US2922175A

US2922175A - Tuyere punches and like machines

Info

Publication number: US2922175A
Application number: US627604A
Authority: US
Inventors: Villiers Willem Johannes De; Bruckman Denis
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-12-12
Filing date: 1956-12-11
Publication date: 1960-01-26
Anticipated expiration: 1977-01-26

Description

.Jan. 26, 1960 w. J. DE VlLLlERS ETAL 2,922,175

TUYERE PUNCHES AND LIKE MACHINES Jan. 26, 1960 w. J. DE VILLIERS HAL 2,922,175

TUYERE PUNCHES AND LIKE MACHINES Filed Dec. 11, 1956 TIME STROKE 6 Sheets-Sheet 2' Jan 26, 1960 Filed Dec. 11. 1956 W. J. DE VILLIERS ETAL TUYERE PUNCHES AND LIKE MACHINES Jan. 26, 1960- w. J. DE VILLIERS ETAL 2,922,175

' TUYERE PUNCHES AND LIKE MACHINES 6 Sheets-Sheet 4 Filed Dec. 11, 1956 Jan. 26, 1960 w J DE v s ETAL 2,922,175

TUYERE PUNCHES AND LIKE MACHINES Filed Dec. 11. 1956 r 6 Sheets-Sheet 5 Jan. 26, 1960 w. J. DE VILLIERS ETAL 2,922,175

TUYERE PUNCHES AND LIKE MACHINES Filed Dec. 11, 1956 v 6 Sheetg-Sheet 6 United rates Patent TUYERE PUNCHES AND LIKE MACHINES Willem Johannes De Villiers and Denis Bruckman, Kitwe,

. Northern Rhodesia Application December 11, 1956, Seriai No. 627,604

Claims priority, application Union of South Africa December 12, 1955 Claims. (Cl. 15-104.16)

This invention relates to tuyere punches of the kind used to clear fluid passages leading into a mass of molten material in a furnace such as a copper converter.

The most widely used practice in punching tuyeres during the operating cycle of a copper converter involves the use of manual labour. The tuyeres are provided with "ball valves. These are displaced by the insertion of a punch rod which is manually reciprocated to clear the tuyere passage. Thus on each converter a number of manual labourers are required.

It has been proposed to replace manual labour with mechanical devices. One such device consists in a pneumatic punching machine arranged to travel from hole to hole like a manual labourer. The disadvantage here is that a furnace seldom keeps to its original shape and that the lining up procedure maybe very difficult. In another arrangement a pneumatic machine is mounted at each tuyere. In this case it has been found that the machine operates satisfactorily except at some plants where the slag encountered seems to be of too refractory a nature for existing machines.

A big drawback of pneumatic machines is that'constant preventative servicing is necessary and that maintenance costs are high. In fact the maintenance and servicing personnel may be as large as the labour force required for manual punching.

An object of the invention is to provide a machine which allows of faithful service over relatively long periods and which is automatic to a relatively large extent.

Ina machine according to the invention a tuyere punch rod is actuated by means of an armature to which a magnetic force is applied at least during the working stroke of the rod. Preferably magnetic forces are applied to the armature on both the working and return strokes of the punch.-

Conveniently the magnetic force is applied by means of one or more solenoids (which are preferably iron clad) through which the armature passes. In order to achieve the long stroke necessary, there will usually be at least two solenoids. In the latter case current is applied to one solenoid to start the working stroke and move the armature into the sphere of influence of the next solenoid and the current is switched from the first to the next solenoid while the armature is moving at speed.

Optimum operating efliciency is obtained where the active length of the armature lies between 1.5D+K and 2D+K, where D is the distance between the pole pieces and K is a design constant.

The invention also provides that the armature is built into or forms part of the punch rod.

In the preferred form of the invention the armature length extending beyond the pole pieces of any one solenoid when the armature is in mid-position between the pieces is formed to provide a magnetic path of reducing cross-sectional area as the ends of the armature are approached. As a result the armature continues to exhibit thmst after the longitudinal air gap between a pole piece and the armature has closed. Thus the leading end of the armature is extended into the sphere of influence of the adjacent solenoid. I

To provide the path of reducing cross-sectional area the armaturcis tapered and preferably by forming conical indentations at its ends. The angle of slope has not been found to be critical and in any case the angle is dictated by design considerations.

