People often divide the water into 1, external moisture or surface moisture, which covers the surface of the particles. When it is stored, this part of the water gradually evaporates until it becomes "air-dried". 2. Analyze moisture or absorb moisture: its content in the material is related to the water vapor pressure and the relative humidity of the air. 3, when combined water or mineral water of crystallization trials, to be measured is mainly the first two, the sum of these two is called a total moisture or moisture free moisture. The moisture of ore and products will affect the process and equipment selection of washing, crushing, sieving, storage, dehydration, etc. It is more decisive for judging whether minerals may be selected by wind sorting or dry magnetic separation. significance. First, the moisture sample is taken as the sample will gradually evaporate when exposed to air (instead, the dry sample can continuously absorb moisture when placed in humid air), so the moisture sample must be taken quickly and timely, the collected moisture The sample should be stored in a closed tank and measured as quickly as possible. For quick-drying samples, the simplest method is preferred. Although this method may not be accurate enough, the error caused by it is often caused by the exposure of the sample to the air for a long time when sampling with an accurate method. The error is smaller. However, it should be noted that the surface of the pile tends to have low moisture. Therefore, the surface of the pile should be excavated when sampling, and then directly sampled from the inner layer. The process samples for the optional test are usually placed in the laboratory for a long time, so the external moisture has gradually dried out and can only be measured for moisture analysis (water absorption). In order to determine the external moisture or total moisture, it is necessary to additionally take a moisture sample. Second, the external moisture determination method The basic principle is that the sample is air-dried to constant weight at room temperature, and then the external moisture content is calculated according to the difference in weight before and after. For example, 500-1000 grams of sample can be weighed and evenly spread on a square tray. The plate should be pre-weighed to the nearest 0.1 gram. The thickness of the sample layer should not exceed 1-2 cm. The temperature was 20 ° C, the relative humidity was normal and the air was air-dried for several days and nights until the weight of the sample was substantially constant. Then, the external moisture W 1 =[(a 1 -b 1 )/a 1 ]·100% is calculated by the following formula: a 1 - the original weight of the sample; b 1 - the residual weight after the sample is air-dried. Bulk material can only be measured in situ. For example, the weighing can be weighed immediately after sampling, the weighing accuracy should be as high as 0.2%, and then spread on the steel plate for a few days and nights until constant weight. However, it should be noted that the weather (temperature and relative humidity) during the measurement should be basically anal. Third, the analysis of moisture (sorption of water) in the laboratory, generally after the air-dried sample is broken to 1 mm or less (for example, 0.2 mm), determined by drying or distillation, the latter is mainly used Materials that are afraid of heat and oxidation, such as solid fuels, oil shale, etc. (1) Drying method (oven method) In the laboratory, generally 25 grams of air-dried sample pulverized to 1 mm can be taken. For a small amount of water, 50 g of sample can be taken and placed in a glass bowl of about 100 ml. a frosted glass cover lid (also available iron lid box) was weighed accurately to 0.01 g. Then place the glass bowl in the oven (drying box), let the lid slant open, dry to a constant weight (about several hours) at 105 ± 2 ° C, then transfer to the dryer for cooling (about half an hour) ), after cooling, quickly cover the lid and take out the weighing from the dryer. Then press the test to calculate the moisture (sucking water). W 2 =[(a 2 -b 2 )/a 2 ]·100,% where: a 2 - the thickness of the air-dried sample; b 2 - the residual weight of the sample after drying. (2) Distillation test equipment: 1. A distillation bottle with a volume of 500 ml; 2. A reflux spherical condensation tube or a straight tube condensation tube with a length of 300-400 mm; 3. A measuring cylinder with a minimum division of 0.1 ml. Wash the hot wash solution and rinse it with distilled water several times until there is no grease on the wall of the vessel. Test operation: Weigh 25 g (50 g of water) to an air-dried sample of 1 mm, place it in a distillation flask, weigh it to the nearest 0.01 g, and add 100-200 g of industrially saturated water. Toluene (or car gasoline), shake well. Then the retort is heated, starting slowly, and then it can be faster, so that the dimethyl and water are distilled out, condensed in the condensing tube and then flow into the measuring cylinder. After a short time, the dimethyl and water are layered. The scale directly reads out the water volume C 2 (ml). W 2 =(c 2 /a 2 )·100,% where: a 2 - the original weight of the air-dried sample, gram; c 2 - the amount of water measured, ml. IV. Determination of Total (Free) Moisture There are two methods for determining total moisture: firstly, external moisture is separately measured and moisture is analyzed (water absorption), and then total moisture is calculated as follows: W=W 1 +W 2 [W 2 (100-W 1 )]/·100 where: W-total moisture, or simply water, %; W 1 - external moisture, % W 2 - water analysis of moisture (water absorption), % The second method is Take the un-dried original sample and directly measure the moisture by measurement - mainly by the drying method, and then calculate the total moisture according to the weight before and after drying: W 1 =[(a-b)/a]·100 , % where: a- the original weight of the sample that is not air-dried; b- the residual weight of the sample after drying, if the sample size is larger, and the sample amount is correspondingly larger, then when using the drying method (oven method) Large vessels must be used, but subject to laboratory equipment conditions, the weight of moisture samples in the laboratory must not exceed 10 kg. If the sample size is too large (such as the original ore sample), and the required sample weight exceeds 10 kg, the measurement can only be carried out in two steps, that is, the external moisture is first measured at the sampling site, and then the external moisture is measured. After the air-dried sample is broken, a small amount of sample is taken out and analyzed in the laboratory to analyze the moisture (water absorption), and finally calculate the total moisture. Measuring rock moisture using a rock density meter is actually a special balance for measuring density and moisture. When measuring the specific gravity, instead of weighing the ordinary balance, the specific gravity value can be read directly without having to calculate it temporarily; similarly, when the moisture is measured by the oven method, if the rock density meter is used instead of the ordinary balance, it can be directly read. The moisture value is obtained without having to temporarily calculate the formula, thereby speeding up the measurement. The measurable sample weight is limited to not more than 100 grams.
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