CA1125388A

CA1125388A - Process and a device for connecting pipe components made of weldable plastic

Info

Publication number: CA1125388A
Application number: CA326,181A
Authority: CA
Inventors: Werner Sturm
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-04-24
Filing date: 1979-04-24
Publication date: 1982-06-08
Also published as: DE2945196D2; SE7909893L; WO1979000973A1; DE2945196C1; CH633746A5; FR2424118B1; IT7922126A0; GB2038508A; ATA901179A; FR2424118A1; GB2038508B; NL191577C; NL191577B; SE416279B; NL7903071A; AT368264B; JPS55500194A; IT1112733B; JPS6315905B2

Abstract

ABSTRACT OF THE DISCLOSURE

Pipe components, i.e., pipes, fittings and valves, made of weldable plastic, are connected to each other by means of electrically welded joints. The welding process is made possible by the fact that a welding collar is connected to the output of the welding device. A power monitor permits the switching on of a switch stage of the welding current circuit.
Thermal energy is generated by squaring the welding or the line voltage in a pulse generator which produces a pulse frequency that is dependent on this value. The pulses of this pulse fre-quency are summed in a counter. Once a count value that corres-ponds to the thermal energy has been reached, the switch stage is switched off. In the event that the count value is not reached a function monitor generates a warning signal.

Description

3~

The present invention relates to a process ~or connect-ing pipe components made of weldable plastic, by -~elding their ends by means of elec-trical resistance heating, and a device for carrying out the process.
When piping made of weldable plastic is being assembled the process and the device with which the piping components are connected to each other by means of electrical resistance heating play a very considerable role. The expression "piping components"
means pipe, fittings and valves that are combined to form pipe systems and are to be connected to each other. The completion of the connections for these piping components is a costly sub-operation, and in addition determines the quality of the piping and for this reason has -to be very carefully completed.
Either sleeve joints, that constitute a part of the pipe fittings or welding couplings that are separate from the pipe fittings and are installed on the ends of two fittings and connected to them, are used to connect the pipe components. A
coil of resistance heating wire is installed in the overlapping areas of these connectors and this coil is heated electrically ~ ~
to make the connection, so that in the area around the coil the -material of the overlapping ends of the piping components melts, thereby welding these components together. The thermal energy ~ -that is passed through the coil is quantitatively regulated in such a manner that an optimum connection results, i.e., neither insufficient nor excessive heating is applied to the components that are to be connected. A device in which the adjustment of the thermal energy is made either manually or automatically is used for regulating the thermal energy according to the pipe com-ponents that are to be connected.
When welding the aforesaid connections by using such a device it is impossible to avoid the situation that, since the connections are to be completed on a construction site, some of .253~3~

the connections will npt be of sufficient quality. In some cases this IS because the amount oE thermal energy that is applied in making the conne~tion is too small with regaxd to the type of connection and the prevailing environmental ~actors, e,g., the ~mbten-t tempe~ature or a fault~r connection~ ;eO~ example, loss of contact at a plu~ tn connector, in most instances this leads to the condition that although the connection is capable of withstand-ing mechanical loads it is not tight, Thus, the present invention arranges a process of the type described above, in such a manner that the laryest number of influencing factors are taken into consideration, at least approximately.
According to -the invention there is provided in a pro~
cess for joining piping components made of weldable plastic which comprises welding their ends by applying heat from an electrical resistance heater having a welding voltage applied thereto, the improvement in which the welding voltage is monitored, squared and converted to a pulse train having a repetition frequency corresponding to the square of the welding voltage , the pulses are counted by a counter, and the welding process is terminated once a preselected pulse count is reached.
The present invention also provides a control device for use with welding apparatus for joining pipe components made of weldable plastic by welding their ends by applying heat from a resistance heater having a welding voltage applied thereto, said device comprising means for measuring the welding voltage, means for driving the square of said welding voltage, means for producing a train of pulses having a repetition frequency corresponding to said square o~ the welding voltage, a counter for counting said pulses, and means for terminat~n~ the welding when the pulse count in said counte~ reaches a preselected ~alue representative of the total welding energ~

