www.leister.com
Author: Eddie Weiser, Technical Sales Engineer, Leister Switzerland
Many people are unaware how the Leister Quality System (LQS) can improve quality on geomembrane installation projects. This Article will give you a complete info.
How to find out where the Leister Quality System (LQS) can help you
To see how LQS can help you, it first needs to be understood that all plastic welding is a combination of three parameters.
- Heat/Energy
- Speed/Time
- Pressure
But it’s not enough to just know that. Each material has its own specific welding window. These welding windows are specific for each type of material and welding machine combination. The values can be predefined by carrying out test welding’s. After this test welding you know the welding window of your materials to be welded.
Why wouldn’t it be important to ensure that welding operators are then sticking to these parameters?
LQS allows you to document and record these three critical welding parameters continuously. This ensures that the welding parameters used during the test welding are maintained throughout the entire project.
In Germany this technology has been in use for many years now and it has been well documented that the welding quality on such projects is of the highest standard to be found anywhere in the world.
Other industries such as aeronautical, automobile or pharmacy have shown us that through reliable quality documentation we can learn a lot about what we have done in the past and what we can improve for the future.
So why is this technology not standard in the geomembrane industry?
By using such technology, we can only improve on the quality of projects in the future. To help us understand why this is so important it is necessary to understand the welding process in more detail. The welding window can be illustrated in the following diagram to help us understand different materials.
Magic triangle – finding the “sweet spot”.
As you can see the welding window is quite large and it’s not enough to just find ourselves somewhere in the welding window. We need to aim for the “sweet spot” inside the welding window.
Why do we need to find the “sweet spot”?
Quite simply, because when the material is welded in the “sweet spot” the material will be welded but still maintain the important characteristics of the material.
Let us look closer at HDPE
Everyone has seen a virgin piece of HDPE being put through a shear test (material has not been welded) in a tensiometer. Normally the sample will display signs of necking or stretching as seen in the picture 1 below. These are qualities in the material that we want and need to ensure for long term containment.
Picture 1: Samples which display signs of necking or stretching.
Picture 2: A sample which displays a clean break outside of the weld.
Picture 3: This sample also passed the standard requirements. But we also see that the membrane has retained the ability to stretch and not break.
But when we test, welded samples in a peel test (2 pieces welded together) on the tensiometer. How often do we still see the necking as in picture 3? What we commonly and more often see is a clean break outside the weld such as in the picture 2 above. Technically this welded sample passed the requirements as we know them, but we don’t see any necking anymore.
Wouldn’t it be better if we could pass the requirements and still maintain this desirable feature of the material, being able to stretch and still maintain its ability to contain? With a result like in the picture 3 above?
Both welds in Picture 2 and 3 are made within our welding window. But the welding in Picture 3 was inside the sweet spot. This enables the membrane to keep some very important characteristics, such as the ability to stretch. And this is where the big advantage for data recording is to be found.
European experiences have shown that by using this technology, it can lead to large improvements in the general quality of welding. There have even been recognized studies to show that zero leaks are possible and not just a pipe dream – Müller and Wöhlecke et el (2017).
Productivity over quality?
One of the main problems that exist is the drive for productivity over quality. This leads to measures which in turn are not beneficial to the welding process. The installer is faced by the fact the faster the material is installed the quicker they can move on to the next job. This leads to inconsistencies in the welding parameters, another problem is the lack of properly trained welding technicians. These are good reasons why we should be using a data recording system such as the LQS to help us track and maintain the consistency of the three welding parameters. This in turn automatically improves the quality of the welding. LQS helps us maintain the quality and improve the efficiency at the same time. If you prevent quality problems, you don’t waste time fixing them.
Welding at maximum temperatures
Another common problem is to run the welding process at the maximum temperature which the machine allows. This results in a degradation in the physical characteristics within the plastics which are welded. A good example is picture 2, where you can see the weld still passed the standard requirements, but some important characteristics have been lost. Most commonly we see welds that have been made with too much heat. These welds then snap just outside of the weld. The material loses its ability to neck or stretch, if it has been subjected to too much heat. In worst case scenarios we hear that 3–8 years down the track the welds are breaking just outside the welded zone, leaving the membrane unable to carry out its primary role of containment.
How to set the right welding pressure settings?
The pressure setting of many Geo welding machines is a guessing game to say the least but once again this is a critical setting which plays a much larger role in the quality of the weld than most people are willing to acknowledge. Not enough pressure results in poor bonding of the materials. Too much welding pressure means that the plasticized material is squeezed away only to create what we call a cold weld. The cold weld will also be outside of the sweet spot of our welding window.
So why do so many machines not have the ability to display the actual welding pressure?
Machines need to fulfill certain standards, but still we don’t see requirements for tolerance limits, calibration standards or calls for Closed loop control systems for welders. LQS machines do however fulfill all the above requirements. Imagine if there were no safety standards for cars travelling on our public roads? Imagine the chaos.
By having a system which keeps track of the ideal welding parameters, we would be a huge step closer to ensuring the conditions are right for good welding to take place. Such systems can also be setup to include minimum and maximum tolerances for the three critical parameters. LQS also makes it possible to constantly display the voltage. Voltage fluctuation and cable quality is also a major cause of problems when it comes to ensuring stable performance of the welding equipment
All of this then sets the stage for the “Smart Destructive Testing” which can then be implemented along with the recorded data to establish, when and where testing should be carried out. It would then be a lot easier for an inspector or owner to determine from the recorded data where potential problems may be found. Used properly this technology could be the basis for laying the foundation as to how welding and destructive testing could be carried out in the future. It is common in some countries for the inspector to examine the welding data to decide where the destructive tests will be taken from. We are firmly of the belief that our aim should be to improve the welding quality. We all know the expression the chain is only as good as the weakest link. Now the weakest link is the welding. The technology is available to help us improve our welding why aren’t we taking full advantage of it? In the future we also plan to incorporate other “Smart Welding and Testing equipment” such as “Smart Extruders” and “Smart Tensiometers”. This equipment would also record and document relevant parameters for data acquisition and quality control purposes and would automatically match test results to welding data making the documentation even more complete
