US2420003A - Temperature control mold - Google Patents

Description

May 6, 1947. R. J. MILLER TEMPERATURE CONTROL HOLD Filed Sept. 14,- 1942 IN VEN TUR.

. f i 0. i3 v wf/0% 0%.V O 0 u i A Patented May '6, 1947 uNi'rEo STATE TEMPERATURE CONTROL MOLD l Raymond J. Miller,

direct and -mesne assignments, to

Detroit, Mich., asslgnor, by

Miller Engl neering Corporation, Detroit, Mich., a corpo.V

ration of Michigan Application September 14, 1942, Serial No. 458,265 i 20 Claims.. (Cl. 22-113) This invention relates to the art of casting and more particularly to a simple and economical mold to control the transfer of heat from molten alloy or metal to delay solidication of lighter molten sections, land to accelerate the solidiiication of heavier molten sections to reduce undesirable effects of shrinkage strains caused by the heavier sections of the casting solidifying and attempting to draw metal from lighter sections of the casting already solidiiled.

Cooling of a casting begins immediately upon the molten alloy or metal being poured into a mold, and when the temperature drops to a predetermined degree the molten alloy or metal solidies to form the casting. Solidication of molten alloy or metal is accompanied by shrinkage or a reduction inlvolume due to contraction of the space between molecules of the alloy or 4 metal upon passing iromva liquid to the solid state.

The period of time required for molten alloy or metal to solidify depends upon the rate of heat transfer therefrom. Where the casting has sections of varying volume, the period of time required for solidiiication depends upon 'the ratio of the area of the cooling surface of the mold to the volume of the casting, and is influenced by the rate of heat transfer over various sections of the mold.

In the formation of castingshaving sections of varying contour, the lighter moltensections have a greater ratio of surface area to volume in contact with the mold cavity than do the heavier sections. The thinner sectionstherefore cool more rapidly and will solidify while the heavier sections o f the casting are still molten.

In castings having light or thin sections between heavy sections and the feeder, the thin sections tend to solidify while the heavy sections remain molten. As the thin sections jell or solidify they form a pointof anchorage for the molten alloy or metal and also cut oi the heavy sections from the shrinkage compensating supply of molten alloy or metal from the feeder.

The supply of molten metal or alloy in the pensating for shrinkage. Whensolidication oi the heavierr sections of the casting occur shrinkage strains of considerable magnitude are set up in the casting because of the isolation of the heavier sections from the supply of molten alloy or metal to maintain the mold completely lled.

In order to prevent shrinkage strains in castings it is desirable that the feeder be accessible v to and remain in communication with the ventire casting tosupply molten alloy or metal to maintain the mold completely filled with alloy or metal until the entire casting has completely solidified. This may be most easily effected by controlling the cooling of the casting lto cause 'all sections of the casting to cool progressivelyv remote from the shrinkage com-v` from points pensating supply of metal in the feeder chamber towards said chamber. A continuoussupply. of molten alloy or metal'will therefore be available at all times to maintain the mold. completely iilled and prevent the introduction ofshrinkage strains caused by one portion ofthecasting attempting to draw metalv from surrounding solidied portions.

To obtain this desirable progressive cooling in castings having varied contours and eliminate the undesirable eiects of shrinkage strains it is Anecessary `to dissipateheat more rapidly from the larger or thicker sections and to retard the. transfer of heat from the thin or lighter sec y tions.

When molten alloy or metal is poured into a mold to form a casting, an envelope or skin is formed on the outer surface of themolten substance by contact with the air or gases within the mold. If themolten alloy or metal is poured f into the mold slowly and ata substantially con.

feeder chamber to compensatefor reduction in stant rate theenvelope 'or skin can be progressively expanded to surround the entire casting and maintained throughout the ,entire .castinguntil the solidification occurs substantially pro.. gressively or uniformly over the entire casting.

