Residual Binder Research Articles

Influence of agglomeration upon dewaxing properties of greenware for low pressure molding

This paper presents the influence of agglomeration upon the flow property of the slurry and dewaxing properties of the greenware for low pressure molding. (Zr, Sn)TiO 4 powder agglomerate was pulverized by a high speed mixer. The agglomeration state was evaluated by tapping density and residual of #350 sieving. The flow property was measured by viscosity and grindmeter scratch. The dewaxing properties were evaluated by pore size distribution, the fraction of residual binder after dewaxing and rejection ratio of greenware due to crack. Pulverization of the agglomerate reduces the thixotoropy of the slurry, contributing to uniform pore size and residual binder distributions. They all contribute to reduce cracks in greenware.

凝集が低圧射出成形体の脱脂性に及ぼす影響

This paper presents the influence of agglomeration upon the flow property of the slurry low pressure molding. (Zr, Sn) TiO4 powder agglomerate was pulverized by a high speed mixer. The agglomeration state was evaluated by tapping the density and residual by #350 sieving. The flow property was measured by the viscosity and scratch of a grindmeter. The dewaxing properties were evaluated by pore size distribution, the fraction of residual binder after dewaxing, and the rejection ratio of greenware due to crack.Pulverization of the agglomerate reduces the thixotoropy of the slurry, contributing to uniform pore size and residual binder distributions. They all contribute to reducing cracks in greenwares.

Thermal debinding of powder injection molded parts: Observations and mechanisms

The mechanisms of thermal debinding for powder injection molded parts were investigated in this study. Mercury porosimetry analysis on specimens made from carbonyl iron powders shows that fine interconnected pores, smaller than 0.8 μm, are developed at the initial stage of de- binding. These pores are formed due to the decomposition of low-temperature binders. In the intermediate stage, most pores consist of 0.8-μm interparticle voids. The fine pores which were developed at the initial stage are now filled by the binder and give a flat region on mercury intrusion curves. Scanning electron microscopy (SEM) pictures show that the binder-vapor inter- face moves slightly inward at the initial stage. As debinding temperature increases, the binder has a low viscosity and is pushed to the compact surface by the internal decomposed gas, leaving a nearly binder-free region at the center of the compact. Concurrently, liquid binder redistributes within the compact due to capillarity and causes nonuniform binder distribution within the part. At the final stage, residual binders are all trapped at contact points between particles. These binders, though accounting for less than 20 pct of the original amount, are holding particles together with the capillary force.

ポリエチレングリコールを有機バインダに用いたセラミックスの射出成形

Rod like test piece and bobbin type test piece were produced by the injection molding of alumina or zirconia powder with several organic binders including polyethylene glycol(PEG). Following injection molding, these test pieces were submerged in a alcohol to extract PEG in the organic binders for 1-12 hour at room temperature. After the solvent debinding process of PEG by alcohol, the test pieces containg the residual binders were heated up to 400°C at a rate of 20-200°C/hr, and then sintered at 1300-1620°C. The main results are summarized as follows: 1)This solvent debinding process(SDP)of PEG by alcohol is nearly 5-10 times faster than conventional thermal debinding process. 2)The density of the sintered test pieces go up to over 99% of theoretical values by means of SDP. 3)It makes possible to produce the CIM parts with ultra fine zilconium powder(>15m2/g) by means of SDP.

Sintering Carbides by Means of Fugitive Binders

A method of sintering carbides has been evolved that permits fabrication of dense, strong pieces having accurate dimensions and containing no residual binder metal. To aid in sintering, a small percentage of a binder such as cobalt or nickel, or their oxides, is added, but this is later removed by volatilization during the high‐temperature vacuum sintering operation. The method has been applied to tungsten carbide, tantalum carbide, and columbium carbide. The good mechanical properties of the products are cited as evidence for the carbide‐skeleton theory advanced to account for the high strength of cemented carbides.