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Molded Polyurethane Foam Industry Panel
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 May 2006 Feature
Roy Pask is supervisor of polymer physics for the BASF Urethanes R&D Department. He has over 30 years of experience in testing urethane foams. In addition to serving on the Molded Urethane Foam Industry Panel, Pask is chair of ASTM Subcommittee D20.22. He also is co-chair of the Automotive Materials Association’s Interior Materials Committee. Additionally, Pask represents BASF on various other committees in the Society of Automotive Engineers, and on the Alliance for the Polyurethane Industries, the Polyurethane Foam Association and the Carpet Cushion Council.

Molded Polyurethane Foam Industry Panel

Auto Manufacturers and Tier Suppliers Team Up to Establish Best Practices

A group of automobile tier suppliers has partnered with manufacturers in a unique effort to make a difference in supplying car seats. The Molded Polyurethane Foam Industry Panel has begun the process of revising automotive seating foam specifications to establish commonality in test methodologies, to eliminate non-valued added requirements and to establish best practices for measuring seating foam performance. The team has put aside competitive differences to accomplish these goals.

In selecting team members, Woodbridge Foam Corporation, which established the panel, chose experts in their fields. This included raw material suppliers, polyurethane foam molders and seat fabricators as well as material engineers from Ford, General Motors and DaimlerChrysler. Over 300 years of experience are represented on the team. A side benefit of the group’s activities is the coordination of similar activities in standards developing organizations such as ASTM International and the Society of Automotive Engineers. This allows for the pooling of resources and for minimizing the duplication of efforts.

Molded Polyurethane Foam Industry Panel

OEM Participants

DaimlerChrysler
Ford Motor Company
General Motors

Industry Participants

Bayer MaterialScience
BASF Corporation
Lear Corporation
Dow Chemical
Johnson Controls Inc.
Woodbridge Foam










Click here for another sidebar on the panel.

The Process
To put things in perspective, the team first looked at the complexity of the existing specifications for seating foams. Their investigations showed, for example, that there are 32 methods for measuring foam firmness, 10 compression set methods and 12 different fatigue tests for seating foam cushions. No one version of any of these tests has ever been proven to be any better than the others. If the team could at least agree on some common methodologies, then the situation would be greatly improved. After compiling the list of tests present in existing specifications, each test was evaluated and team members were surveyed to indicate which tests were most important and which ones added very little value to seat performance.

The tests were also evaluated to determine which ones were relevant to various steps in the manufacturing process, including molding/demolding cushions, covering the cushions, and building the finished seats. The relevance to in-service seat durability and comfort was also analyzed. As an example, whereas tear strength has much relevance in the molding, demolding and covering of seat cushions, tensile and elongation properties were deemed to have very little relevance to these processes. When would a seating foam ever get stretched anywhere near its ultimate elongation? After analysis, a set of core physical properties for seating foams was agreed upon. In addition, a set of mandated tests was also identified. Armed with a common set of tests, the panel began a Phase 1 process of revising current original-equipment-manufacturer seating foam specifications.

Phase 1
The group began with DaimlerChrysler. Their seating foam specification, MS-DC634, had not been revised since 1980. The bulk of the test requirements referenced ASTM D 2406, Method of Testing Flexible Cellular Materials-Molded Urethane Foam, which was discontinued in 1980. MS-DC634 also called for a number of Chrysler in-house methods. The goal of the Phase 1 revision was to 1) use the consensus core methods, wherever possible, 2) replace discontinued and in-house methods with industry or international standards and 3) remove non-value added and non-descript requirements.

To accomplish this, a number of changes to ASTM D 3574, Test Methods for Flexible Cellular Materials — Slab, Bonded, and Molded Urethane Foams (which replaced D 2406), were orchestrated through Subcommittee D20.22 on Cellular Materials — Plastics and Elastomers. This revision included the addition of a standard hysteresis loss test for flexible foams, the addition of the wet heat aging conditions and the addition of a line call-out system for flexible foams, which can be used on seat cushion engineering drawings.

Through the process of cooperation and the sharing of knowledge and resources, the Industry Panel was able to revise MS-DC634, obtain all the approvals at DaimlerChrysler, and publish the specification in about four months. The changes were so substantial that the specification was assigned a new number, MS-DC648, to minimize the confusion of a radically altered MS-DC634. Similar activities are now ongoing with Ford and General Motors to revise their seating foam specifications, with a goal of accomplishing this in 2006.

Phase 2
The Phase 1 revisions will be fairly straightforward. However, to accomplish the other goals of identifying best practices in the industry and improving the precision of existing methods used in automotive seat cushion specifications, a great deal of work needs to be done. A number of teams were formed to deal with specific areas of investigation. The timeline for the Phase 2 revisions depends on the success of these teams.

Volatiles Team
The Volatiles Team has a number of objectives. In odor testing the team is trying to address test result subjectivity and test lab health concerns with SAE J1351, Hot Odor Test for Insulation Materials. This method utilizes human nose panels to assess odors for objectionability. An Instrumented Odor Assessment Committee in the Automotive Materials Association was formed to develop an instrumented odor measurement standard to replace SAE J1351. Volatiles Team members have joined that AMA committee to coordinate activities.

Odor testing per SAE J1351
Fogging tests simulate the deposition of volatile materials on the windshield glass, which could potentially impair the driver’s vision. The goals for the team are to commonize test parameters, to compare gloss measurements with gravimetric measurements and to validate test instrument differences. Activities are being coordinated through the Automotive Material Association, which is responsible for SAE J1756, Test Procedure to Determine the Fogging Characteristics of Interior Automotive Materials.

