Extrusion welding | unitracc.de

Definition: <p><span/></p><table><tbody><tr><td> (Image: Welding of the liner ends by means of Extruder welding - Extruder with welding additive) <span/> <p>Extrusion welding serves to connect</p><ul><li> <b>thick-walled semi-finished products </b>and</li> <li> <strong>f</strong><b>oils </b></li> </ul><p>made of thermoplastics.</p></td> </tr><tr><td> <span/> <p>Extrusion welding is a welding method that is mainly carried out manually by continually adding filler material (welding additive).</p></td> </tr></tbody></table><p/>
Application areas: <p><span/></p><table><tbody><tr><td> <table class="picturegroup"><tbody><tr><td> (Image: Watertight welding of the stud course and Preliner)</td> </tr><tr><td> (Image: Extruder-welding device  end of welding procedure)</td> </tr></tbody></table><span/> <p>The method is applied e.g. in the following fields:</p><ul><li>Plant construction and container construction</li> <li>Pipeline construction and sewer construction (rehabilitation methods)</li> <li>Landfill construction</li> </ul></td> </tr></tbody></table><p/>
Storage of material: <span/> <table><tr><td> (Image: Temperature) </td><td><span/> <p>In order to balance the <b>temperature differences</b> between the components to be welded, the components have to be stored before the welding procedure under the same conditions for a sufficient period of time. </p></td></tr></table>
Preparatory work: <p><span/></p><table><tbody><tr><td> (Image: Attention!) <span/> <p><span lang="en"><span class="hps">The</span> <span class="hps">joint faces</span> <span class="hps">and</span> <span class="hps">adjacent</span> <span class="hps">edges</span> <span class="hps">must</span> <span class="hps">be machined</span> <span class="hps">before welding</span> <span class="hps">(e.g.</span> <span class="hps">with a grinder</span><span>)</span><span>.</span></span></p></td> </tr><tr><td></td> </tr><tr><td> <span/> <p>Regions damaged by climatic or chemical influence have to be reduced down to the undamaged zone.</p><span/> <p>No detergents that have swelling effects on plastics may be used for cleaning the joining areas.</p></td> <td> (Image: Roughening the stud course for later welding)</td> </tr></tbody></table><p/>
Procedure: <p><span/></p><table><tbody><tr><td> <table class="picturegroup"><tbody><tr><td> (Image: Schematic view of an extruder)</td> </tr><tr><td> (Image: Extruder-melting device)</td> </tr></tbody></table><span/> <p>Extrusion welding is characterised by the following features:</p><ul><li>A welding additive of the same kind and the same moulding material is used in the welding procedure.</li> <li>The extruded and plastified welding additive (extrudate) leaks as a line from a plastifying unit.</li> <li>The extrudate is homogeneous and completely plastified.</li> <li>The joining layers are heated up to the required welding …</li></ul></td></tr></tbody></table>
Welding additive: <span/> <table><tr><td> (Image: Welding of the liner ends by means of Extruder welding - Trovidur welding additive) <span/> <p>The preparation of the welding additive is continually carried out by an extruder (screw) during the welding process.</p><span/> <p>The welding additive used generally consists of the same material as the joining parts and is added to the extruder as an endless wire or as pellets.</p></td></tr><tr><td> (Image: Attention!) <span/> <p>The welding additive has to be clean and dry.</p></td></tr></table>
Heating-up of joining layers: <span/> <table><tr><td> (Image: Welding of stud hose using the HD-PE-fleece and extruder welding device  a brief look at the temperature display) <span/> <p>The heating of joining layers at the joint sides is carried out by thermal gas or, occasionally, by thermal radiation.</p><span/> <p>The basic material is superficially melted at the surface of the joint sides. During the welding process, it mixes with the extrudate that has been added.</p></td></tr><tr><td> (Image: Attention!) <span/> <p>In addition to the welding parameters …</p></td></tr></table>
Welding speed: <div class="clearfix layout-row columns-2"><div class="layout-column first column-1"><p>The extrudate is provided by the extruder with constant mass flow and added to the welding shoe of the seam. This influences the inlet and pressure of the extrudate in the joint as well as the shape of the seam.</p></div><div class="layout-column last column-2"><div>(Image: Possible shapes of welding seams during extrusion welding)</div></div></div><div class="clearfix layout-row columns-2"><div class="layout-column first column-1"><div><div class="clearfix box important"><div>(Image: Attention!)</div><p>The welding seam results as a dependent variable from the mass flow of the extrudate and the necessary seam-filling volume.</p></div></div></div><div class="layout-column last column-2"><div>(Image: Possible shapes of welding …</div></div></div>
Joining procedure: <span/> <table><tr><td> (Image: Welding the top hat sleeve - detail) <span/> <p>The welding shoe is well adapted for the geometry of the joint and enables the development of hydrostatic pressure in the welding seam joint in that it encloses the extrudate forming a chamber that is closed in front and at the top and at the same time shapes the upper side of the seam [Gehde03].</p></td></tr></table>
Cooling-off phase: <p>After the joining process is carried out under pressure, a substance-to-substance bond is produced during the subsequent unpressurised cooling-off phase.</p><p>The thermal contraction and recrystallisation of the material lead to a volume reduction of the welding seam of up to 8 % [Gehde03].</p><div class="clearfix box important"><div><div class="clearfix layout-row marginalia"><div class="layout-column side-note"><div>(Image: Attention!)</div></div><div class="layout-column text"><p>In order to enable the sinking of the seam during the cooling-off phase and therefore to work against cavity formations in the centre of the seam, …</p></div></div></div></div>
Quality assurance measures during extrusion welding: <p>(Table: Quality assurance measures during extrusion welding)</p>
Standards and regulations for extrusion welding: <p><span/></p><table><tbody><tr><td> <div class="areaTable">(Table: Standards and regulations for extrusion welding (as of 12.2005) [FI-Steina])</div></td> </tr></tbody></table><p/>