1. Polishing characteristics
Polishing roller generally adopts iron roller, and the working principle of iron roller polishing is basically the same as that of iron roller grinding. It is still polishing and grinding, which is completed by the joint action of 5 processes including collision, polishing pressure, tumbling, axial conveying, and spraying water. But polishing is not to remove the whole bran layer, but to remove the fine bran powder and the fine starch grains raised on the rough surface. Polishing and grinding white from the way of work compared, there are the following differences:
① Low polishing pressure; (2) The fluid density of polished rice grains is small; ③ The rice leaves the iron roller faster when polishing; ④ Large polishing movement area per unit output. 3. Analysis of factors affecting the polishing effect of rice polishing machine
2. Rice-making process
At present, the commonly used rice-making process is grinding white - polishing white - spray water polishing. First, the white rice is crushed by grinding, and the brown rice is cut and ground by the sand roller. Then wipe away the remaining bran layer and bran powder to improve the finish and color of the rice grain surface. After polishing the rice, a small part of the bran powder remains on the concave surface and there is roughness. Then, the bran powder is polished by spraying water and grinding. At the same time, under the action of polishing pressure and associated friction temperature, the starch fine end is semi-gelatinized to form a smooth surface.
3.1 Polishing pressure
The polishing pressure is established by the speed and collision force of rice grains in the polishing chamber. There are many factors that affect the whitening pressure, but the polishing pressure can be adjusted and controlled through the pressure door at the outlet of the polishing chamber. The polishing pressure is large, the collision movement is violent, and the crushing after polishing is much. The polishing pressure is small, the collision movement is relaxed, and the crushing after polishing is less. Therefore, the polishing pressure should be small, but the polishing pressure is too small, it will affect the process effect. The general polishing pressure is about 400-700g/cm2.
3.2 linear velocity
The linear speed of the polishing roller is the main factor that determines the speed and impact force of rice grains. When the linear speed is low, the speed of rice leaving the iron roller is low, the collision motion is moderate, and the crushing after polishing is less, but the rotational speed is too low. When the rolling of rice is not enough, the local grinding of rice is too much, resulting in the phenomenon of over-grinding. Over-grinding will reduce the rice yield but also make the local grinding of rice not enough, and the polishing is uneven. When the linear velocity is high, the speed and collision force of rice grains are large, the rolling chance of rice grains is increased and the polishing is more uniform, but when the rolling of rice grains is excessive. Will make both ends of the rice grain ground off, and broken rice increase will also reduce the rate of rice. Therefore, it is very important to select a reasonable rotational speed to obtain an appropriate polishing roller speed to reduce the breaking rate of rice and improve the polishing brightness of rice. Generally, the polishing roller speed should be 6-7m/s.
3.3 the water
During polishing, the rice in the polishing room is evenly sprayed with water according to the ratio of ***, so that the surface of the rice is wet, which is conducive to the separation of bran powder on the surface of the rice. At the same time, under the action of polishing pressure and friction temperature generated in the polishing process, the starch on the rice surface is gelatinized to form a glial layer, so as to achieve the purpose of improving the light of the rice. However, too much water will cause an abnormal flow of rice grains, resulting in too much pressure in the polishing machine, which will increase the crushing and even lead to a "stuffy car". Therefore, in the use of the polishing machine, the water quantity should be controlled first, and the water quantity is generally controlled at about 0.5%.
3.4 air absorption
The buffing air supply form has hollow shaft jet air, strong pull suction air, jet air, and suction air combination. For the axis water polishing machine should be in the form of strong suction wind. The strong pull of wind energy makes the water into the hollow shaft atomize rapidly under the action of strong negative pressure, thus improving the uniformity of the water. The strong suction wind can also increase the chance of rice turning and improve polishing accuracy. The separation between rice grains and bran powder is beneficial to removing bran. Reduce the humidity and temperature of white rice after polishing, and play the role of cooling rice. However, if the suction is too large, the polishing pressure will be increased and the broken rice will be increased. Therefore, we should choose the right suction volume according to the specific model, in order to effectively reduce the crushing, conducive to the play of polishing role.
3.5 Rice Flow
During the polishing process, the flow rate should be stable. If the flow rate is too small, there will be too many chances for rice to turn over in the polishing room, resulting in too much friction and impact force, resulting in over grinding phenomenon. Over grinding will not only make the surface of the rice lose light, but also seriously affect the rice yield; If the flow is too large, the rice is not easy to roll in the polishing room, so the chance of contact between the rice and the iron roller and the rice sieve is too little, and the processed rice can not reach the polishing effect. Therefore, in the polishing process, according to the specific processing raw material varieties, specific practical operation, and appropriate control of flow, in order to make the rice in the polishing room appropriate flipping, impact, extrusion, and friction, to ensure that the polishing machine processed rice to achieve the complete rice, surface bright process effect.
The above factors are interrelated and influence each other, which should be considered comprehensively in practical application to obtain the best polishing effect.