With the small space usually available behind tuyeres, it is essential to keep the solenoid dimensions as small as possible. The result is that the solenoids handle large currents for small periods of time. The supply and control of such currents is of prime importance. It has been found that the supply should be in the form of pulses of the required duration and properly phased to give the required thrust characteristics. At the current levels and switching speeds involved, mechanical switches will not have a long life and for that reason it is preferred to control the current supply electronically. v

With two coils it is necessary to have a pulse to start movement under the action of the first coil, a pulse in the second coil to take over from the first and also to act as a braking force at the end of the stroke and a third pulse to the first coil to return the rod to its starting position. The invention provides in this case that the coils be fed from two separate supply lines each of which carries the required pulses. Although it is possible to achieve this pulsing by electromagnetic or electronic chokes in a three phase alternating current supply, it is preferred to use direct current with two electronic rectifiers having a common return.

Grid biased rectifiers give the best result, the grids being normally biased to prevent current from flowing and the bias being lifted according to the current pulses required to work the solenoids. The lifting of the grid bias is controlled by electronic timing circuits which also control the switching to the various punching machines in a series.

The invention is further discussed hereunder by way of example with reference to the accompanying drawings,

Figure 3 is a graph showing. armature movements inthe configuration of Figure 2 Figure 4 is a wiring diagram showing the power supply circuit of the machine;

Figure 5 is a block diagram showing the various electrical circuits;

Figure 6 is a circuit diagram of an arrangement for generating triggering pulses for the power circuit;

Figure 7 is a circuit diagram of the master timing circuit;

Figure 8 is a circuit diagram of the distribution circuit;

Figure 9 is a circuit diagram of an addition to the timing circuit, and

Figure 10 is a circuit diagram of an ancillary circuit.

The machine shown in Figure 1 and its associated circuitry have been designed for use on the tuyeres of a copper converter. The converter has a horizontal line of about fifty tuyeres the centres of which are spaced at six inches so that the maximum outside diameter of each punching machine is 5.75 inches.

Basically the machine consists in two

coils

11 and 12 housed in mild steel barrels 13 separated by a mild steel disc 14 which provides a centre pole piece. The ends of the barrels are closed by mild steel plates 15 and 16 (the end pole pieces) which support Phosphor bronze bushes 17. These bushes act as the bearings and guides for a composite plunger 37 comprising an armature 18 of soft iron which is cone-spigoted on two pieces of nonrest.

magnetic stainless steel 19 and 2% by means of a high tensile steel screwed stud 21, and a punching section 22 securedto the front end of the piece 20. The section 22 7 is secured by means of a ball and. socket connection 23 so that the section 22 has a limited degree of play to a follow distorted tuyere pipes and to. be pulled loose when At the rear the piece 19 has a recessed screwed member 24 which providesan annular projection 25. The

piece 19 moves in a rear cover 26 which is adapted to telescope .on a pipe 27 projecting from the pole piece 15.

' Thear'rangement is such that the projection 25 clears the'pipe 27'and abuts against the pole piece 15. At the rear of the pipe 27 there is a cap 28 providing an annular recess 29 having a sloping wall converging forwardly towards the axis of the punch rod. A ball 30 is housed:

in the recess .29. g

If the machine is moved out of its normal working plane, 'e.g. to tilt the furnace, in the direction of the arrow 31, the ball rolls down the sloping recess 29 and obstructs the projection 25 (see Figure 1) thus preventingthe, punch rod from moving into the cavity of the furnace .At the. same time the telescopic cover 26 moves down" until its back contacts the cap28. The total clearance of the machine while tilting is thus considerably aperture 35 The plunger 37 is actuated by means of the two coils Hand 12. The magnetic circuit involved is diagrammatically illustrated in Figure 2. As shown the armature 1 8 is at its starting position relatively to the rear pole 15. The'dotted line positions are positions relatively to the

other poles

14 and 16 of the front end 40 of the arma ture 18.

