How Tapio Analysis Helps Solve Barring Problems

In paper and board production, calender roll barring is a significant problem which can lead to unscheduled maintenance breaks and visible defects in the end product. Although the exact root cause of barring is not always immediately clear, it can originate from small thickness or basis-weight variations already present in the sheet before calendering, or from mechanical vibration in the calender stack.

Tapio Measurement Technologies provides measurement, analysis and troubleshooting services for detecting, diagnosing, and ultimately helping to prevent barring problems.

Pinpointing the barring frequency

Solving a barring problem starts with identifying its exact frequency. In most cases, barring is clearly visible in the thickness (caliper) data measured with a Tapio Analyzer. As the analyzer runs, it records a continuous machine-direction profile of the sheet with multiple sensors. Each sensor is set up to measure the same physical spot in paper.

Data is obtained from either CD strips or MD rolls holding several kilometers of paper or board (see the sample preparation instructions). After measurement, the data is analyzed with the open-source Tapio Analysis software, enabling studies between the different channels for correlation, spectral analysis, spectral coherence and much more.

Repeating deviations that stand out from the noise appear as distinct peaks in the frequency spectrum, and when the rotating speeds or diameters of the rolls are known, the Tapio Analysis software can automatically suggest which rotating machine elements are likely sources of product variations. This is explained in more detail in Find likely machine-element sources with Tapio MD Analysis.

Once the exact barring frequency is identified, it becomes a concrete reference point for the entire investigation. Without this step, troubleshooting remains largely guesswork.

Investigating the origin of the frequency

After identifying the exact barring stripe frequency and wavelength (as well as the rotating frequency of the roll that has the barring pattern), the Tapio Analysis software can be used to compare the data across multiple measurement channels. Overlaying spectra from different sensors quickly reveals whether the same frequency already exists in the base paper and where it could be originating from.

Frequency visible in basis weight suggests a wet-end influence. If the basis-weight channel shows a matching peak, the variations are likely originating at the wet end. In practical terms, this points toward upstream process elements such as pulp consistency, approach flow stability, headbox hydraulics, or forming fabrics. By detecting these early-stage variations, the Tapio Analysis software helps determine whether corrective actions are needed before the sheet even reaches the calender.

Transmission data can point to press-section influence. Transmission measurements, based on light passing through the sheet, are highly sensitive to density variations. If the same barring frequency appears in both thickness and transmission data, the press section often plays a role. Non-uniform press nips, uneven felt condition, or roll hardness variations can imprint a repeating density pattern that survives downstream. The Tapio Analysis software makes it straightforward to compare transmission spectra with caliper data, supporting investigation of press-related candidate causes.

Ash sensor data can be used to investigate coating evenness. When the ash signal shows the same frequency as the caliper variation, the variation is likely being reinforced or introduced during coating. This may be caused by subtle periodic disturbances in coating formulation, mixing, pumping, or application. Typical root causes include worn pumps, pulsating flow, or misaligned applicator components. The Tapio Analysis software highlights these coating-level variations and directs attention to the parts of the process where maintenance or tuning is most effective.

Comparing samples from situations with and without barring. Often an additional practical step is to compare two consecutive machine-direction rolls: one in a situation with a barring problem and one from a situation with no problems (for example, uncalendered paper). Differences in their frequency spectra may explain the root cause of the problem.

Tapio Analysis as a Service

Not every mill has the time or resources to perform a detailed barring investigation internally. For these cases, Tapio Measurement Technologies offers Tapio Analysis as a service. If you have a barring problem on your production line, send us samples and any available process data. We will help you interpret the variation and find where to look first.

By providing samples (MD rolls) to Tapio Measurement Technologies, the customer will receive:

1. Identification and confirmation of the barring frequency, where present in the samples
2. Determination of which process stages show likely matching variations
3. A clear written report with figures and a meeting with Tapio experts to look at the data in detail and discuss potential corrective actions

To analyze barring, provide:

1. MD roll(s) of the product in problematic production conditions
2. Known roll diameters and speeds (if available)

The Tapio Analysis service covers a wide range of paper, board, tissue and nonwoven grades; we confirm suitability before you ship samples.

MD rolls that are too large to measure directly can be cut to size by our partner; please confirm the scope with us before shipping. Instructions for preparing samples: Sample preparation instructions