US3044139A - Control system for molding presses - Google Patents

Description

July 17, 1962 Filed Nov. 1'7, 1959 E. A. MORTON ETAL CONTROL SYSTEM FOR MOLDING PRESSES 3 Sheets-Sheet 1 YDAVID G. BRANT ATTORNEYS July 17, 1962 Filed NOV. 17, 1959 E- A'. MORTON ETAL 3,044,139

CONTROL SYSTEM FOR MOLDING PRESSES 3 Sheets-Sheet 2 INVENTOR EUGENE A. MORT N DAVID G. BRANT ATTORNEYS July 17, 1962 E. A. MORTON ETAL 3,044,139

CONTROL SYSTEM FOR MOLDING PRESSES Filed Nov. 17, 1959 3 Sheets-Sheet 3 EUGENE A. DAVID G. BRANT ATTORNEYS Patented July 17, 1962 3,944,139 CONTROL SYSTEM FOR MOLDING PRESSES Eugene A. Morton and David G. Brant, Titlin, Ohio, assignors to Basic Incorporated, Cleveland, Ohio, a corporation of Ohio Filed Nov. 17, 1959, Ser. No. 853,571 2 Claims. (Cl. 25-45) ple, the mold cavity is defined by a stationary side-wall forming mold member, a pad movable within the stationary member and forming the bottom of the mold, and a plunger which is reciprocated into and out of the stationary member of the mold. The pad, as well as the plunger, is driven, and the construction is such that the machine operates automatically to carry out a brick forming cycle in which, with the plunger retracted to open the mold, the mixture is supplied to the stationary mold member and supported therein by the pad, the plunger enters the mold pressing the mixture and forcing the pad downwardly, the pad starts upwardly shortly before the plunger reaches the limit of its downward movement, and then the pad and plunger both move upwardly to eject the pressed brick and resume their initial positions for the next cycle of operation. The originators of this press appreciated the need for providing some form of adjustment which would take into account significant changes in the density of the brick-forming mixture, which would if uncompensated result at least in variation in size and other physical characteristics of the bricks produced, and they accordin ly provided means for adjustably setting the initial or rest position of the pad thereby to regulate the volume of the mixture supplied to the mold.

As shown by US. Patent No. 987,124, this adjustment was originally accomplished solely by manually actuated positioning means, with the skilled operator of the press relying on his inspection of the bricks produced to detect irregularities calling for appropriate change in the volume of the material fed to the mold. Much later, the pad positioning mechanism was motorized and a control system therefor provided to effect the proper adjustment automatically in response to elongation of the side bars of the press as an indication of the magnitude of the pressure applied in the brick-forming cycle. One such control system, disclosed in US. Patent No. 2,293,815, is mechanical in nature, with an extensometer bar attached to a side bar of the press and actuating a lever system which mechanically magnifies side bar elongation during the pressing of a brick. Such movement operates switching means to provide an electrical signal, and the latter is applied to actuate the mold depth control mechanism of the press. In this prior system, the adjusting motor is operated for only a short period of time during the actual pressing stroke, and while gradual changes in the characteristics of the brick mix material fed to the press can be compensated in this manner, an abrupt change cannot thus be counteracted.

Another and still later developed form of automatic control of the mold volume, which is disclosed in US. Patent No. 2,455,823, employs electrical strain gauges for measuring elongation of the side bars of the press. In this further system, the gauges provide an electrical signal which is applied to an electronic controller for the mold cavity depth adjusting mechanism. The circuit thus provided has a slow speed of response, to the extent that a conditioning circuit is used to feed a controllable and independently developed signal to the instrument which will hold the same near the desired control condition. At a predetermined point during the pressing cycle, a switch actuated by the press cuts out this conditioning or holding circuit and closes the actual measuring circuit; at a further point in the cycle, a second such switch closes the depth adjusting mechanism circuit for actuating the motor of the positioning mechanism in the event that the instrument is not then at the desired and previously set control point.

