EP0138985A1 - Procede de moulage par pression utilisant des noyaux de sel et composition pour fabriquer des noyaux - Google Patents

Procede de moulage par pression utilisant des noyaux de sel et composition pour fabriquer des noyaux

Info

Publication number
EP0138985A1
EP0138985A1 EP84901655A EP84901655A EP0138985A1 EP 0138985 A1 EP0138985 A1 EP 0138985A1 EP 84901655 A EP84901655 A EP 84901655A EP 84901655 A EP84901655 A EP 84901655A EP 0138985 A1 EP0138985 A1 EP 0138985A1
Authority
EP
European Patent Office
Prior art keywords
core
process according
salt
bath
article
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.)
Withdrawn
Application number
EP84901655A
Other languages
German (de)
English (en)
Other versions
EP0138985A4 (fr
Inventor
Robert W. Foreman
Michael T. Ives
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.)
Park Chemical Co
Original Assignee
Park Chemical 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
Application filed by Park Chemical Co filed Critical Park Chemical Co
Publication of EP0138985A1 publication Critical patent/EP0138985A1/fr
Publication of EP0138985A4 publication Critical patent/EP0138985A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C33/00—Moulds or cores; Details thereof or accessories therefor
    • B29C33/44—Moulds or cores; Details thereof or accessories therefor with means for, or specially constructed to facilitate, the removal of articles, e.g. of undercut articles
    • B29C33/52—Moulds or cores; Details thereof or accessories therefor with means for, or specially constructed to facilitate, the removal of articles, e.g. of undercut articles soluble or fusible

