Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D13/00—Centrifugal casting; Casting by using centrifugal force

Definitions

• ABSTRACT Alloys having wear-resistant surfaces are produced by incorporating in the molten matrix metal wearresistance imparting components with a specific gravity lower or higher than the specific gravity of the matrix metal and centrifugally casting the resulting alloy in the form of a hollow cylinder whereby the component, if lighter, is concentrated in the inner surface portion of the cylinder wall, or, if heavier, the component is concentrated in the outer surface portion of the cylinder wall.
• Work pieces, such as sealing strips for rotary piston engines, may be formed from selected portions of these cylinders.
• the present invention relates to a method for producing alloyed materials with wear-resistant surfaces suitable particularly for the production of cast-iron sealing strips for rotary piston engines.
• wear-resistant metallic materials are known, both ferrous and nonferrous.
• Such wear-resistant alloys in all cases have a relatively soft but tough matrix in which the wear-resistant phases, such as carbides, nitrides or hard metallic compounds, are embedded.
• wear-resistant particles solidify from the melt and are uniformly distributed throughout the article in the usual casting procedures. If the number of wearresistant particles in the surface portions of such cast pieces is to be increased, it is necessary to do so throughout the casting and this is possible only to the extent permitted by the phase diagram of the particular alloy which more or less corresponds to the equilibrium state.
• wear-resistant particles are frequently carbides or compounds of relatively expensive elements such as, for example, tungsten, vanadium, niobium etc.
• the further addition of such elements to the alloy even if it were possible according to the phase diagram would substantially increase the ultimate cost.
• a wear-resistant cast-iron material in which, due to its dry running properties, unbound carbon is to be maintained in the structure, only a very slight concentration of such elements is permitted since otherwise there will result substantially complete carbidic hardening with consequent difficulties inv the machining, particularly by cutting or milling procedures. This is particularly disadvantageous where only one surface or edge of a piece is intended to have wear-resistant properties.
• Wear-resistant layers can also be applied to materials by a flame spraying process, for example.
• the process according to the present invention permits the material and the wear-resistant surface to be prepared in a single casting, thus being less expensive, and it is possible in this way to have graphite available in addition to the hard components to obtain anti-friction properties, which is not possible in such spray procedures due to the oxidative destruction.
• the present invention is based on the fact that materials which contain components forming hard phases with one another which components deposit simultaneously during cooling according to the phase diagram, form hard layers during solidification of the melt and under the simultaneous influence of centrifugal forces and cooling. These phases are deposited on the inside in alloys where they have a lower specific gravity than the surrounding matrix, and will be deposited toward the outside where their specific gravity is higher than that of the matrix. Thus, by selection of the particular alloying components and control of the temperature, cooling rates and other operating conditions, the wearresistant properties can be developed at the inner or the outer tubular wall as desired.
• This principle can be used to produce ferrous metal tubes by the centrifugal casting process.
• the basic ferrous metal or matrix is alloyed with hard-substance forming materials, such as titanium, vanadium, niobium, tantalum or tungsten.
• hard-substance forming materials such as titanium, vanadium, niobium, tantalum or tungsten.
• these substances are concentrated on the surface of the tube, either the inside or the outside, as carbides, nitrides or borides, depending on their specific gravity, so that tubes with predetermined wear-resistant surfaces are produced.
• the presence of such wear-resistant phases can be determined by chemical analysis, physical analysis or from a photomicrograph of a ground surface, according to conventional procedures.
• Other known alloying elements such as copper, nickel or tin, which do not lead to the formation of carbides, nitrides or borides, can be added to modify the properties of the basic metal.
• sections can readily be removed for fabrication of articles, for example sealing strips for rotary piston engines, wherein the zone of maximum wear-resistant alloy concentration will be situated in the portion of the article to be subjected to the maximum wear or contact with other elements in use.
• the proportion of the added substance to produce the desired wear-resistant layer may vary from 3 about 0.3% to about 5.0% of the final mixture to be cast.
• the melt of the cast iron is heated to 1,350 to 1,450 C and chilled into an iron mold which has the temperature of 400 to 600 C and the form of a tube with a diameter of 294 mm.
• the melt of the cast iron solidifies by forming an iron tube.
• the cast iron tube is cooled down to about l,000 C so that the rotation may be stopped and the cast tube can be removed.
• the cast iron tube is annealed for one hour at 820 to 950 C and then quenched in oil. Then the cast tube is tempered in air for one hour at about 300 to 500 C.
• the resulting pipe was martensitic, with an outer zone hardness of Hv 584-623 kp/mm while the inner surface had a hardness of Hv 666-713 kp/mm the inner region being highly enriched with carbides and nitrides.
• Titanium appears principally as the carbide although some of it may be in the form of the nitride. Graphite appears in sufficient quantities at the wear-resistant surface to provide the desired anti-friction properties.
• the hardness of the matrix material decreased to about Hv 350 kp/mm corresponding to that of the outer zone, thus permitting easy machining.
• the hardness of the inner layer decreased slightly to about HV 600 kp/mm since the carbides and nitrides do not decompose under these conditions.
• the invention provides a simple and effective procedure for the preparation of alloy materials having a wear-resistant surface, which can be readily fabricated into wear-resistant parts or elements essentially by machining with little or no grinding.
• alloy materials are produced according to this invention at substantially less cost due to the small quantities of expensive additives which are required.
• the wear-resistant surface contains the graphite whic' is necessary in machine parts which are subjected to sliding wear.
• Process for producing materials with wear-resistant surfaces comprising forming a melt of a matrix material and at least one substance which forms at least one hard solid phase having a density other than that of the matrix material and which separates from the basic matrix material during hardening, casting the resulting melt and subjecting the molten casting to mass acceleration during the hardening process.
• the added substance is a metal selected from the group consisting of titanium, vanadium, niobium, tantalum, tungsten, copper, nickel and tin.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Pistons, Piston Rings, And Cylinders (AREA)
• Coating By Spraying Or Casting (AREA)
• Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=5849851

Family Applications (1)

Country Status (6)

Cited By (6)

Families Citing this family (1)

Citations (5)

Family Cites Families (1)

• 1972
  • 1972-07-06 DE DE2233148A patent/DE2233148C3/de not_active Expired
• 1973
  • 1973-05-02 FR FR7315649A patent/FR2191960A1/fr not_active Withdrawn
  • 1973-06-15 GB GB2866773A patent/GB1434113A/en not_active Expired
  • 1973-06-15 IT IT25456/73A patent/IT989223B/it active
  • 1973-07-05 US US376297A patent/US3929181A/en not_active Expired - Lifetime
  • 1973-07-06 JP JP48076460A patent/JPS4956801A/ja active Pending

Patent Citations (5)

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