WO1979000973A1 - Process and apparatus for joining tube elements of weldable synthetic material - Google Patents

Process and apparatus for joining tube elements of weldable synthetic material Download PDF

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Publication number
WO1979000973A1
WO1979000973A1 PCT/CH1979/000055 CH7900055W WO7900973A1 WO 1979000973 A1 WO1979000973 A1 WO 1979000973A1 CH 7900055 W CH7900055 W CH 7900055W WO 7900973 A1 WO7900973 A1 WO 7900973A1
Authority
WO
WIPO (PCT)
Prior art keywords
welding
value
voltage
circuit
switching stage
Prior art date
Application number
PCT/CH1979/000055
Other languages
German (de)
English (en)
French (fr)
Inventor
W Sturm
Original Assignee
W Sturm
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by W Sturm filed Critical W Sturm
Publication of WO1979000973A1 publication Critical patent/WO1979000973A1/de

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/50—General aspects of joining tubular articles; General aspects of joining long products, i.e. bars or profiled elements; General aspects of joining single elements to tubular articles, hollow articles or bars; General aspects of joining several hollow-preforms to form hollow or tubular articles
    • B29C66/51—Joining tubular articles, profiled elements or bars; Joining single elements to tubular articles, hollow articles or bars; Joining several hollow-preforms to form hollow or tubular articles
    • B29C66/52—Joining tubular articles, bars or profiled elements
    • B29C66/522—Joining tubular articles
    • B29C66/5221—Joining tubular articles for forming coaxial connections, i.e. the tubular articles to be joined forming a zero angle relative to each other
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/24—Electric supply or control circuits therefor
    • B23K11/25—Monitoring devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
    • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
    • B29C65/34—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated elements which remain in the joint, e.g. "verlorenes Schweisselement"
    • B29C65/3404—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated elements which remain in the joint, e.g. "verlorenes Schweisselement" characterised by the type of heated elements which remain in the joint
    • B29C65/342—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated elements which remain in the joint, e.g. "verlorenes Schweisselement" characterised by the type of heated elements which remain in the joint comprising at least a single wire, e.g. in the form of a winding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
    • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
    • B29C65/34—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated elements which remain in the joint, e.g. "verlorenes Schweisselement"
    • B29C65/3472—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated elements which remain in the joint, e.g. "verlorenes Schweisselement" characterised by the composition of the heated elements which remain in the joint
    • B29C65/3476—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated elements which remain in the joint, e.g. "verlorenes Schweisselement" characterised by the composition of the heated elements which remain in the joint being metallic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/50—General aspects of joining tubular articles; General aspects of joining long products, i.e. bars or profiled elements; General aspects of joining single elements to tubular articles, hollow articles or bars; General aspects of joining several hollow-preforms to form hollow or tubular articles
    • B29C66/51—Joining tubular articles, profiled elements or bars; Joining single elements to tubular articles, hollow articles or bars; Joining several hollow-preforms to form hollow or tubular articles
    • B29C66/52—Joining tubular articles, bars or profiled elements
    • B29C66/522—Joining tubular articles
    • B29C66/5229—Joining tubular articles involving the use of a socket
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/80—General aspects of machine operations or constructions and parts thereof
    • B29C66/87—Auxiliary operations or devices
    • B29C66/874—Safety measures or devices
    • B29C66/8748—Safety measures or devices involving the use of warnings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/90—Measuring or controlling the joining process
    • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
    • B29C66/912—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by measuring the temperature, the heat or the thermal flux
    • B29C66/9131—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by measuring the temperature, the heat or the thermal flux by measuring the heat or the thermal flux, i.e. the heat flux
    • B29C66/91311—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by measuring the temperature, the heat or the thermal flux by measuring the heat or the thermal flux, i.e. the heat flux by measuring the heat generated by Joule heating or induction heating
    • B29C66/91313—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by measuring the temperature, the heat or the thermal flux by measuring the heat or the thermal flux, i.e. the heat flux by measuring the heat generated by Joule heating or induction heating by measuring the voltage, i.e. the electric potential difference or electric tension
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/90—Measuring or controlling the joining process
    • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
    • B29C66/914—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux
    • B29C66/9161—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the heat or the thermal flux, i.e. the heat flux
    • B29C66/91651—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the heat or the thermal flux, i.e. the heat flux by controlling or regulating the heat generated by Joule heating or induction heating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/90—Measuring or controlling the joining process
    • B29C66/96—Measuring or controlling the joining process characterised by the method for implementing the controlling of the joining process
    • B29C66/961—Measuring or controlling the joining process characterised by the method for implementing the controlling of the joining process involving a feedback loop mechanism, e.g. comparison with a desired value
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/90—Measuring or controlling the joining process
    • B29C66/94—Measuring or controlling the joining process by measuring or controlling the time
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C66/00—General aspects of processes or apparatus for joining preformed parts
    • B29C66/90—Measuring or controlling the joining process
    • B29C66/94—Measuring or controlling the joining process by measuring or controlling the time
    • B29C66/949—Measuring or controlling the joining process by measuring or controlling the time characterised by specific time values or ranges