- The firstpoint to be noted in connection with the magnetic circuit is that the length 38 of the armature 18 is between 1.5D+K and 2D+K where D'is the distance between the centres of the

pole pieces

15 and 14 andfK is a design constant. The distance between the centres of, the

pole pieces

14 and 16 is larger than D for reasons indicated below, but in this case also the equation should be satisfied, with the same constantjK and D1 being the distance between the

poles

14 and 16 the length'38 of the armature 'must lie between l.5D1+K and 2D1+K.

. Assuming that current be applied to the coil 11 then movement of the leading end 4410f the armature 18 in relation to time is shown in the graph 41 plotted in Figure '3. At about the point 42 (corresponding to dotted line position 42 in Figure 2) the armature will come to It now the coil 11 is de-energised and the coil 12 fed with current, the curve 43 represents further'movement of the armature '18. The punching stroke is achieved by a combination of the curves 41 and 43 to the form shown in the curve 44, i.e. an almost sinusoidal stroke may be achieved. The stroke shown in curve 44 is attained by switching off the current in coil 11 when the leading end 40 has passed'the pole piece 14 (e.g. at point 45) and applying current to the coil 12.. The amplitude of the oscillation will be larger than for coil 7 11 becausethe armature possesses the combined kinetic Y depend on the starting point, the distance between pole pieces, the overshoot of the plunger and the timing of the switching. v I

In practice the switching will'be determined by the dynamic response of the machine. The overshoot has been found to depend on the depth of the conical indentations 48 and the starting point may be chosen at will within limits. Thus the stroke of the a question of geometry. r

The actual length of the coils is determined by the current loading and the desired length of the power stroke. The maximum displacement being dependent only on the length of the armature, the depth of the cone and the starting point, the percentage of the total stroke under power depends on the length of the coil 12. To ensure that at least 75 percent of the plunger stroke is under I to the coil 11 by about one third.

, to space limitations the coils are relatively small and Any suitable form of switching may be used, but there are several important factors that have to be taken into consideration. Firstly the current pulses applied to the coils must be very accurately controlled. Secondly due extremelylarge current densities (of theorder'of 1500 amps. per square centimetre) are involved. The basic switching problemis then to handle large power pulses for very short but well-defined periods and to ensure that the loading'on any one coil is not repeated too often.

- By using grid-controlled mercury arc rectifiers the switching problems are simplified to a large extent. The rectifiers serve the functions of converters and contactors. As said above, the use of direct current is preferred for the reason that suitablemagnetic materials for the use of alternating current are not easily available.

Figure 4 showsa circuit which was devised to-use mercury arc rectifiers of the kind made by the English Electric Company and known as excitrons. 'In this -circuit six excitrons 49 have been arranged in sets of three,

each set feeding a

supply line

50 or 51 and the sets having a common return 52 in a well known manner. Briefly all the cathodes of the excitrons 49 are connected 'to the common return 52. The anodes in a set are connected to a secondary 54 of a double wound three phase trans former 53;

In addition to grid control the excitrons have dipping anodes SS for striking the arcs.. Both grid and excita-- tion voltages are provided by separate rectifiers 56 from transformer secondaries-57. The dippinganodes are extracted by' excitation chokes 58. Resistances 59 are on-load current limiting resistances and 60 are stabilising resistances; 'Grid limiting resistances 61 and loading resistances 62 for pulse transformers are alsoprovided.

The excitation currentis interrupted by contact 71 in a manner to .be described later on. r a

The arrangement is such that the grids of the ex citrons are normally sufiiciently' biased to prevent the tubes from firing even if the dipping anodes are extracted.

