Fusion through Butt welding operation in polyethylene high density pipes (HDPE) it is based on a union throughout two surfaces, which are heated due to the application of a specific heat temperature, from that point a precise pressure it is implemented till both surfaces finally get fused.
The heat changes the plastic molecular structure, from the crystalline state to a shapeless state, so when the pressure it is performed produces the mixture of these molecules. With the cooling, the molecules come back to their crystalline state, achieving an excellent welding result.
As a general rule, if once the welding process has been completed and occurs that we have some doubt in the resulting weld, such as if it has been performed with the total warranties, we must cut the pipe and repeat step by step the whole butt welding operation.
During the welding process it is possible that we must face the following errors:
Appearance of a flat part on the top of the Bead, or an excessive wideness of the double bead.
This is caused by an overheating of the welding surface, that has been originated reason of an excessively strength during the union operation.
The bead gets rolled over the Surface.
In case that we found a superficial V channel, that should be originated due to an insufficient heating, together with an insufficient union strength.
besides that, if the case is a deep V channel, the origin will be an insufficient heating and an excessive union strength.
A V Channel enough deep in the double bead.
The origin of this incident is the application of pressure during the heating, and an excessive union strength or an insufficient heating.
The presence of bites and bubbles on the Bead Surface.
This point as well as a rugose fusion, resulting a sandpaper touch are the usual pollution examples in the welding process, it is originated by the presence of hydrocarbons in the operation.
Irregular Bead size, around the union.
The possible causes of this are the misalignment, that the heating tool is defective, maybe that the equipment it is worn out, or the facing process has been incomplete.
External Bead square end.
This is consequence of having applied an pressure before time during the HDPE. heating.
Different Bead sizes.
If one of the beads is bigger that the other, this is an indication that there is a misalignment. Could it be because to the heating tool it is defective, or to the welding equipment it is not in proper conditions or because the facing process has been incomplete.
Beads too small or too big.
Small Beads are the result of insufficient union strength or reason of an insufficient heating, while those that are too big are due to excessive heating.
the Butt-welding process is a method simple faster and cheaper to joint polyethylene pipes (between each other and with their accessories tubes) without the need of use additional elements in the union.
That means that the tubes which are cut are the ones – that once heated to a fusion temperature and through a pressure application- to conform the welding.
The welding process indicated as following:
- Install the Butt-welding equipment (there are mechanical as Hydraulic ones) we must follow the manufacturer’s instructions
- We must procedure with the cutting of the pipes that has to be joined. To start the process both pipes sides must be aligned using a press for that purpose, in order to avoid any axial movement.
- Once they are aligned and clean, you must heat the thermoelement until it reaches the appropriate fusion temperature: in the case of less than 10mm of wall thicknesses, it will oscillate between 210 ± 5ºC and for wall thicknesses greater than 10mm. it will be between 200 ±.
- The surfaces to be welded must be pressing the thermoelement, with a strength proportional to the pipe diameter, decreasing it afterwards until the regular Bead gets formed around the circumference. (Look at the machine’s welding table).
- Once the heating time has elapsed, remove the thermoelement (taking care to do not touch the soft material) so the briefly possible, check both ends, that has the be the same fusion uniform.
- Put together immediately, both ends applying a gradually strength (that will come indicated by the pipe thickness) from lowest to highest, starting from 1,5 Kg. strength (Look at the machine’s welding table).
- The final pressure should it be equal to the first one, for the Bead formation and keep it as much time as the indicated at the welding table, without accelerating this process with water, solvents, or water flows.
NOTE: Parameters such as the starting heating strength, the starting welding strength, the heating time and the cooling times are the manufacturer’s recommendations and they will be included in their specifications inside the welding tables.
See below video where you can check and see all the process