Since 2006, Focus on rubber seals

optimization of the production of epdm sponge rubber seals for automotive use.

by:ORK      2020-03-23
The production of rubber profiles on continuous vulcanization devices is the most important process in the rubber industry.
The value of the annual sales profile is around 0. 59 to 0. 72 million U. S.
German dollars
Auto Body seals are a world market close to 100 kt/.
Automotive seals have unique wind and rain resistance, physical performance and processing performance.
In order to meet these needs, they are mainly a combination of solid materials and cell materials (refs. 1-3).
Starting at 1990 s, ethylene-propylene-
Rubber (EPDM)
With the performance that meets the requirements, it is increasingly used for automotive seals and profiles.
Although the foam/sponge represents only a small part of the profile, its production constitutes an important part of the application technology of the ethylene-based product, which requires a high level of knowledge. how.
All aspects of B-C rubber
This manufacturing process usually involves compounding.
The product performance required for sponge body seals is continuously improving, such as the complex configuration of producing accurate tolerances, load deflection independent of temperature and smooth housing, due to the large number of process variables in the manufacturing process, and the complex process is caused by the formula effect.
In this article, the results of the impact of a large number of parameters on product performance are summarized.
Therefore, we will study the impact of different acceleration systems on product performance.
When selecting different accelerator systems, the possible synergy between different types of accelerators is not noticed.
Then, the effect of different process parameters on product performance (
Sponge rubber tube)
The belt speed and power of UHF are studied. generator.
In order to avoid synergy as much as possible, further analysis was carried out and the same acceleration type was retained.
In each test, in order to determine the relationship between the quantity used and the performance of the product, the number of accelerators is reduced.
In addition, a wide range of studies have been carried out on the rheometers to measure the flow parameters describing the uncured compound.
The mathematical description of the temperature distribution change of the seal during processing is used to find the temperature distribution used for temperature measurement, which is similar to the production process.
This is to ensure that the flow parameters are measured under conditions similar to the processing conditions.
In addition, the mechanical properties of seals manufactured in the automotive seal industry production plant are also measured.
Finally, the correlation between the flow parameters and the mechanical properties is found, which makes it possible to predict the properties of the product and sponge.
Sponge Rubber technology while auto body seals can be made from many rubber such as B-c rubber, NR, br, CR, NBR or LSR, B-C rubber is the most important in sponge rubber production worldwideref. 3).
Manufacturing process of B-C rubber
The seals can be divided into three typical steps: * mixing operations: the quality of dispersion and distribution of all components is critical to the quality of the final product, especially for the smooth surface of the profile.
* Extrusion: temperature setting must be controlled to avoid the early start of blow agent degradation.
* Curing: vulcanization and simultaneous blowing reaction have the most important influence on the quality of the final seal.
Very little is known about the best options for the process.
Liquid curing medium (LCM), hot-
Air or microwave, Superhigh-frequency (UHF)
Curing is a common system.
One of the most important systems in the world is UHF/thermal-Air combination.
This results in the rapid and uniform heating of even very complex shape profiles in extremely high frequency units at a very short distance.
The heat below
The air system maintains the curing temperature to complete the curing and blowing reaction.
The studies described below focus on sponge mixtures and ultra-high-frequency curing processes.
As shown in Table 1 below, the materials and experimental techniques of three different types of industrial processing sponge rubber compounds were studied.
For chemical changes in the composition of compounds, materials A and B are used.
The purpose of the change between compound A1 and A4 is to find the optimal temperature difference between the start of vulcanization and the temperature before the blowing reaction, without noting the possible synergy between different types of accelerators.
Therefore, four different accelerated systems were selected to study their effects on the vulcanization reaction.
The formula reaches rapid acceleration from Avery (A1)
By using the maximum number of accelerators, it depends on the solubility in ternary rubber until a very slow accelerated compound (A4)
Contains a small number of accelerators.
Due to the change of accelerator quantity, the vulcanization reaction should be realized within a larger temperature range.
The change of the second compound B1 to B5 is generated by avoiding the synergistic effect as much as possible.
Using the same type of accelerator, only their amount changes with the maximum solubility they have in ternary rubber. Table 1 -
In order to find the correlation between the flow parameters and the performance of the final product, the production compound C was used.
The vulcanization reaction and degradation of the sulfur agent should be optimized.
The results measured under the following conditions are shown in Figure 1.
The start of spray degradation can be delayed (C2)
The effect of accelerating the system can be increased by delaying the vulcanization process.
Therefore, the change of coke burning time and vulcanization rate occurs simultaneously: the decrease of the amount of guanidine accelerator (C1)
And increase the amount of aromatic amine accelerator (C3)
Increase the speed of vulcanization.
