US3046624A - Method and apparatus for weather responsive moisture compensation - Google Patents

Description

July 31, 1962 H w. DIETERT ETAL 3,046,624

METHOD AND APPARATUS FOR WEATHER RESPONSIVE MOISTURE COMPENSATION Filed Dec. 21, 1959 4 Sheets-Sheet 1 I I I I I l INVENTORS HARRY W. DIETERT y RA DQL H. w. DIETERT ETAL 3,046,624 METHOD AND APPARATUS FOR WEATHER RESPONSIVE MOISTURE COMPENSATION July 31, 1962 4 Sheets-Sheet 2 Filed Dec. 21, 1959 FIGA.

INVENTORS HAR Y -W. DIETERT.

OLPH L.DIETERT July 31, 1962 H. w. DIETERT ETAL 3,046,624

METHOD AND APPARATUS FOR WEATHER RESPONSIVE MOISTURE COMPENSATION Filed Dec. 21, 1959 4 Sheets-Sheet 3 FIGS.

IN V EN TORS HARRY W. DIETERT DO PH L.DIETERT TTORNEY July 31, 1962 H. w. DIETERT ETAL 3,046,624

METHOD AND APPARATUS FOR WEATHER RESPONSIVE MOISTURE COMPENSATION 4 Sheets-Sheet 4 Filed Dec. 21, 1959 INVENTORS HARRY W. DIETERT R ND LPH L.DIETERT 3,046,624 METHGD AND APPARATUS FOR WEATHER RESPONSW'E MUISTURE COMPENSATION Harry W. Dietert and Randoiph L. Dietert, Detroit, Mich,

assignors to Harry W. Dieter-t Co., Detroit, Mich, a

corporation of Michigan Filed Dec. 21, 1959, Ser. No. 860,749 19 Claims. (CI. 22-89) The present invention relates to method and apparatus for weather responsive moisture compensation, and more particularly to method and apparatus for taking a measurement of compensated moisture content of granular or comminuted material such for example as foundry sand, and either indicating this measurement or using it as a control factor in the addition of water to the material.

While'the invention is capable of use with many different materials, a typical use in conjunction with foundry sand will be described in detail.

Foundry sand is tempered by the controlled addition of water and working of the sand such as by the use of rollers, to bring it to the proper consistency for use in forming molds for casting. the sand was tested by the skilled artisan who could determine from the feel of the sand its approximate condition. Today more accurate results are obtained by actual measurement of the moisture content of the sand. However, it is customary to measure the moisture content of the sand either at the batch hopper, conveyor, or at a mill in which the sand is mixed, so that in all cases there is at least some loss of moisture during the interval following mixing and measuring before which the sand is actually used in the foundry. One factor which has a very substantial effect on the loss of moisture from the sand between mixing and use is the actual temperature of the sand. Other factors are of course the time during which the moist sand is subjected to moisture loss before it is used, and the temperature and humidity of the room air in the foundry.

In accordance with the present invention a measurement of a small specimen of sand within a larger vessel, such for example as a batch hopper, conveyor, or mixer, is subjected to a predetermined drying action after which its instantaneous moisture content is measured. The loss of moisture by the controlled brief drying of the specimen will bear a direct relationship to the moisture which the sand will lose during the interval between mixing and use.

The measurement of the compensated moisture content is made by instruments measuring an electrical condition existing across a pair of spaced electrodes. This electrical condition may be capacitance, resistance, a combination of these, or other conditions. Since both the capacitance and/or resistance existing between a pair of spaced electrodes exposed to a moist granular material is a function of its moisture content, the probe constituted by the electrodes will be sensitive to the moisture content of the sand in the container reduced by the expected or anticipated loss of moisture during the interval between mixing and use as a result of its elevated temperature, and the temperature and/or humidity or moisture content of the room air.

The controlled drying of the small portion of sand in direct proximity to the spaced electrodes is effected by a substantial flow of air which will exert a drying action on the sand dependent upon the volume and the temperature and/or moisture content of the air, the temperature of the sand, and the character of the sand as to particle size, clay inclusion, etc. Preferably, the air is emitted through an orifice located in the general plane of the specimen contacting surfaces of the electrodes and is caused by the presence of the bulk of sand overlying the electrodes to Originally, a condition of.

3,46,624 Patented July 31, 1362 move across the electrodes and through that portion of the sand in closer proximity to the electrodes.

With the foregoing general statements in mind, it is an object of the present invention to provide a method and apparatus for measuring a compensated moisture content of moist granular material in which the moisture content is compensated for its own temperature, and the tem perature and/ or humidity or moisture content of ambient air.

It is a further object of the present invention to employ the measurement obtained in accordance with the preceding paragraph to operate an indicator or to control automatic mechanism for adding water to the granular material.

It is a further object of the present invention to provide a method and apparatus in which drying air whose temperature and/ or moisture content is varied in accordance with room or ambient temperature, is passed for a controlled interval through a specimen of moist'sand to reduce its moisture content as measured by the variable electrical condition across a pair of spaced electrodes.

More specifically, it is an object of the present invention to provide a method and apparatus in which air or controlled characteristics is caused to flow continuously across the surface of a probe including spaced electrodes soras to exert a drying effect on moist granular material in contact therewith.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating preferred embodiments of the invention, wherein: e

FIGURE 1 is a diagrammatic view including a wiring diagram, showing a preferred embodiment of the present invention.