. The transformers 70 are arranged to providetriggering pulses (by means to be discussed later on) synchronised with the main supply" and phased to trigger the excitrons off as the voltage on their anodes rises in the positive direction. r

The overall circuit arrangement is shown in Figure 5 where 72 represents. the power circuit such as that discussed with reference to Figure 4, 73 represents the pulse generator for providing incipient triggering pulses, 74. 7 represents a timing circuit, '75 a distribution control cir cuit, and 76 and 77 ancillary circuits; In this scheme the circuit 73 continuously produces trigger pulses, syn-' chronised to the main supply. The timing circuit 74 is arranged to provide gating pulses to the circuit 73 to allow only some of the incipient trigger pulses to pass and become trigger pulseswhich actuate the excitronsin the circuit 72. The timing circuit is also interlocked machine is largely with a distribution circuit 75, so that gating pulses are only generated when the distribution circuit is in order and so that the distribution connections are made relatively in phase with the gating pulses. The circuit 76 is arranged to act manually or automatically to allow the distribution circuits to operate as and when punching strokes are desired or required. The circuit 77 is arranged to'interrupt the distribution circuit when certain predetermined outside conditions are not satisfied or when manually operated for maintenance or other purposes. The circuit 75 also includes a relay which is adapted to close the contacts 71 in the circuit 72.

If the frequency of the main alternating current supply is at fifty cycles, the frequency of the trigger pulses from the circuit 73 must be at 150 cycles per second. The gating pulses are conveniently of such a nature that the line 50 carries power pulses suitable to energise the coils 11 of a series (say fifty) of punching machines.

The line 51 carries the pulses necessary to work the coils 12 of the series. The sequence is then a pulse on line 50 to start an armature 18 moving, a pulse on line 51 to continue such movement and return the armature toward the first coil and finally a pulse on line 50 to move the armature back to its starting position. While the circuit 75 switches over to the next punching machine there is an interval during which neither

line

50 or 51 carries any pulses. At the end of a salvo, i.e. when all the machines in a series have been operated to punch, there may be a predetermined delay or the circuit 76 could take over. It is, however, essential that the three power pulses must follow each other in sequence to ensure that a punch rod returns to its starting position and the circuit 77 is therefore so arranged that it can only interrupt a salvo at the end of a set of three power pulses to the same machine. The circuit 75 operates power contactors 78 which close the circuits to the

solenoids

11 and 12 just before a set of power pulses is due to arrive and open them just after such power pulses have terminated.

Numerous detailed circuit arrangements are possible to achieve the general conditions outlined above. Figure 6 illustrates a circuit suitable for generating the incipient trigger pulses. A separate three phase secondary winding 79 is wound on one of the excitation transformers 57 (Figure 4) and feeds a bank of star connected germanium diodes 80. The ripple voltage superimposed upon the rectified voltage is applied inverted to the grid of a triode 81 which modulates a unistable flip-hop c1rcuit comprising triodes 82 and 83. This circu1t is adjusted to pass square waves of a time duration depending on the value of the grid resistance 84. The 150 cyclesper second ripple voltage locks the flip-flop to the third harmonic of the mains frequency. I

The resultant square wave pulse is differentiated in the circuit including condenser 85 and resistance 86, so that its trailing edge develops a positive going pip the phase of which in relation to the ripple pulse is controlled by a variable resistance 87.: These positive going incipient trigger pulses are applied through condensers 88 to the grids of a pair of power amplifiers 89 and 90 to the bias voltage of which is such that they will not normally conduct even in the presence of the incipient trigger pulses. If the bias is reduced by, say fifty volts, the tubes 89 and 90 wil conduct for the period of each incipient trigger pulse. This bias is controlled by gating pulses from the timing circuit to be described later on.

The outputs of the amplifiers 89 and 90 are fed to the transformers 70 described with reference to Figure 4.

A suitable timing circuit for deriving gating pulses is illustrated in Figure 7. This circuit is well known in the art and fundamentally consists in what are known as univibrator circuits. The circuit therefore includes pairs of triodes, the pairs being numbered 100 to 104. The members of each pair are so interconected that they pro- 'vide a unistable circuit. Normally, i.e. in the stablestate,

the one tube conducts and the other does not. When a negative going signal is applied to the grid of the conducting tube (the right hand one in th drawings) its anode potential will rise thus progressively reducing the bias of the second or left hand tube until the bias exceeds the cut-off potential of the second tube. If the input signal is sufficiently large in amplitude the second tube begins to conduct. This results in a violent feed back between the tubes causing the grid of the first tube to be depressed to the full of the change of voltage on the condenser between the anode of the first tube and the grid of the second tube, thus cutting off the first tube and attempting to raise the potential of the second tube. The pair remains in this condition until the charge on the condenser 105 gradually leaks away through a variable resistance 106 and a resistance 107. As soon as the potential of the first tube passes the cut-oil. point, violent feedback again results and rapidly restores the circuit to the normal stable state.

