US 3795726 A
Description (OCR text may contain errors)
March 5, 1974 L. R. ZIFFERER ET AL 3,795,726.
REDUCTION OF RESIDUAL uoxxous GASES IN GAS HARDENED MOLDS AND coREs Filed Aug. 17, 1971 3 Sheets-Sheet 1 Q \-?o A|R CHAMBER LS-l CHAMBER '1 l2 ATMOSPHERE 2-WAY SOL. PRESS.
VALVE S W. '0 CORE ox I l s-2 CO2 40 FILTER L ll VALVE I I I /-PRESS.
3o s w. REAGENT GAS VAQS 2-WAY SOL. VALVE ll 28 F% 2-WAY s0| VALVE 2.2 44 l k u I PRESS. 32 46 n sw. 22.
EFFLUENT AIR JFATMOSPHERE OR CO2 VAC. PUMP 52 CIRCUT CONTROL UNIT 0 INVENTORS l v LOTHAR R-. Z IFFERER 58 LESTER F. STUMP JR.
I BY jWM AT TOR Y United States Patent 3,795,726 REDUCTION OF RESIDUAL NOXIOUS GASES IN GAS HARDENED MOLDS AND CORES Lothar Robert Zilferer and Lester F. Stump, Jr., York, Pa., assignors to Alphaco, Inc., York, Pa. Continuation-impart of application Ser. No. 22,586, Mar. 25, 1970. This application Aug. 17, 1971, Ser. No. 172,524
Int. Cl. B22c 9/12 US. Cl. 264-82 13 Claims ABSTRACT OF THE DISCLOSURE A process and apparatus to produce foundry cores and molds by the use of toxic and noxious basic, i.e., alkaline, reagent gases, such as an amine gas, to cure certain mixtures of sand and resin binders, the binders being cured by the reagent gases to stabilize the cores and molds. The cores and molds may also, if desired, include a combination of two diiferent binder systems including a relatively expensive resin binder, especially to produce precise working surfaces on fine sand surfaces and a more economical back-up mass of coarser sand bonded by less ex pensive binders such as sodium silicate. The noxious and toxic gases are removed from the products to a sufficient degree for tolerance from a health and comfort standpoint. This result is accomplished by using air to force the amine gas into the interior of the mold or core and a combination of vacuum and air purging steps.
This application is a continuation-in-part of Ser. No. 22,586, filed Mar. 25, 1970, and now abandoned.
BACKGROUND OF THE INVENTION In general practice, sand cores and molds are made by mixing sand with from 1% to liquid binder to obtain a free flowing mix which is formed around a pattern in a flask or in a core box to the desired shape. Binders, depending upon the type used, may be dried or cured to harden the sand form by heat or by the use of reagent gases. In all instances, the hardened sand forms are held together by the cured or dried binder to provide operative working surfaces which, in the case of cores, form cavities in metal castings or, in the case of molds, form the outer or finished surfaces of metal castings.
It is important in founding metals that the cores which are used have certain desired characteristics which enhance the economics of the operation. Among these characteristics are; the necessity that the curing process must be rapid and such as to minimize the cost of pattern equipment. The core which is produced must retain its form and strength until the metal stabilizes or freezes and then the core should disintegrate as rapidly and completely as possible to minimize the cost of removing the residual sand component of the core from the internal voids and cavities in the casting. Other properties of a core which are deemed necessary are that it not cause hot tears in the castings, pinhole porosity or other surface defects which Wouldsubtract from dimensional tolerances or the physical strength of the casting, and that the core retain its properties in highly humid atmospheres. Cores formed by the use of resin binders excel in these properties, as compared with cores formed with conventional non-resin binders.
Many processes are used at present for the production of cores, but resulting advantages increasingly favor cores which are cured in the core box or pattern before being removed therefrom. These are called precision cores and are distinguished from cores which are transferred from boxes into dryers for drying in ovens, which result frequently in warping or abrading in handling. The econ omy of production and improved quality of cured-in-thebox precision cores greatly exceeds conventional cores and great emphasis is being put at present on methods and processes which can improve the production speed and minimize the pattern cost to produce such quality cores.
Prior Pats. Nos. 2,824,325; 2,876,510; 2,928,149, and 3,098,269 of one of the instant applicants are directed to curing sand binder mixes in a core box by the use of C0 gas or other acid gases which react with sodium silicate binder and can be neutralized. In some instances, the core box containing the sand binder mix is placed in a vacuum chamber while in other instances, the core box is equipped with a check vent and the core is cured in the box without the use of a chamber. By these means, acid gases are used as a reagent for the binder to produce precision cores. The gases used as reagents were either nontoxic or could be neutralized successfully and the various apparatuses described in these patents were satisfactory for their intended purposes.
