PROCEEDINGS
OF THE TOMSK ORDER OF THE OCTOBER REVOLUTION AND ORDER OF THE RED BANNER OF LABOR POLYTECHNIC INSTITUTE named after S. M. KIROV

Volume 296

1976

GAMMA FLAW DETECTOR FOR MONITORING WOOD QUALITY IN THE TECHNOLOGICAL FLOW OF TREE-LENGTH LOG PROCESSING

V. I. GORBUNOV, A. N. KARMADONOV, A. N. KISELEV,
Yu. I. LITOVCHENKO

A major reserve for further increasing labor productivity and the quality of manufactured products is the automation of production processes at various stages of processing wood raw material, based on the broad application of nondestructive methods for monitoring the quality of forest materials.

Nondestructive testing methods make it possible to assess, while the tree is still standing, the suitability of trees for the harvesting of high-quality assortments; to select, carefully and without error, those parts during the bucking of stems that are suitable for producing high-quality assortments for special purposes; to obtain from stems round industrial assortments of more uniform quality, thereby increasing the average grade of the raw material; and to direct logs more rationally into sawing according to a specified schedule in the production of lumber and blanks, improving the quality and useful yield of products per unit volume of raw material.

The most important of these stages is quality control of tree-length logs before their conversion into assortments during the primary processing of wood, since detecting defects at the earliest possible stage of production helps improve the quality of wood products and reduce waste in subsequent operations.

When tree-length logs are cut into assortments at the lower yards of timber-industry enterprises, the main losses of merchantable wood occur because of inaccurate separation of the merchantable and fuelwood parts of tree-length logs; the latter is determined mainly by the presence of defects inadmissible under GOST standards—internal rots. Therefore, at this stage of wood processing, the most important aspect of quality control is the detection and determination of the location of internal rots in tree-length logs before bucking. Research and development of methods and means of nondestructive quality control of forest materials under production conditions are being carried out at the Research Institute of Electronic Introscopy at the Tomsk Polytechnic Institute.

At present, as a result of the scientific research conducted, it has been established that, from the entire arsenal of methods of modern flaw detection, the radiation method is the most expedient—and in a number of cases the only possible one—for monitoring the quality of round timber [1, 2, 3, 4, 5, 6].

The results obtained made it possible to proceed to the development of experimental

models of flaw detectors for monitoring the quality of round timber directly under the conditions of the technological flow of tree-length log bucking [7, 8]. On the flow line of the lower landing of the Timiryazevsky timber-industry enterprise of the “Tomlesprom” association, the experimental flaw-detection installation “Taiga-1,” developed at the Research Institute of Electronic Introscopy, was installed and underwent production tests. It is intended for objective monitoring of the quality of round timber directly in the technological flow of bucking tree-length logs on semi-automatic lines at the lower landings of timber-industry enterprises. The quality of the wood in tree-length logs before bucking is determined by the operator of the bucking unit on the basis of visual inspection and the use of the results of gamma-flaw-detection monitoring [8].

The gamma flaw detector measures length, detects sapwood and heartwood rot in tree-length logs, and the results of flaw-detection monitoring, in the form of data on the presence and extent along the length of internal grade-forming defects, are recorded on the illuminated display of the bucking operator’s control panel. This creates the necessary conditions for rational bucking of tree-length logs, taking into account the location of the principal faults and defects, and makes it possible to increase the yield of merchantable and high-grade wood.

The automatic flaw detector “Taiga-1” consists of a gamma-radiation source and detector, equipment for recording and processing the results of measurements of the internal condition of the wood, and a photoelectric system for synchronization and for determining the length of the round timber being inspected.

The irradiation system of the “Taiga-1” flaw detector is installed in the flaw-detection section, which is a special room constructed at the break between the receiving and feeding conveyors that move the inspected tree-length log to the bucking site.

The room is equipped with the necessary radiation-safety means. In the same room, sensors for measuring the length of the tree-length log are mounted.

The recording equipment and illuminated display of the flaw detector are installed in the operator’s control room.

Automatic quality control is carried out by irradiating the timber, moving along the conveyor, with a rotating gamma source. The flux of gamma radiation from the source is continuously recorded by the detector; during each revolution of the source, the gamma ray crosses the object under inspection twice in its transverse section, which makes it possible to obtain line-by-line information on the internal condition of the wood in adjacent sections throughout the entire inspected timber.

Transitions between sound and affected zones are reliably recorded by measuring and comparing the radiation intensities in each pair of sections, and from the comparison results the beginning and end of internal rot are determined [6].

The choice of the optimal distance between the compared sections of the tree-length log made it possible to eliminate the influence on the inspection results of the nonuniform distribution of moisture along the length of the stem and of slow changes in the geometric dimensions of the inspected object. This made it possible to obtain a dependence of the comparison signal only on local inhomogeneities of the timber.

Measurement and comparison of radiation intensities, processing and analysis of signals carrying information on the presence and location of defects in the inspected object, are performed automatically by the gamma flaw detector apparatus, with subsequent output of the inspection data to the illuminated display of the operator’s control panel.

