The designer may omit the hub and immediately attach the blades to the shaft by welding (4′). Impeller hubs welded to the shaft are preferred over removable hubs. hubs, blades, end cap) is still preferred. (d) An all-welded impeller assembly (e.g. The corners of the spanner flats on the end cap have been radiused (9′). Keyways (5), where employed due to mechanical design considerations, shall have edge radii not less than 3 mm. (c) Food quality gaskets under controlled compression respectively may seal the propeller hub to the shaft (8) and to the end cap (8′). The sharp corners of the spanner flats (9) on the end cap may be difficult to clean. In that way, the keyway (5) also may retain product and microorganisms. The non-welded impeller hub-to-shaft and hub-to-end cap connections give rise to crevices and metal-to-metal joints (respectively 6′ and 6″) that may allow the ingress of product and bacteria. (b) Once the hub (2) is secured to the shaft (1), an end cap (impeller nut, 7) is screwed on the interior male thread end of the shaft.
spray ball and wand additions, increased CIP flow and adjusted spray coverage. Keyways may require additional design and/or cleaning practice to ensure drainage and cleanability, e.g. Keyways (5) exposed to product are not recommended, because product and microorganisms may be retained in the keyway. To avoid the latter problem, the joint between the blade and the lug on the hub can be sealed by a thin gasket. These exposed screw heads (even bolts with dome head nuts and washers of suitable food grade material) again will create a food safety hazard, and the blade-to-hub connection gives rise to a new metal-to-metal joint (6).
Agitator blades (4) should be welded to the hub, although screw connections are sometimes observed.
The hub-to-shaft connection gives rise to a metal-to-metal joint (6′) that may permit the ingress of product and bacteria. (a) The hub (2) is secured to the shaft (1) by means of a screw (3), which is exposed to product that may collect in and around the screw head.
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