CH668741A5 - Precise welding process for plastics - by heating work using resistance element up supplying heat in pulses according to set curve - Google Patents
Precise welding process for plastics - by heating work using resistance element up supplying heat in pulses according to set curve Download PDFInfo
- Publication number
- CH668741A5 CH668741A5 CH3057/85A CH305785A CH668741A5 CH 668741 A5 CH668741 A5 CH 668741A5 CH 3057/85 A CH3057/85 A CH 3057/85A CH 305785 A CH305785 A CH 305785A CH 668741 A5 CH668741 A5 CH 668741A5
- Authority
- CH
- Switzerland
- Prior art keywords
- heating element
- heating
- power
- temperature
- welding
- Prior art date
Links
Classifications
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- 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"
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- 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
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- 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
- B29C66/90—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
- B29C66/9121—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 temperature
- B29C66/91211—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 temperature with special temperature measurement means or methods
- B29C66/91212—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 temperature with special temperature measurement means or methods involving measurement means being part of the welding jaws, e.g. integrated in the welding jaws
- B29C66/91213—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 temperature with special temperature measurement means or methods involving measurement means being part of the welding jaws, e.g. integrated in the welding jaws and measuring the electrical resistance of a resistive element belonging to said welding jaws, said element being, e.g. a thermistor
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- 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
- B29C66/9121—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 temperature
- B29C66/91221—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 temperature of the parts to be joined
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- 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
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- 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
- B29C66/91315—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 current intensity
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- 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
- B29C66/91317—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 electrical resistance
-
- 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
- B29C66/9141—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 temperature
- B29C66/91411—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 temperature of the parts to be joined, e.g. the joining process taking the temperature of the parts to be joined into account
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- 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
- B29C66/9141—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 temperature
- B29C66/91431—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 temperature the temperature being kept constant over time
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- 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
- B29C66/91653—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 by controlling or regulating 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
- B29C66/91655—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 by controlling or regulating the current intensity
-
- 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
- B29C66/919—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux characterised by specific temperature, heat or thermal flux values or ranges
- B29C66/9192—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux characterised by specific temperature, heat or thermal flux values or ranges in explicit relation to another variable, e.g. temperature diagrams
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- 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
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
- G05D23/24—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element having a resistance varying with temperature, e.g. a thermistor
- G05D23/2401—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element having a resistance varying with temperature, e.g. a thermistor using a heating element as a sensing element
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- 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
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- 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
- B29C66/81—General aspects of the pressing elements, i.e. the elements applying pressure on the parts to be joined in the area to be joined, e.g. the welding jaws or clamps
- B29C66/812—General aspects of the pressing elements, i.e. the elements applying pressure on the parts to be joined in the area to be joined, e.g. the welding jaws or clamps characterised by the composition, by the structure, by the intensive physical properties or by the optical properties of the material constituting the pressing elements, e.g. constituting the welding jaws or clamps
- B29C66/8126—General aspects of the pressing elements, i.e. the elements applying pressure on the parts to be joined in the area to be joined, e.g. the welding jaws or clamps characterised by the composition, by the structure, by the intensive physical properties or by the optical properties of the material constituting the pressing elements, e.g. constituting the welding jaws or clamps characterised by the intensive physical properties or by the optical properties of the material constituting the pressing elements, e.g. constituting the welding jaws or clamps
- B29C66/81262—Electrical and dielectric properties, e.g. electrical conductivity
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- 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
- B29C66/9121—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 temperature
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- 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
- B29C66/919—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux characterised by specific temperature, heat or thermal flux values or ranges
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- 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
- B29C66/919—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux characterised by specific temperature, heat or thermal flux values or ranges
- B29C66/9192—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux characterised by specific temperature, heat or thermal flux values or ranges in explicit relation to another variable, e.g. temperature diagrams
- B29C66/91921—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux characterised by specific temperature, heat or thermal flux values or ranges in explicit relation to another variable, e.g. temperature diagrams in explicit relation to another temperature, e.g. to the softening temperature or softening point, to the thermal degradation temperature or to the ambient temperature
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- 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
- B29C66/944—Measuring or controlling the joining process by measuring or controlling the time by controlling or regulating the time
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- 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
- B29C66/95—Measuring or controlling the joining process by measuring or controlling specific variables not covered by groups B29C66/91 - B29C66/94
- B29C66/959—Measuring or controlling the joining process by measuring or controlling specific variables not covered by groups B29C66/91 - B29C66/94 characterised by specific values or ranges of said specific variables
- B29C66/9592—Measuring or controlling the joining process by measuring or controlling specific variables not covered by groups B29C66/91 - B29C66/94 characterised by specific values or ranges of said specific variables in explicit relation to another variable, e.g. X-Y diagrams
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- 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
- B29C66/967—Measuring or controlling the joining process characterised by the method for implementing the controlling of the joining process involving special data inputs or special data outputs, e.g. for monitoring purposes
- B29C66/9672—Measuring or controlling the joining process characterised by the method for implementing the controlling of the joining process involving special data inputs or special data outputs, e.g. for monitoring purposes involving special data inputs, e.g. involving barcodes, RFID tags
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Lining Or Joining Of Plastics Or The Like (AREA)
Abstract
Plastic mouldings are welded together using an electric heat element, whose power supply is controlled according to the temp. measurements on the element. The element is first raised to the desired welding temp.; the power supplied to it is then fed in at intervals in which the times of power supply are shortened in accordance with definite curves until the power reaches or approaches a limit, and the power is then cut off. ADVANTAGE - Produces excellent welds for a wide variety of applications even under extreme conditions. It provides guaranteed welds that do not need testing.
