Metal founding – Means to shape a forming surface
Patent
1989-08-09
1993-03-02
Batten, Jr., J. Reed
Metal founding
Means to shape a forming surface
164228, 164412, 264 44, 264 60, 264122, B22C 700, B22C 2300
Patent
active
051900947
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a gas-permeable form tool for manufacturing casting and core moulds from hardenable moulding sand and a process for its manufacture and an expedient application of such tool.
Casting moulds from moulding sand find wide-spread utilization in the manufacture of metal mould-mass produced parts. In the manufacture, only single-use, expendable massive or dish-shaped moulds are used. To manufacture the casting mould a fine-grain moulding sand is provided with hardenable bonding additives, conveyed over a sand intake to a form tool and hardened there. Hardening is performed thermally--at high energy costs--or, recently, alternatively also by means of reaction gases which are pressed under pressure through the mould sand in the form tool. In accordance with the latter variant, gas is compressed into the sand at the sand intake and must exit from the form tool through bores, jets or other channels and openings mechanically applied to the wall of the form tool.
Pursuant to an execution known in the art (DE 24 03 199, DE 30 39 394), bores in the wall of the form tool are sealed on the outside of the mould by high-pressure valves. Such form tools are disadvantageous because of their high tooling costs. The valves frequently become plugged up by grains of moulding sand entrained by gas and must be cleaned. Above all, however, the wall of the form tool displays no homogeneous gas permeability characteristics with the result that the reaction gases are unable to homogeneously permeate the moulding sand, and as a result, the moulding sand does not harden uniformly. Core moulds can only be manufactured on a massive scale.
DE 30 02 939 describes a form tool having a wall into which ribs and slits of varying dimensions have been mechanically placed. Reaction gas entering the moulding sand through an intake is sucked off through the slits.
The slits, however, fill up with sand. Moreover, manufacturing is quite expensive and does not permit fabrication of a truly fine-meshed network of slits and bores. In this execution of a form tool, too, sand is only unevenly permeated by the reaction gas. Additionally, excessive amounts of reaction gas are consumed, that is, in far greater amounts than are required according to the stoichiometry of the desired reaction.
Calls have already been made for the manufacturing of the form tool from porous and gas-permeable materials.
Transformation of this request into reality has heretofore been unsuccessful owing to the technical difficulties, which were to be expected, inherent in transforming complex geometries of casting moulds in a form tool made of porous materials as well as the requirement of ensuring homogenous gas-permeability of the wall in the micro-range as well as its mechanical stability and of assuring, at the same time, that the moulding sand, when pressure charged with reaction gas, does not block the form tool pores or even exit through the pores of the form tool wand.
The purpose of the present invention is the production of a form tool having a homogenous gas-permeable wall even in micro areas. The aforementioned known methods and techniques are not suitable for doing this. More specifically, the purpose of the invention is to produce a heteroporous form tool by combining known techniques for the production of porous materials so that the form tool has adequate microporosity in the first region adjacent to the form and has a large porous supporting skeleton in the region adjacent to the first region. A form tool of this sort is suited to the production of casting moulds of forms in great numbers, particularly the production of non-massive casting moulds in the forms of shells. In accordance with this purpose, the surface of the form tool which comes in contact with the form sand has to be especially wear-resistant The blocking of pores by this form sand will no longer cause the form tool to fail. Pores which become blocked by form sand can now be regenerated, easily clearing and reopening the pores.
The task of devising a gas-permeable form tool is r
REFERENCES:
patent: 3101514 (1963-08-01), Callender et al.
patent: 3550673 (1970-12-01), Gallagher et al.
patent: 4291740 (1981-09-01), Michelson
patent: 4419413 (1983-12-01), Ebihara
Michelson, Anatoly, New Market for Large, Complex Porous P/M Parts HPM Corporation, Mt. Gilead, Ohio 43338, USA, 1987.
Giesserei Lexikon, by E. Brunhuber (1986), pp. 650-651.
Rietzscher, "Filtrieren von Eisenschmelzen", Giesserei 72, No. 20, (1985), pp. 571-576.
Batten, Jr. J. Reed
Sinterstahl GmbH
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