US2508540A

US2508540A - Temper control for molding sand

Info

Publication number: US2508540A
Application number: US770118A
Authority: US
Inventors: Theodore K Riggen
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-08-22
Filing date: 1947-08-22
Publication date: 1950-05-23
Anticipated expiration: 1967-05-23

Description

WITNESS:

y 1950 T. K. RIGGEN 2,508,540

TEIPER CONTROL FOR MOLDING SAND Filed Aug. 22, 1947 Wade/v44 a Y6 fa 60/053 4m. (mt zm.

ATTORNEY Patented May 23, 1950 UNITED STATES PATENT OFFICE TEMPER CONTROL FOR MOLDING SAND Theodore K. Itiggen, Elmira, N. Y. Application August 22, 1M7, Serial No. 770,118

2 Claims. 1

The present invention relates to a temper control for molding sand, and more particularly to a means for automatically controlling the addition of water to molding sand in order to maintain a desired percentage of water content.

In one system for tempering foundry sand which is commonly employed, the sand is transported to the molder by means of a conveyor belt, and the necessary water to temper the sand is added while from time to time, judges the percentage of water and manually controls a valve in a water system to regulate the sprinkling of the water on to the moving belt.

It is an object of the present invention to provide a novel system for adding water to molding sand, which is arranged to automatically maintain the desired percentage of moisture with a high degree of accuracy. I

It is another object to provide such a device which utilizes the electrical conductivity of the moistened sand as a gauge of the percentage of water in the sand.

It is another object to provide such a device which can be readily adjusted to provide any desired proportion of water in the sand.

It is another object to provide such a device including a pair of electrodes adapted to be inserted in the tempered sand in spaced relation, and means for opening a sprinkler valve when the resistance of the sand between the electrodes rises above a predetermined value, and for closing the valve when said resistance falls below said value.

It is a further object of the invention to provide such a device including means whereby when said resistance between the electrodes exceeds a predetermined value, such as might happen when there is no sand on the conveyor belt, the water supply valve will be quickly and completely closed.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing which illustrates diagrammatically a preferred form of the invention.

In the drawing, numerals I and 2 indicate electrodes or "feelers of any suitable form adapted to be inserted in the molding sand on a travelling belt after it has passed the sprinkling system for adding water to the sand. Inasmuch as the con- 2 veying and sprinkling system is well known in the art and forms no part of the present invention, illustration thereof is deemed unnecessary.

Electrode I is grounded as indicated at 3 and electrode 2 is connected to the secondary 4 of a transformer 5 the primary 6 of which is energized from a suitable source of alternating current such as the usual -vo1t power line indicated at X, Y. A second similar transformer I has one end of its secondary 8 connected to the secondary 4 of transformer 5 at the point 8. The primary ll of transformer l is also connected to the same source of alternating current as the primary i of transformer 5, and the connections of the secondaries of these transformers are such that the connected ends of the secondaries are at all times degrees out of phase.

The free end of the secondary 8 of transformer I is connected to the ground through a variable resister I2. It will be appreciated therefore that the predominant phase of the voltage existing between the point 9 and ground is dependent upon the relative value of the resister I2 and the resistance of the path through the sand between the electrodes I and 2. In other words, the instantaneous voltage between the point 9 and ground will be the algebraic sum of the instantaneous voltages across the secondaries 4 and The signal appearing thus at the point 9 is ex-- pressed across a resister l0 and applied to the grid I3 of a vacuum tube l4 whereby the signal is amplified, and the output of tube I4 is coupled by a transformer l5 to a push-pull stage of amplification comprising tubes l6, II. The output of tubes l6, I1 is transmitted through a transformer 18 to the armature IQ of a reversible motor 2| which actuates the sprinkler valve 20 for controlling the addition of water to the molding sand.

The field 22 of motor 2| is energized by an alternating current of the same frequency as the amplified signal impressed on the armature. For this purpose, an oscillator 23 preferably the same source X, Y of alternating voltage which energizes the primaries of transformers 5 and l is arranged to impress a signal on the grid 24 of an amplifying tube 25 by means of a variable gain control 26. The output of tube 25 is coupled by a trans-- former 21 to a push-pull stage of amplification including tubes 28, 29, and the output of this stage is transmitted through transformer 3| to the field 22 of the motor. Since the alternating current supplied to the field 22 of the motor is thus of the same frequency as the energization of the armature thereof, rotation of the motor will 3 obviously depend upon the phase relationship between the armature and field, which phase rela tionship is dependent upon the relative predominance of the voltage generated in the secondaries l and 8 of transformers and 1 respectively.

In the operation of the device as so far described, the signal developed at the point 8 is expressed across the grid resistor l0 and hence produces an alternating voltage on the grid it of tube it. After being amplified by this tube the signal is fed through transformer I5, the pushpull stage IB, ll and hence through transformer iii to the armature I 8 of the control motor 2!. Since the field 22 of the control motor is being concurrently energized at the same frequency, the direction and angular velocity of the armature of the control motor will be a function of the amplitude of the signal transmitted by transformer i8, and the phase relation between this signal and the signal transmitted by the transformer 3| to the field 22.