This envelope ori skin formed on the outside of the molten'alloyjA orVv metal contacts the surface of the mold cavity and is maintained v during cooling of the molten alloy or metal. The resulting casting face free from roughness due to a breaking-of the surface skin or. envelope. By yeffectively maintaining the feederopen until the entire has a ne textured smooth: surf 3 casting solidiiles, a more solid casting having higher physical properties 4less susceptible lto warpage results. y I

In the so-called Capaco process of casting as disclosed in Patent No. 2,201,037, issued May 14, 1940, plaster is used as the mold body. During the formation of the plaster mold an excess of moisture is present and the plaster mold is there- 'after subjected toa drying process whereby virformed of low heat conducting material particularly of the so-called plaster type. -Varies almost in direct proportion to the external surface area of the mold to the unit volume of the casting to be formed. By .increasing the ratio of external surface area to the volume of the mold cavity over the. thicker or heavier sections of the casting the rate of heat dissipation may be accelerated. Likewise by reducing the ratio of the external surface area to fthe volume of `the mold cavity the rate of heat dissipation from the thinner portions of the casting may be retarded.

No means has heretofore been available to vary e l 35 bers in a desired spaced relation to form a mold the rate of heat transfer from castings formed in. low heat conducting materials suchas plaster molds. The use of the so-called plaster molding process has therefore been limited to objects having substantially uniform cross section or objects wherein shrinkage strains caused by uneven cooling of various sections of the castings would not be unduly objectionable. In order that this process may be used in the casting of articles having varied cross sections it is necessary that some means be available to' compensate for variation in thickness of the sections of a casting to permit progressive cooling of all sections of the castirisr towards the point of feed.

My copending application, Serial No. 455,862, led August` 24, 1942, discloses a plaster mold wherein the ratio of the external surface area of the mold is substantially proportionate to the volume of the mold cavity throughout. These temperature control molds may be formed between a pattern of the article to be cast and a contour forming member for the external surface of the mold. An external mold contour'forming member must of necessity be made for each article to be cast. .While excellent results can beaccomplished by the use of that method, the expense involved in making the mold former is disproportionately high where only a few castings of an article are desired. j

An object of this invention resides in the provision of a simplified plaster mold forming member to facilitate the formation of plaster molds having external surface area substantially proportionate to the volume 'of the mold cavity throughout.

Another object of the invention is to provide a plaster mold forming member having movable pegs adapted to be positioned in varied spaced l relation to a pattern to form a plaster mold having a substantially lproportionate ratio of external surface area to the volume of mold cavity. Y:

may be controlled to provide substantially pro- 6 gressive cooling towards the 'feeder over' the entire area of the casting.

Another object of the invention resides in the provision of a simplified method for controlling the rate of heat transfer from a casting by accel- 10 erating the rate of heat transfer from thicker or heavier sections and delaying the rate of heat transfer from thinner or lighter sections of the casting.

A further obj ect is to provide a relatively porous mold having a progressively decreasing ratio towards the feeder, of external surface area to the volume of sections of varying contour of the casting to be formed to control the rate of heat transfer from molten alloy or metal to give progressive cooling towards the feeder.

Yet a still further object ofthe invention 'residesin the provisipn of a low heat conducting mold having' an apertured surface toincrease the external surface area and hence therate of heat g5 transfer of portions of the mold surrounding thicker or heavier sections of the casting.

Yet another object resides in the provision of an economical method of forming temperature control mold sections having cooling surface area proportionate to the cross section of castings throughout to control the'rate of heat transfer from sections of varied contour. A further object is to provide a simple and emcient method of lholding aperture forming memhaving varied surface area.

Another object is to provide av plaster temperature control mold formed of low heat conducting material having a substantially constant 40 volume of mold forming substance throughout to permit moisture 'to escape uniformly over the mold surface to insure substantially uniform drying of the mold.

' Other objects and advantages of this invention will be apparent from the following detailed descripticn consideredin connection with the accompanying drawings, submitted for purposes of illustration only, and not intended to define the scope of the invention, reference being had for 5o that purpose to the subjoined claims.

In the drawings wherein similar reference characters refer to similar parts throughout the several views:

Fig. l is a sectional view of a typical article to be formed.

Fig. 2 is a sectional View of a pattern for forming the article of Fig. 1 having a temperature con..

trol mold former superimposed thereon.

Fig. 3 is a sectional view of the temperature control forming mold for making a plaster mold having variable external surface area to provide different rates of heat transfer' over various portions thereof.

