Mixer, method of mixing raw material for powder metallurgy binder for injection moulding composition

Patent metadata

Field	Value
Publication number	US-9908261-B2
Application number	US-201414268227-A
Country	US
Kind code	B2
Filing date	May 2, 2014
Priority date	May 7, 2013
Publication date	Mar 6, 2018
Grant date	Mar 6, 2018

Abstract

A mixer for ceramic feedstock pellets with a tank, a mixing shaft, and a heat exchanger including a cooler for the cooling of the content of this tank is provided. A controller controls the heat exchanger which includes a heater arranged to heat the content of this tank to a temperature comprised between a lower temperature (TINF) and a higher temperature (TSUP) stored in a memory for a specific mixture, and the heater exchanges energy with a heat exchange and mixing temperature maintenance circuit, external to this tank, and wherein the thermal inertia of this circuit is higher than that of this fully loaded tank. The invention also concerns a method for mixing raw material for powder metallurgy, implementing a specific injection molding composition and a specific binder.

First claim

What is claimed is:

1. A method of mixing raw material for powder metallurgy, for manufacturing a given type of ceramic feedstock pellets from a specific mixture including at least one inorganic powder of at least one oxide or cermet or metal or nitride type element or of at least one compound including at least one of said elements and at least one binder, according to which method:
the mixture is added to a tank of a mixer including at least one mixing shaft and paddles and/or blades; the temperature of said tank and the content thereof is stabilized, by connecting a heat exchanger to a first heat exchange and mixing temperature maintenance circuit, close to a mixing temperature comprised between a lower temperature above which the specific mixture becomes a paste, and a higher temperature below which said specific mixture is maintained, and said heat exchanger, which includes a heater arranged to heat said tank or/and the content thereof, is controlled to a temperature comprised between said lower temperature (TINF) and said higher temperature (TSUP), said lower temperature (TINF) and said higher temperature (TSUP) being stored in a memory, for said specific mixture for a given type of ceramic, so that that said heater exchanges energy, in a first connection, with a first heat exchange and mixing temperature maintenance circuit, external to said tank, and wherein the thermal inertia of the first circuit is higher than that of said tank fully loaded with said specific mixture;
said mixing shaft is set in motion at a speed lower than or equal to 700 revolutions per minute (rpm);
said mixture is mixed until a compact homogeneous mass is obtained;
the high temperature stabilisation of said tank ( 2 ) and the content thereof for which a reduction in temperature has been authorised is stopped at a temperature equal to or above a temperature (T5) which is specific to the mixture concerned and a characteristic of the compact homogeneous mass.

2. The mixing method according to claim 1 , wherein the thermal inertia of said first circuit is higher than that of said tank fully loaded with said mixture by a first factor (K1) higher than 2.

3. The mixing method according to claim 1 , wherein, to limit or reduce the temperature of said specific mixture, or/and when the high temperature stabilization of said tank and the content thereof is stopped at a temperature above or equal to a temperature specific to the mixture concerned and the characteristic of the compact homogeneous mass, the temperature of said tank and the content thereof is reduced, and a negative temperature gradient controls said heat exchanger, which includes a cooler which exchanges energy, in a second connection, with a second circuit at ambient temperature close to 20° C., external to said tank, and separate from said first circuit, and wherein the thermal inertia of said second circuit is higher than that of said tank fully loaded with said mixture.

4. The mixing method according to claim 3 , wherein the thermal inertia of said second circuit is higher than that of said tank fully loaded with said mixture by a second factor higher than 2.

5. The method according to claim 3 , wherein specific cooling is carried out in the following:
a temperature regulator for the tank is started at a maximum temperature T0=180° C. by activating said heater and deactivating said cooler;
said compact mass is cooled by deactivating said heater and activating said cooler;
a “cake” is cooled to a temperature comprised between T9=95° C. and T10=110° C., said cooling being carried out either by switching a temperature regulation system to cooling mode, with a negative gradient of around −2° C. per minute, or by deactivating said heater and activating said cooler.

