1、Designation: D5795 95 (Reapproved 2008)D5795 16Standard Test Method forDetermination of Liquid Water Absorption of CoatedHardboardWood and Other Composite Wood BasedProducts Via“Cobb Ring” Apparatus1This standard is issued under the fixed designation D5795; the number immediately following the desig
2、nation indicates 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is intended to
3、 serve as a means for measurement of liquid water that passes through a wetted paint film,and which is subsequently absorbed and retained by the underlying wood or wood-based substrate. Alternative techniques for theuse of the “Cobb Ring” apparatus are described.1.2 The values stated in SI units are
4、 to be regarded as the standard. The values given in parentheses are for information only.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practic
5、es and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D9 Terminology Relating to Wood and Wood-Based ProductsD16 Terminology for Paint, Related Coatings, Materials, and ApplicationsD1193 Specification for Reagent WaterD5235 Test Method fo
6、r Microscopic Measurement of Dry Film Thickness of Coatings on Wood ProductsD6132 Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an UltrasonicCoating Thickness GageE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE691 Pract
7、ice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Cobb unit (C.U.), nThethe weight of distilled water absorbed by the underlying wood substrate in grams per 645 cm2(100 in.2) of surface area (
8、discounting additional areas contributed by texturing or grooves) per 24-h time period.3.1.2 Cobb unit (C.U.) factor, na dimensionless mathematical term which, for a given ring size, may be multiplied times theweight change after 24 h to calculate the Cobb unit value.3.1.2.1 DiscussionThe C.U. facto
9、r is calculated as follows:SI UnitsC.U.Factor5 100Area ring!5100pir 2 (1)1 This test method is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.52 on Factory Coated Wood Products.Current editio
10、n approved June 1, 2008July 15, 2016. Published June 2008October 2016. Originally approved in 1995. Last previous edition approved in 20002008 asD5795 - 95 (2000).D5795 95 (2008). DOI: 10.1520/D5795-95R08.10.1520/D5795-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contac
11、tASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standardsstandards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes h
12、ave been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official d
13、ocument.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1C.U.Factor 5 64516RingAreamm2! 564516pir 2 (1)Imperial UnitsC.U.Factor 5 100RingAreain.2!5100pir2 (2)where:r = radius, mm (in.)where:r = radiusFor example, for 101.6-mm (4-in.) 1
14、00 mm (4 in.) inside diameter ring.oror50C.U.Factor5 1003.142!2 5 10012.5657.96 (2)mm (2 in.) internal radius ring:C.U.Factor 5 645163.1450!2 2 645167850 28.22 (3)3.1.3 composite wood based products, nboards or other form of structured or decorative materials manufactured from woodfibers, flakes or
15、strands or veneers and various resin binders.binders otherwise known as engineered wood products or woodcomposite.3.1.3.1 DiscussionOne example is hardboard.3.1.4 hardboarda generic term for a panel manufactured primarily from interfelted lignocellulose fibers consolidated underheat and pressures in
16、 a hot press to density of at least 31 lbs (13.95 kg) per cubic foot (cubic metre).34. Summary of Test Method4.1 Suitable size rings of metal or plastic are adhered or clamped to the flat, coated surface of composite wood panels to betested.4.2 The assembly is equilibrated at a constant temperature
17、and humidity and weighed.4.3 The weighed assembly is placed on horizontal surface3 surface in a controlled temperature and humidity room orenvironmental chamber. Water is placed in the ring and left in contact with the board face for 24 h.4.4 After 24 h the remaining water is removed from the ring,
18、the assembly blotted dry and reweighed.4.5 The increase in weight of the assembly due to water uptake is calculated by simple subtraction and then converted to Cobbunits through the use of the C.U. factor (see 3.1.2).5. Significance and Use5.1 This test method provides a simple quantitative measure
