compound selection for dynamic shaft seals.
There may be various reasons for seal leakage.
Based on long-term global experience, the following most important rubber properties must be considered when selecting or developing rubber compounds: * elasticity;
* Resistant to lubrication and wear;
* Degree of expansion of oil;
* Resistance to hard deposits in the lips (carbonization);
* Initial stiffness;
* Ability to seal the pump;
And * cold resistance.
It is necessary to take into account that dynamic shaft seals may leak if any of the above rubber properties do not meet certain specifications or limitations.
The limitation of all performance depends on the actual application, sealing design and operating conditions.
At present, it is possible to evaluate rubber performance using different methods and procedures.
The method or program for each test can provide different results.
In order to select the test methods and procedures for each rubber property, it is necessary to understand the deformation conditions and types that primarily represent the true sealing function.
The basic purpose of our investigation is to select or develop test methods and replace seal tests with rubber plate tests, which will reduce the time and cost of developing or selecting rubber compounds.
Elastic elasticity is the ability to maintain large deformation and quickly recover to the original structure when the deformation force is removed.
For dynamic shaft seals, it is necessary to maintain rubber elasticity throughout the period of use of the seals.
The elasticity of the rubber components provides a seal that, during shaft vibration and surface defects on the shaft, the sealing lip is able to follow the shaft.
If the seal is not properly followed, the gap between the shaft and the sealing lip may be the main cause of the sealing leakage.
There are many ways to measure the elasticity of rubber in terms of stretching, compression, distortion, etc.
The most typical deformation for dynamic shaft seals is bending.
Test Method for \"recovery from bending (RFB)
It represents the following nature of the seal and has a good correlation with the life of the seal.
At present, the recovery FKM bending test is approved as the standard ASTM D6515 test.
A strap 100mm long, 2mm thick and 10mm wide is bent and clipped by a paper clip.
The clamping sample is soaked in oil with inflation.
In the previous investigation, it was found that for engine seals, only the inflated oil immersion test could replicate the real site conditions (ref. 2).
For oil, change the oil every 168 hours. (oneweek).
For Gear Oil, immersion is carried out without oil change, and for transmission fluid, the immersion test can be carried out without inflation and oil change.
After aging, the sample is released from the fixture and cooled.
Measure the distance between the end points and calculate the RFB.
The heat resistance index can be calculated by using the dynamics and equation 1 of the bending change Recovery (equation 2). (1)R = L -
Support span, cm (in. ); b -
Beam width, CM (in. ); m -
Slope of the tangent of the initial straight line part, kg/cm (lb. /in. ); and d -
Beam depth, CM (in. ).
Figure 8 shows the correlation between the experimental radial load and the performance of the four types of rubber.
The stiffness has the best correlation with the radial load and can better predict the radial load of the seal. [
Stiffness measurement during bending provides more information than hardness or stretch molding, especially for sealing compounds, which can be recommended for sealing design, rubber compound development, and rubber selection.
Sealing pumping capacity the ability to rotate the lip seal to pump the oil from the air side to the oil side is another important sealing feature.
The drilling mechanism has been studied for more than 40 years.
At present, no theory can fully explain all the experimental results.
R. Recently made state-of-the-art comments on the investigation in this area. Salant (ref. 9).
Although the theory of sealing pumping is not fully disclosed, the ability of the sealing top pump depends on two main factors from a practical point of view: sealing design and rubber performance.
The purpose of this paper is not to discuss the theory and factors that affect the pump speed.
It is necessary to determine the pump speed level to guarantee the required sealing life.
Unfortunately, it is not possible to test the capacity of the seal pump if the test molded seal is unexpected.
Therefore, the seals of the two compounds were tested on the study pump tester.
NBR compound with initial pump speed of 14 x [10. sup. -2]
Ml per minute, HNBR compound with an initial shock of 4 x [10. sup. -2]
Test ml per minute.
During the continuous pump test (
Measurements are provided every 24 hours)
, Leakage of NBR seals with high pump speed 2-
1/2 times earlier than HNBR seals (figure9). [
Figure 9 omitted
The experiment shows that the initial pump speed is not the main factor affecting the sealing life.
HNBR rubber has better heat resistance and maintains elasticity and proper follow-up for a longer period of time.
When the NBR rubber loses its follow, there is a gap between the sealing lip and the shaft, and the sealing leaks.
Therefore, the sealing pumping capacity is a very important factor.
If the seal does not have a pump, the seal leaks immediately.
There is no need to have a very high initial pump rate.
The initial impact is limited.
This limitation depends on the design of the seal, interference, speed and spring load.
In the future, all the theories about the pumping mechanism must take into account the gap between the sealing lip and the shaft.
Only when the gap between the sealing lip and the shaft does not exceed a certain level of water, the sealing can pump.
The experiment described above is done with a normal lip seal.
If the seal is made with a fluid dynamics fixture such as a screw, then the requirements of the seal, especially the rubber compound, will change dramatically.
