Studies Of The Key Technologies On Χ-ray Profile Density Analyzer For Wood-based Panel

Recent years, the wood-based panel industry of China has been developing rapidly, and playing a more and more important role in the country's economy. The quality of wood-based panel products correlates closely to its vertical profile density. So to measure the vertical profile density of wood-based panel accurately, would be propitious to ameliorating the hot-pressing technical parameters, improving the quality of wood-based panel products, saving wood material and decreasing the energy consumption. And this would help the wood-based panel corporations to increase benefits and promot the healthy and sustainable development of China's wood industry.In this study, some key technologies were solved in developing the X-ray profile density analyzer for wood-based panel. The key technologies were to select the X-ray tube used in the instrument, to calculate the technical parameters of the high-voltage source connected to the X-ray tube, and to evaluate the characteristics of the instrument. And in this study, designing of other parts of the system were also refered, including selection of X-ray detector and stepping motor, X-ray radiological protection, programming and test of the system. After discussing in theory and analyzing the experiment data, the main results are summarized as following:1. Selecting the X-ray tube used in the instrumentWhen X-ray among 20-50keV was used in measuring the vertical density profile of wood-based panel samples,whose density was among 0.4-0.9g/cm3 and dimension was 50mm×50mm,the best sensitivity would be got. The sensitivity of former measurement using 60keVγ-ray emitted from 241Am radioactive isotope wasn't the best.When measuring using 20-50keV X-ray, the effects of the two factors--moisture content and wood species of the panel--on the mass attenuation coefficient were both extremely significant. When measuring using 20-30keV X-ray, the effect of resin content on the mass attenuation coefficient was extremely significant. If the X-ray energy increased to 40keV, its effect was significant, and 50keV, its effect was not significant.2. Calculating technical parameters of the high-voltage source connected to the X-ray tube There are three factors related to the stability of the voltage output from the high-voltage source connected to the X-ray tube: temperature-drift, time-drift and ripple voltage, among whom the temperature-drift and time-drift don't impact the uncertainty of the results. And only the ripple voltage can impact the uncertainty of the results.If the X-ray energy used in measuring were 20keV, 30 keV, 40 keV, or 50 keV, the corresponding ripple voltage coefficient of the high-voltage source connected to X-ray tube must be lower than 1.5%,0.79%,0.60% and 0.52% so as to ensure most of the possible results can be included in (ρ? 0.01g /cm3 ,ρ+0.01g/cm3).3. Designing systemIn this study, scintillation detector made up of plastic scintilla and photomultiplier was selected as X-ray detector of the profile density analyzer. And hybrid two phases stepping motor was selected as its stepping motor. The shell of the instrument was made of 1mm-thick-lead.VB6.0 language was used to programme to realize transition from X-ray intensity value to vertical density profile. The programme was made up of the following parts:self-check, startup of X-ray tube, filling-in data of sample,setting stepping speed,scanning sample and counting, computing vertical density profile, plotting the density curve and exiting the programme.Tube voltage and current of X-ray tube being 40kV-1.0mA and 50kV-1.0mA are two normal working state of the tube. When X-ray tube working at 40kV-1.0mA state,the intensity value of X-ray from X-ray tube is 1910, and 1756 as intensity value is selected as boundary in determining sample's edge. When X-ray tube working at 50kV-1.0mA state,the value of X-ray is 3415, and 3226 is selected as boundary in determining sample's edge.When setting step length of stepping motor in one second to 1421, the stepping speed can be considered as 0.10mm/s. When setting step length of stepping motor in one second to 721, the stepping speed is 0.050mm/s.4. Evaluating the characteristics of the instrumentIn this study, the characteristics of repeatability and sensitivity of the instrument measuring the vertical density profile, were evaluated according to JJF 1094-2002 National Standard"Evaluation of the Characteristics of Measuring Instruments". It was found after evaluating the repeatability of the X-ray profile density analyzer using basic method, largest residual error method and range method that, the repeatability of the instrument is bad when the few points near the edge of samples are measured, and the repeatability is good when instrument is measuring the points inside the samples. When the tube-voltage and tube-current of X-ray tube are working at 50kV-1.0mA state, the repeatability of the instrument is better than working at 40kV-1.0mA state. And when X-ray tube working at 50kV-1.0mA state, the average experiment standard deviations calculated in the three methods are 0.012-0.024,0.011-0.018 and 0.012-0.021.It was found after evaluating the sensitivity of the X-ray profile density analyzer that, when measuring different samplesm, the sensitivity of the instrument is related to three factors: vertical density profile, length of X-ray traverses through in the samples and mass attenuation coefficients of samples. When measuring one sample, the sensitivity is only related to the vertical density profile, and their map is negative exponent. So sensitivity of the instrument is higher when it is measuring the lower density points, and the sensitivity is lower when it is measuring the higher density points.