Tires after vulcanization recommended pressure. What is vulcanization of bicycle rubber at home? Initial data for calculations

There are several ways to repair a puncture or cut in a bicycle tube, one of which is hot or cold vulcanization of the tires. This method can be confidently called reliable and durable; a wheel secured with raw rubber will serve like new and will not go flat at the most unexpected moment. You can easily carry out such repairs yourself, both at home and outdoors on a hike, if you have some necessary parts. The hot vulcanization method differs from the cold method only in how the patch applied to the wheel is fixed - with or without heating.

What is vulcanization? It's such chemical process, thanks to which, with heat consumption, strength properties rubber improves, it becomes elastic and hard. You can apply a patch to a puncture using a piece of an old tube or a ready-made patch from a repair kit, and to secure them you need raw rubber with your own hands, which is sold in rolls with a protective film. This is a very plastic material, it sticks to any surface, easily sticks together into a lump, etc. raw rubber instructions for use are indicated on the packaging.

• There are two types of vulcanization - cold and hot, let's look at both of them in more detail.

Application of cold vulcanization

The material for such repairs appeared back in 1939 in the USA, almost immediately began to be successfully used and is popular among cyclists and motorists around the world to this day. With its help, you can easily and hassle-free repair any camera; the cold method is very easy to use at home. For the convenience of consumers, some manufacturers offer ready-made repair kits (cold wet rubber, instructions for use are indicated on the packaging), which include several patches various sizes in the form of a plaster, sandpaper (sandpaper), which is used to clean a puncture or scratch on rubber, as well as a special quick-drying glue for cold vulcanization. It is this that reacts with the layer of raw rubber on the patch - it is applied in bright color around black. This causes a vulcanization process, making the rubber of the chamber easily glued together without heat (i.e. cold process). This method is best suited for repairing wheels on the go, when there are no more tools at hand. You won’t find a single cyclist who hasn’t been helped out by a kit like this at least once in his life. It does not take up much space in a bag or backpack, and its importance is difficult to overestimate, especially if you are alone on a trip without friends far from the city. The entire process of repairing a tire using cold vulcanization using a patch for the inner tube will take the cyclist no more than ten minutes, and the wheel will be like new.

Do-it-yourself hot vulcanization technology for tires

This technology is used a little longer than cold technology. At a time when there weren’t so many tire shops around, car and bicycle enthusiasts repaired their vehicles in the garage using exactly this method, which uses an electric or gasoline vulcanizer, which you can easily assemble with your own hands. The technology here is as follows: the master burns gasoline, which warms up the rubber using a piston. As soon as the temperature rises to 90 degrees, the raw rubber for vulcanization begins to strengthen; if you raise the temperature to 147 degrees, the process goes noticeably faster and with better quality. But it’s better not to raise it above 150, because... the material begins to deteriorate and loses its properties. After 160 degrees, raw rubber begins to char. Perfect time warming up during hot vulcanization of raw rubber - about 8-10 minutes. A fragment of material is applied to the puncture site on the camera and compressed using a clamp so that during the chemical reaction bubbles do not form and air does not collect, forming dangerous voids.

The technology of using hot vulcanization of raw rubber at home will be 40% more effective for a tire than cold vulcanization, so if possible, it is better to use this method.

In field conditions, it is much more difficult to carry out such an operation for cameras, but it is still possible: if there is a piece of raw rubber, you can heat it over a fire. You can determine the temperature of the flame by looking at a piece of sugar or a piece of paper: both begin to melt/char at a temperature of 145 degrees – exactly what is required for vulcanization. You can use a flat heavy stone, a wooden log or any other suitable object as a clamp.

The entire operation will take you about 20 minutes. Do not forget that the area where the tube patch is glued must be cleaned with sandpaper or at least wiped with gasoline to remove dirt from the tire.

Cement for vulcanization and its application

Another alternative option for repairing bicycle wheels while traveling is a can of cement vulcanizer. You can buy them, for example, at the car market - this material is very popular among car enthusiasts. The composition is sold in tin and aerosol cans under pressure from brands such as Abro, BL, Zefal, Top RAD and many others. In terms of their composition, they are not hazardous to health and are not toxic, because... they do not contain chloride and aromatic hydrocarbons, so they can be used freely both at home and outdoors without a protective mask. In order for tire cementation to occur, a temperature of 18 degrees Celsius is required. The composition is also used for hot vulcanization (150 degrees required). To repair, you need to remove the foreign object that caused the puncture from the rubber of the inner tube, fill the inner tube with a cement vulcanizer through the nipple, slightly inflate it with a pump and ride a bicycle for 2-3 kilometers to adjust the pressure in the wheels. This tire repair technology is simple and is also used everywhere. To consolidate the result, it is possible to use a patch of plaster followed by the hot vulcanization method - exactly the same as described in the instructions above. The technology is suitable for any tire cuts. patch for repairing cameras in in this case applied before filling the tire with cement.

