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Publication numberUS3657825 A
Publication typeGrant
Publication dateApr 25, 1972
Filing dateJul 2, 1970
Priority dateJul 2, 1970
Also published asCA935898A1
Publication numberUS 3657825 A, US 3657825A, US-A-3657825, US3657825 A, US3657825A
InventorsHerbert W Helm, Edgar V Weir
Original AssigneeSmithe Machine Co Inc F L
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method and apparatus for controlling the heat intensity of an envelope machine drier
US 3657825 A
Abstract
Envelope blanks with a wet adhesive applied to the seal flap portion are conveyed through a drier by an endless chain conveyor. The conveyor is driven at the same speed as the other machine components to serially convey the blanks as they are supplied to the conveyor from the seal gum applicator and collator section of the machine. A wound rotor motor is provided to drive the machine components and the drier conveyor. The rotor voltage of the wound rotor motor varies inversely with the speed of the motor, the maximum voltage being generated when the motor speed is at a minimum. A drier circuit is provided that includes a separate source of current with the drier resistors and silicon controlled rectifier in series. The source of current for the the drier circuit is also connected to the output coils of a magnetic amplifier in a heater control circuit. The magnetic amplifier is connected to a pulse transformer and the output coils of the pulse transformer provide a signal to control the gates of the silicon controlled rectifiers. With this arrangement the magnetic amplifier controls the firing angle of the SCRs and the current flowing through the heater resistors. The heater control circuit is arranged so that the magnetic amplifier without a substantial feed-back voltage from the rotor is full on and supplies heat to the drier at the maximum intensity. This condition is approached when the machine is running at maximum design speed where a minimum voltage feed-back is generated. As the speed of the machine and of the wound rotor motor is reduced, the rotor voltage increases and a feed-back of this rotor voltage through the input coil of the magnetic amplifier serves as a negative control on the magnetic amplifier to reduce the current flow through the output coils and in turn reduce the current flow through the SCRs to the heater resistors. As the speed of the motor and the machine is reduced further, the rotor feed-back voltage increases and thereby increases the voltage in the magnetic amplifier input coil to apply an increased negative control and further reduce the current flow through the SCRs to the heater elements. The rotor voltage supplied t the heater control circuit as a feed-back from the wound rotor motor, increases or decreases the heat intensity of the drier. As the motor speed increases, the rotor voltage decreases and the drier heat intensity increases. Conversely, when the motor speed decreases, the rotor voltage increases and as a negative control, decreases the drier heat intensity proportionately.
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Description  (OCR text may contain errors)

United States Patent Helm et al.

[ 1 3,657,825 [45'] Apr. 25, 1972 [54] METHOD AND APPARATUS FOR CONTROLLING THE HEAT INTENSITY OF AN ENVELOPE MACHINE DRIER [72] Inventors: Herbert W. Helm, Hollidaysburg; Edgar V. Weir, Butler, both of Pa.

[ 73] Assignee: F. L. Smithe Machine Company Inc., Duncansville, Pa.

[22] Filed: July 2, 1907 [2]] Appl. No.: 51,754

Smith Kullgren et al ..34/48 X Primary Examiner-Carroll B. Dority, Jr. Attorney-Stanley J. Price, Jr.

[ ABSTRACT Envelope blanks with a wet adhesive applied to the seal flap portion are conveyed through a drier by an endless chain conveyor. The conveyor is driven at the same speed as the other machine components to serially convey the blanks as they are supplied to the conveyor from the seal gum applicator and collator section of the machine. A wound rotor motor is provided to drive the machine components and the drier conveyor. The

