AT501639A2 - METHOD AND DEVICE FOR NON-DESTRUCTIVE TESTING OF WOOD COMPONENTS - Google Patents

Description

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The invention relates to a method for non-destructive testing of timber components, in particular of finger joints in solid construction timber, as well as a device for checking the strength of wood components, in particular rod-shaped wooden components, with means for applying a tensile force on the timber component.

The invention is directed in particular to a non-destructive testing of bonded wood joints, preferably in one-piece finger-jointed solid wood, which is manufactured in series.

The increasing use of wood-based materials in the construction industry is closely linked to the development and spread of finger-jointed, one-piece or multi-piece logs. One-piece bar wood is so-called structural solid wood, multi-part bar wood is, for example, glulam or duo or triolam.

By means of visual or complex mechanical sorting methods, it is possible to sort out quantity parts with different strength classes from a quantity of cut raw wood. The proportion of high strength values can be reduced by cutting out local defects, e.g. Knotholes, cracks or bends, are significantly increased from individual pieces of wood. The assigned to a certain strength class and freed from defects pieces of wood are then joined together with finger joints to a rod-shaped wooden component. This wooden component then has the same strength class as the pieces of wood used for it. This makes it possible to provide component lengths of 50 m or more, ie considerably larger than the length of the usually available raw wood would allow.

A finger joint does not work in any way to reduce the strength of the wood component. For the correct execution but a high mechanical engineering effort with careful operation and complex process monitoring is required. Manufacturers wishing to make finger jointing have to be certified by an independent testing institute first, then they will get a gluing approval. In addition, they must become a diligent

• Self-monitoring is mandatory and is additionally checked by a third-party monitoring performed by the certification body. For self-monitoring, two additional finger jointing joints must be produced for each sorting class and working layer and, after curing, the adhesive bond must be loaded in a bending test bench until it breaks. The breaking force is measured and documented and allows a statement about the basic compliance with the required production parameters. External monitoring also randomly takes samples from the production plant over longer periods of time. Of the 20 samples taken, only one sample should fall below the characteristic strength value (5% fractiles). A disadvantage of this review process is the destructive testing of the finger jointing or the timber component and the high temporal offset of the test to the production.

Overall, however, these test measures have led to a high level of production safety and, as a result, to a high level of acceptance and distribution of one-piece finger-jointed solid wood and glued laminated timber. However, individual cases of damage, even if they occur infrequently, question this acceptance again and again. In extreme cases, the strength of a single finger joint may depend on the stability of an entire building.

To achieve even greater production reliability, the so-called "proof loading method" is used. applied. Each component is tested by a special test system, which is usually integrated in the production process. The component is clamped at both ends and loaded with a predetermined tensile load, which is assigned depending on the dimension of the component and the strength class. Components with a significant error fail, are sorted out and can be improved. A disadvantage of this method is that defects that just survived the test load, are not recognized. However, the test load can lead to damage at these defects, which adversely affect the strength of the timber component.

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Increasing the test load would increase safety, but could cause further damage and increase the level of the committee.

From AT 1699/2003 A a method for quality assurance of long wood is known in which long timber is subjected to a defined tensile load. During the tensile load, the elongation of the entire component is measured. As a result, increased security in the detection of defects can be ensured, the problem of damage to the wooden components remains. In addition, the localization of a defect is possible only in case of failure of the long wood.

The object of the present invention is to provide a method and a device for testing wooden components with which a statement about the strength can be obtained without destroying the wooden component.

According to the invention this object is achieved by a method having the features of claim 1 and a device having the features of claim 17.

Advantageous embodiments and further developments of the invention are described in the subclaims.

The method according to the invention provides that the wooden component is loaded in sections with a defined tensile force below its characteristic strength and at the same time a measurement of parameters with respect to the acoustic emissions and / or the vibration and expansion behavior of the wooden component in the region of the tensile load is performed. The simultaneous, nondestructive measurement of test parameters of the loaded section makes it possible to obtain information about its strength. It is advantageous that the applied test load, ie tensile force, can be much lower than the breaking load of a fault to be detected. Minimal imperfections in the considered timber component section, such as a partially defective finger joint or other imperfection, generate under the stress at the tips of the tines or in the defect areas emissions in the ultrasonic range, which are detected by a suitable sensor. Defects can also be detected by nonlinearities in the local strain field. The local vibration behavior can be measured together with the application of a tensile force as well as without tensile force and contributes to the improvement of the accuracy of the statement.