The decrease in thiophosphateaccelator vulcanization rate (C4). [
Figure 1 illustration omitted]
For the study of uncured compounds, a mobile dierheometer (ref. 4)
It can measure pressure.
Constant temperature and non-constant temperature
Constant temperature measurement.
Although the way the Heat is transmitted to the material through a thermometer (heatconduction)
Still different from the production process (UHF)
, Can achieve heating similar to the manufacturing process.
In the following study, the process of torque is mainly considered, which is the measurement of composite viscosity and the torque gradient representing the vulcanization rate.
Samples of different compounds are produced in industrial production plants for related purposes, as shown in figure 2.
The manufacturing profiles related to physical and mechanical properties are analyzed. [
Figure 2 illustration omitted]
Before discussing the evaluation of these test results, calculate the UHF-
Heating is described.
First, the temperature distribution in the UHF unit is calculated, and the temperature distribution of the flow measurement is calculated.
On the theory of microwave, power density [P. sub. w]
After being absorbed by the compound, it can be calculated according to equation 1 (refs 5 and 6). (
The terms used are summarized in Table 2)(refs. 5 and 6). (1)[p. sub. w]= 2[Pi]f [multiplied by][E. sup. 2][multiplied by][[Epsilon]. sub. 0][[Epsilon]. sub. r][multiplied by]tan [Delta]Table 2 -
In this equation ,[[Epsilon]. sub. 0]
Is the electric field constant.
Frequency f and electric field E are the parameters of the equipment while the relative dielectric constant [[Epsilon]. sub. r]
Tan 8 is a material parameter of sponge rubber composite material that is greatly affected by temperature.
Get the value from Fettke and Ippen (refs. 7 and 8).
Temperature difference caused by absorption due to energy balance-
Calculate power through Equation 2 (ref. 9). (2)Q = m [c. sub. p][Delta][Upsilon]with in = [Rho]
After connecting equation 2 with the volume of the material, it is related to Equation 1, temperature difference [Delta][Upsilon]
It can be calculated as follows :(3)[
Mathematical expressions that cannot be reproduced in ASCII]If [[Epsilon]. sub. r]tan [Delta]
Is constant, rising at a UHF temperature-
The unit is proportional to the residence time (
Figure 3. Curve 1)
And the temperature dependence [[Epsilon]. sub. r]tan [Delta]
Curve 2 and curve 3 (ref. 8).
As the first approximation, we use linear relations (curve 1). [
Figure 3 illustration omitted]McCrum et al. (ref. 10)
Explain the dependence of the parameters of the uncured material on temperature and frequency, because the resonance frequency of the dielectric constant shifts to a higher frequency as the temperature increases.
Frequency of extra high frequency
The generator is fixed at 2.
According to the law, it is used to produce 450 MHz of sponge rubber profiles.
If the resonance frequency is higher than the ultra-high frequency ,[[Epsilon]. sub. r]tan [Delta]
Increases as the temperature rises.
If the resonance frequency is lower than the special frequency ,[[Epsilon]. sub. r]tan [Delta]
Decrease as the temperature rises.
Therefore, the heating of profiles becomes unequal. If[[Epsilon]. sub. r]tan [Delta]
As the temperature rises, the heating speed of the part will accelerate.
Reduce words][Epsilon]. sub. r]tan[Delta]
Resulting in more equal and even warming up.
Depth of penetration [[Delta]. sub. M]
The microwave inside the material also affects the temperature distribution inside the profile.
Depth of penetration [[Delta]. sub. M]
Is caused by the absorption of microwave in the material (ref. 11).
If the absorption is high and the penetration depth is low, the core of the material is cooled than the surface.
Therefore, a temperature gradient appears in the material. A higher [[Epsilon]. sub. r]tan [Delta]in the UHF-
Temperature rise per unit (equation 3)
Depth of penetration [[Delta]. sub. M]
As absorption increases, the number of microwaves decreases (ref. 11).
This also results in uneven temperature distribution of compounds.
Temperature rise]Delta][Upsilon]
This material is inversely proportional to the penetration depth [[Delta]. sub. M]
Microwave [[Delta]. sub. M]=f([Delta][Upsilon], [c. sub. p]).
If the temperature is changed due to other additives in the compound ,[[Epsilon]. sub. r]tan [Delta]
Therefore, the specific heat capacity of rubber compounds will also change.
Therefore, a compromise between the two effects, namely, the maximum penetration depth and the maximum heating rate, must be found.
The measurements take into account compounds A1 to A4 and B1 to B5, while analyzing the effects of the accelerator system on theological and mechanical properties.
