Grading and washing test

First, the classification test
The grading operation is used to control the particle size of the grinding product in the grinding circuit. The commonly used grading EQUIPMENT is a mechanical classifier and a hydrocyclone; before the sorting operation, it is regarded as a preparation operation, aiming at reducing the difference in particle size. For the adverse effects of sorting efficiency, the commonly used classification equipment is a multi-chamber hydraulic classifier with a rising water flow and a hydrocyclone. Although hydrocyclones have the advantages of small footprint and easy maintenance, they do not completely replace those traditional equipment that is graded in the gravitational field. Especially in the coarse particle range, the cyclone energy consumption is too high, and the classification efficiency is not as good as the mechanical classifier, so it is preferred to use a mechanical classifier instead of a cyclone in the rough grinding circuit. Similarly, the use of a simple multi-chamber hydraulic classifier prior to the classification of the shaker is easier than multi-stage with a cyclone.
In the beneficiation process test, the classification operation and the classification equipment itself are generally not required to be investigated. The classification before the beneficiation is mostly for the purpose of obtaining the different grades of materials for the next step test. Therefore, there is no strict requirement for the type of the classification equipment, and sometimes even a sieve can be used instead of the classification machine.
The figure below shows a laboratory free-falling single-chamber grading box, which can be called a slit-type grading box. When using, first calculate the free sedimentation velocity Ï… 0 of the boundary particles according to the separation granularity, and then calculate the water consumption according to the following formula:
W=Fv 0
Where W is the amount of water, m 3 /s;
F—the total area of ​​the gap in the classification box, m 2 ;
υ 0 — The free sedimentation velocity of the demarcated particles, m/s.
In the picture   Laboratory single room grading box
1. grit collection bottle; 2. classification box; 3. rubber tube;
4. baffle; 5. flow trough; 6. feed trough
If it needs to be divided into several grades at one time, and there are many samples, and the single-chamber classification box is gradually graded for too long, the self-made multi-chamber laboratory free-falling classification box can be used. The formation is made up of a plurality of single-chamber classification boxes, and the classification area of ​​each chamber is gradually increased from coarse to fine. The size of each chamber is designed according to the conventional classification ratio. When the sample volume is large (for example, several hundred kilograms), a laboratory-type multi-chamber hydraulic classifier with mechanical stirrer should be used, and the current domestic model is 200/515 × 1040 mm interference sedimentation hydraulic classification. machine.
There are many factors affecting the work of the mechanical classifier. In addition to the basic hydraulic factors affecting the sedimentation of the particles, the conditions of agitation, the dewatering time of the grit, the slope of the dewatering zone, the depth of the subsidence zone, etc., are required to be adjusted in the laboratory. The mechanical classifier used must be straightforward to industrial equipment. Even so, it is difficult to say that the laboratory test results are in complete agreement with industrial production. [next]
It is also difficult to make a cyclone test in the laboratory because the processing capacity is usually too large for a slightly thicker graded material if the appropriate size of the cyclone is selected according to its separation size. Therefore, the hydrocyclone is used to classify the test material only when the separation particle size is small or the separation particle size is large but the amount of the sample to be classified is also large.
The laboratory hydrocyclone is usually small in size and generally has a diameter of 25 to 125 mm. In order to facilitate adjustment of various structural parameters, a set of removable parts with different sizes should be provided. Since the feed of the cyclone must be fed continuously and at a constant pressure, the test device must be accompanied by a set of attachments and instruments such as a mining bucket, a sand pump and a pressure gauge.
In order to obtain the required separation particle size, in addition to the preliminary calculation according to the theoretical formula, it must be explored through experiments. Only after the test results show that the separation particle size and classification efficiency have met the requirements, can be used for the classification of the formal sample. The purpose of the laboratory cyclone test is usually limited to the grading of the test material and the determination of its separation size. In order to determine the type, size, structural parameters and pressure of industrial production cyclones, designers often rely more on their own experience than on laboratory small test results. Some commercial laboratories and manufacturers abroad have been working for nearly 20 years. In this regard, sufficient experience has been accumulated, and it is often possible to use a computer program to make recommended data based on the sample data, density and slurry concentration of the sample.
Second, washing test
Washing is generally a preparation operation, but it is also a pre-selection operation, and sometimes it can be a main sorting operation. The purpose of the washing is to use mechanical scrubbing and hydraulic flushing to wash the clay and fine particles from the surface of the massive ore. The mechanical and hydraulic forces required depend on the washability of the ore or the ease of washing. The purpose of the washing test is to determine the washability and ore washing index of the ore.
1. Evaluation of ore washability
The washability of the ore is related to the nature of the clay and the mud content of the ore. The nature of clay refers to the plasticity, swelling and permeability of clay.
The plasticity of clay refers to the property of clay with a certain humidity that does not crack after compression and produces fixed deformation, which can be measured by the following plasticity index:
K=B h -B 1
Where K is the clay plasticity index, %;
B h - the upper limit of clay plasticity, that is, the moisture content when the clay begins to flow, %;
B 1 - the lower limit of clay plasticity, ie the moisture content when the clay begins to be crushed, %.
The larger the K value, the more difficult it is to wash the ore. The ore washability expressed by the K value is shown in the table below.
The washability of ore in the table
K value
The hardest
The swelling property of clay refers to the extent to which the clay is increased in volume after wetting. The greater the swelling, the easier it is to wash. Permeability refers to the ability of clay to penetrate water. The greater the permeability, the easier it is to wash.
Other criteria can be used to assess the washability of the ore. For example, the amount of electricity consumed per ton of ore can be used as a disturbance. The ore with a power consumption of 1 to 0.5, 0.5 to 0.25, and <0.5 kWh per ton of raw ore is classified as difficult to wash, medium washable and Easy to wash ore; washability can also be evaluated by the depth of penetration of a standard cone on a clay sample.
2. Washing test equipment and method
Commonly used washing equipments are tank washing machines, cylinder washing machines, washing screens and spiral classifiers. In the laboratory, manual washing can also be carried out using a container such as a drum and a hand sieve. Experimental washing machines are generally reduced in proportion to industrial equipment. For example, a 360 × 2000 mm trough-type washing machine or a cylinder Ф350 × 650 mm in washing machines.
The purpose of the laboratory indoor washing process test is to investigate the ore washing effect of a certain ore, that is, the washing process index. The washing effect can be determined by the particle size analysis result of the washing product and the content of the useful component in the product and its respective grades. Distribution rate assessment judgment. Operating parameters need to be adjusted in order to obtain the best process specifications, but the latter cannot be directly used as a basis for industrial design.

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Patents related to tandem bicycles date from the late 1890s.In approximately 1898, Mikael Pedersen developed a two-rider tandem version of his Pedersen bicycle that weighed 24 pounds, and a four-rider, or "quad", that weighed 64 pounds. They were also used in the Second Anglo-Boer War. Tandem popularity began to decline after WWII until a revival started in the late sixties. In the UK The Tandem Club was founded in 1971, new tandems came on to the market from the French companies Lejeune and Gitane, and in the USA Bill McReady founded Santana Cycles in 1976. Modern technology has improved component and frame designs, and many tandems are as well-built as modern high-end road and off-road bikes.

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