FIGURE 2 is a vertical sectional view through a weather probe used in the present invention.

FIGURE 3 is a fragmentary elevational view of a portion of the probe.

FIGURE 4 is a diagrammatic view illustrating the supply ofair to the weather probe.

FIGURES 5 and 6 are views similar to FIGURE 1 showing different embodiments of the present invention.

As seen in FIGURE 1, there is provided a sand mill or mixer ill adapted to receive sand from one or a plurality of hoppers 12, and Water is added to the sand in the mill'through sprinklers id connected to a receptacle 16 which receives water from a pipe 18. The sprinklers are illustrated as supported by a vertical shaft 20 which serves as drive means for the relatively heavy rollers 22.

In FIGURE 1 the sprinklers 14 appear as directly above the rollers 22, but in practice they are preferably circumferentially spaced therefrom.

The sand mill in is of the type including the relatively heavy rollers previously referred to, and in addition to the rollers there is provided a plow or plows 24 having a leading edge spaced only slightly above the bottom wall of the mill and adapted to scrape the sand therefrom after it has been compacted by the rollers.22.

Located in the bottom wall of the mill is a moisture probe 26 which includes a conducting element separated by a predetermined distance from grounded conducting elements. A probe of this type is disclosed in detail in FIGURE 2 and will be subsequently described. For the present it is sufiicient to note that it senses an electrical capacitance and/or resistance between spaced electrodes in contact with the sand.

As the heavy rollers pass over the probe a specimen of tained the compressed specimen 'is removed from the" probe by the succeeding plow 24.. Actually, while the plow does not contact the bottom wall of the mill nor engage the moisture sensitive surface of the probe, the plow is effective to remove all or substantially all of the compressed material from the surface of the probe.

The moisture probe 26 is connected by lines 50 and 52 to a moisture measuring bridge indicated at 53 which is a measuring instrument identified as a modified Tektoe Unit #101, manufactured and sold by the Fielden Instrument Division of the Robertshaw-Fulton Control Company. It should also be understood that in place of a Fielden Unit, a MEK manufactured by Machinery Electrification, Inc., may be used, or as far as that goes, any modified inductance capacitance bridge. The line 50 represents a grounded shielding for the conductor 52, the ground connection being indicated at 54. The line 52 is connected through a high capacity capacitor 56 to instrument connector X.

The instrument connector X is connected to the grid of a vacuum tube 57, for example a 6SN7 tube, connected as shown to have its output applied to a relay coil M which actuates switch contact arms M1 and M2. Also connected to the instrument connections are an adjustable first point capacitor 62 and an adjustable end point capacitor 64. The end point capacitor 64 is connected in parallel with a high capacity, as for example 2000 MFF, fixed capacitor 66, by normally closed contacts R7a of a relay R7 later to be described.

With reference to FIGURE 1, the mill frame is stationary and rigid. Underneath the mill is a. motor and gear box (not shown) which drives or rotates the vertical shaft which, in turn, causes wheels 22 and plows 24 to revolve circumferentially within the mill. The initial starting of the mill is by a manual motor starter switch (not shown). The release of the clamps or dump doors of the batch hopper may be done manually to dump the sand into the mill where mixing operations are applied.

It is ordinarily desirable to allow substantial mixing of the sand before attempting to determine its moisture, since sand of different moisture content may be dumped into the mill from different hoppers.

After a predetermined interval of mixing, operation of the moisture control device is initiated and water is added through the pipe 18. A timer is started which will insure rechecking the moisture content after a predetermined interval even though the instrument may previously have indicated sufiicient moisture. This is because of the loss of moisture due to evaporation during the mixing or the possibility of a false reading and rechecking after a predetermined interval will insure continued operation of the instrument until the average moisture content of the mixture is adequate.

During operation of the instrument, a first point valve Va and an end point valve Vb are both opened and water is supplied to the sand while it continues to be mixed. Inasmuch as the mixing operation comprises the passing of the rollers 22 over the moisture probe 26, followed almost immediately by passage of the plow 24, it will be appreciated that even when the sand reaches the required moisture content, this correct moisture content will be indicated only at intervals determined by the passage of the rollers 22 over the probe. After the scraper or plow 24 has passed over the probe, the sensing system will indicate a moisture deficiency until the succeeding sample of moist sand is compressed against the probe.

At this time it is desired to add the water rapidly to bring the moisture content approximately up to but definitely somewhat below the desired value. Accordingly, at this time control of the instrument is by the first point capacitor 62. Eventually, the instrument senses the proper moisture content for a brief interval and the system is arranged at this time to close the large capacity first point valve Va and to shift control of the instrument to the combination of the end point capacitance 64, and the modifying capacitance 66. Capacitance 66 is a large value capacitance, for example 2000 MFF, which is suflicient to start the 6SN7 tube to oscillate and in turn de-energize the relay M causing contact M2 to connect to contact M2c and complete a circuit through contact RSa to energize relays R7 and R4, thus taking capacitance 66 out of the r circuit at contact R7a for the remainder of the cycle,

leaving the control of the instrument to the end point ca pacitance 64. Thereafter, water continues to be added to the mill at a reduced rate by the end point valve Vb until the first indication of the ultimate desired moisture is obtained. It is recognized however, that this first indication may be a flash indication resulting from sensing the moisture content of a small specimen not indicative of the true average moisture content of the sand. Accordingly, means are provided at this time to close the end point valve while the mixing of the sand continues. During the following interval moisture readings are taken periodically as the rollers 22 pass over the sand probe. So long as these moisture readings all indicate sufiicient moisture the value Vb remains closed. A timing means is provided to operate over, for example, three seconds, which prevents opening of the end point valve during the brief intervals between successive sensing operations. For example, re-sensing may occur every two seconds and the timer may be set to time out in three seconds. At the end of two seconds if the sensing of moisture indicates sufficient moisture, the timer is reset to zero.

