Water Screening Theory and Application

Author: Wen Shuming
Editor-in-Chief: Zhang Dengke
Publisher:
Publish Date: 1998-05-01
Features:
Content Summary This book provides an in-depth discussion of the theory of water sieves from the perspectives of hydraulics and two-phase flow. It also introduces domestic and international water sieve equipment and applications, and summarizes in detail the research achievements in the field of water sieve equipment over the years. The book includes an introduction, theoretical foundation of water sieves, basic principles of water sieves, influencing factors of water sieves, water sieves in a gravitational field, and water sieves in composite force fields. This book is suitable for engineering technicians engaged in the research and production of particle size separation of bulk materials, as well as for reference by teachers and students in universities and colleges.
Excerpt:
II. Average Particle Size and Material Uniformity In practical production, using only the particle size range or individual particle size to represent the size of materials is often insufficient. Sometimes, it is necessary to consider the average size of a batch of materials or a grade of materials. For the particle size of a batch of materials, different statistical methods can yield different average particle size values. The most commonly used methods are as follows:
(1) Weighted Arithmetic Mean Method
(2) Weighted Geometric Mean Method
(3) Harmonic Mean Method
III. Particle Size Analysis Methods
1. Sieve Analysis Sieve analysis is a method of determining the particle size composition of bulk materials by sieving. For materials with particle sizes greater than 6 mm, the sieves used in sieve analysis are generally non-standard sieves (hand sieves). Non-standard sieves can be made by punching holes in steel plates or weaving steel wire. The method of sieve analysis involves sieving the material with a set of sieves of different mesh sizes, dividing the material into several particle size ranges, and then weighing each range separately to calculate the mass fraction of each range in the total material. For materials with particle sizes ranging from 6 mm to 0.043 mm, sieve analysis is performed using laboratory-standard sieves. The sieves are arranged in order of mesh size, and the material to be analyzed is placed on the screen of the top sieve. The sieves are then placed on a sieve shaker for sieving or shaken by hand. When the sieve analysis is carried out for 1 minute and the amount of material retained on the sieves is less than 1% of the material passing through the sieves, it is considered that the sieve analysis has reached the endpoint. The material retained on each sieve is weighed separately, and the mass fraction of each range in the total feed is calculated. Sieve analysis can be performed using dry sieving or wet sieving. Generally, wet sieving is more accurate than dry sieving, and when precise results are required, a combination of dry sieving and wet sieving is often used for sieve analysis. The purpose of sieve analysis is to determine the mass fraction of each particle size range in the feed, thereby determining the particle size composition of the material. The sum of the yields of all ranges above a certain sieve opening is called the cumulative yield above the sieve or the positive cumulative yield, and the sum of the yields of all ranges below a certain sieve opening is called the cumulative yield below the sieve or the negative cumulative yield.