JPH0553608B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Industrial Application Field The present invention relates to a method of curing or vulcanizing an article by heating. Although the present invention has particular application in curing tires, it can also be used in other rubber products such as hoses, in which specific amounts of vulcanization can be achieved to achieve complete vulcanization without actually uncuring or over-curing. Can be used in any other product that requires heat. (2) Prior Art Tire vulcanization typically involves a device for inflating the tire with a hot fluid medium (usually steam or boiling water) and a heated mold that receives the unvulcanized or green tire carcass. Performed in a press. The press has the effect of forming the tire into the desired final shape of the tread pattern, and hardens the assembly while causing vulcanization by heat directed into the tire from the mold and liquid medium. Prior art systems for controlling vulcanization began by simply holding the tire in a heated press for an empirically determined period of time. More recent techniques have been developed to calculate ``vulcanization units'' (i.e., units of heat) and terminate once the required amount of ``heat units'' have been input. This technology has evolved into a process that senses a predetermined number of measurements that are monitored by small temperature sensors placed inside the tire. Similarly, a method was proposed in U.S. Pat. No. 4,371,483 that measured only the temperature outside the tire and iteratively calculated the number of vulcanization units along an imaginary line above the tire shoulder. Ta. The minimum cure point on that line is then selected and the press opens when that point receives the requested cure units. The traditional method of calculating the extent of vulcanization (i.e. the number of vulcanization units received) at one given station is a fairly inaccurate approximation and the complex calculations require significant computer power. Therefore, recent efforts have been made to improve this method and find a single algorithm that can be used to simplify the calculations for each tire during repeated tire curing processes.
Such an algorithm is described in the above-mentioned US patent no.
4371483. (3) Object of the invention The object of the invention is to provide a further improved control of the vulcanization of products such as tires, which requires only limited computer functionality, such as can be easily performed on already available microcomputers. The purpose is to provide a method. The second objective is to accurately measure the vulcanization time despite the changing working conditions of tires from one tire to another with the same arrangement and structure, thereby accounting for changes in the initial temperature of the green tire and mold. The objective is to provide a corresponding method. (4) Structure of the Invention In achieving these objectives, one fixed algorithm cannot accommodate the wide variation in critical temperatures and, therefore, the wide variation in time to complete vulcanization. I ran into a problem where I couldn't do it. For example, in the 11.00-22.5 radial truck tire example, adjustment of the 35-60 minute cure time had to be assisted by empirically varying the initial conditions in the manufacturing environment. However, given the set of values as constants, one particular basic algorithm can be used to precisely control the vulcanization process, so that a series of similar algorithms can be used. According to the invention, the method of vulcanizing a heat-vulcanized product comprises placing the product in a press mold heated by a medium, heating the product to compress the product and start vulcanization. filling the interior of the product with a pressurized fluid medium;
It is characterized by the following steps: (a) monitoring the temperature T _n of the mold; (b) measuring the time t _n reaching the maximum mold temperature; (c) measuring the temperature T _MW of the medium heating the mold. (d) Monitoring the value of the temperature of the hot fluid medium T _MW after the initial or basic vulcanization time, log _e C=A _1tL +
A _2tL t _n +A _3tL T _n +A _4tL T _MS +A _5tL T _MS A _6tL t _L (C is the vulcanization received after the time t _L from the start of vulcanization, constant A _1tL , ……… A _6tL is selected from a series of sets of constants described above, each set of which is applied for a given time interval during vulcanization, and the set selected for each calculation is the one immediately preceding the calculation time _tL . This is determined for each elapsed cure time for a predetermined minimum cure point in the product using a set of algorithms given by t _L > t _n ). Iteratively calculating the number of vulcanization units accepted by the minimum vulcanization point; (e) known number of vulcanization units for complete and accurate vulcanization and vulcanization units for the minimum vulcanization point; (f) terminating the vulcanization when the calculated number of vulcanization units reaches the number of complete vulcanizations; (g) removing the product from the mold. The set of constants is determined by performing detailed finite element analysis on a cross section of the product divided into zones using standard techniques. Standard techniques include, for example, ``Application of the finite element method to heat flow in rubber products'' (G.D. Hütsbad and
GM Simpson, newsletter "International Rubber Association" 1979.
This is a technique that has been published in public magazines such as (Venice). These calculations are complex and require the power of large computers, but once performed on the product to be cured, a set of results is produced for which separate time intervals are selected and these By fitting the curve to the time interval, an accurate linear regression fit is achieved. A suitable interval is 5 minutes, and for each 5 minutes, set a constant, A _1tL ...
A _6tL is discovered. Part of the present invention is that when such intervals are used with a precise set of constants, accurate cure times can be determined, which does not require significant computational power at the press site. In fact, each set of constants allows an unambiguous calculation of the total vulcanization units for the measured temperature. for example,
For intervals of 1 minute, it is sufficient to change the constant for each 5 minutes. When vulcanizing a tire, the mold temperature T _n is preferably measured by a thermocouple located within the body of the mold adjacent to the surface of the tire. Furthermore, the temperature of the fluid heating the mold
Temperature of the fluid in the product as measured by the temperature of the vapor measured at the point where the _TMS enters the mold
Preferably, T _MW is the temperature of the hot water measured at the point leaving the tire. Further details of the invention and in particular the deviations in the set of constants will appear from the description below. This is an example of a vulcanization control method for an all-steel radial 12.00-20 truck tire manufactured by Dunlop Co., Ltd. sold under the trade designation SP311. (5) Description of Examples First, a finite element analysis is performed on a cross-section of a tire using the mesh shown in the drawing. There, half of the cross-sectional view of the tire is divided into a number of triangles 10, the vertices of which are radial measurement points. Assume that the heat flow through each triangle is linear and that the properties of the elements are as shown in Table 1. Table 1 Element/Material Thermal conductivity Thermal diffusivity K (W/m℃) k
(m ² /s) Diamond/rubber 0.25 0.139x10 ^-6 Steel wire/rubber composite 0.37 0.121x10 ^-6 Initial conditions are 25°C to carcass temperature
100℃, and the mold temperature changed from 100℃ to 150℃. The extent of vulcanization after removal from the mold was limited to 20 minutes, and calculations were performed for different mold patterns: surface temperature and internal fluid temperature. Many different calculations are performed and a set of constants
A statistical analysis was performed using a multiple regression procedure giving A _1tL ……………A _6tL . One set is 35-40 minutes, 40-45 minutes, 45-50 minutes, 50-55 minutes respectively.
minutes, given for 55-60 minutes. These 5
A set of two constants was found to be sufficient to cover all possible vulcanization conditions for compressions based on 5 minute intervals. Constants are shown in Table 2 for exemplary tires.

