工程塑料挤出焊接技术.doc

EXTRUSION WELDINGGeneralThe extrusion welding is applied under other connecting of thick-walled parts. Welding done by addition of welding wire or granulate. For PVC can be applied, the extruder welding proceeds this limited may not be turned off during company (burning material). For PVDF are special worms in the extruder necessary. Temperature Guideline values for the plastic welding by Extrusion weldingSubstance.Air in L/min.Temperaturein( C)TemperatureAir( C)Welding amountKg/hPE- HWU, HWST- HWU-B- HML 500- HMG 1000 300 300 300-200 to 230200 to 230200 to 230-250 to 300250 to 300200 to 250-0 50 50 2PP- DWU, DWST- DWU-B- PPs 300 300 300200 to 230200 to 230200 to 230250 to 300250 to 300200 to 2500 50 20 2PreparationJust before the welding both binding surfaces as the adjacent material cleaned. In addition, damage must be removed. This is particularly important in repair work on tanks and pipework in which chemicals are stored or transported. Cleaning products that solve the plastic surface may affect or be used under any condition. We suggest always the welding by two persons to perform (this in relation to the weight of the equipment and addition of the welding wire in the extruder). Influence of humidity Plastics generally take on moisture. usually this moisture to the surface of the plastic only saved. This humidity evaporated at welding. To find the place in the extrusion welding evaporation extrusion zone, as a result, the moisture locked up and this causes porosity in the weld. It is also important that the heating air moisture free and thus cannot ensure moisture inclusions in the weld. A moisture problem can be fixed in advance by the append material moisture free and at constant temperature to store and a water separator in the air system. We must also ensure that there is no excessive temperature fluctuations occur before or during welding which fought on the welding wire or can sell on the granulate (outside/inside). Extrusion Welder. Extrusion welding device is a portable welder consisting of a small unit by an electro motor and runs if extruder (drill) is powered. The heating and heating of extruder and weld by a hot air device with a compressed air connection provided.The extrusion welding has the following characteristics: Add material in the form of wire or granulate has the same properties as the parent material. The welding medium is in the hot zone is completely plasticized and homogeneous structure. The welds by means of warm air preheated on Welding temperature and the plasticized plastic in the weld is printed. The laminated material by means of a welding nozzle in the weld divided and pressed. In comparison with hot gas welding in larger welds lower tensions in the weld and shorter working hours. Design of the welding nozzleThe laminated material by means of a welding nozzle in the weld divided and pressed.The following points are important in the form of the welding nozzle. Priming Volume Fill Rate Welding Angle Material Addition Weld Design Even pressure The welding nozzle must be adjusted for each seam shape. Generally, the broader the weld how longer the welding nozzle is . The material that is applied to create a welding nozzle is PTFE. This is because this plastic has a high temperature resistance and retains its shape is at higher temperatures. Also, we use the low friction coefficient and the anti-adhesion of PTFE.Revising the weld In general, be made so that there is no post processing welds is necessary. Extrusion welding seams must be evenly and smooth surface without border zones. For notching in the weld seam to avoid when a V it is recommended to use one welding wire as raw seam. The material on the sides of the welding nozzle acts during welding should in particular at high forced connections with the appropriate tools, such as knife and scraper rework.A homogenous weldAt the extrusion welding may be blisters in the weld. This can have two causes: 1. By moisture, as discussed previously2. By shrinkage in the weldThe blisters caused by the contraction in the weld can be prevented by changing the cooling speed or by changing the welding parameters. Blow molding (hollow spaces) in particular with large wall thicknesses or at low welding temperature settings. They arise from the outside of the weld cools faster than the core causing a rigid skin on the weld ensures that the volume reduction of the plastic in the core can be captured. A slow and therefore evenly cool of the weld seam of the weld reached by hedging with insulation blankets. Weld FormsSemi V-seam A free opening of 1 2 mm ensures a good perusing. Double half V-seam X seamAngle K SeamDouble Angle K SeamDouble Angle SeamParameters for a good extrusion welding seam Temperature of the weld metal Temperature on the work piece Welding-Air temperature Amount of append material per unit of time Volume hot-air supply Welding Speed Welding forceRejection criteriaHere too, money that the welding in 3 categories.Assessment groupQuality requirementIHigh requirements t. o. v. Security and/or tax (Chemistry *)IIStandard requirements t. o. v. Security and/or tax (water)IIILow requirements t. o. v. Security and/or tax (air treatment *)Accept the rejection and is shown in the following AnnexTESTING OF THE WELDSimple bending test-DVS 2203 part 5 directives according to describe a simple bend test in the workplace can be performed to get an impression of the quality of a weld. This trial is limited to a wall thickness of 10 mm. the test shall be carried out with a welded plate. This plate is about a rounded stamp of 6 mm thick curved so far that both ends hitting the stamp. This should not break the plate bending or Nick. Bending Test The bend test on the bending bank should, along with other tests, for the assessment of the weld execution. Bending angle and broken image give a picture of the quality of the weld connection. The quality of the weld joint is limited only by assess this bending test.(If the weld is not damaged, there may be a low weld factor) WELDED JOINTS Performances of welded jointsNotch effect and unfavorable transitions of wall thickness reduce the strength of the weld. Joints are generally not homogeneous and because the welds in General not be rework surface irregularities arise contributing to a reduction of the tensile strength of the weld relative to the parent material. Following figure shows 4 different corner welding in different implementation. If this corner joints with a bend test shall be tested it becomes clear that rectangular connections generally much less favorable than a round corner connection with a weld outside the roundness. Rounding generally give a better distribution of the forces and form a 10 times higher resistance than a conventional rectangular connection. T-shaped connections in a single weld significantly worse properties than a double-sided weld. See below image.Also important is that the pull side of the laden part has no staking. It is also a extrusion seam with a certain rounding a more favorable connection form than a not finished weld with welding wire.Following figure shows connections that are taxed on trek. In the weld created trek-and shear strains. A seam gives a high quality because post-edited V the power lines are straightforward and the notch operation is minimized. In a single-sided welded lap joint arise both trek and shear strains with a bending moment on the weld. The form resistance is low and the power lines are strongly influenced. In contrast, a two-sided welded lap joint creates a favorable reception of the forces and the resistance form is positively influenced. This also applies to a cross connection. (Image)Positioning of welds The following examples are in accordance with DVS 2205 sheet 3.High forced welds, it is important to the implementation so that dimensioning both the intersection as the force lines are properly collected and calculated. It is recommended not to run but in the welds by angles. In the welding of plates with different thicknesses can it is better to not stomp but evenly. The crosses of welds must be avoided.Cool, heat-shrink tension by weldingIn the welding of thermoplastics arise depending on the welding methods different tensions, which are located in the transverse direction, length and direction in thicker work pieces also perpendicular to the weld. These tensions arise when welding by