Extruder Gearbox Bearings Multi-Stage Cylindrical Roller Thrust Bearings F‐59224 In Stock

Food Extruders
Longitudinal section of a screw extruder of thermoplastic polymers. Plastic pellets are fed from a hopper into the barrel of the extruder, where the pellets are gradually melted by mechanical energy generated by a turning screw and by heaters arranged along the barrel. The molten polymer is forced through a die, which shapes the extrudate into products such as the examples shown.

Extruders are used to produce long continuous products such as tubing, tire treads, and wire coverings. They are also used to produce various profiles that can later be cut to length. Multiroll calenders are used to make wide sheeting.

Many types of extruders are used in the food industries and several designs are possible for a food extruder. The most commonly used extruder consists of the flighted screw(s) or worm(s) rotating within a sleeve or barrel to be termed as the screw extruder. However, the piston type extruders are possible though they are used in other type of industries. The flights on the screw push the plasticized material forward and discharge through an opening or the die. The details on the different type of extruders and their components are available (Harper, 1981; Yacu, 2012).

A variety of extruders have been developed to manufacture different types of food products. On the basis of the number of the screw, extruders can be classified as a single-screw or twin-screw extruders. The twin-screw extruder is partially developed on the experience and the knowledge derived from the understanding of single-screw extrusion cooking.

A conventional single-screw extruder usually has three sections: feed, transition, and metering zones. The extrusion screws sequentially convey the incoming feed in the feed section, and heats the feed to form a continuous plasticized mass (in transition and metering sections), while rotating in the barrel. The screw can be designed either as a single piece or as several small segments. Twin-screw systems are costlier and more complex than the single-screw extruders. However, the twin-screw extruders are preferred by food industries due to improved mixing abilities, uniform temperature distribution features, facility to control the feed residence time, and enhanced positive displacement capacity. The twin-screw extruders, on the basis of rotation, can be categorized as counter-rotating and corotating twin-screw extruders. The food industries prefer fully-intermeshing corotating twin-screw extruders because of several technological features, particularly, the better control of machine and product, and the efficient operation during extrusion cooking.