Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C3/00—Selection of compositions for coating the surfaces of moulds, cores, or patterns

Definitions

• the failure of the metal from the splash to be incorporated into the main body of a metal ingot results in surface discontinuities, which must be removed from the ingot by burning, scarfing, grinding or other suitable means prior to fabrication of the ingot into shapes or sheets. If the discontinuities are not removed by one of these types of operations, they will result in defects in the finished metal products.
• the flammability of some of the prior art materials is undesirable from a safety point of view and all of the materials result in smoke and/or noxious fumes of one form or another.
• the materials containing a higher percentage of graphite are the least flammable and result in the lowest amount of smoke; however, they are extremely dirty'and difficult to handle and apply to the mold walls.
• an object of the invention to provide a mold coating which is easy to apply, adheres well to mold walls and results in a substantial improvement in the surface quality of the metal.
• Another object of the invention is to provide a mold coating which is capable of being shipped and handled in a liquid phase.
• a further object of the invention is to provide an improved method of forming steel ingots which comprises coating an ingot mold with an adherent organic coating, which is characterized as being efficient in repelling splashes of molten steel, and pouring molten steel into the ingot mold to form an ingot which has greatly improved surface characteristics.
• the coating is characterized as being extremely adherent to mold surfaces, when applied by brushing, spraying or other suitable methods to a mold which is at a temperature of from room temperature to 900 F.
• the coating is further characterized as being extremely efiicient in repelling splashes of molten metals and preventing their adherence to the surface of the mold.
• the characteristics of the mold coating of the subject invention make it extremely useful in a process whereby steel ingots are formed which have extremely good surface characteristics.
• the ingots are formed by pouring molten steel into a cast iron mold which is coated with the coating of the subject invention.
• the mold coating of the subject invention comprises a humic acid compound exemplified by alkali metal salts of humic acid and alkali earth metal salts of humic acid. Particularly, for applications in which the coating is applied to molds at an elevated temperature, it is essential that the coating contain an organic bonding agent in addition to the humic acid or humic acid salt.
• alkali metal salts of humic acid which are useful in the subject invention are sodium humate, potassium humate and ammonium humate.
• alkali metal salt will be construed to include ammonium salts.
• the alkali earth metal salts of humic acid which are particularly useful in the subject invention are calcium humate and magnesium humate.
• the humate salts which are useful in the subject invention are products of the reaction of humic acid with alkali metal or alkali earth metal hydroxides or ammonia.
• the humic acids are a generic group of acids which are derived from humus, which is most often concentrated in top layer of soil and contains the organic decomposition products of vegetation and other organisms. Sources of humic acid are brown coal, lignite and the like.
• leonardite One of the preferred sources of humic acid for use in the subject invention is leonardite, which is often found in association with lignite.
• Leonardite is primarily mined in Bowman County, N. Dak., Divide County, N. Dak., and in and around Alpine, Tex. Spectral analysis has indicated that leonardite is generically a mixture of humic acid and salts thereof.
• Leonardite is considered to be made up of a large condensed ring polymeric molecule containing carboxyl groups; however, the exact nature of the molecule has not been proven conclusively.
• a typical leonardite sample which is comprised of calcium, sodium, magnesium, potassium, etc., salts of complex organic acid and free organic acid is partially analyzed as follows:
• the equivalent weight of the above sample of leonardite was determined to be 256.
• humate salts of the inventio it is only necessary to add an alkali metal or alkali earth metal hydroxide or ammonia to the humic acid.
• the salt-forming reaction is preferably carried out in the presence of water.
• a more preferred humate salt is sodium humate and most preferably sodium leonardite.
• organic bonding agent for use in the subject invention is not critical except that it must be one which is capable of adhering to a hot or cold metal surface whe applied in spray or droplet form.
• Preferred organic bonding agents are lignosulfonic acid, alkali metal salts of lignosulfonic acid, alkali earth metal salts of lignosulfonic acid, sugars and dextrins.
• the organic bonding agent used is sodium lignosulfonate.
• the sugars which are useful in the subject invention are any of the materials having the general formula, (c H O These materials are classified generally as carbohydrates, monosaccharides, furanoside or pyranoside. A broad range of these materials have proven to be useful as organic binders in the mold coating of the subject invention. The most preferred of the sugars for use in the subject invention are monosaccharides.
• Glycols are useful as aids to organic bonding as they raise the boiling point of the mixture when it is used in an aqueous slurry.
• the aqueous slurry then has less of a tendency to spatter when applied to a hot mold surface.
• the glycols are considered to be the group of diatomic alcohols of the aliphatic series.
• the most preferred material from this series for use in the subject invention is ethylene glycol.
• Ethylene glycol is also useful as a freezing point depressant for use when the mold coating is shipped or used as an aqueous mixture in cold Weather.
• the lignosulfonates which are useful in the subject invention are the ammonium, alkali metal and alkali earth metal salts of lignosulfonic acid and lignosulfonic acids themselves.
• Methods of manufacture of lignosulfonic acid and various lignosulfonate salts are well known to the art. Suitable methods for the production of lignosulfonic acid and the isolation of various lignosulfonate salts are given by Friedrich Emil Brauns in the Chemistry of Lignin, published in 1952 by the Academic Press, Inc. of New York. A particlar method for isolating lignosulfonic acid and manufacturing the various lignosulfonate salts is discussed on pages 111-125.