Fig. 4 is a plan view of the former illustrated in Fig. 3. n Fig. 5 is a sectional view of a temperature control plaster mold having a casting therein.

Fig. 6 is a sectional view illustrating a modified form of holding mechanism for the recess forming members.

l Fig. 7 is a fragmentary plan view of a mold embodying recesses of a different shape.

Fig. 8 is an elevational view showing a tapered recess forming member.

Il Referring now to the drawings. Fig. 1 is illusaxially extending anges 24 on a hub member 28..

The hub and rim are interconnected by a plu.. rality of radially extending spokes 28 of relatively small cross sectional area in proportion to the cross sectional area of the rim 22. The ratio of the volume to the externalsurface area of the rim 22 and anges 24 of the article 28 is much greater than the ratio of the volume .to the ex' ternal surface area of the spokes 28. The ratio' of the B. t. u. or heat content of large molten sec-y tions in proportion to the area of the mold cavity is therefore higher than the B. t. u. or heat content of the smaller molten sections in proportion to their area in contact with the mold cavity.

In the casting of the article 28, such' as the flywheel, a feeder would preferably be positioned at one side of the rim 22 to supplymolten alloy or" metal through'the rim 22 and spokesl 28 to the hub 26.

If no means are provided for controlling the rate of heat transfer from themolten alloyv or metal of which the casting is formed, the. spokes 28, having greater external surface area in proportion to the B. t..u. or heat content of their molten metal will be subjected to more rapid cooling and will reach the solidification point before the rim 22 and hub member 28 wherein the ratio of the B. t. u. or heat content to the mold cavity is considerably higher.

After the alloy or metal forming-the spokes 28 cools to a substantially predetermined point it will jell and solidify and the flow of molten alloy or metal to the hub 28 will/be cut off. As the mass of alloy or metal forming the hub 26 solidifies it shrinks or contracts and attempts to draw metal from the spoke ,forming sectionsV 28.

Since the supply of molten metal to the hub y 28 is effectively interrupted by solidiflcation of the alloy or metal forming the spokes, shrinkage of the hub 28 upon solidication results in a force being exerted to draw metal through the spoke forming segments and shrinkage strains of con siderable magnitude result. The resulting casting is not homogeneous or solid' and does not possess the desired degree of strength. The casting is pre-stressed and is susceptible of warping, and in any ensuing machining operations or use whereby strains would be relieved, further warping results.

Flg. 5 illustrate a temperature control mold 38 having upper and lower sections 32 and 34. The mold 38 is Vpreferably formed of a low heat conducting porous moldable substance, or a substance such as plaster susceptible of being rendered porous after being formed.

The rate of heat dissipation of such material by radiation is almost directly proportional to the ratio of the external surface area of the mold to the volume of the mold cavity.

The cooling effect of the mass of the body portion of a low heat conducting material such as aA the casting at any point.

In order t'o effect uniform cooling of sections of varied volume of the article to be cast in the mold 88, the ratio of the heat radiating surface of the mold should substantially be in direct propor-l v tionto the volume of the articie' to be cast. By

progressively decreasing the ratio of the external mold surface to the volume of the moldjcavity heavier portions towards th'e feeder progressive cooling towards the point offeed may beI accomplished. j

Controlled cooling may thus be effected whereby all parts of the casting cool progressively towards the feeder, and the feeder and the lighter sections of the casting are maintained open until l the heavier or thicker sections of the casting solidify. Since a constant supply of molten metal is' available from the feeder, shrinkage of the metal will merely draw more molten alloy or metalfrom the shrinkage compensating feeder ch'amber and shrinkage strains will be eectively avoided.V

y Whne the meid a0 may be formed of upper and f trol mold 38 may, for example, be formed with a-plurality of relativelyciosely spaced recesses or apertures 88 terminating close to the sections of largervolume of the article28, such as around the rim 22- and flanges 241mg over the hub 28 respectively, to increase the ratio of the external surface area of the mold Ato the volume of the mold cavity to permit rapid transfer of heat from these portions of the heavier sections of the casting. The recesses 36 should terminate a sufficient distance from the article to be castv to provide the moldV with sufficient strength to adequately support the alloy or metal 48 poured into the mold 38 to form the article 28.