The period of the quasi-stable state depends on the supply voltage, the load resistance of the tubes and the coupling time constant of the condenser105 and the

resistance

106 and 107.

As shown the anode of the first tube in a pair is connected to the grid of the first tube of the next pair of the five pairs via a small capacitance 108 and a large resistance 109 for the next pair to trigger into the unstable state as soon as the former pair returns to the stable state. In this way the pair 100 triggers the pair 101 and so on to the fifth stage 104 which in turn starts the cycle. It should be noted that the values of the various resistances are so chosen that a stage cannot trigger any stage beyond the next stage.

The grid voltage of the left hand tube of each of the stages 100 and 103 is applied to a potential divider 110 which feeds the grid of the power amplifier 89 (see Figure 6) with the result that only if the stages 100 and 103 are in the unstable state, the tube 89 allows current to pass through its transformer 70. Likewise the grids of the left hand tubes of the

stages

101 and 102 are connected to a potential divider 111 which feeds the tube 90.

Diodes 112 are provided to prevent paralleling of the grid circuits of the timing circuits.

The output from stage 103 is fed to stage 104 which is the interval timing stage. The latter is arranged for a much longer quasi-stable state to provide the time interval for switching from one punching machine on to the next. The right hand grid of stage 104 is also permanently conected to a negative supply potential through a resistance 113 and to ground through a pair of contacts 114. The latter form part of the interlock with the dis- I tribution circuit discussed below. It should at this stage be noted that if the contacts 114 are bridged, the stage 104 operates in the normal way. With the ground point removed, this stage is held in the unstable state. By operating the contacts 114 gating pulses may be initiated or stopped at will but only in complete batches.

Stage 104 also feeds into a further stage consisting of a single tube 115 which works in tanden with it. The tube 115 cuts off with the second tube of stage 104 to de-energise a relay in the distribution circuit. As soon as the time delay involved in the circuit including a condenser 116 and a variable resistance 117 allows, the relay 120 is re-energised.

Depending on the number and time intervals of the individual timing stages in the circuit, so a wide variety of output pulses may be applied to the power amplifiers 89 and 90. It has been found in practice that good punching results are obtained by arranging stage 100 to gate five trigger pulses, stage 101 one such pulse, stage 102 eleven pulses and stage 103 five pulses. The fifth stage 104 is arranged to give a delay to suit the reaction time of the distribution circuits. In each situation it is best to determine the correct timing by experiment.

' to ground.

timing circuit. There is also athird relay128 which locks itself to ground through contacts 138, closes a pair of contacts 130 and moves a contactor arm 131 from the position shown to a position where it puts a selector 132 in circuit.

The relay 124 is connected to a uniselector the arm 133 of whichsweeps across a bank of contacts 134 (the first one) and 135 of which there are as many as. there are punching machines. The uniselector 133 and the selector 132 if it is of the traction type are driven by magnets 136. The contact 127 is in circuit with a relay 137 which closes. the contacts 71 referred to with reference to a Figure 4.

The circuit 76 includes means to complete it for the purpose of initiating a salvo or a train. of salvos. The circuit 77 includes various means for'interruptin'g a salvo V or a train of salvos.

Starting from the position where the selector arm 133 connects the contact 134, if the

circuits

76 and 77 are completed, the relay 124 is energised by being connected This relay then locks itself to ground by means of the contacts 125 (which it closes) and the contacts 123 which are normally held closed by the relay 120.. At the same time the contacts 114 are closed to initiate the timing circuit to start a train of power pulses. The relay 124 also closes the contacts 127 which by means of the relay 137 close the excitation contacts 71. The other contacts 126 governed by the relay 124 are also closed, but the relay 128 remains de-energised as the relay 12% holds the contacts 122 open.

