JPS6315905B2 - - Google Patents

Abstract

Tube elements, i.e. pipes, shaped pieces and armatures of weldable synthetic material, are interconnected by electric welding. The welding operation is made possible by means of a welding sleeve (3) which is connected to the output (4) of the apparatus. A monitoring device (11) allows the engagement of a stage (7) of the welding circuit. The heating power is determined by a quadratic mean of the welding voltage of the network voltage respectively, in a pulse generator (9) which generates a pulse frequency depending upon this value. The generator pulses are added in a counter (10) and when the counted value corresponds to the heating energy, the stage (7) of the circuit is disengaged. If this value is not reached, a monitoring device (5) produces a failure signal.

Description

Claim 1: A method for welding adjacent ends of pipe elements made of weldable plastic material by electrical resistance heating, comprising supplying a welding voltage to a resistance heating wire of a welding sleeve and generating a multiple product of said welding voltage. , converting the multiple product into a corresponding pulse frequency, counting pulses of the pulse frequency, and stopping the supply of welding voltage to the resistance heating wire when a predetermined pulse count is reached. How to weld adjacent ends of.

2. The welding method according to claim 1, wherein an alarm signal is generated if the predetermined pulse count has not been reached before the supply of welding voltage to the resistance heating wire is cut off.

3. The pulse frequency is formed by charging a capacitor via a resistor and discharging the capacitor via a switch stage when a charging voltage corresponding to a predetermined partial value of the welding voltage is reached. The welding method described in item 2 of the scope.

4. The pulse frequency is formed by charging a capacitor via a resistor and discharging the capacitor via a switch stage when a charging voltage corresponding to a predetermined partial value of the welding voltage is reached. The welding method described in item 1.

5. The welding method according to claim 1, wherein the multiple product is a square law product of the welding voltage.

6. A device for controlling a welding cycle for welding adjacent ends of pipe elements made of weldable plastic material by electrical resistance heating, comprising means for coupling the resistance heating wire of the welding sleeve to a power source via switching means; and said power source. multiplying means for forming a multiple product of voltages from; converter means for converting said multiple product into a corresponding pulse frequency; means for counting pulses of said pulse frequency; means for opening said switching means to cut off the supply of voltage to said resistance heating wire when a pulse count is reached.

7. The welding cycle control device of claim 6, further comprising means for monitoring the voltage supply to the resistance heating wire and detecting a break in the voltage supply.

8. The welding cycle according to claim 6, further comprising means for activating an alarm signal if a predetermined pulse count has not been reached before the supply of voltage to the resistance heating wire is interrupted. control device.

9. A welding cycle control device according to claim 6, wherein the multiplication means forms a square law product of the supply voltages.

10 said converter means comprising a capacitor charged via a resistor and means for discharging said capacitor via a switch stage when a charging voltage corresponding to a predetermined partial value of the supply voltage is reached; A welding cycle control device according to claim 6.

11. The welding cycle control device according to claim 6, comprising a welding sleeve made of thermoplastic material in which an electrical resistance heating wire is embedded.

Description The present invention relates to a method for welding and connecting conduit elements made of weldable synthetic material at their ends by electrical resistance heating, and to an apparatus for carrying out the method.

In constructing conduits from weldable synthetic materials, methods and devices for interconnecting conduit elements by electrical resistance heating play an important role. The term "conduit element" is here understood to mean tubular materials and parts that are connected to each other in combination to form complete conduits and conduit systems. Carrying out such a connection of conduit elements is not only a very laborious operation, but also has an effect on the quality of the conduit and must therefore be carried out reliably. When connecting pipe elements,
Either sleeve connections forming part of the conduit elements or welded sleeves separate from the conduit elements are used which are inserted into and connected to the ends of the two conduit elements. A winding consisting of a resistively heated wire is inserted into the overlap region forming such a connection, and this winding is electrically heated to form the connection, thereby causing an overlap of the conduit elements around the winding. The material of the mating ends melts, so that welding of the winding element parts is achieved. The thermal energy applied by the winding should in this case be selected as follows.
That is, in order to avoid underheating or overheating of the connected parts, it is recommended to use devices for manual or automatic setting of the thermal energy so as to adjust the thermal energy depending on the connected conduit elements. connection must be achieved.

When welding such connections using equipment as described above, it may not be possible to weld a given connection satisfactorily, especially in view of the fact that the welding has to be carried out on site. Occurs often. The cause is often that the welding energy supplied to the connection is excessive in view of the configuration of the connection and the environmental conditions during welding, such as environmental or conditional factors such as ambient temperature or breakage in the bayonet connection, etc. There are small things to do. Therefore,
In most cases, the connections made are mechanically strong enough to withstand stress, but the result is an incomplete seal.

The object of the invention is therefore to improve the method mentioned at the outset by taking into account, at least approximately, as many influencing factors as possible. According to the invention, this problem is solved by forming the square value of the welding voltage from the measurement of the welding voltage, converting this into a pulse frequency corresponding to the square value, and counting the pulses by a counter to a threshold value. This is achieved by interrupting the welding process after the number of pulses has been achieved. In this way, the supplied welding energy is kept very precisely in accordance with the setpoint welding energy value, and furthermore certain environmental influencing factors are taken into account, for example the external temperature, the temperature of the sleeve, etc.

