths, the crown arc radius is adjusted using the following ratios:

[0062] Nominal section width (mm) coefficient% Crown radius (mm) 205 78％ 649.15 215 81％ 680.81 225 85％ 712.48 235 89％ 744.14 245 92％ 775.81 255 96％ 807.47 265 100％ 839.14 275 104％ 870.81 285 108％ 902.47 295 111％ 934.13 305 115％ 965.8

[0063] In addition to the crown arc radius ratio, the grinding profile is composed of three arcs, and there is a tangent transition between the arcs. The transition position will affect the force transmission. For the case where the total length of the tread arc is 240mm, we adjusted the ratio of the lengths of the three arcs and conducted a comparative study. The results are as follows:

[0064]

[0065] It was further found that only in Example 13, when the arc length ratio was 55:30:15, a good grinding performance was achieved. In Comparative Examples 10-12 and Comparative Example 13, the grinding target was not achieved, and adhesion occurred again in Comparative Example 13.

[0066] By integrating the experimental conditions of Example 3, Example 5 and Example 6, we made a number of worn tire test pieces on the tire grinding test machine and measured the mean values ​​of the relevant data (units not indicated are mm) as follows:

[0067]

[0068]

[0069] The above table shows that the dimensions of the finished worn tire parts must meet the tolerance requirements specified in the standard. Figure 7 This is a photo of the tread after production. Its surface roughness has been listed in the table above. It can be seen from the picture that the tread is smooth and delicate, without large local adhesive lumps, which fully meets the subsequent experimental requirements.

[0070] The above content only describes the preferred implementation mode of the present invention, and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solution of the present invention by ordinary technicians in this field should fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a worn tire, wherein a rotating grinding wheel is used to reciprocate on the tread to achieve tread grinding while the tire rotates, characterized in that: A carbon dioxide jet is sprayed onto the tread to cool it down. The temperature of the carbon dioxide jet at the tread is -30 to -50°C, and the average flow rate of the carbon dioxide jet is 0.25 to 0.75 kg / min.

2. The method for preparing a worn tire according to claim 1, wherein: The carbon dioxide jet follows the point of contact between the tire and the grinding wheel.

3. The method for preparing a worn tire according to claim 2, wherein: The distance between the contact point and the outlet of the carbon dioxide jet is 0.5 to 0.9 m.

4. The method for preparing a worn tire according to claim 1, wherein: The carbon dioxide jet is injected at intervals, and the ratio of the interval time to the injection time in one working cycle is 3.5 to 14.

5.

5. The method for preparing a worn tire according to claim 4, wherein: The injection time of the carbon dioxide jet in one working cycle is 75 to 135 seconds.

6. The method for preparing a worn tire according to claim 1, wherein: During the tread grinding process, the grinding profile is composed of three tangent arcs, and the ratios of the radii of the tangent arcs from the tread centerline to the sidewall are 1000:(250~300):(30~45).

7. The method for preparing a worn tire according to claim 6, wherein: The ratio of the single-side arc length of the tangent arc from the center line of the tread to the sidewall is 55:30:

15.

8. A tire grinding machine for preparing worn tires using the method for preparing worn tires according to any one of claims 1 to 7, comprising a mounting seat for mounting and driving the tire and a grinding wheel for grinding the tread, characterized in that: Also included is a carbon dioxide injection system for injecting carbon dioxide into the tread.

9. The tire grinding machine according to claim 8, wherein The carbon dioxide nozzle of the carbon dioxide injection system follows the movement of the contact point between the tire and the grinding wheel and points to the contact point.

10. The tire grinding machine according to claim 9, wherein The carbon dioxide nozzle is arranged on the side of the rotating surface of the grinding wheel and is perpendicular to the rotating surface of the grinding wheel.

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