A pellet mill, also known as a pellet press, is a type of

mill Mill may refer to: Science and technology * * Mill (grinding) * Milling (machining) * Millwork * Textile mill * Steel mill, a factory for the manufacture of steel * List of types of mill * Mill, the arithmetic unit of the Analytical Engine early ...

machine press A forming press, commonly shortened to press, is a machine tool that changes the shape of a work-piece by the application of pressure. The operator of a forming press is known as a press-tool setter, often shortened to tool-setter. Presses ...

used to create pellets from powdered material. Pellet mills are unlike

grinding mills A mill is a device, often a structure, machine or kitchen appliance, that breaks solid materials into smaller pieces by grinding, crushing, or cutting. Such comminution is an important unit operation in many processes. There are many different ...

, in that they combine small materials into a larger, homogeneous mass, rather than break large materials into smaller pieces.

Types

There are many types of pellet mills that can be generally grouped into ''large-scale'' and ''small-scale'' types. According to the production capacity, pellet mills also can be divided into flat die pellet mill and ring die pellet mill.

Large-scale

There are two common types of large-scale pellet mills: ''flat die'' mills and ''ring die'' mills. Flat die mills use a flat die with slots. The powder is introduced to the top of the die and as the die rotates a roller presses the powder through the holes in the die. A cutter on the other side of the die cuts the exposed pellet free from the die. In the ring die there are radial slot throughout the die. Powder is fed into the inside of the die and spreaders evenly distribute the powder. Two rollers then compress the powder through the die holes. Two cutters are used to cut the pellets free from the outside of the die. Large scale pellet mills are usually used to produce animal feed,

wood pellets Pellet fuels (or pellets) are biofuels made from compressed organic matter or biomass. Pellets can be made from any one of five general categories of biomass: industrial waste and co-products, food waste, agricultural residues, energy crops, and ...

, and fuel pellets for use in a

pellet stove A pellet stove is a stove that burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces. By steadily feeding fuel from a storage container (hopper) into a burn pot area, it produces a con ...

Small-scale

Small-scale mills are usually variations of

screw press A screw press is a type of machine press in which the ram is driven up and down by a screw. The screw shaft can be driven by a handle or a wheel. It works by using a coarse screw to convert the rotation of the handle or drive-wheel into a small d ...

es or

hydraulic press A hydraulic press is a machine press using a hydraulic cylinder to generate a compressive force. It uses the hydraulic equivalent of a mechanical lever, and was also known as a Bramah press after the inventor, Joseph Bramah, of England. He ...

es. The same basic process is used for both types. A die, also known as a mold, holds the uncompressed powder in a shaped pocket. The pocket shape defined the final pellet shape. A

platen A platen (or platten) is a flat platform with a variety of roles in printing or manufacturing. It can be a flat metal (or earlier, wooden) plate pressed against a medium (such as paper) to cause an impression in letterpress printing. Platen m ...

is attached to the end of the screw (in a screw press) or the ram (in a hydraulic press) which compresses the powder. Some platens are heated to speed up the time it takes and improve the overall structure of the pellet. They may also have water ports for quick cooling between uses.

Applications

One of the more common applications is to produce KBr pellets which are used in

infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...

applications. Animal feed pellets are usually a mixture of dry powdered feedstock, such as flour,

sawdust Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling, planing, and routing. It is composed of small chippings of wood. These operations can be performed by woodworking machine ...

, or

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns a ...

, and a wet ingredient, such as molasses or steam. Feedstocks for pellet mills can sometimes break down and then re-form, or

polymerize In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many for ...

, under the extreme heat and pressure of the pellet mill.

References

{{DEFAULTSORT:Pellet Mill Grinding mills