Description
BESCHREIBUNG
Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Verschweissung von Kunststoff-Formteilen, gemäss dem Oberbegriff des Patentanspruchs 1, sowie eine Vorrichtung zur Durchführung des Verfahrens.
Eine bevorzugte Verwendung findet das beschriebene Verfahren bzw. die Vorrichtung bei der Erstellung von Rohrleitungen aus schweissbarem Kunststoff. Dabei werden Rohrleitungselemente oder ähnliche Kunststoffteile unter Einsatz eines elektrisch beheizten Widerstandsschweissgerätes miteinander verbunden. Zum Verbinden von Rohrteilen werden sogenannte Rohrmuffen verwendet, in welche die zu verbindenden Rohrteile eingesetzt werden, so dass die Enden aneinanderstossen oder einander überlappen. Die Rohrmuffen enthalten im Verbindungsbereich ein elektrisch betriebenes Heizelement, welches mit einem Steuergerät in Verbindung steht. Unter dem Einfluss des Heizelementes wird der Kunststoff im Übergangsbereich der zu verbindenden Teile zum Schmelzen gebracht und - dadurch die Verschweissung dieser Teile erreicht.
Bei diesem Verfahren ist der Dosierung der Heizenergie eine besondere Beachtung zu schenken, insbesondere im Hinblick auf die relativ kritische Temperatur, welche Voraussetzung für eine optimale Schweissverbindung ist. Wird die Temperatur nicht vollständig oder nicht gleichmässig erreicht, ist die Verschweissung nur unvollkommen, was insbesondere bei eingelassenen Rohrsystemen im Bauwesen zu schwerwiegenden Folgen führen kann. Ähnlich folgenschwer kann sich eine Überhitzung der Schweissbereiche auswirken, wobei Kunststoff aus dem Schweissbereich auslaufen oder sich gar chemisch zersetzen kann, so dass Löcher an denjenigen Stellen entstehen, die eigentlich hätten dicht verbunden werden sollen.
Es wurden bereits verschiedene Vorschläge gemacht, welche die selbsttätige Einhaltung einer bestimmten Temperatur an der Schweissstelle oder einer bestimmten Heizenergie für das Heizelement sicherstellen sollen. Beispielsweise ist aus der CH-PS 602 310 eine Vorrichtung zum Regeln der Temperatur von dauerbeheizten Bändern zum Schweissen von Kunststoffolien oder ähnlichem bekannt, bei welchem Spannungs- und Stromwerte des Schweissbandes einem Quotientenbildner eingegeben werden. Der so gebildete Quotient wird als Ist-Wert einem Regler zugeführt, der die Leistung des Heizstromkreises entsprechend der Abweichung des Ist-Wertes von einem vorgegebenen Soll-Wert anpasst.
Dabei wird die bekannte Tatsache benutzt, dass der elektrische Widerstand des verwendeten Heizelementes, welcher dem Quotient aus Spannung und Strom entspricht, temperaturabhängig ist und dementsprechend bei Kenntnis des spezifischen Widerstandes bzw. seiner Temperaturabhängigkeit ein Indikator für die jeweilige Temperatur am Heizelement ist.
Der Quotient wird einem Regler im Heizstromkreis zugeführt, dessen Einfluss die Temperatur am Heizelement konstant halten soll.
Die bisher bekannten Massnahmen zur Regelung der Temperatur am Heizelement sind jedoch insofern ungenügend, als der Temperaturausgleich zwischen dem Heizelement und dem zu verschweissenden Kunststoffmaterial, insbesondere bei relativ schnellem Aufheizen, variiert, wodurch die Temperaturmessung am Heizelement nicht unter allen Umständen ein genaues Bild von der Temperatur an der Schweissstelle liefert. Damit ist gerade bei extremen Bedingungen die Qualität der Verschweissung in Frage gestellt.
Es ist Aufgabe der vorliegenden Erfindung, ein Verfahren und eine Vorrichtung der eingangs genannten Art dahingehend zu verbessern, dass die Qualität der Schweissungen in einem breiteren Anwendungsbereich auch unter extremen Bedingungen merklich verbessert werden kann und damit die Zuverlässigkeit der Schweissungen unter allen praktisch auftretenden Bedingungen gewährleistet ist, so dass zusätzliche Prüfvorgänge, z.B. auf Dichthalten der Verbindung, überflüssig werden.
Diese Aufgabe wird erfindungsgemäss durch die in den Ansprüchen 1 und 5 definierten Merkmale gelöst.
