US2908054A - Method of and means for casting metals under the influence of vacuum - Google Patents

Description

Oct. 13, 1959 Filed March 3, 1958 w. G. WILKIN METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUM TSheets-Sheet 1 Inventor WILLIAM G. Wuxms J agys.

1959 w. G. WILKINS 2,903,054

METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUM Filed March :5, 1958 7 Sheets-Sheet 2 I 1i J! Jr J I, 1F JV Jr J I M it 1? JF l JF'Jl '1 IF I J[ J[ JF J] Il 41F ll JP J l y Q O 2' Inventor WILLIAM G. WILKINS O 2 @05 w ag Oct. 13, 1959 w, w s 2,908,054

METHOD OF AND MEANS FOR CASTING METALS UNDER 'THE INFLUENCE OF VACUUM Filed March 3,. 1958 7 Sheets-Sheet 3 wmmnl A g ,7

entor WILL G. WILKINS Oct. 13, 1959 w, w K s 2,908,054

METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUM Filed March 3, 1958 7 Sheets-Sheet 4 Inventor WILLIAM G. WILKINS b ,:..1..-.,@;;w ;m J

Oct. 13, 1959 'w.,c-z. WILKINS 2,908,054

ma'mon or AND. MEANS FOR CASTING METALS UNDER THE INFLUENCE OF? VACUUM I Filed March :5, 195a 7 Sheets-Sheet 5' -m, Gwfiwm 0515 N 6% days 1959 ,w. e. WILKINS 2,903,054

- METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUM Filed March :5. 1958 7 Sheets-Sheet 6 jae/aay 13m, 625m. #M f fa @zzawzm Oct. 13, 1959 w, w 2,908,054

, METHOD OF AND MEANS FOR TING METALS UNDER THE INFLUENCE VACUUM Filed March 3, 1958 7 Sheets-Sheet 7 "ISO H56 I v United States Patent 9 METHOD OF AND MEANS FOR CASTING METALS UNDER THE INFLUENCE OF VACUUM William G. Wilkins, Chicago, Ill., assignor to Universal Castings Corporation, Chicago, Ill., a corporation of Illinois Application March 3, 1958, Serial No. 712,182

Claims. (Cl. 22-73) The present invention relates generally to casting, especially of metals, and more particularly to a new and improved method of casting and apparatus by means of which the method can be practiced.

The invention finds particular, though by no means exclusive, utility in precision casting as is frequently employed in forming devices embodying cored openings of arcuate or irregular shape, those having extremely thinwalled portions, and those from which no substantial metal removal by machining is to be subsequently efiected. In conventional practice the material to be cast is first heated to a temperature well above its melting point and is introduced into a mold by way of a sprue opening which is connected to the mold cavity by Way of a runner,

provision being made to vent the mold cavity and to incorporate risers and shrinkheads to insure filling of the cavity and by providing additional metal to compensate for shrinkage during cooling. By way of example, in the casting of aluminum the temperature is initially raised to approximately 1600 F. so as to obtain desired fluidity. This extremely high temperature has been found necessary in conventional practice where castings having thin- Walled sections are to be made. In the casting of such devices by conventional methods only about one-third of the metal poured is utilized to form the casting per se, the remainder going into the runners, risers, shrinkheads, and sprue openings. Furthermore, under conventional practice at extremely high temperatures required, it has been found that up to 70% of the castings so formed had to be scrapped because of incomplete filling of the mold cavities and because of high porosity which results in poor physical properties, primarily with regard to tensile strength. Investigations have led to the belief that as a result of the requisite high temperature required to obtain the required fluidity, there is a substantial increase both in the occlusion of gases and-in oxide formation. X-ray pictures indicate such porosity as literally hundreds of interstices of voids. Further, the incomplete formation of the edges of remote portions of castings made under conventional practice is believed to be caused by the incomplete removal of air and other gases from remote portions of the mold cavity.

Accordingly, it is a general object of the present invention to provide an improved method of casting'by means of which the above-mentioned difliculties are substantially eliminated.

rapid and economical practice, and whereby the initial temperature to which the metal to be cast need by raised is only slightly above its melting point so as to achieve the 7 It is a related object to provide a method of casting metals permitting" of more complete filling of the mold cavity with the molten cast- 2,%8,54 Patented Oct. 13, 1959 castings are obtained.

Another and equally important object of the invention is to provide apparatus by means of which the new and improved method of casting can be practiced for producing ferrous as well as non-ferrous metal castings.

The objects or" the invention thus generally set forth, together with other objects and ancillary advantages, will become apparent as the following description proceeds taken in conjunction with the accompanying drawings, in which:

Figure 1 is an elevation of a casting apparatus embodying features of the present invention and by means of which the novel method can be practiced.

Fig. 2 is a top plan view of the apparatus shown in Fig. l.

Fig. 3 is a vertical section taken in ofiset planes along the line 3-3 in Fig. 2.

Fig. 4 is a bottom plan view of the top plate of the apparatus shown in the preceding figures.

Fig. 5 is a bottom plan view of a typical top mold' section.

Figs- 6 and 7 are perspective views of castings of complex form which havebeen successfully made through the practice of the instant invention.

Figs. 8 and 9 are central vertical sections taken through a casting like that shown in Fig. 7, the former being made by conventional practice and the latter according to the present invention. These figures comprise reproductions of actual photomicrographs.

Figs. 10 and 11 are vertical sectional views similar to Fig. 3 but illustrating modified forms of apparatus embodying features of the present invention.

Figs. 12 and 13 are elevation and plan views, respectively, of a further modified form of the apparatus as employed in casting metals having an extremely high melting point, such as ferrous metals.