The mold 38 over the spokes 28 may be relatively thick and provided with fewer recesses lor area to the volume of the mold cavity to produce substantially uniform or progressive cooling of the casting.

The size of the mold 38 is dependent on the size and contour of thearticle 28 to be cast, the amount of heat to be dissipated from the alloy. or metal of which the article 28 is formed 'Il'he rate of heat conductivity of thesubstance of which the temperature control mold 38 is formed, the rate` of heat transfer from the surface of the mold 38 to the atmosphere and other factors.

The lower section 34 of the temperature control 4mold 38 may be supported during the casting operation at its edges to permit air to circulate freely into the apertures 38. If the article being formed is so large that the mold could not be supported at its edges it may be supported on a suitable framework or' on downwardly extending feet or flanges positioned to underlie the of thearticle to be cast.

' The upper section 32 of the mold 38 may be formed with a riser and feeder member 42, The feeder'and riser forming member 42 is formed with a feeder'chamber `44 to supply molten alloy or metal through a passageway 46 to compensatefor shrinkage of the casting. The feeder 44 7 is surrounded by a suitable mass 46 of the substance from which the mold 30 is formed to decrease the-ratio of external surface area to volume of the mold cavity at this portion to prevent solidication of alloy or metal in'the feeder The sections 32 and 34 of the temperature con..`

trol mold 30 may be formed between male production patterns of the article. to be cast .and suitable contour forming members superimposed on the pattern. J v

As illustrated in Flg. v2, a male production pat#- tern 50 is suitably attached to a flask 52 having side wall members 54. The flask may be of any desired contour such as round, rectangular, etc., to accommodate the pattern 50, A cover plate 56 having a plurality of spaced apertures 66 therethrough may be superimposed on the side walls 54 of the flask 52, and may be located in` a predetermined angular relation thereto able dowelpins 60.

The apertures 58 may be of uniform size and may Vbe closely spaced as illustrated in Fig. 4, and are adapted to receive vertically movable members or pins 62 adjustably mounted therein to vary the distance from the bottom ends. 64 of by suitthe members or pins relative to the cover plate Any suitable means may be provided to maintain the members 62 in any vertically adjusted position relative to tl'e plate 56. An apertured I `a l i ing ofthe casting may belcontroiled by varying the height'l of the lower 'ends 64 of the plnl l2 above the pattern I.4 For example, the mold Il over the heavier sections 22. -24 and 24 ofthe article 2l to be cast, mayhave many closely spaced apertures 66 terminating close to the mold cavity. The mold Il` over the lighter or' thinner sectims 26 of the article to be cast may have relatively few apertures 36 terminating a greater distance from thevmold cavity toreduce the ratio of the surface area to the volume of the mold substance and delay the transfer of heat from the lighter porl tions of the mold.

' After the recess forming members 62 have been adjusted vertically to vary the external mold surface to accelerate the transfer of heat from heavy sectionsof the casting and to retard the transfer of heat from the light sections of the casting, the

v mold forming substance may be introduced inw resilient sheet 66, such as a sheet of rubber, may

be attached to the cover plate 56 to engage the pins 62 and hold them in any vertically adjusted Position to which they are moved.

Ring springs 61 positioned in slots 69 in the plate 56 may also be' employed to engage the recess forming members 62 to hold them in any vvertically adjusted pOsition to which they are moved as illustrated in Fig. 6. y

The recess forming members62 may be of any desired contour in cross section to provide recesses of varied configuration such for examplesas the' hexagonal recesses 1| illustrated in Fig. 7.' As illustrated in Fig. 8 the recess forming members 13 may be tapered to provide the mold surface with varied external surface area. and to facilitate the dissipation of moisture and heat from the mold during the drying of the mold vand the cooling of the casting.

In the formation of the sections of the mold 3U. any suitable mold forming substance such as low heat conducting plaster may be introduced into the space Within the flask 54 to cover the pattern 50 to a desired height on the pins 62. The cover plate 56 may be assembled on. the iask 52 having the pattern 50 therein. lThe pins 62 may then be pushed downwardly into contact .with the surface of the pattern 50. The cover plate -56 maythen be elevated and a spacer 68 interposed betweenl the side walls 54 of the ilask andthe cover plate 56 to elevate the lower ends 64 of the pins 62 a predetermined distance above the surfaceof the pattern 50. Spacers 68 of different thickness may be provided for use in forming temperature control molds for various articles.

