Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B31/00—Machines or devices designed for polishing or abrading surfaces on work by means of tumbling apparatus or other apparatus in which the work and/or the abrasive material is loose; Accessories therefor

Definitions

• the invention relates to a method for producing ceramic components that have at least one flat or curved sliding and sealing surface.
• Ceramic objects with a flat or curved sliding and sealing surface are usually produced by shaping a green ceramic body, sintering, grinding and then lapping or polishing the ground surface.
• a polishing agent e.g. B. diamond grain
• polishing the molded parts for a long time with a paste or emulsion of a polishing agent e.g. B. diamond grain
• polished and in special polishing machines on rotating surfaces e.g. grooved flat steel discs, pressed. Rough spots are leveled in this way.
• Lapping and polishing machines require high investment costs; their operation is wage-intensive and therefore involves high unit labor costs.
• Valve disks for mixing valves are known from EP-OS 043456, which have a zirconium oxide content and an average roughness of less than 0.3 ⁇ m. A lapping or polishing treatment is required to manufacture these discs.
• the object was therefore to specify a process for the production of ceramic moldings with flat or curved sliding and sealing surfaces, with the aid of which surfaces of the same sliding and sealing behavior can be produced in a simple and inexpensive manner.
• the present method solves this task. It is a process for the production of ceramic bodies which have at least one flat or curved sliding and sealing surface, by shaping a green ceramic body, sintering, grinding and subsequent smoothing of the sliding and sealing surface formed and subsequent washing. This method is characterized in that the smoothing is achieved by abrasive polishing in the presence of an aqueous phase.
• polishing small parts, which are usually in large numbers, are moved together with an aqueous phase in a container for a long time. This process is used to deburr or polish metal parts in electroplating.
• the method according to the invention can be used in particular for smoothing the surfaces of bodies made of silicon carbide, steatite and aluminum oxide.
• the average surface roughness Ra depending on the grinding wheel used, is 0.8 to over 1 ⁇ m. It is possible, but in most cases it is not necessary to wash the ground ceramic bodies before polishing and thus to remove sanding dust. Washing or degreasing is particularly useful if the ceramic body is contaminated with grinding oil.
• the process according to the invention lacks finely divided abrasive substances, such as sand. With flat sliding surfaces, grinding is carried out by face grinding, with curved ones by cylindrical grinding.
• the polishing scrub takes place in a scrubber.
• a scrubber For example, scrubbing drums can be used in which the ceramic bodies roll over like in a washing machine. This is advantageous if, in addition to smoothing the sliding and sealing surface, rounding the edges is also desirable. Scrubbing vibrators can also be used, in which the bodies perform short, oscillating movements of high frequency. Larger parts in particular can be treated in these vibrators without risk of damage.
• the scrubbing apparatus is usually filled with 10 to 90% by volume, preferably 30 to 60% by volume, with the ceramic bodies which are to be polished by polishing. A part of the volume of the apparatus, for example 0 to 30%, in particular 0 to 10% by volume, can remain empty. The rest is filled with an aqueous phase.
• the amount of water should at least be so large that all ceramic parts are covered by water even during the scrubbing.
• the correct degree of filling can be determined by simple tests and is usually in the range from 15 to 45% by volume.
• the scrubbing time is several hours, e.g. 5 - 40 h and depends somewhat on the adjustable intensity of the movement. Scouring screens are also suitable, even if the time required is longer than with vibrators.
• the smoothing process measured in terms of average roughness, proceeds quickly at first and then slower, so that there is hardly any danger consists in obtaining a polished body with undesirably low roughness.
• the smoothing effect is not optimal and there is a possibility of breakage due to the overturning of individual parts. If the filling is too large, the relative movement between the parts is insignificant, which leads to long machining times.
• the method according to the invention is particularly suitable for the production of sealing and regulating disks (for sanitary use), slide rings, plungers, shafts, shaft protection sleeves, bearing rings and balls for ball valves.
