US2929120A - Method of definning sand cores - Google Patents

Description

March 22, 1960 o. w. BRANDT ETAL 2,929,120

METHOD OF DEFINNING SAND CORES Filed Dec. 4 1957 v INVENTORS Q 4;

ATTOA EV METHGD F DEFTNNING SAND (IORES Otto W. Brandt, Rochester, and Philip West, St. Clair Shores, Mich, assignors to General Meters (Iorporation, Detroit, Mich, a corporation of Delaware Application December 4, 1957, Serial No. 7%,583

4 Claims. (0. 22--194) This invention relates to preparing and cores for metal casting operations and more particularly to a method of removing fins formed on the surface of such sand cores during the production thereof.

A typical mold or core box used in making dry sand cores is formed of two halves. When the two halves of the core box do not mate accurately the inner surfaces of the core box which define the core-forming cavity are not uniform and continuous at the junction of the core box halves. A space or gap in these surfaces therefore exists adjacent the abutting edges of the core box half. During the core-blowing operation, sand accumulates in this space and forms a thin ridge on the surface of the core. The shape and size of this ridge depend upon the accuracy of the mating of the core box halves. Hence, excessive finning is found on cores made from poorly mated core box halves and on cores made in extensively used core boxes which have been worn into a poorly fitting relationship.

Generally, at least a small amount of finning occurs in the molding of most sand cores and a subsequent definning operation is usually necessary. Heretofore, it

has been customary in the art to remove fins from sand core surfaces employing slow, crude mechanical operations such as hand abrading or striking the fin with a suitable implement so as to break the fin from the core body. These methods of definning the core merely chip .away the fin and often leave a ragged portion of the fin. Moreover, these methods involve excessive handling of the cores, which often causes breakage thereof or damages the surface of the core so that it is unfit for use. In

addition, complex cores cannot usually be satisfactorily definned by these methods since some fins are in inaccessible recesses in the core. Prior to the present in- .vention, therefore, it Was necessary to produce complex sand cores with more costly precise techniques in order lto insure that excessive deleterious finning did not occur.

Accordingly, it is an object of the present invention to provide a method for rapidly definning sand cores and which reduces the handling and breakage thereof. An-

other object of the invention is to provide a method of definning sand cores which can be employed to defin complex sand'cores. A still further object of this invention is to provide an automatic method of definning sand cores ,by a low pressure sand blast.

Briefly, in accordance with this invention, fins on the surface of sand cores are removed by means of a low pressure sand blast treatment. A conventional sand blast nozzle is employed to direct a blast of sand under low air pressure upon the surface of a sand core substantially perpendicular to a major surface of a fin.

- Other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof and from ;the figures, in which:

Figure 1 is a somewhat schematic elevational view in 2,2,l2 Patented Mar. 22, was

Figure 2 is an enlarged fragmentary sectional view of a finned sand core during sand blasting; and

Figure 3 is a view similar to Figure 2 of a sand core 7 after the definning operation.

Sand cores are conventionally formed of a suitable mixture of sands derived from lake beds or from the shores of rivers, lakes, etc., respectively referred to as lake sand and bank sand. Typically, a mixture of 50% lake sand and 50% bank sand is used, although in some instances pure silica sand is employed. The sand is mixed in a dry condition with a suitable cereal binder such as corn meal, wood pitch, corn flour or the like. After the cereal binder has been homogeneously distributed throughout the dry sand, approximately 2% by weight of water is uniformly combined with the mixture. Thereafter, a core oil binder, such as linseed oil, corn, oil, soybean oil or hempseed oil is normally added and thoroughly blended into the sand mixture. The relative amounts of the binder and core oil can vary, and the specific proportions thereof are dependent upon the desired characteristics of the finished sand core. Generally, sand core mixtures consist, by weight, of approximately 2.0% to 3% water, 0.75 to 1.2% core oil binder, 0.75% to 1.25% cereal binder and the balance substantially all sand. A typical mixture which can be used comprises 2% by weight of water, 1% by weight of core oil binder, 1% by weight of cereal binder and the balance substantially all sand.

After mixing, the sand is compacted, usually by blowing, into the desired form in a suitable mold or core box. The core thus formed is then removed from'the core box and baked or cured at an elevated temperature for approximately one to three and one-half hours. Any fins which have been formed on the surface of the core are removed after the curing operation. In accordance with this invention a low pressure sand blast is directed onto the fin of the cured core, preferably at substantially right angles to the fin. It is preferred to direct the sand blast generally parallel to the adjacent surface of the sand core and at substantially right angles to the major surfaces of the fin being removed. By such action the sand blasting particles directly impinge on only the principal ex posed surface of the fin, thereby reducing the possibility of deleterious effects on the core surface itself. The sand blast is under an air pressure which is high enough to remove the fin, yet sufficiently low that abrasion of useful core surfaces is negligible.

