Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/02—Contacts characterised by the material thereof
  • H01H1/021—Composite material
  • H01H1/027—Composite material containing carbon particles or fibres
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/14—Treatment of metallic powder
  • B22F1/148—Agglomerating

Definitions

• the invention relates to methods for granulating non-flowable metal powders or metal powder mixtures, in which a pellet is mixed with a granulation agent in a liquid as a solution or emulsifier, the mixture is converted into a flowable fine granulate and the fine granulate is dried while evaporating the liquid.
• the invention relates to special granules made flowable.
• Flow time t F which indicates the time in seconds during which 100 g of the metal powder flow out of a standardized 60 ° metal funnel.
• the metal funnel usually has a nozzle diameter of 4 or 6 mm and a nozzle length of 4 mm.
• the nozzle diameter of the flow funnel used for the flow test is given as an index, e.g. B. tF4 .
• a flow time t F4 20 to 40 s / 100 g applies to free-flowing powders. Since many starting powders do not flow through the specified funnel or do not flow sufficiently, they must be granulated, ie made flowable.
• granulation of non-flowable metal powders can be carried out by mechanical compaction and subsequent comminution (mechanical granulation), by pre-sintering of the filled, tapped or pressed powders (thermal granulation) or else by means of granulation additives.
• a granulating agent is added to the powder mixture via a liquid as a solvent or granulating agent and the granulate is produced therefrom. This can e.g. by passing the mixture through a perforated plate or a sieve. After evaporation of the solvent, the thread-like particles are cut. The granules subsequently show good flow properties (planned reports for powder metallurgy, volume 13, 1965, pages 81 to 89).
• the object of the present invention is to simplify the previously known granulation process by means of granulation additives.
• the aim is to ensure that carbon-containing metal powder mixtures, such as are required for contact materials, for example, can be processed further without graphite powder being lost. Due to this undesirable phenomenon, graphite surplus had to be used in the powder metallurgical manufacture of such materials.
• the object is achieved by method steps a) and b) of claim 1.
• Flowable granules specially produced therewith are specified in claim 13.
• the method according to the invention it is largely possible to work with a mixer, which simplifies the workflow in order to achieve uniform wetting of the powder surface with granulating agent.
• the granulating agent dissolved or emulsified in a solvent or emulsifying agent is expediently applied to the powder moving in the mixer by instillation or spraying.
• the mixer and the mixture therein are preferably heated above room temperature, the level of the temperature being such that the solvent or emulsifier evaporates at least partially.
• the amount of granulating agent depends on the type of powder, the particle shape and particle size. The smaller the powder surface, the less granule content is required for the granulation, e.g. 1 to 3% mass fraction based on the amount of powder. With a larger surface, i.e. more finely divided powders, about 3 to 10% by weight of granulating agent additive is required. In the case of metal powder mixtures, the solids content of the amount of granulating agent is advantageously measured at 1 to 10% by mass.
• the proportion of solvent or emulsifier based on the solids content in the granulating agent is very important. 30:70% to 50:50% has proven to be a particularly favorable ratio.
• the predetermined amount of granulating agent is sprayed with a larger proportion of solvent or emulsifying agent as a mixture.
• the mixture of powder bed and granulating agent is brought to an elevated temperature so that the excess solvent or granulating agent evaporates and thereby forms a concentration of granulating agent in the solvent in which granulate particles are formed from the powder.
• the most favorable concentration range is passed through the evaporation process. After granulation, the excess solvent or granulating agent can be removed. This process can take place immediately after the granulation in the mixer by increasing the temperature to a value above the boiling point of the solvent or emulsifier. The process is complete when no more solvent condenses in the cold template.
