GB1573954A - Device for metering energy supplied in welding - Google Patents

Description

(54) DEVICE FOR METERING ENERGY SUPPLIED IN WELDING (71) We, ROLLMAPLAST AG., a Swiss Body Corporate of, Gerlafingen, Switzerland, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a device for metering energy supplied in welding.

The joining of parts of pipelines of weldable thermoplastic material by applying current to a metallic resistance located between the parts is known. Various types of device for metering the energy supplied have been developed to match the welding power and the welding time with the particular requirements. The power setting depends on the type and size of the joint to be welded and affects the welding time via the energy requirement, there being a relationship between the welding time and the energy requirement. A constant energy requirement for joints of identical type and identical size can only be assumed, even under thermally identical starting and ambient conditions, if welding is always carried out at an at least approximately equal power. Metering the energy without a simultaneous stabilisation of power thus implies either that an extact control is not provided or that an additional welding parameter, which can be accounted for only with difficulty by a control system, is accepted. It is therefore clearly desirable to maintain preset values of power and time as precisely as possible, but experience shows, that a relatively high technical effort is required in order to be able to ensure accurate control of power. Furthermore, in practice, the narrower the working margin, the greater the chance of inaccuracy and inadequate welding. Expenditure on improved power control is only realistic if there is protection against control faults and. in fact. only the power itself can serve as the fault criterion. A large additional effort, appropriate to the accuracy of power control, is thus necessary.

According to the present invention there is provided a device for metering energy supplied in welding, such device including means to stabilise welding power, and means to compensate for deviation from a set power value by automatically adjusting the welding time.

More particularly the invention provides a device for metering energy supplied in welding including means to stabilise the welding power or the root mean square value J or U of the welding current J or the welding voltage U respectively at least approximately at the set value, and means to compensate for, deviation of the actual value from the set value by automatically adjusting welding time tin such a way that the integral

respectively, gives at least approximately the value determined for the particular welding operation.

Thus, the present invention provides a solution of the problem, which avoids the difficulties described, so that the desired control can be realised in a satisfactory manner without requiring an accuracy higher than that of commercially available component control circuits. The time compensation, which is ensured, for the limited, deviations in power from the set value makes it possible to reduce the demands on the quality of the power control to such an extent as can be justified having regard to the dependence of the set value of the energy on the welding time. Experience shows that this is the case if the welding time does not deviate by more than about 10 to I 5?/, from that set welding time which corresponds to the set value of the welding power. Approximately the same margin can be expected even when metallic resistances located between the parts being jointed in welding thermoplastic tubes are characterised by a pronounced temperature dependence and the power control takes account of only one of the two power components as the control variable. Thus, a current or voltage control which operates to an accuracy of about +6% can be satisfactory. In the present state of electrical control engineering, it is no problem to design the adjustment, which in most cases is necessary anyway, of the welding power, in conjunction with known stabilising measures, in such a way that over a wide range it can be set accurately and is satisfactorily stable. The possibility of utilising the welding time as an indicator for the correct operation of the energy metering device is a further and equally important advantage of the invention. The invention may, to this end, include means to detect the difference between the welding time t and a reference time given by a separate time circuit, said means comprising a third time circuit effective to give a signal when a tolerance limit is exceeded. There must be a fault in the metering of the power or/and in the welding time circuit if the welding time deviates from a given set value by more than a certain extent, and time control faults, apart from gross power control faults, and even those of only linear proportions, can have an adverse effect on the welding process. Furthermore, the welding time factor offers the advantage that it is particularly suitable for making the checking of the device automatic, and it is merely a question of the design of the reference time circuit whether it is possible to detect even the very improbable case of a superposition of power control fault and a fault in the welding time circuit, which has a compensating effect in relation to the indication of an operational fault. An automatic detection of operational faults meets in an ideal manner the demand for increased safety in connection with pipelines for conveying hazardous media.

Amongst the two possibilities already mentioned for restricting the power control to only one of the two power components, the control of the welding current is more advantageous inasmuch as it is not necessary for control purposes to take into account the voltage drop in the connecting line between the control device and the user resistance. Furthermore, the control of the welding current is particularly suitable for unifying the set control values within a particular zone of application by mutually matching the parts which are being joined and belong to the programme. Of course, with energy metering devices of the invention, there is also the possibility, which has been known for a long time and is occasionally used in practice, of automatically matching the welding energy to a temperature characterising the boundary conditions for the welding process-for example the ambient temperature-since an appropriate influence can be exerted in the customary manner with the aid of temperaturedependent control elements on the welding time control and, if necessary, also on the reference time circuit.