Figs. 14 and 15 are elevation and plan views, respectively, of yet another modified form of apparatus embodying features of the present invention.

Fig. 16 is a bottom plan view of the vacuum plateshown in Figs. 12, 13, 14 and 15.

Fig. 17 is an enlarged vertical sectional view along the line 1717 in Fig. 12.

Fig. 18 is a fragmentary perspective view looking upwardly at the underside of a modified form of clamping preferred embodiments, but it is to be understood that is is not thereby intended to limit the invention to the specific forms disclosed, but it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

Referring more palticularly to the drawings there is shown a casting apparatus embodying features of the present invention which comprises generally a mold 20, including an upper section 2011 and a lower section 20b, mounted between-a bottom supporting plate '22 and a top clamping plate 24. As shown, the two mold sections are arranged to meet in a flat parting plane as indicated at 25, and may be equipped with positioning dowels 25 (Figs. 3 and 5). The mold sections have formed in their contiguous faces appropriate recesses which define tion as at" 39' to any suitable means (not shown) for raising and lowering, the upper plate into and out of engagement with the top mold section 20a. The top plate h'asa collared'opening 40' therein which is adapted to receive an annular ceramic insert 42 and hold same in registry with the sprue opening 32 in the top mold section 20a whereby to direct the molten material to be cast from a ladle or the like (not'shown) into the mold 20.

To direct a ladle or the like into proper position for pouring its contents into the open endof the ceramic insert 42 in the top plate 24, a V-shaped guide 44 is provide'd. The guide, as shown, is formed of ordinary angle-iron sections 44a held in rigid relation by means of' a cross strip 44b welded thereto.

The guide 44 is mounted on the top plate'24 over the spider 38, in such a position that its legs extend outwardly to include therebetween the collared top plate opening 40'.

The present invention contemplates casting under the influence of vacuum indirectly applied to the mold cavity. This is to the end that air and other gases are positively removed from the cavity and the molten material to be cast is drawn from the sprue opening and runner into the cavity against the walls thereof even in the most remote regions of the cavity. More particularly, it is content plated that evacuation of the mold cavity is to be efiected through the walls of the mold that define the cavity.

Thus there is a complete removal of air and the like from the cavity and a drawing of the material being cast directly. against the cavity walls where it is held until solidification. Itwill be seen, therefore, that the cavity is qui'clsly'filled and complete filling is assured with the result that the necessary initial temperature of the casting material need be only slightly. above the meltingpoint thereof. ducedeven in such far reaches of a complex cavity as define knife-thin cast sections. As a result of the lower casting temperature porosity is minimized and shrinkage is substantially reduced. These'things both contribute markedlyto a high yield percentage of good sound castings for the quantity of castingmarterial poured.

In carrying out the invention molds formed of porous ceramic material are utilized and the'cavities therein are subjected to an indirectly applied vacuum. That is to say, vacuum is applied exteriorly of the mold, and the cavities therein are evacuated through the walls thereof by virtue of the porous character of the material of which the mold sections are formed. This positively and completely evacuates the mold cavity, eliminates the time and necessity for air or the like trapped in remote regions thereof to be absorbedby the mold, and the molten material introduced into the cavity is drawn quickly against the walls thereofr In the form of the invention illustrated in Figs. 1-5,.

inclusive, of the drawings, the mold 20 is formed of a One 65 gredients substantially in the following proportions by porous'ceramic material such as molders plaster. suitable form of such plaster comprises the following in- For use the plaster is mixed with water in adequate amount to obtain the desired molding consistency. This plaster will set in a comparatively short time and is in-.

Further, completely formed castings are proplaced in superimposed relation on the bottom supporting;

. 4 hibited against cracking. Subsequent to the setting of the plaster, green mold sections a and 2% are removed from their molding boxes and are heated in a suitable oven to a suitable temperature for a sufficient time to cure them and to remove a cavity forming material if such was used.

The mold sections 20a and 2012, thus formed, are then plate 22iandithe top plate 24-is lowered into clamping engagement therewith.

In the present instance, the cavities 28' of the. mold '20 are evacuated by subjecting the mold to a vacuum applied to the top surface of the mold section 20a so as to withdraiw air and other gases from the cavities-28 and to draw the molten material being cast against the cavity walls. As shown, the top plate 24 is formed Witha wafile-iron-like lower surface so as to define a pattern of interconnected passages 46 over substantially theentire upperfsurface of-the. upper mold section 20a; To provide communication between these interconnected passages and a vacuum pump, the top plateis' provided:

with an opening 47which is suitably adapted. for the reception of a fitting '48 for accommodating a vacuum.

hose 49.

The wafile-iron-like formation of. the underside of the top plate 24 "is preferable to a singleuniform cavity formation, which might be used, because the topplatc serves. not only as the medium for the application. of

'vacuum to the mold 20, but additionally. through theoperation of :tlieolamping means, includingthe spider 38, to. apply a clampin'gforce to the mold 2.0 so as to main- The wafiie-iron-like formation provides feet or pads 50 distributed over the entire top surface of the top mold section 20aso' as to.

uniformly; apply the clamping pressure thereto. Thus, the. mol-drsections 20a and 2% are firmly held together so as to minirriize.leakage into the mold cavities 28 between the mold sections 20a and 20b along the parting plane 25.

To further insure the application ofvacuum to the mold cavities 28 and to further minimize leakage top plate 241s equipped with suitable knife edges which are'adapted to bite. into the relatively soft upper surface of the top mold section 20a.

for the reception of knife-edged inserts 51. The inserts are suitably sized for press-fitting into the grooved under:

surface. oftop plate 24 and project downwardly there-f by way'of the porous walls of the mold 20. This particular construction is advantageous, too, in that it readily" perm-its replacement of the knife-edged inserts-51 and 52 ifthey should becomedull or damaged.