As the resistance of the moistened sand between the electrodes I, 2 is increased from a low value to equality with the value of resister l2, the motor will change from one direction of rotation at full'speed, through a stalled condition, to full speed in the opposite direction. If the value of resister I2 is set so as to equal twice the resistance of the path between the electrodes I, 2 when the sand is correctly tempered, the point 9 will then be 90 degrees out of phase with the oscillator 23, and consequently the armature I! of the motor will be 90 degrees out of phase with the field. There will therefore be no rotation of the motor under this condition and consequently no change in the opening of the valve controlled by the motor.

If the sand arriving at the electrodes I, 2 has insufilcient water content, the phase relation between the point I and ground will shift in such a direction as to cause the armature I! of the motor to rotate in a direction to open the sprinkler valve wider. Conversely, over-damped sand will similarly cause the armature of the motor to rotate in the opposite direction so as to reduce the opening of the sprinkler valve.

The structure thus far described provides an accurate means of controlling the percentage of water in the sand as long as the electrodes l, 2 are covered by the sand. Inasmuch however as it will some times happen that the supply of sand on the conveyor is interrupted, it is necessary to provide means for rapidly closing the sprinkler valve when the resistance of the path between the electrodes l, 2 becomes inordinately high. For this purpose, means are provided for reversing the phase relation of the field of the motor when the electrodes I, 2 are substantially open-circuited.

As here shown this means includes a tube 32 the grid 33 of which receives the signal from the point 9 through an adjustable gain control ll. The cathode 35 of tube 22 is biased beyond cutoff by means of a voltage divider l8, 31 whereby the tube ordinarily transmits no signal. The output of tube 22 is coupled through a condenser to a second amplifier tube 32 having in its plate circuit a filter comprising a condenser ll and choke 42. The principal purpose of the tube 2! is to isolate the filter from the cut-oi! characteristics of the tube 22. In other words, when there is sufilcient signal appearing on thegrid II to cause the tube 32 to transmit a. signal, the transmitted signal is merely a series of pulses, and the tube 8. and filter ll, 42 by its fly-wheel" efiect oper- 4 ate to change these pulses into a signal which approaches a sine wave.

This reconstructed signal is then impressed through a coupling condenser 48 and a resister H on. the grid 24 of oscillator tube 25, this signal being thus expressed across the gain control 2| gscillator 23 and resister II in series therewit The total signal existing on the grid 2! of tube 25 is therefore the algebraic sum of the signal from the oscillator 23 and from the filter. These signals are arranged to be of opposite phase when the current flowing through the secondary 8 of transformer I predominates over the current flowing through the secondary l of transformer 5, or in other words, when the resistance between electrodes I, 2 is greater than the setting of the 7 variable reslster l2.

The gain controls 24 and 2. are so adjusted in relation to the co-operating elements of their circuits that when the electrodes I, 2 are open-cireulted, the signal then transmitted through the tube 32 and the filter is at least twice the amplitude of the signal from the oscillator 23. The tube 25 therefore under those circumstances has an out-put approximately the same in amplitude as before, but opposite thereto in phase. This signal, when transmitted through transformer 21, amplifier 28, 28 and transformer 3i energizes the field 22 of the motor 180 degrees out of phase from its normal energization.

The high resistance between the electrodes I, 2 causes energlzation of armature ll of the motor in such phase that the motor would normally open the sprinkler valve, but since the field is now reversed in phase, the motor closes the valve. When electrodes I, 2 are open-circuited, the a!- mature current is approximately twice its normal high-speed value, and since the field voltage is substantially the same as its normal value, the motor will operate to close the sprinkler valve much faster than its movement in normal operation. This will prevent flooding an empty sand belt.

Although but one embodiment of the invention has been shown and described in detail, it will be understood that other embodiments are possible without departing from the scope of the invention.

What is claimed is:

1. In an electronic control for tempering molding sand, 9. pair of electrodes arranged in be submerged in spaced relation in the moistened sand, valve means for controlling the addition of water to the sand, a reversible motor for actuating said valve means, and control means responsive to an increase in resistance of the sand between the electrodes above a pre-set value for causing rotation of the motor to open the valve means, and responsive to a decrease in said resistance below the preset value to cause rotation of the motor to close the valve means, in which the control means includes means for supplying alternating current of a fixed frequency to the field of the motor, means for supplying alternating current of the same frequency to the armature of the motor, and means for varying the phase relation between the armature and field in accordance with deviations of the resistance of the-sand between the electrodes from the pre-set value; including further, means for inverting the phase of the field responsive to an open circuit condition between said electrodes.

2. In an electronic control for tempering molding sand, 9. pair of electrodes adapted to be inserted in fixed spaced relation in the sand, means for passing an alternating current of fixed frequency through said electrodes, a variable resister, means for passing the same alternating current through the variable resister, means so 5 connecting the circuit containing the electrodes to the circuit containing the variable resister that the currents of said circuits are 180 out of phase at the point of junction; a sprinkler valve motor having an armature and a field, means for energizing the field by an alternating current of the same frequency as said first mentioned alternating current, and means for amplifying the signal appearing at said junction point and en- 6 ergizing the armature thereby; including further means forreversing the phase relation of the field and armature responsive to an open-circuit between said electrodes.

THEODORE K. RIGGEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,270,732 Jones Jan. 20, 1942 2,413,120 Swanson Dec. 24, 1946