1、Designation: D 5795 95 (Reapproved 2000)Standard Test Method forDetermination of Liquid Water Absorption of CoatedHardboard and Other Composite Wood Products Via“Cobb Ring” Apparatus1This standard is issued under the fixed designation D 5795; the number immediately following the designation indicate
2、s the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is intended to serve as a me
3、ans formeasurement of liquid water that passes through a wetted paintfilm, and which is subsequently absorbed and retained by theunderlying wood substrate. Alternative techniques for the useof the “Cobb Ring” apparatus are described.1.2 The values stated in SI units are to be regarded as thestandard
4、. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bil
5、ity of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1193 Specification for Reagent Water2E 177 Practice for the Use of the Terms Precision and Biasin ASTM Test Methods3E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method
6、33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Cobb unit (C.U.), nThe weight of distilled waterabsorbed by the underlying wood substrate in grams per 645cm2(100 in.2) of surface area (discounting additional areascontributed by texturing or grooves) per 24-h time period.3.1.2
7、 Cobb unit (C.U.) factor, na dimensionless math-ematical term which, for a given ring size, may be multipliedtimes the weight change after 24 h to calculate the Cobb unitvalue.3.1.2.1 DiscussionThe C.U. factor is calculated as fol-lows:C.U. Factor 5100Area ring!5100pr2(1)where:r = radiusFor example,
8、 for 101.6-mm (4-in.) inside diameter ring.orC.U. Factor 51003.142!2510012.565 7.96 (2)3.1.3 composite wood productsboards or other structuredor decorative materials manufactured from wood fibers, flakesor strands and various resin binders.3.1.3.1 DiscussionOne example is hardboard.3.1.4 hardboarda
9、generic term for a panel manufacturedprimarily from interfelted lignocellulose fibers consolidatedunder heat and pressures in a hot press to density of at least 31lbs (13.95 kg) per cubic foot (cubic meter).44. Summary of Test Method4.1 Suitable size rings of metal or plastic are adhered orclamped t
10、o the flat, coated surface of composite wood panels tobe tested.4.2 The assembly is equilibrated at a constant temperatureand humidity and weighed.4.3 The weighed assembly is placed on horizontal5surfacein a controlled temperature and humidity room or environmen-tal chamber. Water is placed in the r
11、ing and left in contact withthe board face for 24 h.4.4 After 24 h the remaining water is removed from the ring,the assembly blotted dry and reweighed.1This test method is under the jurisdiction of ASTM Committee D-1 on Paintand Related Coatings, Materials, and Applications and is the direct respons
12、ibility ofSubcommittee D01.52 on Factory-Coated Wood Products.Current edition approved Oct. 10, 1995. Published December 1995.2Annual Book of ASTM Standards, Vol 11.01.3Annual Book of ASTM Standards, Vol 14.02.4“Todays Hardboard”, American Hardboard Association, 1210 W. NorthwestHighway, Palatine, I
13、L 60067.5The specification of a solid, continuous horizontal surface or a discontinuous(wire rack, expanded metal, etc.) is required. Surface must be consistent fromlaboratory to laboratory since this can influence the rate of evaporation of moistureand, thus, retention of moisture and Cobb values.1
14、Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.5 The increase in weight of the assembly due to wateruptake is calculated by simple subtraction and then convertedto Cobb units through the use of the C.U. factor (see 3.1.2 ).5. Signi
15、ficance and Use5.1 This test method provides a simple quantitative measureof water absorption by coated composite wood products.Although primarily used to evaluate factory-primed compositewood products, this test method may be of service for otherwood substrates and coating systems.5.2 This test met
16、hod has demonstrated utility for compositewood siding products ranging in thickness from approximately6.35 to 25.4 mm (14 to 1 in.). Extension of this test method towood substrates of other types and thickness may be useful.5.3 Conditioning of substrate, coated sample preparation,application method,
17、 dry film thickness, cure conditions, andnumber of replicate specimens should be agreed upon betweenthe purchaser and the supplier of the coating material.5.4 Such measurements are used as indicators or predictorsof the anticipated performance of coated composite woodproducts during exterior exposur
18、e. They may be used fordevelopmental evaluation of coatings, substrates, or both. Theymay also be useful for quality control or monitoring of theproduction of coated composite wood products.6. Apparatus6.1 Rings, may be cut from stainless steel, aluminum orPVC pipe. The ring diameter can be any size
19、, but useful resultshave been obtained with rings of 101.6 mm (4 in.) or larger6inside diameter, wall thickness of 9.53 mm (38 in.) and heightof 25.4 mm (1 in.).6.2 Environmental Chamber, set at 23 6 2C (73 6 4F)and 50 6 5 % relative humidity, or other agreed upon options.6.3 Saw, suitable for cutti
20、ng of samples.6.4 Caulk Gun or Applicator, or, a clamp and gasket devicefor holding the ring tightly against the board is needed.6.5 Balance, with sufficient capacity (typically 400 g) and0.01-g accuracy.7. Materials7.1 Butyl or Silicone Caulk, which has been determined notto contribute to assembly
21、weight change through absorption ofwater or interaction with the coating.7.2 Distilled Water, (see Specification D 1193).7.3 Test Boards, appropriately identified, coated or un-coated,7cut to a square size that is 25.4 mm (1 in.) greater thanthe ring diameter. A minimum of three replicates is recom-
22、mended.7.4 Control Samples, coated or uncoated without rings willalso be required. These will be used to assess the degree ofequilibration that is achieved.8. Hazards8.1 Use saws with goggles, dust mask, and proper machinesafeguards to prevent injury.8.2 Caulking compounds may be flammable and conta
