GB/T 24192-2009Chromium ores - Determination of particle size by sieving (English PDF)

3.1 Particle size

The size of ore particles, which is expressed as the smallest mesh opening size of the sieves used in the sieving test.

3.2 Sieving

The process of separating granulated ore into two or more groups of particle sizes using one or more sieves.

3.3 Hand sieving

Sieving operation by holding and shaking one or one set of sieves.

3.4 Mechanical sieving

Sieving operations involving intermittent or continuous sieving using one or more mechanically supported and vibrated sieves.

3.5 Sieving end

The sieving has progressed to a situation in which further sieving does not significantly increase the amount of sample passing through the sieve, that is, the amount of sample passing through the sieve of this specification per minute is no more than 0.1% of the charge quantity.

3.6 Charge quantity

The mass of the sample loaded onto the sieve in a single sieving operation.

4.1 Overview

First, the sample is sieved using a specified sieve. Then, the remaining sample is sieved using sieves of different sizes. The sample that passes through each smallest mesh opening is weighed to obtain the percentage content of each particle size range, and then the percentage content of different particle size ranges of the whole batch of goods is determined.

4.2 Precision of particle size measurement

According to the overall precision requirements, the precisions of the division and the division and measurement combination for particle size determination are shown in Table 1.

4.3 Preparation of particle size specimens

Particle size specimens shall be prepared from each uncrushed bulk sample, subsample, or increment sample. Particle size determination is generally performed in its natural or practically operable state.

NOTE: When the sample is too wet to be sieved, the sample can be dried before particle size determination. The drying temperature shall generally not exceed 110 °C.

4.4 Instruments

4.4.1 Sieve

4.4.1.1 Mesh opening shape and size

The mesh openings are square, and the mesh opening dimensions and tolerances shall conform to the provisions of GB/T 6003.1 and GB/T 6005. The aperture of the metal wire mesh shall not exceed 50 mm.

NOTE: To improve the effectiveness of sieve mesh protection and sieving, sieves generally have sieve meshes with an intermediate aperture for backup.

4.4.1.2 Sieve mesh material

The sieve mesh material shall comply with the provisions of GB/T 6003.1. When the mesh opening size exceeds 200 mm, carbon steel wire or carbon steel plate shall be used.

4.4.1.3 Maintenance and inspection of sieving equipment

Regularly check the size of the mesh openings to ensure that the size of the mesh openings is within the specified allowable deviation. For metal wire sieve mesh with a mesh opening of < 1 mm, the sieve mesh shall be thoroughly cleaned of oil before use to avoid the adhesion of ore powder. The sieve surface can be cleaned with a soft brass wire brush or similar products. Handle with care to prevent damage to the sieve surface.

4.4.2 Sieving machinery

This includes continuous sieving machinery and intermittent sieving machinery, both of which consist of a single sieve or a set of sieves.

4.4.3 Weighing apparatus

Before sieving, the weighing apparatus shall have a range close to the sample volume to be sieved, with the minimum graduation not exceeding 0.5% of the range, and the sensitivity of other balances shall not exceed 0.1% of the range.

4.4.4 Clocks

It is used to check the sieving operation time.

4.4.5 Drying oven

The drying oven shall have automatic temperature control (temperature not exceeding 110 °C) and a sufficient capacity to hold containers for particle size samples.

4.5 Operation

4.5.1 Hand sieving

4.5.1.1 The charge quantity at one time is generally determined by the sieve opening, sieve surface and the maximum particle size of the sample, as shown in Table 2.

4.5.1.2 Hand sieving operations shall be carried out according to the following procedure.

a) Place the sample on a sieve with the largest aperture used for the measurement.

b) When using a sieve with an aperture of 50 mm or larger, the ore particles remaining on the sieve can be tested by hand to see if they pass through or not.

c) When sieving particles smaller than 50 mm, use the sieves in order of mesh opening size from top to bottom.

d) The sieving end is reached when there is virtually no ore passing through the sieve (the amount passing through in 1 minute is no more than 0.1% of the charge quantity).

e) Weigh the samples in each particle size range after sieving.

NOTE: To prevent the loss of small particles, a sieve cover and a sieve bottom tray shall be used during sieving. […]