.As the first timing cycle is completed, the relay 120 is momentarily de-energised and the contacts 122 close to energise. the relay 128, so that the arm13 i1 moves to connect the selector 132 in. circuit, the contact 130 is closed in the circuit of the magnets 136 of the selectors on the selectors. If the contact 135 in question is still connected to ground via the circuit 77 the next cycle proceeds and so on until all the contacts |135in the bank have been wiped by the arm 133/ The latter now again proceeds to the contact'134 and if the circuiti76 is now open the relay 124 which has no ground connection when the relay 12tl is momentarily de-energised, drops out and punching stops until such time as the circuit 76 is again completed. if for any reason the circuit 77' is interrupted at any time during a salvo, the relay 124 will act in the same way, but only at the end of a cycle. The contactor arm 1 31 is initially connected to a relay 1'29 which when energised actuates a .contactor to connect a dummy load across the

lines

50,51 and 52 Thus whenever the relay 124 has dropped out, at the end of a salvo was a result of an interruption of a salvo, the dummy load is first connected to the power supply before punching machines. are connected in circuit. The arms 133 and 131 are prevented from moving as the relay 128 is not energised. Thus the excitrons 49 have time to settle down before being called upon to operate a punching machine. After the first power pulses, the relay 1 2i 'is' momentarily dia -energised and the relay 128 comesinto operation and remains energised as long as the relay 124 is energised. These

lectors

133 and 132 are stepped on by opening and closing the contacts 121.-

1; In order to ensurethat the line contactors do notopen before the heavy current impulses to the punchingmachine i coils. have terminated, the contacts of the relay are arranged to'have a ten millisecond delay'on opening. f I

.The circuit 77 includes various means for stopping punching operations. Thusthere may be manual. switches at the'main control room and on strategic points at the punching site.. Furthermore where airv pressure drops below a predeterminedminimum it is desirable to stop punching altogether. Eorthis purpose a pressure switch operating on this low pressure is included in the circuit. As it is also undesirable, in the case. of a rotary converter to punch. during tilting, the circuit also includes a mercury tilt switch on the converter as well as. a limit switch on the tilting motor brake arranged to open while the motor is in motion. Any of these switches will immediately stop the next punching cycle and a salvo will be completed only if the stop circuit 77 is again completed.

For initiating a salvo a timing clock maybe arranged to operate the circuit 76. A suitable arrangement is shown in Figure 10. In this case salvo frequency is determined. by overall air flow to the tuyere. Differential pressure switches 140, 141 and. 142 are-arranged to be responsive to different minimum volumes of air flow and on such minimum flow being reached each allows a pair of

contacts

143, 144 and 145 respectively to close. The

spring contacts 146 which are'helcl open bycams 147, 1'43 and 149. The camshavenotches to allow closing of the contacts 146' depending on the speed at which the cams are rotated by the motor of a timing'clock. If the switch 140 allows the contacts '143 to close, the overall initiating circuit by means of thecam 147; with four notches will be. closed four times per revolution of the motor 150; Theswitch 1 41 and" the cam'148 closes the circuits twice and the switch 142 and the cam 149 once only. V j v i Thus the camsin sequence initiate a lesser number of salvos per revolutionof the motor 150 untilgat a predetermined maximum flow the punching machines remai inoperative. V g

- It has been 'found that there is a dip in the. back developedby the coils 111and1'2, as they are."

straddled by the armature 18. p This fact may be utilised for automatically switching the coils. j 'A" suitable circuit is illustrated in Figure 9. In'thiscase thecoil (say 11),

is connected to the .power.

supply lines

50 and ,52 through a resistance 151. .Two further rmista nces 152and 153 are connected between .thelines in'series with one another andin parallel with the resistances 1 1 and 151.

