Lee Spring provides customer assist service to UK manufacturing

As a manufacturer of industrial springs, Lee Spring carry over 23,000 catalogued items but it is just as common to find that a variant or complete custom item is required to suit a new project or a revised assembly process where a special spring design may contribute added quality to the operation of a product or to its longevity, often with significant savings in component cost and/or assembly time.

The Lee Spring in-house technical capability, derived from global experience since 1918 working alongside customers of all types, enables them to develop project specifications to international standards such as RoHS, REACH and DFARS. This means that they can hand-hold customers through the specification prototyping, development and trials process to final sign-off and mainline production. Expert staff in the UK are capable of dealing with full CAD modelling through prototyping and supply chain management for commercial, industrial, aerospace and military sectors. Custom springs may be subsequently stocked in depth to meet customers' production schedules, so enabling efficient and timely delivery throughout the world.

From long experience it has been found that while spring technology is a well-established and well-understood engineering discipline, their design is both complex and variable. This means that it is difficult for design engineers to be aware of everything - and it is therefore important to consult the spring manufacturer at an early stage in order to decide on the function of the spring and its detail design before working on the rest of the application. If this is not done then there is a risk that retro-fitting to suit space already designed may not be possible, or may be very much more expensive than otherwise. Lee Spring has an experienced team ready and waiting to help.

Of course, the first step is often to explore a typical custom variant from the standard spring range and this will include varying finishes, alternative materials for enhanced performance, polishing or coating, non-standard loadings, non-standard sizes, matching to suit exceptional environments, demands for extreme longevity or specific concerns regarding materials matching, etc. Equally, a common request is often to meet tighter tolerances which may be required for specialist housing designs. The broader custom process frequently encompasses meeting of special standards, non-standard finishes - for aesthetic or functional reasons, such as colour matching or colour coding; also special shapes, special end forming, retaining clips, wire forms and stampings or other formed metal parts (fourslide parts), trim clips etc.

Special finishes

A vital part of custom design is the selection of secondary operations such as assembly, colour coding, electro-polishing, grinding, heat treating, looping, passivation, powder coating, shot peening, spring setting, plating for example with nickel or zinc, and use of other special finishes such as black oxide.

Although the development of springs could be described as evolution rather than revolution, in recent years manufacturing processes and changes in end-use criteria have impacted on the specification of these ubiquitous products. For example, medical, aerospace, food and toy applications demand special load characteristics and treatments, such as ultrasonic cleaning, while RoHS, WEEE and REACH have influenced the types of finishes offered.

The most popular types are compression, extension, torsion, wave and disc springs. Added to these are conical, swivel hook, battery and drawbar springs. More recent additions include continuous-length extension springs, light-pressure springs as featured in Lee Spring's latest stock spring catalogue and the Mini Compression BANTAM type.

Probably the most important consideration for a custom spring design is the choice of material which can greatly influence the size, suitability, performance and longevity of the finished item. Most standard stock springs are manufactured in music wire, stainless steel, oil-tempered MB, chrome silicon steel or Elgiloy, a cobalt/chrome nickel alloy, and these are options for custom variants and for full one-off designs.

Key factors affecting material choice for a particular application include: meeting stress conditions, either static or dynamic; capability of functioning at a required operating temperature; compatibility with surroundings, for example a corrosive environment; and special requirements such as conductivity, constant modulus, weight restrictions, magnetic limitations, etc.

Music wire springs are normally supplied with a zinc plating baked for hydrogen embrittlement relief, while die springs are painted different colours to denote duty.

Enhanced resistance to wear

Battery springs are produced in music wire and nickel coated, as most alkaline batteries use nickel-plated containers. Here the use of similar materials removes the possibility of galvanic corrosion and enhances resistance to wear. In addition, nickel helps to break down the oxide that forms on the surfaces of batteries.

All of Lee Spring's 316 stainless steel springs are passivated and ultrasonically cleaned to offer medical- and food-grade levels of cleanliness. Other special finishes may be specified.

Spring performance is affected by temperature, which should not exceed 120degC for music wire, 260degC for stainless steel and 245degC for chrome silicon steel.

However, the specification of full custom springs or components can involve production in a wide range of materials, such as beryllium copper, brass, hard drawn carbon steel, oil-tempered carbon steel, oil-tempered chrome silicon, oil-tempered chrome vanadium, Elgiloy, Hastelloy, Inconel, Monel, music wire, phosphor bronze, plastic composites, 300 series stainless steel, and 17-7 stainless steel.

Over recent years some innovative spring materials have been brought into use for mainstream catalogue products and are available for custom designs. Plastic composite springs, chosen for their strength, non-toxicity and anti-corrosion properties, are used in medical applications and have even been considered for food and drink machinery, and for aviation seats. Elgiloy, a lightweight malleable material is often found in applications such as smart phone production or medical instruments.

So what's next? Saving the planet is a recurring theme for everyone so recyclable or ecologically friendly materials being put into new products is good news. For many industries, especially automotive or aerospace then robustness, lightness, and resistance to corrosion and flammability are also critically important. The team at Lee Spring are on hand to help.

Further information on Lee Spring products can be found on the website at www.leespring.co.uk.