19、of water absorption by coated composite wood products.Althoughprimarily used to evaluate factory-primed composite wood products, this test method may be of service for other wood substratesand coating systems. wood or wood based products.5.2 This test method has demonstrated utility for composite wo
20、od siding wood or wood based products ranging in thicknessfrom approximately 6.356 to 25.425 mm (14 to 1 in.). Extension of this test method to wood substrates of other types and thicknessmay be useful.5.3 Conditioning of substrate, coated sample preparation, application method, dry film thickness,
21、cure conditions, and numberof replicate specimens should be agreed upon between the purchaser and the supplier of the coating material.5.4 Such measurements are used as indicators or predictors of the anticipated performance of coated composite wood wood orwood based products during exterior exposur
22、e. They may be used for developmental evaluation of coatings, substrates, or both.They may also be useful for quality control or monitoring of the production of coated composite wood wood and wood basedproducts.3 The specification of a solid, continuous horizontal surface or a discontinuous (wire ra
23、ck, expanded metal, etc.) is required. Surface must be consistent from laboratoryto laboratory since this can influence the rate of evaporation of moisture and, thus, retention of moisture and Cobb values.D5795 1626. Apparatus6.1 Rings, may be cut from stainless steel, aluminum or PVC pipe. The ring
24、 diameter can be any size, but useful results havebeen obtained with rings of 101.6 mm (4 in.) or largerplastic pipes. To avoid damage to the test assembly caused by warping ofthe wooden substrate due to water inside diameter, wall thickness of 9.53 mm (absorption on one side only, it is recommended
25、38in.) and height of 25.4 mm (1 to use flexible rings. Measure the rings diameter to the nearest 1 mm (0.040 in.).NOTE 1The ring diameter can be any size, but useful results have been obtained with rings of 102 mm (4 in.) or larger inside diameter, wall thicknessof 10 mm (38 in.) and height of 25 mm
26、 (1 in.). Rings of 100 to 254 mm (4 to 10 in.) are commonly used. If suitable flexible rings cannot be purchased,they can be prepared in the laboratory. To prepare flexible rings, an appropriate film made from a semi-flexible non-absorbent plastic (for example, surfacetreated polyethylene film with
27、thickness about 0.10 mm (0.004 in.) could be used. Wrap the film around on a rigid pipe of the required diameter, and heatweld or glue the wrapped film along its edge. Subsequently cut the pipe with wrapped and welded polyethylene film into suitable rings.6.2 Environmental Chamber, set atcapable of
28、maintaining 23 6 2C (73 6 4F) and 50 6 5 % relative humidity, or other agreedupon options.6.3 Saw, suitable for cutting of samples.6.4 Caulk Gun or Applicator, or, a clamp and gasket device for holding the ring tightly against the board is needed.6.5 Balance, with sufficient capacity (typically 400
29、g) and 0.01-g accuracy.7. Materials7.1 Butyl or Silicone Caulk, which has been determined not to contribute to assembly weight change through absorption ofwater or interaction with the coating.7.2 Distilled Water, (see Specification D1193).7.3 Test Boards, appropriately identified, coated or uncoate
30、d, cut to a square size that is 25.4 mm (1 in.) greater than the ringdiameter. A minimum of three replicates is recommended.7.4 Control Samples, coated or uncoated without rings will also be required. These will be used to assess the degree ofequilibration that is achieved.8. Hazards8.1 Use saws wit
31、h goggles, dust mask, and proper machine safeguards to prevent injury.8.2 Caulking compounds may be flammable and contain toxic solvents. See manufacturersmanufacturers instructions forproper use and disposal.9. Procedure9.1 Measure and record the coating thickness on the samples designated for test
32、ing, including thickness of individual coats (ifdistinguishable). Follow procedures described in Test Methods D5235 or D6132 (if applicable).9.2 Sealing of Rings to the Coated Face of the Samples:9.2.1 A continuous bead of caulk is applied to one edge of the ring. The caulked side of the ring is the
33、n attached to the samplewith gentle pressure and a slight twisting motion; to maintain an accurate and uniform test area, only minor caulk “squeeze-out”should occur inside of the ring. Carefully wipe out remove this minor caulk“ squeeze-out”caulk “squeeze-out” to prevent errorsin later calculations.