To carry out the method, it is provided that the wooden component is clamped in clamping devices and the clamping devices are moved away from one another, in particular a hydraulic loading of the clamping devices is provided. This makes it possible to perform a timed measurement and review of the timber component.

Alternatively, the wood component can be subjected to two opposing driving forces, for example via pairs of rollers or pairs of tracks, which are driven with opposing drive torques.

Instead of a clocked measurement or test, the wood component can be conveyed clamped between two conveyors with different drive torques, wherein a measuring device or measuring devices between the conveyors record the respective parameters.

Local strain measurements are preferably performed at the measuring point in order to detect nonlinearities in the local strain field. The measurement of these strains can be carried out contactlessly with a laser extensiometer or with contacting cutting edges and a strain gauge-based measurement.

It is also provided that an acoustic emission is recorded at the measuring point, wherein sound emissions in the ultrasonic range are detected, which occur under load in the area of the defects or joints. The coupling of the measuring device or sensor to the wooden component is preferably carried out without coupling aids, such as e.g. a gel.

As an alternative or in addition, it is provided that a vibration wave is transmitted to the vibration • • • • · · · · · · ··· ··· · · ································································· _ ·· 5 ··· ···· excitation of the timber component and the vibration behavior of the timber component is measured by a sensor. Since imperfections represent a disturbance of the local rigidity within the timber component, these disturbances can be characterized by transmission parameters, for example for ultrasonic waves. For the measurement of the transmission parameters, high-energy, preferably low-frequency ultrasonic waves or pulses are applied to the wood component, and the passage of these sound waves is measured and evaluated with a suitable sensor. The transmission behavior is measured with or without induced tensile forces.

It is envisaged that less than 70% of the characteristic strength of the timber component is applied as a tensile force, so that the wooden component or a junction of two wooden parts is not undetected damaged or pre-damaged by the reduced load level and by the use of non-destructive testing and measuring. Thus, it is possible to check wooden components with a low, but still permissible strength without material destruction, only connections and defects with a very low, not more permissible strength are destroyed in such a process. These wooden components would have to be sorted out or repaired in any case. Due to the low tensile force, which is applied in the examination of the wood components, the mechanical complexity of the test apparatus is reduced, so that the system can be made easier and cheaper. Possible damage, which can be caused by the mechanical introduction of the tensile force on the surface of the component, ie in the field of force application, are reduced because the tensile forces are much lower than in the conventional test methods dimensioned. The required contact pressure for the test equipment or pressure rollers is lower than in conventional methods, so that in the field of clamping of the timber component in a test device, a reduced material interference occurs.

Preferably, the measurement is performed at a joint of two wooden components, where they are glued together. ···· · · · · · · ············ ··· ··

In particular, in the case of a clocked method, it is provided that points of the timber component to be checked are marked, the wood component is conveyed through a corresponding test device and the point to be checked is determined by means of a sensor. Measuring devices are positioned in the area of the point to be tested depending on the sensor data. This makes it possible that selectively selected locations of the timber component, such as joints, can be checked by the exact location to be tested can be assigned to the corresponding measuring device.

Detected as a defect areas of the timber component can be marked and removed later, as by local application of a tensile load, a local resolution of the measurement results. The measurement results can be reliably assigned to the respective wooden component section, so that by means of the combination of a low test load, an additional measurement of non-destructively obtained parameters and a local resolution, the accuracy of the statement about defects and the location of the defects can be significantly increased.

In addition to marking and separating recognized defects, it is possible that determines the strength or the strength class of the timber component and assigned the wood component of a strength class and marked accordingly by the method.

The device according to the invention for checking the strength of wooden components, in particular rod-shaped wooden components, with means for applying a tensile force to the wooden component, provides that at least one measuring device is provided for recording parameters with respect to the sound emission and the vibration or expansion behavior of the timber component the sound emissions, the vibration or expansion behavior of the timber component between the means for applying the tensile force is detected. The measuring device or measuring devices are designed as Extensiometer or vibration sensor, in particular ultrasonic sensor, wherein the Extensiometer can be constructed as a laser extensiometer or on the basis of strain gauges. - • • 7 • · • • • ff ff ff ··· ffffff: <

To determine the vibration behavior is provided that a vibration exciter or a pulse exciter of the measuring device is assigned, are introduced via the vibrations or a pulse in the timber member. Due to the impulse response or the transmission behavior of the timber component, it is possible to detect defects and to determine the strength of the timber component.

