Vulcanization of rubber products in molds

from "Rubber Technology"

In this case, the rubber product blank is placed for vulcanization in a metal vulcanization mold, which consists of two or more collapsible parts. There is a cavity inside the mold, the dimensions of which must correspond to the dimensions of the finished vulcanized products, taking into account the shrinkage of products that occurs after vulcanization by 1.5-3%. The mold is equipped with locking devices that keep it closed during vulcanization.
At the end of vulcanization, steam is released, the boiler is opened and recharged. With this method of vulcanization, it is necessary to use special molds, which require considerable time to recharge. During prolonged recharging, the molds cool down significantly, which leads to increased steam consumption.
Operations related to recharging boilers and molds are difficult to mechanize, therefore the method of vulcanizing rubber products in molds in horizontal vulcanization boilers is used only for large-sized products that cannot be vulcanized in hydraulic vulcanizing presses or in press autoclaves, as well as for medium-sized products, produced in small quantities.
There are vulcanization presses of different designs with a hydraulic drive, with a lever-mechanical drive and with a lever-pneumatic drive.
Hydraulic vulcanizing press platens are usually heated by steam, sometimes hot water, or electric current. A constant vulcanization temperature during electric heating is maintained using an automatic electronic regulator such as EPD or an electronic machine Mars-200.
To hydraulically drive the vulcanization press and create the necessary pressure during vulcanization, low and high pressure water is used as a working fluid. Low pressure water (20-50 kgf/cm) is used to lift the plunger and press plates, high pressure water (100 - 300 kgf/cm) is used to maintain the required pressing force during vulcanization.
Product blanks should be slightly larger in weight and volume than the finished product. This is necessary so that it is always possible to ensure complete molding of the entire surface of the products, even with some difference in the sizes of the mold cavities. To facilitate the insertion of a rubber product blank into a vulcanization mold, the blank is made slightly smaller than the dimensions of the mold cavities (in length and width). A certain excess of rubber mixture is created along the height of the product; the amount of excess is determined depending on the size and shape of the product being vulcanized.
During the vulcanization process, the excess amount of rubber mixture is pressed out of the mold into the connectors between its parts and forms a vulcanized extrusion, which is trimmed after vulcanization. The amount of waste in the form of vulcanized extrusion varies from a fraction of a percent in the manufacture of large products and up to 50-60% or more in the manufacture of small products.
During vulcanization, the molds are gradually heated, and the rubber mixture gradually expands when heated in the molds. The coefficient of volumetric expansion of the rubber mixture is several times greater than the coefficient of volumetric expansion of steel, so a lot of pressure arises inside the closed mold. Under these conditions, the softened plastic rubber mixture easily fills the entire internal cavity of the mold.
With subsequent heating, gradual vulcanization occurs, the rubber mixture loses its plasticity and turns into durable, elastic rubber.
After the set time has elapsed, the high-pressure liquid is released, the press is opened and the vulcanization molds are recharged. Hot vulcanized products are cooled with water to quickly stop vulcanization.
Heating of molds during vulcanization is carried out only from two sides - top and bottom; therefore, it is impossible to vulcanize high-height products on a press in order to avoid uneven vulcanization. The temperature of different parts of the slabs of the vulcanization press is not the same; the temperature of the middle part of the slab surface is 3-5 ° C higher than the temperature of the slab surface at its edges, due to more intense cooling of the slab edges. Due to heat transfer, the surface temperature of steam plates is slightly lower than the coolant temperature. The vulcanization temperature on presses is usually in the range from 140 to 160 °C. The duration of vulcanization on presses depends on the vulcanization temperature (coolant temperature), the size of the products and the rubber formulation. It usually ranges from 6-10 minutes to 60-90 minutes.
Vulcanizing presses are installed in rows (sections). Each press section is served by one or two reloaders. Presses with one-sided and two-sided service are used. Multi-storey presses usually have two-way service, i.e. they are reloaded simultaneously by two workers on both sides; on one side, one worker recharges the upper floors, the second worker, on the other hand, recharges the lower floors of the press.
The hydraulic part of the press is controlled by a spindle distributor. Recently, semi-automatic control distributors with a pneumatic head have become widespread. Presses with a semi-automatic distributor have a push-button starter and, upon completion of vulcanization, are automatically opened using a CEC.
At the Kauchuk plant, on the basis of a hydraulic frame press, semi-automatic presses have been created for the vulcanization of products in cassette molds with a device for extending and opening the molds. Four-story semi-automatic presses with two-way service, two-story presses with one-way service.
Currently, industry has begun to use semi-automatic carousel hydraulic presses of the MPA brand, manufactured according to the project of the All-Union Scientific Research Institute of Artificial Leather (VNIIK). In Fig. 86 shows a general view of the semi-automatic press MPA. The press has a rotating table-carousel, on which separate press points are installed around the circumference (18 single-story presses with a 350x510 plate, covered with an exhaust ventilation hood. The supply of high-pressure liquid, steam and condensate removal is carried out through a manifold, the lower part of which rotates together with the table, the plates have steam heating, the maximum operating excess steam pressure is 12 apg. Steam heating can be replaced by electric heating. The duration of the vulcanization cycle from 4 to 16 minutes can be changed in accordance with the specified mode by changing the number of revolutions of the rotary table using a speed variator. Currently, designs of 10-, 24- and 32-point semi-automatic presses have also been developed.
And their extension when reloading is carried out automatically. The working press operator only lays the blanks and removes the vulcanized parts. The set vulcanization temperature is maintained automatically.