The present invention is similarly concerned with automatic regulation of 'the mold volume in response to the magnitude of the pressure applied in a forming cycle as indicated by side bar strain or elongation, and strain gauges are employed to provide the control signal as in the last-noted patent. However, our system has a much higher speed of response than has been available heretofore, whereby the rapidity of correction or compensation is materially enhanced and it is feasible efliciently to mold compositions subject to very abrupt density change. For example, in the manufacture of brick from a heated tar bonded material, the bulk density thereof is greatly infiuenced by fairly quick change in temperature and drastic alteration in the amount of material placed in the mold cavity required for proper compensation. In the handling of this material in particular, it was found that the changes were so large that an excessive number of cycles were required to correct for the new situation by conventional controls and, in some cases, where an excessive amount of material Was placed in the mold, the resulting excess pressure was so extreme that the mold plunger would be deformed, with consequent down time for repair.

In addition to improving the response time of the control, our new system provides a continuous indication of strain on the side bars of the press. The invention also provides a low pressure warning signal to indicate that the applied pressure is below a minimum value during the peak of the pressing cycle, whereby the operator of the press is alerted to take further corrective action as may be appropriate. Another object of the invention is to provide such a system in which operation of the press will be automatically stopped in the event that the pressure exceeds a safe limit.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawings:

FIG. 1 is a semi-diagrammatic sectional elevation of a Boyd brick press;

FIG. 2 is a wiring diagram of the control system for such press in accordance with the present invention;

FIG. 3 is an enlarged elevational view of one of the control assemblies used in such system; and

FIG. 4 is a front view of a recording controller likewise employed in the system.

Referring now to the drawings in detail, the press illustrated' in FIG. 1 will be seen to comprise a vertical frame 1 in which a head, designated generally by reference numeral 2, is slidable. This head conventionally includes a side bar 3 supported at times by a spring 4, on each side, a shaft 5 rigidly interconnecting the side bars at the top, and a beam 5 secured between the lower ends of the side bars. While this Boyd brick press may have a plurality of molds across the width thereof, as is wellknown, the several such assemblies are identical, with common actuating mechanism therefor, and it will suifice for a full understanding of the present invention more simply to consider the press as having a single mold.

. This representative mold comprises a stationary member 6 fixed in a work table 7 and having an opening the wall of which defines the' side wall of the mold cavity. A plunger 8, which extends into the opening of the stationary mold member 6 in the'press condition shown, is carried by a'transverse bar 9, and the latter is connected to the head 2 at the upper shaft thereof by a pair of toggle links 10 and 11 having an intermediate pivot 12. This intermediate common pivot is actuated by a pitman 13 which is reciprocated by a crank 14 on the main shaft 15 of the press. Such drive of the pitman of course causes the plunger to move up and down through the actuation and under control of the toggle links.

'A saddle 16 is telescoped over the lower beam 5 of the head 2, and a pad 17 is mounted on the saddle to extend upwardly therefrom into the opening of the stationary member of the mold. The saddle is urged upwardly relative to the beam by a compression spring 18 therebetween, with a rod 19 secured to the underside of the saddle extending downwardly through the beam. A stop 20 secured to the lower end of the rod 19 is adapted, when the saddle and hence the rod move upwardly relative to the beam 5, to engage the end 21 of a lever 22 mounted intermediate its ends on a horizontal pivot 23 carried by and thus movable vertically with the head.

The other end of the lever 22 is bifurcated and transversely slotted to engage with lugs of a nut 25 threaded on a vertical adjusting screw 26. This screw can be manually actuated to change the vertical position of the nut 25 thereon by means of a connected shaft 27 extending upwardly at the front of the press and having a hand wheel 28 secured at its upper end. 7 While the pressis illustrated in closed condition in FIG. 1, it will be clear that when the plunger is fully withdrawn from the stationary mold member, the saddle has been lifted for the pad to eject the brick, and the following downward movement of the head swings the lever 22 downwardly about its pivotal end attachment to the nut 25 to engage stop 20 on rod 19 and thereby draw the saddle down relative to the beam 5. Accordingly, the pad position in the fill condition of the press can be adjusted by the screw 26, and this adjustment determines the depth of the mold cavity during filling thereof with the brick-forming mixture. The manner in which the feed is accomplished is also conventional in the Boyd press, with a charger 29, open at the bottom, horizontally reciprocated on the work table 7 over the stationary mold member 6. The mixture is supplied to the charger, and such reciprocation thereof not only carries the mixture to'the mold but removes the normally provided excess so that the fill is level with the top of the mold member.