As this art has progressed, various resinous binders have been discovered to be useful which can be cured very rapidly with basic or alkaline reagent gases to produce cores that have good physical properties and have excellent collapsibility after the molten metal has been stabilized or frozen. These two properties are in many situations superior to those of cores and molds produced by sand which includes sodium silicate reacted with CO reagent gas as a binder. The various resin compositions of the binders currently used require the use of NH or, preferably, one of the amine gases or vapors such as trimethylamine or triethylamine as curing agents. These gases are basic and do not injure the internal part of vacuum pumps, automatic valves, patterns or core boxes employed in the process and apparatus, and therefore are desirable from this standpoint. However, these basic gases or vapors are toxic and noxious, and it is therefore necessary that concentration thereof in the work area be maintained below 25 parts per million of air so as to be reasonably tolerable for comfort and safety of the operators.
To date, it has been extremely difficult to develop pattern equipment or core boxes with seals that can dependably contain these gases while they are pressurized to permeate completely through the sand-resin mix. In addition to this difliculty, the use of a mixture of air and basic triethylamine, according to presently used pressurizing methods, leaves a residue in the cured core or mold of triethylamine condensate which slowly emanates from the core as a noxious vapor after the same has been cured and removed from the box. As a result, cores cured by such reagents require very expensive pattern equipment and continue to release concentrations of triethylamine into the work area to such extent that the 25 parts per million concentration established as a minimum health standard cannot be maintained economically. The toxicity hazard and odor characteritsics of this process therefore has handicapped its acceptance by the industry.
While 25 ppm. of trimethylamine or triethylamine are deemed adequate as a concentration to meet the minimum health standards, the realities are that such amines are the same gases as are given off by decaying fish or meat and are so noxious that much lower concentrations must be achieved if the processes using these reagents are to gain acceptance. As an example, a person walking through an area with a concentration of 25 ppm. of such reagent gases can absorb enough of the odor in his clothing that it can only be removed by aerating the clothing for two or three days in a wellventilated space. While some other amines are less noxious than trimethylamine and triethylamine, the difference is only a matter of degree, since all amines have this characteristic of objectionable odor.
SUMMARY OF THE INVENTION It is the principal object of the present invention to provide apparatus and methods which can be used to:
(a) positively assure work area concentration of noxious binder reagents below objectionably detectable levels,
(b) conserve the use of costly reagents,
(c) make possible the use of simple pattern equipment which can be made from substantially any materials and eliminate the need for expensive seals,
(d) greatly increase the speed of the curing process, and
(e) make possible the complete curing of large cores in large boxes which is not currently feasible by present pressurizing methods.
It is another object of the invention to provide a control system which sequences positively and in a foolproof manner by means of sensing the pressures in the chamber and thus minimizes the total machine cycle time irrespective of the size of core or mold being cured or of the size of the chamber employed and produces a predictable concentration level of noxious gases in the void spaces between the sand grains of the cured core, the desired steps of the process occurring strictly and automatically in an uninterruptable manner until the cycle is completed to provide mold and core products which present no health hazard and are technically satisfactory.
It is a further object of the invention to provide a core or mold composed of two different sand and binder systems to minimize the overall cost thereof while providing maximum smoothness on the working surfaces with adequate strength furnished by less expensive backup sand and binder material.
Details of the foregoing objects and of the invention, as well as other objects thereof, are set forth in the following specification and illustrated in the accompanying drawings comprising a part thereof.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic layout of an exemplary system capable of employing the principles of the system comprising part of the preesnt invention.
FIG. 2 is an exemplary electrical circuit for the system shown in FIG. 1.
FIG. 3 is an exemplary graph of pressures employed in a preferred cycling sequence of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of facilitating the comprehension of the present invention, some basic situations and characteristics of molds and cores with which the invention is concerned are set forth, as follows.
100 pound core requires approximately 1 cu. ft. of sand and there will be approximately 4 cu. ft. of void space between the sand grains. Therefore, the residual concentration of gases therein at the end of the cure would be or 1 part in 80,000 or approximately 12.5 p.p.m. As these trapped gases which occupy void spaces in the core are given off, they are diluted by the surrounding air and, as an example, the concentrations in the work area will be maintained below 1 p.p.m. if the .4 cu. ft. of reagent air mix further mixes with 5 cu. ft. of ambient air. At levels below 1 p.p.m., the amine gases cease to be detectable or noxious. As the reaction chamber is opened to atmosphere, air is used to purge it so that the chamber itself when opened has a concentration of less than 1 p.p.m. and this concentration likewise cannot be detected.
