1. Scope
1.1 This test method covers the prediction of the borderline pumping temperature (BPT) of engine oils through the use of a 16 h cooling cycle over the temperature range from 0 °C to -40 °C. The precision is stated for temperatures from -34 °C to -15 °C.
1.2 Applicability to petroleum products other than engine oils has not been determined.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3.1 Exception - This test method uses the SI based unit of milliPascal second (mPa•s) for viscosity, which is equivalent to centipoise (cP).
1.4 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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
E563 Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
E644 Test Methods for Testing Industrial Resistance Thermometers
E1137 Specification for Industrial Platinum Resistance Thermometers
E2877 Guide for Digital Contact Thermometers
2.2 ISO Standards:
ISO 17025 General Requirements for the Competence of Testing and Calibration Laboratories
ISO Guide 34 General Requirements for the Competence of Reference Material Producers
3. Terminology
3.1 Definitions:
3.1.1 apparent viscosity, n - the determined viscosity obtained by use of this test method.
3.1.2 Digital Contact Thermometer (DCT), n - an electronic device consisting of a digital display and associated temperature sensing probe.
3.1.2.1 Discussion - This device consists of a temperature sensor connected to a measuring instrument; this instrument measures the temperature-dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output, or display of the temperature, or both. This device is sometimes referred to as a digital thermometer.
NOTE 1 - Portable electronic thermometers (PET) is an acronym sometimes used to refer to a subset of the devices covered by this definition.
3.1.3 Newtonian oil or fluid, n - an oil or fluid that at a given temperature exhibits a constant viscosity at all shear rates or shear stresses.
3.1.4 non-Newtonian oil or fluid, n - an oil or fluid that at a given temperature exhibits a viscosity that varies with changing shear stress or shear rate.
3.1.5 shear rate, n - the velocity gradient in fluid flow. For a Newtonian fluid in a concentric cylinder rotary viscometer in which the shear stress is measured at the inner cylinder surface (such as the apparatus being described), and ignoring any end effects, the shear rate is given as follows:
where:
γ = shear rate at the surface of the rotor in reciprocal seconds, s(-1),
Ω = angular velocity, rad/s,
Rs = stator radius, mm,
Rr = rotor radius, mm, and
t = time in seconds for one revolution of the rotor.
For the specific apparatus being described in 6.1.1,
3.1.6 shear stress, n - the motivating force per unit area for fluid flow. Area is the area under shear. For the rotary viscometer being described, the rotor surface is the area under shear.
where:
Tr = torque applied to rotor, N•m,
M = applied mass, g,
Ro = radius of the shaft, mm,
Rt = radius of the thread, mm,
τ = shear stress at the rotor surface, Pa, and
h = height of the rotor, mm.
For the dimensions given in 6.1.1,
3.1.7 viscosity, n - the ratio between the applied shear stress and rate of shear. It is sometimes called the coefficient of dynamic viscosity. This value is thus a measure of the resistance to flow of the liquid. The SI unit of viscosity is the pascal second (Pa•s).
3.2 Definitions of Terms Specific to This Standard:
3.2.1 borderline pumping temperature, n - the maximum temperature at which the critical yield stress or critical viscosity occurs, whichever is the higher temperature.
3.2.2 calibration oils, n - those oils for establishing the instrument's reference framework of apparent viscosity versus speed from which the apparent viscosities of test oils are determined.
3.2.3 critical viscosity, n - the maximum viscosity at a defined shear rate to allow adequate flow of oil to the oil pump in an automotive engine. A higher viscosity can cause failure to maintain adequate oil pressure through the limiting of flow through the oil screen or oil inlet tubes.
3.2.4 critical yield stress, n - the maximum yield stress that allows oil to flow to the inlet oil screen in an automotive engine. With a higher yield stress, air may be drawn into the pump and cause failure to maintain adequate oil pressure through air-binding of the pump.
3.2.5 test oil, n - any oil for which the apparent viscosity and yield stress are to be determined by use of the test method under description.
3.2.6 yield stress, n - the shear stress required to initiate flow. For all Newtonian fluids and some non-Newtonian fluids, yield stress is zero. Some engine oils have a yield stress that is a function of their low-temperature cooling rate, soak time, and temperature.