Extrusion and hot-air hand welders


With plastic welding, workpieces made of thermoplastic are joined inseparably to one another using a combination of thermal energy and pressure. Central factors are welding speed and the length of the welding process. Plastic welding is used in many areas: For the processing of tarpaulins and plastic sealing sheets, on the roof, in earthworks, hydraulic engineering or tunnel construction, for floor coverings, in vehicle repairs and in equipment construction.

Welding seam geometries galvanic tank

Various seam geometries are used in the welding of galvanic tanks.

A. Fillet weld

The fillet weld is one of the most frequently-use seam geometries. It is produced by welding two workpieces that meet in a T-joint.

B: Interior corner seam

Interior corner seams are generally used on difficult-to-reach locations. Free forms and spline-shaped weld seam geometries are welded most efficiently like this.

C: Corner seam appearance

The outer corner seam is a fillet weld in which the weld seam runs along the edge of the workpieces which are standing together. Consequently, the weld is made along the outer longitudinal side (edge).

D: X-seam (also double-V seam)

The double-V seam is also known as an X-seam. It is a type of butt weld and consists of a combination of two V-seams on each of the two sides of the components to be joined.

D: V-seam

In order to achieve the V-shaped angle that is typical for the V-seam, the workpieces are either beveled or positioned at an appropriate angle to each other.

E: Lap seam

Lap seams are mainly used for plastic sheets. Here, the sheets are arranged on top of each other and the weld seam is laid on the upper exposed material edge.

Thermal joining of plastics

Plastic welding requires a correspondence between the three welding parameters temperature, pressure and speed. In contrast to other joining methods, welding can achieve high resiliency and a strong, homogeneous welding seam. Plastic compounds are extremely robust and perfectly sealed when processed correctly. They can also be repaired without a loss of strength.

Hot gas welding with the torch separate from filler rod (WF)

Hot gas welding with the torch separate from filler rod is used primarily for areas that are difficult to access and for short seams. This welding process is preferred for processing amorphous plastics, in particular PVC. Especially with manual welding, pay special attention to maintaining uniform pressure and constant speed.

During welding, press the wire by hand vertically onto the groove. The force applied depends on the base material chosen and the dimension of the welding wire. Apply the heat flowing out of the tubular nozzle alternately to the welding wire and to the joint in an oscillating motion in the direction of welding until the end of the seam is reached. When realized correctly with the right temperature and appropriate pressure, a welding seam is formed on both sides of the weld bead in the form of a uniform double bead.

High-speed hot gas welding (WZ)

 High-speed hot gas welding requires a high-speed welding nozzle that corresponds to the shape of the fill material. The process is faster, more uniform, and consequently more efficient than pendulum welding. Furthermore, larger cross-sectional surfaces of the welding wire can be processed in one pass. This leads to less residual stress and thus to a lower welding effort.

Hold the welder with one hand, and with the other hand, press the welding wire into the nozzle. The nozzle design divides the hot gas, which in this way heats both the base material and the fill material. The latter is led through a preheating chamber and plasticized shortly before the two materials meet. The presser flap on the end of the nozzle is responsible for the welding force. You can finish the resulting weld seam using a suitable scraper after the welding process.

Hot gas extrusion welding (WE)

Hot gas extrusion welding is preferred over high-speed hot gas welding for wall thicknesses from about 6 mm. With extrusion welding, shorter working times, higher strength and lower internal stress is expected compared to manual welding. This leads to higher process reliability and greater efficiency.

For this, you require a welding shoe corresponding to the welding geometry and a welding filler consisting of the same material as the base material, which is plasticized in the extruder.

First, put joining surfaces into the thermoplastic state using hot air. Immediately press the extrudate onto the surfaces or into the joint using the welding shoe. Depending on the working position, you should apply different intensities of pressure. Welding speed is determined by the quantity of extrudate and by the dimensions of the weld seam. In addition, it must correspond to the prewarming of the base material.

Welding errors

In addition to a failure to adhere to the welding parameters, the following errors can lead to cavities, vacuoles and poor weld quality:

  • Excessively high temperature
  • Residual moisture in the welding filler
  • Excessively high air humidity
  • Wet hands
  • Excessively cold welding shoe
  • Low-quality plastic

Base material and welding filler made of polyolefins can absorb moisture. The thicker the seam, the more frequently these phenomena occur. For this reason, you should store materials in a dry place and in their original packaging. You should avoid temperature differences between the welding parts to prevent the formation of condensation. Very thick welding seams must be welded in several work steps.

Vacuoles are caused by the excessively fast cooling of large weld seam cross-sections.

Rough surfaces on the seam can therefore be because...

  • ...the welding shoe is too short.
  • ...the welding shoe is too cold.
  • ...the surface over which the welding shoe glides is too rough.

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