ASTM D7836-13(R2020) pdf free download

ASTM D7836-13(R2020) pdf free download.Standard Test Methods for Measurement of Yield Stress of Paints, Inks and Related Liquid Materials
1. Scope
1.1 These test methods cover three approaches for determin- ing yield stress values of paints, inks and related liquid materials using rotational viscometers. The first method uses a rotational viscometer with coaxial cylinder, cone/plate, or plate/plate geometry. The second method uses a rheometer operating in controlled stress mode with similar geometries. The third method uses a viscometer with a vane spindle. 1.2 A non-rotational technique, the falling needle viscom- eter (FNV), also can be used to measure yield stress values in paints, 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 the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Summary of Test Methods
4.1 Test Method A uses a viscometer with coaxial cylinder, cone/plate, or plate/plate geometry running a several different low rotational speeds. The materials is sheared at each speed and a shear stress value is measured. By plotting shear stress versus shear rate, a dynamic yield stress value is determined by extrapolating the data curve to zero shear rate. “Dynamic” indicates that the material has been allowed to flow and that the yield stress value is mathematically calculated by using a best-fit line through the measured data points. 4.2 Test Method B uses a controlled stress rheometer to determine a yield stress value. This can be done more readily with cone/plate or plate/plate geometry, but can also be accomplished with coaxial cylinder geometry. The rheometer applies a stress ramp to the material, starting at zero and increasing to a preset stress value above the yield stress of the material. As the torque applied to the spindle increases, the spindle will start to move when the yield stress in the material is exceeded. The stress reading at the onset of spindle rotation is the yield stress value for the material. 4.3 Test Method C uses a rotational viscometer or rheometer with a vane spindle immersed in the material. The vane spindle is rotated slowly at a fixed speed and the torque value is recorded continuously. The yield stress value is determined when the torque value reaches a maximum.
9. Procedure
9.1 Test Method A determines the yield stress of a material mathematically using data from a rotational viscometer. Yield stress may be determined at several discrete temperatures if necessary. Allow the specimen to equilibrate to the desired temperature before proceeding with the test. Coaxial cylinder, cone/plate, or plate/plate geometry may be used to measure shear stress versus shear rate. Ayield stress value is determined by extrapolating the data for the measured shear stress values to zero shear rate. A best fit line applied to the accepted mathematical procedure for determining the stress value at which the material yields. 9.2 Test Method B determines yield stress based on a controlled stress ramp being applied to a material. Yield stress values may be determined at several discrete temperatures if necessary. Cone/plate or plate/plate geometry is typically used because the specimen undergoes minimal disturbance when it is placed on the plate. When using coaxial cylinder geometry, the spindle is immersed causing disturbance to the material structure; therefore, time must be allowed for the specimen to reestablish its structure before proceeding with the test. The smaller sample size required for cone/plate or plate/plate geometry permits rapid determination of the yield stress value because temperature equilibration of the specimen is quickly established. The stress ramp applied to the material goes from zero to a preselected maximum value which exceeds the yield stress of the material. The rate at which the stress ramp is applied may have an effect on the measured yield stress value. The torque applied to the spindle gradually increases until rotation of the spindle commences. Once the spindle starts to rotate, the torque value at that instant is converted into a yield stress value.