Improvements to the vacuum gassing equipment of the aforementioned patents which comprise part of the present invention also makes possible the use of the noxious reagent gases such as trimethylamine and triethylamine with low cost wooden core boxes or conventional equipment and completely eliminates the hazard of undesired reagent gases in the work area by the use of automatically sequencing control means' 'Further in accord with the invention, a number of process steps are necessary to achieve a substantially complete cure of the binder and to achieve the extremely low residuals of reagent gas in the cured product. These process steps are necessitated by the kinetics of gas movement and by the rates of diffusion between two dissimilar gases. The following sequence of events takes place at various stages of the process. For purposes of illustration, atmospheric pressure will be assumed to be 760 mm. of Hg.
An exemplary core box 10 containing a cavity is filled with a sand-resin mix in which the resin may be selected from any suitable organic resin such as those referred to, for example, in Pats. Nos. 3,428,110, dated Feb. 18, 1969, and 3,409,579, dated Nov. 5, 1968. An appreciable range of such resins are referred to therein, such as epoxy, polyester, petroleum polymers, alkyd, and phenol-formaldehyde thermosetting resole resin, which are supplemented by various additives, including polyisocyanate, one sepcific example of which is 4,4 diphenylmethaneisocyanate. The foregoing are merely illustrative rather than restrictive, as long as the same may be reacted with an appropriate amine such, for example, as those referred to above, in suitable proportion to set the resin and thus solidify the sand mold or core.
In the foregoing curing procedure, the chemistry involved actually is that the trimethylamine or triethylamine is a catalytic reagent gas which accelerates chemical reaction of phenolic resin binder, for example, in one part of a suitable solvent with polyisocyanate in another part of a solvent. Only relatively minute traces of the amine, such as less than 0.1%, by weight, of the mixture, are required for such catalytic purpose. The polymerization reaction of the phenol and isocyanate effects a rigid resin bond upon the sand particles which, per se, do not enter into such chemical reaction which produces the bond. This phenomenon distinguishes this process over certain prior processes in which the sand filler or aggregate engage chemically in forming the bond of the product.
The core box 10 is placed in a vacuum chamber 14. The chamber may be of the bell-type, raised and lowered by a cylinder and piston unit 16, or base 18 may be raised relative to the bell 14, if desired. When the chamber is closed, the pressure therein is reduced by means of a vacuum pump 20 to approximately 12 mm. of Hg, as shown in FIG. 3. Further reduction in pressure is not practical as the solvent in which the resin is dissolved would vaporize. At this point, the chamber pressure is of an atmosphere of absolute pressure.
A solenoid-operated valve 22, which preferably is actuated by a pressure-responsive switch 24, is connected in conduit 26 between the vacuum chamber and the pump 20. Valve 22 is closed when said aforementioned degree of vacuum is reached, and a solenoid-actuated valve 28, which is operated by another pressure-responsive switch 30, is opened to connect the vacuum chamber to a source of reagent gas in supply source 32. The exemplary tank 32 is merely illustrative of any suitable source of reagent gas such as trimethylamine or triethylamine.
When the reagent gas enters the chamber, the atmosphere of air within and surrounding the core box feeds into the core box ahead of the reagent gas before diffusion between the two gases can take place. It is necessary to limit the pressurization of the chamber with such reagent gas to approximately 50 mm. of Hg absolute pressure, as also shown in FIG. 3, and this is controlled by means of the pressure-responsive control switch 30 which closes valve 28. Subsequently, atmospheric air from inlet 34 is introduced through a 3-way valve 36 and solenoidactuated valve 38, controlled by a further pressure-responsive switch 40, to bring the chamber pressure, through conduit 42, to about 735 mm. of Hg. The incoming air which follows the reagent gas forces a sufficient quantity thereof into the extremities of the core box and especially into the voids within the core to at least partially cure the same during the time within which the air is increasing the pressure to said exemplary pressure of about 735 mm. of Hg. Such time is adequate to cure the resin to a substantial degree but not completely.
When vacuum gassing foundry sand cores and molds to remove reagent gasses of the type employed in the present process, it has been found that single cycle gassing is not sufficient to produce fully cured products. There are occluded pockets of air in the innermost voids which are not removed by a single evacuation and the reagent gas is precluded from entering such voids. Hence a second cycle of evacuation and applications of reagent gas and atmospheric air are undertaken according to this invention, as follows.
