環境溫濕度對於塑膠自攻牙螺絲柱的軸向與扭轉鎖附強度特性之影響

Abstract

塑膠被廣泛的運用於日常生活各類產品當中，仔細觀察這些產品，除了塑膠材料之外，也同時大量使用了金屬自攻螺絲將各部零件作緊固結合，成就了產品及其功能。設計者依其需求，選擇合適的自攻螺絲作緊固。這種情況下，因應塑膠螺絲柱(Boss)與自攻螺絲緊固所產生的鎖附力顯得非常重要，為設計者所必須重視之課題。 本研究的目的乃針對運送過程中貨艙內所處環境因素的差異以加嚴測試的條件來探討運輸工具運送前後對於塑膠螺絲柱與金屬自攻螺絲緊固之軸向負荷與扭轉負荷之影響，同時探討螺絲與不同塑膠材料緊固時，彼此之間對於軸向負荷、扭轉負荷之關係，以方便設計者參考及了解其特性，強化設計者信心度與產品可靠度。 本研究選用三種常見之金屬自攻螺絲以及四種常見之塑膠Boss材料，應用溫濕度機施予環境溫濕度因素來模擬塑膠Boss使用環境的變化，在施予環境溫濕度因素前後進行螺絲柱與自攻螺絲緊固之相關試驗，包括鎖固時之最大扭力測試以及鎖固後之抗拉拔力測試，比對不同種類塑膠之Boss在環境變化前後之差異，以及不同塑膠材料之間的緊固特性關係。 研究結果顯示，在最大鎖附扭力部份，塑膠材料在經過溫濕度變化的儲存環境之後，其最大鎖附扭力與儲存前的差異約僅2.0%~4.3%，其變化率依序為ABS>PA>PC>POM。此外，當相同塑膠材料鎖附不同螺峰直徑的螺絲時，其最大鎖附扭力值依序為TP2.0螺絲>TP2.5螺絲>3.0螺絲；而當相同螺峰直徑的螺絲鎖附不同材料時，得到最大鎖附扭力值依序為PC>POM>PA>ABS。 在最大鎖附抗拉拔力部份，塑膠材料在經過溫濕度變化的儲存環境之後，最大鎖附抗拉拔力與儲存前的差異約為1.8%~3.2%。此外，當相同塑膠材料鎖附不同螺峰直徑的螺絲時，其最大鎖附抗拉拔力值依序為TP3.0螺絲>TP2.5螺絲>2.0螺絲。而當相同螺峰直徑的螺絲鎖附不同材料時，得到的最大鎖附抗拉拔力值依序為POM>PC>PA>ABS。 在提高緊固能力的部分，研究結果發現，欲增加自攻螺絲的最大鎖附扭力以及最大鎖附抗拉拔力的方法為增加鎖附深度。當鎖附深度增加，螺絲鎖附的牙數跟著增加，螺牙之間的材料愈多，其材料所提供的抵抗能力愈大。 本研究提供塑膠Boss在經過環境因素前後之緊固特性變化，以及不同塑膠材料之間的緊固特性關係。設計者可依據這些特性以及所賦予之產品需求來選用合適材料，設計出符合不同功能與環境之產品，對於消費者來說，其所使用之產品可具有更高安全性以及可操控性，產品品質更加提升。

Plastic is widely used in current products of daily used. In addition to plastic, self-tapping screws are often used in tandem with plastic products, such as bosses, for constructive purposes. In a given design, specific requirements must be considered in choosing the appropriate screws and plastic bosses. Considering the effect of interaction between self-tapping screws and plastic bosses, fastening performance is critical. Regarding design, fastening performance is the primary topic of this paper. The aim of this study was to investigate the effect of axial and torsion loadings between plastic bosses and self-tapping screws after shipping in various environments. The axial and torsion loading variations among self-tapping screws of various resins and diameters were also investigated to compose reference for designers. In this study, our experimental materials composed three self-tapping screws of varying diameters and four plastic bosses composed of different resins. These materials were placed in a temperature-humidity controlled chamber to simulate various environmental conditions. Axial force and torque were then tested for various combinations of engagement between plastic bosses and self-tapping screws. The experimental results illustrate that the variance in maximum screwing torsion before and after the environmental changes was not substantial, with a value of approximately 2.0%~4.3%, the variance ratio was in the sequence of ABS>PA>PC>POM. Additionally, using the same boss resin, which was engaged with self-tapping screws of various diameters, the maximum variances in screwing torsion was in the sequence of TP_2.0 > TP_2.5 > TP_3.0. Conversely, for each self-tapping screw of a particular diameter engaging with various boss resins, the maximum screwing torsion was in the sequence of PC > POM > PA > ABS. Regarding the maximum pulling force after a screw was engaged, the variance in maximum pulling force before and after the application of environmental changes was also not substantial, approximately 1.8%~3.2%. Furthermore, for each boss resin engaging with self-tapping screw of various diameter, the maximum pulling force was in the sequence of TP_3.0 > TP_2.5 > TP_2.0; Conversely, for each self-tapping screw of a particular diameter engaging with various boss resin, the maximum pulling force was in the sequence of POM > PC > PA > ABS. The research result shows that the most effective approach to increase the maximum screwing torsion and maximum pulling force is to increase the screwing depth. In turn, the fastening capability can be improved. When the screwing depth increases, the amount of material threads also incereses, accompanied by a greater resistant force in the resin. This paper provides a portfolio of fastening characteristics before and after different environmental factor changes as well as descriptions, the fastening variation between different resins. Designers can employ this information regarding product requirements in choosing suitable resins for various function and environments. Furthermore, observing our findings, consumers may select safer and higher-quality products.