METHOD AND DEVICE FOR MEASURING THE GAS AND/OR LIQUID PERMEABILITY IN THE SURFACE LAYER OF AN OBJECT

Abstract: The invention relates to a method and a device for measuring the gas and/or liquid permeability in the surface layer of an object, especially for identifying wet storage dam­ ages on timber. The method implies that a gas or liquid via a nozzle is applied at pressure to the surface of an object, that the nozzle is applied with a certain force against the surface, and that the gas/liquid is caused to pass through parts of the surface layer. The pressure in the gas/liquid and the flow are measured and used as a measure of the per­ meability of the object.

Description: Method and device for measuring the gas and/or liquid permeability in the surface layer of an object This invention relates to a nethod of measuring the gas and/or liquid permeability in the surface layer of an object. The invention particularly refers to a method of identifying timber damaged by wet storage. The invention also refersxto a device for carrying out the method. The invention is based on the problem that it is not possible to visually distinguish timber with wet storage damage from timber without such damage. The problem has been emphasized in investigations, which were carried out on timber with the object of determining which disadvantages are involved in wet storage from an applicationtechnical aspect. Timber, which is not sawn before the warm season, must be wet stored in order to prevent crack formation, blue, insect attack and other damages. It is generally known, however, that wet storage during the warm season causes an increase in the permeability of the timber for liquids. This increase in permeability is of disadvantage in different connections and can have the effect, that the timber cannot be used for certain purposes, for example glazing. Great volumes of timber are wet stored during the warm season. The storage time for the greatest part of wet stored timber is so long, that there are serious risks of increased permeability - "wet storage damages Timber with wet storage damages cannot be distinguished visually from timber without such damages, neither prior nor subsequent to dying. The object of the development work, which has resulted in the invention, therefore, had been to develop a method and an equipment for indentifying timber damaged by wet storage. The invention is based on the idea that a gas via a nozzle abutting the surface of an object is pressed into the object, and that the gas flow indicates the permeability of the object. A modification of this basic idea is to use vacuum instead of overpressure and to measure the air flow sucked out of the object. Another modification is to use liquid instead of gas as measuring medium. The invention is described in greater detail in the following by way of an embodiment thereof and with reference to the accompanying drawings, in which Fig. 1 is a schematic diagram of an arrangement according to the invention, and Figs. 2 and 3 show two different embodiments of the nozzle used according to the invention. The air pressure required for obtaining the measuring pressure and, respectively, contact pressure for the nozzle is delivered from a compressor 1 or other pressure source. The desired measuring pressure is adjusted by means of reducing valves 3 and 5, and air flows into the system when the valve 2 is opened. The pressure before an air filter 7 is read by a pressure transducer 4. Upon opening a valve 6 the air continues to flow via an air filter 7 to an electric flow meter 8, which is connected to a multi-point printer (not shown). The air pressure after the flow meter (the measuring pressure) is recorded continuously by a pressure transducer 9 connected to a multi-point printer. The air is passed through a valve 10 to the nozzle 12. For venting the system, the valve 11 is opened. The contact pressure for the nozzle 12 against the test specimen 13 is effected by using a compressed-air piston 19 with air from the compressed-air source 1 via the valves 2,3,20 and 15. The contact force is adjusted by reducing valves 3 and 20 and is read/recorded by pressure transducer 14. This arrangement implies that the measuring pressure and the contact force of the nozzle can be adjusted independently of each other. The system is vented by a valve 16 for rendering lifting of the nozzle 12 possible. Compressed air from the source 1 is used also for lifting the nozzle 12 from the test speciment. This is effected through a conduit via the valve 17. The system can be vented through a valve 18. At the measurements carried out two different types of nozzle have been used, which can be exchanged against each other (Figs. 2 and 3). According to the embodiment shown in Fig. 2, the nozzle consists of a cylinder 23, which downwardly has a flange for inserting a gasket 21 therein. The gasket is so designed and of such a material, that it yields at a given contact pressure good sealing against the test specimen 13. The embodiment according to Fig. 3 shows a so-called punch nozzle, at which the cylinder 23 at its lower edge is provided with a sharp edge 22, which is pressed-in slightly into the test specimen and thereby brings about the desired sealing against said specimen.. When the equipment described is used for measuring the gas permeability in the surface layer of timber in order thereby to determine the occurrence of wet storage damages, the nozzle 12 is positioned against the timber surface. When the valve 2 is opened, the nozzle 12 attached to a compressed-air piston 19 is pressed by air pressure against the timber 13. Upon opening the valve 5, the air flows via an electric flow meter 8 connected to a multi-point printer into the nozzle and into the timber. The measuring pressure and flow are recorder the printer. After the measurement, the valves 2, 10 and 15 are closed, and the valves 11 and 16 are opened for venting the nozzle 12 and compressed-air cylinder 19. Thereafter the reducing valve 17 is opened for lifting the nozzle from the test specimen. A new test place or a new test specimen can now be measured. For unplaned timber the punch nozzle according to Fig. 3 is used, for planed timber the nozzle with sealing gasket according to Fig. .is used. The contact force of the nozzle is proportional to the air pressure acting on the compressed-air piston. At the majority of measurements the contact force of the nozzle was about 40 kp. The flow meter used at the tests has a measuring range of 0 - 10 limit. The error in measurement is estimated to be about -0,1 limit. This implies that the relative error in measurement at small air flows, for example at flows below 0,5 l/min, is quite essential. Problems of this kind can be eliminated by inserting into the conduit system an additional flow meter with a smaller measuring range and lower error in measurement. Table 1 shows the flow values obtained for different types of wood. The Table shows substantial differences between timber with and without wet storage damages, between pine and spruce sapwood and between pine sapwood and pine heartwood. The values in Table 1 refer to room dry wood. TABLE 1. Air flow at 2,5 atmos-pheregauge measuring pressure for different wood types Wood type Air flow 1/mien Pine sapwood with wet storage damages 1,6 - 8,7 Pine sapwood, not wet stored 0,3 Pine heartwood, not wet stored 40,1 Spruce sapwood with wet storage damages 1,5 Spruce sapwood and heartwood, not wet sored 40,1 The air flow at pine sapwood with wet storage damages was 5 - 30 times greater than at pine sapwood without such damages. Pine sapwood with wet storage damages, thus, can easily be distinguished from pine sapwood without such damages. From Table 1 appears also the possibility to distinguish, for example, pine and spruce sapwood. Fig. 4 shows that there is a linear relation between air flow and measuring pressure, and that the difference in air flow between timber with and without wet storage damages is greater the higher measuring pressure. is used. Measuring peessures of up to 5 atmospheric gauge have been used, but it is fully possible to use higher measuring pressures. The invention does not imply special requirements on the dimensions of the test specimen. It also is possible to carry out measurements on a construction in situ. The invention is not restricted to the embodiment shown, but can be varied within the scope of the invention idea. It is, for example, possible to connect in parallel two flow meters with different measuring ranges. The object of such arrangement is that in cases when the flow is too small for one flow meter, the second one intended for smaller flows can be switched in. When the invention is applied on an industrial scale, the valves can be controlled via a microprocessor.