'Ihe ratio of the external surface area to the volume of the mold cavity and hence the rate of coolthe flask through an opening 1l, airbeing permitted to escape through another of these openings. The quantity of plaster or other mold forming substance employed is dependent on the nature and size of the casting to be formed, the rate of'heat transfer, etc..

The portions pr the pins or pegs 62 projecting into the mold forming substance may be coated with any suitable parting material 12 to facilitate.

separation of the pe'gsfrom the mold forming substance.

If desired the lcover piste n and the resilient sheet 64 may be transparent to such an extent as to enable the molder to observe the position of the lower ends 64 of the pins 42 relative to the pattern '54. Where the pins 42 are of uniform length the outline of the pattern' 6l will be reproduced at the upper ends of the pins 42 projecting above the cover plate 56 to aid .the molder in making the necessary adjustments. The diameters of the pins may be varied if desired to give more definite control of the external surface area of the mold.

The composition of the plaster or other moldA forming substance is preferably such as to fornia relatively porous mold structure whereby gases formed during the casting operation and entrained air may readily escape through the body of the mold. `This relatively porous plaster mold structure may be achieved by initially mixing the plaster forming ingredients with somewhat of an excess of moisture and .thereafter drying the mold to drive of! virtually all of the moisture.

The mold 30 is preferably such as to adequately supPOrt the casting when poured but does not possess suilicient strength to resist the forces to which -it is subjected when the casting shrinks upon solidication. shrinkage of the casting may, therefore, crack or break` up the mold and thus avoid the introduction of shrinkage strains within the casting. Y

'I'he upper section 32 of the mold 3l may be interlocked with the lower mold section 34 by means of circumferentially extending interlocking Y iianges 14, and the sections 32 and 34 may be held together by means of suitable clamps 14.

In the casting of an article 2li in the temperature control mold 3l, molten alloy or metal 4l is introduced through the opening in the feeder positioned at any convenient place as at one side or in the middle of the mold. The molten alloy or metal 46 hows through the controlled gate 46 into the space within themold Il and completely mls the space within the mold 3l. Y

Gases formed upon contact of the molten alloy or metal 4l with the internal surface of the mold The upper and lower sections 32 and 34 of the mold 30 dissipate heat from the molten metal 40 v substantially uniformly over the entire area of the casting. The increased external surface area of the mold due to the presence of the recesses or holes 36 coupled 'with the sections of relatively thin mold section over heavy portions of the casting permit rapid dissipation of heatffrom the heavier sections of the casting, and the walls of the mold having less apertures tend to retain the heat in the thinner sections of the casting, such, for example,as the spokes 28.

Virtually the entire casting cools progressively or simultaneously. The controlled supply gate 48 and the feeder chamber 44 provide an ample supply of molten metal to compensate for contraction of metal upon solidiiication. Thethinner spoke forming sections remain molten during cooling of the heavier sections andv all parts of the casting solidiiies progressively towards the feeder or simultaneously.l

' If desired, air may be circulated over the mold f .sections to assist in the dissipation'of heat from the mold. The cooling air may be controlled as to direction to subject only a portion of the mold 30 to the cooling action, to give more accurate and positive control over the cooling of the casting. The temperature of the air directed over thevmold 30 may'also be controlled-to producel the desired cooling of various portions of the casting f to insure uniformcor progressive solidiflcation of the casting.

