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Variable Speed Marine Pump

An industrial pump manufacturer approached SPIROL with a new heavy duty marine application. In a smaller version pump, the company currently uses a heavy duty .187” diameter Coiled Pin to attach an aluminum shaft to a powdered metal rotor. The shaft / rotor is exposed to 12.5 ft/lbs of torque in this application. This existing application has worked well for years. The new heavy duty marine design exposes the shaft / rotor to 20 ft/lbs of torque and the pump designer wanted help to ensure that the pin was properly selected to absorb the additional torque. The customer wanted to use the same pin in both applications, but in their trials, the pin sheared in the heavy duty application.

Coiled Pin fastens the shaft to the rotor

app coiled pin variable speed marine pump problem

Shortcomings of the original design: A) Excessive distance between planes. B) End of pin is < 1 diameter away from shear plane.

app coiled pin variable speed marine pump solution

SPIROL solution: A) Countersink removed and distance between shear planes reduced. B) End of pin is > 1 diameter away from shear plane.

SPIROL Application Engineers evaluated the application and suggested three design improvements: (1) the relationship between the Shaft OD and the rotor ID be changed to have a maximum clearance of .005” which minimizes the shear plane between the two, (2) the shear plane be moved to at least one diameter length away from the end of the pin (currently .125”) which ensures that the pin interfaces securely with the hole without significant movement, and (3) eliminate the lead-in on the aluminum shaft which contributes to a poor shear plane at the shaft / rotor joint. The existing design elements were placing extra shear requirements on the pin which could be minimized with the above changes.

SPIROL Application Engineering also suggested a change to the pin. In this case the pin is installed in a soft aluminum shaft. During cycling, the heavy duty Ø.187 pin - which is strongest yet least flexible Coiled Spring Pin available - breaks down the edge of the hole on the aluminum shaft deteriorating the shear plane. Heavy duty pins are not recommended for use in soft materials. SPIROL recommended that the customer move to a more flexible Coiled Pin, which in this case was the standard duty pin. The increased flexibility protects the soft material by allowing the pin to absorb the dynamic forces rather than transmitting them to the host. Additionally, by correcting the shear plane issues above, the customer could move to a smaller diameter Ø.125” pin. With the smaller diameter standard duty pin, there is a commensurate pin price reduction.

By incorporating SPIROL’s suggestions, the customer can use the same pin in both applications, reduce machining costs for the lead-in on the shaft, and reduce the cost of the pin in the assembly. These cost savings were accomplished with an increase in performance of both pumps.

SPIROL Products in this Application Story

Coiled Spring Pins

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