The pressure to be employed in removing fins from sand cores primarily depends upon the hardness of the core surfaces which in turn depends upon the composition of the sand mixture. For example, sand cores having a relatively high proportion of binder and core oil will produce a sand core having a surface which is comparatively hard. A low proportion of these constituents in the sand mixture will produce a sand core having a surface which is relatively soft.

Referring more particularly to the drawings, Figure 1 schematically shows an apparatus which can be used to practice this invention. Sand in a storage hopper or magazine lit is conveyed to a standard sand blasting nozzlelzby a connecting conduit 14 which communicates with a port in a lower portion 16 of the hopper. Conventional sand blast nozzles are internally constructed to function as a jet pump. Compressed air, introduced into the nozzle by the attached hose 18, produces a partial vacuum in the nozzle which is used to draw the sand from the storage cabinet into the compressed air stream 20. The amount of sand being drawn to the nozzle can be varied by adjusting a slip collar 22 around the sand delivery conduit. The collar 22 covers an aperture (not shown) in the conduit 14 and can be adjusted to expose part orall of the aperture. Adjustment of the collar 22 affects the amount of air entering the sand delivery conduit and correspondingly affects the amount of sand drawn from the storage hopper It A cured sand core 24 is positioned on a suitable supporting rack 26 in a sand collection cabinet 27 in such a manner that the sand blast 21) is substantially at right angles to the fin 28 which is to be removed. The lower wall 30 of the sand collection cabinet 27 slopes downwardly toward its center to a sand collection aperture (not shown). A suction line 32 conveys the sand from a collecting device 34 in the aperture to the storage hopper 16. A jet pump 36 is attached to the line 32 to provide the required partial vacuum conditions to draw the used sand up the return line for recycling.

The impingement of a sand blast 26 on a fin 28 of a sand core 24 is shown in Figure 2. In most instances, superior results are obtained if the sand blast 20 is substantially at right angles to a major surface of the fin 28 and generally parallel to the adjacent surface of the core itself. Such action produces a substantially complete removal of the tin, such as shown in Figure 3.

The limiting ranges of the air pressure employed for the sand blast are critical and the specific preferred air pressure is dependent upon the hardness of the core surface, the thickness of the fin, etc. Usually, the highest air pressure which can be used is dependent upon the hardness of the core and can readily be identified by a pitting of the core surface. In most instances the definning can be accomplished satisfactorily with an air pressure of two to six pounds per square inch when using silica sand. A sand blast under an air pressure of four pounds per square inch is generally preferredfor definning most sand cores.

This method of definning sand cores can readily be adapted to a continuous and automatic operation, such as required for modern high production of materials. The sand core can be placed on a moving. conveyor and passed through a sand blast apparatus similar to that shown in the drawings. The sand core is automatically definned as it is carried continuously through the sand blast region. Although in many applications a single sand blasting nozzle can be used to remove the fins from a core, in some instances it is more advantageous to employ a plurality of sand blasting nozzles. A plurality of sand blasting nozzles can be strategically located in a sand blast cabinet so that each is eifectively directed to defin a particular part of the core as it passes through the sand blast region.

This method is further applicable to definning sand cores other than those made in the conventional manner hereinbefore described and, for example, may be used to defin some shell mold sand cores. A shell core is a relatively thin-walled hollow structure made from a mixture which consists essentially of sand and a thermosetting resin binder. The molding material generally used is a dry mixture comprising a major proportion of silica sand and a minor proportion (1% to by weight) of the thermosetting binder. Phenol formaldehyde and melamine formaldehyde resins are typical examples of the type of thermosetting resin binder used. The sand employed is preferably free of metal oxides, clay moisture and organic matter.

A shell molded sand-resin core can be produced by a method such as disclosed'in United States Patent No. 2,688,780 in the name of Arthur I. Anderson. This patent teaches a method of making sand-resin cores which involves allowing the dry mixture of sand and resin powder to come into contact with the surface of a hot metal core box for a short period of time. A layer of the mixture adheres to the heated metal surface due to a plasticizing of the resin which entraps the sand with which it is intimately mixed. The resin is then hardened or thermoset to stabilize the mixture to accurately reproduce core box details.

