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Eucalyptus is a fast-growing timber species with a short growth cycle, strong adaptability, and high yield. It is considered one of the world's three fastest-growing tree species recommended by the Food and Agriculture Organization of the United Nations, along with pine and poplar.
Eucalyptus is not a single tree species, but a collective term for all species of eucalyptus, with approximately 808 species and 137 subspecies or varieties, totaling 945 species. Among them, more than 100 species have important economic uses, and the vast majority of eucalyptus trees are distributed in the Australian mainland and its neighboring islands.
About a hundred years ago, eucalyptus trees were introduced to China as garden trees, protective forest trees, and roadside greening trees. After the founding of the People's Republic of China, large-scale commercial planting began in the Leizhou Peninsula of Guangdong and Guangxi.
Since the introduction of eucalyptus trees into the country, eucalyptus forests have developed rapidly, and eucalyptus timber now accounts for more than 30% of the country's timber, timely making up for the timber shortage and greatly safeguarding the country's timber security.
▲Eucalyptus veneer
▲Eucalyptus tree cubes
Eucalyptus timber has become an important source of plywood and solid wood in the timber market, but due to the growth stress of eucalyptus itself and the limitations of processing technology, the yield of eucalyptus is not high.
During the sawing process, the release of growth stress makes the wood prone to defects such as end cracks, splits, and warping, which greatly limits the use of wood in solid wood processing.
Problems encountered in eucalyptus sawing
When eucalyptus is sawn laterally, the longitudinal growth stress at the new wood ends is released and transformed into tangential and radial tensile stress. The tensile stress exceeds the tensile stress that the wood itself can withstand, causing cracks and deformation at the wood ends.
During the eucalyptus lumbering process, the tangentially cut boards sawn from the outer side of the log will bend outwards due to the release of longitudinal tensile stress.
When sawing a tangentially cut board near the pith, the longitudinal compressive stress is released, and the board bends towards the pith.
When sawing the board at the center diameter, opposite tensile stresses are generated on both sides of the core at the end of the board, causing the two ends of the board to crack along the two sides of the core.
Eucalyptus sawing often results in severe cracking and warping of the boards, lowering their quality grade and even rendering them unusable, significantly reducing the yield and utilization rate of eucalyptus wood. The sawing quality also affects subsequent processing and drying processes.
Therefore, wood processing enterprises and researchers have been working hard to explore sawing equipment and methods suitable for eucalyptus to reduce cracking and deformation of boards.
Development of eucalyptus sawing equipment
In the traditional sawing and lumbering stage, the traditional sawing equipment used for eucalyptus timber is mainly divided into band saws, circular saws, and frame saws.
With the advancement of science and technology, eucalyptus sawing techniques have been continuously innovated and improved.
The lumber industry integrates high-tech technologies such as CNC and intelligent systems into sawing equipment. The application of advanced technologies such as chipping-lumbing combined systems, scanning technology, saw blade monitoring systems, and control systems not only greatly improves the yield of eucalyptus wood, but also effectively suppresses warping of sawn timber and reduces thickness tolerance.
band saw
Band saws are traditional lumber processing equipment. Commonly used band saws include carriage band saws and double band saws.
"Car band saw" generally refers to a single-blade band saw, which allows for sawing based on the material being cut.
Double band saws use a dual-blade sawing device, sawing both sides of the log simultaneously, which can evenly release growth stress during the sawing process. Double band saws cannot cut along the log, but they are more efficient than trolley band saws.
▲ Sports car band saw
Band saws are more suitable for sawing large-diameter eucalyptus trees, producing high-quality sawing with narrow kerf and a high log yield. However, the thickness of the sawn timber varies greatly, and there is significant loss during secondary processing of sized timber.
circular saw
Circular saws were widely used in European countries in the early days of wood processing, and the most widely used type today is the dual-shaft multi-blade circular saw.
Dual-shaft multi-blade circular saws are more suitable for sawing large-diameter eucalyptus trees. They can produce boards of the required specifications in one sawing. The process is simple, the production efficiency is high, and the processing accuracy is high, but the kerf loss is large and the yield is low.
Frame saw
A frame saw is suitable for sawing eucalyptus trees with smaller diameters.
Compared with band saws and circular saws, it has the advantages of being able to cut multiple pieces of sawn timber of different thicknesses at once, high production efficiency, low cost, and simple production process, and it is easy to use in conjunction with a single re-splitting saw system.
Chipping-Wood Processing System
The chipping-slab processing system uses a slab chipper to chip the veneer and edge strips of the original wood planks to produce standard-sized timber or square timber, which is then cut into boards using a multi-blade saw. It integrates chipping, longitudinal slitting, and edge trimming equipment, and has a compact structure.
Scanning technology
Scanning technology is mainly used in log positioning in sawing systems. By scanning the shape of the end face or cross-section of the log, relevant data is analyzed, and the precise parameters analyzed are provided to the computer control system to ultimately determine the optimal sawing position.
In the application of sawing logs, it can increase the yield by 3% to 5%.
Saw blade monitoring system
The saw blade monitoring system mainly consists of three parts: a display, an oscilloscope, and a non-contact position sensor. It is widely used in multi-unit band saws and carriage band saws to ensure the feeding speed of the sawing system.
