Wood chipper is used in paper mill to produce chips from pulpwood so that cooking chemicals penetrate the wood quickly, completely and uniformly during manufacturing of chemical pulp or mechanical pulp. The process from pulpwood to chips is known as chipping process. The sizes of the good quality chips can be 5/8 to 5/4 inch long and 3-6 mm thickness. Oversize chips can create cooking problems which increases screen rejection. On the other hand, fine chips and rotten chips cause lower yield and strength problem. The available chippers are many sizes and styles. They are portable or stationary. Both types’ chippers have almost the same functions. Often, a truck or van is attached behind the portable wood chipper.
The pulpwood enter into the chute and then the inside blade cut the woodpulp into chips. The pulpwoods are feeded into the chipper as logs or as whole tree. Before entering into the chipper, it should be free of bark. So a debarker may be used before the chipper. Some chipper has both the debark and chipping system. The efficiency of the chipper depends on productivity, power demand, fuel consumption and product quality.
Types of wood chipper
The wood chipper or tree chipper can be different types such as disc type, drum type, high torque roller, screw type etc. Among them the disc chipper and drum chipper are most common chipper in pulp and paper industries. They have some advantages and disadvantages. So you have to choose which is right for you.
Disc chipper
The disc chipper consists of steel disc, spout and chopping blades or knives. The knives are mount on the disc. The number of knives may be 4, 8 or 12. The older chipper had 4-knifes which was lower capacity and produce more waste. Therefore, comes in multi-knives chipper containing 8, 10 and 12 knives which are higher capacity and produce less waste and quality chips. All of them have almost same function. The spout of the chipper may be rectangular or oval shaped. The rectangular shape spout produces more uniform chipper. Usually, the logs are fed to the disc by a sloping spout so that they remain at an angle. After some hours the knives may be changing for sharpening. This process consumes huge energy but produces uniform woodchips. When the disc spins, then the blades cut the pulpwood into chips. The sizes of the chipper depend on disc diameter, number of knives, spout etc.
Drum chipper
The drum chipper consists of large steel drum and blades or knives. The drum is parallel to the hopper. It has some drawback. For example, it creates large uneven chips and has safety issue. But it is more energy efficient compare to disc type chipper. It produces more productive chips.
After the wood chipper, the chips are passing through screens for separate acceptable sizes chips from fine and oversized chips. The chips should be free of dirts, sand, mud, stone and other foreign materials. Hence the chips are wash after screen scetion. Then they are send to storage tank with conveyor velts or pipe line for storage like silos. The outside storage has some disadvantages. The surfaces chips can contaminant with air borne pollutant.
