1、 CHINESE JOURNAL OF MECHANICAL ENGINEERING Vol.23,aNo.3,a2010 312 DOI:10.3901/CJME.2010.03.312,available online at ; Permeable Steel and Its Application in Plastic-injection Mould ZHOU Zhaoyao,CAO Wenjiong*,WU Zhengqiang,YU Minqiang,and LI Yuanyuan School of Mechanical and Automotive Engineering,Sou
2、th China University of Technology,Guangzhou 510640,China Received July 13,2009;revised March 30,2010;accepted April 27,2010;published electronically April 29,2010 Abstract:The gas in plastics mould has great influence on performance,appearance and lifespan of the injection molded parts.Venting chann
3、el and its appendix system should be used for gas exhausting in general.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.Currently a kind of mold material which has gas permeabili
4、ty has been developed in abroad,but the applications of this mold material were restricted by its higher cost and smaller size.In this research,a porous material which was made by powder metallurgy was applied to plastic mould to replace the venting system.Permeability of the steel with different se
5、condary processing was tested and compared with a special apparatus.The metallographic samples of the steel with different secondary processing were prepared and investigated.Finally an actual injection set was established to investigate the applications of permeable steel.The metallographies indica
6、te that the micro-holes inside permeable steel were interconnected.Moulds made of permeable steel exhibit good permeability in the plastic-injection experiments and gas generated in the mould cavity was smoothly exhausted.The melted plastic did not penetrate into the mould or block in the micro-hole
7、s.After several times of plastic-injection experiments,the mould still retained good permeability.The strength of this permeable steel is between 200250 MPa and suitable for industrial applications.The venting systems simplified by permeable steel in plastic-injection have simple structures,which ca
8、n be applied into any place that requires gas exhausting.Key words:powder metallurgy,permeable steel,plastic-injection mould,venting system 1 Introduction The plastic-injection process is one of the important manufacturing methods to polymers,which provides products with high dimensional steadiness,
9、low manufacture cycles and costs1.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 system2.However,the dependence on the venting system complicates the mould
10、 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
11、the mould and the venting system is unnecessary anymore.Moreover,the mould structure and design becomes simple,whereas the venting and aspirating function is preserved3.Many researchers have been attracted by permeable metals forming,measurements and applications.ZHANG,et al4,studied the effects of
12、warm compaction on fabrication of porous iron and adopted macromolecule polymer to generate porous in permeable iron.NORMITUS,et al5,*Corresponding author.E-mail: This project is supported by Guangdong-Hong Kong Key Project of China(Grant No.2007Z010),and National Basic Research Program of China(973
13、 Program,Grant No.2007CB616905)investigated the effects of partially alloyed and prealloyed powders with different compositions of alloying elements and compacting pressure on the Youngs modulus and Poissons ratio of sintered low alloy steel.ZHANG,et al6,chose NH4HCO3 to generate porous in NiTi shap
14、e memory alloys and formed gradient porosity by changing the amount of NH4HCO3 added.LIN,et al7,analyzed the effects of sintering processing parameters and compaction pressure on the filtration performances of stainless steel porous metal.ZHOU,et al8,investigated the reason of porosity formation,eff
15、ect of pressure on porosity and linking of pores in metallic porous material.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 havent b
16、een 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
