40
Schüco Guide Factory Production Control (FPC)
Work procedures
AA 05 Welding and cleaning the profiles
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Work area: Machine :
1. Welding and cleaning Corona CT 70 profiles
Fabrication stage Inspection criteria/ method
Tolerance
Prepare outer frame vent, mulion, transom and sash bar
1. Temperature check
2. Visual check

Profile temperature min. 17°C

Cleanliness
Welding machine
Tool
Page 1 of 6
Inspection frequency

Temperature gauge For 1.) Every quantity prepared
For 2.) Every profile
Welding

Welding machine

-
P 4.1.3
1. Visual check
2. Operational check
(corner stability)
3. Measurement (weld
For 1.) See part 2
For 2.) See part 2
For 3.) Woodgrain
0.2 mm bead restriction)
4. Measurement
(welding temperature, welding time and cooling time
For 4.) General welding guidelines (DVS
2207)

Corner stability test device

Vernier caliper

Temperature gauge

Stop watch
For 1.) Every profile
For 2.) At the beginning of the shift
For 3.) At the beginning of the shift
For 4.) At the beginning of the shift
Clean P 4.2 1. Visual check / touch test
Automatic comer cleaner
For 1.) Touch test or using jig if necessary
(max. 0.5 mm groove depth)

Jig For 1.) Visually check every groove / measurement twice per shift
General cutting inspection at the start and end of a shift
Tasks at the beginning of the shift:

The welding machines must be heated up at least
30 minutes before welding.

Functional test: parameters set must be checked by the machine operative, such as temperature of the welding mirror, pressure and welding times.

Must replace the welding films after 150-200 welding sessions.

The welding temperature of the weld seam restrictor must be checked twice per shift (if required) and must be 35°C –40°C (hand-hot). Decorative profiles can only be restricted to 0.2 mm.
The work area must be cleaned at the end of the shift.
Records
The results when fabricating the window are documented on form FB 04.1/04.2 System certificate.
2. General instructions
The welded joints of PVC-U profiles are produced by heating element butt joint welding. The surfaces to be joined are connected in plastic under pressure. The quality of the welding joints depends on the welding conditions and external influences.
Welding conditions are:

Heating element temperature

Heating time and pressure

Jointing time and pressure
External influences are:

Ambient temperature

Draught

Surface moisture
To keep the surface moisture of the joints to a minimum and to avoid inherent stresses in the area of the weld seam, the profiles to be welded must be kept at room temperature, as mentioned in the introduction.
The welding conditions are determined by the following varying data for the welding machine:
1. Heating mirror temperture
 250°C (±5°C) *
2. Melting pressure
3. Welding time (= melting time)

3,8 bar

32 sec
4. Cooling time (= jointing time)

45 sec
* The setting at the thermostat of the welding device must be increased by 8
– 15°C with heating mirrors covered with welding film
(reduces bonding).
The values listed above apply to dry profiles at room temperature and may vary depending on the type of machine
(The welding parameters must always be adjusted with the manufacturer of the welding machine).
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Guide Factory Production Control (FPC)
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Work procedures
AA 05 Welding and cleaning the profiles
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For 1.) Heating mirror temperature
The heating mirror temperature is one of the most important factors in welding. If it is too high, the material burns and a brown discolouration appears in the seam area.
If it is too low, the joint parts are not welded together properly. The heating mirror temperature must be set to
250°C at the T area for PVC-U profiles.
Too low Correct Too high
Material merely “stuck” together Material fuses together correctly Brown, burned areas (damage to material)
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42
Schüco Guide Factory Production Control (FPC)
Work procedures
AA 05 Welding and cleaning the profiles
Work area: Machine :
For 2.) Melting pressure
The melting pressure must press the parts being joined on the heating mirror so that a weld bead of the same size can be created.
If the pressure is too low, the material does not melt sufficiently and the joint seam is weak.
If the pressure is too high, the material melts too much at the weld bead and the rest of the joining material is not hot enough. The joint seam is also affected.
There is no risk of melting the material too much since the melting area is limited by the machine stop.
For 3.) Welding time
The welding time (=melting time) is the dwell time of the profile on the heating mirror.
If this is too brief, not enough material melts and the melt is not taken to the material temperature necessary.
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Page 3 of 6
If it is too high, a brown decolouration forms and the material being joined is damaged.
For 4.) Cooling time
The cooling time (=jointing time) is the time taken for the profiles being melted at the joint surfaces to be joined under pressure.
The cooling time must be long enough for the welding seam to cool to a temperature to be able to take the frame from the machine without damaging the welded joints.
Created by:
The cooling time of the weld seam cannot be accelerated since there are pressures at the seam, which may lead to cracks later.
To check the correct setting of the welding elements, test welds are recommended with assessment of the seam.
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Work procedures
AA 05 Welding and cleaning the profiles
Work area: Machine :
The following occurs with incorrect welding conditions and environmental factors
What happens when welding if the surfaces of the joint are too cold or too moist?
Humidity condenses on the cold surfaces of the joint.
Existing moisture evaporates when it comes into contact with the heating mirror, and the temperature of the heating mirror drops dramatically. The resulting temperature difference cannot be equalised quickly enough by the temperature control of the machine and the welding is then carried out at a temperature that is too low.
If the surfaces of the joint are not at the specified temperature, the temperature difference has comparable consequences. In addition, with this moisture, vapour is locked in the seam on the joint surfaces by the welding, which reduces the stability of the weld.
A welding temperature that is too low results in a “poor” weld seam.
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Potential areas for error when welding

The temperature on the display does not correspond with the temperature at the welding mirror.
This can be checked by a temperature gauge.

The welding mirror cools on one side due to a draught.

The melting temperature, time and pressure do not correspond to one another within a sufficient measure.

The cooling time was too short.

The weld sprue restriction allowances are too narrow.

The surfaces to be welded are dirty or damp.

The welding mirror is dirty.

The surfaces to be welded are not parallel to the welding mirror due to incorrect clamping or sawing.
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44
Schüco Guide Factory Production Control (FPC)
Work procedures
AA 05 Welding and cleaning the profiles
Work area: Machine :
Assessment of the weld quality by how the weld bead looks
How a perfect weld bead looks:
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
Creamy-white to light rough weld bead

Compression area of 3
– mm from left to right of the weld seam
Poor weld seams
Created by:
Deep bead notch
Causes:

Melting pressure too low

Melting time too short

Jointing time too short
Bead too narrow
Causes:

Temperature of heating mirror too low

Joint pressure too low

Melting time too short
Band error
Causes:

Dirty joint surfaces

Temperature of heating mirror too low

Temperature of heating mirror too high

Changeover time too long
Shrink holes
Causes:

Joint pressure too low

Cooling time too short
Pores
Causes:

Vapour forms during welding (humidity condensation on joint surfaces that are too cold)

Dirty heating mirror

Dirty surfaces
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Work procedures
AA 05 Welding and cleaning the profiles
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Assessment of the quality of the weld seam using the surface of the split when checking the stability of the corners (compression bending test)
Good split
The split is in the corner with the maximum span and runs vertically to the weld seam; a visible split surface is not the joint surface. The split goes through the material.

High quality weld seam
Bad split
The split is in the corner with the maximum span and runs exactly along the weld seam; a visible split surface is the joint surface, i.e. a flat, even surface.

Low quality weld seam
Other applicable documents:
Note: other applicable documents must be defined by the manufacturer and ascertained for their company.
PA 01 General quality and test procedures
FB 04.1/04.2 Monitoring of production/Monitoring of orders
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