The next series of steps in the process of the invention is for purposes of finally and substantially completely curing the cores in the innermost portions and comprises again reducing the chamber pressure to approximately 12 mm. of Hg, followed by pressurizing the chamber with reagent gas to 50 mm. of Hg, and again introducing atmospheric air to the chamber to restore the pressure to 735 mm. of Hg to force the reagent gas ahead of the air into the innermost voids of the core to effect curing the resin binder completely throughout the product and thereby produce a relatively rigid core having adequate strength throughout the mass thereof. This operation also intimately mixes the residual air and reagent gas incident to producing a fully cured core. Obviously, molds may also be made by the foregoing procedure and a substantially fully cured mold likewise will be produced at the completion of said process. At this stage of the process, a reagent to air mixture of approximately 1 part in 20 is present in the chamber and in the core.
The chamber 14 is again reduced to 12 mm. of Hg by the pump 20 and, when that degree of negative pressure has been reached, air from inlet 34 again is introduced to increase the pressure to about 735 mm. of Hg. This procedure also preferably is repeated to positively insure adequate purging of the chamber and core or mold of the reagent gas, except that in said repetition of such procedure the pressure is raised to 760 mm. of Hg and the chamber 14 then is opened at a controlled rate by cylinder 16 while the vacuum pump 20 preferably continues to operate to remove, by scavenging, the 12.5 ppm. of reagent gas-air mixture from the chamber and thereby reduce the chamber concentration of reagent gas preferably to less than 1 p.p.m.
While a typical and preferred embodiment of the process has been set forth when using either trirnethylamine or triethylamine as a reagent gas, it is possible that other amines would permit the elimination of the last stage of purging with air. The extent to which an odor is deemed tolerable also can permit different absolute pressures inthe evacuation and repressurization with the reagent gases.
The preferred steps essential to achieving an acceptable cure substantially throughout a core or mold have been outlined above. It should be noted that the double repressurization of the chamber with reagent gas from 12 to 50 mm. requires of an atmosphere of reagent gas per stage or of an atmosphere per machine cycle. Such economy which is realized in the use of reagent gas by this process is as important to its commercial acceptance as the elimination of noxious odors in the work area.
This invention also is adapted to produce a core or mold composed of two chemically cured sand systems. Inthis regard, it often is desirable to take advantage of the properties of a chemically cured organic binder in one part of a mold or core and to use another binder material, such as sodium silicate, in another part. Thus, the different properties of two binder systems can be used to best ad 6 vantage. Sometimes large quantities of a cheaper binder can be used in lieu of a more expensive binder system.
As an example of the foregoing, a relatively thin facing of an organic binder-sand mixture on a pattern can be backed up by a more massive sodium silicate-sand mixture. In the gassing process used to cure the binders, an amine gas is first introduced into the chamber, after initial evacuation to 12 mm. of Hg, to repressurize the chamber to 50 mm. of Hg, and then CO gas, rather than air, is introduced to complete pressurization of the chamber to about 735 mm. and thereby force the amine gas into the voids of the core or mold being formed. This is accomplished by an initial manual setting of 3-way valve 36 in the apparatus system shown in FIG. 1 to connect the tank 44, containing CO under pressure, to chamber 14. Such procedure is repeated and then the two purging stages using air, as described above, are used, whereby the chamber is re-evacuated to 12 mm. and pressurized with air which, on the final stage, raises the pressure to 760 mm. before opening the chamber. To accomplish this Without disturbing 3-way valve 36, a solenoid-operated valve 46, which communicates with the atmosphere and is controlled by pressure-responsive switch 48 is connected to conduit 26 and is suitably controlled to effect such cycling.
In some limited situations, it may be desirable to use the sodium silicate-sand mixture as a facing and the organic binder-sand mixture as a back-up material to obtain the benefit of the collapsibility and low gas evolution which characterizes the resin binder.
The ability to obtain full cures of a two binder system can contribute substantially to the flexibility and economy of the process in certain operations, such as described in a copending application in the name of one of the instant applicants.
In the above-described procedures and operation of the systems therein described, it is preferred that when the pump 20 evacuates the chamber 14 and the molds or cores contained therein, the noxious and toxic reagent gases withdrawn therefrom may be rendered harmless and unobjectionable by passing the pump discharge into a bath 50. Said bath may be of a neutralized nature, such as a solution of phosphoric acid, and the neutralized product then may be discharged to atmosphere through conduit 52. Otherwise, if desired, the exhaust from the pump may be burned, such as by combining it with acetylene.
