| In recent years,with the deterioration of the surrounding environment,people's strengthening awareness of the health and living standards is for the better,the medical products of the miniaturization,precision,quality with a higher and more stringent requirements.The development of traditional molding technology behind the micro-extrusion technology.Especially in the medical catheter,this is high-profit and demand is more and more,and compare with foreign,our molding extrusion technology is behind,so study of medical catheter micro-extrusion molding become more important.The miniaturization of the product of the medical catheter leads to some extrusion problems,such as the extruded product due to the size is change.The wall slippage of the melt in the fine runner,the surface tension,etc.causes the swelling of the size,resulting the extruded product non-compliant.And the gas-assisted extrusion is in the extrusion process by adding compressed gas to limit the extrusion of the swelling,making the extrusion size to meet the requirements.In this paper,the thermoplastic elastomer TPE was selected as the experimental material,and the rheological properties of the materials were analyzed.The endothermic peak temperature of the DSC test material was 211.1 ?,and the steady-state data were fitted to fit the Bird-Carreau equation.The zero shear viscosity of TPE elastomer is 3619501Pa·s,the non-Newtonian index is 0.06 and the relaxation time is 33.4s,and the activation energy of non-viscous flow is calculated to be 153KJ/ mol,which provides the basis for gas-assisted micro-extrusionOn the basis of the theory of the traditional extruder,a gas-assisted micro-extruder head was designed and an extruder head with rounded filament diameter of 1 mm was designed.The extrusion compression angle was 40°,The length of the section is 5mm.An extruder with an outer diameter of 2 mm and an inner diameter of 1.4 mm was designed with a compression angle of 45° and a gas-assisted inlet gap of 0.1 mm.The influence of process parameters such as the head temperature,the pressure of the air supply and the rotation speed on the diameter,surface roughness and mechanical properties of the extruded filament were analyzed by experiments.Compared with the absence of gas-assisted,under the same conditions,the addition of gas can restrict the extrusion swelling,the maximum reduction in extrusion diameterof 0.6mm,the tensile strength is almost unchanged,but will increase the surface roughness of extruded filaments.The designed to squeeze the microcapsules of gas-assisted micro-extrusion head installed,through the experimental extrusion tube,analyzed the head temperature,screw speed,only to the auxiliary gas,both inside and outside the gas-assisted process molding process parameters influence on the outer diameter and the wall thickness of the extruded microtubules.Compared with the gas-assisted and gas-assisted extruded microtubules,it was obtained that the screw speed and the auxiliary gas inlet pressure increased when only the inner layer was gas-assisted,and the outer diameter and the wall thickness of the extruded microtube were increased Large,the molding temperature will reduce the outer diameter and wall thickness;in the both inside and outside are gas-assisted,with the side and outside air pressure increases,the outer diameter of the extruded tube and wall thickness will be reduced Small,the temperature of the formation of microtubules on the outer diameter and wall thickness has no effect,the outer layer of gas-assisted roughness than the lack of gas.Through the analysis and comparison of the data,it is found that under the condition that the gas pressure is 0.3MPa and the internal pressure is 0.15 MPa,the head temperature is 210? and the screw speed is 17.5r/min,0.4MPa and the inside of the gas-assisted pressure of 0.2MPa,the head temperature of 215? and screw speed12.5r/min under the conditions of the extrusion of the microtubules is closest to the design pipe size of the outer diameter of 2mm,diameter 1.4mm. |
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