• the treatment liquid is a surfactant, e.g. B. soft soap, in amounts of 0.05-20 g / l, preferably 0.1 to 10 g / l. In this way, the formation of scratches is suppressed and the speed of the smoothing process is increased.
• a surfactant e.g. B. soft soap
• Scouring bodies with a density of 2 to are preferred 4 g / ml, preferably scouring body of the same composition as the ceramic body to be smoothed.
• the scouring body can consist of Al2O3, SiC or boron carbide. If you work in the presence of scouring bodies, the scrubbing units should be filled to 10-90% by volume, in particular 40-75% by volume, with ceramic bodies to be smoothed plus scouring bodies.
• the weight ratio of scouring body / ceramic body to be smoothed can be 0: 1 to 5: 1, in particular 1: 1 to 3: 1. Another excess of scouring pads is not harmful, but only uneconomical.
• the use of scouring pads also makes sense if the sliding and sealing surface is easily accessible, but curved. This applies e.g. B. for cylindrical outer surfaces of plungers and shaft sleeves. The use of scouring pads is not necessary for components with a flat sliding and sealing surface.
• surfaces can be obtained in the case of ceramic objects whose average roughness depth Ra is between 0.1 and 1.0 ⁇ m, preferably 0.3-0.8 ⁇ m. If the components have a flat sliding and sealing surface, flatnesses of at least 0.3, preferably at least 0.6 ⁇ m and at most 1.2 ⁇ m, preferably at most 0.8 ⁇ m can be produced. This applies in particular to objects made of aluminum oxide.
• a content of Al2O3 is not critical. Can be used for.
• the mean roughness depth Ra is referred to as the arithmetic mean roughness value according to DIN 4762.
• the term flatness is replaced by the term surface accuracy, which indicates the maximum difference between the measured dimensions and the dimensions given by the mathematically defined shape of the body.
• the surfaces produced by the method according to the invention show a surface with rounded tips when recorded in a scanning electron microscope. This surface is significantly poorer on sharp burrs than a surface of the same average roughness that was produced by polishing (e.g. with diamond polishing paste). This may be due to the much lower working pressure when polishing.
• Valve disks that were produced by the method according to the invention require up to 50% less displacement force than polished or lapped valve disks of the same composition. They are sealed against liquid media in the range of 0 - 20 bar. At least up to a pressure of 6 bar, there are no differences in the sealing behavior against water compared to polished valve disks.
• Ceramic bodies can be produced with reduced labor costs according to the specified process. Another advantage is that large numbers of units per unit time can be smoothed in simple apparatus. It is surprising that the brittle ceramic parts are hardly damaged or destroyed during the polishing process. In DE-PS 1949318, column 9, it is proposed to lap aluminum oxide valve disks in order to give them an extremely smooth surface.
• the polished surfaces are less shiny than polished, but more polished than. They look matte and do not reflect.
• the invention further relates to a machine component made of ceramic, which has at least one sliding and sealing surface, whose average roughness (Ra) is over 0.1, in particular over 0.3, and at most 1 ⁇ , in particular at most 0.8 ⁇ m.
• the flatness or surface accuracy of this sliding and sealing surface lies in at least one measuring direction in the range from at least 0.3, in particular at least 0.6 ⁇ m to at most 1.2 ⁇ m, preferably at most 0.8 ⁇ m.
• B components made of steatite or silicon carbide.
• Preferred are components based on aluminum oxide, in particular with a content of at least 80 wt .-%, preferably at least 90 wt .-% Al2O3. Materials containing zirconium oxide and / or Hafnium oxide according to EP-PS 043456 can be used, but are not preferred.
• the shape of the components according to the invention is not critical. The only essential thing is the presence of a sliding and sealing surface. As intended, this machine component will later be in flat contact with another component. Both components should be able to be moved against each other and the gap formed by them should be sealed against fluids such as e.g. B. water under pressure.
• the component according to the invention can, for. B. adopt spherical shape.
• the shape of a disk, a cylinder or a hollow cylinder is preferred.
• Components with the shape of a cylindrical tube can serve as a piston jacket. It is important that the outer surface of the cylindrical tube is designed as a sliding and sealing surface.
• the end faces of the tubes are preferably also designed as a sliding and sealing surface.
• Another embodiment of the component according to the invention has the shape of a hollow cylinder closed on one side.
