The MuCell process for producing microcellular injection molded parts is accepted as a technology for providing a more dimensionally stable part through a reduction in residual stress with increased productivity over compact molded parts. A much larger improvement in productivity can be realized by designing parts to take advantage of the unique process enhancements provided by the MuCell process.
Trexel Inc and the MuCell Process
Trexel Inc., located in Wilmington, Massachusetts is an investor and employee-owned company specializing in the development and commercialization of microcellular foam processes for the plastics industry. Trexel has Sales and Support Offices in key regions of the world, and also has many alliances with equipment companies, contract manufacturers, materials suppliers, and premier molding organizations, all dedicated to the optimal use of the MuCell Process to improve quality and reduce manufacturing costs.
The MuCell microcellular foam injection molding technology is a complete process and equipment technology which facilitates extremely high quality and greatly reduces production costs. The MuCell process begins by converting the inert gas, nitrogen or carbon dioxide, into a supercritical fluid, or SCF, for precise dosing capability. The SCF is injected into the barrel during screw recovery by the SCF interface kit that is mounted to the barrel. A specially designed MuCell screw with a disperses the SCF into the polymer melt creating a single-phase solution. The SCF acts as a temporary polymer plasticizer, reducing the viscosity of the resin up to 30%. This provides the inherent benefit of improved filling of thin-wall sections and flexible members.
During filling and cooling, microscopic cell growth takes place within the cavity, creating all of the internal pressure needed to completely fill the part. Thus pack and hold, a contributor to cycle time and major source of molded-in part stress in conventional molding, is eliminated with the process. Peak cavity pressure is reduced by up to 80%. Cooling time is often shortened due to reduced mass, lower mold and melt temperatures and less warpage control required. Cycle time reductions averaging 20% to 30% translate into capital cost avoidance and freed machine capacity. A uniform closed-cell, microscopic cell structure is created throughout the part with a solid skin. Stress induced warpage is eliminated and sink marks are eliminated without a chemical change to the polymer. The elimination of the hold phase results in a significantly lower peak clamp tonnage requirement. This allows machine size reduction by up to 50% using MuCell processing and reduced operating costs through the use of the lower corresponding hourly machine rate.
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