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NEC Birmingham(B40 1NT)
25/09/2019 - 26/09/2019
Sensors & Instrumentation Live will celebrate its 10 year anniversary in 2019 and the UK’s (more)
NEC, Birmingham(B40 1NT)
01/10/2019 - 03/10/2019
The UK’s largest ever event in the processing and packaging sector calendar. With over 350 exhibitors (more)
The modern take on flat wire spring technologyEdge wound wave springs offer an alternative to the conventional wave washer where performance and space are key requirements.
Simple 'wave' or 'spring' washers, as they are commonly known, are traditionally manufactured by die-stamping from annealed sheet metal and then hardened by an austempering process. They are formed using bespoke tooling in an irregular shape so that, when loaded, they act like a spring, deflecting and providing a pre-load between two surfaces. This characteristic can be used to pre-load shafts or bearings, absorb shock, or compensate for dimensional variations.
This type of wave washer has been used worldwide for almost a century and will continue to be in demand where non-critical control of load and space restriction is not an issue. However modern enhanced quality standards and the onward march towards a more compact and lighter end-product mean that today's designers are demanding ever increasing levels of load control and tighter space envelopes in which the springs must operate. Traditional die-stamped methods of manufacture cannot reliably offer these features. However, TFC's Smalley edge wound wave springs can provide the solution.
Manufactured from flattened round wire and edge coiled to exact specifications, Smalley single turn wave springs are made with either a gap or overlap end configuration. These two types of design permit radial expansion or growth in diameter within a cavity, without the binding or hang-up normally associated with die stamped wave washers. Just as their terms imply, the gap type is split to retain a gap between the ends, while the overlap type has overlapping ends. Thus, the ends are free to move circumferentially as the spring outside diameter grows during compression. Also, since they are cold-rolled and, unlike a die-stamped product that requires heat treatment after manufacture, a greater control of spring force is achieved.
Another significant advantage offered by the edge-coiling process is that there is no costly tooling involved therefore, bespoke designs can be produced, as quickly as a standard product, in economic prototype batches with a diameter range from 5mm to over 2000mm. If necessary, the spring design can be altered, with minimal cost, to provide the exact specification without the need for any compromise on the part of the customer.
Utilising the same edge-winding technique enables several innovative spring types to be available. Crest-to-Crest wave springs essentially pre-stack the springs in series. This decreases the spring rate proportionally to the number of turns. Uses are typically applications requiring low-medium spring rates and large deflections with low-medium forces.
Traditionally, when a low working height compression spring like this was required, it was necessary to physically assemble a series of single die stamped wave washers by welding or riveting at the wave peaks or by inserting a shim between individual springs to form a stack. Since Smalley Crest-to-Crest wave springs are manufactured with a single filament of wire, the spring is integrally formed and the wave peaks hold their configuration without the need for such costly and unreliable processes.
As a replacement for helical compression springs, Crest-to-Crest springs can develop similar forces, yet occupy one-half or less the axial space. This allows for strict space constraints. Crest-to-Crest wave springs will maintain the same force and load specifications of a conventional round wire spring, but with the advantages of lower operating heights, free heights and solid heights.
Crest-to-Crest wave springs are also available with squared-shim ends. Shim ends provide a 360° contact surface when compared to the wave point contact of plain ends. The shim-ends under load more evenly distribute the spring's force upon adjacent components. Shim ends have also been used to affix springs to mating components, as a flat locating surface that may be attached by various methods in the assembly.
An interlaced Crest-to-Crest wave spring is formed from two or three constituent wave springs of similar thickness, amplitude and frequency. The constituent wave springs are wound together to interlace them so that the turns of each spring align each other for the entire length of the interlaced spring. This interlacing effectively increases the thickness of each turn to provide increased loading whilst maintaining similar deflection.
Nested wave springs are pre-stacked in parallel from one continuous filament of flat wire. The need to stack individual springs for higher loads is no longer necessary. Nested springs result in a spring rate that increases proportionately to the number of turns. They can exert tremendous forces yet maintain the precision of a circular-grain wave spring. In many applications, nested wave springs replace belleville springs, particularly in cases where space is tight and accurate force is needed.
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