From the foregoing it will be seen that when molten metal or other material is poured into the funnelled open end of the ceramic liner. 42 which is received within the'collared opening 40 inthe top clamping plate 24 and into the sprue opening 32 in the top mold section, it isimmediately drawn along the runner 30 into the mold cavities 28 and against the walls. of thelatter by the-vacuum indirectly-applied thereto to the top mold section 20a:

In Figs; 6-9, inclusive, there of. impellers, generally denoted 60'and 62, as illustrative of the type of complex precision cast products. which have been successfully made by the practice ofxthe'present invention. Both of these deviceszare'of' a form makbe precision madebecause they areintended for rotationat. extremely high speds thereby'requiringgthatlhey; be

7 Thus, adjacent the marginal edges of the underside thereof, the top plate 24 is suitably grooved are shown: two. forms.

dynamically balanced. Figures 8 and 9 are central longitudinal sections taken through impellers of the type shown in Fig. 7, and comprise reproductions of actual photomicrographs. The impeller section shown in Fig. 8 was made by conventional practice wherein the aluminum alloy of which the device was fabricated was heated to an initial temperature of substantially 1600 F. introduced into a mold and permitted to cool. The section shown in Fig. 9 was made by the practice of the present invention and with aluminum alloy from the same original melt but heated to any initial temperature of only 1275 F. and introduced into apparatus such as that herein before described and shown in Figs. 1-5. The relatively high porous character of the casting section shown in Fig. 8 is at once apparent. In Fig. 9, however, the casting section there shown is homogeneous and substantially free of voids.

In Fig. 10 there is shown a slightly modified form of the apparatus embodying features of the present invention. Where practical, identical reference characters have been utilized in the description of these modified forms as have been utilized in connection with the form of the invention shown in Figs. 1-5, inclusive. In this device the mold 20 comprising the mold sections 20a and 20b and the top clamping plate 24 are identical with the preceding form. In this form, however, not

only is avacuum indirectly applied to the mold cavities- 28 by directly applying the same to the top surface of the upper mold section 20a, but in addition a vacuum is applied uniformly over the bottom surface of the bottom mold section 2012. Thus the device shown in Fig. 10 is equipped with a bottom supporting plate 26A which, like the top plate 24, has the upper surface thereof, which is engageable with the mold 20, made of waffle-iron-like form so as to provide a pattern of interconnected spaces or passages 66 and suitable supporting pads 68. a suitable vacuum hose connection 70 which communicates with the system of passages 66 by way of a port 71 formed in the bottom plate 26A in the outer end of which the hose connection 70 is received. This form of the invention tends to more quickly exhaust the mold cavities 28 and to draw the metal from the sprue opening 32 runner 30 and mold cavities 28 at a somewhat greater rate. It will be appreciated of course that shortly after the molten material to be cast is introduced into the mold the lowermost surfaces of the mold cavities, the sprue opening 32 and the runner 30 are covered by the molten material which substantially closes oif the outflow of air therefrom. This construction, however, reduces the time required to fill the mold completely by a substantial amount. Not only is the mold evacuated more quickly by way of the top section 20a and, initially, in conjunction with the evacuation by way of the bottom plate, but several additional advantages come about by this construction. Among the advantages is the fact that both mold sections 20a are held firmly against the contiguous plates thereby permitting of ready separation of the two mold sections by the action of atmospheric pressure on the adjacent sides of the sections as a result of evacuating the spaces behind the same. Of course, since the molten material to be cast covers the lowermost interior surfaces of the mold cavities 28 and the runner 30, the vacuum indirectly applied to the bottom mold section 2% has relatively little effect on the further exacuation of the mold cavities because the pores of the material of which the lower mold section is formed are in effect sealed off by the molten material. However, some evacuation is had by way of the interconnected pores around these surfaces. Thus, the hold-down action on the bottom mold section and the additional exhaust of the interior of the mold makes this construction not only practical but desirable as well.

The form of the invention shown in Fig. 11 includes The bottom plate 26A is equipped with a mold 20B comprising upper and lower mold sections defining mold cavities 28B disposed between a top clamping plate 243 and a lower supporting plate 26B. In this form of the invention, however, the molten material to be cast is introduced in the interior of the mold 20B by way of a. sprue opening 32B formed .in the lower section of the mold 20B'which is in registry with an opening 75 formed in the supporting plate 26B, the latter being lined with a suitable ceramic insert 76. The mold cavities 28B are connected with the opening '75 in the bottom section of the mold 20B by Way of a runner 30B.

In this instance it is intended that the molten material to be cast be drawn upwardly through the opening '76 in the supporting plate 26B and in the bottom section of the mold 20B and thence by way of the runner 30B into the mold cavities 28B by means of vacuum indirectly applied to the top section of the mold 20B. Thus the clamping plate 24B is also waffie-iro'n-like form, providing a pattern of-interconnected passages 79 which serve to apply a vacuum substantially uniformly over the upper surface of the top section of the mold 20B. The passages 79 are connected to suitable evacuation apparatus (not shown) by way of an opening 80 formed in the clamping plate 24B which is adapted to receive a vacuum hose connection 81.