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With the aid of this dev~ce the welding energy that is usedcanbe kept Ve~ close to the'n`omi,n~l value o~ the welding energy and~ in ~dd~t~on, certain environmental factors, e.g., amb-ient temperature and coupllng tenl~e~àture can be taken into consi-deratlon.
~ n additional safety feature with regard to the production of a welded joint is provided by a device that is suitable for the process accordin~ to the invention and has an electrical circuit that has a switch stage that can be switched off after the welding energy has been supplied, in, so far as the switch stage incorporates interrupters if there is a failure of the power circuit.
The present invention will be further illustrated in the accompanying drawing which is a schematic representation of a device for connecting piping components made of weldable plastic . :
in accordance with one embodiment of the present invention and is presented in the form of a block diagram.
In the device illustrated in the drawing, a power is sup-plied through a power connector 1. The power circuit is controlled by means of a switch stage 7 . A welding collar 3 is connected to the output of the switch stage through a schematically represented plug 4. A power monitor 6 is incorporated at the output of the switch stage 7. This device monitors the flow of current and maintains the switch stage, which incorporates, for example, a relay, in the operating position.
A po~er pack 2 is connected to the power circuit, and this power pack provides a low voltage supply, e.g. i2 volts, that powers the device. The power pack 2 also feeds the line voltage U
to a transducer ~ where it is measured and converted to a s~uared product of the supplv ~oltage U2, The output of the transducer 8 is connected to the in~ut of a pulse generator 9, that generates a pulse frequency that correspond$ to the square of the voltage.

- 3 -This squared value is forMed from the charging curve of a con-denser that is supplied directly or indirectly through a resis-tance from the voltage -that is applied to -the welding co]lar.
If this colldenser is connected to a DC source -the condenser voltage can only increase as high as the level of the supply voltage. Its -time constant T, i.e., the time in which 63% of the maximum possible condenser voltage is reached, is determined from the equation T = C . R, wherein C is the capacity of the condenser and ~ is its ohmic resistance. As is known, the con-denser voltage does not increase linearly, but according to the equation UC = U (1 - e-t/T~
wherein Uc is the condenser voltage, U is the charging voltage and t is the charging time. If, when a specific charging voltage is reached, the condenser is discharged by means of a switch stage which incorporates, for example, a comparator, a new charge cycle will begin and will result in a frequency that is controlled by the charge voltage or the supply voltage.
The formation of the square function of the supply voltage in the range, for example, from 180 - 260 V can be achieved by the fact that the switch point of the discharge, e.g., to a value of 0.39 of the supply voltage is set at 220 V.
If the voltage deviates from this value, there will be an over-compensation of the squared supply voltage. At low supply vol-tages, this over-compensation is necessary to counteract the large thermal loss in plastics, that occurs as a result of the lengthy welding time. Thus the welding time is not only increased correspondingly to the low supply voltage, but additionally as well. It is thereby possible to achieve a constant weld quality, even if, for example, at 180 V the welding time increases by a factor of 1.5. In a similar manner, suitable selection of the partial value of the charge voltage or line voltage provides for ~~ 91.2S3~38 r1~
over-compcnsation at vo]tages that are in e~cess of the selccted value o~ the charge or line voltage.
A counter 10 is incorporated at the output of the p-~lse ellerator, and the pulscs are suMmed in this countcr. The ca~a-city of this counter amoullts, for exall~p:le l:o 28 _ 224 plllses.
In accordallce wi.th tlle`dependellcy o~ the pulse ~rc~uency of the ~ulse g~llerat:or 9 on the scluare value oE the voltage, a total nurnber of pulses surnmed in the counter 10 will indica~e a speci-fic thermal energy~ ~
It is important that during welcliny of the welcling collar 3 the number of pulses in the coun~er 10 corresponds to the desil-ed weldiny energy. This is ensured by means of a fun~c-tion monitor 5. In the event that the ~ulse coullter 10 has not yet reachcd itS prese]ected pulse COUllt, e.g., as a result of a break in the power circu;t between the device and t}le ~elding collar during the welcling process, the function moni~or generatcs a warnillg siynal~ e.g., a red ~arnillg liqht will flash. ~s soon as the Warllinc3 sic~nal staL-tS~ this indicates that the co~npleted ~re]ding of the welding collar 3 is to be checked. At tlle same tilne as the t.7arning signal is displayed, -the line voltage to the teldillg col]ar is cut oEf by the s~itch unit 7. Switching on the potver cirucit by switching on the switch stage 7 is controll-ed by a pGWer mon1tor 11. The power~mon;tor 11 uses a low volta~e `
-to detorr,line whe~her a wel(~ g collar 3 or an equivalent resis-tarlce is connected to the po~er Cil-Cuit outpilt 4. It is expeclient that the pcwcr moni~or system l~e rlesi(3ned in such a mal~ner that the pot.er circuit call only be switched on whell the user resis-tance is smal1er than a certain value, e.g., 3 k-ohms.
The device cllsu~es m.lx;mll3ll o~eratillg safety. The out-~0 uut Eor L:he p~wcr circuit of Llle dcvicc rell)c~ s locked until a u:^;er resistallce having a res;sl:allce th-l~ is lower than a thrc~llold lcsistLIllce ;s coJ-Inectcd. It~is only tllcll l.]~.lt thc ~ower mclli lor -- S --~.~

