Preparation And Application Of New Polyaldehyde Binder For Metal Powder Injection Molding

Metal powder injection molding was a new type of near-net powder metallurgy molding technology, and the property of the binder was the key factor for metal powder injection molding. Appropriate flowability, good molded body retention,higher powder loading and environmentally friendly properties were required for feedstocks. The binders which were suitable for 17-4PH stainless steel metal powder injection molding were studied in the paper. The main contents were summarized as follows:By comparing the advantages and disadvantages of the adhesive systems such as wax base and polyaldehyde, Polyformaldehyde (POM), Low density polyethylene(LDPE),EVA paraffin (PW) and stearic acids (SA) were selected as binder components based on the compatibility of each component in the polyaldehyde binder system. A series of binders used for powder injection of 17-4PH stainless steel binder were prepared by mixing, and extrusion. The effects of binder formula on the flowability of binder, rheological properties of feedstock and powder loading were studied. The results indicated that suitable composition of binder included 35 wt. %POM2?18.6 wt. % LDPE?1.4 wt. % EVA?3 wt. % SA?42 wt. % PW1,the corresponding loading of 17-4PH stainless steel metal powder feedstock was as high as 91.1 wt. %, the flow rate of the feedstock reached 150 g/10 min under the loading of 10 kg, the activation energy of the viscosity was 103 kJ/mol at 7.5 kg, and the molded body exhibited good shape retention during the degreasing process. The melting properties of the components of the binders were analyzed by Differential Scanning Calorimeter (DSC). The thermal decomposition process of the binders and the feedstocks were analyzed by thermogravimetric (TG). The environmental process of thermal degreasing and sintering of the green body were determined by one-step method, which avoid traditional catalytic degreasing process of the polyaldehyde binder system.The feedstocks particles have been mass produced with preferred binder and 17-4PH stainless steel metal powder in the related enterprises, and the effect of application was good.