On the other hand, if during this rechecking interval a moisture sensing operation indicates insuificient moisture, the moisture valve opens and remains open until a second sensing of adequate moisture. This operation continues for an interval determined by an additional timer which operates to terminate the rechecking operation and to maintain the end point valve Vb closed, thus ending the cycle.

Oscillation of the 6SN7 tube is dependent upon the algebraic sum of the capacities connected to the instrument connections X and Y.

The addition of water through the discharge pipe 18 is through a first point valve Va which is air controlled and the supply of air controlling the valve is in turn controlled by a winding Val which will subsequently be described. At the same time an end point valve Vb is provided also controlled by air, which in turn is controlled by solenoid Vbl. The arrangement is such that when the solenoids Val and Vb1 are energized the corresponding valves are closed. The valves of course are open when the respective windings are de-energized.

The operation of the complete system will be described in connection with the illustrated circuit, which will be described to the extent necessary to understand the system. A -volt power line indicated at 70 is connected to the control circuit through a manual control switch 71. The control circuit includes the transformer Ta which is energized whenever the manual switch 71 is closed and which in turn supplies the primary of a second transformer Tb having the 250-volt and 6.3-volt secondary windings illustrated in the Tektor unit 53.

The sand is dumped into the mill 10 without regard to the moisture content thereof. Where sand is dumped in from a plurality of hoppers, some of the sand may be relatively moist and some of it may be relatively dry. Accordingly, the sand which initially contacts the probe may be either too dry or too moist. In order to insure that this condition does not prevent the required addition of water, the control circuit includes timing means operable to provide a cycling of the control system after a predetermined interval irrespective of whether or not the instrument initially cut oif the supply of water during the first timed interval. This means comprises a timer resistance TI having a switch arm TIa associated therewith. The switch arm TIa may for example be in the form of a bimetal contact member which is normally open and which closes after the resistance TI has been energized for a substantial period, as for example fifteen seconds. A momentary opening and closing of the manual push button switch 11 starts heating resistance element Tl through contact R211, the contact being in the illustrated position when the relay R2 is de-energized.

After the predetermined initial period, as for example fifteen seconds, has elapsed, the switch arm Tla closes energizing relay R2 and moving relay arm R2a to its lower position establishing a holding circuit through the relay R2 and simultaneously de-energizing the timer TI. The relay-R2 remains energized for the remainder of the cycle. In addition, energization of relay R2 shifts relay arm R212 to the left energizing relay R1. Energization of relay R1 shifts relay arm Rla to the left establishing a connection to the lower portion of the circuit through the jumper line 80, around arm R2b, which remains to the left, holding relay R1 in. This begins the second phase of the cycle in which, if necessary, water will be added to the sand in the mill through both valves Va and Vb.

During the interval measured by the timer TI it may be possible for sufficient water to have been added to the sand and mixed therewith, in which case the operation should be terminated. In other cases a false signal may result in closure of the valves Vaand Vb. When the timer TI times out the switch arm R2bmoves clockwise, thus momentarily breaking the circuit to the lower poi-tion of the system. When the switch arm R2b is in its lowermost or clockwise rotated position it energizes relay R1 which closes a circuit through switch arm Rla, thus re-energizing the lower portion of the circuit. The interval between energization of relay R2 and the energization of relay R1 is substantial and all circuits completed through portions of the wiring diagram below relay R1 in the figure are dc-energized so that all holding circuits drop out. When the switch arm Rla completes its movement all circuits are again re-energized and checking of the moisture of the sand is resumed. If in fact, the moisture content of the sand is suflicient this recheck results in quick cycling of the instrument to close the valves Va and Vb and they will remain closed for an interval determined by energization of a timer E82 later to be described, which finally completes the cycle.

The operation of the system during the interval controlled by the timer TI is exactly the same as it would be if the timer were omitted. The function of the timer is to re-start the complete cycle after a predetermined interval so that additional water can be added if the operation of the system was terminated as a result of a false signal during the first timed interval. A second important function of the initial timing period depends upon the following: It may happen that during the initial timing period a first signal is received from the moisture measuring unit which will have the efiect of closing the large capacity valve Va and leaving additional water to be supplied through the relatively smaller end point valve Vb. If the false signal was the result of a small quanw my of very moist sand happening to contact the moisture probe, 9. large volume of Water may in fact be required to bring the average moisture content of the sand to the required value. During the initial interval timed by the timer TI, water will be added through the small capacity valve Vb. However, when the timer Tl times out the control circuit is completely dc-energized and re-energized, thus starting afresh with the large capacityvalve Va open and this valve will remain open until the measuring unit makes the first signal indicating adequate moisture, which signal is sometimes referred to as a wet signal. Assuming that insufficient water has been added t the sand, the rollers and plows continue to rotate and water is now added to the mill through the valves Va and Vb. The solenoid Val of the first water valve Va is energized through lines 72, 74, 76, selector switch SS1, switch arm R3a, switch arm Rla, and jumper 80. Energization of solenoid Val maintains the first point valve Va open. In like manner, the end point valve Vb and its solenoid Vbl are energized through lines 72, 74,78, selector switch SS2, switch armRSb, switch arm ESla, switch arm Rla, and jumper 80. The addition of water and mim'ng of the sand continues concurrently'until the moisture content of the sand approaches a value near to but definitely below the final required value. At this time the value of the capacitance of the moist sand as sensed by the moisture probe 26 is such that the various capacitances connected to the points X, Y, including the first point capacitance, operate to cause the 6SN7 tube '57 to stop oscillating, thereby establishing a current through the relay coil M sufiicient to shift the contacts M1 and M2 to the left from the position shown.

