EP1060814A1 - Entfernung von Rückständen des verlorenen Giessmodells von einem Gussstück - Google Patents

Entfernung von Rückständen des verlorenen Giessmodells von einem Gussstück Download PDF

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Publication number
EP1060814A1
EP1060814A1 EP99121791A EP99121791A EP1060814A1 EP 1060814 A1 EP1060814 A1 EP 1060814A1 EP 99121791 A EP99121791 A EP 99121791A EP 99121791 A EP99121791 A EP 99121791A EP 1060814 A1 EP1060814 A1 EP 1060814A1
Authority
EP
European Patent Office
Prior art keywords
coating
casting
pattern
acid
aluminum
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP99121791A
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English (en)
French (fr)
Other versions
EP1060814B1 (de
Inventor
Nicholas Edward Sargent
June-Sang Siak
Mei Cai
Thomas C. Pederson
Sheila Farrokhalaee Kia
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Motors Liquidation Co
Original Assignee
Motors Liquidation Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/335,851 external-priority patent/US6901989B1/en
Application filed by Motors Liquidation Co filed Critical Motors Liquidation Co
Publication of EP1060814A1 publication Critical patent/EP1060814A1/de
Application granted granted Critical
Publication of EP1060814B1 publication Critical patent/EP1060814B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
    • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
    • B22C1/14—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives for separating the pattern from the mould
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
    • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
    • B22C1/165—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents in the manufacture of multilayered shell moulds
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C7/00—Patterns; Manufacture thereof so far as not provided for in other classes
    • B22C7/02—Lost patterns
    • B22C7/023—Patterns made from expanded plastic materials
    • B22C7/026—Patterns made from expanded plastic materials by assembling preformed parts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D29/00—Removing castings from moulds, not restricted to casting processes covered by a single main group; Removing cores; Handling ingots
    • B22D29/001—Removing cores
    • B22D29/002—Removing cores by leaching, washing or dissolving
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D31/00—Cutting-off surplus material, e.g. gates; Cleaning and working on castings
    • B22D31/002—Cleaning, working on castings