Der Vorteil dieser Massnahmen liegt im wesentlichen in der präziseren Steuerung der dem Heizelement zugeführten Leistung auf grund von Temperaturmessungen am Heizelement, welche ein besseres Abbild der wahren Temperatur-Verhältnisse an der Schweissstelle sind. Eine entscheidende Voraussetzung für das Lösungskonzept ist das Einbeziehen der Wärmeausgleichsvorgänge zwischen dem Heizelement und der Schweissstelle bei der Bestimmung der Steuerungsparameter. Dadurch ergibt sich eine zuverlässigere Steuerung der Heizleistung aufgrund aussagekräftigerer und präziserer Temperaturmessungen, und es ergeben sich besonders einfache schaltungstechnische Lösungen für entsprechende Schweiss-Geräte bzw. deren Steuerungen.
Im folgenden werden Einzelheiten der Erfindung anhand bevorzugter Ausführungsbeispiele mit Hilfe der Zeichnungen näher erläutert.
Es zeigen:
Fig. 1 ein Diagramm zur Erläuterung des Verfahrens,
Fig. 2 ein erstes Ausführungsbeispiel für ein Steuergerät nach der Erfindung, und
Fig. 3 ein zweites Ausführungsbeispiel für ein erfindungsgemässes Steuergerät.
Im folgenden wird zunächst kurz das Prinzip der vorliegenden Erfindung erläutert. Obwohl als bevorzugtes Anwendungsbeispiel gelegentlich auf die Herstellung von Verbindungen mit Schweissmuffen hingewiesen wird, ist die Erfindung nicht auf dieses Gebiet beschränkt. Die beschriebenen Merkmale für das Verfahren sowie für entsprechende Steuerungsgeräte können in allen Bereichen eingesetzt werden, welche das Schweissen von Kunststoffteilen betreffen.
Wie bereits einleitend erwähnt, erfolgt die Wärmezufuhr an die Schweissstelle über ein elektrisch beheiztes Heizelement, welches beispielsweise durch einen Widerstandsheizdraht gebildet ist. Die Wärmeenergie wird der Schweissstelle nach den bekannten Regeln der Wärmeleitung übertragen. Die Bedingungen für die Wärmeleitung hängen im vorliegenden Fall vom zu verschweissenden Material, von der Geometrie des Systems und den Thermopotentialunterschieden zwischen dem Heizelement und der Schweissstelle ab.
Die Energiezufuhr für das Heizelement wird auf bekannte Weise dann unterbrochen, wenn aufgrund ausgewählter Messkriterien festgestellt oder erwartet wird, dass die Schweissstelle die gewünschte Temperatur erreicht hat. Im vorliegenden Fall wird dazu die an sich bekannte Temperaturabhängigkeit des einen ohmschen Widerstand darstellenden Heizdrahtes herangezogen. Dabei werden die Art und der Verlauf der Temperaturabhängigkeit des jeweils verwendeten Widerstandsmaterials als bekannt vorausgesetzt. Besonders einfach sind die Verhältnisse beispielsweise für ein Widerstandselement, dessen spezifischer Widerstand nur in sehr geringem Mass oder nach einfacher Gesetzmässigkeit von der Temperatur und damit von der Belastung abhängt (z.B. Resistherm o. dgl.).
Für solche Materialien kann nach Erreichen einer Anfangstemperatur in dem hier interessierenden Temperaturbereich mit einem praktisch linearen Zusammenhang zwischen Temperatur und ohmschem Widerstand gerechnet werden.
Zu Beginn der Schweissung weist die Schweissstelle eine relativ niedrige Temperatur auf. Im allgemeinen entspricht die Anfangstemperatur der Umgebungstemperatur. Das Heizelement wird am Anfang relativ stark aufgeheizt, so dass sich eine erhebliche Differenz der Wärmeenergie-Potentiale zwischen dem Heizelement und der Schweissstelle ergibt. Dieser anfänglich hohe Temperaturgradient bewirkt einen hohen Energiefluss vom Heizelement in das zu verschweissende Kunststoffmaterial. Wegen der nur mässigen Wärmeleitung des Kunststoffmaterials nimmt der materialinterne Wärmeausgleich, welcher schliesslich zum gleichmässigen Schmelzen des Materials führen soll, eine gewisse Zeit in Anspruch.
In dieser Phase des Aufheizprozesses bestünde ohne Anwendung der erfindungsgemässen Lehre die Gefahr, dass gerade bei anfänglich schneller Aufheizung eine Temperaturmessung am Widerstandselement alles andere als das gewünschte Abbild der Schweissstellen-Temperatur darstellt. Bekannte Regelungen oder Steuerungen, welche eine Stellgrösse oder Führungssignale aus solchen Messungen ableiten, sind besonders in Extremsituationen wegen dieser Erscheinung stark fehleranfällig. Andererseits ist es aus praktischen Erwägungen nicht erwünscht, einen Thermofühler direkt an der Schweissstelle anzubringen.
Die eiündungsgemässe Lehre sieht nun angesichts der zuvor beschriebenen Erkenntnis vor, die Leistungszufuhr an das Heizelement gegen Ende der Aufheizperiode stufenweise zu reduzieren, insbesondere die Aufheizung in zeitlich gestaffelten Intervallen vorzunehmen, wobei die Einschaltintervalle z.B. monoton verkürzt werden, bis sich aufgrund besonderer Messkriterien ergibt, dass sich das Wärmepotiential der Schweissstelle nur noch um einen unwesentlichen Betrag, entsprechend einer vorgegebenen Toleranz, von dem der Heizwicklung zugeführten Wärmepotiential unterscheidet. Ist dieses Kriterium erfüllt, wird die Energiezufuhr an das Heizelement automatisch unterbrochen. Die erwähnten Messkriterien werden aufgrund zuvor ermittelter materialbezogener Parameter, unter Berücksichtigung aktueller Prozess-spezifischer Messwerte, abgeleitet.