Closure of the switch Ml establishes a current through relay R3, switch M1, switch arm Rla, and jumper 80. Energization of the relay R3 moves switch arm R3a downwardly from the illustrated position, thus breaking the circuit through the solenoid valve Val and closing the first point valve Va. Switch arm R3a completes a circuit through the relay R3 and through the solenoid 82 of a switch having contacts indicated generally at 82a. Energization of solenoid 32 moves the switch contacts 82a upwardly, thus disconnecting the first point ca pacitance 62 and connecting the end point capacitance c4 and the bias capacitance 66 into the circuit. It will be observed that the circuit through the relay R3 is held closed by the'switch arm R361, and hence from this time to the end of the cycle, relays R1, R2 and R3 remain closed.

in addition to the foregoing, energization of the relay R3 shifts the switch arm R3b downwardly, thus preparing a circuit for subsequent energization of relay R5. This circuit extends from the switch arm R4b which is open at this time, to contact M211, switcharm M2, switch arm R3b, switch arm Rla, and jumper 80.-.

Since this first indication of adequate moisture was based upon control of the first point capacitance 62, subsequent passages of the rollers over the moisture probe will not result in indication of adequate moisture until a substantial additional quantity of water has been added through the valve Vb. Ordinarily, it is preferred to add approximately of the water while the first point valve Va remains open, the additional 20% being added at a much slower rate through the smaller end point valve Vb. A

As soon as the scraper has removed the moist specimen of sand from the moisture .proble following this first indication, relay coil M is tie-energized and contacts M1 and M2 again return to the illustrated position to the right. At this time a circuit is completed through relays Rd and R7, the normally closed switch arm R551,

contact M20, contactMZ, switch arm R3b which is closed by first energization of the relay M, switch arm Rla, and

jumper 8t). Energization of the relay R4 closes switch R ta establishing a holding circuit for the relays R4 and R7 which keeps these relays in throughout the balance of the cycle. 'Energization of the relay R7 opens nor mally closed contacts R7a, thus disconnecting bias capacitance 66 from the circuit and leaving the end point M2 to connect to contact M2a now energizes relay R5' through switch arm R lb, contact M241, switch arm M2, switch arm R3b, switch arm Rla, and jumper 80. Ener gization of relay R5 shifts switch arm R'Sb to the lower position, thus breaking the circuit to the solenoid Vbl and closing the end point valve Vb. This would normally constitute the end of the cycle but additional provision is made for rechecking the moisture content a number of times to insure against premature termination of the cycle while the average moisture content of the sand is below that required.

The brief interval in which the switch arms M1 and M2 are to the left (before the next succeeding passage of the plow 24) has closed the end point valve Vb but downward movement of switch arm RSb has established a holding circuit through the relay R5 which includes switch arm ESla of a short interval timer E51. Thus, as long as the switch arm ESla remains closed the relay R5 will remain energized and the end point valve Vb will remain closed. The motor of the timer ESl is at this time energized through the switch arm R541, contacts M2c and M2, switch arm R3b, switch arm Rla, and jumper 80. The timer ESl may be set for an interval, for example of three seconds, and after three seconds the switch arm 1351:: will open if the timer is permitted to run its course. However, during the three seconds in which the timer ES]. is timing out, there will be a subsequent sensing of moisture content and if the moisture content of the sand is adequate, relay M is momentarily energized andswitch arm M2 will engage contact M2c briefly, and then return to engage contact M2c. This will have the efiect of breaking the circuit to the motor of timer ES1 at the contact M2c and return of the switch arm M2 to the contact M2c will re-start the timer for timing out the same interval. Thus, so long as the pe riodic moisture sensing operations sense adequate moisture, the timer will be automatically rc-started so that the timer contact arm ESla will never open and the relay R5 will remain energized through the switch arm R511, switch arm ESla, switch arm Rla, and jumper 80. This will interrupt the circuit through the solenoid V111 at switch arm R5b and the end point valve will remain closed. If, however, passage of a roller 22 over the moisture probe gives a dry signal, there will be sufiicient time for the timer ESl to time out, causing opening of the timer switch arm ESla and breaking the circuit to the relay R5, thus restoring switch arm R5b to its illustrated position. This will complete the circuit through the solenoid Vbl and reopen the end point valve Vb. The end point valve Vb will remain open until a subsequent sensing of moisture content indicates the correct value thereof at which time the end point control valve will close and re-checking will resume. The timer motor B81 is re-started and switch arm ESla closed when the relay R5 is next energized by the next wet signal.