Using a saw blade detection system can increase lumber production by 5% to 7%.
control system
The control system coordinates various functions through a central microcomputer. The central microcomputer calculates and identifies the size, shape, and quality of the logs by scanning system data, then selects the optimal sawing profile and adjusts the position of the logs on the machine tool.
Development of Eucalyptus Sawing Technology
The sawing method has a direct impact on the log yield and sawn timber quality. The choice of sawing method also depends on the tree species, timber diameter, and intended use.
Currently, the sawing techniques applied to eucalyptus mainly include tangential plane balanced sawing, flipping sawing, three-sided sawing, four-sided sawing, radial plane sawing, wedge sawing, and curved sawing.
String-plane balanced sawing method
The tangential balance sawing method involves symmetrically sawing the log from both sides along the pith direction. Since the sawing direction of the board is parallel and symmetrically distributed on the cross-section of the log, the growth stress can be released evenly during the sawing process, which can alleviate the warping of the board.
The tangential balance sawing method is mainly used for sawing small and medium diameter eucalyptus (approximately less than 400 mm in diameter) to obtain the widest possible sawn timber.
Flip-down sawing method
The flip-down sawing method starts by sawing vertically from one side of the log, then flips it 90° three times before sawing again. The number of boards cut from the first three sides depends on the diameter of the log.
This method yields a high yield of warp-cut boards. Because the growth stress on radially cut eucalyptus boards is more even than that on tangentially cut boards, there are fewer end cracks and warping phenomena in warp-cut boards compared to tangentially cut boards, thus improving the overall quality level of eucalyptus boards.
Three-sided sawing method
The three-sided sawing method begins by sawing off one side of the bark from the edge of the log, then flipping it 90° outwards so that the cut surface is placed face down on a bench, and then sawing it into boards in parallel.
For medium-diameter eucalyptus (approximately 300–500 mm in diameter), the three-sided sawing method can be used for sawing, which not only reduces the amount of trimming work but also yields wider lumber.
The principle of the three-sided sawing method is similar to that of the tangential balanced sawing method, except that the three-sided sawing method has an additional cutting surface. This cutting surface helps stabilize the eucalyptus wood on the machine tool, improving sawing stability and board dimensional accuracy. At the same time, this method is simple to operate and highly efficient, so it is widely used by eucalyptus processing enterprises.
Four-sided symmetrical tangential sawing method
The four-sided symmetrical tangential sawing method, also known as the rough square sawing method, involves turning the log 180° once and symmetrically sawing the bark on both sides of the log to obtain two rough squares. Then, the log is turned 90° outward and sawn into boards of the required specifications in sequence.
This method was invented based on the wood structure and growth stress characteristics of eucalyptus. By symmetrically sawing the bark on both sides of the eucalyptus first, a portion of the growth stress can be released evenly, reducing residual stress. This effectively reduces the occurrence of cracking and bending due to the release of growth stress during subsequent sawing.
This method is suitable for sawing large-diameter eucalyptus (approximately 400mm or more in diameter), which can reduce the cutting height of rough squares and the amount of edge trimming work, and the resulting sawn timber has a more uniform specification.
radial sawing method
The radial sawing method involves first sawing the log into quarters, and then sawing each quarter into radial boards of the required thickness.
This method is relatively complex to operate and increases labor and time costs, so few companies use this method to process eucalyptus.
wedge sawing method
The wedge sawing method, also known as the radial sawing method, is an innovative method for efficient sawing of small-diameter logs in plantations. Small-diameter logs with a diameter of <400mm can be effectively sawn using the wedge sawing method, which can effectively increase output value.
The wedge sawing method cuts eucalyptus wood according to the growth ring sequence, with the width of the board aligned with the direction of the growth rings. This results in low residual stress, uniform distribution of growth stress, and more even distribution of drying stress during the subsequent drying process. This improves the overall dimensional stability of the board and effectively reduces defects such as cracking, warping, and transverse bending.
However, due to the complexity of this sawing method and its high processing cost, it is generally only used for processing boards for special purposes.
Curve downward sawing method
Curved sawing is a method of sawing based on the structure and shape of the log. It can not only cut along straight lines, but also perform curved sawing within the range of parameters, which can significantly improve the yield and utilization rate of logs.
Curved lumber produced by the curved sawing method can be straightened through drying and other processes, thus improving the properties of the wood.
Summarize
The harvesting and utilization of fast-growing eucalyptus trees in plantations mainly involves small and medium-diameter timber, and the cracking and deformation of small and medium-diameter logs are more pronounced.
Currently, most small and medium-sized enterprises in China mainly use traditional trolley band saws, dual-axis multi-blade circular saws, and simple three-sided sawing methods. These are mainly traditional sawing equipment, which are low in cost and easy to operate.
The three-sided sawing process is simple, with high yield and processing efficiency, but it cannot effectively suppress defects such as cracking and deformation of the sawn timber. Therefore, the sawn timber obtained is difficult to use directly for processing and utilization of wooden products such as furniture and handicrafts.
The future direction of eucalyptus sawing lies in developing a fully automated sawing system suitable for eucalyptus processing, combining current intelligent sawing technologies with automation to improve product precision and quality.