Understanding the Differences Between Live Shaft and Dead Shaft in Pulleys

July 1, 2019

Dead shaft pulleys are laid out just as an observer would expect. That shaft is one long, uninterrupted tubular rod. It enters the pulley, carries on through to the other side, and then it exits the drum at the other end. Moving over to a live shaft configuration, a fixed face occupies each of the pulley sides, so there are two discrete shafting elements, one supporting each pulley cap.

Live Shaft Basics

Joined to each fixed cap face, the shaft elements connect. That means the shaft and roller drum are attached to one another. As soon as the conveyor system picks up speed, the drum cylinder and shaft rotate as one. To a casual bystander, the pulley architecture looks simple. The whole cylinder, shaft included, looks like a single-piece construct. That leaves the bearings, which are mounted on the machine frame, not inside the pulley drum. Built as pillow block or as flange-mounted bearings, the shaft rotates within those lubricated fittings.

A Dead Pulley Comparison

Upon getting up close, the differences are obvious to see. Dead pulleys use a single long shaft, and that runs through the centre of a pulley drum. Furthermore, the mounting bearings aren’t fixed to a frame. Rather, they’re installed inside the drum, where they encircle the shaft. Architecturally, the two shafting configurations are different. Of course, the differences don’t stop there. Let’s keep going so that we can see if the bearing and shafting dissimilarities also affect pulley performance. And, should there be performance contrasts, how does that affect application issues? We’ll start with live shaft pulleys again.

Live Shaft VS. Dead Shaft Application Differences

In a live shaft, with the unibody design in charge, the pulley bearings are mounted on the machine frame. In high-temperature usage areas, that’s a desirable feature, for the drum’s heat won’t affect bearing performance. And this feature applies to other pulley attenuating forces. So, for chemical attacks, dirt and grit, even for high moisture environments, the distancing of key rotating parts is application beneficial. Also, from a maintenance standpoint, it’s easier to lubricate bearings when they’re mounted on a frame. As for the benefits of dead shaft systems, they’re cheaper to fabricate. Dead shaft pulleys also tolerate load deflections in a way that live systems find hard to imitate.

The advantages continue to accumulate. Dead pulley shafts are superior free-rollers, for the roller body and shaft are fabricated as separate constructs. Accessing this feature, this pulley type delivers low inertia rolling. Expect dead pulley shafts to be installed in applications that require cheap idlers. Live systems, on the other hand, are used in machines that favour high-precision idlers and active process rollers.

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