1、 T 460 om-11 TENTATIVE STANDARD 1943 OFFICIAL STANDARD 1949 REVISED 1975 OFFICIAL TEST METHOD 1983 REVISED 1988 REVISED 1996 REVISED 2002 REVISED 2006 REVISED 2011 2011 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee
2、and the Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published.
3、 Approved by the Standard Specific Interest Group for this Test Method TAPPI CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such
4、 use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals wh
5、ich may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chem
6、icals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and dispo
7、sal of these chemicals. Air resistance of paper (Gurley method) 1. Scope 1.1 This method is used to measure the air resistance of approximately 6.45 sq. cm. (l sq. in.) circular area of paper using a pressure differential of 1.22 kPa. The recommended range of the liquid column instrument is from 5 t
8、o 1800 seconds per 100 mL cylinder displacement. For more impermeable papers the time requirements become so excessive that other techniques are preferable. 1.2 This method measures the volume of air that passes through the test specimen, along with any possible leakage of air across the surface; th
9、erefore it is unsuitable for paper or paperboards which cannot be securely clamped so as to avoid significant surface and/or edge leakage. 1.3 For a similar method of measuring air resistance that tests paper at a higher pressure (approx. 3 kPa), and has higher resolution in measuring smaller air vo
10、lumes, refer to TAPPI T 536. For a method of measuring air permeance at pressures up to 9.85 kPa, using both smaller and larger test areas, refer to TAPPI T 547. 2. Summary This method measures the amount of time required for a certain volume of air to pass through a test specimen. The air pressure
11、is generated by a gravity-loaded cylinder that captures an air volume within a chamber using a liquid seal. This pressurized volume of air is directed to the clamping gasket ring, which holds the test specimen. Air that passes through the paper specimen escapes to atmosphere through holes in the dow
12、nstream clamping plate. 3. Significance The air resistance of paper may be used as an indirect indicator of Z-directional fluid permeance, as well as other variables such as: degree of refining, absorbency (penetration of oil, water, etc.), apparent specific gravity, and filtering efficiency for liq
13、uids or gases. Air resistance is influenced by the internal structure and also the surface finish of the T 460 om-11 Air resistance of paper (Gurley method) / 2 paper. Internal structure is controlled largely by the type and length of fibers, degree of hydration, orientation, and compaction of the f
14、ibers; as well as the type and amount of fillers and sizing. The measurement of air resistance is a useful control test for machine production; but due to the number and complexity of factors outlined above; careful judgment should be used in the specification limits for air resistance. 4. Definitio
15、n Air resistance is the resistance to the passage of air, offered by the paper structure, when a pressure difference exists across the boundaries of the specimen. It is quantified by obtaining the time for a given volume of air to flow through a specimen of given dimensions under a specified pressur
16、e, pressure difference, temperature, and relative humidity. 5. Apparatus15.1 Oil sealed instruments 5.1.1 Air resistance apparatus, consisting of a vertically positioned outer cylinder which is partly filled with a sealing fluid, and an inner cylinder that can slide freely in the outer cylinder. Air
17、 pressure, generated by the weight of the inner cylinder, is applied to the specimen which is held between clamping plates. The outer cylinder should be filled with a sealing fluid to a depth of about 125 mm, as indicated by a ring on the inside surface of the cylinder or to a depth specified by the
18、 manufacturer 5.1.2 The clamping plates are located at the bottom of the apparatus, and a center feed tube directs the pressurized air to the clamping plates. The top of the floating inner cylinder is closed. NOTE l: On some earlier instruments, the clamping plates are mounted on top of the floating
19、 inner cylinder. Refer to Appendix A.l for additional details. Some versions of this apparatus utilize a hand-tightened capstan (jackscrew) arrangement to tighten the clamping plates together, while other versions are equipped with a dead weight (typically 0.907 kg) loading a lever arm. The recommen
