US3268962A

US3268962A - Method of casting

Info

Publication number: US3268962A
Application number: US349567A
Authority: US
Inventors: Claude L Roles
Original assignee: Eaton Yale and Towne Inc
Current assignee: Eaton Corp
Priority date: 1964-03-05
Filing date: 1964-03-05
Publication date: 1966-08-30
Anticipated expiration: 1983-08-30
Also published as: NL6410801A; GB1014707A; DE1284573B; ES304975A1

Description

Aug. 30, 1966 c. L. RoLEs 3,268,962

METHOD 0F CASTING Fiied March 5, 1964 2 sheets-sheet 1 INVENTOR (2m/@f an WMM/#M Aug. 30, 1966 c. l.. RoLEs METHOD oF CASTING Fiiled March 5, 1964 2 Sheets-Sheet 2 INVENTOR 14,4005 @aff United States Patent O 3,268,962 METHD F CASTHNG Claude L. Roles, Vassar, lid-lich., assigner to Eaton Yale il Towne Inc., a corporation of @trio Filed Mar. 5, 1964, Ser. No. 349,567 4 Claims. (Cl. 22--200) This invention relates to a method for casting metal and more particularly relates to a method of casting gray iron in a permanent mold of a similar metal.

The method embodying the invention was developed in connection with casting of gray iron in gray iron molds and will be dealt with in such connection in the following description. However, it will be recognized that the method of the invention may be used in metal casting involving materials other than gray iron.

After molten iron has been poured into a permanent mold, is has been found that said iron expands during a part of its initial cooling period. Specifically, as the temperature of the ir-on drops, such exansion takes place and continues until a temperature of about 1400 degrees Fahrenheit is reached, at which point expansion ceases and the iron casting begins to contract. It should be noted that initial expansion followed by a contraction has been found to occur in other instances of metal casting using a permanent mold and that the broad phenomenon of initial expansion followed by a subsequent contraction during cooling in a permanent mold is not dependent on the iron composition.

Molds used for casting metals usually comprise a fixed mold half co-operating with a movable mold half to define a mold cavity. In the past, an air cylinder has often been used for moving the movable mold half into contact `with the fixed mold half and for maintaining said contact during pou-ring of the metal into the mold. This has been found satisfactory when the mold is relatively small in that the mold will be held closed during pouring by an air cylinder, said air cylinder being weak enough to allow controlled expansion of the cooling material within the mold. However, attempts to similarly mold larger pieces have shown that air cylinders capable of maintaining the mold closed during pouring will not displace sufficiently to allow proper expansion of the molding during cooling. As a result, breakage of the molding apparatus, typically the movable mold half, has occurred in several instances.

In existing molding machines, the parts associated with the movable mold half are often confined within a relatively small space by other parts of the molding machine and in consequence the size of the individual parts associated with the movable mold half must often be maintained below a prescribed maximum. In this connection, it has been found that conventional air cylinders when fed by normally available shop air pressures and when made large enough to hold a mold closed for pouring for a large casting, are too large to fit within the available space in existing molding machines.

Therefore, the objects of this invention include:

(l) To provide a method for allowing expansive movement of a permanent mold during the cooling of the casting therein.

(2) To provide a method, as aforesaid, wherein the mold halves are housed snugly together during the pouring of metal into the mold wherein the expansion above mentioned is then permitted and wherein the mold parts are allowed to follow the contraction of the casting.

(3) To provide a method, as aforesaid, wherein a predetermined rst closure force is exerted on the mold to maintain same closed during pouring and a second predetermined closure force of lesser magnitude is exerted on the mold after the casting has cooled sufficiently to achieve skin hardness and during the expansion phase of molding operation.

(4) To provide a method, as aforesaid, which will prevent damage to the molding apparatus due to expansion of the material being molded, wherein the quality of the casting produced is in no way degraded and wherein the time and effort required for making such a casting is in no way increased.

(5) To provide a method, as aforesaid, which may be practiced by apparatus of relatively simple construction which will not add appreciably either to the original cost of the molding apparatus or to its operating or maintenance cost. i

(6) To provide a method, as aforesaid, which may be practiced by apparatus which is reliable in its operation and which will have a long and relatively trouble-free service life.

(7) To provide a method, as aforesaid, which may be practiced by existing molding machines with only readily made and economical additions thereto or .modifications thereof.

Other objects and purposes of the invention will become apparent to persons acquainted with the devices of this general type upon reading the following specification and inspecting the accompanying drawings.

In the drawings:

FIGURE l is a side View of a typical molding apparatus incorporating a permanent mold and capable of carrying out the method of the invention.

