What does it take to design the right spring or pressed part?
29 December 2015
Nick and Dan Goss attempt to shed some light on this, basing their article on past experience and the huge variety of projects their companies – Goss Spings and PMT - have undertaken for clients.
Goss Springs and its press and multi-slide tooling subsidiary, PMT, have earned an enviable reputation for their wire component and press part design and manufacturing expertise. Their approach is to work closely with the customer to develop a design that fits the available envelope, rather than offering a ‘standard’ catalogue item that might or might not quite fit the brief. Let’s examine some of the main criteria:
The type of application in which the spring is to be used 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, Nick Goss says the more expensive the material used, the longer the life of the component. An automotive engine valve, for example, will require a compression spring that must function faultlessly at up to 8,000 cycles per minute; the best materials 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 involving high pressures and temperatures. When heated, Inconel forms a thick, stable, oxide layer that protects the surface from further attack.
Goss Springs is equally competent at selecting the appropriate design, material and manufacturing process for a spring that might have intermittent duty cycle, but must nonetheless be ready to work when called upon. There are many applications where a spring will be held and stored for long periods of time - usually in a compressed state - and in such cases a high tensile stainless steel spring would normally be selected.
For many standard duties, a spring is manufactured from range 3 music wire or high tensile stainless steel. A standard stainless steel will operate at temperatures of up to 300°C. Some grades of stainless steel, however, have 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 such as the processing of citrus fruits where type 316 should be used instead; incidentally, this grade is also suitable for operations where contact with blood may occur or in low salt conditions.
Staying with the medical sector, components 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.
In addition to the manufacture of custom high performance components, Goss will readily turn its hand to high volume, simple components, which represent a ‘bread and butter’ business for the company. Very simple compression springs are made in their thousands for products such as oil and water filters where they are used to retain the positions of other filter components.
Press & Multislide Tooling (PMT), managed by the Goss family on the same site in Epping, specialises in the production of pressed and formed parts, where more standard materials tend to be used. Some materials are easier to form and press than others and in order to ensure long lasting, high quality components, finishing processes, such as hardening, heat treatment and plating, are critical.
An electrical contact, for example, will typically be made from brass, which is a good conductor of electricity. If the contact is going to operate under degrees of stress a material with some ‘spring’ is required – hence the use of phosphor bronze and, moving up the scale in terms of performance, beryllium copper, which combines high strength with non-magnetic and non-sparking qualities. Notably, phosphor bronze, beryllium copper and gold (which is also often used) are all recyclable – an important consideration when it comes to cost and the environment.
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, for example. And for those common household appliances requiring difficult-to-form components that are manufactured from standard ‘soft’ materials, Goss is also able to help with materials such as bronze - often without the requirement for heat treatment.
In addition to wire and press parts, Goss also manufactures coiled tubes. The company is able to coil stainless steel tubes into shapes suitable for the transfer of gas and liquids in cooling applications with great precision using specialised manufacturing techniques developed over many years.
So, whatever your requirement for a wire drawn spring, press part or multislide tooling, Nick, Dan and their team of experts are ready to advise you on material choice and component design.
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