20、ded clamping force is 180 30 newtons. This mechanism provides a technique to give uniform loading, and thus minimize the operator influence on the test. Controlled clamping force is the preferred method of clamping the specimen. 5.1.3 An elastomeric gasket is attached to the clamping plate on the si
21、de exposed to air pressure to minimize the leakage of air between the surface of the paper specimen and the clamping plate. The gasket is 28.58 0.13 mm inside diameter and 34.93 0.13 mm outside diameter. A satisfactory material is Thiokol, grade ST, polished plate molded, 0.8 0.1 mm thick, 50-60 IRH
22、D (International Rubber Hardness Degrees ISO 48). Other materials may be recommended by the instrument manufacturer. Since the hardness of the elastomer will change with age, this gasket must be replaced on a periodic basis to ensure optimum sealing characteristics. For alignment and protection, the
23、 gasket is cemented in a groove machined in the clamping plate. The groove is concentric with the aperture in the opposing plate. The groove is 28.45 +0.000 /-0.08 mm inside diameter and about 35 mm outside diameter to fit the outside diameter of the basket, at a depth of 0.50 0.03 mm. 5.1.4 The out
24、er cylinder is 254 mm high with an internal diameter of 82.6 mm. It has four vertical bars, each 245.5 mm long, 2.4 mm wide and 2.4 mm thick, mounted equidistantly on the inner surface of the outer cylinder to serve as guides for the inner cylinder. It has a fluid level indicator to assist in adding
25、 the proper amount of sealing fluid. 5.1.5 The inner cylinder is 254 mm high with an outside diameter of 76.2 mm, an inside diameter of 74.1 mm, and has a total mass of 567 0.5 g, so as to produce a nominal pressure of 1.22 kPa. It is made of an aluminum alloy and has graduation marks on the outside
26、 diameter which represent the volume circumscribed within the cylinder. These marks are used to indicate a certain volume of air that passes through the clamping area that holds the paper specimen. The cylinder is graduated in units of 50 mL with a total range of 350 mL. NOTE 2: Some inner cylinders
27、 are also graduated in units of 25 mL for the first 100 mL, and have a graduation at the 400 mL interval. 1Names of suppliers of testing equipment and materials for this method may be found on the Test Equipment Suppliers list, available as part of the CD or printed set of Standards, or on the TAPPI
28、 website general Standards page 3 / Air resistance of paper (Gurley method) T 460 om-11 5.1.6 A stopwatch or electric timer, capable of recording time to the nearest 0.1 second, is required. Some instruments are available with automatic timing devices. 5.2 Electronic instruments 5.2.1 There is anoth
29、er technique in use (1) that utilizes an electronic mass airflow meter to measure the outflow of air from a paper specimen that is subjected to a pressure differential of 1.22 kPa. By measuring the outflow (discharge of air) from the specimen, surface leakage does not bias the measurement. The test
30、results are virtually identical to those obtained from the liquid column instrument when there is no surface leakage at the clamping rings of the liquid column instrument. 6. Materials Sealing fluid: The outer cylinder is filled to the liquid level indicating mark with a lubricating oil having a kin
31、ematic viscosity of 10 to 13 mm /s (60-70 s Saybolt Universal) at 38C and a flash point of at least 135C. The specific gravity at 23C must be between 0.86 and 0.89. NOTE 3: A light spindle oil is suitable for this purpose. Oil must be used instead of water because it does not affect the moisture con
32、tent of the specimen. Also, the higher specific gravity of water will affect the volume of air that passes through the specimen, as there is a “manometer effect” that causes a different amount of air to pass through the specimen than indicated by the graduations on the inner cylinder. 7. Calibration
33、 7.1 The instrument can be tested for air leakage by clamping a thin piece of smooth impervious metal foil or cellophane between the clamping plates. A maximum leakage of 50 mL in 5 h is allowable. This test does not ensure a similar low surface leakage for a paper specimen under test. 7.2 Electroni
34、c timing devices should be checked in accordance with the manufacturers instructions. Calibration flow restrictor plates will facilitate this test. Perform the calibration checks in accordance with the manufacturers instructions. 8. Sampling Obtain a sample of the paper in accordance with TAPPI T 40
