The purpose of the thesis was to find factors that influence the mechanical characteristics for copper-wire products that are insulated with foamed polypropylene. This specific insulation material is new to the company and suitable machine-settings are unknown. The project was carried out as a Six Sigma improvement project according to the DMAIC-cycle. Six Sigma focuses on process improvements and reducing variation.
Initially, relevant literature for the area was studied to get a deeper understanding of the problem. Some of the literature is summarized in the theory chapter of the thesis. According to the DMAIC-cycle, the process was then defined and mapped out. Which characteristics to improve were also chosen, in this case elongation for the insulation, before and after ageing.
Factorial experiments were conducted later in the process to find out which factors influenced the chosen responses. The results showed that line speed and preheating were two important factors for a satisfying elongation. To maintain the elongation after ageing, the temperature in the main extruder and the tank position for the cooling bath was discovered to be important.
The suggested factors were adjusted to suitable levels. Factors that did not influence the chosen characteristics were adjusted to the most preferable level. For example, a cheaper granulate could be chosen when it was discovered that the investigated granulates made no difference for the elongation of the insulation.
To reduce the variation a higher speed is recommended. Unfortunately this results in a deteriorated surface for the cable. The surface, which was not in the scope of the project, could also be improved with a tank position near the extruder head.
The measurement method for elongation was changed according to the method proposed by UL (Underwriters Laboratories). This resulted in a reduction of the variation between each tensile test within a sample.
Recommendation for additional research is further investigation of the effect from different temperatures of the main extruder. Another interesting area to study could be the factual changes in the polymer structure from different machine settings. It could also be in the company’s interest to test if the findings are applicable to other products.
Author: Nyrén, Gustav
Source: Lulea University of Technology
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