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本帖最后由 a64578626 于 2011-1-4 12:35 編輯
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. l' j: L: l9 k9 {" h" n4 ~ The plastic-injection process is one of the important manufacturing methods to polymers, which provides products with high dimensional steadiness, low manufacture cycles and costs. One of the problems affected on the quality of the final product is the gas entrapments occurred in the mold filling stage. Generally,the residual gas in mould is exhausted through the venting system.However, the dependence on the venting system complicates the mould design. Furthermore in certain condition, it is difficult to integrate the venting system into the mould. Now this problem can be avoided by using permeable steel to make mould or mould inserts. With permeable steel, gas generated in the mould cavity can be exhausted directly through the micro-holes of the mould and the venting system is unnecessary anymore. Moreover, the mould structure and design becomes simple, whereas the venting and aspirating function is preserved. Many researchers have been attracted by permeable metal’s forming, measurements and applications. ZHANG,studied the effects of warm compaction on fabrication of porous iron and adopted macromolecule polymer to generate porous in permeable iron. NORMITUS,investigated the effects of partially alloyed and prealloyedpowders with different compositions of alloying elements and compacting pressure on the Young’s modulus and Poisson’s ratio of sintered low alloy steel.ZHANG, chose NH4HCO3 to generate porous in NiTi shape memory alloys and formed gradient porosity by changing the amount of NH4HCO3 added. LIN, analyzed the effects of sintering processing parameters and compaction pressure on the filtration performances of stainless steel porous metal. ZHOU, investigated the reason of porosity formation, effect of pressure on porosity and linking of pores in metallic porous material.
$ L# ?3 d" x* g% u9 w$ I However, though permeable steel is very important for making plastic-injection mould, how to obtain proper permeable steel, apply it into plastic-injection process, and retain the permeability after secondary machining haven’t been well studied. In this work, a kind of permeable steel was obtained by controlling the compact and sintering processes. The details of these processes were presented in section 2. Section 3 demonstrates the permeability of this material through macroscopic experiments, microscopic metallographs and scanning electron microscope(SEM) images. Since most plastic-injection moulds require secondary machining, the effect of different machining methods on the permeability of porous material is also presented in section 3. In section 4, the permeable mould was used along with an injection set to make real plastic-injection parts. The high quality of the parts further validated the good permeability and venting function of this permeable steel.- b/ c& \; j5 Q
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