FIGURE 2 is a top view of the apparatus in FIG- URE 1.

FIGURE 3 is an end elevational view of the apparatus of FIGURE 1, as taken from the rightward end thereof.

FIGURE 4 is a schematic diagram of apparatus for controlling the operation of the molding apparatus of FGURE l in accordance with the method yof the invention.

General description In general, the invention consists of providing a permanent mold apparatus including fixed and movable mold halves with a pressure fluid cylinder affixed to `said movable mold half for holding said mold closed with two alternately applied forces of differing magnitudes. To apply the first of said forces, control means are provided for maintaining said pressure fluid cylinder under a high pressure for holding the mold closed during pouring and until the casting reaches a particular, preselected, physical state following said pouring. The second of said forces is of lower magnitude than said rst force and is applied by the pressure cylinder to firmly but resiliently resist opening of the mold until expansion of the casting overcomes same and to prevent breakage of parts of the apparatus due to such expansion, Upon contraction of the casting, said second, lower, force urges reclosing of the mold to maintain a preset pressure on the casting until it has cooled sufiiciently to be released from the mold.

Detailed description port. Further, it will be understood that the followingV description of the structure and operation of certain apparatus has been selected for illustrative purposes only as a convenient and appropriate means for acquainting those skilled in the art with the method of the invention. It is further recognized that said method may be practiced by apparatus -other than that hereinbelow described. Moreover, although the following description is specifically directed toward molding of metals in permanent molds and more specically toward molding of gray iron in iron molds, it will be apparent that the method of the invention is applicable in Iother instances, wherein separation of the mold parts tends to occur during the molding process due 'to-expansion of the casting during curing or the like.

Turning now to FIGURES l, 2 and 3, the method embodying the invention may be practiced for purposes of illustration on the molding apparatus generally indicated at 10. The molding apparatus includes a fixed base 11 of any convenient type which supports a rightwardly (FIGURE l) extending framework 12. The framework 12 comprises a spaced, generally parallel pair of extending

members

13 and 14 vfixed at corresponding ends thereof to the base 11 and joined at their remaining ends by a generally upwardly extending support block 16. An upstanding, generally planar backing plate 17 is afiixed to the inner face of the support block 16 and includes a sidewardly extending pair of ears 1S. A fixed mold part 21 defines the stationary portion of the mold generally indicated at 22 and includes a pair of sidewardly extending and vertically widened lugs 23 which are normally disposed adjacent and preferably in contact with the ears 18 for engagement therewith by nutted bolts 24 whereby the fixed mold part 21 is positively supported on the framework 12. The lugs 23 are preferably vertically slotted for vertical sliding movement thereof with respect to the ears 18 for effecting a vertical adjustment of the mold part 21 on the framework 12. A positioning finger 26 is fixed to each side of the support block 16 and extends therefrom to a position under lug 23. Each of the positioning fingers 26 has a vertical positioning screw 27 threaded therein for supporting the lugs 23 and thence mold part 21 prior to the tightening of the bolts 24.

The

members

13 and 14 and block 16 are preferably hollow to allow communication between suitable forced ventilation means not shown in the base 11 through suitable openings in the backing plate 17 with gas exhaust passages of any convenient type in the fixed mold part 21 for relieving gas pressure within the mold and for cooling said mold in a substantially conventional manner.

A generally vertical flange 31 extends outwardly from each side of the backing plate 17 above the ears 18 and an upright 32 is fixed to and extends upwardly from a base 11 opposite each of said flanges 31. A guide, or strain, rod 33 is supported on and between the opposed ones of the flanges 31 and uprights 32 and is fixed thereto by nuts 34 threadedly engaging the ends of said guide rods. The guide rods 33 are parallel and spaced from each other by the mold 22, said rods being generally parallel to the leftward (FIGURES l and 2) portions of the extended

members

13 and 14 and being perpendicular to the parting plane of the mold 22. A carriage 36 extends from and between axial bearings 37 slidably mounted on the guide rods 33 whereby the carriage 36 is slidable axially along the guide rods 33 toward and away from the parting face of the fixed mold part 21. The carriage 36 has affixed thereto a pair of ears 18a and a pair of positioning fingers 26a with positioning screws 27a which are preferably identical to and opposed to corresponding parts of the support block 16. A movable mold part 39 has sidewardly extending lugs 23a fixable to the ears 18a on the carriage 36 by bolts 24a for supporting said movable mold part 39 with respect to the carriage 36. The mold 22 has a sprue 38 in the upper face thereof communicating with a suitable mold cavity, not shown, for filling same with molten metal. A pressure fluid cylinder, here a hydraulic cylin- 4 der 41, is mounted on the base 11 and has a plunger 42 extending rightwardly (FIGURES 1 and 2) therefrom and afiixed by a bolt 43 and bracket 46 to the carriage 36. Said plunger 42 is preferably parallel to the guide rods 33 and spaced therebetween for moving the carriage V36 and mold part 39 along the guide rods 33.