• the preferred lignosulfonates are the ammonium, sodium, and calcium lignosulfonates and combinations thereof.
• the mixture may be blown or dusted on to the mold surface as a dry powder, or applied to the surface in an aqueous slurry by means of brushing, dipping, pouring, spraying or other suitable means.
• the mixture is in an aqueous slurry consisting of from about 20% to about by weight of the mixture of the subject invention, and from about 20% to about 80% by weight of water. More preferably, the aqueous slurry contains from about 30% to about 60% by weight of the mixture of the invention, and from about 40% to about 70% by weight of Water. In one particularly preferred embodiment of the subject invention, the slurry contains about 40% of the mixture of the subject invention and about 60% Water.
• Ingot molds are usually coated hot, at a temperature of from about 200 F. to about 800 F.
• the coating of the subject invention can be used at temperatures ranging from room temperature to temperatures in excess of 1000. F.
• the most preferred temperature for coating when an aqueous slurry is used is approximately 300 F. This temperature is preferred, as it provides an efficient coating with a minimum of spattering, and violent steam emission with the attendant waste of material.
• the humic acid or humic acid salt should be present in an amount equal to from about 20% to about 80% by weight of the dry mixture. More preferably, the humic acid or humic acid salt should be present in an amount of from about 30% to about 60% by weight. In a greatly preferred embodiment of the invention the humic acid salt is sodium humate, present in an amount equal to about 40% by weight of the dry mixture.
• compositions may be added to the mixture in minor quantities in an aqueous slurry.
• the addition of these adjuvants is made to enhance the properties of the slurry as to characteristics such as bacterial stability and freezing point.
• a variety of bactericides has been used in quantities of less than 1% by weight to enhance the stability of the mixture in an aqueous slurry. It is of course understood that the invention is not limited to the use of any particular bactericide or to any particular amount of bactericide. Any of a number of known agents can be used to inhibit bacterial growth in an aqueous system which is high in organic bonding agents such as sugars.
• aqueous slurry of the mixture of the subject invention are freezing point depressants, for use When the slurry is shipped or used in cold weather.
• the glycols are particularly useful as freezing point depressants for use in the subject invention, as pointed out above.
• a particularly preferred glycol is ethylene glycol.
• a typical mold coating composition of the subject invention was made up as follows:
• the lignosol X-D is an alkali earth metal lignosulfonate of the following typical analysis Ingredient Percent Moisture Lime as CaO Ash 2 Red. bodies 2 Sulphur Iron (max) Insolubles (27% soln) vol. Methoxyl Sulphonate sulphur Sodium as Na swr ez sr ps HUlW-WSODOQR The sodium humate which was used in the preparation of this mold coating was made by causticizing a crude leonardite mud.
• a small amount of crystalline caustic was added to the mold coating to provide an excess of sodium for reaction with any humic or lignosulfonic acid from the sodium humate or lignosol and to produce a coating mixture at a pH of over 2.5. It was found that maintaining a pH above 9.5 was desirable for adherence to mold walls when the coating was applied in the form of a spray.
• the coating was applied to a series of over 100 ingot molds.
• Various carbon and alloy steels which were made in a basic oxygen furnace, were ,poured into the ingot walls and metallurgical analyses were run on the ingots which were formed. All of the ingots were found to have surface properties which were superior to ingots formed in uncoated molds and to ingots which, were formed in molds where a prior art graphitic mold coating was used.
• the ingots were also tested for the presence of nonmetallic inclusions which might have resulted from the mold coating. No unusual inclusions were discovered and the conclusion was reached that the mold coating had no deleterious effect upon the steel. Furthermore, no build-up of the coating was noted on the molds after the mold had been stripped.
• the objects of the invention to provide mold coating which is easy to apply, adheres well to mold walls and results in a substantial improvement in the surface quality of metal, have been achieved. Since the mold coating, as typically made in the above example, is in the form of a stable slurry, it can be shipped as a bulk liquid; therefore, the additional object of the invention to provide a mold coating which is capable of being shipped and handled in a liquid phase has also been accomplished.
• an improved surface for contacting any molten metal can be achieved by coating the surface with a humic acid compound or a mixture of a humic acid compound with other useful adjuvants, as disclosed above.
• a specific example of a surface which can be improved by use of the coatings of the subject invention is the surface of sand or ceramic cores and molds for use in the casting of metals.
• Another example of a coated surface is the surface of graphite or ceramic crucibles for use in the melting or containing of molten metals.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Materials Applied To Surfaces To Minimize Adherence Of Mist Or Water (AREA)
• Coating By Spraying Or Casting (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24552662

Family Applications (1)

Country Status (6)

Cited By (1)

Citations (2)

Family Cites Families (1)

• 1967
  • 1967-05-08 US US636623A patent/US3474852A/en not_active Expired - Lifetime
• 1968
  • 1968-02-27 GB GB31186/69A patent/GB1216772A/en not_active Expired
  • 1968-02-27 GB GB9502/68A patent/GB1216771A/en not_active Expired
  • 1968-03-08 FR FR1563233D patent/FR1563233A/fr not_active Expired
  • 1968-03-11 DE DE19681608347 patent/DE1608347B1/de active Pending
  • 1968-03-11 NL NL6803429A patent/NL6803429A/xx unknown
• 1969
  • 1969-04-15 ES ES366037A patent/ES366037A1/es not_active Expired
  • 1969-04-15 ES ES366036A patent/ES366036A1/es not_active Expired

Patent Citations (2)

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