Technologically, the vulcanization process is the transformation of “raw” rubber into rubber. As a chemical reaction, it involves the combination of linear rubber macromolecules, which easily lose stability when exposed to external influences, into a single vulcanization network. It is created in three-dimensional space due to cross-sectional chemical bonds.

This seemingly “cross-linked” structure gives the rubber additional strength properties. Its hardness and elasticity, frost and heat resistance are improved while solubility in organic substances and swelling are reduced.

The resulting mesh has a complex structure. It includes not only nodes connecting pairs of macromolecules, but also those that combine several molecules at the same time, as well as transverse chemical bonds, which are like “bridges” between linear fragments.

Their formation occurs under the influence of special agents, the molecules of which partially act as building materials, chemically reacting with each other and rubber macromolecules at high temperatures.

Material properties

The performance properties of the resulting vulcanized rubber and products made from it largely depend on the type of reagent used. Such characteristics include resistance to exposure to aggressive environments, rate of deformation during compression or increased temperature, and resistance to thermal-oxidative reactions.

The resulting bonds irreversibly limit the mobility of molecules under mechanical action, while simultaneously maintaining the high elasticity of the material with the ability to undergo plastic deformation. The structure and number of these bonds is determined by the rubber vulcanization method and the chemical agents used for it.

The process does not proceed monotonously, and individual indicators of the vulcanized mixture in their changes reach their minimum and maximum at different times. The most suitable ratio of the physical and mechanical characteristics of the resulting elastomer is called the optimum.

The vulcanizing composition, in addition to rubber and chemical agents, includes a number of additional substances that contribute to the production of rubber with specified performance properties. According to their purpose, they are divided into accelerators (activators), fillers, softeners (plasticizers) and antioxidants (antioxidants). Accelerators (most often zinc oxide) facilitate the chemical interaction of all ingredients of the rubber mixture, help reduce the consumption of raw materials and time for processing, and improve the properties of vulcanizers.

Fillers such as chalk, kaolin, carbon black increase the mechanical strength, wear resistance, abrasion resistance and other physical characteristics of the elastomer. By replenishing the volume of feedstock, they thereby reduce rubber consumption and reduce the cost of the resulting product. Softeners are added to improve the processability of rubber compounds, reduce their viscosity and increase the volume of fillers.

Plasticizers can also increase the dynamic endurance of elastomers and abrasion resistance. Antioxidants that stabilize the process are introduced into the mixture to prevent “aging” of the rubber. Various combinations of these substances are used in the development of special raw rubber formulations to predict and adjust the vulcanization process.

