▎ 摘　　要

NOVELTY - Biaxial stretching device, comprises stretching assembly composed of two symmetrically arranged circular tracks, a plurality of chain clamps for clamping the sides of polytetrafluoroethylene film, and chain clips are driven by driving mechanism to rotate around circular track; stretching space is left between the two circular tracks, and stretching space is divided into heat balance zone, transverse stretching zone, longitudinal stretching zone and shaping zone through the width change of circular track; electromagnetic heating device is located in preheating zone; stretching heating assembly includes first heating matrix, second heating matrix, third heating matrix, and sintering and shaping device located in shaping zone, first heating matrix, second heating matrix, and third heating matrix include plurality of uniformly distributed heating elements; the polytetrafluoroethylene film is evenly filled with iron powder, graphite micropowder or graphene nanosheets as fillers. USE - The biaxial stretching device is useful for improving the uniformity of expanded polytetrafluoroethylene film (claimed). ADVANTAGE - The biaxial stretching device effectively improves the thickness uniformity of the stretched expanded polytetrafluoroethylene film. DETAILED DESCRIPTION - Biaxial stretching device, comprises stretching assembly composed of two symmetrically arranged circular tracks, a plurality of chain clamps for clamping the sides of polytetrafluoroethylene film, and chain clips are driven by driving mechanism to rotate around circular track; stretching space is left between the two circular tracks, and stretching space is divided into heat balance zone, transverse stretching zone, longitudinal stretching zone and shaping zone through the width change of circular track; electromagnetic heating device is located in preheating zone at the front end of entrance of the stretching space to preheat polytetrafluoroethylene film; stretching heating assembly includes first heating matrix located in heat balance zone, second heating matrix located in transverse stretching zone, third heating matrix located in longitudinal stretching zone, and sintering and shaping device located in shaping zone, first heating matrix, second heating matrix, and third heating matrix include plurality of uniformly distributed heating elements; the polytetrafluoroethylene film is evenly filled with iron powder, graphite micropowder or graphene nanosheets as fillers. An INDEPENDENT CLAIM is also included for biaxial stretching method for improving the uniformity of expanded polytetrafluoroethylene film, comprising pre-heating polytetrafluoroethylene film by the electromagnetic heating device, where the polytetrafluoroethylene film is uniformly filled with iron powder, graphite powder or graphene nanosheets as a filler, clamping the polytetrafluoroethylene film by chain clip, and driving the chain clip by driving mechanism to drive the polytetrafluoroethylene film to move axially along the stretching space, when the polytetrafluoroethylene film passes through the heat balance zone, thermally balancing the polytetrafluoroethylene film through the first heating matrix, maintains uniform temperature of the polytetrafluoroethylene film, when the polytetrafluoroethylene film passes through the transverse stretching zone, heating the polytetrafluoroethylene film by the second heating matrix, under heating environment, transversely stretching the heat-balanced polytetrafluoroethylene film, where heating temperature of the heating elements in the second heating matrix is distributed in a gradient decreasing manner from the lateral center of the polytetrafluoroethylene film to the lateral two sides, when the polytetrafluoroethylene film passes through longitudinal stretching zone, heating polytetrafluoroethylene film by third heating matrix, under heating environment, longitudinally stretching the polytetrafluoroethylene film after transverse stretching, when the polytetrafluoroethylene film passes through the shaping zone, sintering and shaping polytetrafluoroethylene film by sintering and shaping device to obtain an expanded polytetrafluoroethylene film.