35、0 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product.” 9. Test specimens Prepare 10 test specimens of sufficient size from each test unit of the sample. A 50 mm square, or larger size, is generally adequate. NOTE 4: The test results for some grades of paper
36、board may be affected by specimen cut size when there is inadequate stick-out from the clamping rings. This is due to transverse through the edge of the specimen, rather than all of the air flowing through the sheet in the Z direction. 10. Conditioning Condition and test the specimens in an atmosphe
37、re in accordance with TAPPI T 402 “Standard Conditioning and Testing Atmospheres for Paper, Board, Pulp Handsheets, and Related Products.” 11. Procedure 11.1 Oil sealed instrument 11.1.1 Place the instrument on a level surface, free of vibrations, so that the outer cylinder is vertical. T 460 om-11
38、Air resistance of paper (Gurley method) / 4 11.1.2 Raise the inner cylinder before inserting the specimen in the test clamp until its rim is supported by the catch. Clamp the specimen between the clamping plates. Some versions use a hand-tightened capstan (jackscrew), while other versions are equipp
39、ed with an eccentric cam lifting mechanism. Since the capstan version has no measurement or control of the clamping force, tighten with care in order to ensure proper specimen sealing. Over tightening, as well as under tightening, can cause erroneous results. Excessive clamping force may overstress
40、the structural parts of the instrument and affect the parallel alignment of the upper and lower gasket surfaces. The eccentric cam lifting mechanism is actuated by turning one of the two knobs to the left or to the right of the lifting assembly. This self-locking design decreases the potential of us
41、ing excessive clamping force. After the specimen is properly clamped, gently lower the inner cylinder until it floats. NOTE 5: To avoid spilling the oil, raise the inner cylinder with no test specimen in the clamp area. Raise the cylinder slowly. 11.1.3 As the inner cylinder moves steadily downward,
42、 measure the number of seconds, to the nearest 0.1 s, required for the inner cylinder to descend from the 150 mL mark to the 250 mL mark, referenced to the rim of the outer cylinder. NOTE 6: The interval between the 150 to 250 mL marks is specified as cylinder buoyancy effects limit the generation o
43、f 1.22 kPa average pressure to that specific interval. See Appendix A.2. NOTE 7: If the results of the first two tests are less than five seconds or greater than 1800 seconds, stop testing and report that the air resistance is outside the range of this test method. NOTE 8: One manufacturer of this e
44、quipment recommends a working range from a minimum of 10 seconds, with no upper limit. They advise caution in using the instrument for measurements below 10 seconds because the inner cylinder does not have adequate time to achieve a stable velocity of descent. 11.1.4 If after testing there is an ind
45、ication of oil stains on the specimen, this is an indication of oil being spilled inside the air passages in the instrument. Discard the test result. Disassemble the instrument and clean the sealing fluid from the inside of the inner tube and clamping plates per manufactures instructions. 11.1.5 Ref
46、er to Table 1 and Table 2 for the appropriate correction factors if displacement intervals other than the 150 to 250 mL marks are used. Multiply the measured time by the correction factors from the appropriate table to obtain a corrected result for the alternate interval. It may be expedient to use
47、shorter intervals for relatively impervious papers, and longer intervals for more porous papers. Also, instruments that use electronic timing devices may be adjusted to use different intervals. If the correction factors are not used, the percentage error related to the measurement interval can be de
48、termined from the data in the tables. 11.2 Electronic instruments 11.2.1 Refer to manufacturers instructions for calibration and measurement procedures. 11.3 Test five specimens with the top side up, and test five specimens with the top side down. Table 1. Correction factors for timing 100 mL indica
49、ted displacement Scale markers used Correction factor (multiplier) 0 to 100 mL 1.017 50 to 150 mL 1.011 100 to 200 mL 1.006 150 to 250 mL 1.000 200 to 300 mL 0.994 250 to 350 mL 0.988 5 / Air resistance of paper (Gurley method) T 460 om-11 Table 2: Correction factors for timing 50 mL indicated displacement Scale markers used Correction factor (multiplier) 0 to 50 mL 2.040 50 to 100 mL 2.029 100 to 150 mL 2.017 150 to 200 mL 2.006 200 to 250 mL 1.994 250 to 300 mL 1.982 300 to 350 mL 1.970 12. Repo
