Effect of Roller Mill on the grinding stabilities of wheat milling-2 Edit by：www.immy.cn www.immyhitech.com

Effect of Roller Mill on the grinding stabilities of wheat milling-2

Edit by：www.immy.cn  www.immyhitech.com 

Obviously, the convexity or taper value in the grinding roller is too large or too small will cause the inconsistency of the grinding distance and affect the grinding, in order to ensure the overall powder yield, it will inevitably lead to the grinding area local (middle or both ends) rolling distance is too small, resulting in part of the grinding phenomenon, increasing the floating powder content and generating mechanical vibration, so the grinding roller must be ground in strict accordance with the process requirements, and the crown or taper value in the grinding roller must not be too large or too small. In actual production, it is necessary to continuously optimize the convexity or taper value according to the production situation, so that it is constantly close to the best compensation value in actual use.

1.2.2 Dynamic imbalance of grinding rolls

Factors such as casting defects or uneven materials of the grinding roller blank make the centrifugal inertia force generated by each microelement on the roller body not cancel each other when the grinding roller rotates, causing vibration, producing noise, accelerating bearing wear, shortening the life, and radial deformation of the roller body, so that when the roller mill grinding roller rotates and grinds the material, the grinding roller will inevitably have regular intermittent intermittent rolling distance changes in the grinding due to dynamic imbalance, and the larger the unbalance value, the greater the radial deformation of the grinding roller, as shown in Table 1 "the maximum deformation of the grinding roller in the state of unbalance level”。 When the deformation is at the unbalanced point, the rolling distance of the grinding roll will become larger, which will affect the stability of the grinding. To this end, it is necessary to reduce the radial deformation of the roller body due to dynamic imbalance as much as possible, which affects the grinding stability of the mill.

In order to improve the service life of bearings and related parts and reduce the radial deformation of the roller body, it is necessary to dynamically balance the grinding roller to achieve the allowable balance accuracy level, or to reduce the radial deformation and mechanical vibration amplitude of the roller body within the allowable range, GB/T 34669-2017 requires that the dynamic balance of the grinding roller should not be less than G2.5, and the allowable eccentric wheelbase should be 39.9 μm[3].

1.2.3 Radial runout of grinding rollers

The radial runout of the grinding roller is the main reason for the grinding performance of the roller mill, and it is also one of the main factors that cause the regular vibration of the roller mill, especially in the heart grinding process position of the small rolling distance between the rollers, the radial runout value of the grinding roller has a great impact on the stability of the grinding, the original Ministry of Commerce standard requires that the coaxiality of the grinding roller facing the bearing position should not be greater than 0.04 mm, with the continuous improvement of the equipment requirements of science and technology and pulverizing technology, the national standard GB/T 34669— In 2017, it is required that the radial runout of the grinding roller facing the bearing position should not be greater than 0.01mm, and the radial runout of the grinding roller surface in developed countries can be controlled within 0.005 mm, which has reached a fairly high accuracy level, and the highest manufacturing level in China can be controlled within 0.008 mm, which can fully meet the requirements of modern milling technology.

1.2.4 Stiffness of components and structures

Stiffness refers to the ability of a material or structure to resist elastic deformation when subjected to force, the stiffness of parts and components is the basis of the overall stiffness of the structure, and the ability of the grinding unit of the mill to resist elastic deformation is crucial to the stability of grinding.

The rolling distance lag or change caused by the elastic deformation of the grinding unit of the roller mill grinding material or in the process of clutch and rolling distance adjustment has a certain impact on the grinding stability, when the rolling distance is tightened, the rolling distance is adjusted to the required tightness, after 10~20 min grinding, the rolling distance becomes tighter, and when the rolling distance is loosened, the rolling distance is adjusted to the required tightness, after 10~20 After min, the rolling distance will become looser, so in the actual production to adjust the rolling distance according to the equipment situation to master the rolling distance adjustment skills, do not habitually adjust the rolling distance of the mill frequently, often, the poor grinding stability leads to changes in the scraping rate and powder yield, and the frequent adjustment of the mill grinding distance and other improper operations have a greater relationship.

With the application of new materials and new processes, the stiffness and structural strength of parts have been greatly improved, and the changes caused by elastic deformation of grinding and rolling distance have been basically eliminated.

2  Epilogue

The grinding stability of the mill directly affects the overall process material balance, energy consumption and flour quality of the wheat milling process. The study of grinding stability will also be an eternal topic, and will be continuously improved in the development of mills and milling processes, so that they can meet the requirements of contemporary milling processes as much as possible.