Applications of X-ray Computed Tomography in the Wood Products Industry

Forintek Canada Corp. and the University of Northern B.C. have recently opened the new CT Imaging Centre in Vancouver, Canada. The facility is designed specifically for forest products research and can provide high-resolution CT and radiographic images of logs and other large objects. The system has a 3.5 MeV x-ray source, a scan envelop 1m in diameter by 5m in length, and special equipment for handling large objects. This paper describes the facility, provides a brief overview of wood product research activities, and describes several other practical industrial and research applications. Introduction: Canada is one of the world’s leading manufacturers of forest products, producing about C$66 billion of products annually. The solid wood sector produces about C$30 billion of lumber and panel products, primarily for residential housing construction and renovation. The United States is the largest export market for these products and purchased C$16 billion of goods, or approximately 86% of total Canadian wood product exports [2]. Canadian lumber producers have become an important supplier to global markets because of Canada’s abundant high-quality forests and favorable currency exchange rates. Lumber companies have also invested heavily in technology to improve manufacturing efficiencies and reduce costs. This strategy has helped the industry remain competitive in spite of increased raw material costs, growing social and environmental pressures, and trade barriers in the important U.S. market. Forintek Canada Corp. is Canada’s national organization for solid wood products research. The company plays an important role in delivering technology to the Canadian wood products industry and has research facilities in Vancouver, Quebec City and Ottawa, as well as 6 regional offices across the country. Forintek is a private non-profit organization supported by contributions from government, industry, equipment suppliers and contract research services. Forintek provides value to its members by offering technical support services, and by delivering results from a national research program directed by its members. The company works in the areas of wood building systems, composite wood products, lumber manufacturing, lumber drying and protection, and resource assessment. Forintek Canada Corp. and the University of Northern B.C. recently opened the new CT Imaging Centre in Vancouver, Canada. The facility was designed specifically for forest products research but scanning services are also available to companies and organizations with other applications. Funding for construction was provided by the Canada Foundation for Innovation and the B.C. Knowledge Development Fund. This paper describes the new CT Imaging Centre, briefly discusses applications in forest product research, and provides several other examples of industrial and research applications. 1 All figures are for 2001. The CT Imaging Centre: X-ray computed tomograghy (CT) is a well established technique that provides nondestructive cross sectional images showing an object’s internal features [1]. The mathematical foundation for the technique was developed by Radon in 1917, but it wasn’t until the early 1970s that Hounsfield developed the first medical CT scanner. Since that time, CT scanners have become a common medical diagnostic tool and have found increasing use for military and industrial applications. The CT Imaging Centre has the largest CT scanner in Canada. The scanner has an inspection envelope of 1m in diameter by 5m long and an x-ray unit that is approximately 30 times more powerful than a medical scanner. High x-ray energies and a large inspection envelope mean that large, high-density objects that cannot be accommodated in medical scanners can be readily inspected. Large diameter logs, metal castings, geological samples and fossils are some examples of the types of objects that can be readily scanned. Construction of the CT Imaging Centre started in late 2001. The facility consists of a concrete scanner building that houses the CT equipment and provides radiation shielding, and adjacent office space that houses the control room and electronic equipment. A photograph of the facility is shown below in Figure 1. Figure 1. The CT Imaging Centre at Forintek Canada Corp. CT equipment was supplied by Bio-Imaging Research Inc. from Lincolnshire, Illinois, one of the few companies that supply high power industrial scanners. The CT scanner consists of a 3.5MeV pulsed linear accelerator x-ray source, a 512-channel linear detector array, and object positioning equipment. A computer workstation running BIR’s ACTIS software controls the system, acquires data and reconstructs the CT images. A special material handling system is used to transport logs and other large objects into the scanner bay and position them on a turntable. Logs are placed vertically and are held at the top with a clamp. Smaller objects are either placed directly on the turntable surface or are held with special fixtures. Figure 2 shows the interior of the scanner bay with a log placed on the turntable. During operation, objects are positioned between the x-ray source and detector array. The detector measures x-rays passing through the object and data is collected as the object is rotated. Two-dimensional CT images are then reconstructed on a slice-by-slice basis. These images can be analyzed to identify internal features, measure geometry, and characterize material properties. Multiple images can also be assembled to provide a highly accurate three-dimensional model of an object. Figure 2. Interior view of the CT scanner bay with a log loaded and ready for scanning. General performance specifications for the scanner are given in Table 1. Objects up to 900mm in diameter, 5000mm long and 2000kg in weight can be scanned, providing xray penetration limits are not exceeded. Spatial resolution as high as 0.25mm can be achieved, but actual resolution limits depend on object properties and on the size and density contrast of the features of interest. Table 1. General performance specifications of the CT Imaging Centre scanner X-ray source: 3.5 MeV pulsed linear accelerator Scan envelope: 1000mm diameter x 5000mm long Maximum object size: 900mm dia. x 5000mm long x 2000 kg Maximum x-ray penetration: Water: 100cm