Given a relatively good stability of the controller, a welding time control can, for example, be effected if the power component which serves as the control parameter controls a light source which in turn affects a light-sensitive resistance in the charging circuit of a capacitor in such a way that the times until a certain capacitor potential is reached are approximately inversely proportional to the square of the control parameter. A possibility which is largely independent of the quality of the power stabilisation and is therefore, in addition to other reasons, particularly attractive, results from combinations, of multiplying and integrating electronic elements, a discontinuation of welding processes being triggered when a predetermined integration value is reached.

Thanks to mass production, such elements are obtainable at prices which, for the purpose described, are entirely acceptable economically.

In order to explain the invention more clearly, an exemplary embodiment is represented in the accompanying drawing as a block circuit diagram and will now be described.

Current is supplied via a mains lead 1 and a main switch 2 for the control device. A mains part 3 provides the supply to the various control circuits. When the welding current cable 4 is connected to the user resistance 5, a low-voltage control current, for example, can flow via the contact 6, shown in the rest position, of a contactor belonging to the on/off-switching circuit 7.

This control circuit provides the precondition for triggering welding processes, and this is associated with a switch-over of the contact 6 to the welding voltage. Triggering is effected by actuating the switch button 8. During welding, the power controller 9 which may be of the phase angle control type provides, corresponding to the detector 10 of the actual power value and via the power servo component 11, a matching and stabilisation of the welding power which are appropriate to the user resistance. As soon as the time integration of the welding power data fed by the detector 12 of the actual value to the welding time circuit 13 reaches a predetermined set value, the welding time controller 13 effects the discontinuation of the welding operation via the on/offswitching circuit 7. The differential time circuit 14 determines the time interval between the discontinuation of the welding process and a signal given by the reference time circuit 15, and effects the triggering of the fault indicator 16 if a given tolerance limit is exceeded.

The power can be calculated from the actual root mean square of the current or voltage, or obtained directly as a mean square value using a multiplier, preferably with a thermal converter.

WHAT WE CLAIM IS: 1. A device for metering energy supplied in welding, such device including means to stabilise welding power and means to compensate for deviation from a set power value by automatically adjusting the welding time.

2. A device for metering energy supplied in welding including means to stabilise the welding power or the root mean square value J or U of the welding current J or the welding voltage U respectively at least approximately at the set value, and means to compensate for deviation of the actual value from the set value by automatically adjusting welding time tin such a way that the integral

the value determined for the particular welding operation.

3. A device according to Claim 1 or 2, wherein the means to control the time of welding operation includes multiplying and integrating electronic elements.

4. A device according to Claim 1, 2 or 3 including means to detect the difference between the welding time t and a reference time given by a separate time circuit, said means comprising a third time circuit effective to give a signal when a tolerance limit is exceeded.

5. A device according to Claim 4 wherein the set welding time corresponding to the set value of the welding power or to the set welding current or set welding voltage is selected as the reference time.

6. A device according to Claim 4 or 5 wherein the reference time circuit is arranged to be dependent on the welding power in the same way as the welding time circuit.

7. An electrical device according to any one of Claims 2 to 6 wherein the actual power value is obtained directly as a mean square value using a multiplier, preferably with a thermal converter.

8. A device for metering energy supplied in welding substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. the welding operation via the on/offswitching circuit 7. The differential time circuit 14 determines the time interval between the discontinuation of the welding process and a signal given by the reference time circuit 15, and effects the triggering of the fault indicator 16 if a given tolerance limit is exceeded. The power can be calculated from the actual root mean square of the current or voltage, or obtained directly as a mean square value using a multiplier, preferably with a thermal converter. WHAT WE CLAIM IS:

1. A device for metering energy supplied in welding, such device including means to stabilise welding power and means to compensate for deviation from a set power value by automatically adjusting the welding time.

2. A device for metering energy supplied in welding including means to stabilise the welding power or the root mean square value J or U of the welding current J or the welding voltage U respectively at least approximately at the set value, and means to compensate for deviation of the actual value from the set value by automatically adjusting welding time tin such a way that the integral

the value determined for the particular welding operation.

3. A device according to Claim 1 or 2, wherein the means to control the time of welding operation includes multiplying and integrating electronic elements.

4. A device according to Claim 1, 2 or 3 including means to detect the difference between the welding time t and a reference time given by a separate time circuit, said means comprising a third time circuit effective to give a signal when a tolerance limit is exceeded.

5. A device according to Claim 4 wherein the set welding time corresponding to the set value of the welding power or to the set welding current or set welding voltage is selected as the reference time.

6. A device according to Claim 4 or 5 wherein the reference time circuit is arranged to be dependent on the welding power in the same way as the welding time circuit.

7. An electrical device according to any one of Claims 2 to 6 wherein the actual power value is obtained directly as a mean square value using a multiplier, preferably with a thermal converter.

8. A device for metering energy supplied in welding substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.