Rotating-Core Injection Molding Process Increases Burst Strength and Reduces the Detrimental Effects of Knit Lines; Solvay Advanced Polymers is Building a Development Tool to Evaluate Additional Benefits, Including Improvements in Dimensional Stability

ALPHARETTA, Ga., Oct. 7, 2004 -- In conventional injection molding, cylindrical or conical sections within complex parts are formed by flowing thermoplastic material around a stationary core. A molding process patented by Solvay S.A. has been shown to improve the strength of such parts by injecting the material onto a rotating core.

Two-fold and greater strength increases have been demonstrated in parts molded of semi-crystalline polymers reinforced with glass or minerals or both. The improved burst strength is achieved, in part, by the ability of the process to produce a preferred orientation in the material itself. On a macro-molecular level, the polymer chains become arranged around the circumference of a cylindrical or conical part -- like the reinforcing belts under the tread of a radial tire -- rather than simply along the flow path of the injected plastic. The reinforcing fibers are also arranged in this direction, greatly increasing the part's ability to withstand internal pressure.

Rotating the core during injection also reduces the detrimental effect of knit lines or weld lines -- areas formed when flow fronts meet, which results in incomplete material or fiber interaction across the front and introduces mechanical weakness.

Improved dimensional stability

Now Solvay Advanced Polymers L.L.C. is building a development tool to evaluate additional benefits of the process that have important implications in specific applications. Jeff Peterson, one of the company's global market managers, is encouraged that the rotating-core process can produce cylindrical or conical sections that exhibit improved dimensional stability during operation over a wide range of temperature and humidity conditions. "What's absolutely critical to an automotive throttle body, for example, is that it maintains both its dimensions and its roundness in operation," Peterson points out. "The dimensional design tolerance between the air-regulating valve and the bore is quite tight and ideally would not change with fluctuations in environmental conditions. So any process that improves the bore's dimensional stability over the full range of operating conditions in turn improves engine performance, including efficiency and emission characteristics."

Rotating the core during injection could have other benefits, such as helping control the initial molded dimensions of the bore or improving the quality of the surface finish.

New data will help optimize process for additional applications

Speed and the duration of core rotation during injection are important parameters in maximizing the strength and stability of a finished part. The new development tool will give Solvay Advanced Polymers data to help in optimizing the rotating-core process for a variety of materials and applications. Parts molded in such advanced materials as IXEF(R) polyarylamide and AMODEL(R) polyphthalamide could benefit significantly from this process.

Peterson anticipates that the patented process can produce improvements not only in automotive parts -. such as throttle bodies or brake power-piston cylinders -. but also in similar applications in other industries. He cites such examples as plumbing fittings and thrust washers as applications that could realize significant improvements in strength and dimensional stability.

About Solvay Advanced Polymers

Solvay Advanced Polymers, L.L.C. is a subsidiary of Solvay America, Inc., the U.S. holding company of Solvay S.A. The company produces high-performance polymers that are used in a wide range of demanding applications in the automotive, aerospace, industrial, foodservice, medical, and electronics industries worldwide. More information about this and other Solvay Advanced Polymers products and services can be found on the company's website at http://www.solvayadvancedpolymers.com/ .

Solvay is an international chemical and pharmaceutical group with headquarters in Brussels, Belgium. It employs more than 30,000 people in 50 countries. In 2003, its consolidated sales amounted to EUR 7.6 billion generated by its three activity sectors: Chemicals, Plastics and Pharmaceuticals. Solvay is listed on the Euronext 100 index of top European companies. Details are available at http://www.solvay.com/ .