In the manufacture of hard materials for the jewelry making and watch making industry, or for technical applications such as the medical, electronics, telephone or tooling industry, machining cutting inserts, the consumer goods industry, and particularly for hard materials generally referred to by the generic name of inorganic “ceramics”, powder metallurgy techniques are used. The inorganic synthesis material obtained will be termed “ceramic” here, regardless of the nature of the material, be it sapphire, ruby, artificial diamond, sapphire glass, ceramic, micro-magnet, metal, alloy or other.
The base raw materials are of different natures, some are kept secret in order to protect productions. In a general manner, the raw materials used include at least, on the one hand ceramic powder, and on the other hand organic binders such as resins or plastic materials or similar which allow for injection and for the component created to bind correctly with the mixture of all the raw materials. Other additives may be included in the mixture. It is understood that the raw materials may be of different textures: solid, powder, liquid or a paste. The structure of the mixture may change during its creation, in particular, and not limited to, when the complementary components of a resin undergo a polymerization reaction.
The overall procedure for the manufacture of an inorganic ceramic component includes at least the following steps:                preparing raw materials,        mixing raw materials, or/and pre-mixing two-by-two (or more) if required,        homogeneous mixing,        granulating        moulding, in particular in a moulding chamber, a quantity of powder or feedstock pellets obtained from the mixing and granulating, to create a “green” component. This moulding may be carried out by injection, under pressure, in particular in a screw injector including means for heating this quantity of powder or feedstock pellets obtained from the mixing and granulating;        thermal debinding to burn off and/or dissolve some components of the mixture serving as binder, heat treatment of the “green” component, or sintering;        heat treating the “green” component after debinding, for sintering to give the finished component its final consistency. This heat treatment causes dimensional shrinkage, which makes it possible to obtain a component having the final dimensions,        surface finishing treatment of the component.        
This simplified presentation of the method hides the true complexity of development that is specific to each mixture of raw materials and to each type of finished component according to its physical characteristics, particularly its resistance to wear and appearance, and according to its mechanical and chemical properties.
The performance of each step requires care and demands adherence to exact parameters, failing which irreversible alterations may be made to the characteristics of the mixture, the injected “green” component, the debinded “green” component, or the sintered component.
The homogeneous mixing step is particularly crucial for the subsequent steps of the process. This mixing step may in some cases be combined with the prior step of mixing the raw materials, which may be carried out directly in the manufacturing plant referred to here as the “mixer”.
Indeed, during mixing, reactions occur between some of the raw materials, and these reactions immediately alter the physical conditions of the mixture undergoing mixing. In particular, uncontrolled and uncompensated exothermic reactions may result in a complete alteration of the mixture, which then becomes unusable for the manufacture of the intended finished component. The parameters of temperature, speed and torque must all be monitored closely. It is essential to achieve repeatability of the physical characteristics ultimately obtained, therefore the mixing must be perfectly regulated and the reactions that occur must be anticipated and controlled.
In particular, when a mixture of this type is mixed with rotating blades in a mixer, the temperature of the ingredients in the mixture rises very quickly, under the effect of friction, to exceed the melting temperature of the ingredients causing them to mix with each other in the form of a paste. The problem lies in the extremely high temperature gradient in the mixture when it approaches the melting temperature(s), with a value of around several ° C. per second, notably 10° C. per second. It is therefore very difficult to implement effective cooling to prevent thermal runaway and deterioration of the mixture.
EP Patent Application No 2 338 590 A1, in the name of NITTO DENKO CORP, describes an apparatus and method for the production of resin with a paddle type mixer and according to a very specific arrangement, relating to the output of material at the lower end of the tank, in the form of a curved section equipped with heat exchange means using cooling to control the progressive solidification of the synthetic resin prior to crushing. The materials are melted solely by means of friction. This document is specific to polymer resins and is not intended for powder mixes, and is unsuitable for the manufacture of feedstock.
EP Patent Application No 0 956 918 A1 in the name of LOEDIGE MASCHINENBAU GmbH describes a method for manufacturing an intermediate product for injection moulding, formed by a metallic or ceramic powder and an organic binder. A mixer creates a ring of mixed material, to obtain a powder capable of being poured, and a mechanical treatment is carried out to melt the organic binder, without any heating other than the increase in temperature caused by friction between the materials.
EP Patent Application No 1 344 593 A2, in the name of ADVANCED MATERIALS TECH concerns a method for manufacturing an aluminium alloy item injection moulded from a sintered material from a mixture of at least 95% by weight of aluminium powder and oxides or additives, and describes the very specific parameters for such a mixture. It does not describe a means of heating the materials.
US Patent Application No 2004/217 524 A1, in the name of MORRIS ROBERT CRAIG, describes the manufacture of cermet feedstocks, according to specific parameters and notably with quite low temperatures, without the use of a rotating system, but with premixing in an additional tank feeding a screw extruder.
It is also an object of the invention to offer an optimised binder for injection moulding composition facilitating power metallurgy mixing to obtain ceramics or metals, in order to obtain a product of highly reproducible quality, with a controlled shrinkage coefficient.
There are already known, for example from U.S. Pat. No. 5,145,900, thermoplastic materials (feedstock) for the manufacture of moulded ceramic parts that contain a sinterable inorganic powder and a polymeric organic binder, which is essentially formed of a mixture of polyoxymethylene and of polyoxymethylene and polyoxolane copolymers.
These feedstocks were however found to have a number of drawbacks, such as, for example, insufficient fluidity for injection moulding, and problems with products retaining their moulded shapes which suffered from cracking or lamination. This was particularly the case for parts with complex shapes. They are also responsible for environmental problems caused by the necessity to use aggressive products such as nitric acid, especially in the final removal of the organic phase. Moreover, the use of water in the organic binder removal process is problematic in the event that feedstocks contain metallic materials which risk being oxidised.