# US 2019/0168231 A1 · Vertical grinding mill, screw shaft, and method of designing and/or manufacturing a screw shaft > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0168231 A1 - Document ID: US20190168231A1 - Status: Published application - Kind: A1 - Application number: 15/829,297 - Filed: 2017-12-01 - Published: 2019-06-06 - Earliest claimed: 2017-12-01 - Assignees: Metso Minerals Industries, Inc. - Applicants: Metso Minerals Industries, Inc. - Inventors: Peter Henry Radziszewski - Web page: https://patentgrep.com/patent/US20190168231A1 ## CPC - B02C 19/22: Crushing mills with screw-shaped crushing means - B02C 17/163: {Stirring means} - B02C: CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN ({household tools and machines for pulverising foodstuffs, e.g. coffee and spice mills A47J42/00; pharmaceutical mortars A61J3/02; mechanical processing of refuse and garbage B03B9/06; dressing mould materials by grinding B22C5/04}; obtaining metallic powder by crushing, grinding or milling B22F9/04; {recovery of plastics by disintegrating B29B17/00; crushing raw materials in starch making C08B30/02; beaters for papermaking D21D1/02; crushing devices specially for transport in mines E21F13/002; slag crushing devices F23J1/00; fuel milling devices in combustion apparatus F23K1/00; household devices for crushing coal F24B15/02; ice disintegrating devices F25C5/02}) ## Abstract A screw shaft for a vertically stirred grinding mill is arranged so as to be accommodated within a grinding chamber of the grinding mill while extending in a longitudinal direction. The screw shaft comprises a central shaft and at least one screw flight surrounding the central shaft, and the central shaft comprises an outer shaft wall defining a cavity within the interior of the central shaft, which cavity is closed at least at one longitudinal end of the central shaft. ## Claims ### Claim 1 A screw shaft for a vertically stirred grinding mill, wherein the screw shaft is arranged so as to be accommodated within a grinding chamber of the grinding mill while extending in a longitudinal direction, the screw shaft comprising: a central shaft and at least one screw flight surrounding the central shaft; and the central shaft comprising an outer shaft wall defining a cavity within the interior of the central shaft, which cavity is closed at least at one longitudinal end of the central shaft. ### Claim 2 (depends on 1) The screw shaft of claim 1, wherein the central shaft has the shape of a cylinder which is at least partially hollow and closed at one end so as to define said cavity. ### Claim 3 (depends on 1) The screw shaft of claim 1, wherein said cavity is at least partially filled with a material which has a density smaller than that of the material of the central shaft. ### Claim 4 (depends on 1) The screw shaft of claim 1, wherein an outer diameter (Dshaft) of the central shaft and a mass of the screw shaft are set such that, in a state in which the grinding chamber is filled with a slurry comprising material to be ground and with grinding media, and the screw shaft is at least partially immersed therein, a buoyancy force acting on the screw shaft compensates for at least half of the weight thereof. ### Claim 5 (depends on 1) The screw shaft of claim 1, wherein the buoyance force compensates for between 60 to 100% of the weight of the screw shaft. ### Claim 6 (depends on 1) The screw shaft of claim 1, wherein an outer diameter (Dshaft) of the central shaft and a mass of the screw shaft are set such that a buoyancy force acting on the screw shaft during use is substantially equal to the weight thereof. ### Claim 7 (depends on 6) The screw shaft of claim 6, wherein the buoyance force preferably compensates for 80 to 95% of the weight of the screw shaft. ### Claim 8 (depends on 7) The screw shaft of claim 7, wherein the buoyance force more preferably compensates for 90 to 95% of the weight of the screw shaft. ### Claim 9 (depends on 1) The screw shaft of claim 1, further comprising means for being supported by way of a thrust bearing arranged at a vertically upper section of the screw shaft. ### Claim 10 (depends on 1) The screw shaft of claim 1, wherein an outer diameter (Dshaft) of the central shaft and an outer diameter (Dscrew) of the screw flight fulfil the following relationship: 0.3≤Dshaft/Dscrew<1. ### Claim 11 (depends on 10) The screw shaft of claim 10, wherein the relationship Dshaft/Dscrew≥0.4, 0.5, 0.6, 0.7, 0.8 or 0.9 is fulfilled. ### Claim 12 (depends on 1) The screw shaft of claim 1, wherein the specific gravity of the screw shaft, i.e. the ratio of the mass of the screw shaft and the volume thereof relative to the density of water, is less than 7, preferably less than 6, more preferably less than 5.5. ### Claim 13 (depends on 1) A vertically stirred grinding mill for grinding minerals and/or ore, the mill comprising a screw shaft of claim 1 and a grinding chamber in which the screw shaft is accommodated. ### Claim 14 (depends on 13) The vertically stirred grinding mill of claim 13, further comprising a thrust bearing, wherein the screw shaft hangs from the thrust bearing. ### Claim 15 A method of designing and/or manufacturing a screw shaft for a vertically stirred grinding mill, comprising the steps of: choosing a type of material to be ground by means of the grinding mill, and choosing the type of grinding media to be used; and designing and/or providing a screw shaft to be accommodated within a grinding chamber of the grinding mill, the screw shaft comprising a central shaft and at least one screw flight surrounding the central shaft, wherein the central shaft comprises an outer shaft wall defining a cavity within the interior of the central shaft, which cavity is closed at least at one longitudinal end of the central shaft. ### Claim 16 (depends on 15) The method of designing and/or manufacturing a screw shaft for a vertically stirred grinding mill according to claim 15, comprising the further the step of: setting an outer diameter (Dshaft) of the central shaft and a mass of the screw shaft such that, in a state in which the grinding chamber is filled with a slurry comprising the material to be ground and with the grinding media, and the screw shaft is at least partially immersed therein, a buoyancy force acting on the screw shaft compensates for a predetermined part of the weight thereof and/or a predetermined part of the total forces acting on the screw shaft in the direction of gravity.