In order to render the pad positioning mechanism susceptible to automatic control, the lower end of the screw 26 is coupled to a shaft 30 adapted to be driven by, a reversible electric motor 3 1 through suitable reduction gearing 32. The control system of the invention is operative to determine energization and direction of rotation of this motor, the positioning mechanism -being repeated diagrammatically in the circuit of FIG.' 2. The latter also shows diagrammatically the press drive as comprising an electric motor 33, a pneumatic clutch 34 for coupling the motor shaft to a further shaft 35, and a brake 36, spring-biased and actuated by a pneumatic piston cylinder assembly 37, on the shaft 35. A pinion 38 on such shaft drives the large gear 39 fixed on the main press shaft 15. The clutch 34 and brake 36 are conventional and operated by selective supply of air under pressure thereto through a suitable control valve 40. A solenoid 41 is shown for actuating the valve; energization of the solenoid will here cause the valve to operate to release the brake and engage the clutch and should 54. A capacitor 57 and a volt meter 58 are each con-,

such energization be interrupted, the clutch will of course be disengaged and the brake operated to stop the drive of the press.

The system employs four strain gauges A1, D1 and A2, D2, in the manner disclosed in the aforementioned US. Patent No. 2,455,823, with the gauges A1 and A2 vertically attached respectively to the side bars 3 of the head 2 of the press and the gauges D1 and D2 horizontally attached to the bars. The strain gauges A1 and A2 will thus exhibit an increase in resistance proportional to elongation of the side bars, while the remaining two gauges are substantially unaffected by such strain and provided for temperature compensation.

These gauges are connected into a Wheatstone bridge circuit inwhich A1 and D1 are connected at one point 42 of such bridge circuit, D1 and A2 are joined at point 43, and A1 and D2 at the point 44. Between the last bridge terminal 45 and the remaining ends of the gauges A2 and D2 to be joined, there is provided a balancing circuit comprising two variable resistors 46 and 47 connected in parallel, with the bridge terminal 45 connected commonly to the movable contacts of such resistors. These balancing resistors will be of different value to provide respectively coarse and fine adjustments of the bridge balance.

The system is energized by connection of supply conductors 48 and 49 to a suitable source of electrical energy through closure of main switch contacts 50 and 51 respectively therein and operated in unison as indicated. Current is supplied to the bridge measuring circuit by means of a constant voltage transformer 52 having its primary connected across the conductors 48 and 49. The secondary of such transformer is connected in a loop comprising the fixed resistance 53 and variable resistor 54 with the bridge terminal 43 connected to such loop through a rectifier 55 and bridge terminal 44 connected through rectifier 56 to the movable contact of the resistor nected across the bridge terminals thus supplied with direct current.

The output terminals 42 and 45 of the bridge are connected to a recording controller 59, which is also shown in FIG. 4. The instrument here used is made by Leeds and Northrup Company, Philadelphia, Pennsylvania, as its Speedomax Model R, as fully illustrated and described in the publication of such company entitled Manual for Speedomax issue 5. Basically, this record ing controller, electronic in nature and having a high speed of response, is responsive to the magnitude and direction of the signal produced by unbalance of the measuring bridge circuit and causes an output shaft 60 to turn in accordance therewith. In its application here, the instrument is set up for operation over a range of from -5 to'+5 millivolts' and, as shown in FIG. 4, the shaft 60 has an indicator arm 61 secured to the outer end thereof; the end of such arm moves over a stationary cir cular scale 62. This scale is calibrated in millivolts over the range indicated, with the zero position at top center. Inside the stationary scale 62, there is a record disc 63 mounted on a clockwork driven support, and a pen assembly 64, guided in a stationary bracket 65, is connected to the indicator arm 62 for substantially radial movement, thereby to form a trace on the record disc or chart indicating the movement of the indicator arm.