Definitions

  • the invention relates to a method for connecting pipeline elements made of weldable plastic by welding their ends by means of electrical resistance heating and a device for carrying out the method.
  • pipeline elements When constructing pipelines from weldable plastic, the methods and devices with which the pipeline elements are connected to one another by electrical resistance heating play a significant role.
  • the term pipeline elements is understood to mean pipes, fittings of all types and fittings which have to be put together to form entire pipelines and piping systems and connected to one another.
  • the execution of the connections for these pipeline elements represents a complex partial operation, which also determines the quality of the pipeline and must therefore be carried out reliably.
  • sleeve connections which form part of the pipe element, or welding sleeves separated from the pipe elements, which are attached to the ends of two pipe elements, are used.
  • OMPI IPO duck plug and are connected to them.
  • a winding made of a resistance heating wire is inserted, which is used for the production .
  • the connection is heated electrically, so that the material of the overlapping ends of the pipeline elements melts in the vicinity of the winding, thereby welding these parts.
  • the heating energy supplied by the winding should be metered in such a way that a perfect connection, ie neither inadequate nor excessive heating of the parts to be connected for metering the heating energy depending on the pipe elements to be connected, a device is used to adjust the heating ⁇ gie done manually or automatically.
  • connection energy supplied for the connection is related to the type of connection and the environmental factors present during the welding, e.g. the ambient temperature or a poor connection, e.g. an interruption in a connector is too small. This usually means that the connection can withstand the stresses mechanically, but is leaky.
  • the invention is therefore based on the object of designing a method of the type described in the introduction in such a way that the greatest possible number of influencing factors is taken into account at least approximately.
  • This object is achieved according to the invention in that the quadratic value of the the same is formed and converted into a pulse frequency corresponding to this value, the pulses being counted by a counter and the welding process being terminated after a setpoint pulse number has been reached. This ensures that the welding energy supplied corresponds very precisely to the setpoint welding energy and that certain environmental influences, for example the outside temperature, the temperature of the sleeve or the like, are also taken into account.
  • a further security with regard to the execution of a welded connection is achieved by a device suitable for carrying out the method according to the invention with a circuit having a switching stage which can be switched off after metering the welding energy in that the switching stage is assigned means for interrupting it when an interruption in the circuit occurs .
  • the invention is shown in the drawing in an exemplary embodiment and described below.
  • the drawing shows a schematic representation of a device for connecting pipe elements made of weldable plastic, which is shown as a block diagram.
  • the device shown in the drawing is intended for the production of connections, especially with welded sockets, but there is in principle no restriction with regard to its use for other types of welded connections, e.g. Socket connections or the like
  • the device shown in the figure is supplied with power via a mains connection 1.
  • the circuit is routed via a switching stage 7.
  • a welding sleeve 3 over a schematically shown.
  • Plug contact 4 connected.
  • a current monitor 6 is arranged at the output of the switching stage 7. This monitors the flowing current and keeps the switching stage, which has a relay, for example, in the working position.
  • a power supply unit 2 is connected to the circuit, by means of which a low voltage, e.g. 12 volts, is generated, which serves to supply the device.
  • the output voltage of the power supply 2 is measured in a transmitter 8 and
  • the output of the transmitter 8 is connected to the input of a pulse generator 9 which generates a pulse frequency corresponding to the square of the voltage.
  • This quadratic value is formed from the charge curve of a capacitor, which is fed directly or indirectly from the voltage at the welding socket via a resistor. If this capacitor is connected to a DC voltage source, the capacitor voltage can only rise up to the level of the supply voltage.
  • the rise in the capacitor voltage is not linear, as is known, but according to the equation
  • Charging voltage and t mean the charging time. If the capacitor is reached when a predetermined charging voltage is reached, e.g. has a comparator, discharges, a new charging process begins and a frequency is obtained which is controlled by the charging voltage or by the mains voltage.
  • a predetermined charging voltage e.g. has a comparator
  • the quadratic function of the mains voltage in the range of, for example, 180-260 V can be simulated by setting the discharge switching point, for example, to a value of 0.39 of the mains voltage at 220 V. If the voltage deviates from this value, the quadratic mains voltage is overcompensated. This overcompensation is necessary for smaller mains voltages in order to counteract the greater heat flow in the plastic material, which occurs due to the longer welding time. This not only increases the welding time according to the lower mains voltage, but also extends it further. This enables a constant welding quality to be achieved, even if the welding time is around the same at a voltage of 180 V, for example. Factor increases. In the same way, by appropriately selecting the partial value of the charging voltage or mains voltage, overcompensation can be achieved at voltages which are above the specified value of the charging voltage or mains voltage.
  • the output of the pulse generator is applied to a counter 10, in which the summation of the pulses takes place.
  • the capacity of counter 10 is e.g. 2 - 2 pulses.
  • a pulse number added up in the counter 10 means a certain heating energy.
  • the number of pulses corresponding to the welding energy is reached in the counter 10. This is ensured by function monitoring 5. If the counter 10 has not yet reached its predetermined number of pulses, e.g. in the event of an interruption in the circuit between the device and the welding sleeve during welding, the functional
  • OMPI Monitoring 5 an interference signal, eg the flashing of a red indicator lamp. As soon as the interference signal sets in, this indicates that the welding of the sleeve 3 must be checked. Simultaneously with the display of the interference signal, the mains voltage is immediately switched off from the welding sleeve 3 by the switching stage 7. The switching on of the circuit by switching on the switching stage 7 is controlled by a switch-on monitor 11. By means of a low voltage, the switch-on monitoring 11 determines whether a welding sleeve 3 or an equivalent resistor is at the circuit output 4. connected. The switch-on monitoring is expediently designed in such a way that the switching on of the current circuit is only possible if the consumer resistance is less than a certain value, for example 3 K ohms.
  • Consequence that the welding power is higher at low ambient temperatures provided, however, that the used electrical resistance heating wire is a PTC thermistor.
  • a form factor taking into account the shape of the welding sleeve can depend on the tension or its quadratic value of the pulse frequency are taken into account. Due to the high counter capacity, it is possible to adhere very precisely to the welding time, which can be in the order of magnitude of, for example, 70-80 lake, and to reliably record times of at least 20 minutes.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Lining Or Joining Of Plastics Or The Like (AREA)
PCT/CH1979/000055 1978-04-24 1979-04-23 Process and apparatus for joining tube elements of weldable synthetic material WO1979000973A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH440678A CH633746A5 (de) 1978-04-24 1978-04-24 Verfahren und vorrichtung zum verbinden von rohrleitungselementen aus schweissbarem kunststoff.
CH4406/78 1978-04-24