The ratio ,of the resistance of the coil 11. to the reistance 151 is the same as that of the reistance 153 to the resistance 152. The centre point between the

resistances

11 and 151 is connected to a coincidence differ ential circuit comprising'a high tension supply, a limiting back of a predeterrnined magnitude takes place.

a pulse having the voltage of the coincident circuit differential is formed at 161, This pulse may be injected at point 162, in Figure 7 in order to step the timing sequence on. If. this circuit is used the timing circuits areset at longer intervals than usual, but these would be automatically shortened-by the back characteristic.

A similar circuit could be used for coil 12 and the resulting pulse injected at a point such as 163. In this case the timing circuit of the pair of triodes 101 must gate that portion of the pulse which performs the forward stroke in coil 12 and the timing circuit of the pair of triodes- 102 must control the return stroke.

By using the circuits of Figure 9 the velocity of the plunger 37 is maintained at a maximum level. 'Furthermore if an encrustation is encountered in a tuyere pipe the machine automatically adjusts its stroke to suit the free length of the tuyere pipe, In other words the machine automatically assesses the conditions encountered by the plunger 37 and adjusts the power pulses accordingly.

Instead of the timing circuit shown in Figure 7, a circuit employing dekatron tubes may be used. In this case the pips developed in the circuit of Figure 6 are fed to the grids of the dekatron tubes and required groups of dekatron cathodes are connected to the grids of the power amplifiers 89 and 90. Dekatron tubes may also be used as the selector 132 (Figure 8) and in this case the power to the line contactors 78 is supplied by thyratron tubes the grids of which are connected to the dekatron cathodes.

The punching machine provided by the invention gives satisfactory service under most dificult conditions. A stroke as long at 12.5 inches has been maintained with the machine.

We claim:

1. Tuyere punching apparatus including a series of punching machines each of which has a punch rod, an armature of magnetic material forming part of the punch rod, and a forward and a backward solenoid surrounding the path of the armature, the armature comprising a main portion of substantially uniform cross-sectional area and hollow tapering ends of sufficient length so that by means of the continual increase of cross-sectional area after a solenoid has been bridged, the armature continues to have thrust in the direction of its leading end and while current is flowing in the first solenoid; including two current supply lines, a common return to the supply lines, means to switch any one machine from the series to the supply lines so that when a machine is thus switched the backward coil is connected to the first line and the forward coil to the second line, means to supply current pulses to the supply lines after a machine has been switched to the lines, the current pulses being such that a first pulse in the first line causes the backward solenoid to move the armature from a starting position into the sphere of action of the forward coil, :1 second pulse in the second line follows the first pulse immediately to cause the forward solenoid to move the armature to the end of the working stroke of the rod and to return the armature into the sphere of action of the backward coil and a third pulse in the first line follows the second pulse immediately to move the armature back to its starting position, the switching means being arranged to connect the machines to the lines in turn,

2. The apparatus claimed in claim 1 including two groups of grid biased power rectifiers connected to an alternating current supply, one group being connected to the first line and the other to the second line, and means to generate trigger pulses to lift the bias of the grids to the power rectifiers in phase with the required supply current pulses.

3. The apparatus claimed in claim 2 including a pair of secondary grid biased rectifiers for supplying the trigger pulses to lift the bias of the grids to the power rectifiers, means for generating incipient trigger pulses in phase with the alternating current supply of the power rectifiers, the incipient pulses being so phased that if they were of sufficient amplitude to allow the members of the rectifier pair to conduct, trigger pulses for each half cycle of the alternating current supply would be provided, but being of insufiicient amplitude to lift the bias of the grids of the pair sufiiciently for the pair to conduct, and means to generate gating pulses interlocked with the switching means which added to the incipient trigger pulses allow the members of the pair of conduct and to provide a predetermined pattern and number of trigger pulses to the power rectifiers.

4. The apparatus claimed in claim 3 in which the gating pulses are so interlocked with the switching means that each machine is switched to the lines before the first power pulse arrives and disconnected from the lines after the third power pulse has terminated.

5. The apparatus claimed in claim 4 including a stop circuit so connected with the gating pulse generating means that on the stop circuit being open the gating pulse generating means only supplies gating pulses to operate that machine which is then connected to the lines to the position of rest of the armature.