Definitions

  • This invention relates to the lost foam process for making aluminum castings and more specifically to coating the lost foam pattern with a refractory coating that is readily acid-washed from the aluminum casting.
  • the "lost foam” process is well known in the art, and involves principally the steps of: (1) preparing (e.g., molding) a pattern from a fugitive material such as expanded polystyrene (EPS) foam; (2) coating the pattern with a refractory coating (i.e., about 0.25 mm to about 1.5 mm thick) to stiffen the pattern, provide a barrier between the surface of the pattern and the sand, and control the metal fill rate; (3) drying the coating; (4) investing the pattern in a bed of unbonded sand to form a mold about the pattern; (5) pouring molten aluminum into the mold to vaporize and displace the pattern, and form a casting that replicates the shape of the pattern; and (6) removing the sand from around the casting.
  • EPS expanded polystyrene
  • the casting may or may not be water quenched in the course of a heat treatment following casting depending on the particular aluminum alloy used and the desired final microstructure.
  • A319 aluminum alloys are frequently quenched in water in the course of a T-5 heat treatment to improve its machineability and dimensional stability.
  • EPS pattern coatings typically comprise water-based slurries (i.e., about 45%-70% by weight solids) including various combinations of (1) refractories such as silica, alumina, chromite, mica, zircon, quartz, olivine, aluminosilicates or hollow glass microspheres, (2) binders such as clay and various polymers, (3) surfactants, (4) thixotropic agents, and (5) dispersants. On a dry basis, the coatings comprise about 80% to about 98% by weight refractory, about 0.5-18% by weight binders, and about 2% by weight surfactants/dispersants/and thixotropic agents.
  • water-based slurries i.e., about 45%-70% by weight solids
  • refractories such as silica, alumina, chromite, mica, zircon, quartz, olivine, aluminosilicates or hollow glass microspheres
  • binders such as clay
  • the permeability of the coating is controlled by the size and shape of the refractory particles and serves to control the rate at which liquid and gaseous pyrolysis products escape into the sand which, in turn, controls the rate at which the aluminum enters the mold.
  • the coatings are most commonly applied by dipping the pattern therein, but may also be sprayed, brushed or pumped onto the pattern. Though water is the most common carrier for the refractories, other carriers that are compatible (e.g., a non-solvent) with the pattern may also be used.
  • Some known techniques for removing at least a portion of the coating residue include (1) thermally shocking the coating by plunging the hot casting into water immediately after casting, (2) shot blasting the casting (e.g., with plastic, steel or ceramic shot), (3) scrubbing the casting in an agitated aqueous slurry of abrasive particles, (4) rapping the casting with a hammer(s), (5) immersing the casting in a bath of ultrasonically agitated water, (6) blasting the casting with a stream of water or steam, and (7) dipping the casting in a bath of molten salt, or caustic soda.
  • the present invention is a simple process for readily and economically removing any of the pattern's refractory coating that adheres to an aluminum lost foam casting following removal of the sand.
  • the invention is particularly advantageous in that it permits removal of the coating in areas of the casting (e.g. internal passages) inaccessible to traditional mechanical means for removing the coating.
  • the invention contemplates (1) coating the foam pattern with a refractory coating containing a water-insoluble, acid-gasifiable compound that is thermally stable (i.e. won't decompose) at the casting temperature, and (2) following casting, contacting (e.g.
  • the thermally stable, water-insoluble, acid-gasifiable compound will preferably comprise an inorganic carbonate, more preferably an alkaline earth carbonate (i.e. calcium, magnesium, strontium or barium carbonate), and most preferably calcium carbonate.
  • an alkaline earth carbonate i.e. calcium, magnesium, strontium or barium carbonate
  • Calcium carbonate will preferably be used in concentrations greater than about 10% by weight of the coating, on a dry basis.
  • the particle size of the calcium carbonate can be controlled and used as a means to control the speed/aggressiveness of the reaction. Calcium carbonate will preferably have a particle size less than about 5 microns to provide a large reaction surface for a very aggressive reaction.
  • the casting will be immersed in a bath of the acid.
  • the acid treatment is for the sole purpose of removing the coating and the treatment may be done while the casting is either hot or cold.
  • the quenchant e.g. water
  • the quenchant will be acidified such that coating removal is achieved at the same time that the hot casting is being quenched.
  • any acid may be used so long as it does not attack the surface of the casting, and may include weak acids such as acetic acid, or diluted strong acids such as phosphoric or hydrochloric acid, inter alia. Dilute phosphoric acid is preferred as it is less corrosive of surrounding equipment than many other acids, and yet is just as effective in removing the coating. Dissociation of the gasifiable compound is more rapid with the stronger acids than with the weaker acids.
  • the acid will preferably have a pH less than about 2.5 for rapid dissociation of the compound and more aggressive rupture of the coating.
  • the EPS pattern thermally degrades and deposits a partially oxidized hydrophobic organic contaminant that impedes thorough wetting of the coating by the acid.
  • the affects of the hydrophobic contaminant are neutralized. These affects can be neutralized by the addition of a surfactant to the acid which promotes better wetting of the coating residue and accelerates removal of the coating residue.
  • the casting is heat treated before immersion in the acid bath to remove the hydrophobic contaminant before immersing the casting in the acid.
  • the refractory coatings of the present invention will preferably comprise about 10% or more, by weight dry of calcium carbonate. Below about 10%, there is insufficient carbonate for rapid, effective removal of the coating.
  • concentration of the gasifiable compound in the coating for any given situation will depend on which compound, which acid, and which acid concentration is used and can be determined by routine experimentation. The same is true for the concentration of the acid, which tests have shown can vary from concentrated to very dilute (i.e. as much as 100 parts water to 1 part acid). Accordingly, such concentrations are not part of the present invention.
  • Table III shows the percent of the 20% CaCO 3 -containing coatings removed from the screens in phosphoric acid wash solutions having different H 3 PO 4 concentrations. The data shows that 89% or more of the CaCO 3 -containing coatings was removed with very dilute and concentrated wash solutions while only about 20% of the carbonate-free coatings were removed with only the most concentrated acid wash solutions.
  • the polystyrene products which penetrate the refractory coating during casting form a hydrophobic degradation product, in the presence of air, that is a partially oxidized polystyrene polymer with the oxygen incorporated largely in the hydrocarbon chain rather than the aromatic ring (i.e. a highly oxygenated alkyl chain with the attached phenyl groups remaining largely unmodified).
  • the degradation product impedes wetting of the coating residue by the acid and retards the reaction between the acid and the acid-gasifiable compound (e.g. CaCO 3 ), by restricting access of the acid to the CaCO 3 in the coating residue.
  • the effects i.e.
  • the degradation product is neutralized by adding a wetting agent or surfactant to the acid to promote wetting.
  • the casting is heated for a time and at a temperature sufficient to destroy the hydrophobic degradation product.
  • the heat treatment may be accomplished quickly at high temperatures (e.g. 20 minutes @ 500°C), or more slowly at lower temperatures (e.g. 17 hours @ 320°C).
  • Organic binders hydroxyethyl cellulose (HEC), hdroxypropylmethyl cellulose (HPMC) & polyvinyl alchohol (PVA) Acid bath for removal of coating residues Phosphoric acid, 85% H 3 PO 4, , diluted 1:20 with water for use in acid bath
  • Non-ionic surfactants Triton X-100, Rohm & Haas Co.; & Brij 35, Sigma Chem. Co.
  • Cationic surfactant Hexadecyltrimethylammonium bromide, Sigma Chem.Co.
  • Thermogravimetric analysis (i.e. @ the 10°C/min heating rate) of coatings that had been infused with polystyrene revealed that in the presence of oxygen, both polystyrene and the organic binders for the refractory begin to rapidly degrade and volatilize at temperatures between about 250°C and 350° C. All of the organic binders volatilized at these temperatures, but the polystyrene degradation products (i.e. about 13% of the original polystyrene) survived, and persisted until the temperature exceeded 450°C. Temperatures as low as 320°C are effective to remove the degradation products if sufficient time (i.e. many hours) is allowed for the process to go to completion.
  • the results listed in Table VII compare the efficacy of two types of commercially available CaCO 3 mixed with two commercial coatings and an experimental coating prepared in the laboratory.
  • a principle difference between the two forms of CaCO 3 was their respective mean particle size, which was approximately 30 microns for type CX0110 and 3 microns for type CX0120.
  • the results using the two types of CaCO 3 were clearly dissimilar.
  • the smaller particles of the type CX0120 CaCO 3 were very effective in each formulation, leaving no more than 0.2% of the coating on the screens.
  • the larger particles of the type CX0110 CaCO 3 left significantly more of the coatings on the screens following the acid dip.
  • the larger particle size of type CX0110 was also evidently responsible for increasing the permeability of the coating which can be an undesirable property for casting quality.
  • the use of CaCO 3 with a small particle size is beneficial for both maintaining a low coating permeability and facilitating removal of the coating residue in the acid bath.
  • Treatment time need only be sufficient to remove the hydrophobic residue, and will vary with treatment temperature and size of the casting. Hence, by way of example only, the head of an internal combustion engine requires about 20 minutes treatment time at 500°C to remove the hydrophobic material.
  • Tests were also conducted on the effectiveness of adding surfactants to the acid bath to neutralize the affects of the styrene degradation products and accelerate removal of the CaCO 3 -containing coating residue.
  • a non-ionic surfactant i.e. triton X-100
  • a quaternary ammonium surfactant were tested separately in a concentration of 1 % by volume of the acid bath, and exhibited considerable success with the experimental "clay-free" coatings containing primarily mica, CaCO 3 and a modified cellulose binder, and lesser success with CaCO 3 -containing Ceramcote 545.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Mold Materials And Core Materials (AREA)
EP19990121791 1999-06-14 1999-11-03 Entfernung von Rückständen des verlorenen Giessmodells von einem Gussstück Expired - Lifetime EP1060814B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US335851 1999-06-14
US09/335,851 US6901989B1 (en) 1997-08-28 1999-06-14 Removing lost foam pattern coating residue from a casting

