A tub grinder operates primarily by using gravity to feed material into a powerful hammermill located at the bottom of a rotating tub, effectively breaking down large volumes of organic material like wood into smaller fragments.
The Grinding Mechanism
Tub grinders are designed for high-capacity reduction of various materials, particularly wood and vegetative waste. The core of their operation hinges on a simple yet highly effective process:
- Gravity Feed: Tub grinders rely primarily on gravity to feed the material into the hammermill at the bottom of the tub. Material, such as tree limbs or brush, is loaded into the large, open tub.
- Tub Revolution: As the material rests within the tub, the tub revolves continuously. This rotation helps to agitate and consistently direct the material downwards towards the center, where the grinding action takes place.
- Hammermill Action: Located directly below the revolving tub is the hammermill. This is the heart of the grinding process. As the tub rotates, the hammermill below rapidly rotates, equipped with heavy steel hammers that shatter the wood into smaller fragments. The force of these hammers, combined with the material being constantly fed by gravity and the tub's rotation, efficiently breaks down the input material.
- Fragment Discharge: Once the material is sufficiently reduced in size, it passes through screens or grates around the hammermill, and is then discharged from the machine.
Key operational aspects include:
- Continuous Material Flow: The combination of the revolving tub and gravity ensures a steady and consistent flow of material into the hammermill, optimizing grinding efficiency.
- High Impact Reduction: The hammermill's high-speed rotation and the robust nature of its hammers provide significant impact force, necessary for breaking down dense materials like wood.
- Size Reduction Control: The size of the output material can often be adjusted by changing the screens or grates surrounding the hammermill, allowing operators to achieve different fragment sizes for various applications.
Material Loading Process
While the internal mechanism handles the grinding, getting the material into the tub is also a crucial step. Large material is typically loaded into the tub grinder using heavy machinery:
- Excavator Loading: An excavator is commonly used to feed material into the tub. This machine features a hydraulic system that allows the operator to raise and lower the long boom and bucket, precisely placing large volumes of wood waste, logs, or other organic debris into the grinding tub. This method ensures efficient and safe loading, especially for oversized or irregularly shaped materials.