The flow studies of all uncured compounds were carried out on multi-drug resistance.
Then, produce seals at the production plant (figure 2).
Effects of Different process parameters on product performance, such as belt speed and power of UHF
Generator, investigated (table 3).
The profile was analyzed due to its unit size, geometry, Shore hardness and residual stress under deflection. Table 3 -
Experimental data in order to find the correlation between the results of the flow test and the quality of the final product, all group C compounds were analyzed on the Rheograph and then the seals of these compounds were produced at the production plant.
By using Equation 3, the material parameters of different compounds and the dwell time in the UHF, the temperature process of the rheostat is calculated.
The heating rate is from 0. 17 K/sto 0.
However, 5 k/s can be achieved, and these heating rates are still lower than UHF.
Shear the rubber compound in the rheotor cavity by Artor (
Sine oscillation).
Due to the measurement of its function of maximum torque increasing with time and temperature, information about vulcanization and foaming behavior as well as viscosity can be obtained.
Next, it focuses on the elastic properties of the material.
At the beginning of the analysis, the torque is reduced due to a decrease in the viscosity of the sample.
Then the closing Port, torque and viscosity are increased respectively.
Minimum value of Torque [S. sub. min]
Is a characteristic value of a compound.
At the same time, the blowing agent is degraded and the mold cavity pressure is increased to reach the maximum [P. sub. a,max].
The moment the pressure increases significantly is measured as a multiple of the torque. The value [S. sub. degrad]
This is like the maximum pressure [P. sub. a,max]
Features of blowing reaction.
The flow values of these properties are used for correlation with product performance.
All configuration files (compound C)
Compression and tensile tests were carried out.
Residual stress under bending, compression deflection force, strain at break, tensile strength at break, and specific energy loss were measured.
Only [density]Rho]
Especially the lost energy. Delta]
W, and residual stress under bending (RSD)
This is taken into account in the discussion below.
Test results of the acceleration system on the properties of materials and profiles and interpretation of the Rheo and mechanical effects compound A1-
A4 below, first, the results of the study on the effects of the acceleration system on vulcanization behavior, final profile geometry, and battery size are described.
Subsequently, the effect of different band speeds and ultra-high frequency power on profile unit size was discussed for compound a2 only.
As shown in figure 4, the unit size of the profile made by compoundsA1 is increased to A3.
However, compound A4 has been given small cells.
The behavior of the first three compounds can be explained by an acceleration system, which becomes slower each time.
A1 has the fastest acceleration system, so the vulcanization of compounds A2 and a3 is later than that of compounds A2 and a3.
However, it is still much faster than the vulcanization of other compounds.
Compared with compound a3, the coke burning time of compound a2 is shorter and the vulcanization speed is faster.
Therefore, the cells of A2 are smaller than those of a3.
Due to the tensile stress at the time of fracture and the degree of vulcanization of compound A2 is higher than compound A1, the vulcanization speed of A2 is significantly slower than that of A1.
To sum up, the size of the battery mainly depends on the speed of vulcanization, while the effect on the degree of vulcanization or the burning time is very small.
The diagram of the flow measurement shows that all materials have early blowing, which is unexpected but can lead to larger cells.
In the course of the study, the combination of different types of accelerators produces a synergistic effect, which strongly affects the burning time of the curing reaction, thus affecting the cell size in the final contour. [
Figure 4 illustration omitted]
The study shows that the change of acceleration system has a great influence on the geometry of the contour.
Simple trends cannot be found.
For example, the impact of belt speed and ultra-high frequency power
Units of unit size are discussed below.
Use the high beltvelocity of 0.
In UHF, 18 m/s, the cell size is only compared with UHF-unit.
The profile is not fully heated due to the very high speed of the belt.
Reach the maximum battery size at the power of the 4 generator.
8 KW use slow belt speed 0 in UHF units. 09 m/s.
Cells may grow together due to the slow band speed and vulcanization process.
Studies have shown that the unit size of the profile increases at a lower band speed, however, no proportions were found.
This means that the generation of gas depends on the dwell time of the compound in the UHFUnit or heat-air-channel.
However, the generation of gas and the size of the battery are less affected by the power of the UHF, respectively. unit. Compound B1-
Figure 5 of B5 shows the analysis results of bubble sizes from sample B1 to b5.
The smaller the number of accelerators, the smaller the cells produced.
The amount of accelerator affects the vulcanization speed.
A small amount will increase the degree of vulcanization.
Therefore, the cells become smaller as the degree of vulcanization increases, thus limiting the growth of the cells.
Therefore, the geometry of the profile becomes smaller as the number of accelerators decreases.