Publications (2)

Publication Number Publication Date
EP1060814A1 true EP1060814A1 (de) 2000-12-20
EP1060814B1 EP1060814B1 (de) 2003-10-08

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EP (1) EP1060814B1 (de)
DE (1) DE69911928T2 (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101602087B (zh) * 2009-07-13 2010-12-29 西安建筑科技大学 一种粉煤灰消失模铸铝涂料及其制备方法
CN103084540A (zh) * 2013-01-30 2013-05-08 巢湖诺信建材机械装备有限公司 一种用于铸造耐热钢或耐磨合金钢的消失模涂料配制方法
CN103909211A (zh) * 2014-03-27 2014-07-09 吉安汇诚实业发展有限公司 一种自剥落消失模铸造专用涂料
CN105458167A (zh) * 2015-12-07 2016-04-06 兴化市雅兰机械制造有限公司 大型轮毂消失模铸造工艺
CN106391999A (zh) * 2016-12-15 2017-02-15 李文海 一种水基侵占型消失模涂料
WO2020212433A1 (en) * 2019-04-16 2020-10-22 Ask Chemicals Gmbh Coating composition, method for coating a casting mold, use of the coating composition for coating a casting mold, and casting mold

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0899038A1 (de) * 1997-08-28 1999-03-03 General Motors Corporation Verfahren zum Vollformgiessen von Aluminium mit beschichtetem Modell

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0899038A1 (de) * 1997-08-28 1999-03-03 General Motors Corporation Verfahren zum Vollformgiessen von Aluminium mit beschichtetem Modell

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101602087B (zh) * 2009-07-13 2010-12-29 西安建筑科技大学 一种粉煤灰消失模铸铝涂料及其制备方法
CN103084540A (zh) * 2013-01-30 2013-05-08 巢湖诺信建材机械装备有限公司 一种用于铸造耐热钢或耐磨合金钢的消失模涂料配制方法
CN103909211A (zh) * 2014-03-27 2014-07-09 吉安汇诚实业发展有限公司 一种自剥落消失模铸造专用涂料
CN103909211B (zh) * 2014-03-27 2016-08-24 吉安汇诚实业发展有限公司 一种自剥落消失模铸造专用涂料
CN105458167A (zh) * 2015-12-07 2016-04-06 兴化市雅兰机械制造有限公司 大型轮毂消失模铸造工艺
CN106391999A (zh) * 2016-12-15 2017-02-15 李文海 一种水基侵占型消失模涂料
WO2020212433A1 (en) * 2019-04-16 2020-10-22 Ask Chemicals Gmbh Coating composition, method for coating a casting mold, use of the coating composition for coating a casting mold, and casting mold

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Publication number Publication date
EP1060814B1 (de) 2003-10-08
DE69911928D1 (de) 2003-11-13
DE69911928T2 (de) 2004-07-22

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