Bevel-helical gearboxes B3 ition Mounting position H Mounting position M B3-KH-26-A

Flender/Flender Gear Units/Bevel-helical gearboxes B3

rt, clear, heat sealabil- acid ity at low temperature, inter- mediate 2O barrier, low gas barrier Source : Adapted from Jelen ( and Brown (. 4.4 Coated Films Individual lms are often coated with other polymers or aluminum to improve their barrier properties or to impart heat sealability. For example, nitrocellulose is coated on one sideof cellulose lm to provide moisture barrier but to retain oxygen permeability. coating of vinyl chloride or vinyl acetate gives stiffer lm, which has intermediate permeability. Sleeves of this material are tough, stretchable, and permeable to air and moisture. thin Packaging of Fruits and Vegetables 5 coating of aluminum (termed metallization ) produces very good barrier to oils, gases, moisture, odors, and light. Metallized lm is less expensive and more exible than foillaminates that have similar barrier properties and is therefore suitable for high-speed llingon form-ll-seal equipment. Cellulose, polypropylene, or polyester is metallized by depos-iting vaporized aluminum onto the surface of lm under vacuum. Metallized polyester has higher barrier properties than metallized polypropylene, but polypropylene is nding more widespread use as it is currently less expensive. 4.5 Laminated Films Lamination of two or more lms improves the appearance, barrier properties, or mechani- cal strength of package. Materials that can be laminated to each other include plastic to plastics, paper to plastic, paper to aluminum foil, and paper to aluminum foil to plastic. Several methods can be used to laminate materials, including dry and wet bonding, thermalextrusion, and coextrusion. Laminated materials are used when high gas and moisture characteristics are re- quired for long shelf life. Laminated structures usually consist of an outer protectivetougher layer, .., nylon or polypropylene, middle high gas barrier layer, .., EVOH or PVDC; and an inner heat sealant layer. Low density polyethylene (LDPE) is commonly used as heat sealant la