US3208118A

US3208118A - Method and apparatus for metal casting

Info

Publication number: US3208118A
Application number: US156300A
Authority: US
Inventors: Henry H Harris; Daniel S Eppelsheimer
Original assignee: HARRIS
Current assignee: HARRIS
Priority date: 1961-12-01
Filing date: 1961-12-01
Publication date: 1965-09-28
Anticipated expiration: 1982-09-28

Description

p 1965 H. H. HARRIS ETAL 3,208,118

METHOD AND APPARATUS FOR METAL CASTING Filed Dec. 1, 1961 DAN/EL g ippsz SHE/ME? ATTO R N EY United States Patent 3,208,118 METHOD AND APPARATUS FOR METAL CASTTNG Henry H. Harris, 6 Accoloy Way, Champaign, 111., and

Daniel S. Eppelsheimer, Rolla, Mo.; said Eppelsheimer assignor to said Harris Filed Dec. 1, 1961, Ser. No. 156,300 Claims. (Cl. 22-215) The present invention relates generally to improvements in molding methods and apparatus, and it relates particularly to an improved method and apparatus for the casting of metal.

In accordance with the conventional metal casting practice, the molten metal is poured into a mold by way of an inlet gate or channel and flows therethrough substantially to fill the mold cavity. The speed of the casting procedure and the detail and precision or fidelity of the final casting is a function of, among other parameters, the flowability of the molten metal. A low degree of flowability results in low fidelity and loss of detail, the casting fidelity and detail increasing with fiowability. The flowability of the molten metal, particularly in the case of iron, steel and many of the ferrous alloys is generally considerably less than would normally be expected from the fluidity or viscosity of the molten metal with the consequent lowering in the casting precision.

It is, therefore, a principal object of the present invention to provide an improved molding method and apparatus.

Another object of the present invention is to provide an improved method and apparatus for the casting of metal.

Still another object of the present invention is to provide an improved method and apparatus for the casting of oxidizable molten metals characterized by an increased fidelity and speed of casting.

The above and further objects of the present invention will become apparent from a reading of the following description taken in conjunction With the accompanying drawing, in which the figure is a longitudinal sectional view of a metal casting mold in accordance with the present invention.

It has been discovered that the fiowability of an oxidizable molten metal which has been exposed to an oxidizing ambient atmosphere is radically increased by contacting the surface of the molten metal with a material which releases hydrogen when it is heated by such contact with the molten metal to a predetermined temperature. It is believed that upon exposure to the atmosphere normally encountered in the casting of metal, an atmosphere containing oxygen and steam, the surface of the molten metal is oxidized to form a substantially continuous skin which is an oxide derivative of the molten metal and has a surface tension. The skin envelops the molten metal and greatly impedes the flow thereof and hence decreases its flowability. As a consequence, by reason of the flow-restricting nature of the enveloping skin, many of the mold depressions and recesses are not reached by the molten metal, and the result is an inaccurate casting of low fidelity and lacking in detail. By disposing and locating the heat-responsive hydrogen-releasing material along the path of flow of the molten metal in the mold, the hydrogen released upon contact of the material with the molten metal reduces the oxide skin, thereby to rupture the skin and free the molten metal from the flow restricting effect of the skin envelope. The molten metal, being relieved of the impeding properties of the high surface tension skin, thereupon flows freely, commensurate with the fluidity and viscosity of the molten metal, to fill the various mold recesses and Patented Sept. 28, 1965 depressions, even those of small cross-section, to produce a superior, accurate casting of high fidelity and true detail.

The temperature-sensitive hydrogen-releasing reducer material is advantageously applied as a thin layer or coating to the surface of the mold cavity, along the gates and in the cavity itself, along the path of flow of the molten metal. The reducer material may be applied as strips, in localized areas, or as a continuous coating. The reducer material should be stable at room temperature and at temperatures substantially below that of the molten metal and should also be stable in the ambient atmosphere normally encountered in and about the metal casting molds and particularly in the presence of steam and water. A highly satisfactory temperature responsive hydrogen releasing agent has been found to be calcium hydride. However, by reason of its instability in the presence of water or Water vapor, it is carried or dispersed in a hydrophobic vehicle which permits the release and escape of the hydrogen evolved from the reducing agent upon contact with the molten metal, thereby to counteract its instability. A vehicle which has been found to be highly satisfactory is a natural or synthetic rubber dissolved in a volatile organic solvent. The calcium hydride is preferably in a finely divided state and uniformly dispersed in the rubber base vehicle. The vehicle-carried reducing agent may be applied to the desired areas of the mold in any suitable manner such as by spraying, brushing, or the like.

In place of the calcium hydride, other compounds or mixtures thereof may be employed which evolve hydrogen upon the heating thereof to a temperature somewhat less than that of the melting point of the molten metal being cast, and which are stable at still lower temperatures and at room temperature. The hydrogen generating temperature of the reducing agent is preferably such that the hydrogen is not evolved far in advance of the molten metal but when in contact with the molten metal, the radiant heat being inadequate to initiate the release of the hydrogen under normal conditions. Examples of temperature-responsive hydrogenevolving compounds are various of the metal hydrides as well as other materials which are well known and readily ascertainable. Where the reducing agent is unstable in the presence of moisture, it is carried in a suitable protective vehicle as aforesaid, other suitable vehicles being, for example, a suitable synthetic, advantageously hydrophobic, resin such as polyethylene or the like dispersed or dissolved in a volatile organic solvent. The carrier or vehicle may desirably be a non-aqueous fluid material conventionally employed in the coating of mold surfaces.

