1、Designation: D7836 13Standard Test Methods forMeasurement of Yield Stress of Paints, Inks and RelatedLiquid Materials1This standard is issued under the fixed designation D7836; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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 These test methods cover three approaches for determin-ing yield stress values of paints, inks and related liqui
3、dmaterials using rotational viscometers. The first method uses arotational viscometer with coaxial cylinder, cone/plate, orplate/plate geometry. The second method uses a rheometeroperating in controlled stress mode with similar geometries.The third method uses a viscometer with a vane spindle.1.2 A
4、non-rotational technique, the falling needle viscom-eter (FNV), also can be used to measure yield stress values inpaints, inks and related materials. See Test Methods D5478,Test Method D, Yield Stress Determination for details.1.3 This standard does not purport to address all of thesafety concerns,
5、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 use.2. Referenced Documents2.1 ASTM Standards:2D3925 Practice for Sampling Liquid Paints and
6、 RelatedPigmented CoatingsD5478 Test Methods for Viscosity of Materials by a FallingNeedle Viscometer3. Terminology3.1 vane spindle, nspindle in which several (4 to 6)rectangular vanes are attached to the shaft giving the appear-ance of a cross or star when viewed from the end.3.1.1 DiscussionA vane
7、 spindle can be immersed in aspecimen without destroying the shear-sensitive structure.3.2 yield stress, nthe critical stress at which a materialgoes from being a deformable solid to showing fluid-likebehavior.3.2.1 DiscussionExamples of such fluids include manypaints and pigment pastes and certain
8、food materials such asketchup.4. Summary of Test Methods4.1 Test Method A uses a viscometer with coaxial cylinder,cone/plate, or plate/plate geometry running a several differentlow rotational speeds. The materials is sheared at each speedand a shear stress value is measured. By plotting shear stress
9、versus shear rate, a dynamic yield stress value is determined byextrapolating the data curve to zero shear rate. “Dynamic”indicates that the material has been allowed to flow and that theyield stress value is mathematically calculated by using abest-fit line through the measured data points.4.2 Test
10、 Method B uses a controlled stress rheometer todetermine a yield stress value. This can be done more readilywith cone/plate or plate/plate geometry, but can also beaccomplished with coaxial cylinder geometry. The rheometerapplies a stress ramp to the material, starting at zero andincreasing to a pre
11、set stress value above the yield stress of thematerial. As the torque applied to the spindle increases, thespindle will start to move when the yield stress in the materialis exceeded. The stress reading at the onset of spindle rotationis the yield stress value for the material.4.3 Test Method C uses
12、 a rotational viscometer or rheometerwith a vane spindle immersed in the material. The vane spindleis rotated slowly at a fixed speed and the torque value isrecorded continuously. The yield stress value is determinedwhen the torque value reaches a maximum.5. Significance and Use5.1 The yield stress
13、of a material is a measure of the amountof force required to initiate movement of that material in apipe, through a pump, or from nozzle. The yield stress alsocharacterizes the ability of the material to maintain particles insuspension. Along with viscosity measurements, yield stressmeasurements hav
14、e been useful in establishing root causes offlow problems such as excessive orange peel and sagging andin explaining resistance to such problems. After a coating has1These test methods are under the jurisdiction of ASTM Committee D01 onPaint and Related Coatings, Materials, and Applications and are
15、the directresponsibility of Subcommittee D01.24 on Physical Properties of Liquid Paints andPaint Materials.Current edition approved June 1, 2013. Published July 2013. DOI: 10.1520/D7836-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servic
16、eastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1been applied, flow and leveling tends to be inversely rela
17、ted toyield stress and sag resistance tends to be directly related toyield stress. The ability of an automotive basecoat to keepaluminum and/or mica flakes oriented has been related to yieldstress (direct relationship).6. Apparatus6.1 Multi-speed Rotational Viscometerwith coaxial (con-centric) cylin
18、der (either built-in or as an attachment), cone/plate, or plate/plate geometry or with a vane spindle.6.2 Controlled Stress Rheometerwith cone/plate or plate/plate geometry.7. Sampling7.1 Take a representative sample of the product to be testedin accordance with Practice D3925. Minimal disturbance t
19、o thesample is important since the yield stress property is indicativeof the materials physical structure when at rest.8. Preparation of Specimen8.1 Fill the coaxial cylinder with the proper amount ofmaterial. This is dependent on the spindle and chambercombination in use. Alternatively, for cone/pl
