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What does it take to design the right spring or pressed part?

29 June 2016

Nick and Dan Goss of Goss Springs and PMT, based in Epping, shed light on the vast number of options and considerations they deal with.

Goss Springs and PMT – who specialise in press and multi-slide tooling – have developed a reputation in design and manufacturing in the wire component and press part industry. Their approach to their market place is to work closely with the customer to determine how to design the optimised component for the envelope available rather than offering catalogue range of “standardised” products which may or may not quite fit what the customer is looking for.

Let us examine some of the main criteria and considerations:

Long life expectancy is a must –choice of material crucial

The type of application that the spring is to be used in will of course determine life expectancy, performance requirement and, depending on what the life expectancy might be, the type of material used. As a general rule of thumb says Nick Goss, “the more expensive the material we use, the longer the life of the component”. A typical application for a compression spring in an engine valve might involve 8,000 cycles per minute and the best material to guarantee this sort of performance is chrome silicon.  

The extreme environment of the offshore industry means that Inconel is usually the material of choice. Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme environments and which may be subject to pressure and heat. When heated, Inconel forms a thick, stable, oxide layer protecting the surface from further attack. 

Must perform, even with extremely low duty cycle

Goss Springs are equally at home selecting the appropriate design, material and manufacturing process for a spring which might not be in use constantly, but must be ready to work when called upon. There are many applications where the spring will be held and stored for long periods of time, usually in a compressed state and in such cases a high tensile spring or stainless steel will be selected.

Standard materials are fit for many purposes

Whilst Goss Springs are experienced in the selection, production, heat treatment and finishing processes associated with the most expensive and complex materials the performance limits of normal grade stainless steel are impressive. 

For many standard duties the spring, which basically acts to store energy, is produced from range 3 music wire, or high tensile stainless steel. In operation the material is subject to various degrees of stress and therefore must be highly tensile.

A standard stainless steel will operate in conditions of up to 300°C. Some grades of stainless steel have however restricted environmental operating conditions. The basic “music wire” used for producing springs is available in different grades: type 302 stainless should not be used in conditions where acids are present and is thus unsuitable for applications processing citrus fruits where instead type 316 should be used – which is incidentally also suitable for operations where contact with blood may occur or in low salt conditions.

Indeed, components used in the medical industry will often be made from platinum; iridium or gold may also be used. A readily worked alloy, platinum–iridium is much harder, stiffer, and more resistant to chemicals than pure platinum, which is relatively soft. Platinum–iridium is also very resistant to high-temperature electric sparks and is widely used for electrical contacts.

Springs deployed as a simple “positional” device

High volume, simple components is bread and butter business to the company. Very simple compression springs are made in their thousands as positional devices in oil and water filters where they “hold” in position another component of the filter.

Talking is good

These examples serve to illustrate how important the dialogue between Goss Springs and the customer is in order to design the right product for the job.

PMT – press parts specialist

Turning now to the design and manufacturing knowledge of PMT, managed by the Goss family on the same site in Epping, the materials used for press and form parts tends to be more standard. Some materials are easier to form and press than others and in order to ensure long lasting, high quality components the finishing processes such as hardening, heat treatment and plating are critical.

Electrical contacts

An electrical contact will typically be made from brass, a good conductor of current.  If the contact is going to operate under degrees of stress a material with some “spring” is required, phosphor bronze and moving up the scale the best contact material is beryllium copper which combines high strength with non-magnetic and non-sparking qualities. 

Further protection from severe environmental conditions can be achieved by plating the components with non-corrosive materials. Plastic coated wire will often be found in components supplied to the medical industry.

Phosphor bronze, beryllium copper, gold which is also often used are all recyclable, a positive environmental and cost consideration.

Household applications – simple choices

Goss Springs do not only deal in the selection of, manufacture and finishing of high performance materials for srings and press parts. There are many relatively simple products around the household which are complex to form, but use standard “soft” materials, such as bronze, often without the requirement for heat treatment.

Goss don’t just produce wire or press parts – they also manufacture coiled tubes

High pressure stainless steel tubes can be coiled into shape and are used to transfer gas and liquids in cooling tubes. It is easy to imagine the manufacture of straight line tubing, coiling it accurately is however a specialised manufacturing technique.

Whatever your requirement for a wire drawn spring, press part or multislide tooling let Nick and Dan and their team advise you on the optimum solution for your application.

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