Thermofusion butt welding. Things to Consider

It is a simple and fast method of welding for joining sections of pipe high density polyethylene (HDPE) is joined by heating to melting temperature and mechanical or hydraulic action, the ends of the pipe.

The principle of heat fusion is heat two surfaces to a temperature, and then fuse by applying force. This pressure causes flow of the molten materials, mix and merge. When the tube is heated HDPE, the molecular structure changes from a crystalline state to an amorphous state. When fusion pressure is applied, the molecules of the ends of the tube are mixed. As the joint cools, the molecules return to their crystalline form, the original interfaces disappear and finally the two tubes become a homogeneous tube. The joint area becomes stronger than the pipe itself, either under stress or pressure.

For a good weld it is necessary that the following steps are met:

1. Must install the hot melt equipment according to the manufacturer’s specifications.
2. The pipe ends must be aligned with each other to minimize mismatch or thickness in the tube walls. This is done by adjusting the clamp tubes.
3. Be cut and bevel the ends of the tubes. These should be cut so that the surfaces are clean, parallel and couples and are located perpendicular to the centerline of the tubes.
4. Verify alignment, gently joining the ends facings. cutting perpendicularity then finds, controlling the gap between the faces is not greater than 0.2% thickness.
5. Clean with alcohol Towelie impregnated surfaces or ends of the pipe, not use any other type of solvent and avoid touching surfaces to be joined.
6. The welding surfaces must be compressed against the heater with a force that is proportional to the diameter of the pipe and then be decreased to a value of 0.05 Nw / mm2 plate. This is done in order that the faces absorb heat necessary PolyFusion. This decrease causes the formation of a uniform bead around the circumference, which is directly related to the thickness of the tube.
7. The heating time depends on the thickness of the tube and indicated in the specifications of the machine used hot melt. The pressure at the time of welding should not be less than 0.02 Nw / mm2.
8. Once elapsed heating time of the surfaces to be welded, the heating plate is removed without touching the soft material, this is done uniformly. Time retirement heater plate should be as short as possible, maximum one (1) second per millimeter thickness having the tube. It should inspect the ends of the tubes have a uniform fusión.
9. Immediately gather the two ends of the tubes by applying a gradual force, from a value of 0.15 Nw / mm2 (1.50 Kg. Force) until the final value indicated in the tables. The time during which the force is increased according to the thickness and is given in the diagram total welding time. The final strength must be maintained until the solder has cooled down to a temperature of 70 ° C. should not accelerate cooling with water, solvents or drafty.
10. Inspect that the entire circumference, the shoulder is against the tube. The pipe joint must remain immobile in a period of 10 to 60 additional minutes before handling or testing.

Sources: Procedures Manual HDPE Pipe Welding, Elinsubca C.A.
Welding Procedures, Revinca C.A.