Monitoring Log Temperature Gain for Improved Debarking
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by Zarin Parouz
The wood products industry has been looking for ways to optimize debarking operations for many years. Higher production speeds lead to higher log volumes being processed by each debarker with little opportunity for operator supervision or intervention.
This leads to systematic value loss at the first production step. And as the number of beetle-killed and fire-damaged logs increases, mills face the additional challenge of processing significant numbers of dry logs mixed with green logs. The fragility of dry logs makes them more prone to tearout and damage under typical debarking conditions and even more so in the winter months. FPInnovations’ latest research and trials have shown that dry log tearout in winter can be reduced by decreasing the knife pressure on the second ring of a dual-ring debarker.
FPInnovationssat down with Zarin Pirouz, Senior Researcher, Advanced Wood Manufacturing at FPInnovations, to learn more about the test results.
What are the issues that wood products manufacturers are facing?
ZP: As the number of beetle-killed and fire-damaged logs increases, mills are processing significant numbers of dry logs mixed with the green, which is a difficult challenge due to their different characteristics and robustness.
Sawmills and oriented strand board (OSB) mills recognize the difficulty of removing the bark from dry logs. In winter months when logs freeze, the bark from green logs can only be removed using high knife pressure. While green frozen logs can tolerate high pressures, dry logs cannot due to their fragility – high knife pressure can easily damage or break them. Since pulp mills rely on sawmill wood chips and that they be free of bark, sawmills often must use high knife pressure to ensure maximum bark removal at the cost of damaging dry logs.
The industry has been looking for ways to optimize debarking operations for many years, but since dry and green logs require different debarking pressures, this can only be done if dry logs can be identified before or during debarking.
What did the latest research and trials reveal?
ZP: FPInnovations’ latest research and tests have shown that while relatively high second ring pressure was needed to remove bark from frozen green logs, decreasing it for dry logs was very effective in reducing tearout.
Our research has shown that wood-bark adhesion strength is affected by moisture content at the cambium layer. Bark adhesion strength increases significantly as logs dry to around 40%- 20% moisture content. This means that the bark lingers longer on the surface of dry logs and accumulates heat as it is exposed to the high friction of debarking. We exploit this phenomenon and use the log temperature gain after the first ring in a dual-ring debarker to detect a large portion (>70%) of dry logs. The test showed that this can be done in time to reduce the pressure of the second ring, thereby avoiding excessive tear and breakage.
This project’s results indicated that more than 70% of dry logs were detected, while very few (<10%) of green logs were falsely identified as dry. The solution also uses an analytical approach, which provides an adjustable threshold to limit false positive errors to protect green logs.
During the project, we found out that the heat-up signature of the logs can potentially be used to detect some debarker performance problems. This type of performance monitoring extends the project’s benefits beyond dry log detection and is applicable to both OSB mills and sawmills with single or double ring debarkers.
This exciting new low-cost temperature-based solution is also relatively simple to implement.
What are the next steps in the research?
ZP: We’ll be collecting long-term data to verify this new method through seasonal variations. We’ll also be closing the control loop and passing the log-type predictions to the debarker control computers to improve debarking. Also, images of debarked logs were collected and are being classified to develop an automated AI-based classification systems as a quality control tool to help staff maintain debarker performance and log quality.
In the meantime, the current version of the system can be used to perform monitoring tests for mills wanting to improve their debarking performance or practices.
A full report on this research can be accessed shortly through FPInnovations’ member-exclusive Research Library.
For more information on this project, please contact Zarin Pirouz, Senior Researcher, Advanced Wood Manufacturing at FPInnovations.
