As the market for minimally invasive surgery has grown, the demand for high-precision and high-performance catheters has increased. Catheters for the diagnosis and treatment of cardiovascular or cerebrovascular disease mainly use a braided wire tube with a polymer inner liner and outer jacket to improve the pushability and trackability. The outer jacket should have an accurate inner and outer diameter and while maintaining a wall thickness of 150 µm or less. In this study, we designed and manufactured a tip and die capable of extruding an outer jacket with a wall thickness of 150 µm or less using a medical thermoplastic elastomer for manufacturing 8Fr (2.64 mm diameter) thin-walled tubes. The ovality and inner/outer diameters of the tube were studied according to changes in the screw speed (mass flow rate), puller speed, air pressure applied to the lumen, and distance between the quench and head, which are the main variables of microextrusion processes. The screw speed (mass flow rate), puller speed, and air pressure affected the inner/outer diameter of the tube, with screw speed and puller speed having the largest influence on diameter. The air pressure and distance between quench and head had the greatest influence on ovality. The results show the effect of different processing parameters on the characteristics of the extruded tube, which will help to establish a stable extrusion process for the manufacture of outer jackets for braided catheter shafts.
There are urgent needs to characterize and model the mechanical property of additively manufactured composite materials, known as the digital materials, for the computational design and simulation. In this study, most utilized digital material samples, which are the mixture of base polymers, Tango Black+ and Vero White+, by PolyJet (Stratasys) are chosen. Four polynomial models (Neo Hookean model, and two-, three-, and five-parameter Mooney–Rivlin models) are used to fit mechanical tensile test results up to 30% of strain. The material models were adopted in the finite element analysis simulating the tensile test to validate their accuracy. The simulation results based on the two-parameter Mooney–Rivlin model predict the stress at 30% strain with small errors (8.2, 10.5, 0.9, 5.0, and 8.0 for Tango Black+, DM40, DM50, DM60, and DM70, respectively). Additionally, scanning electron microscopy was utilized to analyze the fracture surface of the base materials (Tango Black+ and Vero White+) and the digital materials.
The temperature of the hot steel strip between roughing and finishing mills is important parameter to manufacture the high-quality products. It has great influences on mechanical properties and manufacturing costs of the steel products. The hot steel strip between roughing and finishing mills has considerable heat loss and temperature drop due to the exposure to cold environment and air. The thermal shield is required to reduce the heat loss and temperature drop of the hot steel strip. Thus, the model prediction for the temperature of the hot steel strip is developed to design the thermal shield and identify its effects. The experiment for the hot steel strip sample is performed to validate the model prediction. The results of the experiment and model prediction have the good agreement for different emissivity and temperature of the thermal shields. In addition, the temperature variation and distribution of the hot steel strip between roughing and finishing mills is predicted for different geometries of the thermal shields. The thermal shield with low emissivity and high temperature reduces the temperature drop of the hot steel strip for practical purposes.
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