Title of Invention	A PROCESS FOR HOMOGENEOUS MIXING OF OXIDES AND CARBIDES OF A REFRACTORY METAL
Abstract	ABSTRACT Disclosed herein is a process for homogenous mixing of oxides and carbides comprising the steps of mixing the refractory oxide and graphite/carbon powder in the desired ratio in a milling drum for 6 to 8 hours in the presence of a mixing media such as herein describe and adding refractory Carbide powders to the mixer obtained and mixing for another 6 to 8 hours in the said milling drum.

Full Text

The invention relates to a process for homogeneous mixing of oxides and carbides of a refractory metal with a mixture of graphite and carbon black powder and refractory carbide for subsequent carburisation and production of solid solution (pre-alloy of mixed crystal used in the manufacture of sintered hard metals. The refractory metal oxide varies by weight depending on the type of oxide (typical ranges 10 - 80% by weight), carbon black/graphite powder mixture varying by weight from 10 - 50% and refractory carbide varying by weight from 1% to 50%. All the constituents are in the form of powder. In the present process of mixing all the constituents (feed) are added in a milling drum aiming at the desired solid solution ratio and the mixing ratio depends on the final composition of the solid solution. The milling drum contains cemented carbide balls of different sizes and along with the powder constituents (feed) is rotated for a duration of 12 to 16 hours. The feed : balls ratio is maintained approximately at 1 : 3 with total weight of feed + balls depending on the size of the drum. After the mixing operation is over the material is subsequently unloaded film the milling drum and screened for separation of feed from the balls. The powder mixture is carburized to have a mixed carbide solid solution. The above mentioned process has the following constraints. Carburisation process of the pre-mixed powder of refractory oxide graphite/carbon black and refractory carbide induces two stage reaction as follows. Carburisation of oxide to the carbide form (by reaction of oxide with graphite and carbon black powder) Solid solution formation of the desired ratio. This reaction progresses only after completion of the first reaction which in turn depends on the contact area between carbon/graphite powder and oxide powder effected during mixing for complete carburisation of oxide to carbide. The shortcomings of the known process as mentioned above are that in the present mixing method that is being followed all the constituents mentioned above are added in the milling drum before proceeding with the mixing operation. This results in reduced contact area between the carbon/graphite powder and oxide particulates due to presence of refractory carbide particulates between the oxide and carbon/graphite powders. The resultant mixture fact the carburizing process contains inhomogeneous solid solution of the two refractory carbides of different ratios deviating from the ratio that is aimed at due to inhomogeneous carburisation of the refractory oxide to the relevant carbide. It is the aim of the invention to overcome the shortcomings of the known process as mentioned above. The two stage reaction occurring during pre-alloy formation of the desired ratio and homogeneity in the carburisation process can be facilitated by Effective carburisation of refractory oxide with increased contact between the oxide and powders. Effective and homogeneous solid solution formation of both the refractory carbides of a uniform ratio throughout the mixture with increased contact between the two carbides of the solid solution. This is achieved by the invention of a mixing process termed as 'partial mixing process'. In 'partial mixing', initially only the refractory oxide and graphite/carbon powder of the desired ratio is mixed in the milling drum for 6 to 8 hours with the same mixing media as mentioned before and later refractory carbide powders are added to the original mixture after the initial mixing and all the constituents together are mixed for another 6 to 8 hours in the same mill. The mixing media is selected from organic liquid like acetone, hexane, propane etc and balls and rods made of hard metal, steel etc. The refractory metal is selected from tungsten, tantalum. Molybdenum, niobium, chromium. The refractory carbide is selected from tungsten carbide, titanium carbide, tantalum carbide etc. Effective and homogeneous sound solution formation of mixed carbide is obtained. Homogeneous mixed carbide distribution in the sintered hardmetal leading to union physical and metallographic properties of the sintered hard metal. Via hardness, crater- wear resistance, toughness. Greater process reliability in subsequent process operations of hardmetal manufacture after powder manufacture viz. pressing of green compacts (Uniform compaction), sintering (uniform shrinkage, consistent sintering temperature) Simpler and more reliable mixing process as only two components are weighed and mixed at any particular time. 1 ■ A process for homogenous mixing of oxides and cat ides of a refractory metal comprising the steps of: a) mixing the refractory oxide and graphite/carbon powder in the desired ratio in a milling drum for 6 to 8 hours in the presence of a mixing media; and b) adding refractory carbide powders to the mixer obtained in step (a) and mixing for another 6 to 8 hours in the said milling drum 2. A process as claimed in claim 1 wherein the mixing media used is selected from and organic liquid like acetone, hexane or propane andballs and rods made of hardmetal or steel 3. A process as claimed in claim 1 or 2, wherein the refractory metal is tungstoen, tantalum, molybdenum, ricobium, chromium. 4. A process as claimed in any one of the preceding claims, wherein the refractory carbide is tungstoen carbide, titanium carbide or tantalum carbide.

Documents:

1602-mas-1996 abstract duplicate.pdf

1602-mas-1996 abstract.pdf

1602-mas-1996 claims duplicate.pdf

1602-mas-1996 claims.pdf

1602-mas-1996 correspondence others.pdf

1602-mas-1996 correspondence po.pdf

1602-mas-1996 description (complete) duplicate.pdf

1602-mas-1996 description (complete).pdf

1602-mas-1996 form-1.pdf

1602-mas-1996 form-26.pdf

1602-mas-1996 form-4.pdf