Alternative methods of associating the hydrogen-releasing reducing agent with the mold and exposing it to the molten metal include forming the reducing agent with or without a binder into small pellets which are located in the mold in advance of the pouring of the molten metal, encapsulating the reducing agent in shells which are ruptured by the heat of the molten metal to expose the reducing agent, and contacting them with the poured molten metal or floating them in the molten metal, or otherwise injecting the reducing agent into the mold so that it is actuated by the molten metal and acts in the manner previously described.

The annexed drawing illustrates a conventional type of mold treated in accordance with the present invention. Reference numeral 1 generally designates the assembled mold which includes a cope 2 and a drag 3 which are provided with corresponding connected flasks 4 and 5 respectively. Cope 2 and drag 3 have registering recesses formed therein which define the mold main cavity as at 6. A funneled, vertical gate 8 is formed in the cope 2 and communicates with the main cavity 6. The mold 1 may be produced in any known manner, of packed sand and a suitable binder, or other refractory mold composition.

In accordance with the present invention, the surface of the mold cavity 6 is provided with a thin coating of the heat-responsive hydrogen-evolving composition of the type earlier described. The hydrogen-evolving coating may cover the complete surface of the cavity 6 or may be applied along spaced areas 9 suitably located on the cavity surface. The areas 9 may be of suitable size and shape whereby to rupture the molten metal oxide skin at or preceding those sections of the mold where maximum metal flowability is required or desired. These areas may be at isolated spots, in the form of longitudinally, transversely and peripherally extending bands or of other shapes. In addition to the main cavity coated areas 9, gate 8 may be similarly coated either uniformly and continuously, or along areas 10 which may be similar to the areas 9.

When a molten metal which normally acquires a flowimpeding oxide skin, for example iron, steel or ferrous alloys, is poured into mold gate 8, it comes into contact with the reducing agent-coated surface of gate 8 to eifect the evolution of hydrogen therefrom which reduces any oxide skin which has formed on the surface of the adjacent molten metal or inhibits the formation of such skin in these areas. As a consequence, the molten metal flows freely along gate 8 without restriction by an enveloping skin. Similarly, the molten metal flows through the main cavity 6, likewise contacting the reducing agentcoated surface of main cavity 6 to effect the evolution of hydrogen and the consequent rupturing and inhibiting of the formation of any flow-restricting skin on the molten metal. The molten metal thus completely fills the various recesses and depressions in the surface of the mold cavity to produce a casting of high fidelity.

While there have been described and illustrated preferred embodiments of the present invention, it is apparent that numerous alterations, omissions and additions may be made without departing from the spirit thereof.

4 What is claimed is: 1. In the casting of molten metal in a mold wherein "said metal in its flow into and along said mold is exposed to an oxidizing ambient atmosphere promoting the formation of a flow-retarding oxide skin on said molten metal, the step comprising applying to a surface of said mold along the path of said flow of molten metal a metal hydride.

2. The method according to claim 1, wherein said metal hydride is carried in a hydrophobic vehicle.

3. The method according to claim 1, wherein said metal hydride is calcium hydride.

4. A metal casting mold having located on and carried by a surface of the cavity thereof along the path of the molten metal therein a heat-responsive hydrogen-releasing substance consisting essentially of a metal hydride.

5. A mold according to claim 4, wherein said metal hydride is disposed along the surface of the gate of said mold.

References Cited by the Examiner UNITED STATES PATENTS 910,564 1/09 Monnot 22189 1,235,071 7/ 17 Sodervall et al. 22-215 2,264,003 11/41 Osenberg 22-202 XR v 2,376,518 5/45 Spence 22-215 XR 2,682,092 6/54 Henricks 22-2165 2,830,342 4/58 Meyers et al 22216.5 2,874,038 2/59 Ruhenbeck et al. 7559 2,979,392 4/ 61 Fiedler et al.

FOREIGN PATENTS 106,489 2/ 39 Australia. 1,222,495 1/ France.

627,083 7/49 Great Britain. I 800,321 8/58 Great Britain. 811,814 4/59 Great Britain. 867,387 5/ 61 Great Britain.

WILLIAM J. STEPHENSON, Primary Examiner, MARCUS U. LYONS, Examiner,

Claims

1. IN THE CASTING OF MOLTEN METAL IN A MOLD WHEREIN SAID METAL IN ITS FLOW INTO AND ALONG SAID MOLD IS EXPOSED TO AN OXIDIZING AMBIENT ATMOSPHERE PROMOTING THE FORMATION OF A FLOW-RETARDING OXIDE SKIN ON SAID MOLTEN METAL, THE STEP COMPRISING APPLYING TO A SURFACE OF SAID MOLD ALONG THE PATH OF SAID FLOW OF MOLTEN METAL A METAL HYDRIDE.