2017-05-10/Pellet mill’s ring die and roller gap Adjustment

Ring die and roller shell is an important adjustment parameter in pellet mill operation. The adjustment is also one of the most important steps before pellet mill operation. The gap adjustment rationality directly affects pellet mill’s utility performance. Proper adjustment will ensure that the pellet mill reaches biggest capacity, prolong roller and ring die’s service time, thus decrease production cost, save product cost, and improve economy benefit.

Generally, ring die rotation direction is clockwise, if the pellet mill is equipped with two rollers, when installing rollers we should put the left roller’s maximum decentered jutting edge into lower right quarter. If the pellet mill is equipped with multiple rollers, also ensure that when the eccentric adjusting block rotates along the contrary direction of ring die movement, rollers shall move along the ring die touching direction. Otherwise the rollers are not installed properly, and shall be install again according to the above steps.

The ring die and roller gap is generally 0.3mmn-0.5mmn, the roller outer surface and ring die inner surface shall be slightly touched when adjusting, and roller slightly moves or even no moves under ring die rotation. Normally, if the ring die hole is small, the gap is a little smaller, while if the ring die hole is big, the gap is a little bit bigger; new roller’s gap is small, while old ring die’s gap is big; tight gap will lead to easy damage between roller and ring die, and also will lead to noise, on the contrary, loose gap lead to material squeezing difficulty.

But ring die and roller shell roundness will get distorted after heat treatment, so during adjusting, the roller biggest external diameter shall touch the ring die smallest internal diameter, the gap is still 3.0mm-0.5mm, the adjusting is generally called saltant contact regulating. Never to touch the ring die biggest internal diameter with roller smallest external diameter, otherwise, once roller biggest external diameter touches smallest roller internal diameter, there will be extra radial force (impact load) and abnormal metal friction noice.

Generally, pellet mill roller and ring die is installed in a hanging way. Due to extra external radial force, the hanging beam vibrates, and the counteractive force goes from roller to ring die, which makes the ring die suffer alternating stress cycle, and tear and loosen ring die’s fixing gasket at the bottom, furthermore the ring die fixing bolts suffer from the shear stress.

Thus we can see that roller and ring die gap not only affects the difficulty of pelleting, but also affects the pellet mill’s service time. During pellet mill operation, if ring die fixing bolt and roller bearing always break, and there is no obvious reason, generally it is because of ring die and roller roundness is out of shape and the ring die and roller gap is too small.