1、Designation:D579516Standard Test Method forDetermination of Liquid Water Absorption of Coated Woodand Wood Based Products Via“Cobb Ring”Apparatus1This standard is issued under the fixed designation D5795;the number immediately following the designation indicates the year oforiginal adoption or,in th
2、e 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 serve as a means formeasurement of liquid water that passes
3、through a wetted paintfilm,and which is subsequently absorbed and retained by theunderlying wood or wood-based substrate.Alternative tech-niques for the use of the“Cobb Ring”apparatus are described.1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses ar
4、e 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-bility of regulatory limitations prior to
5、use.2.Referenced Documents2.1 ASTM Standards:2D9 Terminology Relating to Wood and Wood-Based Prod-uctsD16 Terminology for Paint,Related Coatings,Materials,andApplicationsD1193 Specification for Reagent WaterD5235 Test Method for Microscopic Measurement of DryFilm Thickness of Coatings on Wood Produc
6、tsD6132 Test Method for Nondestructive Measurement of DryFilm Thickness of Applied Organic Coatings Using anUltrasonic Coating Thickness GageE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a T
7、est Method3.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.
8、1.2 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:SI UnitsC.U.Factor 564516RingAreamm2!564516r2(1)Imperial UnitsC.U.F
9、actor 5100RingAreain.2!5100r2(2)where:r=radius,mm(in.)For example,for 100 mm(4 in.)inside diameter or 50 mm(2 in.)internal radius ring:C.U.Factor 5645163.1450!226451678502 8.22(3)3.1.3 wood based products,nboards or other form ofstructured or decorative materials manufactured from woodfibers,flakes
10、or strands or veneers and various resin bindersotherwise known as engineered wood products or woodcomposite.4.Summary of Test Method4.1 Suitable size rings of metal or plastic are adhered orclamped to the flat,coated surface of composite wood panels tobe tested.1This test method is under the jurisdi
11、ction of ASTM Committee D01 on Paintand Related Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.52 on Factory Coated Wood Products.Current edition approved July 15,2016.Published October 2016.Originallyapproved in 1995.Last previous edition approved in 2008 as
12、 D5795 95(2008).DOI:10.1520/D5795-16.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,
13、100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.2 The assembly is equilibrated at a constant temperatureand humidity and weighed.4.3 The weighed assembly is placed on horizontal surface3in a controlled temperature and humidity room or environmen-tal chamber.Water i
14、s placed in the ring 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.4.5 The increase in weight of the assembly due to wateruptake is calculated by simple subtraction and then convertedto Cobb units th
15、rough the use of the C.U.factor(see 3.1.2).5.Significance and Use5.1 This test method provides a simple quantitative measureof water absorption by coated wood or wood based products.5.2 This test method has demonstrated utility for wood orwood based products ranging in thickness from approximately6
16、to 25 mm(14to 1 in.).5.3 Conditioning of substrate,coated sample preparation,application method,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 wood or wood basedproducts during exterior exposure.They may be used fordevelopmental evaluation of coatings,substrates,or both.Theymay also be useful fo