The compost be screened according the different particle size of the compost, that be called compost screening. Trommel screen is a widely used compost screening machine. It is use of rotating cylindrical screen body to screening the material size classification machinery. The screen surface of trommel screen is made by rayon net or sheet with hole. When working, the cylindrical screen body is installed inclination. With the rotating action of the sieve body, the screened garbage turns spirally, and the material whose particle size is smaller than the sieve hole is screened, while the material left on the sieve body is discharged from the bottom end of the sieve body. In this paper, the main design parameters are derived by studying the motion characteristics of materials in the screening process.

Mainly parameter design of compost trommel screen

The parameter design of compost trommel screen can be divided into geometric parameters, motion parameters and dynamic parameters. Geometric parameter includes the length of screen L, the diameter of screen D, inclination angle H, mesh diameter d, motion parameter means the screen vibrating speed n, dynamic parameter means the driving power P.
Commonly, in the trommel screen design, the known conditions are as following: 1. Capacity, it is refers to the trommel screen treatment of compost volume per hour, generally it measured by volume; 2. Screening efficiency G, It means the ratio of the amount of material under the sieve actually measured to the amount of material under the sieve theoretically measured, G= c/ e*100%, where, c is the proportion of the material under the actual sieve to the feeding amount, and e is the proportion of the content of the feeding material less than the mesh size of the sieve; 3. Mesh diameter, It is to limit the boundary between the upper and the lower part of the screen, the size of the screen hole should be considered to determine the drum screen with the purpose of the body, but also should consider the composition of the trash to be screened and the requirements on the upper or lower part of the screen; 4. The characteristic of material, the material characteristics that influence the screening efficiency mainly include the material density, material shape and material friction.
Motion parameter of material
The movement of materials in the trommel screen can be divided into linear movement along the axis of the screen body and plane movement perpendicular to the axis of the screen body. The linear motion along the axis of the sieve body is caused by the inclined installation of the sieve body. The movement of the material in the plane perpendicular to the axis of the sieve body is closely related to the rotating speed of the sieve body.
When the rotation speed of the screen body is low, the material starts to shift and slide with the rotation of the screen body. With the increase of the rotating speed of the sieve body, the material is brought to a certain height and falls parabolic. This movement is called dropping movement, which is conducive to the screening. If the speed of the screen body is large enough, the material does centrifugal motion, at this time the material cannot be screened, then the screen body speed is called the critical speed.
3. Screening efficiency and productivity
The improtant thing for design the trommel screen is that determine its main parameter to meet the design requirement in screening the specific material. Generally, when other parameters of trommel screen are determined, the productivity is inversely proportional to the screening efficiency. In general, we always efine the material flow Q at the feeding port as the productivity.