Drum Screen

Drum screen (or trommel screen) allows dimensional sorting of incoming material into two or more fractions. They can be placed individually or in cascade (primary and secondary screen) to obtain successive sorting refinements.

The drum screen (or rotating sieve) essentially consists of a rotating cylinder (with cylindrical or octagonal section) with perforated walls. Rotation is maintained through rubber wheels by one or more electric motors powered by frequency converters (variable speed).
The drum screen, depending on the size and shape of the holes of the inner metal walls, can perform the function of a sieving drum, therefore remove undesired fractions (scrap, powders, unrecoverable sizes …) or the function of a sorting drum, in which the goal is to divide the incoming flow into two or more fractions (to maximize the% of waste recovery or to obtain the ideal size for the downstream machines, such as ballistic separators).

Working principle

The drum screen, loaded by a conveyor belt to the inlet section of the rotor, has inside perforated metal plates. These holes, which may be of different shape and size, let the fine fraction, smaller than the size of the holes (called underscreen), drop below the sieving drum. This fraction can be collected in bins, dropped to the ground and then handled with scrapers or collected with a conveyor. The waste that does not fall through the holes (called overscreen) is discharged into the hopper in the final section of the rotor.

The drum rotor rotates on a tilted axis (3-4°) on rubber wheels bolted on steel shafts: the advancement of the material within the drum takes place by gravity, thereby maximizing the sieving respect to an advancement with spiral on the horizontal axis.

This separation, if the size of the holes and of the rotor (diameter and length) are well-designed, leads to high values of efficiency, thanks to the continuous shaking of the material, even in presence of wet material. In particular the size and percentage of holes respect the unperforated part sets the separation parameters, while the inner diameter and the length of the rotor are instead related to the hourly production.

In addition to the main function of sorting by size the incoming waste, the drum screen also performs other functions, not less important, as the detachment of stuck materials thanks to the continuous shaking, the buffering function and the even and uniform distribution of the output material (essential for downstream manual and/or automatic waste sorting operations).

Types

The drum screens of Parini srl are build on commission, following the demands of the Customer. For this reason, there isn’t a fixed set of models of drum screens, but according to the product input (size, composition and flow rate) and to the fractions to sort, each time the more suitable sieve is designed. Below, by way of example, a table showing two types of drum screens with dimensions and capacities similar to those of many waste sorting plants.

Equipment and Accessories

The Parini srl drum screen is always equipped with the following standard equipment:

• sturdy frame, housing of the wheels that drive the drum and structural support for walkways and railings;
• precision machined rolling tracks on vertical lathe, which allow high rotational speeds and reduced vibration;
• two longitudinal inspection walkways, along large folding maintenance doors, to ease cleaning operations;
• perforated plates bolted to the structure of the rotor, easily replaceable and accessible;
• top cover in calendered galvanized metal sheets, to contain dust and smell;
• metal sheet labyrinth to avoid that waste comes in contact with wheels and supports.

Since the phases of 3D design, construction and assembly of the drum screen are entirely carried out in our workshop, the accessories/changes that we can offer are several. Below is a partial list of the main ones:

• supporting structure with legs and braces, galvanized or painted;
• unloading hoppers, designed depending on the machine placement and the container in which to discharge;
• perforated walls with calendered sheets welded to each hole, to decrease the wrapping of the material between holes, reducing and simplifying the cleaning operations;
• steel blades welded or bolted inside the rotor designed to open plastic bags;
• Special anti-winding system, to avoid the formation of plastic film tresses that might block the downstream machines;
• perforated plates in anti-wear material;
• flanges for the connection to the centralized air filtering system, to prevent the escape of dust and odors;
• rotating cleaning brushes motorized or idle;
• control panel with inverter;
• rubber coating of the hoppers;
• partial or total casing;
• …