Structural foams offer numerous advantages over their solid counterparts, including greater geometrical accuracy, the absence of sink marks on the final product's surface, lower weight (and, by extension, the need for less material), and a higher stiffness-to-weight ratio. The possibility of achieving a suitable void fraction in structural foams using conventional structural foam molding methods, however, has been of limited success; these methods allow for little control and typically yield large voids and a nonuniform cell structure. This article reports on our use of an advanced structural foam molding machine to achieve a uniform cell structure with a high void fraction. We studied the following processing parameters: injection flow rate, blowing agent content, and melt temperature. The pressure profile inside the mold cavity under various processing conditions was also investigated to elucidate cell nucleation and growth behaviors. By optimizing all processing conditions, we achieved a uniform cell structure and a very high void fraction (over 40%).
Micro-cellular foaming technology draws attention due to the enhancement of mechanical strength, which has been considered as a weak point of current plastic foaming technology. Foam materials produced by this technology offer improved consistency and homogeneity of cell structure, which can result in products with superior properties and uniformity(1). Thus it is widely used for commercial purposes and its market is now growing significantly. However, since the foamed injection parts have swirl marks on its surface, this technology has limited uses such as interior products, in spite of its diverse merits. In this paper, we propose surface treatment of the mold as a way to remove the swirl mark. We injected simple shape specimens with PP and PC/ABS materials and measured the surface quality values such as roughness and gloss. Also we researched the foaming characteristics of both treated and untreated surface using SEM analysis.
This paper investigates the feasibility of injection-molded wood-fiber/high-density polyethylene (HDPE) composite foams that can replace injection-molded HDPE solids in industrial applications. The study applies injection foam molding technology using a physical blowing agent to a wood-fiber/HDPE composite, and examines the effects of the processing parameters on the dimensional and mechanical properties and cell density of the composite foams. In addition, the physical properties and cost of wood-fiber/HDPE composite foams are compared with those of solid HDPE. The experimental results show that wood-fiber/HDPE composite foams that have a 20% weight reduction have superior physical properties, such as density, dimensional properties (68% decrease of shrinkage and 91% decrease of warpage) and mechanical properties (28% increase of Young's modulus). Furthermore, the cost analysis confirms that wood-fiber/HDPE composite foams are much less expensive (by 40%) than HDPE. Therefore, it is concluded that wood-fiber/HDPE composite foams are strong candidates for replacing current injection-molded HDPE products.
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