Types of vulcanization

Most often, commonly used rubbers (styrene-butadiene, butadiene and natural) are vulcanized in combination with sulfur, heating the mixture to 140-160°C. This process is called sulfur vulcanization. Sulfur atoms participate in the formation of intermolecular cross-links. When up to 5% sulfur is added to a mixture with rubber, a soft vulcanizate is produced, used for the manufacture of automobile tubes, tires, rubber tubes, balls, etc.

When more than 30% of sulfur is added, a rather hard, low-elastic ebonite is obtained. Thiuram, captax, etc. are used as accelerators in this process, the completeness of which is ensured by the addition of activators consisting of metal oxides, usually zinc.

Radiation vulcanization is also possible. It is carried out through ionizing radiation, using streams of electrons emitted by radioactive cobalt. This sulfur-free process produces elastomers that are particularly resistant to chemical and thermal attack. To produce special types of rubber, organic peroxides, synthetic resins and other compounds are added under the same process parameters as in the case of adding sulfur.

On an industrial scale, the vulcanizable composition, placed in a mold, is heated at elevated pressure. To do this, the molds are placed between heated plates of a hydraulic press. When producing non-molded products, the mixture is poured into autoclaves, boilers or individual vulcanizers. Heating of rubber for vulcanization in this equipment is carried out using air, steam, heated water or high-frequency electric current.

For many years, the largest consumers of rubber products have been automotive and agricultural engineering enterprises. The degree of saturation of their products with rubber products serves as an indicator of high reliability and comfort. In addition, parts made from elastomers are often used in the production of plumbing installations, footwear, stationery and children's products.

There are more and more tire shops. However, on the road, both a cyclist and a motorist, a situation may arise when a tire breaks and the workshop is far away. A car enthusiast often has a spare wheel, but a bicycle driver does not have such a wheel, and it becomes necessary to vulcanize the inner tube on the road.

Concept of vulcanization

Vulcanization is a chemical process during which raw rubber, improving the properties of the material in strength and elasticity, becomes rubber. In fact, rubber can be used as a special glue to seal a puncture in an inner tube or tire. Rubber vulcanization processes are as follows:

electric;
sulfuric;
hot;
cold.

Types of rubber

Rubber is one of the few materials that has different hardness. Depending on the percentage of sulfur, it is:

soft – contains up to 3% sulfur;
semi-solid – from 4 to 30% sulfur;
hard – more than 30%.

There are also special clamps with a heating element. Such devices can operate from a 220V household network, from a car battery, through a cigarette lighter socket, or from their own battery. It all depends on the performance of each device. These clamps are easy to use; you need to attach a rubber patch to the camera, clamp it and plug it into the network.

Sulfur vulcanization of rubber

This operation consists of a chemical reaction in which sulfur atoms are added to the rubber. When added up to 5%, it produces raw materials for the manufacture of tubes and tires. In the case of gluing two elements, sulfur helps connect the rubber molecules, forming a so-called bridge. This procedure refers to the hot method, but it is unlikely that it will be possible to do it on a hike or on the highway.

Hot vulcanization

Rubber, as a raw material, has the property of being welded into a single composition at a temperature of 150 °C. As a result of this process, the rubber becomes rubber and cannot return to its original position. Thanks to its capabilities, rubber can fix any punctures and cuts in the tube and tire.

It is necessary to vulcanize rubber using a hot method, only using a press. The depth and area of the cut will tell you how long to weld. Typically, it takes 4 minutes of cooking to repair a 1mm cut. Accordingly, if the cut is 4mm, then it needs to be vulcanized for 16 minutes. In this case, the equipment must be warmed up and configured.

By performing hot vulcanization at temperatures above 150C, you can ruin the rubber and achieve nothing, since the material will deteriorate and lose its characteristics.

Using clamps or a press allows you to properly patch the damage. After finishing the work, you should make sure that there are no voids or air bubbles in the seam. If there are any, you need to clean the puncture site from fresh rubber and repeat the whole process again.

In order to hot seal a camera at home, you must do the following. From raw rubber, you need to cut a piece slightly smaller than the patch itself. The tube or tire is cleaned slightly wider at the damaged area, to a rough state, and then degreased with gasoline. When preparing the patch, you need to cut the chamfer at an angle of 45°, also sand and degrease. Then we cover the puncture site with a patch, clamp it in a vice and heat it to the desired temperature.