There is a connection between cell size and final product geometry. [
Figure 5 illustration omitted]
Figure 6 shows the results of residual stress under deflection (RSD)
Test of compound B1 on b5.
Typically, a lower value is required for a relative standard deviation because a lower relative standard deviation represents a high degree of vulcanization.
For Sample B3, the highest value of relative standard deviation can be seen, while for sample b4, there is a better and lower value.
B4 has the highest degree of vulcanization.
This shows that this combination of acceleration systems is very suitable for this application.
More accelerators do not always lead to a higher degree of vulcanization. [
Figure 6 illustration omitted]
Correlation between theological parameters and the quality of final products (compounds C-C4)
The pressure process measured in the flow experiments described above is a major clue to characterize the expansion process.
Figure 7 shows the evaluation of the maximum pressure on different compounds depending on the time heating rate.
As vulcanization begins earlier, the pressure increases from compound C to C3 and decreases in compound C4.
This means that the blowing agent is more likely to degrade at a lower level of vulcanization.
The highest content of zinc oxide is marked (compound C2)
Causes a much higher pressure in the cavity associated with compound C. [
Figure 7 illustration omitted]
If the thermal input is three times faster than the conventional thermal input, the burnt time drops to half the initial value.
The heating rate has an important effect on the performance of the material, as shown in figure 8, the maximum vulcanization rate.
The dependence of pressure on the heating rate leads to a decrease in density p as the heating rate increases.
Previous studies have shown that the process temperature is very important.
In order to avoid the quality fluctuation of the final product quality, it must remain the same. [
Figure 8 illustration omitted]
The further flow results described here allow the conclusion that if the material has a lower viscosity, the blow molding agent is more likely to degrade.
These results show the effect of changes in the acceleration system, zinc oxide and different rates on measurable flow parameters.
Mechanical investigation (compounds C-C4)
The survey results for profiles also show the effect of the heating rate achieved in the UHF unit on profile density.
The increase in heating rate leads to a decrease in density.
The effect of heating rate is stronger than the change in compound formula.
There are similar results for mechanical properties.
Figure 9 shows the relative standard deviation test results for different samples of compound C.
From sample C to Sample C3, the residual stress under deflection is reduced, and the residual stress increases again for sample c4.
The burning time increased due to the change of the mixture.
As a result, blow molding agents are more likely to degrade and larger cells can grow.
At the same time, the sponge will show cells that are mainly open, thus reducing the residual stress under deflection.
Residual stress under deflection is only increased for C4 samples with a longer burning time.
To sum up, the change of formula will not lead to the improvement of the product, and the product should mainly have a closed cell structure.
Due to the reduction of residual stress under deflection, a higher heating rate mainly results in an open foam. [
Figure 9 illustration omitted]
By increasing the heating rate, sponge rubber profiles with lower density can be realized.
However, the cells in rubber are mostly open.
In order to avoid the structure of the open battery, the acceleration system or the B-C rubber itself must be changed.
If sponge rubber has an open cell structure, the gas inside the cell can easily escape if the profile is under pressure.
This results in lower residual stress values under deflection at low density.
If the primary closed unit structure can be produced at low density, the dependence of residual stress on density under deflection is opposite: high residual stress at high density and low residual stress at low density.
The cells in sponge rubber are on average smaller at higher density, so the volume in the sample filled with gas is also smaller.
Therefore, at a lower density, the battery is larger, just like the amount of gas in the battery.
If both rubber samples are compressed to 50% of the original height (ref. 12)
The pressure inside the cell increases.
Therefore, gas molecules smaller than rubber molecules spread out of the compound, equivalent to the pressure between the gas cells and the surrounding environment.
If the load disappears, a partial vacuum is generated inside the battery due to the elastic behavior of the rubber in its original form.
The residual stress under deflection is measured 30 minutes after unloading the sample.
During this time, because of the smaller size, the larger air battery fills the smaller battery faster.
Therefore, a higher value is measured at a lower density and vice versa.
For block pressure (
Compact material).
However, the results can be reduced by the special design of the profile.
Because the design is very complex, it is difficult to find the correlation between the flow parameters and the scratching behavior under residual stress, because the flow test cannot describe the influencing factors \"geometry \".
Finally, the lost energy [Delta]w is discussed.
Become representative of cross-domain
Low connection density, low energy loss means lower irreversible deflection rate and higher elasticity due to higher CrossConnection density.
As the heating rate increases, the energy lost will decrease and therefore cross
Increased connection density.
A good correlation was found between the physical or mechanical properties of the profiles and the flow values.
The main mass criteria are density, strength at break, residual stress at deformation, and compression deformation force.