The sand-resin mixture is blown into the heated core,

box under an air pressure of approximately 40 to 50 pounds per square inch where it adheres to the heated walls of the core box. The blowing is continued until a core wall of sutficient thickness is formed. A mold temperature range of approximately 250 F. to 450 F. is generally suitable although, in some instances, temperatures up to approximately 800 F. can be employed. In most instances, a temperature of approximately 350 F. appears to be satisfactory.

The blowing time may vary considerably, of course, but blowing times of a few seconds to about fifteen seconds have been satisfactorily employed. The actual blowing time which is to be employed frequently depends upon the desired wall thickness; hence, longer blowing times may be necessary to form cores having exceptionally thick walls.

Following the blowing operation a short time interval may be allowed for the thermosetting resin binder to set or plasticize in the core box, a period of time ranging from a few seconds to approximately one minute being appropriate for various applications. A build-up time in the order of about ten seconds is usually sufiicient to form core walls of satisfactory thickness, and oftentimes the setting of the resin will take place to a sufiicient extent during the short blowing period that an additional setting time is unnecessary. The core is then cured while still in the mold at a temperature between approximately 550 F. and approximately 1300" F. A satisfactory baking or curing of the core can generally be effected at a temperature of approximately 650 F. After the core has been cured in the mold, it is stripped therefrom, thus completing the operating cycle.

Aswith conventional cores, shell cores are generally made in a multi-piece core box, and hence fins are also frequently found on the surfaces of shell cores. These fins can sometimes be removed by employing a relatively low pressure sand blast directed at substantially right angles to the surface of the fin. As hereinbefore mentioned, various factors will determine the optimum air pressure which can be employed in the sand blast. However, for most shell mold sand-resin cores, an air pressure of approximately two to six pounds per square inch has provided satisfactory results. In general shell mold sand cores are efiectively definned by a sand blast under an air pressure of approximately four pounds per square inch.

In most applications of this'invention a conventional sand blast nozzle, such as those known in the art, can be employed. Typically, a conventional sand blast nozzle having an outlet orifice of inch in diameter is particularly suitable.

It-is understood that although this invention has been described in connection with certain specific examples thereof, no limitation is intended thereby except as defined in the appended claims.

We claim:

1. A method of removing a fin projecting from a sand core which comprises directing a sand blast under an air pressure of about two pounds per square inch to about sixpounds per square inch substantially perpendicularly against a major surface of a fin projecting from a cured sand core and generally parallel to the surface of said core from which said fin projects.

2. A method for the continuous and automatic removal of fins projecting from a foundry sand core which comprises placing a cured sand core on a conveyor and moving. said sand core through a plurality of sand blasts which are under an air pressure of about two pounds per square inch to about six pounds per square inch wherein each of said sand blasts is directed to impinge substantially perpendicularly against a major surface of a fin and generally parallel to the surface of said core from which said fin projects. 7

3. A method of making a dry sand core which comprises the steps of compacting a mixture of sand, water,

core oil binder and cereal binder in a suitable core box to form a core, removing said core from said core box, baking said core at an elevated temperature, and thereafter directing a sand blast under an air pressure of about two pounds per square inch to six pounds per square inch substantially perpendicularly against a major surface of a fiin projecting from said sand core and generally parallel to the surface of said core from which said fin projects to thereby remove said fin from said core.

4. A method of making a foundry core which comprises the steps of coating 21 hot metal pattern with a mixture of sand and thermosetting resin, allowing said mixture to remain in contact with said hot metal pattern for a sutficient time to plasticize the resin and accurately reproduce pattern details on the sand core, heating said core at an elevated temperature which is suflicient to convert said resin to a thermoset condition, removing said sand core from said heated pattern, and thereafter directing a sand blast under an air pressure of about two 6 v, pounds per square inch to six pounds per square inch substantially perpendicularly against a major surface of a fin projecting from said sand core and generally parallel to the surface of said core from which said fin projects to thereby remove said fin from said core.

References Cited in the file of this patent UNITED STATES PATENTS 554,473 Beeg Feb. 11, 1896 999,485 Carolin Aug. 1, 1911 1,503,586 Hileman' Aug. 6, 1924 2,448,316 Lesavoy Aug. 31, 1948 2,483,956 Workman Oct. 4, 1949 2,507,390 Wallace May 9, 1950 2,618,109 Miller Nov. 18, 1952 2,688,780 Anderson Sept. 14, 1954 FOREIGN PATENTS 935,149 Germany Dec. 29, 1955

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