At present, rice polishing machines have been widely used in China. However, how to reduce breakage, improve the integrity rate of rice grains and the brightness of the surface is a more worthy issue. Here, Shuanghu Grain and Oil Machinery will further analyze the factors that affect the polishing effect of rice polishing machines for your reference.

With the rapid development of China's economy and the continuous improvement of people's living standards, the deep processing technology of rice has emerged in China. Therefore, research and manufacturing units engaged in the grain machinery industry have all set their sights on the rice polishing machine market. They have successively introduced advanced foreign rice polishing technologies and researched and designed various types of rice polishing machines.

1 Polishing characteristics

Polishing rollers are generally made of iron rollers. The working principle of iron roller polishing is basically the same as that of iron roller whitening, which is still the process of rubbing off and whitening. It is completed after the combined action of five processes: collision, polishing pressure, rolling, axial conveying and water spraying. However, polishing does not remove the entire bran layer, but rather the fine bran powder and the raised starch particles on the rough surface. When comparing polishing and whitening in terms of working methods, the following differences exist:

① Low polishing pressure; ② The density of the fluid in polished rice grains is low; ③ When polishing, the rice grains leave the iron roller at a relatively fast speed. ④ The polishing movement area per unit output is large. Analysis of Factors Affecting the Polishing Effect of Rice Polishing Machines

2. Rice-making process

The commonly used rice-making process at present is: grinding and whitening - removing and whitening - spraying water and polishing. First, the brown rice is ground white and roughened by grinding. Under the cutting and grinding action of the sand roller's sand blade, the outer layer of the brown rice is separated. Then, use the rubbing and whitening mill to remove the remaining bran layer and bran powder to improve the smoothness and color of the surface of the rice grains. After the rice is rubbed off and whitened, there is still a small amount of bran powder remaining in the depressions on the surface and a certain degree of roughness. Then, by spraying water and polishing, the bran powder can be removed more thoroughly. At the same time, under the action of polishing pressure and the accompanying frictional temperature, the starch powder is semi-gelatinized to form a relatively smooth surface.

3.1 Polishing Pressure

The polishing pressure is established in the polishing chamber by the speed of the rice grains and the impact force. There are various factors influencing 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 high, the collision movement is intense, and there are many fragments after polishing. When the polishing pressure is low, the collision movement will be gentle, and less debris will be added after polishing. Therefore, a smaller polishing pressure should be used during polishing. However, if the polishing pressure is too low, it will affect the process effect. The general polishing pressure is approximately 400 to 700g/cm ².

3.2 Linear Velocity

The linear speed of the polishing roller is the main factor determining the speed and impact force of the rice grains. When the linear speed is low, the speed at which the rice grains leave the iron roller is also low, the collision movement is gentle, and less breakage occurs after polishing, but the rotational speed is too low. When the rice grains are not rolled enough, some parts of the rice grains will be ground too much, resulting in over-grinding. Over-grinding will reduce the rice yield and also cause some parts of the rice grains to be ground insufficiently, resulting in uneven polishing. When the linear speed is high, the speed and collision force of the rice grains are large, the chance of the rice grains rolling increases, and the polishing is more uniform. However, when the rice grains roll too much. It will cause the two ends of the rice grains to be crushed off, increase the number of broken grains, and also reduce the rice yield. Therefore, choosing a reasonable rotational speed to obtain an appropriate linear speed of the polishing roller is of great significance for reducing the rate of broken rice and enhancing the brightness of rice polishing. Generally, the linear speed of the polishing roller should be 6-7m/s.

3.3 Water Volume

When polishing, water is evenly sprayed on the rice in the polishing chamber in a certain proportion to moisten the surface of the rice, which is conducive to the separation of bran and powder on the surface of the rice grains. Meanwhile, under the action of the polishing pressure and the frictional temperature generated during the polishing process, the starch on the surface of the rice gelatinizes to form a gelatinous layer, thereby achieving the purpose of enhancing the luster of the rice. However, excessive water inflow can cause abnormal flow of rice grains, resulting in excessive pressure inside the polishing machine, which can lead to increased fragmentation and even cause the machine to "stall". Therefore, when using a polishing machine, the water inflow should be controlled first, and it is generally controlled at around 0.5%.

3.4 Suction volume

The air supply forms for polishing include hollow shaft air spraying, strong pull air suction, and the combination of air spraying and suction. For polishing machines with water spraying from the axis, a strong pull suction form should be adopted. Strong suction can cause the water entering the hollow shaft to atomize rapidly under a strong negative pressure, thereby improving the uniformity of the water. The use of strong suction can also increase the chance of rice grains turning over and improve the polishing accuracy. Promoting the separation between rice grains and bran powder is conducive to the removal of bran. Reduce the humidity and temperature of the polished white rice to cool it down. However, if the suction is too large, the rice output will be blocked, the polishing pressure will increase, and the amount of broken rice will increase instead. Therefore, the appropriate suction volume should be selected based on the specific model to effectively reduce fragmentation and facilitate the exertion of the polishing effect.

3.5 Rice Flow Rate

During the polishing process, the flow rate should be stable. If the flow rate is too small, the rice grains will have too many opportunities to flip in the polishing chamber, generating excessive friction and impact force, which will cause overgrinding. Overgrinding not only makes the surface of the rice grains lose its luster but also seriously affects the rice yield. If the flow rate is too high, the rice grains will not roll easily in the polishing chamber, resulting in too few opportunities for them to come into contact with the iron rollers and rice sieves. As a result, the processed rice will not achieve the desired polishing effect. Therefore, during the polishing process, it is necessary to control the flow rate appropriately based on the specific types of processing raw materials and practical operations. Only in this way can the rice grains be appropriately turned over, impacted, squeezed and rubbed in the polishing chamber, ensuring that the rice processed by the polishing machine achieves the process effect of intact grains and a bright surface.