In this article, only the results of the density p and the residual stress under deflection are described.
Regression equation 4 can be found using the flow value to predict the density of the final product :(4)[Rho]= 0. 50468 [multiplied by][kg/[m. sup. 3]]-0. 015628[multiplied by][kg][multiplied by][P. sub. a,max]/[S. sub. degrad]+0. 2334 [multiplied by][kg/[Nm. sup. 4]][multiplied by][S. sub. min]
The density of sponge rubber can be adjusted by the combination of the amount of foaming agent and the acceleration system.
The number of blowing agents has a good correlation with the pressure [P. sub. a,max]
The setting of the acceleration system is related to the value of the torque when the injection agent [degenerates]S. sub. degrad].
In addition, experiments show that the viscosity of the compound is critical for obtaining the required response rubber profile density.
To do this, the minimum value of [torque]S. sub. min]can be used.
Figure 10 shows the measured values and calculated values of density and regression lines.
Correlation coefficient]R. sup. 2]
Represents the quality of relevance (equation 4).
In this case, the correlation coefficient for calculating the density is [R. sup. 2]=0. 81.
A large amount of foaming agent in the compound can lead to higher pressure, resulting in lower density.
If the acceleration system causes early curing, the value [S. sub. degrad]
The density will increase, so will the density.
Compounds with low viscosity can lead to lower [S. sub. min]
Low density. [
Figure 10 illustration omitted]
Regression equation 5 can be found to predict the residual stress of the final product of the open cell sponge rubber under deflection using the flow value :(5)RSD = 52. 671 [%]-0. 17014 [multiplied by][P. sub. a,max]/[S. sub. degrad][multiplied by][kg]+ 12. 0746 [multipliedby][kg/[Nm. sup. 4]][multiplied by][S. sub. min]
The higher the degree of blowing, the lower the density of the response rubber, the higher the trend of the rubber to open.
Therefore, the relative standard deviation increases.
Due to this connection between density and relative standard deviation, the correlation between the flow parameters and relative standard deviation can be found, as shown in equation 5.
The discussion of this relationship is similar to the discussion of density.
The measured values are shown in Figure 11.
The correlation coefficient of the calculated relative standard deviation is [R. sup. 2]= 0. 86. [
Figure 11 illustration omitted]
The correlation does not describe the relative deviation of the contour-closed cell structure, because in this case, the mechanism is different.
If there is a balance between the toughness of the compound or polymer and the pressure in the battery or the gas generation of the blowing agent, respectively, a closed battery structure will be generated.
It is easy to measure the gas volume of the blow agent.
It can also be described by the pressure measured in the flow test.
However, it is more difficult to describe the toughness of the compound with the flow value.
Even viscosity ([S. sub. min])
Not suitable.
To sum up, the study shows that the temperature and acceleration system that allows the start of the vulcanization and blowing reaction have an important impact on the quality of the final product.
It can be seen that a small number of accelerators will lead to the best performance of the profile.
The process temperature must be well known and must be kept constant to avoid quality fluctuations in the final product.
The flow results measured under temperature conditions similar to the manufacturing process lead to a more important prediction of product performance.
Therefore, the development of calculating the temperature in the temperature distribution system. g.
Very useful, UHF system.
In addition, studies have shown that the correlation between the properties of the Rheo material and the performance of the product can be described, so the prediction of the final product quality standard is possible. References(1. )J. W. M.
Rapra 4 th cell polymer Conference, 1 (1997). (2. )G. Stella and N. P.
International Conference on rubber, Paris, 43 (1990). (3. )A.
Hill, Technischer Handel 70 (7), 292 (1992). (4. )J. A. Sezna and H.
Burhin, File.
93 at 146 meeting of the rubber department of the American Chemical Society in Pittsburgh, 1994. (5. )H.
Kautschuk kunmi kunstoffe 29 (4), 187 (1976). (6. )W.
Hoffman, Manual of rubber technology, hanserpublisher, Munich, Vienna, New York, 1989. (7. )M. Fedtke and F.
Schramm of Kautschuk kunmi kunstoffe 51 (3),201 (1998). (8. )J.
Ippen \"Mischungen fur dead kontinuierlicheulkanisation im UHF-
\"Bayer, unpublished report, Leverkusen, 1969. (9. )W.
Wagoner, wumberdege, wogerver, Fort Worth, 1984. (10. )
McCrum, Read and Williams, \"Elastic and dielectric effects in polymer solids\", 1997. (11. )H.
Pushnell, WOM durch Mick Loren, Philippe schtnesche Bibliothek, 1964. (12. )ISO-No. 815, 1972. A. Krusche and E.
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