23、intoxic solvents. See manufacturers instructions for proper useand disposal.9. Procedure9.1 Sealing of Rings to the Coated Face of the Samples:9.1.1 A continuous bead of caulk is applied to one edge ofthe ring. The caulked side of the ring is then attached to thesample with gentle pressure and a sli
24、ght twisting motion; tomaintain an accurate and uniform test area, only minor caulk“squeeze-out” should occur inside of the ring. Carefully wipeout this minor caulk“ squeeze-out” to prevent errors in latercalculations.9.1.2 Alternatively, the assembly may be produced with aclamp and gasket device.8S
25、atisfactory results can also beobtained from clamp and gasket devices that are of self designand locally produced by any machine shop.9.1.3 To inhance reproducibility, do not generate data by acombination of the caulk procedure and the clamp and gasketprocedure.9.1.4 Also, for improved reproducibili
26、ty, all rings must be ofthe same nominal internal diameter.9.2 Equilibration:9.2.1 Allow the samples with rings and controls withoutrings to equilibrate for seven days at 23 6 2C (73 6 4F) and50 6 5 % relative humidity.9.3 Initial Weighing:9.3.1 Weigh (grams) the controls and samples with rings toth
27、e nearest 0.01 g; record the weight.9.4 Fill each ring with the volume of distilled water requiredto achieve a depth of 12.7 6 3.2 mm (12 618 in.) of distilledwater.9.5 Store test assemblies at the same conditions used forequilibrating the panels.9.6 Final Weighing:9.6.1 After 24 h, pour out the wat
28、er and blot the surfaceinside the ring completely dry with a soft paper towel.Immediately weigh (grams); record the new weight of thesamples with rings.9.6.2 After all measurements from 9.6.1 have been com-pleted, weigh (grams) and record the weights of the controlboards without rings. Compare the w
29、eights with the initialweights. If the weight change of the control boards is morethan 20 % of the weight change of the test boards, the absolutevalues of the test results may be questionable.9.7 Additional Procedures:9.7.1 Caulked rings can be removed from the coated boardsby pulling the ring from
30、the board and cleaning in lacquersolvent.9.7.2 For textured boards without a groove in the coatedpanel, apply additional caulk to the outside of the ring to get asatisfactory seal after attaching the ring to the coated board.6Rings of 01.6 to 254.0 mm (4 to 10 in. 1) are commonly used.7The use of th
31、e uncoated test boards is not intended for direct comparison withthe coated samples, but may be used to ascertain the substrate variability and suggestthe number of replicates needed.8The sole source of supply of clamp and gasket devices known to the committeeat this time is the Teledyne Gurley Cobb
32、 Sizing Tester, T.M.I., 400 Bay View Ave.,Amityville, NY 11701. If you are aware of alternative suppliers, please provide thisinformation to ASTM Headquarters. Your comments will receive careful consider-ation at a meeting of the responsible technical committee,1which you may attend.D 5795 95 (2000)
33、29.7.3 For boards with a groove in the coated board, attachthe ring to the board so that at least one groove length will bethe same as the diameter of the ring. Apply extra caulk in thegroove at the appropriate spot before attaching the ring in orderto get a good seal. Extra caulk may have to be app
34、lied in thegroove outside the ring after attaching the ring in order to geta good seal.9.7.4 During equilibration and testing of the boards withrings, store the boards test side up and single high on a flatsurface that is impervious to moisture.9.7.5 If an environmental chamber is used, the controlb
35、oards with ring assemblies must not be stacked upon eachother. It is recommended that the control boards and ringassemblies be stored coated side up and single high on wireracks at least 50.8 mm (2 in.) above or below adjacent rings.Care must be taken so as not to overload the humidity chamberwith r
36、ings containing water.10. Calculations10.1 Calculate and record the weight change by subtractionof the initial weight of 9.3.1 from the final weight of 9.6.1.10.2 Calculate the Cobb unit (C.U.) factor for the ring sizesused (see 3.1.2.1).10.3 Multiply the C.U. factor times the weight changerecorded
37、in 10.1.1 and record the Cobb unit values for thesamples.10.4 Average, then record the replicate results.11. Precision and Bias911.1 PrecisionInterlaboratory Test ProgramAn inter-laboratory study of Hardboard Siding “Cobb Ring” waterpermeability was conducted in accordance with Practice E 691in seve
38、n laboratories with five materials, with each laboratoryobtaining seven test results for each material (see Table 1).11.1.1 The terms repeatability limit and reproducibility limitin Table 1 are used as specified in Practice E 177.11.1.2 Some of the deviations in Table 1 are believed due tothe concer
39、n expressed in 4.3, 9.1.3 and 9.1.4. This will beaddressed in a future round robin.11.2 BiasSince there is no accepted reference material,method, or laboratory suitable for determining the bias for theprocedure in this test method, no statement on bias is beingmade.12. Keywords12.1 absorption; coate
40、d hardboard; Cobb ring; compositewood productsASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, a
41、nd the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revis
42、ion of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you s
43、houldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be ob
44、tained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).9Supporting data are available from ASTM Headquarters. Request RR:D011093.TABLE 1 PrecisionMaterial24-hAverage,gm/100 in.2Repeatability,StandardDeviation, SrReproducibility,StandardDeviation,SRRepeatabilityLimit, YReproducibilityLimit, RE 5.225 0.851 0.880 2.38 2.46C 6.629 1.780 1.917 4.98 5.37A 7.185 2.256 2.398 6.32 6.72D 14.020 1.055 1.596 2.95 4.47B 20.545 1.146 2.117 3.21 5.93D 5795 95 (2000)3