The devices for applying tensile forces to the wooden component are designed as two mutually movable clamping devices which can be fixed to the wood component, in particular clamped. At least one hydraulic cylinder for moving the clamping devices apart is assigned to these clamping devices in order to be able to apply a tensile force to the wooden component. Alternatively, the means for applying the tensile force are formed as mutually braced pairs of rollers or pairs of tracks.

The measuring device is assigned an evaluation unit for the measurement results, so that it can be decided immediately after the test, if there are defects, where they are present, in which strength classes the wood component can be classified and if or where defects must be removed.

In particular, in a clocked examination of the timber component, it is provided that a conveyor for supplying and transporting off the wood components to be tested is provided, which promotes the wooden part to be tested relative to the clamping devices or roller or track pairs. After positioning the section of the timber component to be tested, the clamping devices are placed on the wooden component and bring a defined tensile force. The site to be tested is then examined by the measuring equipment.

If specific points of the timber component, such as a junction of two pieces of wood, to be tested, it is advantageous if a sensor is provided for detecting a mark on the wooden component or for detection of the test point, which is coupled to a controller, which controls the Einrich- ···· t · t · · · · · · · Φ ·· ··· · · · · · · ············································································· Tions for applying a tensile force and preferably also controls the means for conveying the timber component. The timber member is then transported by the conveyor until the sensor detects the mark or spot to be tested.

The sensor is preferably an optical recognition system which detects a connection point or a color marking in the passage. On the basis of the sensor data, the conveyor is then stopped. The tensile forces are applied and measured at the test site.

The device for checking the timber components downstream of a discharge device for timber components insufficient strength. The apparatus may be integrated into the production process of both an existing and a new plant for the manufacture of timber components, in particular one-piece, finger-jointed structural timber.

Hereinafter, an embodiment of the invention will be explained with reference to the drawings. 1 shows a schematic representation of a production plant with integrated testing device; and Figure 2 is a schematic representation of a clocked tester.

FIG. 1 shows a production system for bar-shaped wooden components 20.

In a raw wood storage 1, the sawn raw wood is stacked, which is fed to a first inspection station 2, are marked in the defects and the raw wood is assigned to a strength class. In a subsequent sorting point 3, inferior material is discharged, for example, if the required strength class is not reached or the material is too dry or too moist. The materials to be further processed are sorted and placed in intermediate storage 4. From these intermediate storage 4 they are fed to a Kappsägestation 5, are sawn out in the flaws.

These defects are removed and forwarded to a waste station 13.

After the cross-cut saw station 5, the wood parts of a Keilzin- • ·····························································

6, in which rod-shaped wooden parts are glued to one another at the ends in a finger-jointed connection.

Downstream of the finger jointing installation 6 is a cutting saw 7, which saws the timber component to the desired length. To the cross-cut saw 7 is followed by a so-called hardening bearing 8, which is designed as a continuous or discontinuous flow storage. The wood components linger for a fixed minimum time in the curing storage 8, so that the glue of the finger joint can harden. A check of the strength of the timber component is expediently following the Aushärtelager 8 after curing and reaching the final strength of the glued finger joint, but before finishing. To check the strength of either the joint or the entire wood parts or wood components, the wood component of a test device 9 is fed from the Aushärtungslager 8, in which all timber components are checked. Those wood components that achieve the required strength values are fed to a finished billet 11 in a discharge device 10 for finishing, from which the wood components of the further processing 12 are supplied.

If the test in the test apparatus 9 has shown that the timber component or a part of the timber component does not meet the desired strength requirements, these are sorted out. By means of a Auskappsäge 14, the defects are capped and fed to the waste station 13. The wood components or wood parts corresponding to the respective strength classes are then fed again to the corresponding intermediate storage 4 and re-processed in the finger jointing line 6.

Since the defects found on the wooden components are not readily apparent from a break, the marking of the defects, for example in the form of a color marking, is provided. As an alternative to sawing out the imperfections, it is envisaged that the wood components can be classified after the review in a lower strength class. This is possible if the test of the timber component, although a lower strength than that of the original strength class associated was determined, this strength but still meets a lower strength class. For example, a wood component of strength class MS13 is then classified as one of the class •. • • • • • ······· 'tn · + ··· • MS7.

