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Stacking Density Of Diamond Abrasives

May 17,2023

The stacking density of superhard abrasives is the most commonly used physical quantity to represent the filling characteristics of powder like materials. It is a comprehensive reflection of the physical properties of superhard abrasives, such as density, particle shape, particle surface state, and particle size composition. It is a universal method internationally used to test the physical properties of the product. It is of great significance in controlling the quality of superhard abrasives, classifying varieties, grades, and mold manufacturing.

1. Definition of bulk density

Stacking density refers to the weight of abrasive particles contained in a unit volume of air under natural accumulation, in g/cm ³。
The quality inspection standards for superhard abrasives in China are basically consistent with international standards and the standards of major advanced industrial countries in the world. The equivalent national standard diamond bulk density measurement method is adopted, and the “JB/T 3584-1999 Method for Measuring Bulk Density of Superhard Abrasives” has been developed. This inspection method is suitable for measuring the bulk density of 16/20~325/400 grit diamond.

2. Determination of bulk density

The method for measuring the stacking density of superhard abrasives is to remove static electricity from dry abrasive particles, which flow out of a funnel without vibration, fill a 10ml volumetric cylinder with a fixed height, and scrape off the remaining material with a brass scraper to measure the mass per unit volume.

(1) Experimental conditions

The experiment should be conducted under the following atmospheric conditions: relative humidity: 45%~55%; Temperature: 20-24 ℃.

(2) Preparation of test specimens

The sample to be tested shall be sampled according to the latest standard method, reduced to 25 ± 0.1g, placed in a nickel crucible of about 30ml, dried in an oven at 110 ℃± 5 ℃ for 1 hour, and then taken out. It shall be cooled to room temperature in a dryer and stored for at least 4 hours to adapt to the laboratory atmosphere and eliminate static electricity.

(3) Main measuring instruments

(4) Calibration of measuring cylinder volumeAny measuring cylinder that is newly made or has been used for too long should be calibrated for its volume. The calibration method is to mix a dry empty measuring cylinder with a piece slightly larger than 24 × Weigh the 24mm glass plates together, then cover the glass plates on the measuring cylinder and leave a small opening. Use a burette to drop distilled water with a temperature of 24 ± 0.1 ℃ into the measuring cylinder at a rate of 5ml per minute. When the measuring cylinder is nearly full, tilt the measuring cylinder slightly to discharge the bubbles under the glass plate until the measuring cylinder is full. Smooth the glass plate, cover the measuring cylinder mouth, and wipe off excess water. Weigh the total weight on the Analytical balance (the sensitivity is 0.0001g). Take the average of three measurements as the volume of the measuring cylinder.

The volume of the measuring cylinder is calculated using the following formula:

V – Volume of measuring cylinder, cm ³

W – Net weight of water, g

ρ—— The density of distilled water at 24 ± 0.1 ℃ is 0.9972g/cm ³

(5) Measurement process and precautions

Before each measurement, calibrate the levelness of the instrument, carefully clean the funnel, close the rubber ball valve at the discharge port, and place the cleaned measuring cylinder and aggregate tray on the positioning pin.
Next, pour the prepared sample into the glass feeder. When adding materials, first move along the funnel wall and then move to the center part. While the feeder does not leave the material pile, it slowly flows into the funnel, spreading evenly from the center to the surrounding area, and naturally accumulates into a cone.
Quickly open the rubber ball valve to allow the sample to fall freely and fill the measuring cylinder. Gently support the measuring cylinder with your left hand, and immediately use the edge of the scraper plate to tightly adhere to the edge of the measuring cylinder mouth with your right hand. Scrape off the excess sample at an angle of 5-10 °; When scraping, be careful from beginning to end to avoid vibration, impact, or other interfering factors. Then gently tap the measuring cylinder wall to reduce the sample volume and use a brush to remove scattered particles from the outside and bottom of the measuring cylinder.
Weigh the sample in the measuring cylinder on a balance to the nearest 0.01g. Take the average of three measurements as the result.

The bulk density is calculated using the following formula:

D – Bulk density of abrasive, g/cm ³
W – Measure the weight of abrasive inside the cylinder, g
V – Volume of measuring cylinder, cm ³
For samples with particle sizes of 16/20~325/400, the difference between the maximum and minimum bulk density values determined three times should not exceed 0.015g/cm ³.

3. Factors affecting the measurement of bulk density

(1)Particle size and particle size distributionA,Experiments have shown that there is no fixed relationship between particle diameter and packing density. Generally, the smaller the particle size, the smaller the packing density.
B,The range of particle size distribution has an impact on the bulk density:
If the particle size distribution range is wide, that is, when the size is not equal, the smaller particles fill into the gaps of the larger particles, the porosity decreases, and the bulk density obtained is large; The packing density of particles with narrow particle size distribution range is small.

(2)Particle shape

The closer the crystal shape is to the isomorphic shape, the higher the packing density, so the packing density of the sphere is the highest; Particles with irregular shapes such as rods or sheets have a low packing density.

(3)Surface roughness of particles

If the surface of the particles is rough, the friction force increases, and the humidity on the surface of the particles increases, resulting in strong adhesion and reduced stacking density; On the contrary, the stacking density increases.