The operations of the systems described above and the cycling of the various switches and valves thereof can be rendered foolproof and cyclically irreversible for safety by rendering the steps of such procedure substantially automatic by the use of a stepping relay 54 having an adequate number of stations, whereby there is no danger of miscycling, as by hand operation, and a safe final atmosphere is assured at all times. The relay 54 may be contained, for example, in a control box 56, shown in FIG. 1. Details of the stepping relay 52 and 54 and the circuitry connected thereto are shown in FIG. 2 in which the stepping relay is shown in an exploded diagrammatic manner.
The electric control circuit shown in FIG. 2 in diagrammatic manner operates the system shown in FIG. 1 to perform the procedures and functions described above to correctly cycle any feasible size of chamber with any feasible size of vacuum pump and work load because each stage of the machine cycle is brought to a predetermined desired pressure and this pressure, whether of an increased or decreased nature, when attained, actuates the stepping relay 54. The stepping relay 54 automatically cuts off the power input to the first stage of the method after it has attained the correct pressure and powers the second stage of the method. When the second stage reaches its predetermined pressure, the stepping relay is again automatically actuated to shift the power to the third stage of the process, etc. In this manner, a series of stages of the process are sequentially powered automatically until each stage of operation of the cycle of the system of FIG. 1 has been completed, after which the chamber opens automatically and the system is ready to repeat all of the stages of the process.
It is extremely important that each stage of the system of process achieves an exact predetermined absolute pressure in order for the residual reagent gas in air, in p.p.m., to be an exact quantity at the completion of forming the product. Since the size of the core or mold will vary the space occupied in the chamber and the pumping time required by the vacuum pump 20, it is not practical to use time as a control means. If this were done, the operator would be required to separately adjust the time allotted for each stage of the process to achieve the predetermined pressure necessary for each stage. Factors such as the temperature and pressure of the reagent gases, variable pump efiiciency, depending on lubricant temperature, chamber work load, binder concentration and other factors, make a time-dependent control system impracticable. The method employed by the present control circuit therefore is believed to be the most practical as a control means to repetitively attain a predictable concentration of reagent gases remaining in the work area and completed cores and molds.
It will be seen from the following description that the control system shown in FIG. 2 can be usel substantially equally well either to cure an organic binder-sand mix with either trimethylamine or other amine gas, or to cure a two-binder system consisting of an organic bindersand mix and a sodium silicate-sand mix such as used to make a composite core or mold by the successive introduction of an amine gas and CO gas in a single machine cycle. Either curing method can be selected by operating the manually controlled 3-way valve 34 which selectively permits the introduction therethrough of air for an organic binder-sand core, or CO gas when curing a twobinder core or mold.
CONTROL CIRCUIT To initiate the process, the toggle switch 58 is closed to energize the control system and lights the indicating lamp 60 as visible evidence the system is ready to operate. The button of starting switch 62 then is pressed to close relay 64 and latches the same to establish power to lines 66 and 68. The electrically operated air valve 70 thereby is energized and introduces air to the air cylinder 16 to close the chamber 14. The stepping relay 54 is actuated by means of line 72 to open stepping relay contact SR8 and close stepping relay contact SR1. As the chamber closes, limit switch LS2 closes and power is established in line 74 and at SR1. The vacuum line valve 22 thereby is energized to open the line to the vacuum pump which reduces the chamber pressure to approximately 12 mm. of Hg absolute pressure.
When 12 mm. of Hg pressure is attained, the contacts of vacuum-responsive switch 24 close to energize the stepping relay again to open SR1 and close SR2. Opening SR1 de-energizes and closes the vacuum line valve 22 and the closing of SR2 energizes and opens the reagent supply valve 28 to introduce the amine gas into the chamber. As the chamber pressure rises from 12 mm. of Hg to about 50 mm. of Hg absolute pressure, the contacts of pressure-responsive switch open the circuit which deenergizes and closes the valve 28 and energizes and opens valve 38 either to atmosphere or CO Air or CO depending upon the setting of 3-way valve 36, is introduced under pressure into the chamber to increase the absolute pressure to about 735 mm. of Hg. When the chamber pressure thus reaches 735 mm. of Hg, a second pressure responsive switch 48 operates to de-energize the CO or atmospheric valve 38 and thereby close it and also energize the stepping relay and move it to open SR2 and to close SR3. SR3, when closed, feeds through line 74 to energize and open the vacuum valve 22 which remains open until an absolute pressure of about 12 mm. of Hg is again attained, whereupon the vacuum valve switch 24 operates to again energize the stepping relay to open SR3 and de-energize and close the vacuum valve 22 and also close SR4.