FIGURE 4 discloses a control circuit 51 for controlling the actuation of the hydraulic cylinder 41. The conn trol system 51 includes an electrical portion generally indicated at 52, a portion using a compressible pressure fluid such as air generally indicated at 53 and a portion utilizing a substantially non-compressible pressure fluid such as hydraulic fluid indicated generally at 54.

Considering the air portion 53 of the circuit 51, a source 56 of pressurized air connects through an air line 57 to the inlet side of a reversing valve 58. The reversing valve 58 is movable to either of two positions by any convenient means here indicated for purposes of convenience in reference by

palm buttons

61 and 62. The reversing valve 58 connects also to an exhaust line 63 and through

air lines

64 and 66 connects to the upper end of a pair of upstanding air-over-oil tanks 67 and 68, respectively. The air line 64 has a branch air line 69 which connects the reversing valve 58 through au air pressure regulator 76 and a two-position diverting valve 77 t-o the upper end of a booster cylinder 78. The diverting valve 77 in the position shown closes the line to the regulator 76 and exhausts the upper end of the booster cylinder 78 to the atmosphere. diverting valve 77 connects the regulator 76 with the booster cylinder 78, this latter position being selected by actuation of a solenoid 79 against the urging of a return spring 81. The booster cylinder 78 here includes a double-acting, air-operated piston 84 having a plunger 86 extending through the bottom of the air cylinder portion 87 of the booster cylinder 78 and into a hydraulic cylinder 88. The lower end of said air cylinder portion 87 is connected through an air line 89 and restrictive orifice 91 to a further diverting valve 92. The diverting valve 92 is urged by a return spr-ing 93 into the position shown whereat it connects the restrictive orifice 91 to a source 56 of air pressure. A solenoid 96 is actuable to urge the diverting valve 92 into another position whereat it connects the restrictive orifice 91 to an exhaust line 94.

Turning to the hydraulic portion 54 of the control system 51, a hydraulic fluid such as oil is contained in the lower portion of the tanks 67 and 68. The lower portion of the tank 67 is connected by a hydraulic line 101 and port Iin the upper end of the hydraulic cylinder 88 with a cylindrical passage 102 into which the plunger 86 is snugly reciprocable. The lower end of the passage 102 connects through a hydraulic line 103 with the closed end of the hydraulic cylinder 41 of the molding apparatus 10. The plunger end of the hydraulic cylinder 41 connects through a hydraulic line 104 to the lower end of the tank 68. The booster cylinder 78 and tanks 67 and 68 as well as the air and hydraulic connections thereto are already known and are disclosed here only to indicate one of the number of possible circuits for controlling molding apparatus according to the method of the invention. The electrical portion 52 of the circuit 51 also is known but will be described for purposes of illustration. A supply voltage, which may be of alternating polarity and whose source is not shown, is connected across the lines 106 and 107. A normally open start switch 108 is in series with a relay coil 109 across the lines 106 and 107. A timing motor 111 parallels the relay coil 109. A normally open contact 112 of the relay coil 109 is connected in series with a normally closed contact 113 of the timing motor 111 to parallel the start switch 108. The solenoid coils 79 and 96 are connected in parallel with a further normally open contact 114 of the relay 109 which is connected across the lines 106 and 107.

In the other position, the

Operation The sequence of operation of the molding apparatus and of the circuitry 51 associated therewith normally begins with the plunger 42 of the hydraulic cylinder 41 in its retracted position shown in FIGURE 4 and opposite the position shown in FIGURES 1 3. Hence, the movable mold part 39 will be spaced from the fixed mold part 21. Assuming a source of electrical potential to be connected across the lines 106 and 107 and assuming the air pressure source 56 to be capable of supplying air at a specified pressure, which in the case of a typical factory air source might be about 80 p.s.i., to the

valves

58 and 92, operation of the device is begun by actuating the palm button 61 to move the valve 58 into its position shown in FIGURE 4. This directs air under pressure from the source 56 through the line 57, valve 58 and line 64 into the upper end of the tank 67, thereby pressurizing the oil in said tank. Said oil is thus forced through the line 101, passage 102 and line 103 into the blind end of the hydraulic cylinder 41. This extends the plunger 42 and moves the mold part 39 into contact with the fixed mold part 21 thus closing the mold 22. Upon extension of the plunger 42, uid trapped in the rightward portion of the cylinder 41 is exhausted through the line 104 and into the tank 68 thus displacing air in the upper `half of said tank through a line 66 and exhausting same through the valve 58 and exhaust lines 63. At this point, the hydraulic cylinder 41 is pressurized only by the relatively low pressure of air source S6 and exerts only a relatively low or holding force on the mold 22.