38~3 11 is unlocked and the switch stage can be switched on by means of a push-buttom that is not illustrated.
In addl-tion, environmental Eactors will also be elim-inated, at least in part. Since thermal energy hased on voltage is determined according to the Eormula u2 . t/R, this means that ak low ambient temperatures the welding performance is greater, always assuming that the electrical resistance heating wire is a cold conductor. In like manner a form factor that takes into account the shape of the welding collar can also be considered for the dependency of the voltage or its squared value on the pulse frequency. Because of the high counter capacity it is possible to keep very closely to the welding time, that can be in the order of 70 - 80 seconds, and still stay very closely to times of at least 20 minutes duration.
It is important that because of this layout of the -device, its construction is very simple and at the same time, it ~`
is possible to achieve a weight saving of up to 80~ compared to familiar welding devices.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for joining piping components made of weldable plastic which comprises welding their ends by applying heat from an electrical resistance heater having a welding voltage ap-plied thereto, the improvement in which the welding voltage is monitored, squared and converted to a pulse train having a repeti-tion frequency corresponding to the square of the welding voltage, the pulses are counted by a counter, and the welding process is terminated once a preselected pulse count is reached.

2. A process according to claim 1 in which a warning signal is generated in the event of an incomplete no-load count.

3. A process according to claim 1 or 2, in which the welding voltage is squared by charging a condensor through a resis-tance, and discharging the same through a switch stage once a charge voltage that corresponds to a specific partial value of the welding voltage is reached.

4. A control device for use with welding apparatus for joining pipe components made of weldable plastic by welding their ends by applying heat from a resistance heater having a welding voltage applied thereto, said device comprising means for measuring the welding voltage, means for driving the square of said welding voltage, means for producing a train of pulses having a repetition frequency corresponding to said square of the welding voltage, a counter for counting said pulses, and means for terminating the welding when the pulse count in said counter reaches a preselect-ed value representative of the total welding energy.

5. A device according to claim 1 further including a power circuit having a switch stage capable of being switched off after supplying the prescribed welding energy, the switch stage in-corporating means for interrupting the supply of welding voltage to the resistance heater in the event of failure in the power circuit.

6. A device according to claim 5, in which the means incorporate an indicator.

7. A device according to claim 6, in which the indi-cator is an optical or acoustical (warning) signal.