In order to terminate the cycle after a predetermined interval which may be devoted to re-checking, a longer interval timer B52 is provided having contacts ESZa in a branch circuit connecting the relay R5 across the lines. Thus, when the switch arm ESZa is closed, the relay R5 remains energized, switch arm RSb remains in its lower position, thus interrupting the circuit to the solenoid Vbl and finally terminating the cycle.

Energization of a longer interval timer which finally terminates the cycle is initiated through normally closed switch arm R6a, relay R8, switch arm RSa, contact M2c, switch arm M2, switch arm R3b, switch arm Rlla, and jumper Si}. Energization of the relay R8 closes switch arm R811, thus energizing the relay R6 which in turn closes switch arm R612, establishing a holding circuit through relay R6 and opening switch arm R6a. The continued energization of relay R6 and closure of switch arm R6b maintains the motor of timer ESZ energized for a predetermined interval upon termination of which, timing out of the timer closes switch arm ES2a, thus establishing a circuit through the relay R5 and moving switch arm RSb downwardly from the illustrated position to break the circuit to solenoid Vbl. This finally closes the end point control valve Vb if it was then open and marks the end of the cycle.

Referring now to FIGURES 2 and 3 there is illustrated the use of a special weather probe in the combination shown in FIGURE 1. Before referring further to the drawings it may be mentioned that the operation of the probe shown in FIGURE 2 may be varied but in general it involves the provision of a continuous flow of drying air through ports or apertures located in the probe surface. This air exerts a predetermined drying effect on the specimen of granular material whose moisture content is being sensed. This drying effect is variable in accordance with sand temperature and the temperature, moisture content, and of course the volume of the air flowing through the probe.

Foundry men have long recognized the desirability of taking into account the change in weather in the tempering of foundry sands. Properly tempered moist foundry sand undergoes a drying action during the interval between completion of the tempering operation and the use of the sand. This drying-out of the sand varies in accordance with the time, and the temperature and moisture content or humidity of the room air. In modern operations continuously tempered sand is subjected to a fairly constant time interval so that the condition of the sand at the time of use is dependent almost exactly on the temperature and moisture content or humidity of the room air. This temperature and moisture content or humidity is referred to generally as weather and the present invention therefore may be regarded as relating to a weather-moisture compensated tempering unit.

In accordance with the present invention an automatic tempering unit is provided which determines the amount of water to be added to the granular material in accordance with the following factors: l) The actual moisture content of the sand; (2) the actual temperature of the sand; (3) the temperature of ambient air to which the tempered sand will be exposed before use; and (4) the moisture content or humidity of the ambient room air to which the tempered sand will be exposed.

In accordance with the present invention the system adds the correct amount of water to granular material in reference to the desired amount of moisture required at a processing station which is remote from the mixing station. It adds an amount of water to make up what will be lost by a drying-out or evaporation loss which takes place during transportation and storage. This loss depends upon the difference between the absolute humidity of the air at the Water-air interface and the absolute humidity of the room air.

The greater the difference between the absolute humidity of the air at the water-air interface of the material (sand) and the absolute humidity of the room air, the greater the driving force of the drying-out effect; that is, the greater will be the loss of moisture due to evaporation during transportation and storage.

Technical proof of the foregoing may be derived from the following formula:

A wa.) Where,

Kg=film coeflicient of the water-air interface of material and may be considered as a constant for a given foundry sand.

W:the weight of water loss per hour.

A=the area of the material surface.

H =the absolute humidity of the air at the Water-air interface.

H =the absolute humidity of the room air to which the material is exposed.

Thus, we are only concerned with the absolute humiditics of the air and material water-air interface.

This drying-out etfect may be quickly /2 to second) reproduced for control purposes by blowing room air through a small volume (sample) of the material (sand), thereby evaporating an appropriate amount of moisture, that represents the amount lost due to handling and storage. An electrical moisture test is made on this sample. When the electrical signal reaches a signal strength corresponding to the desired moisture content in a metal tube 106.

that corresponds to the moisture desired at the processing station, then the unit stops adding water.

The blowing of room air through the sample of sand in the mixer or conveyor or in the hopper, causes the sample to be subjected to a drying-out factor by the room air represented by 1-1,, in the above formula:

The sample will possess an absolute humidity H due to its mechanical and physical properties such as chemical composition, grain structure, size of grain and distribution, permeability, purity of water on water-air interface, activ ity of clay bond, ratio of bound and unbound water in the material, vapor (partial) pressure of the water in material, and others.

Thus, both the H and H are duly weighed by bringing the room air and material being processed together under a controlled velocity and volume air drying at the point Where the moisture is measured.

The tempering unit thus adds the necessary water to compensate for the drying-out as will be experienced due to difference of H and I-I and also, due to any mechanical-physical change in the material.

The temperature of the air forced through the probe may be held at room temperature by cooling the blower with a stream of room air secured from a fan. When it is desired to secure a greater degree of compensation for a humidity change, the temperature of the air supplied to the probe will be raised a constant amount above the room temperature with the air of an electrical heater.

Referring again to FIGURES 2 and 3, the probe comprises a center electrode 1% surrounded by an annular insulating body 109. received in a recess 104 provided The insulating body 102 is in the form of an annular thimble or ring having an annular series of air passages 188 each of which terminates at its upper end in a reduced outlet port 110.