Preferably immediately before filling, the switch 100 is closed whereby current flows through the relay 109 to close the contacts 112 and 114 thereof and -through the timing motor 111 to start timing thereby. `Closure of the contact 112 shunts the switch 108 to allow opening thereof while maintaining the relay 109 and timing motor 111 energized. `Closure of the contact 114 energizes t-he solenoids 79 and 96 to move the

valves

77 and 92 away from their positions of FIGURE 4. Thus, the valve 77 connects the upper end of air cylinder portion 87 to the air pressure source 56 and the valve 92 exhausts the lower end of the air cylinder portion 87. In this manner, the plunger 86 is moved downwardly and passes the connection of the hydraulic line 101 to the cylindrical passage 102 preventing escape of hydraulic fluid in the cylindrical passage 102 back into the line 101.

Since the head of the piston 84- is much larger in diameter than the lower end of the plunger 86, the pressure above said piston will exert a much greater force thereon than the similar pressure within the passage 102 exerts upon the lower end `of the plunger 86. Consequently, the plunger 86 will be moved downwardly by the piston 84 until the downward force on the piston 84 is opposed by an equal and opposite force on the end of plunger 86. Such equal and opposite force is generated by a greatly increased pressure within the passage 102 caused by continued downward movement of the plunger 86, said increased pressure being comparable to the air pressure of the pressure source 56 in the ratio of the area of the piston 84 to the cross-sectional area of the end of the plunger 36. In a particular example, the diameter of the piston 84 was five times that of the plunger 86 whereby the area ratio was 25 to 1. Hence, 80 p.s.i. applied to the piston 84 moves same downwardly until a pressure of 2000 p.s.i. results within the passage 102. This greatly increased pressure is applied to the plunger 42 of the hydraulic cylinder 41. Since the mold 22 is already closed, there will be essentially no increase in the extension of the plunger 42 despite the greatly increased pressure bearing thereupon. The mold 22 may now be filled with molten metal from any convenient source, not shown, and through the inlet sprue 38 thereof. The force, which may be termed a clamping force, exerted by the plunger 42 on the mold half 39 is suicient to maintain the mold 22 closed during pouring.

The casting is allowed an initial cooling period before the timing motor 111 times out. Gray iron castings, for example, have been allowed to cool to approximately 1900 to 2000 degrees Fahrenheit before the timing motor 111 times out. At this temperature, the casting has a skin hardness although it is still not hard. inside. Also at this point, expansion becomes significant and tends to separate the mold halves with considerable force. Timing out of the timing motor 111 opens the contact 113 thereof Ithereby opening the current path through the relay coil 109 and timing motor 111. The relay 109 is thus de-energized and the contacts 112 and 114 thereof opened. Contact 113 preferably closes after the opening of the contact 112 to reset the timing motor 111 for a future operation cycle. Opening of the contact 114 de-energizes the solenoids 79 and 96 whereby the

springs

81 and 93 return the

valves

77 and 92 to the positions shown in FIGURE 4. Return of the valve 77 exhausts the upper end of the 'air cylinder portion 87. Return of the valve 92 connects the air pressure source 56 therethrough to the lower portion of the air cylinder portion S7 to move the piston 84 and plunger 86 thereof upwardly. This opens passage 102 to the line 101 and tank 67 whereby the blind end of the hydraulic cylinder 41 assumes once again the low pressure of the air pressure source 56. As a result, the high clamping pressure needed during pouring is reduced to a smaller holding pressure. Thus, the mold is still urged tow-ard a closed position but by a suiciently smaller force that expansion of the casting and a slight opening of the mold is now allowed to take place.

When the temperature of the gray iron casting drops to about 1400 degrees Fahrenheit, the casting stops expanding and begins to contract. The aforementioned holding force maintains the mold parts 21 and 39 in rm contact with the casting during contraction thereof to firmly support the casting at all `times during its cooling.