Vulcanization of thick-walled products

Vulcanization of thick-walled products occurs at variable temperatures, and the greater their thickness, the longer the heating duration. The degree of vulcanization of rubber at variable temperatures is usually assessed by the equivalent vulcanization time - the conditional duration of vulcanization at a constant temperature - which must be spent to obtain rubber with the same properties at variable temperatures real process vulcanization.

During vulcanization, temperatures on the surface and in the center of thick-walled products are not the same. If the duration of the process is determined by the conditions necessary to ensure a given degree of structuring in the center of the product, then the surface layers, especially with effective heat transfer, will be highly over-vulcanized. The higher the vulcanization temperature and the greater the thickness of the products, the greater the over-vulcanization of products from the surface, since the rate of heating of products increases slightly with increasing temperature of the coolant, and the rate of vulcanization is very fast. To reduce the heterogeneity of properties during the vulcanization of thick-walled products, they should not be vulcanized at very high temperatures. Also, during the heating process, you should not achieve complete vulcanization of the workpiece throughout its entire thickness. To reduce the heterogeneity of heating, stepwise heating should be carried out or the rubber mixture should be preheated. For the manufacture of multilayer products obtained by assembling from various parts, rubber mixtures with different vulcanization kinetics are used. Rubber mixtures intended for the manufacture of internal parts must have a high vulcanization rate.

When choosing a vulcanization mode, one should take into account the influence of the main technological factors on this process, i.e. properties of the medium, temperature and pressure.

Vulcanization medium

Rubber products are vulcanized in metal molds or directly in a coolant environment. When choosing coolants, it is necessary to know not only their thermophysical properties, but also their effect on the properties of rubber products upon contact with them.

When choosing a vulcanization medium, the type of product, the composition of the rubber mixture, the equipment used, the specifics of the process and other factors are also taken into account.

Temperature

Most products are vulcanized at a temperature of 140-170 ºС, and in some cases – at 190-220 ºС. Using high temperatures it becomes possible to reduce the duration of vulcanization of products and, consequently, increase equipment productivity. However, for thick-walled products, with increasing temperature, the possibility of over-vulcanization of products from the surface, as well as the unevenness of their vulcanization across thickness, should be taken into account. When intensifying vulcanization processes, it should be remembered that sometimes with increasing temperature the properties (quality) of rubber deteriorate.

Pressure

Vulcanization of rubber technical products can be carried out under excess pressure and without pressure. Most rubber products are vulcanized under pressure. At the same time, they improve appearance And physical and mechanical properties vulcanizates, and mainly eliminates their porosity, which is the cause of premature destruction of products during operation.

To obtain high-quality products, rubber compounds must be vulcanized under pressure exceeding the internal pressure in the rubber compound.

In order to prevent the appearance of porosity, water- and gas-absorbing substances (gypsum and calcium oxide) are introduced into rubber mixtures, which absorb the moisture contained in the mixture, forming fairly stable chemical compounds. A significant reduction in pore formation is observed when rubber mixtures are pre-evacuated during the molding process in worm machines with vacuum suction. Vacuumed rubber compounds can be vulcanized without pressure.

When vulcanizing rubber fabric products, pressure has a great influence on the depth of penetration of the rubber mixture into the fabric; With increasing penetration depth, the product's resistance to repeated bending increases. The depth of penetration of the rubber mixture into the fabric depends on its ability to spread when heated, which in turn is determined by the properties of the original rubber and the components that make up the mixture.

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 of a 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 determining the minimum time for vulcanization 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 mine determination by 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 intensification of vulcanization modes car tires". Abstract of the dissertation for the scientific degree of Candidate of Technical Sciences. Moscow. 1990, pp. 7-9, entered the Russian State Library on December 26, 1990, reg. N 29068T. The imperfection of the method is the lack of accuracy in determining mines due to discrete changes in the thickness of various samples and significant labor intensity (a series of experiments is required) the technical result of the invention is to increase the accuracy of determining the minimum time for vulcanization of rubber mixtures under pressure, ensuring the absence of pores and reducing the labor intensity of the method. The specified technical result is achieved by implementing the method for determining the minimum time. vulcanization of rubber mixtures 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, cut, the presence of pores in it is visually determined and the calculated degree of vulcanization is determined , according to the invention, 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, the maximum radius of the pore formation zone is measured and the minimum vulcanization time is determined, guaranteeing 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.

