Blow molding is a well-established process that lets designers glean more design freedom and drop part cost by easing assembly via parts consolidation.
What is in this article?:
- Blow-moldable TPVs give silicone rubbers the boot
- A few processing and design tips for blow molding Zeotherm TPVs
- Finding the right engineering materials and adhesives
A few processing and design tips for blow molding Zeotherm TPVs
TYPICAL PROCESSING PARAMETERS:
Zeotherm 120-90B and 130-90B have a plastic phase of nylon (polyamide) 6. They are typically blow molded using melt temperatures of 482 to 518°F (250 to 270°C), depending on the part and the particular machine. Because nylon absorbs moisture, it is critical to properly dry the TPVs before blow molding. If the material is not properly dried, the parison may exhibit poor melt strength and have regions of porosity.
TYPICAL PART CONSTRUCTION:
- Automotive boots, made from Zeotherm TPVs are typically constructed as monolayer (100% Zeotherm) parts.
- For automotive air-duct applications, Zeotherm TPVs are typically used with a high-viscosity, blow-molding grade of nylon. The TPV furnishes flexibility and sealing, while the nylon provides rigidity. Via a sequential blow-molding process, it's possible to regulate the placement of soft and rigid sections in the part. The combination also gives good economics, as nylon costs less than the Zeotherm TPVs.
PART DESIGN RECOMMENDATIONS:
- For automotive boots, a rounded convolute shape yields the best results in terms of part durability. The convolute shape is more typical of a rubber-boot design.
- For automotive ducts, part design can typically follow what has been commonly used for TPO (thermoplastic polyolefin)/PP ducts. Wall thicknesses are typically 1.5 to 2.5 mm in automotive ducts.
WHY ZEOTHERM TPVs VERSUS OTHER MATERIALS:
- For automotive boots, the materials resist heat to 175°C, features dramatically improved hot-grease resistance (Zeotherm is not degraded by hot grease nor are the greases degraded by contact with Zeotherm), and the TPV is softer and more flexible than copolyesters. On vehicles where the automotive boots are close to a heat source (i.e., exhaust manifold, exhaust pipe routing, engine), TPV temperature performance is advantageous.
- For automotive air ducts, the TPV is more flexible than so-called flexibilized nylons. It also costs less than silicone rubber + aluminum which has been the approach of choice at higher temperatures. The material also better resists oil vapors than TPO/PPs and copolyesters.
Zeotherm TPVs in combination with nylon have been a good fit in North America for 2007 model-year turbo-diesel-powered vehicles. New EPA regulations for 2007 are requiring redesign of diesel engines. And, with the redesign, the temperature demands on clean-air intake (air cleaner to turbocharger) and cold-side charged-air duct (innercooler to throttle body) are increasing above where conventional materials can function.