• the evaporation process can also take place outside the mixer by heat treatment at a temperature at which the solvent or emulsifier evaporates.
• the granulate is poured onto metal sheets.
• the heat treatment for evaporation of the solvent and possibly part of the granulating agent can take place outside the mixing drum at elevated temperature.
• the evaporation is then expediently carried out at elevated temperature under reduced pressure, e.g. at ⁇ 20 mbar.
• the granulate formed is sieved off before further processing, for example to a particle size ⁇ 315 ⁇ m. If roughly agglomerated particles remain on the sieve, they can be crushed and passed through balls on the vibrating sieve.
• the invention can also be advantageously used to produce granules which contain carbon in the form of graphite powder.
• a certain loss could not be avoided in the powder metallurgical processing of powder fillings with graphite powder, so that an exact carbon content was difficult to set.
• the graphite powder is now bound in a suitable manner in the granulate.
• the yield of the particle size fraction ⁇ 315 ⁇ m is 95%.
• the flow properties are good and are 23.6 seconds per 100 g in a 60 ° funnel with a 4 mm nozzle diameter.
• the powder fractions of electrolysis copper powder with an average particle size ⁇ 45 ⁇ m and electrographite powder with an average particle size ⁇ 5 ⁇ m are weighed out and added to the mixer.
• a diagonally rotating double cone mixer is also suitable for the mixing process.
• the mixing vessel After a dry mixing time of approx. 1 hour, the mixing vessel is filled with nitrogen and heated to 70 ° C.
• the granulating agent batch is sprayed in via a spray can, so that it is applied uniformly to the entire surface of the respective powder particles.
• the spraying times are 1 second and the pause time is 2 seconds.
• the amount of granulating agent is 10% by mass of solid polyethylene.
• the amount of emulsifier is likewise 10% by mass, based on the powder batch, so that 50:50 is obtained in relation to the granulating agent.
• the spraying time for a powder batch of 5 kg is about half an hour (spraying + pause times).
• the temperature is raised to 100 ° C., whereupon the water evaporates as an emulsifier. After about 1 hour, the dried granules are removed from the mixer and sieved.
• the larger granulate particles are passed through the sieve by using steel balls on the vibrating sieve, so that the total amount is present in processable granulate.
• the flow time of the granulated powder in the 60 ° funnel with 4 mm nozzle opening is 39.5 seconds per 100 g.
• Cu powders with a comparatively low carbon content are required in particular for the production of contact pieces, in particular for installation switches. What is important here is an exact adherence to a quantitatively predetermined proportion of carbon.
• the switching properties depend on a low tendency of the contact material to sweat, so that in this case natural graphite powder with a more favorable particle size distribution than that of electrographite is assumed.
• the flow behavior of both starting powders and their mixture is, as in Example 2, so poor that processing on automatic presses is not possible.
• the average particle size of the electrolysis copper powder is ⁇ 40 ⁇ m and the average particle size of the natural graphite powder is ⁇ 2 ⁇ m.
• the powder components are weighed and filled into a paddle mixer.
• the moist powder mixture is discharged and dried at a temperature of 120 ° C. under vacuum.
• the dried powder mixture is sieved with a sieve with a mesh size of ⁇ 315 ⁇ m, a powder fraction ⁇ 315 ⁇ m of approx. 60% being obtained.
• the coarser fraction is brought to a particle size of ⁇ 315 ⁇ m using steel balls with the vibrating sieve.
• the flow time of the granulated powder in the 60 ° funnel with 6 mm nozzle diameter is 29 seconds per 100 g.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Composite Materials (AREA)
• Materials Engineering (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Carbon And Carbon Compounds (AREA)

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Citations (7)

• 1983
  • 1983-02-03 DE DE19833303680 patent/DE3303680A1/de not_active Withdrawn
• 1984
  • 1984-02-01 JP JP59016894A patent/JPS59145701A/ja active Pending
  • 1984-02-01 EP EP84101009A patent/EP0118716A1/de not_active Withdrawn
  • 1984-02-03 BR BR8400486A patent/BR8400486A/pt unknown

Patent Citations (7)

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