Such operation of the instrument of course is indicative of the molding pressure in operation of the press, and it will be seen that the system thus far described provides for continuous measurement and recording of such pressure. The indicator is adjusted to zero with the press in the fill position and should return thereto in each press cycle, so that a continuing check for drifting of the instrument can be maintained and the measuring circuit quickly brought to balance condition if necessary. The circuit control functionsof the instrument 59 are accomplished by four eccentric cams 66-69 mounted and individually adjustable on the shaft 60. These cams respectively actuate control switches 70-73 having actuators which ride on the edges of the cams. For convenience of description and understanding, the circuit representations of these switches have been shown apart from, but linked by dashed lines to, their respective enclosures.

The four such switches are physically mounted in a bank or row secured at the forward end to a disc 74 which is normally stationary, with theinstrument shaft 60 extending therethrough, but is adjustable rotatively with respect to the shaft to vary the angular position of' the switches. The disc 74 is thus adjusted by moving a pointer 75 attached thereto and overlapping the circular scale 62 ('FIG. 4). By virtue of the circuits to be described, the setting of the pointer 75 determines the control point of the system, whereby the system is operative to adjust the pad positioning mechanism when the meas-' ured pressure deviates from such point or value, to provide a sensible signal when the actual pressure is below the control point by a predetermined amount, and to stop the operation of the press when the actual pressure reaches a pre-set cut-off point above the selected control point.

The circuits in which the control switches 70, 71 and 72 are located are commonly connected to one side of the supply, the conductor 49, through a Inicroswitch 76 operated by cam means 77 on an extension 78 of the main press shaft 15, the normally closed contacts 79 of a latch relay 80 and a manually closed switch 81. The circuit of control switch 73 is also connected to the line conductor 49 through the relay contacts 79 and switch 81, but this circuit is independent of the microsvvitch 76. As shown more clearly in FIG. 3, this switch 76 has an actuator arm 82 which rides commonly on the surfaces of two cams 83 and 84 driven by the shaft extension 78. Cam 83 is formed with a peripheral depression 85, and a similar depression 86 is provided in the edge of the cam 84, such cams in FIG. 3 being relatively rotated so that their depressions are almost opposite for clarity of illustration. 'In .actual practice, the camsare rotatively adjusted to bring their depressions 85 and 86 in register either fully or with a predetermined overlap. Since both cams engage the switch arm, it will be clear that the point at which the arm moves inwardly into the common depressed region of the cam means and the degree of its travel in such depressed condition can be adjustably predetermined. Microswitch 76 closes upon depression of its arm 82, and in an illustrative program of control for the system, cam means 77 will be set to close the switch for approximately forty degrees of the total pressing cycle, in which peak pressure is applied, this period of closure being subject to variation.

The control system, as earlier noted, operates the electric motor drive of the pad positioning mechanism, and the purpose of the press actuated switch 76 is to, avoid running of the motor during non-critical portions of the press cycle. Such motor 31 has the usual two windings the external circuits for which are respectively designated 87 and 88, with a common connection of the other ends of such windings to the line conductor 48 through a wire 89; it will be understood that these windings are adapted alternately to be energized and that the direction of rotation of the motor depends on such selective energization. In the illustrated system, the motor circuit 87 will be considered effective to drive the motor in a direction to lower the pad, while energization of the I circuit 88 causes the motor to raise the pad.

Manual operation .of the control motor is provided by means of a raise push button switch 90 and a lower push button switch 91. For example, closing the switch 90 to bridge the contacts 92 thereof completes the motor circuit 88 by connection thereof to the line conductor 49 through wire 93, the closed latch relay contacts 79 and switch 81, whereby the motor is driven to raise the pad.

