advances in silicon engine gasket sealing.

by:Keyuan     2020-06-08
OEM requirements for engine seals have grown to include 150,000 miles/10 milesAnnual durability.
These new requirements exceed the capacity of existing silicone rubber materials and pose significant challenges to the development of materials.
Dow Corning works with a Automotive OEM and a Tier 1 supplier to solve problems in material performance, Processing and Design to quickly commercialize the new generation of high-tech products
Consistency silicone rubber technology called High Performance oil (HPO)materials.
HPO compounds have improved significantly in terms of sealing and durability and are currently producing automotive engines.
In this paper, we will discuss the system approach to engine sealing, as well as the development and use of functional tests to better simulate the actual use environment and sealing performance.
Background silicone rubber gasket starts replacing cork-
1980s rubber composite for automotive engine sealing
Since then, high
Consistent silicone rubber (or HCR)
Compounds are widely used in molded car washers and are mainly used for static sealing applications such as Cam/valve covers and oil bottom shells.
Benefits include long term
Long term flexibility, excellent temperature stability and resistance to the fluid in the engine compartment.
The early HCR silicone compound of engine gasket is more than the previous non-
Silicone material.
However, after several years of use, it was found that the volatile components of these formulas were oxidized to amorphous silica in the exhaust flow.
Over time, silica deposition can lead to the dirt of the zirconium element in the exhaust oxygen sensor.
To solve this problem, Dow first developed a new test method for measuring low molecules.
The weight components of silicon materials have become OEM standards since then.
The second generation HCR compound, which has low volatility and improved compression properties, was subsequently developed.
Processing performance is also a key aspect of material development.
Traditional physical performance requirements, including durometer, tensile strength, elongation, modulus and permanent deformation of hot air compression, are retained.
OEM/supplier relationships used to be top notch
The downward hierarchy of gasket and sealing material design and development.
Orders go from OEM to component suppliers, to rubber manufacturers, to material suppliers.
The gasket is considered to be an independent entity of two sealing surfaces, and sometimes it is almost an afterthought when designing engine components.
This often leads-than-
Best performance gasket.
Under the current material development system, the Dow and its OEM/tier one partners have improved their view to see the gasket as part of the overall design of the mold engine sealing system.
For most companies, this represents a shift that more fully integrates the efforts of OEMs and their tiered supply base.
The system approach to engine sealing recognizes that gasket design, material and manufacturing all have an impact on performance.
This approach leverages the unique skills contributed by each SEAL team member: OEM;
Material supplier and manufacturer/Level 1 supplier.
There is no single element in the entire product design and manufacturing process that takes precedence over the other, which leads to a critical balance across all three areas.
This cooperation, while speeding up the commercial cycle of products, produces better design and materials and improves the quality of products.
With the continuous upgrade of gasket performance requirements and manufacturing targets, new material requirements become more and more obvious, and the second generation silicone material obviously fails to meet the new vehicle performance target of 150,000 miles/10 milesAnnual durability.
When they work in a new home, the team has the following design goals
Consistent silicone compound: * provides an effective seal of 150,000 miles.
* Maintain the modulus range of NVH 2nd generation material (
Noise, Vibration, harsh)issues.
* Optimize the oil and compression unitair.
* Improved compression stress relaxation performance.
* Include the cost as shown by the OEM.
* Optimize the processing properties of gasket manufacturing.
Throw out the current OEM specification if needed.
In the process of developing high-tech families
The engineers used a series of experiments designed to optimize the cross-linking density, tear strength and hot oil compression unit.
Since the increased compression setting resistance directly affects the sealing force, it is considered an indicator of a longer gasket life.
Traditional tests of silicone rubber molding plastic for evaluating gasket applications include: * Durometer * tensile strength * elongation * tear strength * modulus at 100% elongation * compression set in hot air * volatile * heat resistant * fluid resistance, the existing methods provide important data and materials engineers who are convinced that they are not the specific representative of the application.
Determining functional testing is a necessary condition to more closely simulate the actual service environment under hot oil conditions and speed up the commercialisation of new products.
As a result, new tests have been developed and integrated with existing tests to evaluate material candidates faster and more accurately.
Dow Corning, first class and OEM engineers have all contributed to new products
Procedures for material screening and validation.
Brief description of each test for functional testing: * hot oil compression test is designed as a tool for material development and performance testing because of the traditional \"hot air\" compression test method (ASTM D-395)
It was found to be a bad indicator of the performance of the actual gasket.