While in the illustrative embodiments molds of general rectangular figuration have been shown for purposes of illustration, it will be readily appreciated that molds may be made of any desired shape-square, rectangular, oval, etc.and the upper and lower clamping plates in such cases will be fashioned to conform thereto. In each instance, along the outer marginal edges of the clamping and supporting plates and about the sprue openings in the molds there is provided a sharp depending flange or knife-edge 51B and 52B adapted to bite quite deeply into the contiguous mold surfaces so that when the mold is clamped therebetween a tight seal is provided between the contiguous plate and mold surfaces thereby insuring that the inflowing air into the plate passages is effected by Way of the pores of the mold section. In this way, with the plates so designed that vacuum is applied substantially uniformly over the entire contiguous mold section surface, the mold designer need have little concern when planning the mold as to location of the mold cavities so long as they are well within the dimensional limits of the mold.

As soon as the sprue opening in the mold is filled with the molten material to be cast which obviously occurs in an extremely short time, the application of vacuum to the mold insures an all-over pull on the mold cavities with the result that residual air and gases in the cavities are withdrawn, and any gases that might be occluded in the molten material to be cast, as well, are withdrawn. Furthermore, the necessity for the provision of large shrinkheads in the top mold section is eliminated, and shrinkage upon cooling can be accommodated by relatively smaller shrink reservoirs located in the bottom mold section. Furthermore, the volume of the runners can be substantially reduced. Thus, with the smaller shrink requirement and the smaller runner volume a substantially larger casting yield for the quantity of melt poured obtains.

Referring particularly to the form of the invention shown in Fig. 11 of the drawings, wherein the molten material to be cast is supplied upwardly to the bottom mold section 26B to the runner 30B, thence to the cavities 28B by the action of atmospheric pressure as a result of evacu ation of the interior of the mold, turbulance in the melt is substantially minimized, particularly as compared to that produced in the case of introduction of melt into a mold by direct pouring and under conventional casting methods.

The forms of the invention shown in Figs. 12-17, inclusive, comprise applications specially adapted for the casting offerrous metals which have an extremely high; melting pointas compared withaluminum, for example.

Such materials include both alloy and carbon steels, which metals must be raised 'toZSOO F." and upwards before melting occurs.

mounted iii depending relation from .the horizontal frame member 85 and a. piston :90 reciprocable Withinthecylinder: by. pressure fluid alternately entering-and leaving thecylinder throughopenings91z. Aclamping frame includingzvertically-disposed tie.-rods-92:and parallel upper andlower cross bars 94, .95, respectively, is rigidly connected at. thelower cross bare 95 to a: piston rod 96. extending.

downwardly from thespis'torr and cylinder 89, 90. As. will be seen; the tie rods 92 pass through suitable openings in thehorizontal frame member. 85 so that the upper crossbar 94 is spaced a distance: above the member 85 sufficient, to accommodate the mold 86'therebetween. In this way the clamping; frame is; adapted for up and down movement with respect to the mold86 as the piston 90 reciprocably traverses the cylinder 89.

In carrying out the invention themold 86, formed of suitable porous ceramic material, and the cavities 98 therein (Fig. 17) are subjected toan indirectly applied vacuum by means of an upwardly facing vacuum plate 99 disposed in mold supporting relation on the horizontal frame member 85. As will be seen, the mold 86 is se curely gripped between the vacuum plate 99 and the upper cross bar 94;when-the metal tobe cast is readyfor pouring.

Because the'hereinbefore described plaster-type moldmaterial' undergoes spalling in the melting temperature range of carbonand alloy steels, e.g. 2500 F. and up, it is necessary to provide an investment material which has the requisite high temperature refractory qualities and-yet is capable of being formed into a porous mold. One. form of such an investment material comprises the following ingredients substantially in the indicated portions by weight:

p Percent Powdered silica 1 40 Ethyl silicate 33 China clay -1 27 For use the above ingredients are mixed with water in an adequate amount to obtain the desired molding consistency. A characteristic of this molding material, however, is that after being mixed it must be heated to a temperature of about 2000 F. before setting up to permit handling. Y

Accordingly, provision is made for sustaining the form of the mold during curing thereof by completely encasing the investment material within a shell or sheath 100 which becomes a permanent part of the mold. With particular reference to Figs. '12 and 17, it will be seen that the illustrative shell 100 takes the formof an open end metal cylinder into, which the investment material is poured after mixing and which serves to completely enclose the mold material during both curing thereof and subsequent casting therein of molten metal; Thus, an empty cylinder 100 may be placed on a suitable flat base (notshown) and filled with'the formable wet investment material there being properly placed within the cylinder a suitablecavity forming materialor pattern. Insertion of the filled, cylinderv inanoven (not shown) maintained at approXimately.-2000 F. foriagsuitable time to curejthe mold material and to melt the cavity forming material if such was usedthenimparts a permanent setzto. the mold.

The 1 sheathed mold -.86' is then in condition t o ,be clamped in" positiomon the vacuumplate- 99 for 'admissionfthereto ofamolten metal.

Interposed between. the a topof the mold: 86 and the upper cross 'bar 94 is a top mold plate 10I having an open- 1 ing: 102 in registry with the mold sprue; opening I 104" whereby-4o dir ect the'molten metal to be cast from a lippour ladle or the like (not shown) into the molds Thus,- th e cavities 98 0f the mold 86' are evacuated bysubjectingthe mold toa vacuum applied to the plate 99 through asuitab'levacrium connection ltls communicat-p ing with avacuum source (not shown); Asbefore, the. vacuum:actionwithdrawsair and:other gases from the.

cavities-98 and also draws. the molten material being cast.

against the cavity. walls.