When a tree-length log is transferred from the feed conveyor to the receiving conveyor of the flow-line flaw-detection section, the start-of-inspection sensor is actuated, the log-length meter of the control and synchronization unit is switched on automatically. The control unit determines the operating cycle of the measuring unit, whose output signal carries information on the presence and location of a defect in the inspected object in the form of a relative change in the results of two successive measurements of the radiation flux that has passed through the compared cross sections of the wood during each revolution of the source. Connected to the measuring unit is an information-conversion unit, which performs the role of a threshold device; its threshold depends on the thickness of the timber being transilluminated, and it analyzes defect signals, issuing information only when the size of the rot exceeds that permitted by GOST standards for merchantable wood of the given diameter. The flaw detector records only the transition points between sound sections of wood and sections affected by defects of considerable length. Therefore, information on wood quality is averaged over several revolutions of the source. This makes it possible to obtain more reliable information on the presence and location of defective sections.

The averaging unit, through an analyzer and a memory unit, is connected to the light display of the operator’s control panel, on which the inspection results are recorded in the form of an electrical model of the tree-length log to scale, consisting of light rulers indicating the length and quality of the timber, with the location and extent of internal rot shown. Synchronization of the operation of the electronic units of the flaw detector is carried out by the control and synchronization unit. Thus, a light indication is provided of the qualitative condition of the inspected tree-length log, with automatic determination of its length and of the location and extent of rot in it. This gives the bucking operator the additional data needed for drawing up programs for optimal bucking of the tree-length log with due regard to wood quality.

The length of the tree-length logs, and the dimensions and location of rot, are recorded on the light display with a graduation of 0.25 m, which meets the requirements of GOST. The rotation speed of the radiation source is 200–600 rpm. Inspection capacity is 0.5–2.0 m/sec. The experimental model of the flaw detector reliably detects third-stage rot with a size of not less than 1/4 of the diameter of the tree-length log.

For industrial verification of the method of inspecting tree-length logs and for obtaining the necessary statistical data on the detectability of various defects in round timber by the gamma-flaw-detection method, production tests of an experimental model of the flaw detector were carried out on the flow line of the Timiryazev timber-processing enterprise.

Verification of the flaw-detector apparatus and of the method for inspecting round timber was carried out on tree-length logs of coniferous and deciduous species in the diameter range from 150 to 500 mm, affected by butt and internal stem rots of various stages, sizes, and extents, at a log feed speed of 0.5 m/sec. The sensitivity obtained in the course of the experiments was evaluated by comparing the flaw-detection inspection data with the results of trial bucking of the transilluminated tree-length logs.

During the production tests of the gamma flaw detector, a series of tree-length logs with characteristic signs of internal rot in them was transilluminated. The test results showed that in 90% of cases the inspection data obtained coincided with the location of internal rots in the tree-length logs; in the remaining cases the rots were of early stages or small sizes, which confirms the possibility of objectiv—

...of quality control of timber materials under the conditions of a technological flow.

The sensitivity of the flaw detector ensures reliable detection of stage III rot up to \(1/4\) of the trunk diameter and 50% detection of stage II rot up to \(1/2\) of the trunk diameter, which satisfies the requirements of the State Standard for round timber.

In the course of operation, the gamma flaw detector has proved to be reliable and convenient in work, suitable for prolonged use under the production conditions of timber-industry enterprises. Thanks to the use of the gamma flaw detector, it is possible to shift to complete inspection of tree-length logs before bucking while maintaining the same productivity of the flow line.

Control of timber materials in the technological flow with the aid of the implemented flaw detector makes it possible, through rational bucking of tree-length logs, to increase the yield of commercial and high-grade wood. With the aid of the flaw detector, the problem has been solved of automating the process of objectively determining the size and location of rot in tree-length logs before bucking, without reducing the productivity of the technological flow of wood conversion.

REFERENCES

1. D. G. Veretennik. Ways of automating the determination of wood defects by the method of transillumination with gamma and X-rays. Kirov, 1965.

2. V. I. Shchetinin. Investigation of the scintillation method of gamma control of wood. Candidate dissertation. Novosibirsk, 1968.

3. A. N. Karmadonov, Yu. I. Litovchenko et al. On the choice of a method for wood quality control. Collection of works of the Institute of Forest and Timber, Siberian Branch, Academy of Sciences of the USSR, Krasnoyarsk, 1969.

4. V. I. Gorbunov, A. N. Karmadonov, Yu. I. Litovchenko et al. Application of radioisotopes for detecting defects in round timber. In collection: TsNIITEI “Radiation Flaw Detection,” Moscow, TsNIITEI, 1970.

5. L. N. Isaeva. Moisture content and density of the wood of the principal forest-forming species of Siberia. Abstract of a Candidate dissertation. Krasnoyarsk, 1970.

6. V. I. Gorbunov, A. N. Karmadonov, Yu. I. Litovchenko et al. Method for detecting rot in round timber. Author’s certificate, class 42и, 46/07 No. 298878 of June 30, 1969. Bulletin of Inventions, Moscow, No. 11, 1971.

7. V. I. Gorbunov, A. N. Karmadonov, Yu. I. Litovchenko et al. Use of the radiation method for quality control of wooden tree-length logs under conditions of flow production (abstracts of reports). Seminar “Isotopes and Isotope Devices in the National Economy,” Moscow, 1971.

8. V. I. Gorbunov, A. N. Karmadonov, Yu. I. Litovchenko et al. Experimental flaw-detection installation for quality control of round wood in a technological flow. Journal “Standards and Quality,” All-Union Scientific Research Institute of Physical-Technical and Radio-Engineering Measurements, Khabarovsk, 1971.