Definitions

  • This invention relates to pressure molding proceses and particularly to a molding process utilizing a salt core or molding core made from a mixture of particles of inert material and relatively low melting temperature salt wherein the core is removed from the finished article by melting the core from the article with the core intact therein into a molten bath of the core material .
  • the cores are made by dip-coating or surface-coating solid sand cores in a molten salt bath or, alternatively, by mixing sand into a molten salt bath and casting the resulting liquid mixture into core form.
  • the patent discloses the removal of the core from the finished article by dissolving, flushing, and leaching out the core as a solute in water or in weak acid solution or by mechanical vibration.
  • our invention constitutes an improvement in the process disclosed in U.S. Patent No.
  • the core is removed from the article by melting the core from the article while the article is positioned over or in a fused or molten salt bath, the constituents of which bath are identical or substantially identical to those of the core itself. Quite unexpectedly, removal of the core at fusion temperature is accomplished readily and without adverse affect on the molded article. Immersion is carried out under bath conditions sufficient with respect to time and temperature to melt the core after which the article is removed, the re ⁇ sulting melted core being drained from the article back into the bath.
  • the core not only is recovered cleanly and efficiently out of the molded article * but, at the same time, is recovered into the molten mix thus replenishing the bath and enabling its further use in making additional cores.
  • Our method thus eliminates the need either for dissolving, or for mech- anical vibration, or for- separately recovering the core material, let alone the need for special apparatus to recover the salt from either acid or water.
  • the inven ⁇ tion also contemplates a preferred embodiment in which the bath, for melt-out purposes, is separate from the main bath and maintained at a different (normally lower e.g. 50 degrees F.) temperature so as to minimize the possibility of adverse effects on the molded article.
  • the core material used in the process comprises fusible salt and particles of inert material such as sand, especially foundry sand and aggregates, and may also include glass fibers, glass beads, carbon fibers, plastic fibers, metal fibers, calcium silicate, pumice, mica flakes, and similar inert particles affording structural strength (compressive, shear and tensile) to solid core material, and selected blends and mixtures of any such materials.
  • Sand is a preferred inert material either alone or in admixture with other inert material. In the following description, the inert material is sometimes described as sand but it will be realized that other inert materials may be used in place of or in admixture with sand for purposes of the invention.
  • the bath is originally constituted by melting a dry premixed combination of the inert particles and salt in the desired relative percentages and having the desired physical and process characteristics.
  • the single figure is a flow chart in block diagram form illustrating a preferred embodiment of the pressure molding process of the present invention.
  • the present process for making core-free (hollow) molded articles by forming a moldable material around solidified salt cores or mold cores made of particles of inert material intimately mixed and covered with fused salt comprising the steps of:
  • step 10 preparing a bath by means of mixing and heating (step 10) the particles and salt (step 12) to obtain a homogeneous molten bath mixture;
  • step 14 forming a mold core (step 14) of given shape from a portion of the molten bath mixture and cooling and solidifying the formed core;
  • step 16 pressure molding a moldable material (step 16) around the resulting solid core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core;
  • step 18 thereafter heating the molded article (step 18) positioned in or over the molten bath under temperature conditions sufficient to melt and recover the core from the article into the bath (bygravity flow with agitation if necessary) but insufficient to adversely affect the article thus freed of the core; and optionally washing (step 20) the article to remove residual salt and/or sand.
  • one uses sand as a core material.
  • one uses washed foundry sand that, with respect to particle size, is sufficiently fine for molding, preferably in the range of mesh sizes from 40 to 500, and more preferably from 80 to 100.
  • a low melting salt mixture which may comprise alkali metal nitrates, nitrites, chlorides, carbonates, sulfates and phosphates.
  • alkali metal nitrates and/or nitrites such as sodium and potassium nitrates and nitrites, optionally with one or more alkali metal chlorides. Eutectic salt mixtures are preferred.
  • the core material comprises one or more alkalizing salts or agents for strengthening purposes, not more than about 5% by weight, such as an alkali metal or alkaline earth metal hydroxide or carbonate, preferably sodium or calcium hydroxide. It is thought that the alkalizing agent serves to provide an advantageously strengthening chemical bond between the inert material and the fusible salt.
  • the core material may be anhydrous or may contain water in small amounts as, for example, ranging from 1 or 2% up to about 10% or more by weight.
  • low melting refers to salt mixtures selected such that, when constituted as intact mold cores in articles ready for melt-out to the molten bath, they can be melted out of the articles to recover the core material without adversely affecting the re ⁇ sulting core-free molded articles.
  • Preferred sand/salt bath mixtures are those melting in the range from about
  • the inert material and salt mixture may vary in its composition, preferably containing about 40 to about 60% by weight inert material.
  • the mixture as is hereinafter described in greater detail, is placed in a suitable heating vessel such as a commercial heat treating furnace and brought to a molten state for casting purposes.
  • the mixture is maintained in a relatively homogeneous condition by means of a mechanical agitator which may be selected from any of various types which are commercially available.
  • such cores are preferably made by casting the molten salt/sand mix using a hinged mold. Thereafter, the cores are used to pressure mold a mold- able material, such as a metal, or a thermoplastic or thermosetting filled or unfilled plastic, in a compres- sion molding or injection molding machine (for a discus ⁇ sion of suitable plastics and compression molding ap ⁇ paratus, incorporated herein by reference, see Plastics, 6th Ed., Van Nostrand, New York, 1981; Modern Plastics Encyclopedia, 1982-1983, McGraw-Hill, 1982).
  • a mold- able material such as a metal, or a thermoplastic or thermosetting filled or unfilled plastic
  • a barrier coating or slip aid to coat the salt core prior to molding.
  • the salt core is covered with a lubricating coating which will make for easier injection molding and a smoother surface and will prevent attack on the salt core.
  • a lubricating coating which will make for easier injection molding and a smoother surface and will prevent attack on the salt core.
