ASTM D4683 for measuring viscosity at high shear rate and high temperature
ASTM D4683 standard test method for measuring viscosity at high shear rate and high temperature by tapered bearing simulator
6. Apparatus
6.1 Tapered Bearing Simulator-Viscometer (Fig. 1) - a viscometer consisting of a synchronous two-speed motor that drives a slightly tapered bearing in a matched stator (Fig. 2).
6.1.1 The motor and rotor are raised and lowered by means of a platform, which, in turn, is cantilevered from an elevator device. The gap between the rotor and stator is controlled by adjustment of the platform height.
6.1.2 The resistive force of the test oil is transferred to the load cell by the turntable on which the motor sits. This turntable has a projecting arm on which is mounted a contact ball. The rotor is spun by the motor at a constant speed of 50 or 60 r/s depending on the frequency of the alternating current. When the rotor encounters viscous resistance, the reactive force presses the ball against the platen of the load cell to register the resistance given by the viscosity of the oil.
NOTE 1 - An automated system for the TBS Viscometer has been developed employing all the steps in the procedure, and it was used for some of the round robin data generated for this test method.
6.2 Console - The console shown in Fig. 3 contains the power source for the load cell, thermoregulator circuit, heating coil, and motor. It also contains the circuitry for regulating and monitoring the temperature of the oil in the test cell, as well as the amplifier and digital readout of the load cell response.
NOTE 2 - The thermoregulator circuit of the TBS Viscometer has evolved as improvements have been made in the solid-state temperature controller and heater. To achieve the five-minute analysis time specified in this test method requires a late model solid-state controller with automatic reset coupled to a thermofoil heater with small heat inertia or a fast-responding thermoregulated oil bath.
6.3 Air Circulation System - A flow of dry compressed air is passed around the stator to provide supplementary cooling when testing fluids of higher viscosity (greater than approximately 9 cP). Ports are provided in the stator housing for the circulation of compressed air.
6.4 Syringe, glass or polypropylene (in the latter case, use a non-lubricated plunger), equipped with Luer needle lock to fit the tip of the filling tube for injection of test oil into the annulus between the rotor and the stator.
6.5 Filter - A filter is used on the syringe to remove particles capable of damaging the rotor/stator cell.
7. Materials
7.1 Calibration Oils are Newtonian oils of known kinematic viscosity and density at 150°C. The defined viscosities in centipoise (mPa•s) are calculated by multiplying the kinematic viscosity in centistokes by the density in grams per cubic centimetre. Approximate viscosities for the calibration oils are listed in Table 1. Certified viscosities are supplied with each oil.
7.2 Idling Oil - See 3.2.3.
7.3 Non-Newtonian Reference Oil is essential in setting the rotor/stator gap to 1 x 10(6) s(-1) shear rate. An approximate viscosity of a suitable non-Newtonian reference oil is given in Table 1. The certified viscosity at 1 x 10(6) s(-1) and 150°C is supplied with the oil and is matched to the viscosity of reference fluid R-400 (see Table 1).
8. Sampling
8.1 A representative sample of test oil is obtained. When used oils are evaluated, it is desirable to change the filter attached to the syringe periodically to reduce injection pressure caused by particle buildup on the filter surface.
NOTE 3 - Precision for used oils has not been determined.
9. Preparation of the Apparatus
9.1 Directions for preparation of the tapered bearing simulator-viscometer and console are supplied with the equipment. One of the most important directions to be followed is the alignment of the rotor/stator before initial use of the viscometer.
9.2 With continuous use, a weekly room-temperature flush of the rotor/stator cell is recommended following directions in 11.4.