The probe 26 senses moisture content of the material directly adjacent its upper surface by sensing an electrical condition of the material, such for example as its capacitance, its resistance, or a combination of the two. For this purpose the center electrode is connected by an electrically conducting rod 112. the lower end of which may be connected to the conductor 52 previously referred to. The exposed edge of the tube 106 constitutes an annular electrode surrounding the center electrode 100 and this will be maintained at ground potential.

In order to perform a continuous predetermined accurate partial drying of the sand whose moisture content is to be measured, there is provided a pipe 114 which admits air to the annular space 116 between the tube 166 and the rod 112. This air passes through the circular array of passages and 110 and escapes into the moist granular material in contact with the upper surface of the probe. In practice this air will for the most part plane radially outwardly across the upper surface of the insulating body 102. Since in usual operation the moisture measurement is taken by causing rollers and plows to pass alternately above the probe, a maximum reading is obtained upon passage of the roller, which compresses a moist specimen against the probe surface. The next passage of a plow removes the compressed specimen and permits a second specimen to drop onto the surface of the probe. This specimen is subjected to the drying action of the air in a controlled manner so that it will be subjected to a drying action which is variable in accordance with sand temperature, and the temperature, humidity and volume of flow of air passing through the probe.

It is desired to emphasize that one of the factors influencing dr ing-out of a tempered sample before use is the temperature of the sample. This is also taken into account by the present invention since the drying action of the air passing through the probe is influenced directly by the temperature of the moist specimen.

Referring now to FIGURE 4, the probe 26 is indicated diagrammatically as connected to the air pipe 114 which receives air from a blower or compressor 120. inasmuch as the action of the blower or compressor on this air may I 10 elevate its temperature, it is possible to cool this air by means such for example as a radiator cooler 122 in which room air is blown over the radiator to bring the compressed air to room temperature. The pressure at which the air is supplied to the probe 26 may be observed by a pressure gauge 124-.

With this arrangement, since the drying air is room air and since its moisture content is not changed by its compression, this compressed room air as supplied to the probe at room temperature will have a drying effect on the specimen of granular material which is a direct function of room or ambientair, temperature, and humidity.

It will be recognized that instead of using drying air having a moisture content and temperature exactly the same as that of the room air, other changes in the operation may be made. I

For example, it is of course possible to measure room air temperature and humidity and to use either or both of these conditions as means for effecting a separate control of the temperature and/ or moisture content of the drying air.

More elaborately stated, the air supplied to the probe may have a constant humidity or moisture content and its drying effect may be controlled simply by controlling its temperature. In a simple case the air may be dried so that it will have the maximum dryingreifect and its temperature controlled in accordance with room temperature. Thus for example, the temperature of the drying air supplied to the probe may be raised by a constant factor of room temperature so as to exert a greater drying action. Alternatively, the temperature of drying air supplied to the probe may be controlled in accordance with room temperature so that the temperature of the drying air has a variable difference from that of the room air.

By way of example, at a room temperature of 70 degrees the temperature of the drying air may be 150 degrees Fahrenheit, a difference of degrees. On the other hand, when room temperature increases to degrees Fahrenheit the temperature of the drying air supplied to the probe may be 200 degrees, a difference of 100 degrees. Alternatively, dry air may be supplied to the probe having a substantially zero moisture content and its temperature may be varied in accordance with room temperature and room humidity or either of these alone.

Referring now to FIGURE 5 the control system may be.

essentially as described in FIGURE 1 and similar reference characters are applied. In this case however, the probe 26 is illustrated as having the temperature of the drying air supplied thereto controlled in accordance with the humidity of room air.

In this case air is supplied to the weather probe 26 .This temperature sensing device may be in the form of a bulb located either at the entrance to the air heater or, preferablyat the location designated 140a where it measures the temperature of the air after'it has been raised to the required temperature;

In order to control the'temperature of the air supplied 7 to the weather probe in accordance with humidity of the room air, an instrument known as a Dewcel 142 is provided. A Dewcel is an instrument furnished by the Foxboro Company of Foxboro, Mass, in which the humidity sensitive element comprises a fabric made of glass wool which is impregnated with lithium chloride, and

which is provided with a pair of electrical conductors,

specifically, laterally spaced silver and gold wires wound around a core covered with the fabric. The lithium chloride absorbs moisture from the surrounding atmosphere and provides an electrical conducting path between the separate electrical conductors. The electric current flowing through the fabric from one wire to the other has a heating effect which dries the humidity sensing element until a point of balance is reached.

The instrument is read by measuring the temperature and this may be converted directly to dewpoint or to absolute humidity as desired.

Referring to FIGURE 5, the temperature may be measured by a device having an electrical output such for example as a thermocouple. On an increase in temperature, representing an increase in moisture content, a potentiometer circuit indicated generally at 144 will operate a motor 146 connected to a variable resistance 143 which is changed until a new balance is reached. At the same time the motor is connected to a dial indicator 150 which may be graduated in moisture content of the room air.

Operation of the motor in response to changes in humidity of the air also operates a pinion 152 which translates a rack 154 to move an electrical contact 156 to the right or left upon a change in air humidity. A second electrical contact 158 is provided on a plunger 160 connected to a piston 162 movable in a cylinder 164 by a passage 166 to the bulb 140 or 140a. Thus, the contacts 156 and 158 are independently movable in accordance with room air humidity and temperature of the drying air supplied to the probe. When the contacts 156 and 158 engage, the relay 168 operates to disconnect the current to the heating elements 138. Thus, the temperature of the drying air supplied to the weather probe is controlled in accordance with room humidity.