• Such a component can, for. B. can be used as a plunger in high-pressure piston pumps. It is therefore necessary that the outer surface is designed as a sliding and sealing surface. It is preferred if the end face of the hollow cylinder is also designed as a sliding and sealing surface.
• the length / diameter ratio is preferably at least 1, in particular at least 2.
• a large variety of ceramic disks is used for valve disks, such as those installed in mixing valves or mixer taps in the sanitary area for regulating liquid flows. At least one side of the disc has a sliding and sealing surface. Stand in the finished controls at least two such valve disks in movable contact with one another, the sliding and sealing surfaces in each case slidingly and sealingly touching one another. Disk-shaped ceramic components with a sliding and sealing surface are preferred, the thickness of the disk in most cases being 1-10 mm, in particular 2-5 mm. It is preferred if the ratio of F 0.5 / D for these disks is 3-12, in particular 5-9, where F is the area of the disk defined by the outer dimensions of the disk and D is the thickness of the disk. Discs with the specified ratio can be processed very well in scouring vibrators. This applies in particular to discs with diameters of 3 - 50 mm.
• a valve disc for sanitary mixer taps is often round or approximately round. It can have recesses on the edge. At least one channel for a liquid is provided in at least one disk of a control element. Usually, however, there are several channels for liquids to be mixed and the mixed liquid. These channels connect both sides of the valve disc. Valve disks with 3 openings are shown in DE-PS 1291957. It is preferred if the sum of the cross sections of the individual channels on each side reaches 5-45% of the disk area. With a larger proportion of the channel area, the mechanical stability of the valve disks decreases. As counterpart to valve disks with channels, valve disks with depressions arranged in the interior of the area also occur. It is preferred if both sides of the valve disk are designed as polished-sliding and sealing surfaces.
• valve cartridges that contain two sealing disks that are in frictional engagement with one another and a sealing O-ring on the back of the movable disk, the risk of injury to the O-ring can be considerably reduced with disks that are smoothed on both sides.
• Ceramic components in the form of a cylindrical washer are suitable as sliding rings in mechanical seals. These rotationally symmetrical parts show a rectangular outline when projected perpendicular to the axial direction. At least one, but preferably both, annular sides of the disk are designed as sliding and sealing surfaces.
• the ratio of the outer diameter / thickness of the disk is in most cases 2.6-15, in particular 3-11, preferably 3.5-9.
• Angle rings can also be produced by the method according to the invention, which can also be used as sliding bodies in mechanical seals.
• These projection-symmetrical ceramic rings show a T-shaped outline when projected perpendicular to the axial direction.
• the ring surface with the larger surface is designed as a sliding surface.
• the ratio outside diameter / thickness is about 2-10. Preferred ranges for this ratio are 2.2 to 7, 2.8 to 5.6 and 3 to 5.
• the invention is illustrated by the example.
• Alumina powder with 96 wt .-% Al2O3 is ground in the presence of water and millstones for 48 hours. With the addition of 2% of a water-soluble binder, such as polyvinyl alcohol or methyl cellulose, a slip is produced and sprayed. The granules obtained are filled into a die and formed into a green body in an automatic dry press with a pressure of 15 kp / mm2. Sintering takes place at 1700-1750 ° C. The disks obtained are ground to a constant height and plane-parallel.
• a water-soluble binder such as polyvinyl alcohol or methyl cellulose

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Sliding Valves (AREA)
• Sliding-Contact Bearings (AREA)

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• 1987
  • 1987-04-07 DE DE19873711749 patent/DE3711749A1/de active Granted
• 1988
  • 1988-03-30 JP JP63503312A patent/JPH02502894A/ja active Pending
  • 1988-03-30 EP EP88903223A patent/EP0363372A1/fr active Pending
  • 1988-03-30 US US07/411,500 patent/US5070658A/en not_active Expired - Fee Related
  • 1988-03-30 EP EP88105160A patent/EP0285996A1/fr not_active Withdrawn
  • 1988-03-30 WO PCT/EP1988/000263 patent/WO1988007913A1/fr not_active Application Discontinuation
  • 1988-04-06 PT PT87174A patent/PT87174A/pt not_active Application Discontinuation
  • 1988-12-06 KR KR1019880701604A patent/KR890700427A/ko not_active Application Discontinuation
• 1989
  • 1989-10-05 FI FI894723A patent/FI894723A/fi not_active Application Discontinuation
  • 1989-10-06 DK DK495189A patent/DK495189A/da not_active Application Discontinuation

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