Publications (1)

Publication Number Publication Date
WO1979000973A1 true WO1979000973A1 (en) 1979-11-29

Family

ID=4275536

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CH1979/000055 WO1979000973A1 (en) 1978-04-24 1979-04-23 Process and apparatus for joining tube elements of weldable synthetic material

Country Status (11)

Country Link
JP (1) JPS6315905B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
AT (1) AT368264B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
CA (1) CA1125388A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
CH (1) CH633746A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
DE (2) DE2945196D2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
FR (1) FR2424118A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
GB (1) GB2038508B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
IT (1) IT1112733B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
NL (1) NL191577C (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
SE (1) SE416279B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
WO (1) WO1979000973A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1981001118A1 (en) * 1979-10-29 1981-04-30 A Kullberg A process and a device for hot working
EP0076043A3 (en) * 1981-09-30 1983-06-01 Fusion Plastics Limited Electro-fusion fitting
EP0067621A3 (en) * 1981-06-16 1984-08-01 Brintons Limited Jointing fabrics

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH653611A5 (de) * 1981-12-23 1986-01-15 Fischer Ag Georg Verfahren und geraet zum verschweissen von leitungselementen.
JPS63160818A (ja) * 1986-12-24 1988-07-04 Sekisui Chem Co Ltd 電気溶着装置
CN111959047A (zh) * 2019-05-20 2020-11-20 株式会社可乐丽 原油及天然气输送用复合柔性管的结构及其铺设方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL80153C (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1949-07-16
CH605082A5 (en) * 1976-03-12 1978-09-29 Rollmaplast Ag Plastic tube welding control

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH518790A (de) * 1970-01-22 1972-02-15 Gebert & Cie Verfahren zum Erreichen einer praktisch konstanten Endtemperatur beim Verbinden von Kunststoff-Formteilen mittels elektrisch heizbarer Kunststoff-Fittings und Steuergerät zur Ausführung des Verfahrens

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL80153C (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1949-07-16
CH605082A5 (en) * 1976-03-12 1978-09-29 Rollmaplast Ag Plastic tube welding control

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1981001118A1 (en) * 1979-10-29 1981-04-30 A Kullberg A process and a device for hot working
EP0067621A3 (en) * 1981-06-16 1984-08-01 Brintons Limited Jointing fabrics
EP0076043A3 (en) * 1981-09-30 1983-06-01 Fusion Plastics Limited Electro-fusion fitting

Also Published As

Publication number Publication date
AT368264B (de) 1982-09-27
IT1112733B (it) 1986-01-20
IT7922126A0 (it) 1979-04-24
JPS55500194A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1980-04-03
DE2945196D2 (en) 1980-11-13
SE416279B (sv) 1980-12-15
NL7903071A (nl) 1979-10-26
CH633746A5 (de) 1982-12-31
FR2424118B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1984-06-29
GB2038508B (en) 1982-10-20
CA1125388A (en) 1982-06-08
NL191577C (nl) 1995-10-03
JPS6315905B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1988-04-06
SE7909893L (sv) 1979-11-30
ATA901179A (de) 1982-01-15
GB2038508A (en) 1980-07-23
NL191577B (nl) 1995-06-01
FR2424118A1 (fr) 1979-11-23
DE2945196C1 (de) 1989-08-03

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