Sharpe Hub and Attachment Options
Most mixer manufacturers, committed to solid shafting even on larger mixing equipment, use cast impeller hubs with bolted blades. These keyed-in-place designs have many disadvantages including weight, high stresses at the point where the bolted blades attach, and problems with removal. These keyed hubs also prevent the use of more rigid hollow shafting.
Sharpe Mixers overcomes these inherent disadvantages with a family of hub designs that are unique in the industry. Depending on the application requirements, Sharpe impellers are normally attached to the mixer shaft by one of the following means:
Sharpe Mixers overcomes these inherent disadvantages with a family of hub designs that are unique in the industry. Depending on the application requirements, Sharpe impellers are normally attached to the mixer shaft by one of the following means:
SPLIT HUB - Not available from other manufacturers, the Sharpe Mixers Split-Hub design allows for a stronger, lighter, more adjustable and more easily removable impeller. Furnished on most of Sharpe's larger (over 24" dia.) impellers, the two-piece hub clamps onto the mixer shaft much like a split rigid shaft coupling. The clamping force transmits the torque without the use of a key on all but the highest torque installations. This means infinite adjustability of the impeller position anywhere along the shaft, without cutting and weakening the shaft with a keyway. Fail-safe operation is guaranteed on higher-torque impellers by welding "torque pins" on the shaft that fit into matching sockets in the bore of the impeller hub. This pin-and-socket joint prevents movement of the impeller in any direction, and welding the pins to the shaft prevents them from falling off and causing damage to pumps, as loose keys have been known to do. The Sharpe Split-Hub design also allows for a strong welded attachment of the blades to the hub. This joint is normally the highest-stressed part of an impeller, and is often the point of failure on bolted-blade designs. Another strong advantage of Sharpe's Split-Hub impellers is the ease of disassembly. Keyed, one-piece hubs can get stuck on the shaft and be difficult (or impossible) to remove. The Split-Hub impeller is easily removed by using a crowbar (if necessary) to pry the two halves of the impeller apart.
Split hubs are available in standard cast form (where cleanability is not a problem) and polished & gasketed "block" style for a more sanitary design.
ONE-PIECE - Sharpe Mixers normally reserves one-piece hubs for smaller, one-piece impellers (without bolted blades) when solid shafting is used. These impellers, usually 24" diameter and below, can pass through an 18" manway without the need for removable blades. The strength of a welded blade-to-hub attachment is retained and ample clearance in the hub bore allows for easier removal from the shaft. Torque is transmitted thru a standard setscrew & key design or a torque "divot" in the shaft. On the "divot" design, one setscrew in the impeller hub extends into one of many sockets machined into the shaft. This pin-and-socket design is similar to the torque pins used on larger split impellers, preventing slippage of the impeller and removing the concern of loose keys damaging downstream pumps.
ONE-PIECE - Sharpe Mixers normally reserves one-piece hubs for smaller, one-piece impellers (without bolted blades) when solid shafting is used. These impellers, usually 24" diameter and below, can pass through an 18" manway without the need for removable blades. The strength of a welded blade-to-hub attachment is retained and ample clearance in the hub bore allows for easier removal from the shaft. Torque is transmitted thru a standard setscrew & key design or a torque "divot" in the shaft. On the "divot" design, one setscrew in the impeller hub extends into one of many sockets machined into the shaft. This pin-and-socket design is similar to the torque pins used on larger split impellers, preventing slippage of the impeller and removing the concern of loose keys damaging downstream pumps.
ALL-WELDED - There are many specific reasons for permanently welding the impeller to the mixer shaft. These include Halar, Kynar, rubber and other coated impeller assemblies and sanitary and pharmaceutical-grade applications that cannot have any cracks or crevices on any wetted parts. Sharpe Mixers specializes in these more "exotic" designs and has the experience to prepare the equipment properly for the coating (or polishing) and to handle and package the equipment following specific procedures to prevent damage to the coating or the surface polish.
Bolted Blades - Sharpe impellers on larger designs (shafts greater than 6 1/2" dia.) are usually built using a welded hub and bolted blades. This is due to the weight problems associated with casting a hub for an 8" or 12" diameter shaft. These impellers are designed specifically for the application, carefully engineering every weld, bolt and section of the impeller to handle the torque, thrust and bending moments generated by the blades. The impellers pictured above are 179" in diameter mounted on a 40' long 12.8" diameter shaft operating in a lime slurry.
Bolted Blades - Sharpe impellers on larger designs (shafts greater than 6 1/2" dia.) are usually built using a welded hub and bolted blades. This is due to the weight problems associated with casting a hub for an 8" or 12" diameter shaft. These impellers are designed specifically for the application, carefully engineering every weld, bolt and section of the impeller to handle the torque, thrust and bending moments generated by the blades. The impellers pictured above are 179" in diameter mounted on a 40' long 12.8" diameter shaft operating in a lime slurry.