The vacuum plate 99 shownis very similar: to the plates. hereinbefore described; except that; the plate shown in, this embodiment is shaped as a-circular disc. to conform.

to the cylindrical mold shape. From Figs; 16 and 17,-it

is seen that =the;plate 99 is provided with awafile-iron-likef upper: surface ltld so. astodefine a pattern'ofv intercon-- nectedxciroular. andstraight passages 108coverysubstantiallythe entire surfaceof'the mold. Communication be;-

tweenthese inner passages 108; and the. vacuurmconnection "-is.-eifected through an opening 109 providedEin" themold cavities 98'andfor minimizing. dissipation of the.

vacuumforces through leakage. the vacuum plate 99-isprovided. with an upstanding circular knife edge 111" adapted to bite intothe relatively soft lower surface of the mold'86r. The knife edge 111fits tightly into anappropriate' groove providedinthe plate so as to be easily re-, placed'when dull.- Thus, any inflow of air into the interof theporousy connectedpassages 108 must be by 'way walls of the'mold 86.

A' preferred form ofthe invention includes an array of closely spaced perforations 113 provided over substantially'the entire surface of the mold shell 100- in order to permit air to be drawn-therethrough andthrough the porous investment material to thereby create, a chilling action; on the castings within the mold. It is found that such an arrangement effects a higher rate of coolingofr thecastings than that normally attainable so as to produceafinely grained casting product having uniform and highly desirable physical characteristics.

The embodiment ,ofthe invention illustrated in Figs. 14

and 15 is similar' to that shown in Figs. 1213 except that the sheathed mold86'a is clamped tothe angularly disposed outlet or month 114 of a rockable furnace 115,

preferably of arr-electric type, which-may be tilted to fill the mold with molten metal. Thus, as shown in the draw-- ings, a frame 116 for supporting the tiltable furnace isprovided and suitable means including a gearmotor 118 and'cradlemember 119-are used for rocking the furnace betweenanupright and a tilted position (shown in phantom in Fig; 14).

The, furnace 115- ispivotally supported on the frame 116, by. arms 120 andtherocking cradle 119 is pivotally' connected to the furnace atsome point 121 above the axis. of the supporting arms. Rotative motion is imparted to.

cylinder 126 is rigidly connected to the upper frame bar V 125,:in depending relationthereto and a reciprocable piston; 126? disposed in the cylinder carriesa vaccum plate, 99a on the lower end of a piston rod 129. The pressure. fluid; operated, piston and cylinder. arrangement 1 28, 1 26 accordingly moves the vacuum plate 99a toward or away from the furnace mouth 114, as desired, to clamp or release the mold 86a.

The mold 86a employed is identical to that used in the apparatus of Figs. 12 and 13, as shown in Figs. 16 and 17, having a sprue opening (not shown) positioned contiguous to the furnace mouth 114. A cylindrical shell 100a surrounds the investment material forming the mold, the shell being preferably formed with perforations 113a to facilitate cooling of the castings after the molten metal has been poured.

As will be observed, the ends of the mold 86a are appropriately sealed from leakage of air or molten metal. Thus, it is preferred to interpose a gasket 130 between one end of the mold and the furnace mouth 114. Likewise the other end of the mold is sealed by the provision on the operating surface of thevacuum plate of a circular raised knife edge adaptable to assume a biting relationship with the mold material.

Operation of the illustrative apparatus of Figs. 14 and 15 is effected by melting in the electric furnace 115 a metal charge to be cast. With the mold 86a clamped firmly to the furnace mouth 114 and when the metal is transformed into molten condition, the furnace 115 is rocked by means of the gearmotor 118 and cradle 119 from theupright to the tilted position. Vacuum may be applied to the vacuum plate 99a simultaneously with the flow of melt from the furnace 115 into the mold 86a, or the vacuum may be applied whenever desired.

The'method and apparatus hereinbefore described have been placed in use under actual production conditions. Through the utilization thereof it has been found that not only does a substantially higher percentage of yield obtain, but additionally the castings so formed do in fact possess improved physical properties. Further, it. has been found that there are substantially no rejects when the molds themselves are properly formed. Precision castings have been successfully made under production conditions and speeds with extremely thin-Walled sections to a specification accuracy of .005 of an inch.

There is shown in Figs. 1820 a modified form of clamping plate which may also be used in any of the illustrative casting apparatuses described herein. An illustrative vacuum clamping plate 150 is there shown which is similar in overall shape and construction to the clamping plates 24, 24B and 26A described above. As shown the plate 150 comprises the top plate for use in one of the illustrative casting. apparatuses and is provided with a wafile-iron-like formation of feet or pads 152 distributed over its entire undersurface.

As before, the spaced feet 152 uniformly distribute clamping pressure over the surface of a porous upper mold section 154 of any of the types described heretofore and define therebetween a pattern of interconnected passages 156 over substantially the entire upper surface of themold section. Evacuation of the mold cavities is accomplished by subjecting the interconnected passages 156 to a vacuum whereby air, occluded gases, and the like are withdrawn through the porous walls of the mold. As in the case of the vacuum clamping plates described above, theplate 150 is preferably provided about the periphery of its clamping surface with suitable knife edges 158 which are adapted to bite into the relatively soft upper surface of the mold and thereby minimize leakage or dissipation of vacuum.

The improvement disclosed here and shown in Figs. 18-20 of the drawings concerns the opening 160 which is provided in the plate 150 to provide communication between theinterconnected passages 156 and a vacuum pump (not shown). In an arrangement similar to those disclosed above as concerns the vacuum plates 24, 24B, and 26A, connection between the plate opening 160 and the vacuum pump is accomplished using a suitable vacuum hose (not shown) which'is secured to the. plate by means of a screw-threaded fitting 162.

' Before describing the modified vacuum plate150; in detail reference should be made to some of the problems which are overcome by using the improved plate construction in a casting apparatus. It has been found in practice that the vacuum hose extending between the clamping plate 150 and the vacuum pump often becomes restricted or entirely obstructed with solid materials such that the vacuum action at the clamping plate is effectively shut oif before all of the occluded gases and the like have been withdrawn from the mold cavities. That is, solid materials are drawn from the mold outwardly through the plate opening and into the vacuum line with theresult that the latter becomes plugged and the effective application of vacuum to the mold iscut ofif.