rotor voltage of the wound rotor motor varies inversely with the speed of the motor, the maximum voltage being generated when the motor speed is at a minimum. A drier circuit is provided that includes a separate source of current with the drier resistors and silicon controlled rectifier in series. The source of current for the the drier circuit is also connected to the output coils of a magnetic amplifier in a heater control circuit. The magnetic amplifier is connected to a pulse transformer and the output coils of the pulse transformer provide a signal to control the gates of the silicon controlled rectifiers. With this arrangement the magnetic amplifier controls the firing angle of the SCRs and the current flowing through the heater resistors. The heater control circuit is arranged so that the magnetic amplifier without a substantial feed-back voltage from the rotor is full on and supplies heat to the drier at the maximum intensity. This condition is approached when the machine is running at maximum design speed where a minimum voltage feed-back is generated. As the speed of the machine and of the wound rotor motor is reduced, the rotor voltage increases and a feed-back of this rotor voltage through the input coil of the magnetic amplifier serves as a negative control on the magnetic amplifier to reduce the current flow through the output coils and in turn reduce the current flow through the SCRs to the heater resistors. As the speed of the motor and the machine is reduced further, the rotor feed-back voltage increases and thereby increases the voltage in the magnetic amplifier input coil to apply an increased negative control and further reduce the current flow through the SCRs to the heater elements. The rotor voltage supplied t the heater control circuit as a feed-back from the wound rotor motor, increases or decreases the heat intensity of the drier. As the motor speed increases, the rotor voltage decreases and the drier heat intensity increases. Conversely, when the motor speed decreases, the rotor voltage increases and as a negative control, decreases the drier heat intensity proportionately.

10 Claims, 2 Drawing Figures METHOD AND APPARATUS FOR CONTROLLING THE HEAT INTENSITY OF AN ENVELOPE MACHINE DRIER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for controlling the heat intensity of an electric drier and more particularly to a method and apparatus for varying the heat intensity of an adhesive drier of an envelope machine according to the speed ofthe machine.

2. Description of the Prior Art In envelope and bag making machines a liquid adhesive is applied to the seal flap of the blank and the blanks with the wet adhesive are conveyed through a drier section of the machine where the adhesive is dried by electric heater units such as quartz drying lamps.

The heat intensity of the heater units is adjusted on start-up of each run and often causes considerable difficulty. Where the heat intensity of the units is preset and switched on as soon as the machine is started, frequently the heat intensity is too high and the blanks char or burn. Where there is a delay in energizing the heater elements after start-up, frequently the heat intensity is inadequate and the adhesive is not dried in the drier. The blanks with wet adhesive cause machine jams and considerable time is required to remove the damaged blanks and remove the adhesive from the envelope machine parts.

The envelope machines have a speed control to increase or decrease the number of envelopes made in a given period of time. Any change in machine speed requires a similar change in the heat intensity of the drier. With present envelope machines the operator manually adjusts the heat intensity with machine speed. Frequently the operator will change the machine speed and forget to change the heat intensity which results in either burned or charred envelope blanks or wet adhesive on blanks leaving the drier. There is a need for a method and apparatus to automatically control the heat intensity ofthe drier in accordance with machine speed.

SUMMARY OF THE INVENTION In accordance with the present invention there is provided apparatus for controlling the heat intensity of a drier in an envelope machine that comprises a drier with heater elements arranged to dry the adhesive on the envelope blanks while the envelope blanks are being conveyed in the envelope machine. A conveyor means conveys the envelope blanks while the blanks are subjected to heat from the heater elements. A variable speed drive means is provided for the conveyor to drive the conveyor at different preselected speeds. The heater elements have control means for changing the heat intensity of the heater elements and the control means is responsive to the speed of the conveyor means so that the heat intensity of the drier is dependent on the speed of the conveyor means.

The conveyor means is driven by a wound rotor motor and the drier heater elements are electric resistors, preferably quartz lamps. The control means associated with the resistors includes a means responsive to the rotor voltage of the wound rotor motor to vary the current flowing through the resistors. Another separate control means is provided to manually adjust the maximum heat intensity of the heater elements at the maximum speed of the conveyor.

The control of the drier heat intensity is accomplished through a control circuit that includes a potentiometer, a magnetic amplifier and a pulse transformer. The drier circuit includes a separate source of current for the resistors and silicon controlled rectifiers to regulate the flow of current through the resistors and thus the heat intensity of the drier. The firing angle of the SCRs is, in turn, regulated by a heater control circuit. The magnetic amplifier is normally full on to provide maximum current flow through the SCRs at maximum machine speed. The rotor feed-back voltage provides a negative control for the SCRs and as the feed-back voltage increases, the current flow through the SCRs decreases and the heat intensity of the drier decreases with the speed of the conveyor.

