Rotational test machine helps predict real-world performance of elastomer seals.

The Detroit Rubber Group sponsors symposia that bring together the Big 3 automotive manufacturers and Tier 1 suppliers with one recurring theme -- cooperation -- working together to meet common goals. At a recent session titled, "Automotive systems and elastomer application expectaTions," the group called for the development of laboratory procedures that can predict real-world performance. At the exact same time "the call" was being made, in the first quarter of 1997, Acadia Polymers' new automatic transmission rotational test machine went on-line. After two years of development and design, verification of test methods and procedures, and endless hours of calibration, the machine is up and running to perform real-world-related testing of automatic transmission elastomer sealing components. First up was the verification of a manufacturing change on a bonded piston seal that will speed manufacturing operations, maintain integrity of the bond, lower production costs, and last, save the customers significant dollars. Here are the details.

The automatic transmission, rotational test machine (RTM) has the capability of testing automatic transmission seals insitu, under the actual performance demands of the most modern designed transmissions. The Automatic Transmission RTM subjects either new or existing design bonded piston seals, shaft seals and Teflon seals to the pressures, rpms, temperatures, cycle times and, the newest parameter, centrifugal forces of advanced design four and five speed transmissions.

Transmission sealing systems for today's standard overdrive transmissions are required to perform at rotational speeds often higher than engine speeds. Acadia has the capability to verify seal design, and then predict seal performance to a much higher confidence level than ever before.

The RTM is capable of testing both front and rear wheel drive configurations, either left or right hand rotation. Powered by a 75 hp DC motor, it will reach and maintain 8,000 rpm (at 75 hp) for selected intervals; even higher than 8,000 rpm at lower horsepowers. Basic control parameters are: Hydraulic pressure from 0-400 psi, fluid temperature from ambient to 300 [degrees] F; transmission case temperature from ambient to 400 [degrees] F (table 1).

Table 1 - basic format of automatic transmission rotational test machine

Physical machine

Basic frame construction similar to a typical transmission dynamometer.

Capable of testing both front and rear wheel drive configurations, left and right hand rotation.

Powered by 75 horsepower dc motor.

Reach and maintain 8,000 RPM for selected intervals.

Heat and cool fluids and transmission housings as programmed.

Control system

The operator can set, monitor and change the following settings:

5 hydraulic circuits

- Pressure 0 - 400 psi

- Automatic shutdown

Temperature

- Fluid temperature from ambient to 300 [degrees] F

- Transmission case temperature from ambient to 400 [degrees] F

- Automatic shutdown

RPM

- 0 to 8,000 rpm

- Automatic shutdown

Fluid leak rate

- Monitor only

- Automatic shutdown Torque-to-turn (monitor only) Cold temperature box

- to -40 [degrees] F

The new automatic transmission RTM, the first of its kind in the industry, complements conventional static test machines that also help verify seal design and performance. Acadia designs special fixtures needed to test clutch packs, transmission modules, even entire transmissions, to provide performance information crucial to a customer's transmission development activities.

Testing rationale

To be able to claim that an elastomer sealing product is completely, 100% tested, a supplier must be able to duplicate, in the lab, the exact in-situ operating parameters experienced once a seal is in service. Before the RTM, a most important parameter, rotation centrifugal forces acting on seals, could not be included in data analysis. And, if a problem or seal failure occurred in the field, it was difficult to isolate one single cause, or failure tendency leading to the root cause of the problem.

In conventional elastomer seal testing, it's relatively easy to control temperature and pressure values, and count on/off cycles. Static automatic transmission seal test machines have been performing satisfactorily for years helping to predict seal failure modes.

But the modem transmissions, and more exotic seal designs subjected to higher pressures, temperatures and rpms, stretch the limit on conventional data gathering and analysis techniques. The RTM eliminates the need to make assumptions on forces that may be acting on the seal.

For example, a dual material seal, often referred to as a two-piece seal, may have an FKM material on the I.D. to provide memory and spring effect that accommodates slight shaft eccentricities, and glass-filled PTFE on the O.D. to serve as the sealing element. The RTM provides engineers the capability to measure drag forces of the two-piece seals with rotation and hydraulic pressure. Having this new data to analyze permits a more complete study of both seal problems and design verification.

Internal/external test requests

Managing sealing systems requires thorough knowledge on all the factors that may cause seals to fail. The seal management concept allows the supplier to have complete control over material and configuration of the seal during the development phase. The RTM is used to confirm and verify that these factors are correct.

Once the seals are in service, seal failure or a tendency toward failure may be traceable to fluid contamination, clutch failure, failure of adjacent components, etc. Problems may also be traceable to an assembly issue; i.e., a pinched or skewed seal. Again, being able to duplicate all real-world operational parameters in the lab will allow quick isolation of the root cause of the problem.

Acadia's account managers and their customers need to quickly resolve problems encountered in the field. Most requests for testing being initiated in the field are the result of close communications between the supplier and customer.

Internal requests for RTM time are initiated either in engineering or quality assurance departments to either qualify new designs or verify changes in material, assembly, configuration, processing techniques or assembly recommendations. All internal requests have one goal in mind, to produce sealing products equal to, or better than, the previous seal.

Basic profiles

The RTM is a computer controlled dynamic profile control and data acquisition system. Systems software empowers an operator to control high volume cycling and analysis of a number of dynamic testing fixtures (up to five pressure circuits at one time).

The machine produces a database for analysis from five profiles created using several interrelated, controlled parameters. In the example profile matrix shown in figure 1, each step is a given number of cycles. A setpoint is applied for a given number of cycles (steps). One cycle is one period of time on, and one period of time off. A sequence of steps makes up a profile. Each profile may be independent of the others. The smallest increment is 100 cycles. Following are the five profiles matrices:

* Motor profile matrix: Numerous steps may be specified using a different rpm setpoint for each step. The rpm motor speed setpoints are in revolutions per second.

* Load absorber profile matrix: Numerous steps with different load setpoints (in pounds of torque) specified for each step may be applied to the drive shaft.

* Pressure circuit (the hydraulic fluid line corresponding to a specific test fixture circuit) profile matrix: Numerous steps with different pressure setpoints (in pounds per square inch) for each step may be specified and applied to the test fixtures.

* Case temperature profile matrix: Numerous steps with different temperature setpoints for each step may be applied to the test chamber.

* Temperature circuits profile matrix: Numerous steps with different temperature setpoints for each step may be applied to the pressure circuits of the test fixture. Units are in degrees Fahrenheit.

[FIGURE 1 ILLUSTRATION OMITTED]