Alternative fasteners confer cost advantages

Written by: Tom Shelley | Published:

Circlips could be an ideal alternative when it comes to reducing the
costs in your next design

Alternative fasteners confer cost advantages

Circlips could be an ideal alternative when it comes to reducing the
costs in your next design. A leading manufacturer sets the scene

Fasteners are undergoing intense scrutiny in the ultimate quest to deliver impeccable quality at a low price in engineering designs. Traditional fasteners like screws, nuts and bolts are the workhorses of this group and deliver excellent retention when applied correctly. However, there are applications which do not require all the holding power of a threaded fastener or similar component. For such cases, the designer should consider the circlip.
Circlips function most effectively on simple shoulders with low static loads. They are lightweight, and generally easy to install (no torque or installation sequences required). They can function in small spaces, with some capable of retaining components in shafts and bores as small as 0.8mm in diameter. Yet, there are circlips capable of withstanding considerable thrust loads. The deciding factor is the application and the capability of the fastener involved as defined by the manufacturer's catalogue.
Simplicity is the hallmark of the circlip. To function, it merely requires the machining of a groove on a shaft or in a housing or bore according to standard catalogue specifications like groove width and groove depth. The circlip is then installed into the groove, and the 'shoulder', which protrudes from the groove, retains the component or assembly.
Circlips are either external, for installation on a shaft, or internal, for installation in a bore. They are further classified as axial, radial or self-locking. Axial clips feature lugs and lug holes for installation using special pliers and make almost complete circular contact with the groove. Radial circlips do not have lugholes and do not extend as far around the circumference of the groove as axial clips, thus accommodating less force. Self-locking rings do not require a groove and can be installed directly on the shaft or in a bore.
Selection of the correct type from the right group can cut costs. In general, radial circlips are less expensive than axial clips, and self-locking clips are the least expensive of the three. However, it is important to know the requirements of the application, especially thrust load, in selecting the right clip at the best price.
The standard circlip line consists of variations of the basic internal and external versions. Each features a subtle design change which accommodates a specific application requirement. But the engineer who is familiar with the different types of clips should be able to select the most cost-efficient and effective design for a given application.
The following are some examples from a standard circlip line:

l Bevelled circlips
Once assembled, components on shafts and in housings sometimes exhibit 'end-play' which can cause unwanted vibration in the assembly. Traditional methods of counteracting this condition included using shims or circlips of different thickness to take up the 'end play'. However, both of these methods can be replaced by a single, bevelled circlip.
A bevelled circlip works on simple engineering principles. Featuring a 15-degree angle on the edge of the ring, the bevelled clip works its way down a complementary 15-degree angle on the outer groove wall during installation, wedging itself between this point and the retained part. The result is a rigid fit that takes up 'end play' and eliminates the need for costly inventories of shims and clips of varying thicknesses.

l Bowed circlip
Bevelled circlips use the wedge effect to totally eliminate 'end play', which is referred to as 'rigid end play take-up'. However, the designer may want a more flexible take-up of the 'end play'. This is accomplished by a bowed circlip. These clips are curved and exert a pre-load on the assembly when installed in the groove. This takes up the 'end play' and acts like a spring, which keeps the assembly in compression. Because of this, the action of the bowed circlip when installed in the groove is referred to as 'resilient end play take-up'.

l Inverted circlip
Sometimes the lugs of a standard axial circlip can interfere with the correct functioning of an application. Standard circlip lines should feature an inverted version, which reverses the lugs.

l Reinforced circlip
There is an impression that the circlip is not capable of functioning in rugged applications. The reinforced external circlip dispels such notions. This is a standard external clip that is extra thick. As such, it is stronger and can withstand greater thrust loads than its standard counterpart, once installed in the groove. A perfect example is the plate and bolt device that connects the treads on a military tank. The reinforced circlip prevents the bolt from loosening and derailing the tread.

Creativity in application

A US transmissions company recently initiated huge cost savings by using bevelled circlips to take up 'end play' in a transmission clutch assembly.
Since the clutch would be subjected to 7,000rpm, taking up 'end play' was critical. The customer originally planned to use two rings of different thicknesses to do the job. After measuring each groove, the operator would select the appropriate ring.
However, this method would require an inventory of two different rings as well as additional time and labour for the operator to measure the groove. Engineers from Rotor Clip suggested a bevelled circlip, which would function in all grooves. Due to the high centrifugal force in the application, they suggested increasing the maximum section of the ring as well as making the Inside diameter slightly smaller. These factors increased the holding power (radial force) of the ring by as much as 25% in the groove. Testing concluded the part would work successfully in the application. (see picture far right)
As a result, the transmission saved 50% in product costs by not having to keep an inventory of two rings. It also saved on the time and equipment needed to measure the groove and determine which of the two rings would be best to use.
The bevelled ring has also been used in other applications in the automotive industry, including turbochargers, air conditioning compressors, transmission assemblies, alternators, starter motors and braking systems.

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