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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 metal core, 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 processing rubber 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 used is the same size as 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:

* 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

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1. Depending on the size of the model, select a clip, taking into account that in the finished mold the distance from the model to the edges of the mold must be at least 8 mm.

2. use a hard brush and soapy water to treat the inner parts of the race and metal liners in contact with the wet rubber, dry the race and liners

3. Wash and dry the master model before molding.

4. Heat the vulcanizer to a temperature of 150°C. The heating temperature should not exceed 163°C.

5. Heat two rubber blanks in contact with the model on the vulcanizer plate to soften them for 5-8 minutes.

6. Pave all cavities of the model, complex bends with pieces of raw rubber, knead with a spatula and heat together with the workpieces

7. place the model between two softened blanks, while the cone of the sprue should be flush with the end of the rubber blanks, carefully compress to avoid misforming

8. Place the prepared rubber bag with the model into the holder. In this case, the sprue cone of the model should fit tightly to the holder

9. Cut rubber blanks to fit the size of the holder. The number of rubber layers depends on the height of the holder and the thickness of the rubber plates (3.2 mm). Molds with a height of 18mm are used - 6 layers of rubber, 20mm - 7 layers, 30mm - 10 layers.

10. Fill the cage with metal inserts 5-7 mm above the edges, then place spacer metal plates on top and bottom and install in the press.

11. If necessary, warm up without pressing the press for several minutes, then compress the clip completely with the press. Program the press timer for the required time, based on the calculation of 10-15 minutes per 1 layer of rubber

12. Carry out preliminary vulcanization for 6-8 minutes. Set the final deformation pressure on the regulator at the rate of 28-30 kg/cm of the mold surface. However, it should not exceed a force of 100,000 N to avoid damage to the mechanical parts of the press.

13. If molding is performed correctly, excess rubber should come out of the holder

14. After the molding time has expired, remove the clip from the press and cool in water, then in air for 20 minutes.

15. Disassemble the cooled clip, rinse with water, remove adhering residues of raw rubber, cut off the flash

16. After cooling, the rubber mold with the model sealed in it is cut in such a way (zigzag) that there is no displacement of the two halves of the mold when obtaining wax models. In some cases, inserts are additionally cut out to facilitate the removal of waxes, and cuts (cuts) are made from the front surface to improve the filling of thin sections of the mold cavity with the model composition.

There are open and closed cuts. When you openly cut a rubber mold in half, the model partially protrudes in one of the halves. In closed cutting, after cutting, the model is under a thin layer of rubber in one of the halves.

Cutting is carried out in the following sequence:

1. Having determined the position of the model in the mold from the groove on the sprue and using the sketch of the model, make cuts from the sprue along the perimeter in both directions, cutting out fixing teeth with a height and frequency of up to 5 mm. To facilitate cutting the mold with a scalpel, it is necessary to use expanding pliers

3. Carefully release the model from the rubber

4. in a mold cut in half, several cuts should be made, starting from the model to the edges of the mold, to allow air to escape during waxing and to prevent deformation of the waxes when removing them

5. Clean the mold with a hard brush and talcum powder.

Tools, equipment, materials used:

Rubber molds are made in metal vulcanization cages rectangular in shape, made of a material that heats up quickly, does not oxidize in water and does not stick to wet rubber (aluminum alloy). The design of the cage must meet the following requirements: quickly and conveniently assembled and disassembled, ensure sufficient tightness during vulcanization of raw rubber, must have wide walls to ensure sufficient strength under the pressure of the rubber mass from the vulcanizer.

Metal cone

1. Rubber vulcanization stepladder

   Silicone rubber

   Stepladder cover

A. Hole in stepladder

B. Cone reference font

Rice. 1 Type and components of the assembled clip ready for vulcanization

Vulcanizing press used for pressing and vulcanizing raw rubber, which is installed in a cage between two heated plates.

Technical parameters of the EV 40N vulcanizer: (if the vulcanizer is different, then do not write this!!!) - supply voltage................................ .....220V, 50/60 Hz - external dimensions......length 310mm; width 250mm; height 550mm - working plane.................................................... ..170x240mm - maximum distance between plates.........80 mm - power consumption........................... .............825 W; - weight................................................ .......................35 kg; - vulcanization temperature range…… from 50 to 200° C - vulcanization time range…………….from 1 to 99 min

The curing temperature and time are set and controlled using a digital programmer. Two aluminum plates are heated evenly, which ensures high-quality sintering of rubber. The maximum mold size is 85x70 mm. Time and temperature are controlled digitally to ensure exact compliance with the parameters set by the rubber manufacturers. A special fan is built into the control panel, allowing you to quickly cool the stamp in automatic mode, and thereby quickly remove the finished matrix from the vulcanizer. Square shaped heating plates provide maximum heat distribution, a feature that allows the vulcanizer to be used with round, rectangular or square dies.