20、ate or plate/plateplace the proper amount of material on the plate.8.2 Allow material to equilibrate to temperature if required.8.3 For testing with vane spindle, insert the vane directlyinto the material. Allow the material to equilibrate to tempera-ture beforehand if required.8.4 The sample being
21、tested experiences some handlingprior to the start of the test. Therefore, there may be someadverse impact on the specimen structure that could affect thetest results. Keeping to a specific step by step procedure forhandling of specimens is very important in order to achieverepeatable results.9. Pro
22、cedure9.1 Test Method A determines the yield stress of a materialmathematically using data from a rotational viscometer. Yieldstress may be determined at several discrete temperatures ifnecessary. Allow the specimen to equilibrate to the desiredtemperature before proceeding with the test. Coaxial cy
23、linder,cone/plate, or plate/plate geometry may be used to measureshear stress versus shear rate.Ayield stress value is determinedby extrapolating the data for the measured shear stress valuesto zero shear rate. A best fit line applied to the acceptedmathematical procedure for determining the stress
24、value atwhich the material yields.9.2 Test Method B determines yield stress based on acontrolled stress ramp being applied to a material. Yield stressvalues may be determined at several discrete temperatures ifnecessary. Cone/plate or plate/plate geometry is typically usedbecause the specimen underg
25、oes minimal disturbance when itis placed on the plate. When using coaxial cylinder geometry,the spindle is immersed causing disturbance to the materialstructure; therefore, time must be allowed for the specimen toreestablish its structure before proceeding with the test. Thesmaller sample size requi
26、red for cone/plate or plate/plategeometry permits rapid determination of the yield stress valuebecause temperature equilibration of the specimen is quicklyestablished. The stress ramp applied to the material goes fromzero to a preselected maximum value which exceeds the yieldstress of the material.
27、The rate at which the stress ramp isapplied may have an effect on the measured yield stress value.The torque applied to the spindle gradually increases untilrotation of the spindle commences. Once the spindle starts torotate, the torque value at that instant is converted into a yieldstress value.9.3
28、 Test Method C uses a viscometer or rheometer with avane spindle to measure yield stress. Yield stress values may bedetermined at several discrete temperatures if necessary byconditioning the material appropriately. The advantage of thismethod is that the material can be tested in the container inwh
29、ich it is packaged, such as a can of paint or ink. The vanespindle is immersed directly into the material with minimaldisturbance to the sample. The spindle is rotated at a slow fixedrotational speed. Torque is measured continuously until amaximum value is achieved. The yield stress is calculatedbas
30、ed on the maximum torque value and the geometry of thevane spindle used. The choice of low rotational speed mayaffect the measured yield stress value.Afaster speed may resultin a higher yield stress value.10. Report10.1 Report the following information:10.1.1 Reference to this test method and the vi
31、scometer orrheometer model and the spindle geometry,10.1.2 Type and identification of the product under test,10.1.3 Test method used,10.1.4 The control parameters for the instrument such asspindle speed (shear rate) or spindle stress (shear stress),10.1.5 If Test Method C was used, report the rate a
32、t whichthe stress ramp was applied,10.1.6 The measured yield stress value, and10.1.7 Temperature of the specimen.11. Precision and Bias11.1 PrecisionAt this time, no precision data is available.Interlaboratory testing for the purpose of developing a preci-sion statement will be attempted. Repeatabil
33、ity (using freshspecimens from a given sample) will be possible to establish,but meaningful Reproducibility is not likely to result from suchtesting. This is because yield stress values of materials vary somuch depending on the handling, storage and shear history ofthe sample. Because of this, few i
34、f any comparisons of yieldstress for a given material are ever made between laboratories.11.2 BiasSince there is no accepted reference materialsuitable for determining the bias values for the procedures inthis standard, bias has no and will not be determined.12. Keywords12.1 coaxial cylinder geometr
35、y; cone/plate geometry; con-trolled stress rheometer; rotational speed; rotational viscom-eter; shear rate; shear stress; vane spindle geometry; yieldstressD7836 132ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this
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38、nsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake 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, Wes
39、t Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained 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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D7836 133