When a plaster mold is subjected to a drying l action the entrained moisture in the mold is transferred to the surface ofthe mold by capillary attraction, and it is transferred to the atmosphere from the Vexterna1 surface of the mold. Largemasses of solid plaster delay the transfer of moisture to the surface, whereas small sections or sections having a larger ratio of surface Aarea to volume readily transfer moisture to the surface for dissipation tothe atmosphere. In molds having wide variation in sections, unequal drying action results andthe lighter or thinner sections are'likely-to become burned and crack before the heavier-,orthicker sections have had an oppor-A mberor the-depth o f the tions .v of theqarticle t0 be seglofjfa -suilcientL number of iermold sections, positioned to during they drying v operation'.` Uniform drying of the mold may thus beeffected-and since these recesses v'are formed in' the mold forming vsubstancetheyihave a` desirable effect on dissipation of heatfromfthefcasting. g Accurate control of the dissipation Vof-.heat'from thecasting may thus Ifclaimry v l. Atem Vrature control'mold forming member comprisinga .ask having a ,patternthereim f a plate superimposedforithewfiask'and having a plurality of closely spacedapertures therein,

`a. plurality of recess forming members movably mounted in said apertures, andresilient means to maintain the recess forming members in any ad.- 5 justed position.

2. A temperature control mold forming member comprising a plate having closely spaced apere' tures therein, members extending through and movable in the apertures, and resilient means to l0 hold the members in any position to which they may be moved.

3. A temperature control mold forming member comprising a ask having a. pattern therein, a plate superimposed on the flask andv having a,

plurality of closelyspaced, apertures therein, a

plurality of pegs extending through said apertures and movable relative to the plate, and resilient means associated with the plate to hold the pegs in any adjusted position to which they may be moved. .Y

4. A temperature control mold forming member v comprising a plate having closely.Y spaced apertures therein, pins extending through andl movable in the apertures, and resilient means carried 5 by the plate to hold the pins in any vertical position to which they may be moved.

5. A mold formingl member comprising a flask having side Walls, a pattern detachably connected to the flask, a, recess forming member `supporting plate carried bythe side walls of the ask, locating means between the plate and ask, a plurality of spaced vertically movable recess forming members carried by the plate, resilient means to hold- -the recess vforming members in any adjusted position, a spacer adapted to be interposed between the flask and the plate', and locating means associatedI with the spacer to maintain alignment between the flask and plate.

6. The method of making a temperaturey con- 40 trol mold comprising superimposing on a pattern of an article to be cast a member having closely spaced movable recess forming members,l adjusting vthe recess forming'members to contact the surface of the pattern, separating the recess forming members from Ythe pattern by introducing a spacer beneath the member, withdrawing recess forming members over light sections of the .casting, and applying to the exposed surface of the pattern and pins a substance capable of being rendered substantially porous to provide a mold having a substantially constant ratio of external surface area to the volume of the article to-be cast.

7. The method of forminga temperature -control mold for castings having varying contours comprising superimposing on a pattern of the article to be cast a plate having closely spaced vertically movable pegs, adjusting the pegs vertically relative to the pattern in proportion to `variations of volume of the casting, and introducing plaster, around the'pattern anddownwardly projecting ends of the pegs to form a temperature control mold having large external surface area surrounding heavy sections of the article to be cast and relatively less externalsur..

' face area over lighter sections of the article to be cast.

8. The method of making a plaster temperature'controlmold comprising superimposing on a pattern of an article to becast a plate having closely spaced adjustable recess forming members, adjusting the recess lforming members t0 contact the surface of the pattern, separating the recess forming members from the pattern by introducing a spacer beneath the plate, withdrawing recess' forming kmembers over light sections of the casting,. applying plaster to the exposed surface of the pattern and recess forming members to form a temperature control mold having a ratio of surface area to volume substantially prosuperimposed on the frame to form spaced re cesses in the external surface of the mold, manually operable means to selectively vary. the spacing of the recess forming members'from the pattern, and means to hold the recess forming members in'any adjusted position.

10. A mold former comprising a flask having a pattern therein, an apertured plate having mold recess forming members superimposed on the pattern to form spaced recesses in the external surface of the mold to reduce the ratio of the mass of the mold forming substance to its external surface `area throughout to facilitate the transfer of moisture to the surface of the mold and accelerate drying of the mold, means to selectively vary the spacing of the recess forming members from the pattern, and means to hold the recess forming members in any adjusted position.

11. The method of forminga non-permanent mold formed of low heat conducting material comfprising superimposing on a' pattern a moldcontour former having closely spaced parallel `mold recess forming members of generally circular cross-section for shaping the external surface of the mold to provide a mold forming space sub- `stantially in inverse proportion to the volume of sections of varying contour of the casting to be formed, lling said space with a low heat conducting mold forming substance, separating the mold from the pattern and contour former, and

thereafter drying the mold.