The entire functional sequence can be carried out and monitored with an automatic control.

To accelerate the described manufacturing process and to save the curing storage 8 and the space required for it, the glue hardening of the finger joint can be significantly accelerated by means of a rapid power supply by high-frequency or microwaves. When using this technology, a so-called hardening tunnel is installed immediately behind the finger jointing line 6. Immediately at this hardening tunnel then the test device 9 can be connected, even before a cutting of the timber components on the cross-cut saw 7 takes place.

An example of the test device 9 is shown in FIG. 2, which is a clocked test device for rod-shaped wooden components 20. The timber component 20 is advanced in the longitudinal direction via conveying devices 30, for example conveying rollers or conveyor belts, as indicated by the arrows in the conveying devices 30 and in the wooden component 20. The timber component 20 is provided with joints 21 in the form of finger joints and is passed through two clamping devices 33. If a timber component section or a joint 21 is now to be checked for its strength, the wooden component 20 is clamped in the clamping devices 33 by clamping jaws 34 being moved in the direction of the wooden component 20 via hydraulic cylinders 35. After both clamping devices 33 are fixed to the timber component 20, a further hydraulic cylinder 31 is activated, which presses apart the clamping devices 33 arranged on a longitudinal guide 32. As a result, a tensile force is introduced into the wooden component 20 between the clamping devices 33. During the application of this tensile force, the joint 21 is measured by means of a measuring device 40. The measuring device 40 can detect either a sound transmission behavior of the timber component 20 or sound emissions. The sound transmission behavior is used as a vibrational response to the introduction of pulses or low-frequency, high-energy ultrasound- ···· ··· · · · · · · ····················································································· • ·· ·· 9 ·· 9 9 .. .. .. .. waves. Such pulses or ultrasonic waves are initiated by an excitation head, not shown.

Alternatively, misalignments or disturbances within the timber member 20 may be measured in a non-contact or contacting manner under tensile loading by using extensometers. A non-contact measurement is carried out via a laser tensiometer, a touching measurement by patch cutting with strain gauge technology. When applying a tensile force substantially below the assumed strength class, e.g. less than 70% of the characteristic strength, measured a non-linear strain within the portion of the timber component 20 to be tested. If there are defects or disruptions in the wood component 20, non-linear strains can occur when tensile forces are detected by the measuring device 40.

Acoustic emissions, vibration responses or non-linear strains are transmitted as sensor data to an evaluation unit 41, in which it is determined whether and to what extent defects are present or whether the strength class of the timber component 20 must be classified differently.

As a rule, only special sections of the timber component 20, such as e.g. Checked finger joints or selected locations in the wooden parts. In order to achieve an exact positioning of the test point between the clamping devices 33, a sensor 42 is provided, which recognizes the KeilZinkenverbindung 21 or a mounted on the wooden member 20 color marking 50 either via an image analysis. The positioning of the section to be examined between the clamping devices 33 then takes place via a control of the conveying devices 30 as a function of the sensor signal of the sensor 42.

As an alternative to the design of the clamping devices 33 with clamping jaws 34 and hydraulic cylinder 35, it is provided that the wooden component 20 is conveyed discontinuously through two sturdy pairs of rollers or pairs of caterpillars clamped against one another and that after positioning the measuring section of the wooden component. • · ·

between the pairs of rollers or pairs of tracks by applying an opposing drive torque by both pairs of rollers or pairs of tracks a defined tensile load is introduced to the timber component. The timber component sections are measured successively in this way. The measuring device 40 or the measuring devices are usefully arranged between the pairs of rollers or pairs of tracks. The timber component 20 can be clocked successively between the pairs of rolls or pairs of crawlers, which are associated with the timber member 20 opposite each other, are passed, so that the entire timber member 20 is checked in sections. Alternatively, only specific portions of the timber member 20, e.g. the joints 21, checked.

The testing device 9 can be integrated into the production process of an existing or new plant for one-piece finger-jointed solid wood or for multi-part, finger-jointed solid wood.

The finger jointing can be cured directly after the press of the finger jointing system 6 by increased energy input and then fed directly to the test device 9.

