Molding

A brief review is given about the development of rubber isostatic pressing (RIP) of powders for magnets and other materials that includes: principles of RIP; RIP apparatuses; recent progress; and advantages of RIP. As the recent progress, a new filling technique, ‘air tapping (AT) and grid separation (GS)’, is presented.

Applying RIP (Rubber Isostatic Pressing) to the ferrite sintered magnets, the following have been developed: (1) Ferrite sintered magnets having energy product as high as 5.12 MGOe (2) RIP setup for arc-segment magnets

Abstract BACKGROUND: The powder reaction moulding process uses a reactive monomer as carrier and binder for the moulding of metal or ceramic powders. De-binding is achieved using thermal depolymerisation which is followed by sintering to give the finished component. Binder can be recovered for re-use. RESULTS: Moulding compounds, with various powder volume fractions, have been prepared using stainless steel, silicon nitride and alumina with n-butyl cyanoacrylate as binder, and the stability of the compounds established.

A method of injection moulding or extruding an article is disclosed in which a ceramic and/or metallic powder is dispersed in a carrier to form a flowable composition. The carrier is preferably a monomeric cyanoacrylate which is reversibly polymerisable so as to yield a solid polymer, which in turn is capable of undergoing a thermally activated depolymerisation reaction so as to yield the monomeric species. The composition is injected into a mould or extruded through a die and the carrier polymerised in the mould or die.

New sintered Nd-Fe-B near net-shape magnets with a high remanent polarization of 1.47 T, a coercivity HcJ of 9.6 kA/cm (12 kOe) and a maximum energy density of 420 kJ/m3 (53 MGOe) can be manufactured by rubber isostatic pressing. The optimization of the remanent polarization by an improved alignment process of the powder particles results in a decrease of the coercivity by 0.4 kA/cm per 1 % ∆fφ for alignment coefficients fφ in the range 96 to 98 %. For alignment coefficients between 98 to 99 % the decrease of the coercivity even increases to about –1 kA/cm per % 1 ∆fφ.