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When to specify stainless steel for component parts

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John Marshall, Technical Manager, WDS Components Parts, explains the advantages of stainless steel for standard and component parts.

Stainless steel is a material often specified for engineering projects due to its combination of strength and corrosion resistance. However, there are various grades of stainless steel to choose from – each with its own characteristic and costs – so it is important to make the right choice for your application. It’s the chromium alloy which gives stainless steel its best known advantage: high resistance to corrosion. The chrome component not only creates the corrosion-resistant chromium oxide protective layer, but also contributes to its hardness, making it highly robust and resistant to impact. However, its relative hardness makes it more difficult to machine than mild steel, which means careful selection of your supplier is required to ensure optimum product quality and accuracy.

The main types of stainless steel for component parts

Type 304 is the most common type of stainless steel for component parts, composed of up to 20 per cent chromium, enhancing its resistance to corrosion. It’s often used in areas which are mildly corrosive or which require only an occasional washdown, for example handles or hinges. For this reason, it’s also a more economical choice. Type 303 has similar properties but slightly improved machinability when very low tolerances are required, but with slightly lower durability. The highest quality stainless steel generally used for standard parts and components is Type 316. Its added molybdenum component makes it highly resistant to corrosion as well as pitting, the effects of which would create a less hygienic environment and accelerate corrosion. Known as ‘food grade’ (though it’s also the first choice in the marine industry), 316 can endure regular chemical washdown or environments of high salinity. While Types 303/4 steels should only be specified for certain conditions, Type 316 could be widely used for any application. These characteristics make it more expensive, although the cost difference between 304 and 316 has reduced over time.

Growing range of stainless steel components

The range of stainless steel components available to designers and machine builders continues to grow through increasing demand across wider industries and applications. Hand knobs, for example, are ubiquitous throughout industry, including food and beverage, marine, and also for machine parts. We ourselves have introduced a range which includes a T Knob with threaded stem as well as a four-spoke threaded hand knob, both in 316 stainless steel. While stainless steel is often selected for its shine, the new threaded hand knob is also available in 316 with a matt finish, usually chosen in order to hide finger prints and maintain the most hygienic appearance.

Another new addition in stainless steel is the handwheel. Handwheels are often provided in aluminium, which can be suitable even for outdoor use if safety, hygiene or regulations allow. However, the new 316 stainless steel handwheel will last far longer and is the choice for use in corrosive environments, such as marine applications. Small craft to superyachts use stainless steel, and not only does 316 provide the anti-corrosivity required, its aesthetic appeal is also more popular in this market sector.

Used as a fixing on a machine when indexing a range of motion or series of positions, a cam action indexing plunger is now available in stainless steel. Indexing plungers and bolts are generally manufactured in Type 304, giving adequate resilience even if it is not required to face the full rigours of a daily wash down.

Similarly, castor wheels for use in food manufacture and preparation must meet the necessary hygiene standards, but at the same time aren’t required to withstand full washdown. Therefore, a stainless steel Type 304 frame is suitable, combined with a nylon wheel. On the same principle, levelling feet with up to 50 degrees of angle tilt are also available in a 304 stainless steel stem and can be fitted with an anti-microbial polypropylene base.

Alternatively, an example of necessary use of the higher 316 grade for the food and beverage industry is on gas struts, precisely because of the essential nature of a regular wash down. Used on food service hatches, mobile catering vans and ventilation grilles, these applications face regular contact with food and grease splashes. For necessary hygiene standards, a regular washdown is needed and Type 316 stainless steel is required to withstand corrosivity.

Further information can be found at www.wdsltd.co.uk.

 
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