  • Any of various coating materials are suitable such as silicones, paraffin waxes or heavy oils dissolved (e.g. 3-5% by weight) in mineral spirits, which after applying in a wet film and air drying leave a smooth hard dry hydrophobic surface.
  • the coating serves not only to provide a smoother better interior surface for the molded part but also to result in lower core breakage.
  • the cores may be used in a variety of forms of metal casting and plastic molding involving a wide range of temperature and pressure con ⁇ ditions.
  • a core that has a melt-out temperature sufficiently lower than the critical temperature, i.e. the softening point or degradation point, of the particular plastic being molded so that under the melt-out conditions employed the molded plastic article is not adversely affected.
  • the choice of core will vary from case to case but in general, for a typical melt-out cycle time, e.g. 2-5 minutes, will be such that the melt-out temperature is lower by at least about 50 degrees F. than the critical temperature of the plastic article undergoing core re ⁇ moval.
  • the core is suitably supported within the mold so that the mold material under compression essentially surrounds and captures the core and thereafter becomes structurally rigid.
  • the thus finished article with the core intact therein is immersed into, i.e., positioned within, the core source bath at step 18 for a time sufficient to effectively melt the core material out of the article and thus directly make up or recover said material back into the bath without the need for leaching or mechanical vibration or other recovery procedure.
  • the finished molded article with the core intact therein is positioned, not within the bath, but over the bath such that when the core is melted (by means presently to be described), the melted core ma ⁇ terial is allowed to flow and drop by gravity into the bath, thus recovering the core material for further ongoing operation.
  • heating of the article for melt-out of the core is done by radiant energy, preferably microwave heating in the zone above the bath.
  • radiant energy preferably microwave heating in the zone above the bath.
  • the molded article be- comes structurally rigid (that is, sets up or is hardened or cured or partially cured).
  • the molten bath (step 18), as indicated, or the mentioned microwave zone or its equivalent melt-out zone, is kept below the temperature which would unduly soften or melt or other ⁇ wise adversely affect the molded article.
  • the article is thereafter washed or rinsed, if necessary, at step 20 to remove all traces of salt or sand therefrom.
  • a small amount of sand/salt mix may be lost in the course of the process, although this amount is far less than would be lost or wasted if the cores were leached out or broken out and discarded. For example, there may be losses both in casting the core and by drag out between the immersion melt-out step 18 and rinse or wash step 20.
  • we mix dry sand and granulated salt and bulk- package the mixture preferably in small (e.g., 501b.) bags for shipment and storage.
  • one or more bags or partial bags of the premix advan ⁇ tageously may be added directly to the bath (step 12) for make up purposes or used to originally constitute the bath at start-up.
  • the invention and best mode of practicing the same are illustrated by the following examples.
  • Example 1 A dry premix is made by blending washed foundry sand (by weight 55 parts, 80-100 mesh, Wedron C-30 sand) and granulated salt (27 parts sodium nitrate, 18 parts potassium nitrate).
  • the resulting dry blended premix packaged in shipper bags (50 lb. capacity), is suitable for shipment and long term storage, without appreciable particle desegregation.
  • the premix melting at about 430 degrees F. can be used for making a molten salt bath operating at a useful working temperature of about 470-480 degrees F. or higher.
  • To a bath apparatus (jacketed resistance band heated steel pot, 15 inches deep by 15 inches in diameter) are added 100 pounds of the sand/salt premix.
  • the bath is heated to melt the premix and the molten bath mixture is maintained at a temperature of about 480 degrees F. and stirred with a heavy duty air motor agitator that keeps the sand uniformly suspended.
  • a split mold of rectilinear shape is used.
  • the mold of heavy aluminum, is of a design that can be quickly opened and closed by means of spring loaded quick release hinges.
  • the mold is jacketed with circulating pressurized hot (230 degrees F.) water.
  • the molten bath mixture is gravity fed to the mold by pouring from a preheated ladle into an opening (sprue hole) in the top of the mold.
  • the thus filled mold is allowed to cool for 20-25 seconds and is then opened and the molded core part removed and held for transfer to compression molding apparatus.
  • the molded core parts are uniform and very smooth.
  • the co pressive strengths at room temperature and 330 degrees F. are greater than 20,000 and 6,000 psi, respectively.
  • the cores can be remelted in 2 to 5 minutes at 475-480 degrees F.
  • a molded core part, prepared as described and maintained at 330 degrees F. is transferred from the core mold to the mold cavity of an injection molding machine.
  • Thermoset phenolic resin bead material (Resin RX660, Rogers, Co., Manchester, Conn.) at a temperature of 330 degrees F.
  • Example 2 A dry premix is made by blending
  • the resulting dry blended premix packaged in shipper bags (50 lb. capacity), is suitable for shipment and long term storage, without appreciable particle desegregation.
  • the premix melting at about 305 degrees F. can be used for making a molten salt bath operating at a useful working temperature of about 350-380 degrees F. or higher.
  • sand/salt premix 100 pounds of the sand/salt premix.
  • the bath is heated to melt the premix and the molten bath mixture is maintained at a temperature of about 350 degrees F. and stirred to keep the sand uniformly suspended.
  • a mold such as the mold described above is used.
  • the molten bath mixture is gravity fed to the mold by pouring from a preheated ladle into an opening (sprue hold) in the top of the mold.
  • the thus filled mold is allowed to cool for 20-25 seconds and is then opened and the molded core part removed and held for- transfer to compression molding apparatus.
  • the molded core parts are uniform and very smooth.
  • the compressive strengths at room temperature and 250 degrees F. are greater than
  • the cores can be remelted in 20-30 seconds at 350-380 degrees F.
  • a molded core part, prepared as described and maintained at 250 degrees F. is transferred from the core mold to the mold cavity of an injection molding machine.
  • a commercially available polyester resin bulk molding compound (BMC) at a temperature of 280 degrees F. and a pressure of 15,000 psi is then injection molded into the mold cavity and around the molded salt core.
  • BMC polyester resin bulk molding compound
  • the molded article polymerizes in the mold suf ⁇ ficiently to solidify and become structurally rigid.
  • the article with the salt core intact is then removed and immersed for 2 to 5 minutes in the salt bath mixture maintained at 350 degrees F. to melt the core. While immersed, the article is positioned to allow the core liquid to drain from cavities of the article, and the article is washed and dried.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