Closing SR4 again introduces the reagent gas, in the manner described above, to again pressurize the chamber from 12 mm. of Hg to about 50 mm. of Hg, after which the pressure-responsive switch 30 operates to close the valve 28 and open the CO or atmosphere valve 38. The second pressure-responsive switch 48 operates at about 735 mm., slightly below atmospheric pressure, to close the CO or atmospheric valve 38 and again energize the stepping relay. This movement of the stepping relay opens SR4 and closes SR5. SR5 opens the vacuum valve 22 and it remains so until the chamber pressure again reaches 12 mm. of Hg. The vacuum-responsive switch 24 then operates to energize the stepping relay to open SR5 and close SR6. When SR5 opens the circuit, line 74 is broken and the vacuum valve 22 is closed. SR6, when closed, causes operation of a second valve 46 which opens to atmosphere to pressurize the chamber a limit of substantially 735 mm. of Hg. When 735 mm. of Hg pressure in the chamber is reached, the pressure-responsive switch 48 in this circuit operates to deenergize and close the valve 46 to atmosphere and also energize the stepping relay line 72 to provide impulse A. The stepping relay thereby opens SR6 and closes SR7. It should be noted that relay CR2 is provided to prevent a feed back to SR8 when SR6 is closed.
When SR7 is closed, the vacuum valve 22 is opened to reduce the chamber pressure to about 12 mm. of Hg, at which pressure the vacuum-responsive switch 24 energizes the stepping relay to open SR7 and re-energize and close both the vacuum valve 22 and SR8. SR8 energizes and closes both CR2 contacts to energize and open the vacuum valve 22 and also energize the time delay re lay 76. The vacuum valve 22 admits air to the chamber until the chamber pressure equals atmospheric pressure. The time delay relay 76 delays the opening of CR1 until the chamber is at atmospheric pressure and then CR1 opens and closes the air valve 70. When the air valve 70 is closed, the air cylinder 16 is operated to open the chamber to permit removal of the core or mold which has been formed therein.
As the chamber opens, limit switch LS2 also opens and disconnects the main power circuit and leaves SR8 as the only closed contact of the stepping relay. The
opening of the chamber causes the switch LS1 to be closed for momentary contact. The time delay relay 76 instantly closes the contacts of switch 24 which energizes the solenoid of the vacuum valve 22 to open it and it will remain open for a predetermined interval to scavange any residual reagent gases which may be left in the chamber. Time delay relay 76 then opens to de-energize the solenoid of the vacuum valve 22 and close it. The chamber is now open. Selectively, it now can be unloaded, reloaded and recycled.
The circuit as described is illustrative to indicate how the functions of the system are performed. In practice, it is sometimes necessary to alter the trip point of the vacuum valve control switch 24 to operate at a higher pressure than 12 mm. of Hg. This may be done, for example, if when curing a composite mold, the ambient temperature of the sand-binder mix is sufficiently high that water vapor is pulled from the sodium silicate. Under these conditions, the vacuum switch 24 can be adjusted to operate at 50 mm. of Hg, for example, instead of 12 mm. of Hg. When this is done, it is necessary to repressurize the chamber with reagent gas to a higher pressure, such as about mm. of Hg instead of 50 mm. To achieve this, the pressure switch 30 which controls the introduction of reagent gas is set to occur at the higher pressure.
It is to be noted that, with a given system cycle, lower residual amounts of reagent gases will occur in organic binder cores than in composite binder cores or molds. Also, when a double air flush is deemed insufiicient, the control circuit can be extended by the use, for example, of a IO-stage stepping relay to make possible three air flushes by repeating the functions performed by SR and SR6. Other circuits which are equivalent also can be devised by substituting normally open valves for some of the normally closed valves illustrated herein or by using limit switches. In this sense, the circuit illustrated herein serves to show how to achieve the functions necessary to the cycle for a given system different from that shown and described.
From the foregoing, it will be seen that the electrical control circuit, the various pressure responsive switches which are in the circuit, and the control valves for forming vacuums and selectively introducing reagent gas and/or atmospheric air are all cooperating elements in a system by which sand cores and molds which are bonded by chemical setting reactions of binders and reagents by the automatic cyclical functioning of the system which, at least during normal intended operation thereof, cannot be interrupted. The processing chamber cannot be opened until both the atmosphere therein and the reagent content of the product has been reduced to a safe residual content which is neither objectionably noxious or toxic to workmen either while making the cores or molds, or using the same in foundry operations.
Furthermore, such products are expendable and therefore, must be produced as cheaply as possible. Thus, speed of production with minimum physical handling and operations is essential. The process of the present invention, which is operable automatically in response to pressures and not time, involves no physical manipulation or handling except for loading and unloading the chamber, whereby operation time is minimal. Even in regard to forming large pieces in correspondingly large cham- Ibers, only enough time is consumed to effect necessary cycling steps of a duration adequate to achieve complete curing of the bonding agents for the sand.
