Manufacturing of small diameter polymeric medical tubes with high dimensional tolerances is a challenging process that requires high end extrusion equipment to meet the strict quality standards. Microextruders along with controllable die systems are used in clean room environments to assure the uniform product quality and sterility. The tube extrusion process is a continuous process that is affected by the polymer melt temperature, pressure of the melt mass inside the extruder, line speed, cooling rate and other parameters which may greatly influence the quality of the finished product. By measuring the surface roughness continuously and monitoring the surface topography on-line during the manufacturing process, one can see the changes in the product in real time, which give indication on changes in the overall quality of the product. If the surface roughness increases or decreases past set boundaries one can take corrective actions immediately, possibly saving time, material and improving the productivity of the process.Optical on-line measurement technique was used in this thesis to measure the surface roughness parameters during the production of small diameter plastic tubes in laboratory conditions. Prior to the laboratory measurements, few commercial samples were acquired and surface roughness was measured from the sample tubes using two different techniques: an on-line method and optical profilometry. The comparison of the results showed similar values with some variation due to differences between the techniques. The laboratory measurements were conducted with two thermoplastic materials, linear low density polyethylene, being the reference material, and thermoplastic urethane, being a material commonly used in medical tubing. In addition, to understand medical tube requirements, materials and manufacturing better, an expert interview was conducted and literature references were studied to form the theory basis of the thesis.Although some challenges were faced, the measurements were conducted successfully and the effect of different processing parameters could be interpreted from the results. The optical on-line measurement technique proved to be a useful tool to control and monitor the quality of the tube during manufacturing, measuring the surface roughness with great precision. In addition, if one wishes to find correct processing parameters for a new material, the technique can provide information when adequate shear rates and material plasticization is achieved. This could be a great benefit in plastic tubing industry where long test runs may be required to find suitable process parameters for new materials.
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