Molded scalpel is a knife with surgical-type blades with a steel or plastic handle, which has grooves for securing replaceable blades. To cut shapes, 3 types of blades are used: - straight, sharpened on one side; straight, sharpened on both sides, and curved.

Silicone based hot vulcanized paste rubber sheetsEconosil company F.E. Knight Castaldo (USA). These are silicone compositions specially developed for lost wax casting technology for the production of high-quality jewelry castings. To work with such rubbers, traditional methods and equipment are used. Paste rubbers are easy to fit into the mold, never produce bubbles, and when laid tightly, fill all voids, because increase in volume during vulcanization. Forms after vulcanization are easily cut with a scalpel blade. Rubbers do not interact with the model material, which significantly improves the quality of the surface. To separate the waxes from the rubber mold, you do not need to use silicone spray - the mold already contains components that facilitate easy separation of the waxes from the rubber. A possible drawback characteristic of some technical rubbers that are not specifically adapted for manual placement into molds, typical for jewelry production, is increased sensitivity to fats. Sebum, always present on the hands, can lead to delamination of the finished form at the point of contact. Vulcanization temperatures are 140–177°C at the rate of 10-15 minutes per layer of rubber to be laid.

Assembling the "Christmas tree"

After making the wax models, they proceed to assembling the wax tree, for which they use sprues - wax risers, which are made from model composition waste from model smelting or special (gating) wax, which, when burned, burns out faster than other waxes of this “herringbone”. This facilitates the free flow of wax molds from the flask. The sprue must be thick enough (5...7mm in diameter) to liquid metal could reach thin parts of the model cavity before hardening. It is intended: for soldering wax models, removing wax during melting, annealing, moving molten metal into a separate cavity, feeding castings during the crystallization process, reducing melt turbulence. For better form filling, saving precious metal To reduce the weight of the gating system, it is recommended to use a conical riser.

The path of the metal in the herringbone must have the correct shape, without kinks, with large radii of curvature, this will help avoid flow turbulence and facilitate the release of wax from the hardened form. Metal particles move in different directions, which can cause the capture of foreign particles, uneven flow and the resulting porosity. The formation of porosity is promoted by the increased fluidity of the metal, i.e. his temperature is too high.

The size of the power channels must be sufficient to fill the model with metal.

If the model has different thicknesses in different places, it is necessary to provide several feeding channels attached to the thickest parts of the model - the liquid mass should flow from the thickest section to the smaller ones, and never vice versa.

Fig.1 Fig.2 Fig.3

Fig. 1 – incorrect sprue location.

Fig.2 and 3 – correct location sprues.

The metal begins to harden in places with the least thickness. The product becomes incomplete and porous if the temperature of the mold and metal is too low. The supply channels should go to the largest parts of the model.

When assembling a “Christmas tree”, 3 conventional options for assembling waxes are used:

- vertical rows;

- horizontal rows;

- in a checkerboard pattern.

The choice of selection option depends on the assortment of waxes, taking into account the possibility of the most dense selection. In this case, the waxes should not touch each other. The distance between the nearest points of the model must be at least 3 mm. When placing the wax on the riser, it is necessary to take into account the possibility of air escaping during vibratory vacuuming of the “herringbone” from the recesses in the wax.

To assemble models into a block, the wax riser is strengthened in a special device - a holder. The holder is designed so that when assembling the wax tree, the sprue with the seal can be rotated around several axes. Then, using a thin blade of an electric spatula, touch the model feeder and the seat at the same time. After this, the knife is quickly removed, and the parts to be joined are lightly pressed against each other until the wax hardens at the soldering site. The operation is repeated, turning the tree as necessary, until the riser is completely filled.

The wax tree should be assembled from wax models of approximately the same wall thickness in sections, since the temperature of metal pouring is set depending on the wall thickness of the models.

If it is necessary to cast models with different wall thicknesses in one flask, then thin models should be placed at the top of the “tree” and closer to the barrel, and thick ones closer to the outside, because the temperature is higher in the center of the flask.

Thick wax models should not be placed with their large surfaces close to each other. It is advisable to place the large surfaces of some models next to the small surfaces of others.

Wax models should be placed at an acute angle to the riser (60° - 80°), this makes it easier to burn out the wax and promotes a smoother pouring of metal over all parts of the model cavity.

The distance from the top of the sprue bowl to the bottom row of wax models must be at least 10 mm, due to the possible formation of underfills in the bottom row of the wax tree.