If you dissolve raw rubber in gasoline, you can get a special glue for rubber, the use of which improves the quality of the seam. Particular attention should be paid to temperature conditions. Vulcanization is carried out at a temperature of 140 - 150 ° C; if there is a smell of burnt rubber, it means the patch has overheated, and if it has not merged with the overall product, then it may not have reached the required temperature. To prevent rubber from sticking to metal, you need to place paper between them.

Cold vulcanization

Nowadays, using this method is not difficult, since you can purchase a repair kit in every auto or bicycle parts store. The contents of this set may vary, but each one contains patches and special glue.

The repair procedure in this case is similar to the hot method. You also need to treat the damaged surface with an abrasive, remove rubber dust and degrease. After drying, apply glue to the camera and glue the patch. In this case, it is not the duration of the pressure that plays a role, but its strength. Therefore, it will not be enough to simply press down with a stone; more force is required.

Do-it-yourself cold vulcanization of rubber is a fairly simple process that can be performed wherever you are if you have a special kit. However, raw rubber is not made with your own hands at home. For such work you need special equipment.

Making a vulcanization device

Each vulcanizer has two main elements - a heating part and a clamping device. The basis of such rubber processing equipment can be used:

iron;
“bazaar” electric stove;
piston from the engine.

In a device with an iron, the heating part is the surface that is used for ironing in everyday life. If we plan to use an electric stove, then the heating coil should be covered with a metal sheet, and when working, you need to place paper between the rubber and the metal. Such a device must be equipped with a thermostat to avoid overheating of the material.

The easiest way to make the clamping part of the vulcanizer is from a clamp. The simplest device to manufacture would be a device consisting of an iron and a clamp. Since they are both metal, joining them using arc welding is not difficult. The iron also has a thermostat.

A piston vulcanizer also uses a metal plate. A rubber bladder is placed on it. The piston, with its smooth part, which is in contact with the explosive mixture in the engine, uses a homemade clamp to press down the patch. Paper is also placed between the piston and the patch. After that, gasoline is poured into the piston and ignited.

Such a device made from a piston is especially useful on the road, when there is no way to connect to the electrical network. However, such a device does not have a thermostat, and the temperature will have to be controlled manually.

Pros and cons of vulcanization

The main advantage of the tire repair process is that it is cheaper to repair than to buy a new one. However, each situation is individual, so it is important to determine whether repairs will save the situation.

The cold method is quite easy to use, it will not take much time, and the costs will be minimal. The main disadvantage of this method is the unreliability of gluing. This procedure is temporary, and you should contact a service station as soon as possible.

Hot vulcanization reliably welds rubber, allows such work to be carried out at any temperature and has a low cost.

So, you can repair a tube or tire in different ways, but it is better to entrust this work to specialists, because it is for your own safety.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

Ministry of Education and Science of the Russian Federation

Federal Agency for Education

Perm State Technical University

Department of KTEI

Calculation work No. 2

Calculation of the technological regime of application and vulcanization

rubber made ofOlations

Completed by: student of the KTEI-04-1 group:

Murzina O.A.

Checked by: teacher of the KTEI department

Popov O.A.

Perm 2008

cable brand: GOST 6598-73

conductor cross-section: S=6mm 2

Rated voltage: U=3 kV

steam temperature in the vulcanization pipe: T P=195°С

1. d pr =0.4mm - wire diameter;

n=280 - number of wires in the core;

N=7 - number of strands; (strand twisting system 1+6);

D from =1.8mm - thickness of rubber insulation;

d = 3.98 mm - core diameter;

2. Rubber type RTI - 1 according to OST 16.0.505.015-79; rubber compound grade TSSH - 35A.

3. Material consumption per 1 m of insulated core:

d etc - wire diameter, mm;

n - number of wires in the core;

n 1 - number of strands in the vein;

G- specific gravity of the core metal, g=8, 890kg/Withm 3 ;

To 1 ,To 2 - coefficients taking into account the twisting of wires into a core and cores into a cable, To 1 =1,0 34 , To 2 =1 ,034 .

d- core diameter;

To 5 - coefficient taking into account technological factors (uneven application, filling voids between wires), To 5 =1, 17 ;

s- insulation thickness.