Claims: Claims 1. A method of non-destructive measurement of the gas permeability of the surface layer of a wood object for the purpose of identifying wet storage damages1 c h a r a c t e r i z e d in that a nozzle is placed in contact with the surface of the object with such force, known as the contact force, that leakage of gas between the edge of the nozzle and the surface is minimized, that the gas in the nozzle is at an overpressure or underpressure, known as the measuring pressure, that gas is caused to pass through parts of the surface layer of the object, that the contact force is regulated and the measuring pressure is measured and regulated, and finally that flow or the time-dependent change in measuring pressure and/or flow is used as a measure of the gas permeability of the surface layer of the object. 2. A method as defined in claim 1, c h a r a c t e r i z e d in that the measuring pressure and the contact force of the nozzle are regulated and measured independently of each other. 3. A device for carrying out the method defined in claims 1 and 2, c h a r a c t e r i z e d in that it includes a replaceable nozzle (12) intended for placing in contact with the surface of an object (13), a source of pressure or vacuum (1), connected to the nozzle, valves (2, 3, 5, 6, 10) to provide the required pressure and flow of gas to the nozzle, pressure gauges (14 and 9) and valves (2, 3, 15, 20 and 2, 3, 5, 6,10) for measurement/regulation of contact force and measuring pressure, and a flow meter (8) for measurement of gas flow. 4. A device as defined in claim 3, c h a r a c t e r i z e d in that the contact force and the measuring pressure are measured and regulated independently of each other by placing the pressure gauge (14) and the valves (20, 15) in one branch of the gas flow and the pressure gauge (9) and valves (5, 6, 10) in a second branch of the gas flow. 5. A device as defined in claim 3, c h a r a c t e r i z e d in that the gas flow is measured/recorded by means of a flow meter (8), for example, an electrical flow meter connected to a data collection unit. 6. A device as defined in claim 3, c h a r a c t e r i z e d in that the nozzle (12) comprises a sharp edge for placing in contact with the surface of the object (13). 7. A device defined by claim 3, c h a r a c t e r i z e d in that the nozzle (12) is provided with a gasket for sealing the contact against the object (13). 8. A device as defined in claim 3, c h a r a c t e r i z e d in that it includes valves (11, 16, 18) used for venting the tube system connecting to the nozzle and the pneumatic air cylinder (19). 9. A device as defined in claim 3, c h a r a c t e r i z e d in that the nozzle (12) is lifted from the surface of the object (13) by compressed air supplied through valve (17) and a pneumatic piston.

Inventors: BOUTELJE, JULIUS BERTHOLD, HAGGLUND, BENGT GORAN, Hägglund, Bengt Göran
Applicants: TRAETEKNIKCENTRUM
Application year: 1984
Main classification: G01N15
IPC codes: G01N15, G01N33