The right load cells can cure common paper mill headaches

Equipment that works fine in the lab can often fail in a tough, industrial environment like the paper industry. The load cells used to measure web tension are a great example, with problems showing up as drifting or unstable outputs. In fact, customers often say that mistrust of load cell data can be one of their biggest headaches when it comes to monitoring web tension.

Solution | August, 2024

That matters because it’s not unusual for paper machines to produce an entire kilometer of five-meter or wider tissue every minute. It doesn’t take much imagination to picture the chaos if the web suddenly tears and the tissue starts spilling onto the factory floor. Even when the consequences are not quite as spectacularly catastrophic, poorly controlled web tension clearly impacts on quality and machine efficiency.

Luckily though, there are load cells available that are designed and built to withstand the common environmental factors and one-off events that can knock other web tension monitoring technologies off track.

Pressductor® technology

The first thing to consider is the underlying transducer technology. The most robust transducers rely on the magnetic properties of certain steels to produce a signal in response to the force applied – also known as the magnetoelastic effect. All ABB Pressductor® load cells are based on this principle. In contrast, many other systems rely on physical movement – essentially bending or stretching the measurement elements – to generate an electrical signal, making them more vulnerable in challenging operating conditions.

Pressductor® transducers rely on two perpendicular windings of copper wire running through four holes of a steel membrane. An electric current is applied to generate a magnetic field in one of the windings. When the transducer experiences a mechanical force, the magnetic properties of the magnetoelastic steel alter the magnetic flow pattern, inducing an AC voltage in the second coil that’s proportional to the force.

This technology copes naturally with overloads of 300 to 1,000 percent of the cell capacity, depending on the type of load cell, while the deflection under typical industrial loads is between just 0.02 to 0.05mm. That’s between 10 and 100 times less than the displacement typically experienced with movement-based devices.

Since ABB introduced Pressductor® technology, the added stability and service life provided by this robust approach has proved invaluable in paper mills and other tough environments such as steel production.

Reducing headaches

For instance, these gauges are more or less impervious to overloads and shocks, which might otherwise throw the calibration off or even destroy other instruments. They are also designed to minimize the impact of interference – whether from induced currents in the signal cabling or other wireless devices. Pressductor® gauges are also able to cope with the everyday vibrations and temperature variations associated with normal mill operations.

While the ingress of contaminants or the onset of corrosion can compromise the function of virtually any load cell installation, especially if they get inside the cables and electronics, the moisture and fumes that are an everyday part of the environment in a paper mill are more likely to impact on transducers that rely on mechanical movement. For example, they can prevent the mechanical stops used as overload protection from working properly. If the stops engage too soon, it reduces the measurement range of the load cell in addition to diminishing sensitivity and/or accuracy.

Of course, even the most robust gauge needs to be properly installed if it’s going to provide a long and reliable service. For instance, it’s easy to underestimate the tendency of the roll structure to flex when subjected to tension in the web. Roll misalignment, improper bearing selection and a failure to take temperature-related expansion and contraction into account can all contribute to the creation of ‘irrelevant’ forces that can falsify measurement values. Even so, choosing the right load cell will go a long way towards alleviating the headaches associated with web tension measurement.

To learn more about ABB’s Pressductor® transducers, including why they are the device of choice for many of the world’s leading names in the paper industry, visit our web tension portal page.