4. Select equipment ANV - 115;

Curing tube length l T= 100 m;

5. Calculation of the sag of the product in the pipe

Where R- mass of 1 m of insulated core, kg/m,

g m/s 2 ,

l T- pipe length, m,

T- permissible tension force, Pa

where S is the cross-section of the conductor, m 2 ,

Tensile strength of core material, Pa,

TO- safety factor, K =2+3;

d uh- diameter of the product, m.

The condition is not met, therefore we take an inclined line.

6. Temperature conditions for rubber processing on a press:

7. Tool dimensions:

8. Press performance - Q= 5 kg/min

Pressing speed:

R from- rubber consumption per 1 m, kg/m .

TO T- technological coefficient, TO T=0,7 ? 0,8

vulcanization insulation power cable

9, Thermophysical characteristics of condensate at a given temperature:

Heat of vaporization - r= 876 10 3 J/kg,

Density - =876 /m 3 ,

Thermal conductivity - =0.67 W/m°C,

Kinematic viscosity of condensate

at steam temperature (set) - =0,16 6 10 -6 m 2 /With.

10. Heat transfer coefficient on the surface of the insulated core - , W/m 2 WITH(horizontal pipe)

Where TO n- coefficient taking into account the roughness of the insulation surface TO n=0,80 ? 0,85 ;

T With- average wall temperature,

where T r is the temperature of the rubber leaving the head, WITH;

g- acceleration of gravity, m/s 2 ,

E t- coefficient taking into account the dependence of the thermophysical characteristics of condensate on temperature

Specific thermal conductivity of condensate at T n And T With respectively, W/m WITH; =0,685W/m°C

MM With- absolute viscosity of condensate at T n And T To respectively, M=140, M With=201 ,

11.To determine the vulcanization time, we will use numerical methods. The calculation is made in the program (Appendix 1).

12. The intensity of vulcanization of the outer layers of rubber does not depend on time and is determined from the expression

Where T uh- temperature of the beginning of intensive vulcanization.

E max maximum permissible vulcanization effect ( 36000 s),

Let's find the maximum allowable time for insulation to remain in the vulcanization pipe

14. Calculation of the dependence of vulcanization intensity at a point with a radius r- U r(t) from time:

Where TO V=2 - temperature coefficient of rubber vulcanization.

For most tires T uh=143 WITH- temperature of the beginning of intensive vulcanization.

Then the vulcanization effect is determined by the formula

N - number of intervals along the axis t,

Where TO 0 =1,16 - coefficient taking into account additional vulcanization of rubber during the initial cooling period (on the inner surface of the insulation, the temperature during cooling decreases to 143 WITH over time).

15. Speed of passage of an insulated core through a vulcanization pipe:

16. Specify the dimensions of the receiving drum and calculate the length of the insulated core on the drum ( L, m).

The drum is used with the dimensions of the output drum for the general twisting machine (3+1) AVM -2400/1800

Where d w- diameter of the drum neck, mm;

d- diameter along the insulation (screen), mm;

l- drum neck length, mm;

D 1 - diameter of winding the product on the drum, mm;

D 1 = D sch- (4 ? 6) d=1 200 - 4 7,58 = 2370 mm,

Where D sch- diameter of the drum cheek,

.

Routing:

Developer organization code KTEI-04-1

Map of sketches of the technological regime of insulation and vulcanization

Cable brand

Document code

Developer

Calculation work No. 2

Kanyukova Yu.I.