[Table] Calculations using the algorithm then give the vulcanization units. Here, 1 vulcanization unit = 140℃ (413.15K)
1 minute. The proper algorithm is the third
Shown in the table.

[Table] However, C = Vulcanization received after time t _L = Time taken to reach the maximum mold temperature _{T n =} Mold surface temperature T _MS = Steam temperature T _MW = Hot water temperature t _L = From the start of vulcanization It's time. The finite element analysis also indicates the minimum vulcanization point for the tire concerned. Following the induction of constants for the algorithm, the tire curing press is connected to a microcomputer equipped with thermocouple inputs from the press to deliver the temperatures and times required by the algorithm. Then, the required number of vulcanization units for the minimum vulcanization point for accurate vulcanization without over or under vulcanization is entered as a target value, and the tire is placed in the press.
The time cycle t _L starts from 0 when the bag is inflated and the press is closed for final tire molding. The steam and hot water temperatures _TMS and _TMW , the mold surface temperature _Tn , and the time _tM are monitored,
After 35 minutes, the first C calculation is performed using the first set of constants in the algorithm, and calculations are performed every minute on the microcomputer, comparing the result for each number of cure units with the target value. It was done. At 40 minutes, the microcomputer is changed to use the second constant, and the ranking constant is changed every 5 minutes thereafter. When the calculated value of the vulcanization units introduced at the minimum vulcanization point equals or exceeds the target value, the microcomputer opens the press and begins to remove the tire and stops applying heat. Such a method of controlling the vulcanization process has been shown to achieve controlled and precise vulcanization despite large differences in temperature in the press and initial temperature of the elements. This method uses limited computer power on the press, resulting in cost savings. It has been shown that it can be successfully used on tires ranging from other truck tires to car tires.

[Brief explanation of the drawing]

The figure is an explanatory diagram showing zone formation on a cross section of a tire. 10...Triangle.

Claims (1)

Claims: 1. Placing the product in a press mold heated by a medium; filling the inside of the product with a hot pressurized fluid medium to compress and heat the product to initiate vulcanization; A method for vulcanizing a product comprising the steps of: (a) monitoring the temperature T _n of the mold; (b) measuring the time t _n to reach the maximum mold temperature; and (c) monitoring the mold temperature T n. (d) monitoring the temperature value T _MW of the hot fluid medium after the initial or basic vulcanization _time , log _e C=A _1tL +A _2tL t; _n +A _3tL T _n +A _4tL
T _MS +A _5tL T _MW A _6tL t _L (where C is the vulcanization received after the time t _L from the start of vulcanization, constant
A _1tL , A _6tL are selected from a series of sets of constants described above, each set of which is applied for a given time interval during vulcanization, and the set selected for each calculation. is the set for the interval just before the calculation time _tL . Also, t _L > t _n . ) for a predetermined minimum cure point in the product, the number of cure units accepted by this minimum cure point for each elapsed cure time. (e) comparing each of the calculated number of vulcanization units for a minimum vulcanization point with the known number of vulcanization units for complete and accurate vulcanization; (f) terminating the vulcanization when the calculated number of vulcanization units reaches the number of complete vulcanizations; and (g) removing the product from the mold. How to vulcanize. 2. The constants are determined by performing finite element analysis to obtain a curve of vulcanization on a cross-section of the product, by selecting a series of discrete time intervals and fitting the curve to each time interval. A method as claimed in claim 1 for obtaining an accurate regression fit. 3. A method according to claim 1, wherein the temperature of the mold, T _n , is measured by a thermocouple located in the mold adjacent to the surface of the product. 4. The method according to claim 1, 2 or 3, wherein the temperature _TMS of the liquid heating the mold is measured by measuring the temperature of the liquid flowing into the mold. 5. The method according to any one of claims 1 to 4, wherein the temperature T _MW of the liquid in the product is measured by a thermoelectric body at a measuring point where the liquid covers the product. 6. The product according to any one of claims 1 to 5, wherein the product to be vulcanized is a tire, the liquid that heats the mold is steam, and the liquid that cools the tire is hot water. Method.