Coal is a mixture that the composition of chemical is very complex. If we want to test the nature and quality of a batch of coal we must sample the most representative coal. The coal sample preparation is a complex and vital stage after coal sampling. It will reduce the mass and size of the gross sample to the degree which tests sample needs. At the same time, the chemical and physical properties are unchanged. Bias from this stage will have a direct impact on subsequent tests. The procedures of coal sample preparation mainly include reduction, division, mixing, sieving and drying. In last article Coal Sample Preparation Procedures Overview (1), we mainly talk about the sample drying and sample reduction in details. So today, our content is going to focus on mixing, sieving and division.
Coal Sample Sieving
Sieving is to separate the non-conforming samples from other samples and continue to crush them to the specified size in order to reduce the sample division bias. In this stage, we should prepare a complete set of sieves with various meshes, such as round hole sieves of 25mm, 13mm, 3mm and 1.5mm and square hole sieves of 3x3mm, 1x1mm and 0.2×0.2mm. In the past, we mainly adopt manual sieving, but with the development of technology, screening equipment gradually replaced manual labor. We totally divide them into stationary screen machine, roll screen machine, cylinder screen machine, shaking screen machine and vibrating screen machine, five categories. Our company mainly offers vibrating screen machine and automatic cylindrical sieve. Among them, XDYS-B TYPE and XDGS-B TYPE are hot sellers.
This cylindrical sieve is used for iron ore, coke and coal briquettes. It can sieve the pellets which granularity is smaller than 5mm and other 5 levels granularity.
The coal vibrating screen sets electronic counts and supports auto power on-off. It has an automatic controlling system and can unload material automatically.
Coal Sample Division
Coal sample division is the most critical procedure in sample preparation. It aims to decrease the mass of the sample without changing the size. The sample division can be either mechanically or manually. In order to minimize human errors, mechanical methods are the way we usually use.
When the mechanical division destroys the integrity of the sample, such as water loss, particle segregation, etc., or when the coal particles are unable to use the mechanical division, they should be divided by the manual method. The coal sample division manual methods are mainly including riffle method, checkerboard method, strip intercepting method, coning and quartering method and nine-point picking out method.
Riffle is a simple and effective divider. It consists of two groups of slots and receivers, which are relatively crossed. The number of slots on both sides is equal, at least 8 on each side. The gradient of the slot on the horizontal plane is at least 60 degrees. Before using this method, mixing is unavailable. When using it, the samples should be oscillated back and forth along the length of riffle and fed into the grid.
Using this method, the samples should be fully mixed and spread into a rectangular block with a thickness of no more than 3 times that of the maximum particle size. Then, we should divide the long block into more than 20 small pieces and sample from the middle of each small block.
Strip Intercepting Method
After the samples are fully mixed, it should be randomly placed in one direction into a long strip which with a length of at least 10 times the width. The sample is intercepted by a sample frame at a certain distance along the length of the sample band. The width of the sample frame should be at least 3 times the maximum particle size and the height should be greater than the thickness of the sample strip. After that, merge all the increments into a sample.
Coning and Quartering Method
Coning and quartering method is a convenient method, but it has particle segregation and it will cause bias if there is improper operation. When we stack cones, samples should be scattered from the top bit by bit to form a regular size distribution from top to bottom and from center to outer edge. After that, pat the cone from the top to the bottom into a suitable flat body, and then, place the cross-split plate in the middle of it and press down to the bottom. The coal sample is divided into four equal sectors. We should keep two sectors as final sample.
Nine-point Picking out Method
Once the sample is mixed, spread it into a round cake with a thickness not greater than 3 times the maximum particle size. Then, use the method that similar to checkerboard method to take 9 sub-samples from 9 points in the picture. This method is only used for the sampling of full moisture samples.
The mechanical division is a method of cutting out a large number of small mass samples from an increment. Various types of mechanical dividers are commercially available. They are mainly including rotating cone type, slotted belt type, container type and cutter chute type. The sample crusher machine XDSP-600 produced by TopSampler is made up of crusher hammer, crusher cavity, sample divider system and electric controlling system. It has wide application and it is applied to various auger sampling system and sample analytics system. Furthermore, we also offer automatic divider and weigh system. It is a good choice for coal sample preparation.
Coal Sample Mixing
Mixing is the process of blending coal samples with each other. The aim is to distribute coal samples as evenly as possible and reduce the bias of division. It only applies to checkerboard method, coning and quartering method and nine-point picking out method. In the use of mechanical division, the mixing before it is not necessary. It will lead to water loss. Therefore, the mixing should be appropriately used. The automatic sample feeder and mixer system from our company include the conveyor belt and solid testing drum machine. If you have a conveyor belt sampler, the automatic sample feeder and mixer system is the best choice for you.
In this article, we introduce the coal sample division, sieving and mixing roughly. And do some recommendation of hot-sale machines from TopSampler. If you have demand for these machines, Please feel free to contact us!