Einzelheiten dazu ergeben sich aus der späteren Beschreibung von bevorzugten Gerätebeispielen, welche zur Ausführung des beschriebenen Verfahrens dienen.
Zur erwähnten Temperaturmessung am Heiz- bzw. Widerstandselement sei der Vollständigkeit wegen auf die an sich bekannten physikalischen Tatsachen verwiesen. Die dem Heizelement zugeführte elektrische Leistung
N = U x I (U = Spannung, I = Strom) ergibt über die Zeit t, in welcher diese Leistung erbracht wird, die Arbeit, in diesem Fall die dem Element zugeführte Wärmemenge.
Unter der Annahme, dass die Wärmeverluste beim Übergang vom Heizelement zur Schweissstelle vernachlässigbar gering gehalten werden können, entspricht der Ausdruck A=Uxlxt gleichzeitig der Wärmemenge, welche der Schweissstelle zugeführt wurde. Durch eine Steuerung der elektrischen Leistung wird also wegen der direkten Proportionalität eine Steuerung der zugeführten Wärmemenge erzielt. Die Leistungssteuerung kann beispielsweise durch eine Stromsteuerung bei bekanntem Spannungsverhalten vorgenommen werden.
Das Widerstandselement des Heizkörpers erfüllt neben der reinen Heizwirkung auch die Aufgabe eines Temperaturfühlers. Wegen der obenerwähnten Temperaturabhängigkeit seines ohmschen Widerstandes wird durch eine laufende Messung des aktuellen ohmschen Widerstandes R während der Aufheizperiode der Verlauf der jeweils herrschenden Temperatur am Heizelement erfasst. Im vorliegenden Fall wird aus Gründen erhöhter Empfindlichkeit und Zuverlässigkeit die Widerstandsmessung vorzugsweise nach der Brückenmessmethode vorgenommen.
Im einzelnen wird zunächst eine Widerstandsmessung am kalten Heizelement vorgenommen. Aufgrund dieser Messung wird die für eine einwandfreie Verschweissung benötigte Wärmemenge U x I x t festgelegt. Das erhaltene Messergebnis wird mit einem Faktor korrigiert, welcher der momentanen Umgebungstemperatur entspricht.
Spannungswerte U, Stromwerte I und die Heizzeit t werden festgehalten, z.B. gespeichert oder zum Setzen programmierbarer Schalter benutzt. Im Verlauf der anschliessend beginnenden Aufheizung wird das Heizelement bei Erreichen der vorgegebenen Temperatur mit immer kürzer werdenden Wärmemengen beheizt, wodurch der Wärmeübergang zwischen dem Heizelement und dem zu verschweissenden Material zu einem Angleichen der Temperaturen in beiden Teilen führt. Sobald eine Messeinrichtung diesen Zustand aus entsprechenden Vergleichsmessungen erkennt, wird die Leistungszufuhr vom Heizelement endgültig abgeschaltet.
Die Führung der Leistungssteuerung erfolgt entlang dem linear abfallenden Teil des in Fig. 1 gezeigten Spannungs-/Strom Diagramms. Dies bedeutet, dass die Führung entlang R = const, d.h. also entlang konstanter Temperatur am Heizelement erfolgt. In diesem Diagramm bedeutet Punkt A das Erreichen der vorgegebenen Schweisstemperatur am Heizelement, im Beispiel 250 C. Ab diesem Zeitpunkt wird das Heizelement durch entsprechendes Führen einer Leistungssteuerung konstant auf dieser Temperatur ge halten. Dies geschieht beispielsweise durch eine entsprechend geführte Stromregelung. In Fig. 1 sind zur Verdeutlichung der Vorgänge vertikale Hilfslinien eingezeichnet, welche gleich lange Zeitperioden entlang der Stromachse begrenzen.
Die angeschriebenen Leistungswerte lassen die verminderte Leistungszufuhr während aufeinanderfolgender Perioden erkennen. Durch diese Massnahme stellt sich im Verlauf der Zeit ein Temperaturausgleich zwischen dem Heizelement und der Schweissstelle ein. Erreicht der erwähnte Leistungswert eine vorgegebene untere Schwelle, welche praktisch gleiche Temperaturen am Heizelement und an der Schweissstelle annehmen lässt, wird die Leistungszufuhr an das Heizelement unterbrochen.
In ihrer Kombination ergeben diese Massnahmen eine überraschend zuverlässige Dosierung der für eine einwandfreie Schweissung erforderlichen Wärmemenge.
Stellvertretend für die Vielfalt möglicher Ausführungsformen für Schweiss- bzw. Steuerungsgeräte, welche entsprechend dem beschriebenen Verfahren ausgelegt sind, werden im folgenden zwei besonders bevorzugte Ausführungsformen beschrieben. Das erste Beispiel ist stärker auf die Verwendung diskreter Bauteile ausgerichtet, während das zweite Beispiel eine hochintegrierte Ausführungsform eines Steuergerätes darstellt.
