US2402913A - Vacuum control means and method - Google Patents

Description

June 25, 1946. 1'. c. P OULTER ETI'AL v cuuu CONTROL MEANS AND mn'rnon Filed Jan. 11, 1943 2 Sheets-Sheet 1 Q {H I M n IYNVENTQRS. N m; N J0mws Patented June 25, 1946 2,402,913 7 VACUUM CONTROLMEANS ANl) METHOD.

Thomas C. Poulter and Charles F. Strom, Chicago, Ill., assignors to American Steel Foundries, Chicago, Ill., a corporation of New Jersey Application January 11, 1943, Serial No. 471,984

7 Claims.

Our invention relates in general to automatic vacuum control means and is illustrated as applied to the control of a vacuum utilized in countergravity pouring of metal, as illustrated and described in co-pendin application, Serial No. 439,186, filed in the United States Patent Ofiice April 16, 1942, in the name of Thomas C. Poulter, entitled Method and apparatus for casting metal.

The general object of our invention is to devise automatic means for controlling the pressure in a vacuum system in accordance with a predetermined time-pressure curve.

A more specific object of our invention is to devise automatic means for controlling the vacuum in a closed chamber Within a fixed maximum limit.

Another object of our invention is to provide such automatic control means as will enable the rate at which the vacuum is developed to be accurately controlled, thus making it possible to increase the vacuum at a predetermined fast rate or slow rate as may be desired. Such control is essential in order to duplicate results obtained from time to time as the equipment may be utilized.

Still another object of our invention is to pro vide such automatic control means as that above referred to wherein automatic compensating means will be afforded for any minor leaks which may occur in the system assuming, of course, that an adequate reserve pumping capacity or source of exhaustion is associated therewith.

Our invention also comprehends such an arrangement as will afford the free and unrestricted passage of any sudden surges of gas as may occur in casting equipment such as that above referred to due to evolution of core gases, and provides for the immediate dissipation of any such surge of gases developed within the system.

Our invention also contemplates such an arrangement as that described wherein the vacuum which is developed within the system may be automatically released after a predetermined period and in which, in fact, the entire cycle of operations is automatically controlled.

In casting ferrous metal, such as steel, by a countergravity pouring method such as that referred to in the above-mentioned copendin application, the mold for the article to be cast is mounted within a vacuum chamber. It is necessary that the metal be drawn into the mold at a uniform rate which may be controlled in spite of leaks which may occur in the system and it is necessary to be able to repeat the process time after time with no significant variation in the vacuum control if successive, substantially identical castings are to be produced.

Our novel equipment is capable of accomplish ing these results.

In the drawings:

Figure 1 is a top-plan view of one embodiment of our invention.

Figure 2 is a side elevation of the structure shown in Figure 1, certain parts being omitted therefrom and a portion of the valve mechanism being cut away to show in section certain parts thereof.

Figure 2A is a fragmentary sectional View showing certain details of the structure shown in Figures l and 2, and Figure 2B is a fragmentary sectional view comparable to Figure 2A but showing a modification of the invention.

Figure 3 is a chart or graph illustrating the manner in which the vacuum is developed and controlled.

Our novel apparatus, in the embodiment illustrated, comprises the power means 2 here illustrated as an electric motor mounted as at 4, 4 on the base or bed plate 6, said motor incorporating a speed control mechanism and serving as actuating means for'the apparatus. The motor 2 may actuate the shaft 8 on which may be mounted the small gear lil meshing as at I2 (Figure 2) with the large gear wheel [4 mounted on the shaft 1 6 for actuation thereof. Also mounted on the shaft 16 may be the cam wheel l8, and the shaft I6 may be suitably supported adjacent opposite ends by bearings as at 20, 20 and mountings therefor at 22, 22. Associated with the cam l8 may be a cam follower 24 in the form of a lever arm fulcrumed at one end as at 26 from the support 28 mounted as at 3% on the bed plate 6. The cam follower 24 may engage the cam [8 as at 32 (Figure 2) and may have pivotal cons, nection at an intermediate point as at 34 to the link 36 which is connected to the valve 38 through the compression spring 40. The maximum strain of the spring All may be controlled by the adjusting nuts 12 mounted on the end of the valve stem 44. The valve 38 is illustrated at rest in its non-operating position where it may be slightly spaced as at 46 from the seat 68 afforded on the cap 51'] within which may be formed a plurality of ports 52, 52 open to the atmosphere. The cap 59 may have threaded connection with the short nipple 54, and the opposite end of said nipple may have threaded connection to the standard pipe T 56 in the line 58. In Figure 2A we have shown in somewhat greater detail the parts enumerated above, and in Figure 23 we have hown a slight modification therefrom, similar in v all respects, except that the connecting spring between the link 36 and the valve stem 54 is in the form of a tension spring 4| instead of a compression spring.

