GB735355A - Improvements in or relating to the production of hollow sand cores for metal casting - Google Patents

Abstract

735,355. Core-making machines. SCHUELER, G. B. E. Nov. 19, 1953 [Dec. 16, 1952], No. 31890/52. Class 83 (1). A process of making hollow sand cores comprises suddenly blowing a sand-resin mix into a closed and heated mould. Mix is delivered to a measuring chamber 2 from a hopper 1 and discharged therefrom to a chamber 7, the supply being controlled by pistonactuated slide valves 3, 5. The lower end of the chamber 7 communicates by a neck 10 and sealing clamp 11 with an electrically-heated mould 12 comprising two parts 13, 14, communication being regulated by a slide 20 actuated by a jack 51. The slide has two ports 21, 22, the port 21 being associated with the chamber 7 and the part 22 with a suction pipe 23 so that excess mixture may be withdrawn after formation of the core, a plunger 25, actuated by a jack 27 through a lever system 26, controlling air vents 29 so that these may be placed in communication with the interior of the mould to allow extraction. The compartment 7 communicates with a supply of compressed air at 50-200 lbs. per sq. in. In order that the mould part 13 may be moved for ejection of a core, the clamp 11 is broken by rotation of a sleeve 31 through a link 35, helical grooves 34 engaging pins 33 on a tube 30 and causing axial movement thereof. In operation, pressure in the chamber 7 is built up and the port 21 then opened to allow the measured quantity of mix in the chamber to be suddenly blown into the mould. After an interval of time, port 21 is closed and port 22 opened to withdraw excess mix. At the end of a curing period the mould is opened and the core ejected. The mould may then be cleaned and lubricated, e.g. with silicone. A series of moulds may be mounted on a rotary table and brought in succession beneath the sleeve 31. In a modification the mix is in the form of a cartridge and shot by air pressure from a gun into the mould, the surface layer of the cartridge disintegrating under the pneumatic pressure. In a further modification the neck 10 is fed from two independent hoppers each having an associated measuring chamber and a pressure chamber. One hopper contains a mix with a relatively high proportion of resin to give a high grade finish, and the other a mix with a resin of poor quality or in smaller quantiy. The high quality mix is introduced first, excess withdrawn and the poor quality mix then introduced to form a backing layer. Re-inforcing elements of metal &c. or pins &c. for registering the core in the casting mould may be positioned in the mould and the core formed therearound. Core materials.-The particles of sand may have an individual coating of resin, applied for example by mixing the sand with a solution of the resin in a solvent and drying out the solvent, or by adding a resin solvent to the mix. Alternatively the sand-resin mix is hot rolled so that the resin just melts. After any of these processes the mix is reground and sieved. A small proportion of a lubricating agent such as calcium stearate, and a hardening accelerator, or both may be added. An exemplified mix comprises 6000 grammes of 100-mesh sand, 1944 grammes of resin solution, e.g. made from a stage A or B phenolformaldehyde, or urea formaldehyde, melamic formaldehyde, or cresol formaldehyde, 100 grammes of hexamethylenetetramine and 108 grammes of calcium stearate.