Procédé de moulage par pression d'un article autour d'un noyau moulé de sel durci provenant d'un mélange de sable et de sel à température de fusion relativement basse, où le noyau est retiré de l'article fini par immersion de l'article contenant le noyau dans un mélange de bain fondu du matériau de noyau afin d'extraire par fusion le noyau de l'article, de récupérer le matériau du noyau et ainsi de remplir le bain utilisable pour la fabrication de noyau supplémentaire. Le bain est formé au départ par la fusion d'une quantité appropriée d'un prémélange sec de sel et de sable.
EP19840901655 1983-03-28 1984-03-27 Procede de moulage par pression utilisant des noyaux de sel et composition pour fabriquer des noyaux. Withdrawn EP0138985A4 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US47758083A 1983-03-28 1983-03-28
US477580 1995-06-07

Publications (2)

Publication Number Publication Date
EP0138985A1 true EP0138985A1 (fr) 1985-05-02
EP0138985A4 EP0138985A4 (fr) 1987-11-23

Family

ID=23896515

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19840901655 Withdrawn EP0138985A4 (fr) 1983-03-28 1984-03-27 Procede de moulage par pression utilisant des noyaux de sel et composition pour fabriquer des noyaux.

Country Status (4)

Country Link
EP (1) EP0138985A4 (fr)
JP (1) JPS60500906A (fr)
CA (1) CA1226106A (fr)
WO (1) WO1984003857A1 (fr)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2613659A1 (fr) * 1987-04-13 1988-10-14 Peugeot Procede de fabrication de pieces rigides et creuses presentant ou non des contre depouilles
GB2246736A (en) * 1990-07-26 1992-02-12 Dunlop Ltd Removing a meltable core from a moulded plastics article by immersion in a heated salt solution
GB9016636D0 (en) * 1990-07-28 1990-09-12 Westland Aerostructures Ltd Method for making perforated composite laminates and moulds for use therein
FI922716A (fi) * 1992-06-11 1993-12-12 Harri Sahari Foerfarande i samband med framstaellning av plaststycken
US6245265B1 (en) * 1999-06-23 2001-06-12 International Business Machines Corporation Method of forming a die-castable hollow core actuator arm with improved damping
ATE496713T1 (de) * 2003-09-17 2011-02-15 Jun Yaokawa Kern zur verwendung beim giessen
JP5737016B2 (ja) * 2011-07-06 2015-06-17 スズキ株式会社 崩壊性中子、及びその製造方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1100359A (fr) * 1954-03-01 1955-09-20 Procédé de fabrication d'objets creux en matières plastiques et en particulier en plastique renforcé
GB828685A (en) * 1955-10-04 1960-02-24 Cole E K Ltd Improvements relating to the moulding of thermoplastic articles
DE1197195B (de) * 1962-08-31 1965-07-22 Union Carbide Corp Verfahren zum Ausschmelzen von Modellen aus Praezisionsgiessformen

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1523519A (en) * 1924-02-12 1925-01-20 Hartford Rubber Works Co Core or filler of fusible material for hollow vulcanizable articles
US3136831A (en) * 1961-07-14 1964-06-09 United Aircraft Corp Casting method
US3518338A (en) * 1964-06-08 1970-06-30 William C Tambussi Molding process
US3356129A (en) * 1964-06-30 1967-12-05 Schmidt Gmbh Karl Process of casting metals by use of water-soluble salt cores
US3692551A (en) * 1970-02-24 1972-09-19 Libbey Owens Ford Co Core for use in pressure molding
US4389367A (en) * 1981-09-30 1983-06-21 Grumman Aerospace Corporation Fluid molding system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1100359A (fr) * 1954-03-01 1955-09-20 Procédé de fabrication d'objets creux en matières plastiques et en particulier en plastique renforcé
GB828685A (en) * 1955-10-04 1960-02-24 Cole E K Ltd Improvements relating to the moulding of thermoplastic articles
DE1197195B (de) * 1962-08-31 1965-07-22 Union Carbide Corp Verfahren zum Ausschmelzen von Modellen aus Praezisionsgiessformen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO8403857A1 *

Also Published As

Publication number Publication date
EP0138985A4 (fr) 1987-11-23
JPS60500906A (ja) 1985-06-20
WO1984003857A1 (fr) 1984-10-11
CA1226106A (fr) 1987-09-01

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Inventor name: FOREMAN, ROBERT, W.

Inventor name: IVES, MICHAEL, T.