6. The mixing method according to claim 1 , wherein, during or after said reduction in temperature, said compact mass is crushed, in said tank at a temperature below 100° C. and at a speed of said mixing shaft higher than or equal to 700 (rpm).

7. The method according to claim 1 , wherein the method is applied to the production of volumes of several liters of a specific mixture of zirconium oxide based ceramic, with the following:
a first part of a load of powder and structurants, including powder and polymer plastics is poured directly into said tank or into a feeder upstream of said tank, a tank temperature regulator is started at a maximum temperature of T0=180° C. by activating said heater, the rotation of said mixing shaft of said tank is started at a speed V0=300 rpm;
once a temperature T1=145° C. for said tank and a speed of rotation of V1=300 rpm for said mixing shaft are attained, a second part forming the remainder of a binder load is added;
once a temperature T2=160° C. for said tank is attained, the rotation of said shaft is stopped;
the contents of said tank and said shaft is inspected and if necessary paddles or/and blades on said shaft are scraped;
said shaft is set in motion again;
once a temperature T3=168° C. for said tank and a speed of rotation V3=700 rpm for said mixing shaft are attained, the rotation of said shaft is stopped;
the contents of said tank and said shaft are inspected;
if necessary the paddles or/and the blades comprised in said shaft are scraped;
said shaft is rotated again, and once a temperature TINF=T4=170° C. for said tank and a speed of rotation V4=700 rpm for said mixing shaft are, attained, the mixture is mixed for a predefined duration D4 specific to the particular mixture;
the temperature of the compact mass obtained, which must be comprised between T5=180° C. and TSUP=T5=190° C., is measured and mixing continues until this temperature range is reached;
rotation of said shaft is stopped, said compact mass is cooled by deactivating said heater;
once a temperature comprised between T7=150° C. and T8=180° C. for said compact mass is attained, said compact mass is set in rotation to unblock the paddles/blades of said shaft and/or to improve shearing;
occasional rotations of said shaft are controlled at V9=300 rpm to form a “cake”, and said “cake” is cooled to a temperature comprised between T9=95° C. and T10=110° C., said cooling being accomplished either by switching a temperature regulation system to cooling mode, with a negative gradient of around −2° C. per minute, or by deactivating said heater.

8. The method according to claim 7 , wherein said mixer is used, equipped with a crusher inside said tank, and said tank, equipped with an internal anti-abrasion coating, and in that after the cooling of said “cake”, the following is carried out directly in said tank:
crushing at V11=700 rpm for said mixing shaft;
the rotation of said shaft is stopped;
the product obtained is evacuated at less than V12=2000 rpm for said mixing shaft at less than T12=85° C. for said tank.

9. The method according to claim 8 , wherein said crushing is carried out a speed higher than 100 rpm for said mixing shaft to obtain flour from the product in powder form, to achieve evacuation by a screw extrusion by screw and the formation of pellets.

10. The method according to claim 1 , wherein the method is implemented by using a binder including:
between 35 and 54% by volume of a polymeric base, between 40 and 55% by volume of a mixture of waxes, and approximately 10% by volume of a surfactant, in which the polymeric base contains copolymers of ethylene and methacrylic or acrylic acid, or copolymers of ethylene and vinyl acetate, or copolymers of ethylene including maleic anhydride or a mixture of these copolymers, as well as polyethylene, polypropylene and acrylic resin.

11. The method according to claim 10 , wherein the method is implemented using an injection moulding c

Assignees

• Comadur Sa

Inventors

• Cartier Damien

Classifications

• B28C5/166 Primary

  Pan-type mixers · CPC title

• C04B35/63416

  Polyvinylalcohols [PVA]; Polyvinylacetates · CPC title

• C04B35/5626

  based on tungsten carbides · CPC title

• C04B35/63428

  of ethylenically unsaturated dicarboxylic acid anhydride polymers, e.g. maleic anhydride copolymers · CPC title

• C04B35/63492

  Natural resins, e.g. rosin · CPC title