Gemäss Fig. 2 ist für die Schweissung von Rohrteilen eine elektrisch beheizbare Schweissmuffe 1 vorgesehen. Die Muffe wird von einer Stromversorgung 2 über ein Leistungssteuerelement 18 und einen steuerbaren Schalter 3, z.B. ein Relais, versorgt. An die Muffe 1 ist ferner ein Messkreis angeschlossen, der aus einer Widerstandsbrücke 4, einem mit diesem verbundenen oder zusammenwirkenden Umgebungstemperaturfühler 5, einem Startschalter 6 sowie einem Analog/Digital-Wandler 7 mit daran angeschlossener Durchmesser Anzeige 10 besteht.
Nach Anschluss der Muffe 1 an den Schaltkreis wird zunächst ihr Kaltwiderstand gemessen und entsprechend der Umgebungstemperatur gewichtet. Der ermittelte korrigierte Wert wird im A/D Wandler 7 der erforderlichen Wärmemenge zugeordnet. Der Ausgang des A/D-Wandlers ist mit programmierbaren Schaltern 8 und 9 verbunden. Diese Schalter steuern im wesentlichen das Zeitverhalten für die Leistungszufuhr an die Muffe 1 aufgrund der vom A/D Wandler 7 erhaltenen Daten.
In der Versorgungsleitung zwischen der Stromversorgung 2 und der Muffe 1 sind ein Stromsensor 11 und ein Spannungssensor 20 angeordnet. Der Ausgang des Stromsensors 11 ist auf einen ersten Operationsverstärker 12 geführt. An den Spannungssensor 20 ist ein zweiter Operationsverstärker 13 angeschlossen. Die Ausgänge beider Operationsverstärker sind mit einem Widerstand 14 verbunden, dessen Spannungsabfall von ersten und zweiten Komparatoren 15 bzw.
16 erfasst wird. Mit Hilfe des zweiten programmierbaren Schalters 9 lässt sich eine Eichung der Spannung am Widerstand 14 derart durchführen, dass bei Erreichen des gewünschten Warmwiderstandes an der Muffe 1 die Ausgangsspannungen der beiden Operationsverstärker 12 und 13 gleich gross sind.
Bei einer Änderung des Warmwiderstandes an der Muffe 1 tritt am Widerstand 14 ein Spannungsabfall auf, wodurch über die Komparatoren 13 und 16 ein Stromsteuerungselement 17 beeinflusst wird, welches die Nachsteuerung der Leistungssteuerung 18 vornimmt. Dies erfolgt so lange, bis am Ausgang beider Operationsverstärker gleich grosse Ausgangsspannungen auftreten.
Hat sich schliesslich unter dem Einfluss des ersten programmierbaren Schalters 8 der Heizstrom für die Muffe 1 derart verringert, dass er dem programmierten Wert entspricht, wird der steuerbare Schalter 3 geöffnet, worauf die Muffe 1 vom Heizkreis abgeschaltet wird. Als Sicherheitselement ist ein Zeitüberwachungsblock 19 vorgesehen, welcher bei Überschreiten einer vorgegebenen Zeitspanne t max den steuerbaren Schalter auftrennt, falls bis dahin die beschriebene Steuerung die Abschaltung noch nicht ausgelöst haben sollte.
Das Ausführungsbeispiel nach Fig. 3 enthält wiederum eine Stromversorgung 21, welche über einen Spannungs- oder Stromreg ler 24 und einen steuerbaren Schalter 25 eine Muffe 26 speist. Die Ermittlung des Kaltwiderstandes erfolgt in einer Widerstandsmessbrücke 27. In dieser Brücke wird auch der Einfluss der Umgebungstemperatur berücksichtigt. Der ermittelte Wert wird in einem A/D Wandler 28 umgesetzt. Der A/D-Wandler liefert die Speicherwerte U, I, t und t2-tl an einen Speicher 23, wobei der letzte Wert die Impulsbreite der Leistungsimpulse für die Muffe bedeutet.
Sobald die Messwerte U, I und t2-tl ihre gespeicherten Werte erreicht haben, wird der Schalter 25 angesteuert und die Muffe 26 von der Versorgung abgetrennt.
Mit Hilfe der im Speicher 23 gespeicherten Zeit t, welche von einem Zeitüberwachungsblock 22 abgeleitet ist, kann eine Gesamt überwachung des Gerätes erfolgen, falls keine durch die Werte U, I und t2-tl beeinflusste Abschaltung erfolgen sollte.
Unter Verwendung eines kleinen Rechnermoduls werden beispielsweise die erwähnten Funktionen der einzelnen Baugruppen gesteuert. Dabei wird die fortlaufende Bildung von U x I veranlasst und der Quotient (U x I)/(t2-tl) gebildet, wobei t2-tl ein vorgegebenes konstantes Zeitintervall darstellt. Dieser Quotient wird laufend mit einem Schwellenwert verglichen, z.B. mit (Us x Is)/(t2-t1). Sobald der erste, aus dem Messwert gewonnene Quotient kleiner wird als die vorgegebene Schwelle, wird die Heizung der Muffe abgeschaltet.