Afer the casting is cooled sufiiciently to be ejected from the mold, the valve 58 is moved leftwardly by the palm button 62 whereby the air pressure of the source 56 is applied to the tank 63 and the tank 67 4is allowed to exhaust its air pressure. Pressurization of the tank 68 sends hydraulic fluid through the line 104 lto retract the plunger -42 of the hydraulic cylinder 41 whereby the mold halves 21 and 39 .separate to allow removal of the casting therefrom. At this point the apparatus is in condition to perform another molding cycle as described hereinabove without further adjustment.

It is contemplated that the timing motor 111 and circuitry associated therewith may be replaced by a suitable pyrometric device whereby the release of clamping pressure wil-l occur at directly measured molding temperature point.

Although a particular preferred embodiment of apparatus appropriate for carrying out the steps of the method embodying the invention has been disclosed in detail hereinabove for illustrative purposes, it will be understood that variations and modification of such disclosure which lie within the scope of the appended claims are fully contemplated.

What is claimed is:

1. A method for casting metal capable of expanding while it is being cooled from a molten condition to a solid condition in a multipart permanent mold, which comprises the steps of:

closing the mold and applying a clamping pressure thereto sufiicient to hold the mold closed during the hereinafter mentioned casting step;

casting molten metal into the mold;

allowing the mold and casting to cool until expansion of the casting begins;

then reducing the clamping pressure while the casting `is undergoing expansion as it is cooled and maintaining a reduced holding pressure on the mold parts urging the mold parts `to a closed position, which holding pressure is `slitlicient to permit the mold parts to move apart in response to expansion of the casting but which maintains the mold parts in supporting engagement with the casting;

allowing the casting to cool to an ejection tempera- Iture and opening the mold and ejecting the casting.

2. A method according to claim l. in which the closing of the mold is effected by a closing pressure which is of lower magnitude than said clamping pressure, said `clamping pressure being applied to hold said mold closed after such closure has been effected by said closing pressure.

3. A method according to claim 1, in which the clamping pressure is reduced and the reduced holding pressure is applied in predetermined timed relation to the step of casting the molten metal into the mold.

4. A method of casting iron in a permanent iron mold which comprises the steps of:

using a constant pressure compressed gas source to apply a holding pressure through hydraulic fluid and a hydraulic cylinder to close said mold; boosting the pressure exerted by said compressed air on said hydraulic Huid to exert a clamping pres- 25 sure on said mold for maintaining same in closed position, said clamping pressure being several times as great as said holding pressure;

filling the mold with iron heated to a castable condition to form a casting;

allowing said casting to cool to a temperature at which it tends to expand;

releasing said clamping pressure but maintaining said holding pressure on said mold, said holding pressure being sufficiently low as t0 resilently resist but allow the required expansion of said casting;

allowing the casting to cool to a temperature whic-h may be ejected from the mold;

opening the mold by reversing the direction of the molding pressure applied to the said hydraulic cylinder and ejecting the casting from the mold.

References Cited by the Examiner UNITED STATES PATENTS 2,145,956 2/1939 Stem 22-92 2,367,727 1/ 1945 McWane 22-92 2,567,715 9/1945 Keunh et al. 2,869,190 1/1959 Schofield 22-92 I. SPENCER OVERHOLSER, Primary Examiner.

MARCUS U. LYONS, Examiner.

Claims

1. A METHOD FOR CASTING METAL CAPABLE OF EXPANDING WHILE IT IS BEING COOLED FROM A MOLTEN CONDITION TO A SOLID CONDITION IN A MULTIPART PERMANENT MOLD, WHICH COMPRISES THE STEPS OF: CLOSING THE MOLD AND APPLYING A CLAMPING PRESSURE THERETO SUFFICIENT TO HOLD THE MOLD CLOSED DURING THE HEREINAFTER MENTIONED CASTING STEP: CASTING MOLTEN METAL INTO THE MOLD; ALLOWING THE MOLD AND CASTING TO COOL UNTIL EXPANSION OF THE CASTING BEGINS; THEN REDUCING THE CLAMPING PRESSURE WHILE THE CASTING IS UNDERGOING EXPANSION AS IT IS COOLED AND MAINTAINING A REDUCED HOLDING PRESSURE ON THE MOLD PARTS URGING THE MOLD PARTS TO A CLOSED POSITION, WHICH HOLDING PRESSURE IS SUFFICIENT TO PERMIT THE MOLD PARTS TO MOVE APART IN RESPONSE TO EXPANSION OF THE CASTING BUT WHICH MAINTAINS THE MOLD PARTS IN SUPPORTING ENGAGEMENT WITH THE CASTING; ALLOWING THE CASTING TO COOL TO AN EJECTION TEMPERATURE AND OPENING THE MOLD AND EJECTING THE CASTING.