12. A non-permanent temperature control mold formed of low heat conducting material to prevent the formation of shrinkage strains in a casting having a feeder and sections of varying cross-sectional area, the external surface area of the mold being contoured with closely spaced generally circular recesses extending substantially perpendicularly to the external surface of the mold so arranged as to dispose the mass ofI the mold material substantially in inverse proportion 'to the cross-sectional area of the casting throughout to vary the rate of the dissipation of heat by conduction from sections l of varying cross-sectional area of the casting to prevent the formation of solidified sections betweenthe feeder and a portion of the casting.

y 13. A non-permanent mold formed of low heat conducting material for forming a casting having sections of varying cross-sectional area comprising'a body portion havingran external surface provided with substantially perpendicularly extending generally circular recesses to .increase the ratio of the surface area of the mold to the mass of the mold forming substance to reduce the distance moisture must travel to reach the external surface of the mold to accelerate drying of the mold without introducing mold shrinkage strains.

14. A non-permanent temperature control mold formed of low heat conducting material comprising a. body portion having va casting cavity and including a substantially at external surface having a plurality of recesses of generally circular cross section extendinginwardly toward the casting cavity substantially pl'pendicularly to the ilat external surface ofthe mold so arranged as to` vary the mass of the mold forming material substantially in inverse proportion to the volume of sections of varying cross-sectional area of the casting to be formed.

15. A temperature control mold havinga casting cavity for the reception of molten alloy or metal to form a casting having sections of varying cross-sectional area comprising a dried mold formed of low heat conducting material having closely spaced recesses of generally circular cross section extending substantially perpendicularly from the external surface of the mold to points adjacent the castingcavity over sections of thel casting of large cross sectional area to increase the ratio of the external surface area of the mold -to the cross sectional area of the casting and permit the rapid transferv of heat from heavy portions of the casting, and spaced recesses extending substantially perpendicularly from the external surface of the mold to points progressively more remote from the casting cavity over sections of lthe casting of progressively smaller cross sectional area to progressively increase the ratio of the external surface of the mold t0 the cross sectional area of the casting but to a lesser degree than the recesses in the mold over the sections of the casting of greater cross section to retard the transfer of heat from light portions of the casting.

16. A temperature control mold having a casting cavity for forming a casting having sections of varying cross-sectional area comprising a body portion formed of low heat conducting material having closely spaced generally circular recesses extending substantially perpendicularly from the external surface of the mold toward the casting cavity to points adjacent the casting cavity where the cross-sectional area of the casting is large and to points more remotely spaced'from the casting cavity where the cross sectional area of the casting is small.

17. A non-permanent mold formed of low heat conducting material comprising a body portion having a casting cavity and a plurality of closely spaced parallel recesses of generally circular cross-section extending inwardly from the external surface of the mold toward the casting cavity to provide a honeycomb-like structure to reduce the mold forming material required and to facilitate the drying of the mold by reducing the distance moisture must travel to reach the surface of the mold to be expelled.

18. A mold former comprising a pattern, a housing surrounding the pattern. and a plurality of mold recess forming members carried by the said housing, said members being shiftable to Y selectively vary the heat dissipating qualities of the mold material.

19. 'Ihe method of making a non-permanen mold formed of moisture containing material, which comprises forming in said material, while itis still wet, a plurality of recesses to'control the heat dissipating properties of the material, remov- 13 bers in said material to different depths to form closely spaced heat flow paths therein overlying and extending along the casting cavity to regulate the lengths ofthe heat flow paths through said mold material and to vary the heat dissipatng properties of the mold in accordance with the spacing of the heat flow paths, and thereafter removing said members.

RAYMOND J. MILLER.

REFERENCES CITED The following references are of record in the ille of this patent:

Number Number UNITED STATES PATENTS Name Date Lee Sept. 25, 1928 Pack Apr. 29, 1919 Lee 'Sept. 25, 1928 Candler Nov. 22, 1927 Sipp July 31, 1928 Sweetnam Oct. 23, 1917 FOREIGN PATENTS Country Date British 1912

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