The method for controlling the heat intensity of the envelope machine drier includes propelling a conveyor in the drier with a wound rotor motor. A current flow control means is connected in a drier circuit with the heater resistors of the drier. A negative control is applied in the drier circuit in response to a signal generated by the wound rotor motor. The signal is arranged to increase and decrease the current flowing through the heater resistors as the speed of the conveyor increases and decreases. The drier circuit includes solid state rectifiers to control the flow of current through the resistors in the drier circuit. The signal generated by the wound rotor motors is transmitted through a heat intensity control circuit that regulates the flow of current through the drier circuit to the heater resistors.

Accordingly, the principal object of this invention is to vary the heat intensity of the drier in an envelope machine in accordance with the speed of the conveyor means that transports the envelope blanks through the drier.

Another object of this invention is to provide a feedback system for an envelope machine drier that includes the machine speed as the input variable and the heat intensity as the output variable.

These and other objects and advantages of this invention will be more completely disclosed and described in the following specification, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings:

FIG. 1 is a schematic drawing in elevation of an envelope machine illustrating the various components of the machine, a pair or wound rotor motors and the drier elements with the endless conveyor chains positioned thereabove.

FIG. 2 is a diagram of a suitable circuit for controlling the heat intensity of the drier in accordance with the speed of the endless conveyor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, and particularly to FIG. 1, there is illustrated an envelope machine generally designated by the numeral 10 that has a front drive motor 12 and a rear drive motor 14. The envelope machine 10 has a plurality of separate sections connected to each other with conveyors to transport the envelope blanks therethrough. The envelope blanks are fed from a rotary feeder 16 in the feeder printer section 18 to a printing unit 20 and then transferred by means of a transfer cylinder 22 to a panel cutter section 24 where panels are cut in the envelope blanks and adhesive is applied around the window or panel portion of the blanks by a gummer mechanism 26.

The envelope blanks are then transferred to a collator section 28 where the glassine patches are cut from a web of glassine 30 and applied to the envelope blanks while the blanks are on a collator roll 32. The blanks are then collated into overlapped relation and adhesive is applied to the exposed seal flap portion of the blanks by the adhesive applicator 34. The blanks are thereafter transferred from an endless belt conveyor 36 that conveys the envelopes past the adhesive applicator 34 to a second belt type conveyor 38 on the collator section 28. The conveyor mechanism 38 slightly separates the overlapped envelope blanks so that the seal flap portions with the wet adhesive thereon are slightly separated to prevent the blanks from adhering to each other.

The envelope blanks are then conveyed to an endless chain type conveyor that has an endless upper reach 40 and a lower reach 42. The chains 40 and 42 are arranged to be in abutting relation with each other to form a conveyor reach 44 that conveys the envelope blanks from the conveyor mechanism 38 across the panel cutter section 24 and the feeder printer section 18 into heat exchange relation with drying elements 46 positioned in the delivery section 48 of the envelope machine 10. The delivery section can, for convenience be considered both the drier section and the delivery section since the adhesive on the seal flaps of the envelope blanks is dried by means of the drying elements 46 positioned beneath the delivery table 50.

The envelopes are conveyed by the endless chains 42 and 44 along the bottom of the folder section 52 to the aligner section 54. The blanks are transferred from the endless chains 40 and 42 to endless belts 56 that separate the blanks from their overlapped condition and convey the blanks to an aligner mechanism 58 where the blanks are transversely aligned. The aligned blanks are fed by the aligner chain to a bottom seal scorer 60 and a side scorer 62 where suitable scores are impressed on the blanks, A plowshare folder 64 folds the side flaps and a gummer mechanism 66 applies adhesive thereto. A flap folder 68 folds the bottom flap and the seal flap in the folder section 52 and the envelopes are delivered to a delivery wheel 70 and thereafter transferred to the delivery table 50 positioned above the drying elements 46.