Obviously, instead of using a Dewcel instrument, the actual temperature of the air supplied to the weather probe could be varied at any desired ratio in accordance with the room air temperature which could be made to act directly on a temperature responsive device such as a bulb 140 exposed to room As an alternative, with the system exactly as illustrated in FIGURE 5, a second gas filled bulb such as indicated in dotted lines at 170, could be connected to the cylinder so that the position of the contact 153 could be varied in accordance with room air temperature as well as the temperature of the air supplied to the weather probe. Alternatively, a modification might be obtained simply by pro-v viding a relatively long passage 166 connecting the bulb and cylinder so that the room air would have an effect on the pressure of the gas. This efiect could further be modified for example, by providing an enlargement in the passage 166 as indicated in dotted lines at 172 and the heat transfer dependent on room temperature could be further increased if desired by the provision of heat trans fer fins 174. In this case it will be observed that the air supplied to the weather probe would be heated to a degree dependent jointly upon the humidity and the temperature of the air in the room.

Referring now to FIGURE 6 there is illustrated a separate embodiment of the present invention which includes the same basic circuit and control mechanism. A description of this mechanism will not be repeated but significant elements bear the same reference characters as applied in the previous figures.

In accordance with the invention as disclosed in FIG- URE 6, a probe 26 is provided in the bottom wall of the mill and is supplied with drying air as in the embodiments of the invention previously described. In this case however, the drying air which passes through the container 132 is not controlled as to temperature and/ or humidity in accordance with room weather or temperature and humidity conditions. Instead, the drying air supplied to the probe is for the specific purpose of producing a variation in Water added to the granular material which is directly proportional to the temperature of the granular material. This arrangement forms the subject matter of a prior application Serial No. 845,727 filed October 12, 1959. Accordingly, water is added to the sand or other granular material in the mill in an amount directly proportional to the temperature of such material and inversely proportional to its moisture content. In other words, the moisture content of the granular material in the mill is brought to a desired level dependent upon the temperature of the granular material.

In this case it may be noted that instead of employing a probe using drying air as shown in the figure, the temperature of the granular material whose moisture is to be controlled may be measured separately as for example by a thermocouple, and this measurement may be taken continually in the mill or it may be taken in a hopper before the granular material is dumped into the mill for tempering.

In accordance with this embodiment of the invention, the amount of moisture added to sand or other granular material in the mill is influenced by means responsive to the temperature of room air or the humidity of room air, or a combination of the two.

It will be recalled that the actual control of the addition of water to the sand in the mill is by increasing the moisture content until the capacitance existing between electrodes of the probe reach a certain relationship to preset capacitances in the control system.

Described in general terms, the present invention comprises the addition of a temperature capacitor 180 and a humidity capacitor 182 controlled respectively by a temperature potentiometer 184 and a humidity potentiometer 186. It will be observed that the capacitors 180 and 182 are connected in parallel with the capacitor 62 or the capacitors 64 and 66, dependent upon the position of the switch contacts 82a.

The temperature potentiometer 184 includes means responsive to room temperature such for example as a thermocouple 188 whose output is supplied to an electric motor 190 through a converter 192, an input transformer 194, a voltage amplifier 196, and a power amplifier 198. Operation of the motor results in movement of a conductor 200 over a resistance 202, the motor thus rotating to a different position in accordance with any particular temperature at the thermocouple junction. Operation of the motor in addition to changing the setting of the variable resistance, also, by cam mechanism suggested at 204, results in changing the setting of the variable capacitor 180.

The arrangement for adjusting the capacitor 182 is similar except that the source of power is a device 206 responsive to room humidity such for example as the Dewcel previously described. The output is supplied to the motor 208 through circuitry similar to that employed in the temperature potentiometer and results in actuation of the cam device 210 for efiecting adjustment of the variable capacitor 182.

With the foregoing system it will be observed that the effective capacitance supplied to the terminals X, Y, will be a function of the room temperature if the temperature potentiometer 134 is connected, or a function of room humidity if the humidity potentiometer 186 is connected, or of both if both potentiometers are connected. Thus, the moisture content of the granular material in the mill 10 required to terminate the addition of water is in this case a function of room temperature or humidity or both.

The humidity potentiometer will decrease the capacitance of condenser 182 with a rise in dewpoint temperature, and will increase the capacitance of the condenser for a decrease in dewpoint temperature. The temperature potentiometer will vary the capacitance of condenser such that a rise in room temperature will increase the capacitance of the condenser 180, and vice-versa.

It will of course be understood that the arrangement is such that upon an increase in room temperature, which tends to cause increased evaporation of the tempered material, the system will operate to provide an increased moisture content in the tempered material to compensate The drawings and the foregoing specification constitute v a description of the improved method and apparatus for weather responsive moisture compensation in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What we claim as our invention is:

1. Tempering equipment comprising a mixer, means for measuring the moisture content of granular material in the mixer, means for adding water to the mixer, and means responsive to the temperature of air to which the tempered material will be subjected subsequent to tempering to vary the amount of water added to said mixer.

2. Tempering equipment comprising a mixer, means for measuring the moisture content of granular material in the mixer, means for adding water to the mixer, and means responsive to the humidity of air to which the tempered material will be subjected subsequent to tempering to vary the amount of water added to said mixer.