These solid materials often comprise particles of the mold itself, such as granulesof sand, gypsum, or other mold material which may be present in a loose state on the surface of the mold or may result from some crumbling of the soft mold material at its surface. Sometimes the sealing knife edges 158, around the periphery of the clamping plate tend to dislodge particles of mold material from the mold surface.

. The most troublesome type of solid material which may clog the vacuum passages is the molten metal itself which is being cast. Occasionally a mold cavity is positioned very close (perhapsMr inch) to the outer surface of the mold such that a fine crack or void in the thin mold wall will permit the vacuum to break the wall. If this occurs, some of the molten metal being poured into the mold cavities is invariably drawn through the break in the mold wall and into the interconnected vacuum passages 156 defined by the plate clamping feet 152. Since the molten metal solidifies within the vacuum hose and often within the pump itself it is necessary to completely disassemble and clean the component parts of the pump, a laborious and time consuming task.

, The use of conventional filtering means on the vacuum lines to protect the vacuum pump has been found to be ineffective since these very quickly become clogged with the molten meltal or mold particles and thus cut off vacuum action. In any event such filters must be placed in the vacuum hose or line at some point between the clamping plate and the pump such that the portion of the vacuum line adjacent the clamping plate is still subject to Plugging- In carrying out that aspect of the invention shown in Figs. 18-20 of the drawings, the illustrative mold clamping plate 150 is provided with means surrounding the vacuum opening 160 for preventing passage of any solid materials into the vacuum hose or pump while yet assuring free passage of gases through the opening 160 so that occluded gases within the mold cavities may be quickly and completely removed therethrough. In this instance the means comprises an approximately square pad 166 integral with the plate 150 and surrounding the plate opening 160 and defined by certain of the interconnected passages 156, and a porous disc 168 covering the plate opening 160 and shouldered within the pad 166 such that it is interposed between the plate and the mold surface 154 (see Fig. 20) during casting.

As will be seen from Fig. 18 which shows the plate without the porous disc 168 in place, the pad 166 comprises a plurality of mold engaging feet 170 which cover substantially the entire area of the pad except for the center thereof through which the plate opening passes. The mold engaging feet are defined by a plurality of pad grooves 172 which extend radially outwardly over the mold engaging surface of the pad from the central plate opening 160 and thereby provide communication between the interconnected passages 156 and the opening 160.

A counterbore 173 somewhat larger than the diameter of the plate opening 160 is provided in the center of the pad 166 in order to provide a shoulder 174 for reception ofthe porous disc 168 which is preferably of flat cylineg-ssatosr 1.1 drical-shape=As-will be seenfmm-FigQ 20 the depth of the counterbore 173 from the surface of the mold enga1gagainst the mold surface.

entry ofthe disc 168- therein andremovaltherefron'r.

The disc 168 is thus a wedge-fit when in-place -within the counterbore 173. Y

Various materials ofconstruction maybe used for the disc or'waf'er 168" so long as the resultingmaterial is.

porous andresistant to whatever high temperature-conditions are encountered withthe particular metalsto-be cast. "One satisfactory such disc isf'ormed as arefractory material bymixing a small amount :ofa suitable binder,

such as the resin binder manufactured and sold I by the Acme Resin Corporation ofForest'Park, Illinois and designated by themas their No. 760' resin, with a suitable coarse grade sand, forming themixture into thedisc shape in a conventional core box, and-then baking the shaped disc at about 800 F. for an hour-or more. The resulting disc is hard; porous due to elimination of "resin components during baking, and resistant to-most-tem'-- peratures encountered in the casting of metal shapes;

Of:cou-rse other binders can be usedas well} and indeed" thedisc-material may beformed of otherhightemperature I resistant materials, such forexample as a suitable sin-- tered metal which has the desired heat resistant qualities.

The modified plate shown-in Figs. 18-20 has many advantages. 7 firmly between the plate opening 160 and the mold surface 154- when the entire casting apparatus is as-sembled The flat disc 168-is, as noted-above, held 12 porous disc 168-thus permits passage of 'air theretliroughi? while yet providing enough resistance to air flow tq-enablje; it to be held in place within the plate under-impctuirof the vacuum. V i i ln the-preferred form of the modified plate there-are; yet other advantageous features. Attention is drawn to;- the difference indepthbetween thepad grooves"172'and'-f the-adjacent interconnected plate passages 1 56. It will" be observed that the grooves 117 2* are preferably; consid erably more shallow than (only about one-third as-decp in this case) the passages 156. These shallow grooves" 172" communicating between the passages 156 and the porous disc 168 function in what' mightbe termcdfa; coarsefiltering action as'compared with: therelatively fine-"filtering action through/the disc168; j This'is'best;

. understood upon aconsideration" of the mechanicsofi and the metal is being cast. As will be clearly seenfrom- -Fig. 20, any solid materials such as-rnold particles of molten metal which'enter the interconnected passages 156 from the mold will. be drawn along those passages to theplate pad 166 and thence through thepadgrooves 172i'until. the particles engage the outer peripheral edge" surface of the disc 1 68. The solid particles are stopped at. thispoint and'must remain lodged against-theouten edge surface of the disc.