With the above described arrangement, the front drive motor 12 is arranged to drive the components in the feeder printer section 18, the panel cutter section 24 and the collator section 28. The rear drive motor 14 drives the components in the aligner section 54, the folder section 52 and the delivery section 48. Also, the endless chains 40 and 42 are driven by the rear drive motor 14 and are drivingly connected to the tape conveyor 38 so that the chains 40 and 42 and conveyor 38 are driven by the rear motor 14. With this arrangement, as described and claimed in a copending application filed under even date herewith, entitled Drive Mechanism For An Envelope Machine and assigned to the assignee of the instant application, a pair of wound rotor motors 12 and 14 drive the various components of the envelope machine in timed relation to feed the envelope blanks to the envelope machine components in desired timed relation so that the envelope blanks are properly spaced and positioned to have the panels or windows cut therein, the glassine patches applied thereto and the seal flap adhesive applied.

The wiring for the various components from the motors and the control devices extends through an elongated wiring trough formed in the base portions of the various segments previously described.

It should be noted that the wound rotor motors l2 and 14 drive the various components of the envelope machine at a preselected speed. The wound rotor motors are controllable by a potentiometer, as later explained, to increase or decrease the speed of the various components of the envelope machine so that the speed of making the envelopes is either increased or decreased and the desired timed relation remains between the various components.

The heat intensity of the quartz drying elements 46 is controlled in accordance to the speed of the motors 12 and 14. A suitable circuit for controlling the heat intensity is illustrated in FIG. 2 where the lines 72, 74 and 76 are connected in the rotor circuit of the wound rotor motors 12 and 14. The voltage of the rotors varies with the speed of the envelope machine 10 and is an indication of how fast the envelope machine is running, When the machine is not running and current is supplied to the wound rotor motors, the rotor voltage is at a maximum. When the machine is running at maximum speed, the rotor voltage is at a minimum.

The lines 72, 74 and 76 are connected to lines 78, 80 and 82 of the heat intensity control circuit between diodes 84 and 86. The heat intensity control circuit has a separate source of DC current connected to lines 88 and 90 in which resistor 92 of potentiometer 94 and resistor 96 are connected in series.

The wiper arm 98 of potentiometer 94 is connected through line 102 to lines 78, 80 and 82. A resistor 100 is positioned between the lines 78, 80 and 82 and potentiometer wiper arm 98. The line 102 and another line 104 are connected to a speed control circuit for the wound rotor motors 12 and 14. The speed control circuit is described and claimed in a copending application, filed under even date herewith entitled Drive Mechanism For An Envelope Machine" assigned to the assignee of the herein described invention. With this arrangement, the potentiometer 94 controls the speed of motors 12 and 14 and the speed can be increased or decreased by movement of the wiper arm 98 along the potentiometer resistor 92. A voltage in proportion to motor speed is fed back from the rotors through lines 78, and 82 to the heater control circuit.

A second potentiometer 106 has its resistor 108 connected at one end by lead 110 to line 88 and the other end connected by lead 112 to line 102 on the other side of resistor 100 opposite the wiper arm 98 of potentiometer 94. With this arrangement the voltage across the resistor 108 of potentiometer 106 is proportionatal to the rotor voltage and the voltage across resistor 108 will vary with the speed of the motors 12 and 14. The wiper arm 114 of potentiometer 106 is connected through a resistor 116 to the input coil 118 of a switching reactor or magnetic amplifier 120. The output coils 122 and 124 of magnetic amplifier are connected at one end to line 148 of the drier circuit power supply and at the other end through line 126 with diodes 128 and 130 on opposite sides thereof to the input coil 132 of pulse transformer 134. The pulse transformer 134 has a pair of output coils 136 and 138.

The drier 46 includes a plurality of resistors 140 connected in parallel across the lines 142 and 144. A separate alternating current power supply is provided for the resistors 140 in the drier 46 through lines 146 and 148. The line 142 is connected to line 148 and provides a current path to one side of the heating resistors 140. The other line 146 is connected to a pair of silicon controlled rectifiers generally designated by the numeral 150 at terminal 152. The line 146 connects one of the pulse transformer output coils 138 in series with the diode 154 and a gate 156. The gate 156 controls the firing angle of the silicon controlled rectifier 158. The other terminal 160 of the pair 150 is connected to line 144 and a line 162 is connected at one end to the terminal 160 and has an output coil 136 of the pulse transformer 134 connected in series with a diode 164 and a gate 166. The gate 166 controls the firing angle of silicon controlled rectifier 168. A pair of heat sinks 170 and 172 are connected to the respective silicon controlled rectifiers 158 and 168. With this arrangement the line 146 provides a current path through the pair of silicon controlled rectifiers 150 to the line 144 connected to resistors 140.