DESCRIPTION
The invention relates to a method and a device for welding molded plastic parts, according to the preamble of claim 1, and a device for performing the method.
The described method and the device are preferably used for the creation of pipelines from weldable plastic. Pipe elements or similar plastic parts are connected to one another using an electrically heated resistance welding device. So-called pipe sleeves are used to connect pipe parts, into which the pipe parts to be connected are inserted, so that the ends abut or overlap one another. The pipe sockets contain an electrically operated heating element in the connection area, which is connected to a control unit. Under the influence of the heating element, the plastic is melted in the transition area of the parts to be connected and - as a result, the welding of these parts is achieved.
With this method, the metering of the heating energy must be given special attention, especially with regard to the relatively critical temperature, which is a prerequisite for an optimal welded joint. If the temperature is not reached completely or not uniformly, the welding is only imperfect, which can lead to serious consequences, particularly in the case of embedded pipe systems in construction. Overheating of the welding areas can have a similarly serious effect, with plastic leaking out of the welding area or even being able to chemically decompose, so that holes are formed in those places that should actually have been tightly connected.
Various proposals have already been made to ensure that a certain temperature at the welding point or a certain heating energy for the heating element is automatically maintained. For example, from CH-PS 602 310 a device for regulating the temperature of permanently heated strips for welding plastic films or the like is known, in which voltage and current values of the sweatband are input to a quotient. The quotient formed in this way is fed as an actual value to a controller which adjusts the output of the heating circuit in accordance with the deviation of the actual value from a predetermined target value.
The known fact is used that the electrical resistance of the heating element used, which corresponds to the quotient of voltage and current, is temperature-dependent and, accordingly, when the specific resistance or its temperature dependence is known, it is an indicator of the respective temperature on the heating element.
The quotient is fed to a controller in the heating circuit, the influence of which is to keep the temperature at the heating element constant.
The previously known measures for regulating the temperature on the heating element are, however, insufficient in that the temperature compensation between the heating element and the plastic material to be welded, in particular when heating up relatively quickly, varies, as a result of which the temperature measurement on the heating element does not always give an accurate picture of the temperature supplies at the welding point. This means that the quality of the weld is called into question, especially in extreme conditions.
It is an object of the present invention to improve a method and a device of the type mentioned at the outset such that the quality of the welds can be markedly improved in a wider range of applications even under extreme conditions, and thus the reliability of the welds is guaranteed under all conditions which occur in practice , so that additional test procedures, e.g. to keep the connection tight, become superfluous.
This object is achieved according to the invention by the features defined in claims 1 and 5.
The advantage of these measures lies essentially in the more precise control of the power supplied to the heating element on the basis of temperature measurements on the heating element, which are a better representation of the true temperature conditions at the welding point. A decisive prerequisite for the solution concept is the inclusion of the heat compensation processes between the heating element and the welding point when determining the control parameters. This results in a more reliable control of the heating power due to more meaningful and precise temperature measurements, and there are particularly simple circuitry solutions for corresponding welding devices or their controls.
Details of the invention are explained in more detail below on the basis of preferred exemplary embodiments with the aid of the drawings.
Show it:
1 is a diagram for explaining the method,
Fig. 2 shows a first embodiment for a control device according to the invention, and
Fig. 3 shows a second embodiment for a control device according to the invention.
The principle of the present invention is first briefly explained below. Although reference is occasionally made to the production of connections with welding sleeves as a preferred application example, the invention is not restricted to this area. The features described for the method and for corresponding control devices can be used in all areas which relate to the welding of plastic parts.
As already mentioned in the introduction, the heat is supplied to the welding point via an electrically heated heating element which is formed, for example, by a resistance heating wire. The heat energy is transferred to the welding point according to the known rules of heat conduction. The conditions for heat conduction in the present case depend on the material to be welded, on the geometry of the system and on the thermal potential differences between the heating element and the welding point.
The energy supply for the heating element is interrupted in a known manner when it is determined or expected based on selected measurement criteria that the welding point has reached the desired temperature. In the present case, the known temperature dependence of the heating wire representing an ohmic resistance is used for this purpose. The type and the course of the temperature dependence of the resistance material used in each case are assumed to be known. The conditions are particularly simple, for example, for a resistance element whose specific resistance depends only to a very small extent or according to simple laws on the temperature and thus on the load (e.g. Resistherm or the like).
For such materials, a practically linear relationship between temperature and ohmic resistance can be expected after reaching an initial temperature in the temperature range of interest here.
At the start of welding, the welding point is at a relatively low temperature. In general, the initial temperature corresponds to the ambient temperature. The heating element is heated relatively strongly at the beginning, so that there is a considerable difference in the thermal energy potential between the heating element and the welding point. This initially high temperature gradient causes a high energy flow from the heating element into the plastic material to be welded. Because of the only moderate heat conduction of the plastic material, the internal heat balance, which should ultimately lead to the uniform melting of the material, takes a certain amount of time.
In this phase of the heating process, without using the teaching according to the invention, there would be the risk that a temperature measurement on the resistance element would be anything but the desired image of the welding point temperature, especially in the case of rapid heating. Known regulations or controls which derive a manipulated variable or command signals from such measurements are particularly susceptible to errors in extreme situations due to this phenomenon. On the other hand, for practical reasons, it is not desirable to attach a thermal sensor directly to the welding point.