Seals for two NBR compounds were tested;
One is the same compound shown in Figure 9, and the second is the compound of the reciprocating seal with zero pump rate on the conventional flat lipseals.
Figure 10 shows that a fluid spiral seal with a rotating compound increases the initial pump speed from 14 to 110 x [10. sup. -2]
Milliliters per minute, the sealing life increased from 700 hours to hours.
The second very impressive fact in the design of the ordinary lip seal, the seal of the reciprocating compound without the pump has a high initial pump speed, and the sealing life is even higher than that of the rotating compound.
A very important conclusion can be drawn from this experiment.
For a rotating dynamic lip seal with a fluid dynamics spiral, it is not necessary to develop a compound that can provide pumping capacity.
In this case, compounds with higher elasticity, better wear resistance and higher physical properties can be manufactured. [
Figure 10 slightly]
Resistance to cold temperature, sealing resistance to cold temperature is in so-
Tested according to ASTM j110 called \"cold box.
It takes a week to test a seal using a cold box.
In order to reduce the test time and avoid the necessity of mold and test seals, a project was established to associate the standard cold rubber sheet test with the test results obtained by the cold box test.
First, the parameters of the cold box test must be determined, which introduces the sealing conditions on site.
It is speculated that the friction between the seal and the shaft increases when rotating the seal at high speed.
When the friction increases, the lower grease temperature is also increased, the rubber is thawed, and the rubber elasticity and sealing follow are appropriately increased.
A thermocouple is installed in the lip area, about 0.
5mm from the sealing contact point, the seal is installed in the cold box tester.
The test starts with an FKM compound with a glass transition temperature ([t. sub. g])of -12. 8 [degrees]C (9. 8 [degrees]F)
Inmineral SAE 5w30 oil.
The seal was soaked before the Test started-40[degrees]
At least 8 hours.
Start spinning at 700 rpm, representing warm-up period.
After five minutes, the speed is raised to 1,500 rpm, which represents the beginning of the actual driving.
After 35 minutes, the speed is increased to 2,000 rpm and 3,000 rpm after 90 minutes.
The test results shown in Figure 11 show that after 1.
25 minutes, the temperature of the lower lip rose sharply, two minutes later, the temperature from-40 [degrees]F to -10 [degrees]F.
In this case, the sealing follow is high enough to prevent sealleakage.
At the same time, the oil bottom shell temperature is still low.
After only 15 minutes, the oil temperature reached the lower lip temperature, and after 2 minutes.
Temperature 275 in 5 hours [degrees]
F. Have confidence in future upgrades. [
Figure 11 omitted]
Oil leakage also depends on the viscosity of the oil.
If the oil viscosity at low temperature is very high, the seal will not leak even if there is a gap between the friction and the sealing lip.
In order to study the influence of oil viscosity, in-40 [degrees]C.
Mineral SAE 5w30 with oil viscosity of 3 x [10. sup. 3]
MPa * s, synthetic oil Mobil 1 with 2. 1 x [10. sup. 4]
MPa * s, automatic transmission liquid (ATF)were used.
Although engines is not used in the engine, it is considered a model because it has a very low viscosity of 0. 9 x [10. sup. 3]
MPa * s, which is 23 times lower than the viscosity of Mobil 1.
All three oil experiments did not show oil leakage, nor did they show any substantial differences in lip temperature, even with the ATF.
The test described above is carried out with a seal with a dynamic spiral.
This has attracted people\'s attention, that is, the spiral has increased the absorption capacity of crude oil and prevented the leakage of crude oil.
To verify this claim, atest is done with a seal without a spiral.
Select the FKM compound with the highest glass transition temperature ([t. sub. g]= 0 [degrees]Cor 32 [degrees]F).
The test results are the same.
There is no spiral with very high glass transition temperature, no leakage will occur in the seal.
From this experiment, it can be concluded that under the test conditions corresponding to the field conditions, in-40 [degrees]
The seal does not leak even when the glass temperature is 0 [degrees]
The viscosity of C and oil is as low as 0. 9 x[10. sup. 3]mPa*s at -40 [degrees]C.
At high rotational shaft speeds, the seals break and leak only when the car starts at very low temperatures without a heating cycle.
In this case, a very important sealing performance is the rubber\'s resistance to impact conditions at low temperatures, such as brittle points.
RMA survey (ref. 10)
A good correlation between seal leakage and astm d 2137 brittle point test was established.
Using this experimental data, the coastal temperature ([t. sub. sl])
Crispy point ([t. sub. bp])
Dynamic operation-out ([d. sub. ro])
, The difference between the Shaftand seal rotation center (eccentricity). [t. sub. sl]= -25 + [t. sub. br]+ 12. 6 x [d. sub. ro]
Table 3 shows a good correlation between the experimental and calculated test results.