In connection with the carrying out of the welding, an apparatus suitable for carrying out the method of the invention is used, which comprises a current circuit with a switch stage which can be opened depending on the set supply of welding energy, the switch stage being provided with an interruption of the current path. Greater safety is achieved by providing a means for opening the switch stage when an event occurs.

The invention will now be described in connection with one embodiment shown in the accompanying drawings. The drawing shows a block diagram of a welding device according to the invention used for connecting conduit elements made of weldable synthetic materials.

The device shown in the drawings is used in particular for forming connections using welding joint sleeves, but does not impose any restrictions in principle with respect to the use of other types of welding, such as sleeve welding, etc. It's not something you do.

The power supply for the device shown in the drawing takes place from the line connection end 1. The current path passes through switch stage 7. A welding sleeve 3 is connected to the output end of this switch stage via a plug contact 4, which is shown schematically. Further, a current monitor circuit 6 is provided at the output end of the switch stage 7. This monitor circuit serves to monitor the current flowing and to keep the switch stage with the relay in operation.

A power supply device 2 is connected to the current circuit, and this power supply device 2 generates a low voltage such as 12 volts, which serves as the power supply voltage of the device. The output voltage of the power supply 2 is measured by a measuring converter 8 and converted into a voltage square value U ² . The output of the measuring transducer 8 is connected to the input of a pulse generator 9, which generates a pulse frequency corresponding to the square value of the voltage. This squared value is determined from the charging curve of a capacitor that is charged with a voltage that is applied directly or indirectly to the welding sleeve via a resistor. If this capacitor is connected to a DC power supply, the capacitor voltage can only rise to the power supply voltage level at most.
Its time constant T, i.e. the maximum possible capacitor voltage
The time to reach 63% can be found from the formula T=C・R,
Here C is the capacitance of the capacitor and R is its ohmic resistance. As is well known, the capacitor voltage rises not in a non-linear manner but according to the formula U _c =U(1-e ^-t/T ), where U _c is the capacitor voltage, U is the charging voltage and t is the charging time. When a predetermined charging voltage is reached, the capacitor is discharged by a switch stage, which may have a comparator, for example, and a new charging process begins, which is controlled in this way by the charging voltage or the supply voltage. frequency can be obtained.

Approximate generation of a square function of current-voltage in the range 180-260V, for example, can be achieved by setting the discharge switching point to a value of 0.39 of a supply voltage of 220V, for example. Overcompensation is performed for the squared power supply voltage whose voltage deviates from this value. This overcompensation is necessary at low supply voltages to compensate for the large heat dissipation that occurs in composite materials due to long welding times. The welding time is therefore not only determined correspondingly to a lower supply voltage, but is also extended beyond the time corresponding to this supply voltage. In this way, even if the welding time increases by 1.5 times at a voltage of 180V, for example, uniform welding quality can be achieved. In a similar manner, overcompensation can also be achieved for voltages exceeding a predetermined set value of the charging voltage or supply voltage by selecting the partial voltage value of the charging voltage or supply voltage accordingly.

The output of the pulse generator is applied to a counter 10;
This counter 10 performs counting and addition of pulses. The capacity of the counter 10 is, for example, 2 ⁸ to 2 ²⁴
It can be pulsed. The number of pulses accumulated by the counter 10, corresponding to the dependence of the pulse frequency of the pulse generator 9 on the voltage squared value, represents the predetermined heating energy.

When welding the welding sleeve 3, it is essential that a number of pulses corresponding to the welding energy is achieved in the counter 10. This function is performed by the function monitoring circuit 5. If the counter 10 does not reach a predetermined count value, for example when the current circuit between the welding device and the welding sleeve is interrupted, the function monitoring circuit 5 sends a fault signal, e.g. a red warning lamp. Generates a flashing signal. When this fault signal is generated, it indicates that the welding of the sleeve 3 being performed requires inspection.
Immediately upon the indication of the fault signal, the supply voltage is cut off from the welding sleeve 3 by means of the switch stage 7.
Closing of the current circuit by closing the switch stage 7 is controlled by a closing monitoring circuit 11. The input monitoring circuit 11 uses a low voltage to check whether the welding sleeve 3 or the equivalent resistor is connected to the current circuit output terminal 4. The switching monitoring circuit is expediently designed in such a way that it only allows switching on of the current path when the consumption resistance is less than a certain value, for example 3KΩ.

With the device described above, maximum driving safety is ensured. The output of the current path of the device is blocked until a consumer resistor with a resistance value lower than the limit value is connected. When such a consumption resistor is connected, the closing monitoring circuit 11 does not prevent the closing of the switch stage 7, and the switch stage 7 can be closed by a button or a key (not shown).

Also, environmental influencing factors are at least partially eliminated. Since the heating energy is obtained from the voltage according to the formula U ² t/R, if the ambient temperature is low and the electrical resistance heating wire used is a cold conductor, the welding power is It grows accordingly. Similarly, the shape factor that takes into account the shape of the welding sleeve is also taken into consideration based on the dependence of the voltage or square value on the pulse frequency. By choosing a large counter capacity, for example 70-80
It is possible to keep the welding time very precisely, which can be in the order of seconds, and also to detect durations of at least 20 minutes with sufficient reliability.

Importantly, the above-described configuration of the device makes the construction of the device very simple and at the same time reduces the weight of the device by about 80% or more compared to known welding devices.