The teaching according to the invention now provides for the knowledge described above to gradually reduce the power supply to the heating element towards the end of the heating period, in particular to carry out the heating at staggered intervals, the switch-on intervals e.g. be shortened monotonously until it emerges on the basis of special measurement criteria that the heat potential of the welding point differs from the heat potential supplied to the heating winding only by an insignificant amount, corresponding to a predetermined tolerance. If this criterion is met, the energy supply to the heating element is automatically interrupted. The measurement criteria mentioned are derived on the basis of previously determined material-related parameters, taking current process-specific measurement values into account.
Details can be found in the later description of preferred device examples which are used to carry out the described method.
For the above-mentioned temperature measurement on the heating or resistance element, reference is made to the physical facts known per se for the sake of completeness. The electrical power supplied to the heating element
N = U x I (U = voltage, I = current) gives the work over the time t in which this power is provided, in this case the amount of heat supplied to the element.
Assuming that the heat losses during the transition from the heating element to the welding point can be kept negligibly low, the expression A = Uxlxt also corresponds to the amount of heat that was supplied to the welding point. By controlling the electrical power, control of the amount of heat supplied is achieved because of the direct proportionality. The power control can be carried out, for example, by a current control with a known voltage behavior.
The resistance element of the radiator fulfills the task of a temperature sensor in addition to the pure heating effect. Because of the above-mentioned temperature dependence of its ohmic resistance, the course of the prevailing temperature on the heating element is recorded by a continuous measurement of the current ohmic resistance R during the heating period. In the present case, for reasons of increased sensitivity and reliability, the resistance measurement is preferably carried out using the bridge measurement method.
In detail, a resistance measurement is first carried out on the cold heating element. Based on this measurement, the amount of heat U x I x t required for perfect welding is determined. The measurement result obtained is corrected with a factor which corresponds to the current ambient temperature.
Voltage values U, current values I and the heating time t are recorded, e.g. saved or used to set programmable switches. In the course of the heating that then begins, the heating element is heated when the specified temperature is reached with ever shorter heat quantities, as a result of which the heat transfer between the heating element and the material to be welded leads to an adjustment of the temperatures in both parts. As soon as a measuring device detects this state from corresponding comparative measurements, the power supply from the heating element is finally switched off.
The power control is guided along the linearly falling part of the voltage / current diagram shown in FIG. 1. This means that the guidance along R = const, i.e. thus takes place along a constant temperature on the heating element. In this diagram, point A means reaching the specified welding temperature on the heating element, in the example 250 C. From this point on, the heating element is kept constant at this temperature by appropriately controlling the power. This is done, for example, by an appropriately guided current regulation. In FIG. 1, vertical auxiliary lines are drawn in to clarify the processes, which delimit equally long time periods along the current axis.
The written power values show the reduced power supply during successive periods. This measure results in temperature compensation between the heating element and the welding point over the course of time. If the power value mentioned reaches a predetermined lower threshold, which allows practically the same temperature at the heating element and at the welding point, the power supply to the heating element is interrupted.
In combination, these measures result in a surprisingly reliable metering of the amount of heat required for perfect welding.
Representing the variety of possible embodiments for welding or control devices, which are designed according to the described method, two particularly preferred embodiments are described below. The first example focuses more on the use of discrete components, while the second example represents a highly integrated embodiment of a control device.
2, an electrically heatable welding sleeve 1 is provided for the welding of pipe parts. The sleeve is powered by a power supply 2 via a power control element 18 and a controllable switch 3, e.g. a relay, supplied. A measuring circuit is also connected to the sleeve 1, which consists of a resistance bridge 4, an ambient temperature sensor 5 connected or cooperating with it, a start switch 6 and an analog / digital converter 7 with a diameter indicator 10 connected to it.
After connecting the sleeve 1 to the circuit, its cold resistance is first measured and weighted according to the ambient temperature. The determined corrected value is assigned in the A / D converter 7 to the required amount of heat. The output of the A / D converter is connected to programmable switches 8 and 9. These switches essentially control the time behavior for the power supply to the sleeve 1 on the basis of the data obtained from the A / D converter 7.
A current sensor 11 and a voltage sensor 20 are arranged in the supply line between the power supply 2 and the sleeve 1. The output of the current sensor 11 is routed to a first operational amplifier 12. A second operational amplifier 13 is connected to the voltage sensor 20. The outputs of both operational amplifiers are connected to a resistor 14, the voltage drop from the first and second comparators 15 and
16 is detected. With the aid of the second programmable switch 9, the voltage across the resistor 14 can be calibrated in such a way that the output voltages of the two operational amplifiers 12 and 13 are the same when the desired warm resistance is reached on the sleeve 1.
When the warm resistance on the sleeve 1 changes, a voltage drop occurs across the resistor 14, which influences the current control element 17 via the comparators 13 and 16, which performs the readjustment of the power control 18. This continues until the output voltages of the same size appear at the output of both operational amplifiers.
Finally, under the influence of the first programmable switch 8, the heating current for the sleeve 1 has decreased in such a way that it corresponds to the programmed value, the controllable switch 3 is opened, whereupon the sleeve 1 is switched off by the heating circuit. A time monitoring block 19 is provided as a safety element, which opens the controllable switch when a predetermined time period t max is exceeded, if the control described above has not yet triggered the shutdown.