3. Tempering equipment comprising a mixer, means for measuring the moisture content of granular material in the mixer, means for adding water to the mixer, and means responsive to the temperature and humidity of air to which the tempered material will be subjected subsequent to tempering to vary the amount of water added to said mixer.

4. Tempering equipment comprising a mixer, means for measuring the moisture content of granular material in the mixer, means for adding water to the mixer, means for measuring the moisture content of the material during the addition of water, and means responsive in part to the temperature of air to which the tempered material will be subjected subsequent to tempering to terminate the addition of water when the moisture content of the material is appropriate for the air temperature.

5. Tempering equipment comprising a mixer, means for measuring the moisture content of granular material in the mixer, means for adding water to the mixer, means for measuring the moisture content of the material during the addition of water, and means responsive in part to the humidity of air to which the tempered material will be subjected subsequent to tempering to terminate the addition of water when the moisture content of the material is appropriate for the air humidity.

6. Tempering equipment comprising a mixer, means for measuring the moisture content of granular material in the mixer, means for adding water to the mixer, means for measuring the moisture content of the material during the addition of water, and means responsive in part to the temperature and humidity of air to which the tempered material will be subjected subsequent to tempering to terminate the addition of water when the moisture content of the material'is appropriate for the air temperature and humidity.

7. Apparatus for measuring the moisture content of granular material compensated for anticipated loss of moisture by evaporation which comprises means responsive to ambient air temperature for partially drying a specimen of the material by an amount dependent on ambient air temperature, and means for thereafter measuring the remaining moisture content of the specimen.

8. Apparatus for measuring the moisture content of granular material compensated for anticipated loss of moisture by evaporation which comprises means respon- 14 sive to ambient air humidity for partially drying a specimen of the material by an amount dependentv on ambient air humidity, and means for thereafter measuring the remaining moisture content of the specimen.

9. Apparatus for measuring the moisture content of granular material compensated for anticipated loss of moisture by evaporation which comprises means responsive to ambient air temperature and humidity for partially drying a specimen of the material by an amount dependent on ambient air temperature and humidity, and means for measuring the remaining moisture contentof the specimen.

10. Apparatus for measuring the moisture content of granular material compensated for anticipated loss of moisture by evaporation which comprises means for passing a current of drying air 'through a specimen of the material for a definite interval, means for controlling the. drying effectiveness of such air in accordance with the drying effectiveness of ambient air to which the tempered material is subsequently to be exposed, and means for I measuring the moisture remaining in the partly dried specimen.

11. Apparatus for measuring the moisture content of granular material compensated for anticipated loss of moisture by evaporation which comprises means for passing a current of drying air through a specimen of the material for a definite interval, means for controlling the temperature of such air in accordance with the drying efiectiveness ofambient air to which the tempered material is subsequently to be exposed, and means for measuring the moisture remaining in the partly dried specimen.

12. The method of tempering granular material by mixing water therewith which comprises increasing the amount of water to compensate for anticipated evaporation, and controlling the addition of water in accordance with the drying effectiveness of ambient air to which the tempered material will be subjected subsequent to final tempering.

13. The method of tempering. granular material by mixing Water therewith which comprises passing a flow of drying air through a specimen of moist granular material for a definite interval to effect a predetermined partial drying thereof, varying the drying effectiveness of the air in accordance with the temperature of ambient air to which the material will be subjected subsequent to final tempering, measuring the moisture content of the specimen, and determining the amount of water to be added bythe measurement of moisture content of the partially dried specimen.

14. The method of tempering granular material by mixing water therewith which comprises passing a flow of drying air through a specimen of moist'granular material for a definite interval to effect a predetermined partial drying thereof, varying the drying effectiveness of the air in accordance with the humidity of ambient air to which the material will be subjected subsequent to final tempering, measuring the moisture content of the specimen, and determining the amount of Water to be added by the measurement of moisture content of the partially dried specimen.

15. The method of tempering granular material by J mixing water therewith which comprises passing a flow of drying air through a specimen of moist granular material for a definite interval to effect a predetermined partial 15 the drying action directly in accordance with the temperature of ambient air, and measuring the moisture content of the partly dried material.

17. The method of measuring the moisture content of granular material compensated for anticipated loss by evaporation to ambient air which comprises passing drying air through a specimen of the moist material, controlling the temperature of the drying air in accordance with the drying properties of ambient air, and thereafter measuring the moisture content of the partly dried specimen.

18. The method of measuring the moisture content of granular material compensated for anticipated loss by evaporation to ambient air which comprises passing drying air through a specimen of the moist material, controlling the temperature of the drying air in accordance with the temperature of ambient air, and thereafter measuring the moisture content of the partly dried specimen.

19. The method of measuring the moisture content of granular material compensated for anticipated loss by evaporation to ambient air which comprises passing drying air through a specimen of the moist material, controlling the temperature of the drying air in accordance with the humidity of ambient air, and thereafter measuring the moisture content of the partly dried specimen.

References Cited in the file of this patent UNITED STATES PATENTS 2,709,843 Hartley June 7, 1955 2,724,903 Ehrisman Nov. 29, 1955 2,825,946 Dietert Mar. 11, 1958 2,854,714 Dietert Oct. 7, 1958 2,863,191 Dietert Dec. 9, 1958 2,902,681 Dietert Sept. 1, 1959

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