An important feature of' this aspect of the invention is that the flat disc 168Jin this condition providesabroad filtering area in engagement with the mold surface 154' such- -that effective vacuum action is exerted upon the inner moldcavities over-the entire fiat area of the disc: Becauseof the substantial area of flat engagement between the disc 168-and the mold 154, thatportion of the moldin contact with the disc is strengthened againstanycracking or breaking of the mold Wall overthatarea;

Since the mold wall remains intact-over the "area of engagement with the disc 1 68, and because any loose solid particles from the mold are retained on the edge surface" ofthe disc, there i's-no' substantial impairment-.of'the: vacuum action being exerted throughthe fiat disc surface upon the-mold cavities. Even in anextreme hypot heti'cali situationin which all of the pad grooves 1-72"-rnight become clogged with solid materials, vacuum" would *still be drawn through. the flatcsurface of the di'sc1'68ienga-ging the mold surface.

Another feature of this modified form ofthe-invention concerns theease with whichthe filtering means' may be cleaned in between successive uses of theycastingi appw ratus. Upon separation of the clamping-plate150-fron1 the casting apparatus and" discontinuation of vacuum action, the disc 1'68 drops easily out of the: plate shoulder.

1741-and the solid particles may be easilybrushednway I from-the disc as well'as from the grooves17-2P'an'dother plate passages. Reassemhlyis accomplished readily by applying vacuum to the clamping plate 150, placing the the path of flow should molten metal' or mold-particlesbe drawn into the interconnected-vacuum passages 156; Goblets or particles of such molten-metal are firstdr'awrr along the relatively large and deep-passages 156-toward.

At this point of entry'of the molten metal particles into V the grooves 172 the velocity of the flow of'gasesand... the like from the mold cavities increases substantially in accordance withthe above-mentioned change in: cross: sectional area of the path'of gas flow such that achilling action takes place tending to slidify the particles .of molten metal. As a result many times the chilledmetalpan ticles, or the smallerparticles of'mold material, are caught within the confines of the narrow grooves 17Z'sq that they never reach the porous disc 168; Of course much of the particulate material will traversethepad' grooves 172 and be drawn up against the edge surfaces of the disc 168 as described above. sectional area of the grooves 172 is invariably considerably greater than the size of the voids in porous. disc 168 the narrow grooves provide what'might be termed a. coarse filtering or screening action. 7

It is found in practice that this arrangement not'onlyj prevents the vacuum line from plugging up but assures.

the maintenance of a positive vacuum against thesurface of the mold for a sufficient period of time to permit'the occluded gases to be withdrawn from the mold cavity.

Thus; while there is still the'possibility that even the 7 While the modified form of" the invention disclosed in Figs. 18-20 of the drawings has been described as applied to the top plate of a casting apparatus and a plate of rectangular form, the invention is in. no wise so: limited. Anysuitable shape castingv plate may be em: ployed and it" may be a bottom plate or the like as well.. as the top plate. Similarly the plate pad 166 need not be-square-shaped but may take any suitable form andI-the-.. disc \168need not be cylindrically shaped but maybe formed as a rectangular or square solid or in anyothel; feasible shape. Likewise this aspect of the invention may be used in permanent molds such as cast iron .or the like used for casting various alloys and aluminum as well as non.

permanent types. In this application avacuum opening is provided on the inner wall. of the permanent mold, with a suitable'recesssurrounding the. opening; themoldfcoma prising-for example .a heavy walledcast iron cylinder... about 10 inches in'diameterand" perhaps Ginches deep,

Since the: cross-. V

13 and the recess being sized and shaped to receive therein a porous disc of suitable contour and of the character described above. The position of the disc within the mold ary 25, 195 6, now abandoned, which is in turn a continua- I tion of my now abandoned application Serial No. 379,210

filed September 9, 1953. s V

I claim as my invention: f M 1. A casting apparatus comprising, in combination, a

mold formed of porous material defining a cavity for the reception of the material to be cast, a plate having a plurality ofinterconnected passages formed in one face thereof and defining a plurality of spaced feet engageable with said mold, said mold and said plate defining spaced passages therebetween, said plate having an opening therein adapted for connection with evacuating means and including on said face thereof a pad surrounding said opening and having a depth substantially the same as the depth of said spaced passages, a counterbore on said plate face within said pad and surrounding said plate opening, said pad having grooves therein communicating between said spaced passages and said plate opening and dividing said pad into a plurality of feet for engagement with the juxtaposed mold surface, means for applying a vacuum to said plate through said plate openi'ng'whereby vacuum is transmitted through said spaced passages to the exterior surface of the mold and indirectiy to said mold cavity through the mold walls defining the same for effecting removal of gases from the mold cavity, said pad grooves having a depth substantially less than the depth of said spaced passages whereby flow of gases from said mold cavity to said plate opening is restricted, and a porous disc within said counterbore disposed in parallel relationship to the interface between said plate and said mold and being of a sufficient thickness to locate the outer surface of the disc in coplanar relationship with the mold bearing surface of said spaced feet so that the disc is held in firm engagement with the contiguous area of the mold surface whereby the disc permits passage there- 'through of gases being evacuated from the mold cavity but positively prevents passage into the plate opening of any solid particles that might otherwise obstruct said opening.

