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
  • B22C1/16—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
  • B22C1/20—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 of organic agents
  • B22C1/22—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 of organic agents of resins or rosins
  • B22C1/2233—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 of organic agents of resins or rosins obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • B22C1/224—Furan polymers
• • 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
  • B22C1/10—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 influencing the hardening tendency of the mould material

Definitions

• the present invention relates to furan resin-based binder systems to be used as binders mixed with sand or similar granular substances for the production of moulds or cores for use in foundries.
• binder systems for foundries normally consist of two or more components which are mixed with sand or similar granular substances so as then to form the cores or moulds around which or into which the molten metal will then be poured.
• Typical binder systems are those of the polyurethane type, for example, normally consisting of a hydroxyl component, a polyisocyanate and a catalyst. Such binder systems are described in the following documents, for example: US-3,409,579; US-3,676,392; US-3,485,797; WO 97/05447 and WO 00/40351.
• no-bake furan binder systems dates from the 1960's and they are still used extensively, being described, for example, on pages 30-34 of the publication "No-bake core & molds" issued in 1980 by the American Foundrymen's Society, incorporated here for reference purposes.
• These binder systems consist of two liquids (furan resin and acid hardener) which, added to the sand, produce without the use of heat cores and moulds suitable for the production of ferrous and nonferrous metal castings.
• Furan resin consists substantially of furfuryl acid condensed to a greater or lesser degree with formaldehyde, modified where appropriate with urea, phenolic resins and various additives; furan resins which can be used in binder systems of the no-bake type are described, for example, on pages B320-6 to B320-15 of the publication "Manual of chemically setting sands", issued by the Centre Technique des Industries de la Fonderie in 1993, incorporated here for reference purposes.
• the acid hardener generally consists of one or more sulphonic acids in aqueous or hydroalcohol solutions and contains varying amounts of sulphuric acid.
• the sulphonic acids most frequently used are benzenesulphonic acid, toluenesulphonic acid, xylenesulphonic acid and cumenesulphonic acid. Of these, toluenesulphonic acid is by far the most widely used.
• Sulphuric acid generally present in small amounts in sulphonic acids as a residue of the sulphonation process, is in some cases added intentionally in very large amounts to the hardener to increase the acid energy and therefore accelerate the reaction of hardening of the binder system.
• Foundries are therefore faced with the problem of not exceeding benzene emission limits, a problem which is not easy to solve since bringing down the benzene contained in the air is much more complex than bringing down the sulphurous anhydride, for example.
• the invention on which the present patent application is based addresses and solves the problem just described with a binder system for foundry sands which can be used in processes of the no-bake type consisting of a furan resin and an acid hardener in which the arylsulphonic acid is completely or partially replaced by an aliphatic acid and by sulphuric acid.
• the invention provides for the use of aliphatic hydroxy acids and in particular of 2-hydroxypropionic acid (lactic acid) and/or of 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid).
• the presence of sulphuric acid serves to increase the acid energy of the hardener which is the subject of the present invention.
• the hardener which is the subject of the invention, coming into contact with the molten metal, does not evolve aromatic hydrocarbons or evolves a reduced amount of them, depending on the quantity of arylsulphonic acid which it may contain.
• the acid hardeners which are the subject of the present invention have the following composition by weight: a) water 10-50% b) sulphuric acid 0.5-40% c) aliphatic hydroxy acid 10-60% d) arylsulphonic acid 0-20% where the sum of the percentages of components a), b), c) and d) is 100 and the components are assumed to be pure.
• the water content is between 25 and 50% by weight
• the sulphuric acid content is between 10 and 35% by weight
• the aliphatic hydroxy acid content is between 20 and 50% by weight; according to a preferred aspect, the aliphatic hydroxy acid content is greater than 20% by weight and in any case not less than 22%.
• Arylsulphonic acid is preferably absent. If present, it must as far as possible not exceed 20% by weight so as not to negate the advantages deriving from the present invention.
• the aliphatic hydroxy acid is selected from lactic acid and/or citric acid; arylsulphonic acid, if present, is preferably toluenesulphonic acid.
• the hardener which is the subject of the invention is mixed with the sand together with the furan resin at ambient temperature to give the cores and moulds suitable for the production of ferrous and nonferrous metal castings; preferably, 100 parts by weight of silica sand or other refractory material are mixed with 0.2-0.8, preferably approximately 0.4-0.6 parts by weight of acid hardener and with 0.6-1.5, preferably 0.8-1.2 parts by weight of furan resin.
• ambient temperature is meant a temperature between roughly 0° and +40° C, preferably between +15 and +30° C, depending on the geographical position (latitude, altitude etc.) in which the foundry is situated.
• furan resins which are preferably used in the embodiment of the present invention are those already described on pages 30-34 of the publication "No-bake core & molds" already cited and on pages B320-6 to B320-15 of the "Manual of chemically setting sands" already cited, both incorporated here for reference purposes.
• the furan resin will have a content by weight of furfuryl alcohol of 60-80%, a nitrogen content of 1-8% and a water content of 5-20%; particularly preferred is a furan resin containing approximately 75% by weight of furfuryl alcohol, approximately 10% of urea-formaldehyde resin (corresponding to about 2% of nitrogen) and about 15% of water.
• Control mixture 100 parts by weight silica sand LA32 0.4 parts by weight hardener 1.0 parts by weight GIOCA NB 2F resin
• GIOCA NB 2F resin is the commercial designation of a furan resin obtained by condensation of furfuryl alcohol, formaldehyde and urea, marketed by Cavenaghi SPA.
• This resin has the following composition:
• Standard +GF bars were prepared with the above-mentioned mixtures.
• the flexural strength of these bars was measured after 3, 5 and 24 hours from the time of discharging the mixture from the mixer; the results obtained are given in the following table: Hardener Setting Flexural strength in kg/cm 2 after Start Finish 3 hours 5 hours 24 hours 1 30' 49' 9 17 23 2 18' 29' 9 11 16 3 17' 29' 14 16 17 4 25' 37' 13 17 19 5 17' 23' 20 23 25

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Mold Materials And Core Materials (AREA)
• Catalysts (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=34430766

Family Applications (1)

Country Status (4)

Cited By (22)

Citations (5)

• 2003
  • 2003-11-14 IT IT002217A patent/ITMI20032217A1/it unknown
• 2004
  • 2004-11-11 EP EP04105709A patent/EP1531018B1/de not_active Not-in-force
  • 2004-11-11 DE DE602004020568T patent/DE602004020568D1/de active Active
  • 2004-11-11 AT AT04105709T patent/ATE428520T1/de not_active IP Right Cessation

Patent Citations (5)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events