Also, in regard to forming cores and molds of two chemically cured sand systems, essentially the same apparatus is used with the exception, for example, of providing an additional source of a second reagent gas and shifting a valve at the beginning of the process. Hence, the savings in labor, floor space and capital investment achieved by combining two curing processes into one constitutes an important advantage over other methods and systems now in use.
It is also to be noted that the processes comprising the present invention are operable without requiring any heat to achieve curing of the binder materials, thereby simplifying the components of the system in which the products are chemically rather than thermally cured. Further, curing the resin binders of the present invention with an amine catalyst and then withdrawing the same from the cured product is superior to neutralizing the same in the product, for example, with an acid gas because such products of neutralization are detrimental to the core and mold by forming a gummy residue that clogs filters and destroys and internal structure of vacuum pumps.
While the invention has been described in relation to preferred usage relating to the degree of vacuum obtained and the sequential introduction of reagent and flushing gases at specific pressures, other levels of vacuums and pressures are usable and the premixing of reagent gases or of a reagent gas with a non-reagent gas are workable alternatives includable within the scope of the method and apparatus as herein set forth.
1. A method of substantially completely curing a molded article for use in foundry casting and comprising a mixture of sand and an organic resin binder curable by reaction with an amine gas, said method comprising the steps of:
(a) subjecting said article to a high degree of vacuum of predetermined amount within a chamber,
(b) introducing an amine reagent gas into said chamber when said degree of vacuum is reached to impregnate said article and react with and at least partially cure said resin binder and thereby decrease said vacuum a predetermined amount appreciably less than atmospheric,
(c) introducing atmospheric air into said chamber to increase the pressure to slightly below atmospheric to force the reagent gas into the voids of the article,
(d) again subjecting said article to a high degree of vacuum when said foregoing pressure has been reached to withdraw the reagent gas and air mixture and thereby enhance withdrawal of occluded air from the remote voids in said article,
(e) introducing said amine reagent gas into said chamber when said degree of vacuum has been reached to cause said reagent gas to penetrate said remote voids and thereby complete the cure of said resin binder substantially throughout said article, so as to permit the effective withdrawal of a hardened sand form from the defining pattern surface, and increase the pressure to a predetermined degree less than atmospheric,
(f) introducing air into said chamber to increase the pressure therein to slightly below atmospheric and thereby force said reagent gas into the innermost voids of said article to effect complete curing of said resin binder,
(g) further subjecting said article and chamber to a high degree of vacuum after said predetermined degree of pressure has been reached to effect substantial withdrawal of said air and reagent gas mixture from said article to establish an absolute high degree of vacuum,
(h) introducing air into said chamber when said high degree of vacuum has been reached to increase the pressure approximately to atmospheric and thereby greatly dilute the residual reagent gas in the article, and
(i) opening said chamber when atmospheric pressure is reached to permit removal of said article in substantially completely bonded condition, whereby rapid curing of the resin binder is effected by consumption of only a minimum amount of reagent gas which is commercially economically acceptable and results in an acceptable safe level of reagent gas in the work area.
2. The method according to claim 1 in which said steps are performed automatically by apparatus responsive only to absolute pressures which are attained at the end of the various steps and thereby control the next step in the cycle of operation of the method.
3. The method according to claim 1 including the further steps prior to opening said chamber of again automatically subjecting said article and chamber to a high degree of vacuum, and subsequently thereto automatically introducing air into said chamber after said high degree of vacuum has been attained to increase the pressure therein approximately to atmospheric and thereby dilute the residual reagent gas in said article to a greater extent than the dilution previously effected in said process by the preceding steps.
4. The method according to claim 1 in which said high degree of vacuum produced in said chamber is approximately 12 mm. of Hg.
5. The method according to claim 1 in which said predetermined amount of decrease in vacuum in said chamber is approximately to 50 mm. of Hg.
6. The method according to claim in which said high degree of vacuum is approximately 12 mm. of Hg.
7. The method according to claim 1 further including the step of neutralizing the air and reagent atmospheres withdrawn from said chamber to produce a safe disposable efiiuent gas and discharging said neutralized gases to atmosphere with approximately no noxious odors being present.