Similarly, closure of the push button switch 91 to bridge its contacts 94 completes the motor circuit 87 in the same manner to drive the motor in a direction to lower the pad. Motor circuit 87 preferably is provided with a limit switch 95 and signal lamp 96 connected thereacross, while the motor circuit 88 correspondingly includes limit switch 97 and indicator lamp 98, these two switches being suitably mounted for actuation by the pad adjusting mechanism respectively to define the limits of the pad motor drive. 7

.The automatic control of the pad motor is accomplished by the switches 70 and 71 through relays 99 and 100 respectively connected between such switches and the line conductor 48. When switch 70 is closed by operation of the instrument 59, relay 99 is energized to close its contacts 101 and 102. A circuit is thus completed from supply conductor 49, through the manually closed switch 81, the normally closed contacts 79 of latch relay 80, the press actuated microswitch 76, wire 103, now closed contacts 101 of the relay 99, normally closed contacts 104 of the push button switch 91, limit switch 97 of the pad motor, the motor circuit 88, and the wire 89 from the motor to the other line conductor 48. With the various switches in this circuit made or closed, the motor is therefore energized and driven in a direction to raise the pad. Such operation of the motor is indicated by illumination of signal lamp 105 upon closure of the relay contacts 102 connecting the same between the wire 103 and the conductor 48.

The circuit from the line conductor 49 to the control swtich 71 is the same as described above for the control switch 70, and closure of the switch 71 will be seen to energize the relay 100 thereby to close its contacts 106 and 107. Such closure of relay contacts 106 continues the noted circuit from the conductor 49 therethrough, through the wire 108, the normally closed contacts 109 of the push button switch 90, limit switch 95, and the motor circuit 87 to the line conductor 48, whereby the motor is now driven in the reverse direction to lower the pad. Signal lamp 110 is illuminated upon closure of the contacts 107 to indicate this further condition of the control. 7 t

Control switch 72, similarly connected at one side to the supply conductor 49, will upon closure energize a warning horn 111 and a signal lamp 112. As will be described more fully below, these visual and audible signals are employed to indicate an undersized brick.

It will be noted that the three control switches 70, 71 and 72 are inefiective except during the period of closure of the press operated microswitch 76. The last control switch 73, however, functions without regard to .closure of the switch 76 and is employed as a safety to stop the press in the event of excessive pressure. Closure of switch 73 will be seen to energize coil 113 of the latch relay 80 and this causes contacts 79 thereof to open, contacts 114 to close, and contacts 115 to open. Such opening of the contacts 79 disables the circuits to the pad motor 31, and closure of the contacts 114 illuminates a signal lamp 116. As shown, the normally closed contacts 115 of the latch relay 80 maintain the solenoid 41 of the valve 40 controlling the press clutch and brake energized and thus in the drive condition; when the contacts 115 open the solenoid is accordingly cut out whereby the clutch is disengaged and the brake operated to stop the drive of the press. The latch relay is of the type which will hold in the condition to which it has been last actuated and it is provided with a reset coil 117 controlled by a reset push button 118. After the operator has cleared the press and is ready to resume operation, the reset button must manually be depressed to return the latch relay 80 to its normal condition before the control system is again rendered operative.

The illustrated circuit also includes a manual switch 119 for bypassing the press shaft operated microswitch 76, so that the operator can manually check operation of the system without having to drive the press. A further signal lamp 120 is connected between the conductors 48 and 49 at the system side of the main switch contacts 50 and 51 to indicate the supply of power to the system.

In establishing the program of the control, the cams 66 and 67 are related to provide a dead zone in which they cooperate to maintain both their respective associated control switches 70 and 71 open. This zone is quite small, for example, equal to about 0.3 rnillivolt movement of the instrument indicator, and in efiect determines the control point of the system. At positions of the cams below such point, control switch 71 is closed and switch 70 held open, while movement of the cams beyond the point reverses this relation to open the switch 71 and close switch 70. The cam 68 is set relative to the control point for closure of the switch 72 at any point which is below the control point by approximately 0.75 millivolt, while cam 69 is set to close at a point Which is approximately 1.5 millivolt above the control point.

