ASTM D6791 Test Method for Determination of Grain Stability of Calcined Petroleum Coke
7. Apparatus
7.1 Analytical Balance, accurate to +/- 0.1 g.
7.2 Rifflers, with hoppers and closures.
7.3 Wire Sieves, 8 mm (5/16 in.) and 4 mm (5 mesh), meeting Specification E11.
7.4 Laboratory Vibration Mill, having two grinding vessels, each filled with 1 kg ofclean, hard steel balls, diameter 10 mm +/- 0.4 mm. The main features of the mill are shown in Figs. 1-5.
7.4.1 The mill and drive motor are mounted on a common base plate. The grinding vessels are installed in the body of the mill, which is supported by four soft, flat springs. The spring suspension system is designed to allow the machine to be operated without any fastenings or anchorage. The grinding vessels are secured by adjustable straps which have a quick-release catch. The oscillator is supported on a bearing, fitted to the body of the mill, and is driven by the motor by way of a special clutch and a hollow flexible shaft.
7.4.2 The peak-to-peak amplitude of the vibration shall be 4 mm +/- 0.5 mm. A reference disc is fitted to the front of the machine to measure the amplitude of vibration.
7.4.3 The motor shall be capable of 1450 r/min to 1470 r/min. The motor may be set up for 50 Hz rather than 60 Hz power. A tachometer can be used to verify that the motor is the specified r/min. The motor speed can be regulated with a dc speed controller to adjust it to the specified r/min. The bearing housing is rigidly connected to the bearings. The shaft rotates inside the bearings with two steel imbalance discs attached and is connected to the motor by way of the clutch. The imbalance discs are shown in Fig. 4.
7.4.4 The imbalance discs rotate eccentrically and the entire oscillating mass follows with a phase lag of 180°, supported by the springs. Each grinding vessel (see Fig. 5) has a total volume of 1 L and an effective volume of 0.3 L. It is closed by a lid with a rubber sealing ring. The lid is held in place by a clamp fitted with a wing nut.
7.4.5 The electric motor is linked to a timer switch having a precision of +/- 2 s.
8. Sample Preparation
8.1 For recommended practice for obtaining, handling, and preparing coke samples, refer to Practices D346, D2013, D2234/D2234M, D6969, D6970, and ISO 6375. Do not precrush the sample. Sieve the sample to collect 200 g of coke of grain size between 4 mm and 8 mm.