With the above described heater control circuit, the amount of current flowing through the resistors 140 in drier 46 is controlled by the silicon controlled rectifiers 158 and 168. The firing angle of the silicon controlled rectifiers 158 and 168 is controlled by the gates 156 and 166 which receive pulses from the output coils 136 and 138 of pulse transformer 134. The input coil 132 of pulse transformer 134 is in turn connected to the output coils 120 and 124 of magnetic amplifier 120 so that the pulses transmitted by the pulse transformer 134 are dependent on the output of the magnetic amplifier 120.

The magnetic amplifier 120 is connected to the heater circuit power supply through line 148 and is arranged to be in a full on condition so that without a negative control being applied to the magnetic amplifier 120 the magnetic amplifier provides a signal current for the pulse transformer 134. The pulse transformer in turn transmits pulse signals to the gates of the silicon controlled rectifiers to maintain the gates closed so that a maximum amount of current flows through the silicon controlled rectifiers to the resistors 140 in the drier 46 and provides maximum heat intensity.

The potentiometer 106 has the wiper arm 114 connected to the input coil 118 of magnetic amplifier 120. The relative position of the wiper arm 114 on the resistor 108 provides a preselected voltage across the coil 118 and thus a negative control to limit the amount of current flowing through the silicon controlled rectifiers into the resistors 140. This provides an independent control for the maximum heat intensity of the driers at maximum machine speed where the voltage across the rotors of the wound rotor motors 12 and 14 is at a minimum.

When, by means of wiper arm 98 of potentiometer 94 the speed of motors 12 and 14 is reduced, the rotor voltage increases proportionately and the rotor voltage is fed back through lines 72, 74 and 76 to the heat intensity control circuit and combines with the voltage of the heat intensity control circuit to increase the voltage across the coil 118 of magnetic amplifier 120. The increase in voltage across coil 118 increases the negative control on the circuit and reduces the output signal from magnetic amplifier 120 to the pulse transformer 134. The pulse transformer 134, in turn, changes the pulse signal transmitted by the output coils 136 and 138 and opens the gates 156 and 166 to reduce the amount of current flowing through the silicon controlled rectifiers 158 and 168 to thereby reduce the heat in the drier 46.

As the speed of the motors is further reduced, the rotor voltage increases and combines with the voltage in the heat intensity control circuit to further increase the voltage across coil 118 and increase the negative control on the magnetic amplifier 120 to an extent that as the speed of both the motors and the machine approach a stopped condition, the control circuit fully opens the gates of the silicon controlled rectifiers and prevents current from flowing therethrough to the resistors 140. The resistors 140 without current flowing therethrough are not, therefore, generating heat and the drier is in the off condition. It will be noted with the above described control system that regulation of the drier heat intensity is dependent on the speed of the wound rotor motors 12 and 14 and as the motors slow down, the rotor voltage increases to increase the negative control on the control circuit so that the control circuit reduces the current flow through the SCRs 158 and 168 to the resistors 140.

Although the above method and apparatus for controlling the heat intensity of the drier 46 was described in conjunction with an electrical control means, it should be understood that the heat intensity of the drier relative to the machine speed can be controlled by other devices, as for example, a tachometer on one of the drive shafts could be employed to regulate the firing angles of the silicon controlled rectifiers and accomplish substantially the same increase or decrease in the heat intensity of the drier relative to the speed of the envelope machine and particularly to the speed of the envelope blanks as they are conveyed through the drier. Although the heat intensity was described in conjunction with motors 12 and 14, it should be understood that the speed of one motor, preferably a rear drive motor 14, could be employed to provide the speed control for the drier heat intensity and any suitable control device may be used in the circuit to control the flow of current through the drier circuit to the resistors in the heater elements.