Name

material

Material grade

material

Name of equipment

Equipment brand

Performance

Pipe length

Steam pressure, MPa

Take-up drum number

OST 16.0.505.015-79

Continuous vulcanization cable line

Core design

Insulation

Tool diameter

Linear speed m/min

Steam pressure, MPa

Length at take-up drum

wired

Core diameter,

insulation

* Note: Temperature conditions for rubber processing:

1 press 1 zone - 60 WITH

2 zone - 80 WITH

Head temperature - 90 WITH

TPG temperature - 80 °C

Steam temperature - 195 °C

Posted on Allbest.ru

Similar documents

Calculation of the technological regime for applying protective covers to the power cable under given parameters. Cushion design and nominal thicknesses. Width and maximum allowable pitch of armor tape winding. Calculation of winding parameters for paper and plastic tapes.

test, added 02/02/2011

Review of advances in cable technology and power cable designs. Calculation of cable structural elements: conductor, insulation; electrical and thermal parameters of the cable. Dependence of short circuit current on protection response time.

course work, added 06/04/2009

Calculation of the cross-sectional area and shape of the current-carrying core. Estimation of the dependence of the electric field strength in the thickness of the insulating layer. Determination of electrical parameters of the cable. Calculation of thermal resistances of structural elements and the environment.

course work, added 01/10/2015

Use of insulation made from modern polyolefin materials subject to vulcanization for power cables. Deterioration of mechanical properties at temperatures close to the melting point. Basic methods of cross-linking thermoplastic materials.

presentation, added 11/07/2013

Use of insulation made from modern polyolefin materials subject to vulcanization for power cables. Processing polyethylene at the molecular level. Methods for cross-linking thermoplastic materials. Cables with cross-linked polyethylene insulation.

presentation, added 07/20/2015

The task of calculating the mode is to determine the characteristic parameters of the mode, the necessary initial data and the main stages. Features of the method for calculating the mode at a given voltage at the end and at the beginning of the power line, their differences, interpretation of the results.

presentation, added 10/20/2013

The main purpose of the Cosmos software package is to solve problems of short-term planning and operational management based on telemetric information. Calculation of the steady state and assessment of the state of the power system mode using telemetry data.

course work, added 02/26/2012

Location of the farm and general information, organizational and economic characteristics. Selection of technological and power equipment. Calculation of heating and ventilation. Development of a scheme for automating the temperature regime and power supply of the barn.

thesis, added 07/25/2011

Vertical network water heaters. Calculation of average water temperature. Determination of the heat capacity of water, the heat flow received by water. Heat transfer coefficient from the pipe wall. Thermophysical parameters of condensate at average condensate temperature.

course work, added 11/28/2012

Features of calculating the parameters of the equivalent circuit of power lines. Specifics of calculating the operating mode of the network taking into account the capacitor bank. Determination of operating mode parameters of the electrical network using the iterative method (method of successive approximations).

The proposed method makes it possible to determine the minimum time for vulcanization of rubber compounds under pressure, guaranteeing the absence of pores, by using a massive sample mold with a spherical molding cavity for vulcanization. The resulting vulcanized spherical sample is cut diametrically and, if there are pores on the cut, the minimum radius of the pore formation zone is measured. Then, using the proposed relationship, the minimum vulcanization time is determined to guarantee the absence of pores. The proposed method provides high accuracy in determining the minimum vulcanization time of rubber compounds under pressure, guaranteeing the absence of pores. 1 ill., 1 tab.