Oneend of the line 58 may lead as at 60 to a source of exhaustion or vacuum supply, such as a pump (not shown). In the line 58 may be mounted the T 62 having a connection as at 64 to the solenoid vent valve assembly 66 affording automatic control means for opening or closing the vent at 68 in the line 58, said vent being open to the atmosphere. The other end of the line 58 may afford connection as at to a vacuum bell or system to be evacuated, such as that illustrated and described in the said copending application. The pipe line 58 and associated parts may be held in assembled relationship with the base or bed plate 6 by means of the brackets l2, l2 afforded for that purpose.

With the power means or motor 2 at rest, the vacuum pump or exhaust means (not shown) may be set in operation while the cam follower 24 is seated as at 32 at the point of minimum radius on the cam wheel l8, and as the air is drawn towards the pump at 60, it may enter the line 58 through the solenoid controlled vent at 68 and through the ports 52 52 of the automatic valve. Thus atmospheric pressure will be maintained in the vacuum bell connected as at!!! at oneend of the line 58, the opposite end of said line being connected as at 69 to the vacuum pump. as already described. This condition of atmospheric pressure in the line and in the vacuum chamber is illustrated at the left of the graph of Figure 3 as at A-A, and at the right of said fi ure as at E-E. When the mold and ladle of molten metal (not shown) are in position for pouring, the electric motor 2 may be startedas by a switch which may. at the same time actuate the solenoid valve '58 to close the vent at 68. As the motor 20perates, the cam wheel I8 is rotated and the cam follower 24 isgradually elevated, bringing the valve 38 into engagement with the seat 48 and closing the ports 52, 52. Thestress of the spring 45 connected between the valve stem 44 and the link 36 varies from a minimum when the cam follower rests asat 32 at the minimum radius of the cannto whatever maximum tension is required to'obtain the desired maximum vacuum, which is reached when thecam follower has moved to the point of maximum radius on the circumference of the cam. The maximum strain thus afforded on the spring may be varied as desired, as already described, by the adj sting nuts at 42. Also, the rate at which the vacuum is developed may be controlled by modifyi the speed of the cam I8 and'the character of the curve joining the point of minimum radius to that of maximum radius thereon. This may conveniently be done by substituting cams of various form as desired.

It will be understood that as the cam follower moves about the cam from the point of minimum radius to that of maximum radius, the valve 38 is forced against the valve seat at 48 withprogressively greater pressure untilthe predetermined maximum is reached. This progressive 7 increase of pressure is illustrated in the graph of Figure 3. The line 3-3 illustrates the condition Y the air in the systemat the time of starting, a

variable amount of ,core gas developed by the contact of the molten metal in the mold with the cores which may form partsof said mold, and any air that may be drawn. into the. system through leaks as, for examplaat the juncture of the bell with the plate upon which, it may be seated, or elsewhere.

The intermediate area of the graph, hown in broken-line cross-hatching, represents the amount of air which maybedrawn into the system through the airports at 52, 52 in order to compensate for the variable amount of gases existing in the bell, and in order to produce the resultant desired pressure, as illustrated by the smooth curve X-Y of said graph illustrating the gradual increase of vacuum in the system. The

time-pressure curve shown at X-Z is controlled by the pressure the cam follower 24 exerts on the sprin 40.

If, at any time during the cycle, a greater vacuum tends to be produced in the bell than has been predetermined, atmospheric pressure will force the valve 38 away from the seat at 48, thus allowing air to, be drawn into the system through the ports 52, 52. In other words, thesystem including the vacuum chamber is being exhausted at a predetermined rate as the strain, of the spring' lfl is gradually increased due to the changing position of the cam follower 24.

It will be understood that there is an ununiform input into the vacuum chamber and the system because of leakages, the amount of which can not beforeseen, and because of the development of a variable amount of ,coregases within the molds. The purpose of the automatic valve is to superimpose on this ununiform input another input which is ununiform, but such that the total input combined with the output through the pump, willadjust the pressure in the system in accordance with thepredetermined time-pressure scale and to a predetermined. final value. The length'ofthecycle is also predetermined by the circumference-of the camdfl and when the said cam has rotated through a complete revolu. tion, the cam follower'24 will again drop tothe point of minimum radiusat which pointthe movails; when the maximum quantity oi gases is being withdrawn fromthe bell and the minimum quantity of air is being drawn into the system through the ports -52,'52. Shortly thereafter, a condition of substantial stability occurs, a s-il lustrated by the line D-D, where the gasesbeing withdrawn from the hell are substantially constant as are also those beingdrawn through the ports, and the straight line Y'Z-represents the maximum vacuum steadily maintained as aresult. The system is restoredto its, startingicondition with atmospheric pressure beingmaintainedin' the line and ,in the ,bell when the cam follower has travelled the circumference .of the cam l 8 and reaches again the startingpoint illustrated in Figure 2 when the motormaybeautomatically cutoff and the, solenoidvalve assembly reenergized. ;The vacuum bell may thenbe dismantled,-the mold removed, a new oneinserted, the bell replaced, and thecyclerepeated.

