CH633746A5 - METHOD AND DEVICE FOR CONNECTING PIPELINE ELEMENTS FROM WELDABLE PLASTIC. - Google Patents

Description

The invention relates to a method for connecting pipe elements made of weldable plastic by welding their ends by means of electrical resistance heating, and a device for carrying out the method.

When constructing pipes made of weldable plastic, the processes and devices with which the pipe 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. To connect the pipe elements, either socket connections, which form part of the pipe element, or welding sleeves separated from the pipe elements, which are plugged onto the ends of two pipe elements and connected to them, are used. In the overlap area of these connections, a winding made of a resistance heating wire is inserted, which is electrically heated to produce the connection, 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, i.e. neither an insufficient 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 on which the heating energy is set manually or automatically.

When welding the connections mentioned with such a device, especially in view of the fact that the connections have to be made at a construction site, it cannot be avoided that occasionally connections are not welded properly. Most of the time, the welding energy supplied for the connection is related to the type of connection and the environmental factors present during i5 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. For example, OE patent 318 988 has disclosed an electrically controlled welding device for connecting plastic pipes or molded parts, with which the final temperature of the welding point is kept within narrow limits in order to achieve a good weld connection. In this case, a special temperature sensor for the welding fitting is unnecessary for the direct influence of heating output or welding time control circuits by the ambient temperature.

This is achieved by a circuit determining the size of the constant heating current for power control and / or welding time with at least one thermally sensitive component which is in contact with the outside air and influences the circuit. This thermal component is mounted in or on the housing of the welding device in a heat-insulated manner; it is an existing circuit component and not a special temperature sensor arranged in the fitting.

A device that would be able to detect and indicate defective welding, even if it is caused by complex influencing factors, would bring a significant improvement in the welding technology of plastic pipes.

The invention is therefore based on the object of designing a device of the type described at the outset in such a way that the greatest possible number of influencing factors is taken into account at least approximately. The object is achieved by the invention specified in the characterizing part of independent claims 1 and 4.

The invention is illustrated and described in an exemplary embodiment with the aid of the figures listed below.

1 shows a schematic representation of a device for connecting pipe elements made of 55 weldable plastic, which is shown as a block diagram and

FIG. 2 shows a more general representation of the range of action of the circuit according to FIG. 1.

The device shown in the drawing is intended for the manufacture of connections, especially with welded sockets, but there is basically no restriction with regard to its use for other types of welded connections, e.g. Socket connections or the like.

The device 65 shown in FIG. 1 is supplied with power via a mains connection 1. The circuit is routed via a switching stage 7. At the output of the switching stage, a welding sleeve 3 is connected via a schematically illustrated plug contact 4. At the output of the switching stage

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7, a current monitor 6 is arranged. 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 unit 2 is measured in a voltage quadrature circuit 8 and converted into a quadratic replica of the mains voltage U2. The output of the voltage squaring circuit 8 is connected to the input of a voltage-dependent pulse generator 9, which generates a pulse frequency corresponding to the square of the voltage. This quadratic value is formed, for example, from the charge curve of a capacitor which is fed directly or indirectly from the voltage at the welding sleeve 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. Its time constant T, i.e. the time in which 63% of the maximum possible capacitor voltage is reached is determined from the equation T = C • R, where C is the capacitance of the capacitor and R is its ohmic resistance. In a known manner, the rise in the capacitor voltage does not take place linearly, but according to the equation Uc = U (l-e ~ t / T), where Uc is the capacitor voltage, U is the charging voltage and t is 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.

The simulation of the quadratic function of the mains voltage in the range of e.g. 180-260 V can be achieved in that the switching point of the discharge z. B. is set 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. A constant weld quality can be achieved, even if a voltage of e.g. 180 V the welding time increases by a factor of 1.5. In the same way, by appropriate selection of 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 connected to a counter 10, in which the summation of the pulses takes place. The capacity of the counter 10 is e.g. 28-224 pulses. Corresponding to the dependency of the pulse frequency of the pulse generator 9 on the square value of the voltage, a number of pulses summed in the counter 10 means a certain heating energy.

In Fig. 2 the part belonging to the effective section is highlighted in a more basic representation for a better overview of the circuit and its mode of operation.

The mains voltage U is squared in the voltage quadrature circuit 8 and this squared voltage value is fed to the input of a voltage-dependent pulse generator 9. At the output of the generator, a frequency f = f (U2), which is dependent on the quadratic value of the mains voltage, appears and is counted by a counter 10 which is subsequently switched on. A counter value is specified on the counter. This count value is counted using a variable count rate that depends on the mains voltage. After the count value has been processed by counting up or counting down, the counter 10 actuates the welding current switching stage 7 and the resistance heating embedded in the plastic is connected to or disconnected from the energy network. A temporary increase in the voltage from the energy network causes an increase in the repetition frequency and the counting takes place more quickly; the welding time of the voltage increase is shortened accordingly. A lowering of the voltage ultimately leads to a corresponding increase in the welding time, and a failure of the voltage interrupts the counting. If the count is not reached, the counter actually reports “energetically imperfect welding”.

It is essential that when the welding sleeve 3 is welded, 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 socket during welding, the function monitor 5 generates an interference signal, e.g. 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. The start-up monitoring 11 uses a low voltage to determine whether a welding socket 3 or an equivalent resistor is connected to the circuit output 4. The switch-on monitoring is expediently designed in such a way that the circuit can only be switched on if the consumer resistance is less than a certain value, e.g. 3 k ohms.

The device described ensures maximum operational reliability. The output for the device's circuit is blocked until a consumer resistor with a resistance value below a limit value is connected. Only then does the switch-on monitoring 11 no longer lock and the switching stage 7 can be switched on by means of a key (not shown).

But environmental influences are also at least partially eliminated. Since the heating energy is determined based on the voltage using the formula U2 • t / R, this means that the welding power is greater at low ambient temperatures, provided, however, that the electrical resistance heating wire used is a PTC thermistor. A form factor that takes the shape of the welding sleeve into account can also be taken into account when the voltage or its quadratic value is dependent on the pulse frequency. Due to the high counter capacity, it is possible to reduce the welding time, which is on the order of e.g. 70-80 sec, can be adhered to very precisely and times of at least 20 min can still be recorded with sufficient certainty.

It is essential that this design of the device makes it very easy to set up and at the same time achieves substantial weight savings compared to the known welding devices, which can be up to 80% and more.

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Claims (6)

633746 PATENT CLAIMS 1. A method for connecting pipe elements made of weldable plastic by welding their ends by electrical resistance heating, characterized in that the square value of the same is formed from the measurement of the mains voltage and converted into a pulse frequency corresponding to this value, the pulses being counted by a counter and after reaching a setpoint pulse number, the welding process is stopped. 2. The method according to claim 1, characterized in that in the event of incomplete empty counting, an interference signal is triggered, in particular after a specific time interval. 3. The method according to claim 1 or 2, characterized in that the quadratic voltage value is formed by charging a capacitor via a resistor and discharging the same via a switching stage after reaching a charging voltage corresponding to a certain partial value of the mains voltage. 4. An apparatus for performing the method according to claim 1, characterized by a control stage controlling a switching stage (7), consisting of a voltage-squaring circuit (8) which processes the electrical voltage used for welding, a voltage-dependent pulse generator (9) and a pulse counter circuit (10 ). 5. Device according to claim 4, characterized in that a from the pulse counter circuit (10) resettable function monitoring (5) is provided, which generates an operating signal at each start of welding and this operating signal is reset by the pulse counter circuit. 6. The device according to claim 5, characterized by a response to the operating signal current monitor (6) for storing the operating state.