6. The apparatus claimed in claim 4 including means sensitive to the flow of air to the tuyeres to cause the gating pulse generating circuit to operate.

7. The apparatus claimed in claim 1 in which the switching means and the current supply means are so interlocked that each machine is switched to the lines before the first pulse arrives and disconnected from the lines after the third pulse has terminated.

8. In combination a series of identical linear electric motors each of which has a thrust arm, an armature of magnetic material forming part of the arm, at least two solenoids surrounding the path of the armature, current supply lines equal in number to the number of solenoids in a motor, a common return for the supply lines, means to switch any one motor of the series to the supply lines so that its solenoids are connected to the lines in a predetermined sequence common to all motors, means to supply current pulses to the supply lines after a motor has been switched to the lines, the current pulses being such that a first pulse in the first line causes the backward solenoid to move the armature from a starting position into the sphere of action of an adjacent solenoid, following pulses in the other lines follow the first pulse and one another immediatelyto cause the adjacent solenoid and following solenoids to move the armature towards the end of the thrust stroke of the arm and the pulse to the forward solenoid acting also to initiate movement of the armature in the reverse direction, pulses follow in reverse order and the final pulse to the backward solenoid moves the armature back to its starting position, the switching means being arranged to connect the motors to the lines in turn.

9. In combination a series of identical linear electric motors each of which has a thrust arm, an armature of magnetic material forming part of the arm, two solenoids surrounding the path of the armature, a current supply line for each solenoid, a common return for the supply lines, means to switch any one motor from the series to the supply lines so that its solenoids are connected to the lines in a predetermined sequence common to all motors, means to supply current pulses to the supply lines after a motor has been switched to the lines, the current pulses being such that a first pulse in the first line causes the backward solenoid to move the armature from a starting position into the sphere of action of the forward solenoid, a second pulse in the second line follows the first pulse immediately to cause the forward solenoid to move the armature to the end of the working stroke of the armature and to return the armature into the sphere of action of the backward coil and a third pulse in the first line follows the second pulse immediately to move the armature back to its starting position, the switching means being arranged to connect the motors to the lines in turn.

10. Tuyere punching apparatus including a series of identical punching machines each of which has a punch rod, an armature of magnetic material forming part of the punch rod, at least two solenoids surrounding the path of the armature, current supply lines equal'in number to the number of solenoids in a machine, a common return for the supplyrlines, means to switch any one machine of thefseries'to the'supply lines so that its solenoids are connected to the lines in a predetermined sequence common to' all machines, means to supply current pulses to the supply lines after a machine has been switched to the linesfthe currentvpulses being such that a first pulse in the first line causes the backward solenoid to move the armature from a starting position into the sphere of action of an adjacent solenoid, a following pulse in another line follows the first pulse immediately to cause the adjacent solenoid to move the armature towards the ,end of the Working stroke, and a pulse inthe last line connected to the forward solenoid follows immediately on the pulse for the solenoid adjacent the forward solenoid to cause the forward solenoid to move the armature to the end of the working stroke of the rod and to reverse the directio'n of movement of the armature, pulses are fed to the solenoids in reverse order to the working stroke and the final pulse V 12 to the backwards fsolenoid moves the armature backto its starting" position, the switching means being arranged to connectthe machines tolthe'lines in'turni f v 1 References Cited in the file of this patent UNITED STATES" PATENTS $07,671 Boekl'en Oct, 31, 1893 637,809 Meissne'r Nov. 28, 1899 1,819,008 Weyandt Aug. 18, 1931 1,999,640 Royse Apr. 30,1935 2,008,795 Olmstead July 23, 1 935 2,182,014 1" Clark Dec. "5 1935' 2,344,758 a Welsh 'Mar. 21, 1944 2,429,581 -Maitlen Oct. 21,1947 '2,640,955 Fisher 7 JuneZ, 1953 2,664,161 Schlecht Dec. 29, 19:53 "2,686,280 I Strong et'al Aug. 10,1954 2,696,979 Berg