Pulverized coal is an important additive in the process of cast iron; Adding pulverized coal into the wet sand can prevent sand sticking defects on the surface of castings, improve the surface smoothness of castings, reduce sand inclusion defects and improve the collapsing function of moulding sand. For wet ductile iron parts, it can effectively prevent the formation of subcutaneous pores. Circular eddy current combustor can be used to prevent the air from preheating.
Main physical characteristics of pulverized coal:
(1) The particle characteristic pulverized coal is composed of the particles with different size and irregular shape. Generally, the diameter range of pulverized coal particles is 0-1000um, most of which are 20-50um;
(2) The density of pulverized coal is small, the new pulverized coal stacking density is too (0.45-0.5) t/m3, and the density after storage for a certain time is (0.8-0.9) t / m3;
(3) The pulverized coal has fine fluidity particles, and the unit mass of coal has a large surface area, and the surface can absorb a large amount of air, so that it has fluidity. This characteristic makes the coal powder easy to pneumatic transport, and the disadvantage is that it is easy to form the pulverized coal flow and easy to leak powder when the equipment is not tight.
Fineness value: the size of fineness of pulverized coal only indicates the size of particles in the pulverized coal which is smaller than and less than x value, but it is not known the composition of pulverized coal particles, that is, the uniformity of its size is unknown.
Uniformity: the index that represents the uniformity of pulverized coal particles, which is called uniformity index, also known as the characteristic coefficient of pulverized coal particles, expressed in n. The pulverized coal is screened by two different sieve numbers.
The n value is generally between 0.8-1.3, and the larger the n value, the better the uniformity of pulverized coal is. The n value is close to the type of coal mill and the type of coarse powder separator. For example, the coal powder uniformity of medium speed coal mill is better than that of steel ball mill, that is, the n value is relatively large.
Physical and chemical properties: the particle characteristic pulverized coal is composed of particles with different sizes and irregular shapes. Generally, the diameter range of pulverized coal particles is 0-1000um, most of which are 20-50um; Coal powder is combustible material, class B fire dangerous goods, dust has deflagration, ignition point is between 300 ℃ ~ 500 ℃, and the lower explosive limit concentration is 34 g / M ~ 47g / M (average particle size of dust: 5 μ m～10 μ m)。 Ignition temperature of dust accumulated on high temperature surface (5mm thick): 225 ℃ ~ 285 ℃, cloud dust ignition temperature 580 ℃ ~ 610 ℃