Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
1999-06-01
2001-08-21
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S040000
Reexamination Certificate
active
06276194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to apparatus and method for testing the sealing effectiveness of dynamic seals, and particularly dust-exclusion seals operating in a dust-laden environment.
2. Related Prior Art
Dynamic seals are used in many engine and machine applications to seal between relatively movable parts. Dynamic oil seals are used to close the annular gap between the crankshaft of an engine and the opening in the block through which the crankshaft extends. Such seals include at least one oil lip to retain lubricant, such as oil or grease, on one side of the seal and include one or more dust lips of the radial or face type to exclude contaminants such as dust and dirt on the opposite atmospheric or air side of the seal.
Various test apparatus and procedures have been proposed and/or are in use in connection with dynamic oil seals to test their effectiveness for particular applications. U.S. Pat. No. 3,987,663, for example, discloses a non-destructive test apparatus for quickly testing the integrity of seals in a production setting. The seals are mounted on a fixture and pressurized with air on one side and monitored on the opposite side for air leakage which would indicate seal failure. The disclosure of the above patent is incorporated herein by reference. While such a test method and apparatus is beneficial for quickly testing seals in a production setting, it is desirable during the development and qualification of dynamic seals to test their effectiveness under conditions which simulate or exaggerate the actual operating conditions which they would likely be subjected to in service.
Many such oil seals are designed to operate industry environment and thus, in addition to the primary lubricant sealing lip, include one or more of the radial or face-type dust lips which operate to exclude dust from entering the seal and contaminating the oil lip. Oil lips are commonly made from low friction flouropolymer materials, such as PTFE. It is well known that such materials perform well only when properly protected. Dry dust-laden conditions quickly degrade PTFE oil lips leading to early seal failure. For this reason, dust lips are often fabricated of materials which tolerate operating in a dry, dusty environment more so than the oil lip.
The traditional approach to testing the effectiveness of such seals operating under dust-laden conditions has been to mount the seals in a housing about a rotating shaft. Oil is maintained on the oil side of the seal as it would be during normal use, and a dust chamber is provided on the opposite side of the seal to expose the dust lip to a dust-laden environment. Housed within the dust chamber is a single mixer blade mounted on an extension of the test shaft. The blade rotates at high speed with the shaft and collects and disburses the dust within the chamber. Over time, it has been observed that the high speed of the blade tends to pack the dust against the wall, forming a trench in the accumulation of dust at the bottom of the chamber in which the blade runs, providing less than the optimum amount of dust available for dispersion within the chamber by the blade. Difficulties are thus encountered in maintaining a uniform dust cloud environment within the chamber over the duration of the test. The seal is operated until oil is observed leaking past the dust lip. Such indicates a failure of the oil lip, likely accounted for by an earlier failure of the dust lip in excluding dust from contaminating the oil lip.
One drawback to such a test is that it does not provide much information about why a test seal may have failed. It would be beneficial to know, for example, when and how much dust passes by the dust lip over the course of the test period and to examine the seal at the conclusion of the test for evidence of dust patterns or accumulations which could aid in the evaluation of the seal and provide information helpful in altering the design of the seal, if necessary, to further improve performance. With current testing techniques, however, the presence of the oil on the oil side of the seal precludes the gathering of such information. Some of the dust which escapes past the dust lip passes through the oil lip and into the oil, making its collection highly impractical. Upon oil lip failure, the oil which leaks past the damaged oil lip wets the remaining dust present between the oil and dust lips, washing away at least some of the dust and disturbing the dust patterns and/or accumulations that may have been present that could be helpful in analyzing the performance of the dust lip.
It would thus be desirable to have a test apparatus and procedure for testing the performance of dynamic lip seals operating in a dust-laden environment which would enable collection and analysis of the dust which passes by the dust lip to provide more information about the performance of the dust lip operating under such conditions. Such is provided by the present invention.
SUMMARY OF THE INVENTION AND ADVANTAGES
Test apparatus for testing the sealing effectiveness of a dynamic dust-exclusion seal in a dust-laden environment of the type having at least one dust-excluding lip comprises a housing having a support wall with an opening therethrough and a test shaft supported for rotation within the opening with an annular gap therebetween to be closed by the seal to be tested. Seal mounting structure is provided for mounting the test seal with the dust-excluding lip of the seal supported in dynamic sealing relation with a corresponding sealing surface of the seal. A dust chamber is provided on one side of the wall for exposing an atmosphere side of the dust-excluding lip to a dust-laden operating environment. The apparatus is characterized by provision of a dry dust-collection chamber on an axially opposite side of the wall in communication with the dust chamber through the annular gap and operative for collecting any dust that may escape past the dust-exclusion lip through the gap.
The apparatus is operated according to a test procedure of the invention by rotating the shaft relative to the seal while maintaining a dust-laden environment within the dust chamber, and collecting any dust that may escape past the seal within the dry dust-collection chamber for ascertaining the effectiveness of the seal while operating in such an environment.
One advantage of the present invention is that it permits quantitative testing of dynamic seals having dust-excluding features operating in a dust-laden test environment. The dry dust-collection chamber on the protected side of the seal enables any dust that may pass by the dust-exclusion lip to be collected and measured during the course of a test cycle. The invention enables the performance of the dust lip to be monitored and evaluated quantitatively throughout the test cycle, independent of the performance of the primary oil lip. A further advantage of the dry dust-collection chamber is that any dust patterns or accumulations of dust that may build up during the course of a test are preserved, even after the ultimate failure of the dust-exclusion lip seal and can be examined to learn the possible cause of leakage and to assist in providing relevant information to continually improve the design and performance of seals. There is no oil present to wash the dust away.
Rather than rely on the leakage of oil past a failed oil lip to indicate a seal failure, the present invention enables seal manufacturers to establish specific quantitative performance criteria for ascertaining the effectiveness of a seal. For a given set of operating conditions, one or several seals may be tested for a given length of time and the leakage of dust monitored as to when and how much dust passes by the seal during the course of the test cycle. With such information available, the manufacturer or end user of dynamic seals can then established standardized quantitative performance criteria for such seals.
The invention also provides a test apparatus having a stationary support wall and a rotatable shaft extending throu
Toth David Michael
Tripathy Bhawani Sanker
Vinton Mark David
Federal-Mogul World Wide Inc.
Garber C. D.
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
Williams Hezron
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