Strict quality control measures are needed in the production process of Molai sand to ensure its performance and quality meet the requirements of industrial application. The following are common quality control measures in the production process of Molaisha:

I. Quality control of raw materials

Selection of raw materials: The raw materials of Molaisha are usually kaolin or bauxite, and the content of kaolinite is required to be greater than 90%. The chemical composition of raw materials must be strictly controlled. Mullite content should reach more than 75%, aluminum element should account for 50%-55%, silicon element should account for 25%-30%, and the total content of impurities should not exceed 5%, among which the sum of metal oxides such as iron, calcium and magnesium should be less than 3%.

Impurity removal: iron impurities are removed by magnetic separation process, and the magnetic field strength is required to be not less than 1.2T. In addition, the crushed ore needs to be washed to remove impurities.

II. Production process control

Crushing and grinding: The combined process of multi-stage jaw crushing and roller crushing should be adopted in the crushing process to ensure that the angular coefficient of particles is between 1.25 and 1.35. Grinding is the key. Molaisha high-efficiency mill can realize stepless adjustment of the fineness of finished products from 80 mesh to 400 mesh.

Particle size grading: the grading screen needs to be equipped with an ultrasonic cleaning device to ensure that the particle size concentration reaches more than 85%. Common moraine sand particle size specifications include 8-16 mesh, 16-30 mesh, 30-60 mesh, etc.

Calcination and sintering: the calcination temperature is controlled at 1100-1500℃, and the calcination time is generally 1-4 hours. The sintering temperature is about 1600℃ and the sintering time is about 48 hours.

III. Testing of chemical and physical properties

Chemical composition detection: the mullite content is detected by X-ray diffraction (XRD), and the sampling ratio of each batch is not less than 10%. The determination of chemical composition shall be carried out according to GB/T6900 or GB/T21114.

Physical performance testing: Particle size testing needs laser particle size analyzer and double verification by wet and dry methods, and the data deviation is controlled within 2%. The determination of bulk density and apparent porosity shall be carried out according to GB/T2999. The determination of fire resistance shall be carried out according to GB/T7322.

Other performance tests: Silicon carbide muffle furnace must be used for high-temperature performance test, with heating rate of 10℃/ min and holding time of not less than 2 hours. The density of moraine sand should be stabilized at 2.5-2.8g/cm, and the bulk density should be 1.4-1.6g/cm.

IV. Quality control of finished products

Appearance and size inspection: according to the provisions of GB/T10326, the size, appearance and section of shaped refractory products are inspected.

Quality acceptance: Mullite is inspected by batches, and each batch of products consists of the same production conditions and the same brand, and each batch does not exceed 100 tons. If one index does not meet the requirements, it is necessary to re-examine the unqualified items with backup samples.

V. Packaging and storage

Packaging: Double-layer coated woven bag with aluminum foil barrier layer inside to prevent moisture.

Storage: the humidity of storage environment must be lower than 40%, and the stacking height should not exceed 6 floors. Rain-proof tarpaulins shall be provided during transportation, and iron grab shall be avoided to directly contact sand during loading and unloading.

Through the above strict quality control measures, we can ensure that Molai sand can meet the high quality standards in the production process and meet the strict requirements of industrial fields such as precision casting and refractory materials.