According to the provisions of the patent statutes, the principle, preferred construction and mode of operation of the invention have been explained, and what is considered to represent its best embodiment has been illustrated and described. However, it should be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. Apparatus for controlling the heat intensity of a drier in an envelope machine comprising,

a drier having heater elements including resistors arranged to dry the adhesive on envelope blanks while said envelope blanks are being conveyed in an envelope machine,

conveyor means to convey said envelope blanks while said envelope blanks are subjected to heat from said heater elements,

drive means for said conveyor means, said drive means including a wound rotor motor, and

heat intensity control means associated with said heater elements for changing the heat intensity of said heater elements, said heat intensity control means being responsive to a signal generated by said wound rotor motor. 2. Apparatus for controlling the heat intensity of a drier in an envelope machine as set forth in claim 1 in which, 5 said heat intensity control means including solid state rectifiers for controlling the flow of current in a drier circuit to said resistors.

3. Apparatus for controlling the heat intensity of a drier in an envelope machine as set forth in claim 1 which includes,

a heat intensity control circuit arranged to transmit a signal to said heat intensity control means, said signal being responsive to the speed of said conveyor means.

4. Apparatus for controlling the heat intensity of a drier in an envelope machine as set forth in claim 2 which includes,

a heat intensity control circuit connected to the rotor of said wound rotor motor, the voltage of said control circuit operable to vary with the speed of said wound rotor motor and transmit a signal to said solid state rectifiers responsive to the speed of said conveyor means.

5. Apparatus for controlling the heat intensity of a drier in an envelope machine as set forth in claim 4 in which,

said heat intensity control circuit includes a magnetic amplifier and a pulse transformer, said pulse transformer arranged to transmit pulses to the gates of said solid state rectifiers in response to the speed of said wound rotor motor.

6. Apparatus for controlling the heat intensity of a drier in an envelope machine as set forth in claim 5 in which,

said magnetic amplifier includes an input coil connected in said heat intensity control circuit, the voltage across said input coil arranged to vary with the speed of said wound rotor motor through said rotor voltage feedback into said heat intensity circuit.

7. Apparatus for controlling the heat intensity of a drier in an envelope machine as set forth in claim 6 in which,

said heat intensity circuit includes a source of control current and a potentiometer,

said potentiometer operable to provide a fixed voltage across said magnetic amplifier input coil independent of the speed of said wound rotor motor to provide a signal to said solid state rectifiers dependent on the position of the wiper arm on the resistor of said potentiometer.

8. A method for controlling the heat intensity of a drier in an envelope machine comprising,

propelling a conveyor in a drier with a wound rotor motor,

connecting a current flow control means in a drier circuit having the heater resistors of the drier, and

applying a negative control to the drier circuit responsive to a signal generated by said wound rotor motor, said signal arranged to change the amount of current flowing through said heater resistors in response to a change in the speed of said conveyor.

9. A method for controlling the heat intensity of a drier in an envelope machine as set forth in claim 8 which includes,

connecting solid state rectifiers in series with said heater resistors in said drier circuit,

transmitting a signal through a heat intensity control circuit to said solid state rectifiers in response to the speed of said conveyor to thereby control the flow of current through said drier circuit in proportion to the speed of said conveyor.

10. A method for controlling the heat intensity of a drier in an envelope machine as set forth in claim 9 which includes,

combining the rotor voltage of said wound rotor motor with 5 the voltage of said heat intensity circuit to provide a combined voltage signal to said solid state rectifiers, the amount of said voltage in said heat intensity circuit being dependent on the speed of said wound rotor motor.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2807096 *Aug 16, 1954Sep 24, 1957Aetna Standard Eng CoApparatus for heating and stretching fabrics
US3078587 *Jan 29, 1959Feb 26, 1963Huck William FCoordinated heater and speed control for web drying machines
US3370360 *Nov 18, 1966Feb 27, 1968Thomas R. SmithApparatus for analyzing moisture content
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4773167 *May 19, 1986Sep 27, 1988Amjo Infra Red Dryers, Inc.Heater
WO1996039604A1 *Jun 5, 1996Dec 12, 1996Sharon F BakalarMethod and apparatus for heat treating webs
Classifications
U.S. Classification34/266
International ClassificationB31B19/00
Cooperative ClassificationB31B19/62, B31B2221/10, B31B2219/6015, B31B19/74, B31B2219/95, B31B21/00
European ClassificationB31B21/00, B31B19/62, B31B19/74