34、 Care must be taken not to smear caulk over the coating surface to avoid invalidating results. Consider the useof caulks with contrasting colors to aid in verification of removal. If flexible rings are used, they should be supported from theinside by a segment of rigid pipe with the appropriate diam
35、eter during the sealing process. Flexible rings with a wall thickness ofless than 0.5 mm (0.20 in.) do not require sealant on the edge against the coating but can be anchored entirely by the caulk filledaround the outside at the base of the ring. After the caulk cures, remove the supporting ring.9.2
36、.2 Alternatively, the assembly may be produced with a clamp and gasket device. Satisfactory results can also be obtainedfrom clamp and gasket devices that are of self design and locally produced by any machine shop.9.2.3 To enhance reproducibility, do not generate data by a combination of the caulk
37、procedure and the clamp and gasketprocedure.9.2.4 Also, for improved reproducibility, all rings must be of the same nominal internal diameter.9.3 Equilibration:9.3.1 Allow the samples with rings and controls without rings to equilibrate for seven days at 23 6 2C (73 6 4F) and 50 65 % relative humidi
38、ty. If flexible rings are used, be sure that the supporting rings are removed before testing after sealant cure.9.4 Initial Weighing:9.4.1 Weigh (grams) the controls and samples with rings to the nearest 0.01 g; record the weight.9.5 Fill each ring with the volume of distilled water required to achi
39、eve a depth of 12.713 6 3.23 mm (12 6 18 in.) of distilledwater.D5795 1639.6 Store test assemblies on a level surface3at so that the water depth is maintained at 13 6 3 mm (12 6 18the in.) over the entiretest area at the same conditions used for equilibrating the panels.9.7 Final Weighing:9.7.1 Afte
40、r 24 h, pour out the water and blot the surface inside the ring completely dry with a soft paper towel. Immediatelyweigh (grams); record the new weight of the samples with rings.9.7.2 After all measurements from 9.6.19.7.1 have been completed, weigh (grams) and record the weights of the control boar
41、dswithout rings. Compare the weights with the initial weights. If the weight change of the control boards is more than 20 % of theweight change of the test boards, the absolute values of the test results may be questionable.9.8 Additional Procedures:9.8.1 Caulked rings can be removed from the coated
42、 boards by pulling the ring from the board and cleaning in lacquer solvent.9.8.2 For textured boards without a groove in the coated panel, apply additional caulk to the outside of the ring to get asatisfactory seal after attaching the ring to the coated board.9.8.3 For boards with a groove in the co
43、ated board, attach the ring to the board so that at least one groove length will be thesame as the diameter of the ring. Apply extra caulk in the groove at the appropriate spot before attaching the ring in order to geta good seal. Extra caulk may have to be applied in the groove outside the ring aft
44、er attaching the ring in order to get a good seal.9.8.4 During equilibration and testing of the boards with rings, store the boards test side up and single high on a flat surfacethat is impervious to moisture.9.8.5 If an environmental chamber is used, the control boards with ring assemblies must not
45、 be stacked upon each other. It isrecommended that the control boards and ring assemblies be stored coated side up and single high on wire racks at least 50.850mm (2 in.) above or below adjacent rings. Care must be taken so as not to overload the humidity chamber with rings containingwater.10. Calcu
46、lations10.1 Calculate and record the weight change by subtraction of the initial weight of 9.3.19.4.1 from the final weight of 9.6.19.7.1.10.2 Calculate the Cobb unit (C.U.) factor for the ring sizes used (see 3.1.2.1).10.3 Multiply the C.U. factor times the weight change recorded in 10.1.110.1 and
47、recordcalculate the Cobb unit values for thesamples.10.4 Average, then record the replicate results.11. Report11.1 Description of the substrate tested, including thickness, type, density and surface characteristics. In the case of wood,include a description of the wood species, surface roughness and
48、 type of grain (flat or edge).11.2 Type of coating applied, including manufacturer.11.3 Method of coating application, including number of coats, drying or curing conditions and conditioning (if any).11.4 Coating thickness, including thickness of the individual coats (if distinguishable).11.5 Intern
49、al diameter of the Cobbs rings and number of specimens tested.11.6 Calculated water absorption in Cobb units.12. Precision and Bias412.1 PrecisionInterlaboratory Test ProgramAn interlaboratory study of Hardboard Siding “Cobb Ring” water permeabilitywas conducted in accordance with Practice E691 in seven laboratories with five materials, with each laboratory obtaining seventest results for each material (see Table 1).4 Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D01-1093. Cont
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