The invention relates to the field of vulcanization of thick-walled rubber products, in particular to the vulcanization of tires, and is intended for the development of vulcanization modes and installation of optimal operating modes of vulcanization equipment. There is a known method for determining the minimum time for vulcanization of rubber under pressure (GOST 12535-78 "Rubber mixtures. Methods for determining vulcanization characteristics"), according to which a thin-walled sample is vulcanized at a given constant temperature, at the same time the kinetics of vulcanization is determined on a Monsanto rheometer and subsequently using a rheogram (dependence “dynamic modulus M d time”) determine the time to reach 15% of the maximum value M d, which is taken as the minimum vulcanization time (hereinafter referred to as min). However, the accuracy of determining mines using this method is insufficient, since the use of thin samples does not make it possible to take into account the influence of diffusion processes on pore formation that occurs during the vulcanization of thick-walled rubber products. This is due to the fact that the volatile products of chemical reactions formed during the vulcanization of rubber in thin samples diffuse relatively quickly from the inside to the surface, and when the pressure is removed, even in insufficiently vulcanized samples, pores are not observed. The closest in technical essence is a method for determining the minimum time for vulcanization of rubber compounds under pressure, guaranteeing the absence of pores, in which a massive sample is vulcanized in a mold at a given pressure, temperature and heating duration, the vulcanized sample is removed from the mold, cut, visually determine the presence of pores in it and determine the equivalent vulcanization time (Zykov M.V. “Technological aspects of intensifying vulcanization modes of automobile tires.” Abstract of the dissertation for the degree of candidate of technical sciences. Moscow. 1990, pp. 7-9, entered Russian State Library 12.26.90, reg. N 29068T. The imperfections of the method are the insufficient accuracy in determining the mines due to discrete changes in the thickness of various samples and significant labor intensity (a series of experiments is required) mixtures under pressure, guaranteeing the absence of pores and reducing the labor intensity of the method. The specified technical result is achieved by the fact that when implementing a method for determining the minimum vulcanization time of rubber compounds under pressure, guaranteeing the absence of pores, a massive sample is vulcanized in a mold at a given pressure, temperature and heating duration, the vulcanized sample is removed from the mold, and it is cut , visually determine the presence of pores in it and determine the calculated indicator of the degree of vulcanization, according to the invention, the vulcanization of a massive sample is carried out in a mold with a spherical molding cavity with a diameter of 10 to 70 mm, the resulting vulcanized spherical sample is cut diametrically and, if there are pores on the cut, measured the maximum radius of the pore formation zone and determine the minimum vulcanization time that guarantees the absence of pores, min (r p) according to the ratio: < r п < R), мм; к - общая продолжительность нагрева резинового образца в пресс-форме, c; K - температурный коэффициент вулканизации, определяющий изменение скорости вулканизации при изменении температуры на 10 o C, выбираемый в пределах 1,6 - 2,4 в зависимости от состава резин и уровня температур, безразмерная величина; t(r п,) - изменение температуры в точке с координатой (r п) по времени (), o C; t экв - постоянная эквивалентная температура, к которой приводятся результаты неизотермической вулканизации, o C; при этом t(r п,) определяют по соотношению t(r п,) = t c ()-, где t c () - изменение температуры среды по времени, o C; - относительная избыточная температура, безразмерная величина;
The proposed method is illustrated by a figure showing a diametrical section of a spherical rubber sample. The proposed method can be implemented as follows. The rubber mixture blank is placed in a preheated mold with a spherical molding cavity with a diameter of 10 - 70 mm, consisting of 2 symmetrical split mold halves and containing a pressing device. The workpiece is pressed under pressure P, the value of which must be at least 10 N/m 2, which exceeds the internal pressure of the volatile products formed during the vulcanization process, and makes it possible to obtain a monolithic vulcanizate. A mold with a rubber blank is placed in a press and vulcanization is carried out at a given pressure, temperature and heating duration, while monitoring them. The vulcanization temperature of the test samples can be, for example, in the range of 140-200 o C, which includes almost the entire range of temperature variations of the coolants used in the production of tires. It should also be noted that the use of heating temperatures below 140 o C can lead to an unreasonable extension of the vulcanization regime, and the use of temperatures exceeding 200 o C is in most cases unacceptable due to the insufficient temperature resistance of rubber. The given range of changes in the dimensions of the spherical forming cavity of the mold is dictated by the need to rationally select the optimal duration of the vulcanization mode at given vulcanization temperatures. The use of a sample with a diameter of more than 70 mm will lead to an unreasonable extension of the vulcanization regime, and the use of a sample with a diameter of less than 10 mm does not provide sufficient accuracy in determining r p on the observed section, since for the correct determination of min (r p) it is desirable to maintain the ratio (R-r p) 3 mm . Upon completion of vulcanization, remove the vulcanized spherical sample from the mold, cut it diametrically and, if there are pores on the cut, measure the maximum radius of the pore formation zone (r p) (see Fig.), then determine the minimum vulcanization time that guarantees the absence of pores, min (r p) according to the ratio:

