Powder testing has always been used in the powder processing industry. There are many methods for detecting the fineness of powder, and the screening method is a relatively common one. Today we will talk about the main methods of operation of the screening method, for everyone to test the reference.
Screening is an ancient, common, simple and intuitive method of particle size measurement and classification. Before the middle of the 19th century, it was mainly used to roughly classify coarser particulate materials according to their particle size. After the high-precision sieve was produced in the mid-19th century, the screening method was widely used as a particle size measurement method.
The basic practice of screening:
A sample of known quality is successively passed through a finely divided screen, and the amount of the sample collected (remaining) on each sieve is weighed, and the mass percentage of each fraction is calculated.
There are two types of screening methods: dry sieve and wet sieve. Screen holes are also available in both round and square shapes. Used to measure particle size and classification. A set of sieves with large to small sieve openings, also called test sieves.
Screen size series
In a standard sieve system, there is a certain proportion of adjacent sieve meshes. Taylor sieve modern sieve or customary is called interval series, which is more commonly used. The series is called a continuous series and is used for special requirements or experimental research.
Screening method (dry method)
Select sieve diameter
First select the large and small sieve diameters - leave about 5% on the coarse screen and pass through the fine screen to determine the coarse and fine sieve aperture, and then press the downward or upward selection of the intermediate sieve series. Or choose between 5-7 sieve diameters between the large and small sieve diameters.
Screening sample dosage
Related to sieve diameter, powder density and particle size:
When 75 μm<D< 250 μm, the amount is about 40-60 g, and 250 μm >D>1000 μm, the amount is about 100-150 g.
A set of sieves is stacked from top to bottom according to the size of the pores, and the coarse material is added from the upper layer, and the lower layer has a container with fine powder.
In the logarithmic coordinate system, the transition time between the phase throughput and the second-stage throughput is the transition time required for the transition between the phase and the two-stage two-stage extension (or continue to sieve for 5 min, if the throughput is less than 0.2 of the total sample volume) %, think of the screening end point.
It is recommended to weigh the sieve residue on each sieve for a certain period of time (15~30min).
Screening result processing
The amount of loss during the screening process shall not be 5% of the total feed amount, otherwise it will be redone (note the removal of the deposit on the sieve surface).
The above is the screening method in the powder fineness test for your reference test.
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