Ring Die and rollers are the key parts of pellet mill, the most important working and abasing components. Their performance and quality will directly affect the production efficiency and product quality of the pellet mill.

1. Die
Ring die is an annular column having a plurality of uniformly distributed small holes. During pelletizing, the material get through the holes on the ring die by the strongly squeezed pressure between the ring die and rollers, therefore the ring die should have high strength and wear resistance.

1) Materials and Processing

At home and abroad dies are generally made of high quality alloy steel, chrome steel and carburizing stainless steel, of which carburizing stainless steel is the best choice due to excellent wear resistance, high breaking capacity, corrosion resistance and low cost. SIMEC uses reliable technology to make the quality of ring die and the rollers to achieve world-class level, and the service life span is about 2,500~3,000 hours to make wood pellets.

2) Die Hole

SIMEC can make straight holes, stepped holes, outer cone, inner cone and so on, to achieve various kinds of compress rates.

Compress rates will be designed based on general analysis on raw material and customers’ requirements.

Opening rate on working surface of die is an important indicator of it, it is the working surface (inner wall) total area of the die hole divided by the total area of the total die working surface area. The opening rate has a great impact on the productivity of the pellet mill, in consideration of the die’s sufficient strength to maximize the opening rate.

3) Die Thickness

Die thickness and pore size are related to the characteristics of the material being pressed, the thicker die, the deeper holes, the smaller aperture, the greater resistance of the hole wall, the more solid material extrusion. To press different materials, not only choose the die by the aperture, but also the appropriate die thickness, that the choice of the best deep (thick) diameter ratio, in order to obtain high-quality pellets without clogging the die holes.


2. The Rollers


Rollers are used to squeeze material into the die and make material pelletized by the die holes.

1) Materials and Processing

Die, roller linear is velocity substantially equal, throller is only 0.4 of die, so the press roller wear rate is 2.5 times higher than the die. To enhance the ability of the press roller to grab, typically drawing at the roller surface in the axial direction (not exceed both ends of the groove, to avoid the material overflow ), or open pit.

2) Number and Size of the Press Roller

Amounts of press rollers in the die are generally 2 for wood pellet mill. The width and diameter ratio of the roller can be determined by two factors: 1. the die cavity pressure limit; 2. the size of the bearing installed in its internal. Considering the two factors mentioned above, the ratio can be decided to 1.0 ~ 1.6.

3) Gap between Die and Rollers


Die and the press roller gap adjustment is extremely important. If the gap is too small, it will exacerbate the mechanical wear die roll; if the gap is too large, easy to cause the material to slip in between the die rolls, impact extrusion materials, the particles quality deterioration.