where r p is the maximum radius of the pore formation zone (0< r < R), мм;
k is the total duration of heating of the rubber sample in the mold, s;
K is the temperature coefficient of vulcanization, which determines the change in the vulcanization rate when the temperature changes by 10 o C, selected in the range of 1.6 - 2.4 depending on the rubber composition and temperature level, dimensionless value;
t(r p,) - change in temperature at a point with coordinate (r p) over time (), o C;
t eq - constant equivalent temperature to which the results of non-isothermal vulcanization are reduced, o C. The specified relationship (1) allows us to determine the equivalent vulcanization time of rubber (A.I. Lukomskaya, P.F. Badenkov, L.M. Kapersha “Thermal fundamentals of vulcanization rubber products". Publishing house "Chemistry", Moscow. 1972, p. 254). In this case, t(r p,) is determined by the relation:
t(r p,) = t c ()-, (2)
where t c () is the change in temperature of the medium over time, o C;
- relative excess temperature, dimensionless quantity;
t 0 - initial temperature of the sample, o C;
The value is determined by the ratio:

where A n = (-1) n+1 2, (n=1,2,3,...), dimensionless quantity;
R is the radius of the vulcanized sample, mm;
n = n, characteristic numbers (n=1, 2, 3...);
F o = (a)/R 2 - (Fourier criterion), dimensionless quantity;
where a is the thermal diffusivity coefficient of the rubber mixture, m 2 /s;
- current vulcanization time (0< к), с. Приведенные соотношения (2) и (3) с достаточной точностью, позволяют оценить изменение температуры по времени применительно к сферическому резиновому образцу при его нагреве или охлаждении в зависимости от граничных и начальных температур, размеров и теплофизических характеристик материала, из которого он изготовлен (А.В.Лыков "Теория теплопроводности". Гос.изд-во технико-теоретической литературы, Москва, 1952 г., с.98). Причем, для корректного определения мин (r п) на наблюдаемом срезе сферического образца разница между радиусами R и r п должна составлять не менее 3 мм. Это необходимо для того, чтобы избежать влияния краевых эффектов и соответствующих погрешностей, связанных с дифффузией летучих продуктов. Пример. Резиновую смесь на основе СКИ-3 и СКД (70:30 м.ч.) с коэффициентом температуропроводности a = 1,61 10 -7 м 2 /с и начальной температурой t 0 = 20 o C вулканизовали в пресс-форме со сферической формующей полостью диаметром 50 мм (R=25 мм) (до снятия давления, равного 10 H/м 2) в течение = 1200 с при постоянной температуре нагрева t c , равной 155 o C. После снятия давления свулканизованный сферический образец извлекали из пресс-формы, разрезали диаметрально и, при наличии пор на срезе, измеряли максимальный радиус зоны порообразования (r п), равный в рассматриваемом примере 20 мм. Замеры делались на одном образце. Далее мин (r п) рассчитывали как функцию времени вулканизации (), радиуса свулканизованного сферического образца (R), максимального радиуса зоны порообразования (r п), критерия Фурье (F 0), температур (t c , t o , , t(r п,)) при температурном коэффициенте вулканизации K = 2 и t экв = 155 o C в соответствии с приведенными выше соотношениями (1), (2), (3). Данные, необходимые для расчетного определения изменения температуры по времени t(r п,) в контролируемом слое, ее значения и эквивалентные времена вулканизации F(r п,) при заданной эквивалентной температуре t экв = 155 o C, рассчитанные с шагом по времени, равным 300 с, сведены в таблицу. За минимальное время вулканизации исследуемой резиновой смеси под давлением, гарантирующее отсутствие пор, мин (r п) принимаем значение эквивалентного времени вулканизации F(r п,), соответствующее конечному моменту времени нагрева резинового образца к, т.е. мин (r п) = F(r п, к) = 7,7 экв.мин при t экв = 155 o C. Таким образом, применение сферического образца для определения минимального времени вулканизации резиновых смесей под давлением позволяет повысить точность способа за счет использования в качестве исходной характеристики максимального радиуса (r п) зоны порообразования, величина которой может изменяться непрерывно, в широком диапазоне значений, причем при использовании одного образца. Заявленный способ, в отличие от известного, позволяет определить минимальное время вулканизации резиновых смесей под давлением мин (r п), гарантирующее отсутствие пор, при исследовании только одного образца, что значительно снижает его трудоемкость.