Keyless Locking Elements

What is a keyless locking element?

A keyless locking element, also known as a shaft clamping element or locking assembly, is a device used to fix a hub, such as a pulley, sprocket, gear, coupling, or lever, onto a shaft without the need for a keyway, spline, or set screws. It works using tapered rings. When the rings are pushed together, usually by tightening screws or a clamping flange, the tapers force the inner ring to contract onto the shaft and the outer ring to expand into the hub bore. This creates a very high clamping pressure that locks the hub and shaft together by friction.

Because there is no key or keyway, the connection has no backlash, the hub can be fixed at any position and angle on the shaft, and the shaft is not weakened by a cut keyway. The connection can also be released easily, making adjustment and maintenance simple.

A typical keyless locking element has:

• Inner ring - a ring with a tapered outer surface that contracts onto the shaft
• Outer ring - a ring with a tapered inner surface that expands into the hub bore
• Clamping method - either a separate pressure flange and screws, or built-in clamping screws on self-contained designs
• Precision bore and outside diameter - matched to the shaft diameter and the hub bore

Key features:

• Keyless connection - no keyway, spline, or set screws needed
• Zero backlash - gives a tight, play-free connection, ideal for reversing drives and precise positioning
• Infinite positioning - the hub can be fixed at any axial position and angle on the shaft
• High torque transmission - transmits torque, axial loads, and bending loads by friction
• Protects the shaft - avoids weakening the shaft with keyways and avoids damage from set screws
• Easy fitting and removal - fitted and released with standard tools, without heating or pressing
• Reusable - can often be removed and refitted during maintenance

In simple terms, a keyless locking element is a set of tapered rings that clamp a hub tightly onto a shaft, giving a strong, play-free connection without a key.

Why are keyless locking elements essential?

Keyless locking elements are essential because many machines need a strong, accurate, and adjustable connection between shafts and hubs. Keyed connections can develop play over time, especially in reversing or shock-loaded drives, and keyways weaken the shaft and can be costly to machine. Set screws can mark shafts and work loose. Keyless locking elements solve these problems with a connection that is tight, precise, and easy to adjust.

Their main benefits are:

• No backlash - ideal for reversing drives, indexing mechanisms, and precise positioning
• Easy adjustment - hubs can be repositioned or timed to the exact angle needed
• Stronger shafts - no keyway means the shaft keeps its full strength
• Lower machining costs - plain shafts and bores are cheaper and quicker to produce than keyways and splines
• Reliable torque transmission - high clamping pressure transmits heavy loads
• Reduced wear - no movement between parts, so less fretting and keyway wear
• Quick maintenance - components can be released and removed easily, reducing downtime
• Overload protection - in some applications, the connection can slip under severe overload, helping protect other parts of the drive

Keyless locking elements are used across a wide range of industries and applications, including:

• Power transmission - fixing pulleys, sprockets, gears, and couplings to shafts
• Conveyors - mounting drive and return drums and pulleys
• Packaging and printing machinery - precise timing and positioning of rollers, cams, and gears
• Machine tools - backlash-free connections for drives and positioning systems
• Pumps, fans, and compressors - mounting impellers, hubs, and couplings
• Agricultural and construction machinery - fixing hubs and drive components
• Robotics and automation - precise, play-free connections for drives and actuators
• Heavy industry - mining, steel, and processing equipment

The main types of keyless locking elements

Keyless locking elements are usually grouped by their design and how they are clamped.

Tapered ring sets:

• Ring pairs - simple sets made up of an inner and outer tapered ring. They need an external clamping device, such as a pressure flange and screws, to push the rings together. They are compact, economical, and suit lower to medium torque applications
• Multiple ring sets - two or more ring sets used together to increase the torque that can be transmitted, with each additional set adding extra capacity

Self-contained locking assemblies:

• Locking assemblies with clamping screws - complete units with built-in screws that pull the tapered rings together. They are easy to fit and do not need a separate clamping flange
• Self-centring locking assemblies - designed to centre the hub accurately on the shaft, ideal where good concentricity is needed
• Compact locking assemblies - shorter or narrower designs for limited space and smaller hubs
• Heavy-duty locking assemblies - designed to transmit very high torque and loads in large drives

Other designs:

• Shrink discs - fitted around the outside of a hollow hub or shaft, clamping it onto the shaft inside. Often used on hollow-shaft gearboxes
• Locking bushes - keyless designs that combine clamping with a flanged or shouldered body for easy fitting

How to choose the right keyless locking element?

Choosing the right keyless locking element means matching it to the shaft, the hub, and the loads in the application. Work through these points in order:

• Shaft diameter - choose an element with an inner diameter that matches the shaft
• Hub bore - choose an element with an outer diameter that matches the bore of the hub
• Torque - check that the element can transmit the required torque, including starting loads, shock loads, and reversals
• Axial and bending loads - consider any axial forces or bending moments the connection must carry
• Design type - choose ring sets for simple, economical connections with an external clamp, or self-contained locking assemblies for easy fitting and higher loads
• Number of ring sets - for ring pairs, use additional sets if more torque capacity is needed
• Hub strength - make sure the hub has enough wall thickness and strength to withstand the clamping pressure
• Concentricity - choose a self-centring design where accurate centring is important
• Space - check the length and outside diameter fit the available space in the hub
• Shaft and bore tolerances - make sure the shaft and hub bore are machined to the tolerances recommended by the manufacturer
• Environment - consider corrosion-resistant versions for wet or corrosive conditions
• Quality and brand - choose elements from reputable suppliers for accurate dimensions and reliable clamping

FAQ - All you need to know about keyless locking elements

How does a keyless locking element work?

It uses tapered rings that are pushed together by screws or a clamping flange. As they move together, the inner ring contracts onto the shaft and the outer ring expands into the hub, creating high clamping pressure that locks the hub to the shaft by friction.

What are the advantages over a keyed connection?

Keyless locking elements have no backlash, do not weaken the shaft with a keyway, allow the hub to be positioned at any angle and position, and are easy to adjust and remove.

What is the difference between a ring set and a locking assembly?

A ring set is a simple pair of tapered rings that needs an external clamping flange and screws. A locking assembly is a complete unit with built-in screws, making it easier to fit and often able to transmit higher torque.

Can I use more than one ring set?

Yes. Using two or more ring sets increases the torque capacity, although each additional set adds less capacity than the first. Follow the manufacturer’s guidance on how many sets to use.

How do I measure for a keyless locking element?

Measure the shaft diameter and the hub bore. The element’s inner diameter must match the shaft, and its outer diameter must match the hub bore.

How do I fit a keyless locking element?

Clean the shaft, hub bore, and element, and apply light oil if the manufacturer recommends it. Slide the element and hub onto the shaft, position the hub, then tighten the screws gradually and evenly in several stages to the recommended torque.

How do I remove a keyless locking element?

Loosen the clamping screws gradually and evenly. Many locking assemblies have threaded release holes, where screws can be fitted to push the rings apart and release the connection.

Do I need a special hub for a keyless locking element?

The hub needs a plain bore of the correct diameter and tolerance, and enough wall thickness to withstand the clamping pressure. Ring sets also need a way to apply clamping force, such as a pressure flange and screws.

Can keyless locking elements be reused?

Yes, they can often be reused if they are clean, undamaged, and show no signs of wear or scoring. Check the elements and screws carefully before refitting.

Why is my hub slipping on the shaft?

Common causes include screws not tightened to the correct torque, uneven tightening, incorrect shaft or bore tolerances, too few ring sets, or a torque load higher than the element can transmit. Check the fitting and the element’s rating.