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Living Hinge Molded Using Polyurethane Reinforced Fabric

Allows for production-like performance in prototypes

An overmolding technique that combines linen and polyurethane provides hinged prototype parts with a production-like performance for physical and field testing. J.P. Pattern Inc., Butler, WI, perfected this technique for customers who needed to incorporate living hinges into their designs. Living hinges can be flexed numerous times without cracking, like the pillbox shown here. Other OEM applications include those in the automotive and packaging industries.

This pill box incorporates a living hinge that can withstand repeated flexing cycles.

Technicians begin hinge production by making a fabric/polyurethane preform. First, a piece of linen is inserted into a 2-part acrylic mold that has been machined to precise dimensions for production of a hinge with a thick center section that tapers out to thin sidewalls. Then, a resilient, Shore 85A hardness polyurethane, such as Ren RP 6402-1 R/H supplied by Vantico (formerly Performance Polymers, Ciba Specialty Chemicals), East Lansing, MI, is applied to the fabric. The mold is closed, squeezing resin into the cloth. The cured polyurethane, which exhibits a tensile strength of 2,200 psi, tear strength of 180 ppi, and elongation of 320%, produces durable hinges that can withstand repeated flexing cycles.

After the linen/polyurethane preform is removed from the acrylic mold, it is placed in a silicone rubber mold. Then, a conventional polyurethane is dispensed into the tool cavity to encapsulate the preform and produce the prototype part. PR 6405 R/H is selected for prototyping projects that require a thermoplastic-like appearance as well as good tensile and tear strengths and that have a deadline that accommodates the system's 24-hour demold time.

The company has produced more than 100 hinged, thermoplastic-like parts from a single silicon rubber mold by using this process.

--KC

For more information:

Circle 501 - J.P. Pattern Inc. or connect directly to their website via the Online Reader Service Program at http://www.1rs.com/010df-565

Circle 502 -Vantico or connect directly to http://www.1rs.com/010df-566