Instead of a clocked test, it is possible to carry out a continuous test of the timber component 20 by two conveyors are provided with different drive speeds in the conveying direction, wherein the downstream in the conveying direction conveyor has a higher conveying speed than the upstream conveyor. As a result, a tensile force is exerted on the timber component section which lies between the conveyors. The corresponding measuring devices, vibration exciters or pulse generators are arranged between the conveying devices and act on the wooden component 20 or are associated with the wooden component 20.

Claims (27)

1. A method for nondestructive testing of timber components, in particular of finger joints in solid construction timber, characterized in that the Wooden component loaded with a defined tensile force below a characteristic strength and at the same time a measurement of noise emissions and parameters with respect to the vibration and / or strain in the range of tensile load or vibration behavior of the timber component is performed. 2. The method according to claim 1, characterized in that the wood component clamped in clamping devices and the clamping devices are moved away from each other. 3. The method according to claim 2, characterized in that the clamping devices are hydraulically pressed apart. 4. The method according to claim 1, characterized in that the wood component with two opposing drive torques for applying the tensile force are applied. 5. The method according to any one of the preceding claims, characterized in that the measurement is performed clocked. 6. The method according to claim 1, characterized in that the wood component is conveyed clamped between two conveyors with different conveyor speeds and at least one measuring device between the conveyors record the parameters. 7. The method according to any one of the preceding claims, characterized in that at the measuring point, a local strain measurement is performed. 8. The method according to claim 7, characterized in that the strain measurement is carried out via a laser extensiometer or a strain gauge arrangement. 9. Method according to one of the preceding claims, characterized in that ···· ···················································································· ·· ·············································································································· 10. The method according to any one of the preceding claims, characterized in that a vibration excitation of the timber component takes place and the vibration behavior is measured by a sensor. 11. The method according to claim 9, characterized in that the wood component is excited by ultrasound or a pulse. 12. The method according to any one of the preceding claims, characterized in that less than 70% of the characteristic strength is applied as a tensile force. 13. The method according to any one of the preceding claims, characterized in that the measurement is carried out at a joint of two wooden components. 14. The method according to any one of the preceding claims, characterized in that to be tested points of the timber component are marked, the wood component conveyed through a test device and a sensor to be examined body is determined and measuring devices in dependence on the sensor data in the area to be tested be positioned. 15. The method according to any one of the preceding claims, characterized in that detected defects are marked and these defects are separated out. 16. The method according to any one of claims 1 to 14, characterized in that the strength of the timber component determined and assigned the wood component of a strength class and marked accordingly. 17. Apparatus for checking the strength of wooden components, in particular rod-shaped wooden components, with means for applying a tensile force to the wooden component, characterized in that at least one measuring device (40) for recording parameters relating to the sound emissions and of the ···· · · · · · • · · · · · · · · · · · · · · · · · ····· • · I · · · · · · · · "- · 15 ·· * ·· vibration - or expansion behavior of the timber member (20) between the means (33) is provided for applying the tensile force. 18. The apparatus according to claim 17, characterized in that the measuring device (40) is designed as an extensiometer or a vibration sensor. 19. The device according to claim 18, characterized in that the extensiometer is constructed as a laser extensiometer or on the basis of strain gauges. 20. Device according to one of claims 17 to 19, characterized in that the measuring device (40) is associated with a vibration exciter or a pulse exciter for excitation of the timber component (20). 21. Device according to one of claims 17 to 20, characterized in that the means (33) for applying tensile forces to the wooden member (20) are designed as two mutually movable clamping devices which are fixable to the wood component (20). 22. The apparatus according to claim 21, characterized in that the clamping devices (33) is associated with a hydraulic cylinder (31) for moving the clamping devices (33). 23. Device according to one of claims 17 to 20, characterized in that the means for applying the tensile force are formed as rollers or caterpillar tracks. 24. Device according to one of claims 17 to 23, characterized in that an evaluation unit (41) for the measurement results of the measuring device (40) is associated. 25. Device according to one of claims 17 to 24, characterized by a conveyor (30) for feeding and removal of the wooden components to be tested (20). 26. Device according to one of claims 17 to 25, characterized -. Indicates that a sensor (42) detects a mark on the image Wooden component (20) or the test point is provided, which is coupled to a control device which controls the means (33) for applying a tensile force. 27. Device according to one of claims 17 to 26, characterized in that a discharge device (14) for timber components (20) of insufficient strength of the device (9) is arranged downstream. AW / ms / cf