If the seal is tested at low speed (60 rpm)
, For the shaft seal, in the gear oil with high viscosity at low temperature, even if the seal test is in-15 [degrees]C (5 [degrees]F).
Figure 12 shows the cold box test for 3 inch FKM seals with Tg-12. 8 [degrees]C (8. 9 [degrees]F)
Emgard in gear oil.
Lip temperature after 12 minutes 【degrees]
F, although the oil temperature is very low, a curved moon surface appears between the sealing lip and the shaft.
This temperature is related to the glass passing through the temperature. [
Experiments show that the low temperature performance of rubber is very important for seals with low rotation speed.
In this case, in order to characterize the cold resistance of the seal, the glass passes through the temperature, astm d 1053 \"Low temperature hardening\" or astm d 1329 \"Low temperature shrinkage\" tests must be used to select rubber compounds.
Conclusion in order to develop or select a rubber compound for dynamic shaft seals, the following Rubber properties and laboratory testing methods can be used.
* Rubber elasticity-
Elasticity is one of the most important factors that affect sealing follow-up.
In order to measure elasticity, it is recommended to use a reply after bending (RFB)
Test astm d 6515 and measure the dynamics of the RFB change at gas filling (
And calculate the heat resistance Index (HRI-r).
* Resistant to lubrication wear-
Measurement of resistance toluene wear (RLW)
Improvement lab LRI-
The 1a tester can be used, which shows a satisfactory correlation with the sealing bench test. Note:HRI-
R and RLW are directly related to the sealing life. * Volume expansion-
The volume expansion of rubber has no direct relationship with the sealing life.
For each seal design and application, there is a limit on volume expansion.
Astm d 471 test method can be used for oil for this application.
Anti-Carbon properties are very important rubber properties, especially heat-resistant compounds used in oils with corrosive oil additives, such as fluorine rubber.
For the purpose of measuring carbide, astm d 1415 International hardness test methods can be used with the procedures described in the references (ref. 7).
If the rubber has insufficient anti-carbon capacity, the seal will leak no matter how good the remaining performance is. * Stiffness -
Stiffness is a very important rubber property for selecting compounds with the required sealing radial load.
Stiffness is more accurately described as rubber stiffness compared to hardness or modulus.
In order to measure stiffness, it is necessary to use the equipment described in reference 8. * Pumping-ability -pumping-
The ability is a very important sealing performance.
Unfortunately, it is not possible to test the sealing pumping-
The ability to use any tablet test method.
If a seal does not have a pump, it will leave.
The initial sealing pump rate is not directly related to the size of the sealing life.
The most important thing is the pumping dynamics. ability. Seal pumping-
The ability can make up for the lead of the shaftimerfections and shafts.
For seals for high-speed applications, theASTM D 2137 brittle point test shows good correlation and can be used to predict the low temperature performance of the seals.
For low-speed sealing, astm d 1053 stiffness at low temperature test can be recommended.
Confirm that \"an improved method for measuring dispersion of uncured drug fillers\" is based on a paper given by the rubber Department at its October 2001 meeting.
Wing function technology
A new rotor technology for Farrel Banbury mixer \"is based on a paper given at the rubber sector meeting in October 2001.
\"Composite selection of dynamic shaft seals\" is based on a document given at the rubber department\'s October 2001 meeting. References(1. )B.
Dinzburg, \"Measurement of rubber elasticity and correlation with sealing life\", SAE Congress, Detroit, Michigan, February 1997, paper 970547;
Cleveland ACS Rubber Division, October1995, paper 71;
Rubber and plastic news, October 7, 1996. (2. )B.
Dinzburg, \"the effect of lubricant additives on rubber properties under conditions similar to those on site\", Lubrication Engineering 51, 10, 796-804, 1995. (3. )D.
Moore, \"friction and lubrication of elastic materials\", Pergamon Press, 1973. (4. )J. M. Bouvier, M.
Geus, \"diffusion of heavy oil in expanded rubber\", rubber chemistry.
Technology, 59,233-240,1986. (5. )C. Neogi, A. K.
Bhowmick, \"Dynamic Analysis of carbon black filled vulcanization rubber under swollenconditions\", rubber chemistry.
Technology, 63,5, 651,1990. (6. )B. Dinzburg, R. Bond and R. W.
Keller, \"Heat resistance evaluation of rubber compounds\", rubber world 197,5, 28-32, 1988. (7. )B.
Dinzburg, \"phenomena and test methods of carbide on dynamic shaft seals\", SAE World Congress, Detroit, MI, March2000, 2000-01-0682. (8. )B. Dinzburg, R.
Rubber World, 20,4, 20-evaluation of stiffness measurement of rubber heat resistance24,1990; Patent 517801Z(9. )R. F.
Salant, Lubrication theory for elastic shaft seals, Proc. Inst. Mech. Engrs.
213, Part One, 189-201, 1999. (10. )
RMA technical announcement oil seal subdivision OS-\"performance of low temperature oil seal and ASTM test method\"10.