Foam

From automotive cushioning materials that take you to work to the pillows and mattresses you lay on, flexible polyurethane (FPU) foam is a part of our daily lives. The incredible diversity of FPU foam products are made possible by the ability of foam materials to be engineered to serve a wide range of performance requirements. The unique combination of load bearing and firmness makes FPU the perfect choice for a dazzling array of products but that same benefit makes it a challenge for a test engineer to confirm performance in specific application.

Oftentimes determining the best foam for a particular task is based on interpretation of test results and opinions. The inaccuracies and reproducibilities of some test methods leave the question open to subjective opinion. Not only that, but test reproducibility from machine to machine and lab to lab can vary quite a bit. Errors ranging up to thirty per cent* result from some test procedures which are compounded by poor test experiment planning and communication. IFD interlab tests often lead to varying results; Compression deflection and flex fatigue testing usually leads to wide differences in test results.

Formulations of Flexible Polyurethane Foam

When formulated with an open cell structure it is most often used for cushioning in a variety of uses including household and industrial furnishings, automotive interiors, carpet underlay and hundreds of other applications. FPU is a complex polymeric product designed for comfort and cushioning. Rigid cellular products are quite different – typically delivered with closed cell structures. FPU also delivers shock absorption to packaging and automotive applications. Viscoelastic polyurethane foam, also known as memory foam, is a special variation that uses chemicals to increase viscosity and density.

Foam Physical Properties Testing

With such a wide range of FPU properties and applications, great care must be taken when contrasting test results with test procedures. In fact the complexity is such that just following standards such as ASTM D3574 is not enough.

Physical property testing plays a critical role in confirming that each material formulation matches the specific application requirements. In most situations, mechanical test results establish that the product is or is not acceptable. Physical testing serves both research and production phases. Compared to other polymeric products, the design and production of foam products is inherently complex due to different chemical formulations with significant rate sensitivity. The testing process, test methods, test machine operators and foam test machines all contribute to the variation in tested outcomes and final test results. Not only is mechanical testing important, it is also relatively complex.

Lots of testing is needed -- driven partly by the fact that variations in foam hardness or firmness can come from either the raw material or from process variations. Another contributing factor is the long value chain from material supplier to foam maker to cushion maker to seat assembly maker (in the example of a car seat manufacturing process). The process involves a constant check to confirm incoming lot qualification is acceptable. From time to time, customers need to set up a new production line which also requires a large test program.

Common Mechanical Foam Test

Multiple ASTM and ISO test methods focus on characterizing flexible polyurethane foam. By far, the most commonly accepted foam industry standard test is ASTM D3574. ASTM D3574 includes a battery of mechanical tests including strength properties (tensile, tear and elongation), indentation force deflection (IFD and ILD), Indentation residual gauge length, fatigue, hysteresis and resiliency.

The indentation force deflection test is commonly used in production line testing applications in spite of the fact that the ASTM D3574 Method B1 procedure can take surprisingly long time (12 minutes in the case of a four inch foam slab) because of the specified hold times.

Shortened test derivatives abound because the process cannot take the time to run the full standard test method. Companies with fast moving production process often develop unique internal tests to monitor quality and shorten the test time. So test methods are wide and varied and require test software and controls that handle the variations. TestResources IFD software package runs the ASTM D3574 as a default setting, but enables the user to alter settings for custom designed test applications.

Flexible Foam Test Data

Correlation

Mechanical testing proves that your foam product performs as advertised. Additionally, online production mechanical testing helps monitor material production processes to confirm they are operating as intended and within engineering limits, which helps reduce scrap, delivery times and costs.

Because of the critical role of testing, it is likely that foam suppliers have multiple foam or IFD test machines to serve all their needs. After a supplier’s first test machine is qualified to meet a customer’s test requirements, the addition of a second machine creates a need for replicate accuracy. This means that the test data produced correlates between the two machines. One approach is to standardize on selection of one manufacturer up front, and the other approach is to run correlation tests when an alternative test machine provider is chosen. TestResources offers a correlation service to correlate our foam testers to test machines and test setups already in place. The data correlation challenge is common to foam testing, and we offer the experience and willingness to solve real testing problems.

TestResources - the best choice for Flexible Foam Test Equipment

TestResources understands soft flexible foam testing applications. With that experience in hand, we developed a specialized foam tester product line using our ‘Smart Design’ process. Test machine competitors commonly offer a ‘one size fits all’ universal test machine configured with special fixtures. That approach forces compromises in value on all users. TestResources modular product line (actuators, load frames, controllers, test fixtures) are configurable which means that we can deliver low cost or high performance as needed by the application. In our experience, foam testing applications can be configured from a platform of affordable product modules with a highly focused application engineered software program optimized to serve ASTM D3574 and all of its derivatives.

In production testing environments, the minimum performance required is to meet the standard test profile defined in ASTM D3574 Method B1. That said, most customers place high value on being able to test shortened versions of ASTM D3574 method B1 that are technical derivatives of the standard. Each application tends to be different in some small way. For instance, customers may want to change the profile length of the test. TestResources IFD Test Software is uniquely engineered in anticipation of customer needs to change the variables of the test method. Our foam testing solutions serve that application perfectly.

Not only that, but TestResources found that FPU production applications place high value on cost effective solutions. Production costs need to be minimized where possible. Our intent is to serve those customers with an automated solution that they can afford.

That’s why we call our approach ‘Smart Design’. Smart design is the difference when it comes to considering the best foam test machine supplier.

Related Articles

• Indentation Force Deflection (IFD) Testing per ASTM D3574
• Car Seat Foam Bolster Testing
• Indentation Load Force Deflection (ILD or IFD) - Urethane Plastic Foam - Test Equipment
• ILD Test of Polyurethane Cushions and Pillows
• IFD Firmness of Flexible Molded Polyurethane Foam Car Seats
• Soft Foam | Tensile Testing Equipment
• Flexible Car Seat Foam Testing

Applicable Standards

• ASTM D3574 Testing Equipment for Flexible Cellular Urethane Foams
• ASTM D5672 Indentation Force Deflection of Flexible Cellular Plastic Foam
• ISO 1798 Tensile Test of Flexible Cellular Polymers
• ISO 2439 Indentation Hardness of Flexible Cellular Plastic Foam
• ISO 3385 Flexible Cellular Foam Fatigue by Constant-Load Pounding
• ISO 8067 Flexible Cellular Polymeric Materials Tear Strength

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