8. A method of curing a molded composite article for use in foundry casting and comprisingan outer operative surface portion formed from a mixture of relatively fine sand and an organic resin binder curable by reaction with an amine gas and a backup body formed from a mixture of sand coarser than said fine sand and sodium silicate binder, said method comprising the steps of:
(a) subjecting said chamber and article to a high degree of vacuum,
(b) introducing an amine reagent gas into said chamber to react with and at least partially cure said resin binder and thereby decrease said vacuum in said chamber to a predetermined amount substantially less than atmospheric,
(0) introducing CO into said chamber to react with and cure said sodium silicate binder and increase the pressure within said chamber approximately to atmospheric while also diluting said amine reagent gas with said C0 ((1) again subjecting said article and chamber to a high degree of vacuum to withdraw said reagent gases and remove occluded air trapped within the innermost pores of said article,
(e) again introducing said amine reagent gas into said chamber to further react with and complete the curing of said resin binder and thereby increase the pressure to a predetermined amount substantially less than atmospheric,
(f) again introducing CO into said chamber to complete the curing of said sodium silicate and increase the pressure within said chamber to a value approximately slightly below atmospheric,
(g) further subjecting said article and chamber to a high degree of vacuum to purge the same of said amine reagent gas and CO and greatly reduce the concentration thereof,
(h) introducing atmospheric air into said chamber to increase the pressure approximately to atmospheric and thereby greatly dilute the residue of amine reagent gas and CO in said article, and
(i) opening said chamber while applying vacuum to the same to further remove residual amine reagent gas and CO and permit removal of said composite article in completed condition and having no appreciably objectionable trace of the odor of said reagent gas, whereby rapid curing of said resin binder is effected by consumption of only a minimum amount of reagent gas which is commercially economically acceptable and results in an acceptable safe level of reagent gas in the work area.
9. The method according to claim 8 including the further steps prior to opening said chamber of again subjecting said article and chamber to a high degree of vacuum, and then introducing atmospheric air thereinto to increase the pressure approximately to atmospheric and thereby purge the same of said amine reagent gas and CO and also greatly dilute the residue of amine reagent gas in said article to said acceptable safe level.
10. The method according to claim 8 in which said high degree of vacuum produced in said chamber is approximately 12 mm. of Hg and said subsequent decrease in said vacuum to a predetermined amount is approximately to 50 mm. of Hg.
11. A system for curing automatically and under conditions safe to the operators a molded core or mold for use in metal founding and comprising a mixture of sand and organic resin binder suitable to be cured by reaction with an organic reagent amine gas in accordance with a method of cyclical steps, said system being operable to perform the cyclical steps of said method automatically and comprising in combination:
(a) a chamber operable to be opened and closed relative to supporting means therein for a sand core or mold,
(b) conduit means connected at one end to said chamber and the other end being connected to a source of amine reagent gas,
(0) conduit means connected at one end to said chamber and open to atmosphere at the other end,
(d) a vacuum pump connected by conduit means to said chamber,
(e) electrically operated valve means respectively in each of said conduit means leading to said amine reagent gas, vacuum pump and atmosphere,
(f) pressure-responsive electric switch means connected to said valve means to control the opertaion thereof, said switch means being operable automatically solely in response to pressure conditions in said chamber resulting sequentially from the cyclical steps of said method, and
(g) sequentially operable electrical relay means connected to said electric switch means and operable stepwise solely in response to differences in pressure within said chamber to effect the successive steps of introducing amine reagent gas, evacuating said chamber, purging said gas by introducing air into said chamber followed by additional evacuation of said chamber, repeating said series of steps, and opening said chamber to remove the cured product, whereby the use of pressure-responsive electric switch means provides foolproof safe operation of the system against possible failure or malfunction of the vacuum pump.
12. The system according to claim 11 further including an additional conduit connectable to a source of CO a 3-way valve in said conduit operable selectively to permit introduction of CO or to communicate with atmospheric air to introduce it into said chamber following the introduction of reagent gas into said chamber, and a pressure-responsive switch and electrically operated valve in said conduit connected to and operated by said switch, said pressure-responsive switch being connected to the circuit of and operable by said stepping relay.
13. The system according to claim 11 further including a neutralizing bath adapted to contain a solution operable to neutralize said noxious organic reagent gas, and a conduit leading from the discharge of said vacuum pump into said neutralizing bath to transmit said noxious organic reagent gas thereinto for neutralization.
References Cited UNITED STATES PATENTS 3,590,902 7/1971 Walker et al. 164--16 2,824,345 2/1958 Ziiferer 1647 2,876,510 3/1959 Zifferer 1647 3,209,420 10/1965 King et al. 16416 3,038,221 6/1962 Hansberg 1647 3,266,108 8/1966 Dunning et a1. 16412 3,528,481 9/1970 Lund 16416 3,556,195 1/1971 Lund 16416 JOHN H. MILLER, Primary Examiner US. Cl. X.R.