Finally, the team has a number of objectives in stain testing. These include establishing industry standard vinyls for stain testing, comparing contact stain methods with vapor stain methods, comparing stain test energy sources like heat or light, and investigating whether outdated gray scale color measurements can be replaced by color spectrophotometer measurements. It is possible that the team will make recommendations for revisions to ASTM D 925, Test Methods for Rubber Property-Staining of Surfaces (Contact, Migration, and Diffusion). When all this work is complete, the Volatiles Team will recommend the best practices to the larger Industry Panel and communicate their findings to the SAE and AMA committees.

Tear, Compression Set, Flammability Team
This team had the mission of investigating the various ASTM and Deutsches Institut für Normung, or DIN, tear tests being used in the automotive industry to find which one is most relevant to seat cushion manufacture and use. They had to compare tear-initiating tests with tear-propagating tests. Their investigations indicated that ASTM D 624, Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers, was much more relevant to seating foams than D 3574, a tear test that is typically called out in seating foam specifications.

(l to r): Trouser Leg Tear 50 mm/min, Die “C” Tear 500 mm/min, DIN Paper Tear 100 mm/min

 

 

 

 




As a side benefit to this work, a direct relationship between the D 624 tear test and tensile and elongation measurements was established. Based on these observations the team was able to recommend that tensile and elongation requirements be removed from the seating foam specifications.

In compression set testing the mission was to 1) commonize test parameters and 2) investigate whether the wet compression set test could replace the two set tests (unaged and humid aged) normally seen in seating foam specifications. The wet compression set value has been demonstrated in past work by team members to directly correlate with seat cushion durability. The flammability requirement for seating foams is required by federal law, so there was not much the team could do. However, one improvement that showed up in the new MS-DC648 specification was a note directing users to the ASTM version of MVSS 302, namely ASTM D 5132, Test Method for Horizontal Burning Rate of Polymeric Materials Used in Occupant Compartments of Motor Vehicles, for more definitive instructions for running the flammability test than what appears in the Code of Federal Regulations. D 5132 also contains test method precision data for refereeing purposes. Based on their work, this team was able to make their final recommendations to the Industry Panel and their task is essentially done.

CPF/ Hysteresis Loss Test IFD Test

 

 

 

 






Firmness Team
The Firmness Team has the mission of sifting through some 32 methods for measuring load bearing that can be found in automotive seating specifications. Their goal is to find which method has 1) the best precision, 2) the best correlation to H-point measurements (performed on fully installed automobile seats to determine the height of the driver’s eyes in relation to the windshield viewing area) and 3) the best correlation to seat cushion durability. Part of their investigation included studying test parameters such as preloads and dwell times to see what impact they have on test method precision. They also compared current IFD (indentation force deflection) and IRGL (indentation residual gauge length) methods found in ASTM D 3574, as well as a CPF (constant penetration force) test often used by some seat designers.

The CPF test is very similar to ASTM D 5672, Test Method for Testing Flexible Cellular Materials Measurement of Indentation Force Deflection Using a 25-mm (1-in.) Deflection Technique, which has been used in the upholstered furniture industry for many years. Additional studies are being performed to investigate the relationship between hysteresis loss and seat cushion durability.

Early indications from the team have shown good H-point correlation with both the IRGL test and the CPF test, while hysteresis measurements seem to correlate with cushion fatigue loss. A combination of hysteresis loss and CPF could possibly be used to adjust H-point values as well as predict durability. This combination test could be run in three minutes compared to the 10 minutes it takes to run the standard IFD test. Again, as with the other teams, when all their work is complete the Firmness Team will make their best recommendation to the Industry Panel for a consensus vote.

Durability Team
Like the Firmness Team, the Durability Team has a large number of fatigue tests for seat cushions to investigate. The most heavily cited method for fatigue in automotive seating foam specifications has been the constant force pounding test from ASTM D 3574. But seat designers are not sure this test method provides them with the correlation to in-vehicle seat response that they need. As part of evaluating all the tests, the team hopes to quantify the effects of deflection, cyclic rate, and time (number of cycles) on the fatiguing process. They are also investigating the effects of the indentor shape (round, cylindrical, butt-shaped, etc.) and the effects of test temperature (ambient versus elevated).

ASTM D 3574 Constant Force Pounding Test
After some discussions the team felt that the most important variables in the fatiguing process were frequency, the number of cycles and the amount of loading or deflection applied to the cushion. This was not unexpected. The loading and unloading process in the test is very interesting. Whereas the constant force pounding test applies a 750N load on and completely off the cushion during each cycle, another test cycles between 150N and 750N. Still another test cycles between 45-and 55-percent deflection. Frequencies range from 1Hz to 5Hz. Test cycle durations range from 80,000 to 300,000 cycles. What firmness measurement is best for measuring before and after cycling? What influence does creep play in the fatiguing process? Is there viscous heat build-up in a cushion at the higher frequencies? These are all things that the team hopes to understand before they make their recommendation for a consensus fatigue test.

Summary
The power of this team lies in its members and its member companies. Without the commitment to share resources and knowledge, and without a great deal of cooperation, this would not be nearly the success story that it has turned out to be. A summary of the Molded Polyurethane Foam Industry Panel’s mission and accomplishments was recently presented during a three-hour automotive industry session presentation at the API (Alliance for the Polyurethane Industries) World Conference in Houston in October 2005. Over 1,300 attendees were at the conference. Other groups are beginning to recognize the value in creating a vertically integrated Industry Panel like this one.

There will still be obstacles. No one is expecting to have identical specifications for each original equipment manufacturer. But, on the other hand, if the panel can achieve a portion of its objectives, then the situation would be greatly improved in terms of developing cost-effective, higher performing automobile seats. After all is said and done, the group hopes to capture its work by publishing “Best Practices, History, Design, Manufacturing and Testing of Automotive Seating” for future use in the industry. //

 
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