2. A casting apparatus comprising, in combination, a mold formed of porous material defining a cavity for the reception of the material to be cast, a plate having a plurality of interconnected passages formed in one face thereof and defining a plurality of spaced feet engageable with said mold, said mold and said plate defining spaced passages therebetween, said plate having an opening therein adapted for connection with evacuating means and including on said face thereof a pad surrounding said opening and having a depth substantially the same as the depth of said spaced passages, a counterbore on said plate face within said pad and surrounding said plate opening, said pad having grooves therein communicating between said spaced passages and said plate opening and dividing said pad into a plurality of feet for engagement with the juxtaposed mold surface, means for applying a vacuum to said plate through said plate opening whereby vacuum is transmitted through said spaced passages to the exterior surface of the mold and indirectly to said mold cavity through the mold walls defining the same for effecting removal of gases from the mold cavity, said pad grooves extending radially outward from said plate opening and having a narrow depth as compared with the depth of said passages whereby flow of gases from said mold cavity to said plate opening is restricted, and a porous disc within said counterbore disposed in parallel relationship to the interface between said'plate and said mold and being of a sufiicient thickness to locate the outer surface of the disc in coplanar relationship with the mold bearing surface of said spaced feet so that the disc is held in firm engagement with the contiguous area of the mold surface whereby the disc permits passage therethrough of gases being evacuated from the mold cavity but positively prevents passage into the plate opening of any solid particles that might otherwise obstruct said opening.

3. A casting apparatus comprising, in combination, a mold formed of porous material defining a cavity for the reception of the material to be cast, a plate having a plurality of interconnected passages formed in one face thereof and defining a plurality of spaced feet engageable with said mold, said mold and said plate defining spaced passages therebetween, said 'plate having an opening therein adapted for connection with evacuating means and including on said face thereof a pad surrounding said opening and having a depth substantially the same as the depth of said spaced passages, a counterbore on said plate face within said pad and surrounding said plate opening, said pad having grooves therein communicating between said spaced passages and said plate opening and dividing said pad into a plurality of feet for engagement with the juxtaposed mold surface, means for applying a vacuum to said plate through said plate opening whereby vacuum is transmitted through said spaced passages to the exterior surface of the mold and indirectly to said mold cavity through the mold walls defining the same for effecting removal of gases from the mold cavity, and a porous disc within said counterbore disposed inparallel relationship to the interface between said plate and said mold and being of a sufiicient thickness to locate the outer surface of the disc in coplanar relationship with the mold bearing surface of said spaced feet so that the disc is held in firm engagement with the contiguous area of the mold surface whereby the disc permits passage therethrough of gases being evacuated from the mold cavity but positively prevents passage into the plate opening of any solid particles that might otherwise obstruct said opening, said pad grooves terminating adjacent said plate opening against the peripheral edge surfaces of said porous disc so that any solid particles accumulate along these edge surfaces whereby the flat surface of the disc lying in the plane of the mold surface remains free and unobstructed to passage of gases therethrough.

4. A casting apparatus comprising, in combination, a mold formed of porous material defining a cavity for the reception of the material to be cast, a plate having a plurality of interconnected passages formed in one face thereof and defining a plurality of spaced feet engageable with said mold, said mold and said plate defining spaced passages therebetween, said plate having an opening therein adapted for connection with evacuating means and including on said face thereof a pad surrounding said opening and having a depth substantially the same as the depth of said spaced passages, a counterbore on said plate face within said pad and surrounding said plate opening, said pad having grooves therein communicating between said spaced passages and said plate opening and dividing said pad into a plurality of feet for engagement with the juxtaposed mold surface, means for applying a vacuum to said plate through said plate opening whereby vacuum is transmitted through said spaced passages to the exterior surface of the mold and indirectly to said mold cavity through the mold walls defining the same for effecting removal of gases from the mold cavity, said pad grooves having a depth substantially less than the depth of said spaced passages whereby flow of gases from said mold cavity to said plate opening is restricted, and a '15 mold 'bearing lsurface of said spaced feet so that the disc is held in firm engagement with the contiguousareaflof the mold surfacelwhereby the disc permits passage therethrough of gases being evacuated from the mold cavity but positively prevents passage into the plate openingwof; any solid particles that might otherwise obstruct said' mold'forrned of porous material defining a cavity forthe 7 reception oflthe material to be cast, a support for the mold, a plate having a plurality of interconnected 'passages formed in one face thereof and defining a plurality of.spaced feet engageable with said mold opposite said support, means for clamping said plate against said mold, said mold and said plate defining spaced passages there'- between, a perforated member entirely surrounding the exposed mold portions for sustaining the form thereof and" permitting-passage of air therethrough, said plate having an opening therein adapted for connection with evacuat ing means and including on said face thereof a pad surrounding said opening and having a depth substantially the same as the depth of said spaced passages, a counterbore on said plate face within said pad and surrounding said plate opening, said pad having grooves therein communicating between said spaced passages and said plate opening and dividing said pad into a plurality of feet for engagement with the juxtaposed mold surface, means for.

applying avacuum to said plate through said plate open-j ingwhereby vacuum is transmitted through said spaced. passages to the exterior surface of'the mold andlindirectly to said mold cavity through the mold walls defining the same for effecting removal of gases from the mold cavity; and for drawing air into the mold'through said perforated" mold supporting member, said pad grooves having fa. depth substantially less than the depth of r said 'spacedt'i passages whereby flow of gases from said mold cavity to said plate opening is restricted, andia porous discw'ithinr said counterbore disposed in parallel relationship to the interface between said plate and "said mold and being off. a suflicient thickness to locate the oute'r surface ofthe,

disc in coplanar relationship with the moldb'earin'gfsup face of said spaced feetso that the disc is held in firm engagement with the contiguous area of the;moldfslirface whereby the.discpermits passage-therethrough off'gasesj being evacuated from themold cavity but positivelyprei vents passage into the plate opening of any s'olid particles" that might otherwise obstruct said opening.

References Cited in' the file of this patent UNITE-D STATES-PATENTS,

1,031305- West' July-2, 1912' 133 62182 1-,ss'1,4=4-s 2-,1'9"s;497;' 2,209,081 23220316;

Wetherby t June 6, 1911 Moore" Feb. 22; T921 1 Lake Mar. 3'1, I925

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