To those skilledin theart, itwill bounderstood that in asystem such as this itisnecessary to evacuate at a uniform rate. the vacuum,.or bell within which the castingis,,to be, poured. It will also be understood that there is an ununiform input into this vacuum bell due to leakages which are irregular and to the evolution of gases from the cores forming a part of the mold. The mechanism herein described superimposes on the above-mentioned ununiform input another input which is also ununiform but is such that the total of the two inputs, combined with the output to the pump or source of the vacuum, so adjusts the pressure in the dome or vacuum hell that it corresponds with a predetermined time-pressure cycle and reaches a predetermined final maximum value, as clearly set forth in the accompanying graph.

It will be understood that our automatic valve arrangement readily allows the free passage of any sudden surges of gas within the vacuum bell, such as may be caused by the admission of core gases to the vacuum pump, because the passage between the pump and the bell is free and unrestricted. Any such surge is immediately dissipated because an increase in pressure in the system allows the spring ll) immediately to close the automatic valve 38, thus greatly reducing the compensating values normally being drawn into the system.

To those skilled in the art it will be apparent that the function of the solenoid valve is merely auxiliary to the opening afforded by the autoat the valve 38 than would otherwise be possible.

In other words, if the solenoid valve were omitted, there would be a tendency for a slight vacuum to be created within the system before the valve 38 were entirely closed by the cam follower, and this slight vacuum might be developed in such manner as to interfere with the uniform degree of pressure within the system which is desired in order to flow the metal smoothly into the mold. By providing the vent 63 with the solenoid control therefor, it is possible to provide a large opening to the atmosphere which may be instantly closed when it is desired to begin reducing the pressure in the bell. The valve 38 will automatically control the rate at which this pressure is reduced.

It is to be understood that we do not wish to be limited by the exact embodiments of the device shown which are merely by way of illustration and not limitation as various and other forms of the device will, of course, be apparent to those skilled in the art without departing from the spirit of the invention or the scope of the claims.

We claim:

1. In a vacuum system having an ununiform gas input and exhaustion means therefor, automatic means for controlling a second ununiform input such that the total input combined with the output due to exhaustion thereof automatically adjusts the pressure therein at a predetermined rate of change, said automatic means comprising a valve in said system having an opening to the atmosphere, and means automatically responsive to the pressure in said system for controlling the input at said opening, said responsive means comprising yielding means under stress for maintaining said valve normally closed, and means for modifying said stress.

2. In a vacuum system having an ununiform gas input and exhaustion means therefor, throttling means for controlling a second ununiform input such that the total input combined with the output due to exhaustion thereof automatically adjusts the pressure therein at a predetermined changing rate, said throttling means comprising a valve in said system having an opening to the atmosphere, and means automatically responsive to the pressure in said system for controlling the input at said opening, said responsive means including yielding means under stress associated with said valve for maintaining said valve normally closed, and means for varying said stress at said predetermined changing rate.

3. Control means for a vacuum system having a vacuum source such as a pump, a chamber to be evacuated, and a connecting line therebetween, comprising a valve in said line, and automatic control means for said valve responsive to the pressure within said line to adjust the opening of said valve to atmospheric pressure, said means comprising resilient means connected to said valve and under stress to maintain said valve normally closed, and means for modifying said stress at a rate commensurate with the desired change of pressure in said system.

4. Control means for a vacuum system having an exhaust source such as a pump, a chamber to be evacuated, and a connecting line therebetween comprising a valve in said line, and automatic control means for said valve including yielding means responsive to pressure within said line to adjust the opening of said valve to atmospheric pressure, and means for varying the stress of said yielding means.

5. In a vacuum system having a source developing said vacuum, control means having a cycle operable to increase said vacuum in said system at a predetermined rate, said means comprising a valve in said system having an opening normally closed to the atmosphere at the beginning of said cycle, yielding means under stress at the beginning of said cycle to maintain said valve in said closed position, and means for varying said stress at a rate commensurate with said predetermined rate.

6. In a pressure regulating system for vacuum casting, a chamber to be evacuated, an exhausting pump, a connection between said pump and chamber, a differential valve in said connection having one side exposed to pump pressure and the other side to atmospheric pressure through a restricted opening, yielding means supporting said valve substantially closed, and control means connected to said yielding means and operable to modify the stress thereof at a rate commensurate with the desired rate of change of pressure within said system.

7. In a vacuum system having a source developing said vacuum, control means operable to increase said vacuum in said system at a predetermined rate, said means comprising a valve in said system having an opening normally closed to the atmosphere, yielding means operable to maintain said valve in said closed position, and means for varying the stress of said yielding means at a rate commensurate with the desired rate of change of pressure in said system.

THOMAS C. POULTER. CHARLES F. STROM,

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