These settings are internal and provide the desired relationships among the several points of switch actuation. Accordingly, adjustment of the disc 74 to select a particular control point by the indicator 75 on the instrument scale does not alter the interrelation of the cams but shifts the level or control point of the system as the result of the relative change in positioning of all the switches with respect to the cams. By way of example, it will be assumed that the pressure desired in the brick-forming cycle is equivalent to a reading of 2 millivolts on the indicator scale, and the pointer 75 is moved to such position. Although the instrument continuously indicates, and records, the pressure, the compensating controls and the undersized brick signal are efiective only when the pressing cycle reaches the point at which the shaft-operated microswitch 76 closes. At this occurrence, if the indicator arm 61 is at or substantially coincident to the 2 millivolt mark, no compensating controls are effected, the actual pressure being that desired. If, during the active period of control determined by the microswitch 76,.the measured pressure is between 1.2 and slightly less than 2 millivolts, the controlswitch 71 is closed to drive the pad motor to lower the pad and thus increase the volume of the mold cavity to compensate for the lower measured pressure. Should the reading be below 1.25 millivolts, the switch 72 will additionally be closed to energize the horn and light which indicate an undersized brick. If the reading during this period is between slightly more than 2 millivolts and less than 3.5 millivolts, control switch 70 closes to drive the pad motor to raise the pad, thereby to increase the mold cavity volume and compensate for the higher than desired detected pressure. If the pressure exceeds 3.5 millivolts, control switch 73 is actuated to disable the control system and stop the press as described above.

In such manner, the system is thus operative to apply deviations detected in one cycle automatically to adjust the press to compensate for the changed condition in the next cycle. The low pressure warning of course alerts the operator to discard the brick on that particular press ing as inferior, While the protection against excess pressure obtains throughout the entire operation. 7

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. In combination with a mold having an adjustable bottom closure and driven pressure applying means including a reciprocable plunger which enters the mold to compress molding material therein, with adjustment of the bottom closure varying the volume of the mold cavity and hence the charge of molding material in the same; a control system comprising means for generating an electrical signal which varies in accordance with and in proportion to changes in the pressure applied to the material in the mold throughout the full period of compression thereof by the plunger, controller means, means for continuously applying said electrical signal to said controller means for operating the latter, the controller means having an output shaft which turns in response to and in accordance with the direction and magnitude of changes in the electrical signal thus applied to the controller means, mold volume determining means for adjusting the bottom closure of the mold, first circuit means including first switch means actuated by turning of said control shaft for operating said mold volume determining means in response to deviations of said electrical signal irom a preset control value and the direction thereof, the bottom closure being thus operated by the mold volume determining means to increase the mold depth when the pressure is below the pre-set control value and to decrease the mold depth when the pressure is above said value, said first circuit means including second switch means actuated in response to predetermined advance of the plunger in the mold, with said second switch means efi ective to limit operation of the mold volume determining means by I the first circuit means to a predetermined portion of the total pressure stroke in which the application of peak pressure to the molding material would normally be expected to occur, cutoff means for disabling the drive of the pressure applying means, and second circuit means including third switch means actuated by turning of said control shaft for operating said cut-ofi means to disable said drive in response to a predetermined excessivepressure in the mold, said second circuit means being independent of said first circuit means, and hence the second switch means, and operable throughout the total pressure stroke to disable the drive whenever the pressure becomes excessive.

2. The combination set forth in claim 1 characterized further by the provision of sensible signal-producing means, third circuit means including fourth switch means and said second switch means, the latter in common with the first circuit means, for operating said sensible signalproducing means when the pressure is below the pre-set control value by a predetermined amount during the same portion of the pressure stroke in which the first circuit means controls operation of the mold volume determining means.

References Cited'in the file of this patent UNITED STATES PATENTS 2,232,545 Lum a... Feb. 18, 1941 2,432,215 Stocker Dec. 9, 1947 2,455,823 Tauber et al. Dec. 7, 1948 2,588,066 Weisberg Mar. 4, 1952 2,786,234 Beyer Mar. 26, 1957

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