The new procedure is executed as follows: square, Crosssection o-ring (25 mm O. D. x 17 mm I. D. x 4 mm thick)
15 minutes in 171 [compression moldingdegrees]C. The o-
The ring is placed in a steel clamp that is compressed 20%, submerged in the Mobil Super HP 5 w-
30 SH oil at 150 hours [degrees]C.
Cool the fixture to room temperature every 2 weeks, remove from the oil, remove and measure the height loss.
The compressed set is then calculated from these data.
Every check changes 6il before restarting the test.
The loop lasts until a compressed set of 100%.
Compared to the firstand second-
Generation of materials, the new family of HPO materials in the compression of permanent deformation resistance (see figure 1).
* Accelerated function tests have been developed to evaluate the tightness of the design of a specific rocker cover Assembly (
Gasket, cover, fasteners included).
In this case, the lid assembly is installed on the test fixture and placed in the environment room.
Then connect the oil line and heat the oil to 120 [degrees]
C cycles through the cover assembly at a speed of 2 1/min and 7 kPa.
In addition, heat the fixture and chamber to 150 [degrees]
C. Simulation of thermal engine conditions.
The test did not proceed until the sealing system failed and the pressure of 7 kPa could not be maintained.
This functional test provides an opportunity to observe the performance of accelerated washers/covers/fasteners in conditions close to actual use and allows engineers to more accurately predict the reliability of the sealing system.
Performance Results of HPO products in accelerated functional testing show that durability has increased by nearly four times compared to previous commercial materials (see figure 2).
* Thermal aging/pressure testing is developed to test the durability of sealing system components exposed to heat and oil.
The attenuation of the tightness over time is the final result.
The test fixture is prepared by connecting the part with the gasket to be tested to the metal fixture plate.
Perform a gas pressure test to verify the integrity of the system and then fill the fixture with Mobil Super HP 5 w-
30 SH oil, put in a ventilated oven.
To prevent an increase in internal pressure, the fixtures are discharged into the atmosphere.
Heat oven to 150]degrees]
C and test fixture heating three-or four-day intervals.
At the end of the specified cycle, cool the fixture and remove it from the oven, drain the oil and perform a gas pressure test.
The pressure required to cause the leak (
If the maximum test pressure is less than 35 kPa)is recorded.
Add fresh oil and repeat the test cycle until the sealing system is not able to hold 7 kPa.
The test shows that third
A generation of HPO materials is better than the previous commercial materials (see figure 3).
* Compression stress relaxation (CSR)
Test with 19mm O. D. x 12. 5 mm I. D. x 2 mm thick o-rings die-
Cut from the plate according to ASTM procedure.
The ring is in xiaobley-
Wallace test fixture, compress 25%, then immerse yourself in rm903 oil.
Hot air circulation oven for heating fixtures and oils to 150 [degrees]C.
The sealing force measurement is carried out in one and three days and then in six-
Weekly test cycle (1,008 hours)
After that, determine the percentage of sealing force retention.
Compared with previous production materials, the new HPO materials significantly increased the CSR retention rate (see figure 4).
* As part of the design/material/processing triangle, the manufacturer uses the most stringent molds available to perform molding tests on the new HPO material.
These tests allow to check the demoulding, deflating and reject rates of new materials compared to existing production materials.
In order to find the best balance between physical properties and processing properties, changes in several materials were evaluated.
Key mold parameters were identified to reduce material processing
Sensitive and new recipes have proven the same or improved processing compared to 1st-and 2nd-
Generation products.
* During the mold dyno test phase, the OEM evaluated the HPO material at 300 hours, 500 hours and other engine durability cycles.
They were found to provide the necessary life span for all dyno tests, followed by OEM approval.
* HPO materials also conducted extensive fleet testing using taxis, limo and police fleet as test platforms.
These are deliberately chosen to expose test vehicles to high mileage accumulation and extreme temperatures.
Fleet evaluation shows that HPO materials provide a higher service life than previous materials, so the United StatesS.
OEM started using new compounds in production in the second quarter of 1995.
Sum up the new, 3rd-
At present, a new generation of HPO materials are being used in the application of rocker cover and Cam cover.
The regular chain cover gasket and oil bottom pad were also evaluated.
These materials have improved for a long time
Long-term durability of the engine seal system without sacrificing the processing properties. Along with its-
As a partner, Dow future, while continuing to develop rapidly and commercialize new silicone materials, adopts a systematic engine sealing method.
Cooperation between OEM, material supplier and manufacturer/Level 1 supplier leverages the advantages of all parties involved in engine sealing, optimizing design, processing and performance features.
Future material objectives include continuous improvement of compression setting values, compression stress relaxation properties, and functional properties of hot oil. [Figures 1-
4 illustration omitted]by Lawrence D.
Thomas J. Feidler
Edward M. Hada
Mark H. Cusinski
Li, Dawn company
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