The embodiment of FIG. 3 again contains a power supply 21, which feeds a sleeve 26 via a voltage or current regulator 24 and a controllable switch 25. The cold resistance is determined in a resistance measuring bridge 27. In this bridge, the influence of the ambient temperature is also taken into account. The determined value is implemented in an A / D converter 28. The A / D converter supplies the stored values U, I, t and t2-tl to a memory 23, the last value meaning the pulse width of the power pulses for the sleeve.
As soon as the measured values U, I and t2-tl have reached their stored values, the switch 25 is activated and the sleeve 26 is disconnected from the supply.
With the aid of the time t stored in the memory 23, which is derived from a time monitoring block 22, overall monitoring of the device can take place if there is no shutdown influenced by the values U, I and t2-tl.
Using a small computer module, for example, the functions of the individual modules mentioned are controlled. The continuous formation of U x I is initiated and the quotient (U x I) / (t2-tl) is formed, with t2-tl representing a predetermined constant time interval. This quotient is continuously compared with a threshold, e.g. with (Us x Is) / (t2-t1). As soon as the first quotient obtained from the measured value becomes smaller than the predefined threshold, the heating of the sleeve is switched off.
Claims (10)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CH3057/85A CH668741A5 (en) | 1985-07-15 | 1985-07-15 | Precise welding process for plastics - by heating work using resistance element up supplying heat in pulses according to set curve |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CH3057/85A CH668741A5 (en) | 1985-07-15 | 1985-07-15 | Precise welding process for plastics - by heating work using resistance element up supplying heat in pulses according to set curve |
Publications (1)
Publication Number | Publication Date |
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CH668741A5 true CH668741A5 (en) | 1989-01-31 |
Family
ID=4247646
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CH3057/85A CH668741A5 (en) | 1985-07-15 | 1985-07-15 | Precise welding process for plastics - by heating work using resistance element up supplying heat in pulses according to set curve |
Country Status (1)
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CH (1) | CH668741A5 (en) |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2656950A1 (en) * | 1990-01-11 | 1991-07-12 | Gaz De France | METHOD FOR SUPPLYING ELECTRICAL POWER WITH RESISTANCE, ELECTRICAL CIRCUIT, AND USES THEREOF |
WO1994014599A1 (en) * | 1992-12-23 | 1994-07-07 | J & W Tipper Hire Limited | Welding together plastics materials |
WO1995016557A2 (en) * | 1993-12-15 | 1995-06-22 | Tokushu, Kogyo Kabushikigaisha | Electrofusion fastening apparatus |
WO1997020682A1 (en) * | 1995-12-05 | 1997-06-12 | Hürner Gmbh | Method and arc welding device for automatically welding heater coil fittings |
DE4435393B4 (en) * | 1994-09-26 | 2004-12-23 | Toua Kokyu Tugitevarubu Seizo Co., Hirakata | Method for automatically controlling the welding of thermoplastic articles |
US6953917B2 (en) | 2000-04-10 | 2005-10-11 | Chenault David O | System and method for ensuring the qualification of a workman to perform a task having established required standards |
DE202005005126U1 (en) * | 2005-03-29 | 2006-08-10 | Wolf, Hans | sealer |
-
1985
- 1985-07-15 CH CH3057/85A patent/CH668741A5/en not_active IP Right Cessation
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2656950A1 (en) * | 1990-01-11 | 1991-07-12 | Gaz De France | METHOD FOR SUPPLYING ELECTRICAL POWER WITH RESISTANCE, ELECTRICAL CIRCUIT, AND USES THEREOF |
EP0437149A1 (en) * | 1990-01-11 | 1991-07-17 | Gaz De France (Service National) | Procedure for supplying electrical power to a resistance, the electrical circuit to produce this effect and the uses of this circuit |
US5138136A (en) * | 1990-01-11 | 1992-08-11 | Gaz De France (Service Nation) | Method, circuit and apparatus for supplying an electrical current to a resistive heating element |
WO1994014599A1 (en) * | 1992-12-23 | 1994-07-07 | J & W Tipper Hire Limited | Welding together plastics materials |
WO1995016557A2 (en) * | 1993-12-15 | 1995-06-22 | Tokushu, Kogyo Kabushikigaisha | Electrofusion fastening apparatus |
WO1995016557A3 (en) * | 1993-12-15 | 1996-02-29 | Tokushu Kogyo Kabushikigaisha | Electrofusion fastening apparatus |
DE4435393B4 (en) * | 1994-09-26 | 2004-12-23 | Toua Kokyu Tugitevarubu Seizo Co., Hirakata | Method for automatically controlling the welding of thermoplastic articles |
WO1997020682A1 (en) * | 1995-12-05 | 1997-06-12 | Hürner Gmbh | Method and arc welding device for automatically welding heater coil fittings |
US6953917B2 (en) | 2000-04-10 | 2005-10-11 | Chenault David O | System and method for ensuring the qualification of a workman to perform a task having established required standards |
DE202005005126U1 (en) * | 2005-03-29 | 2006-08-10 | Wolf, Hans | sealer |
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