Fasteners are expected to withstand the test of time, but strategically choosing the right fasteners, with corrosion in mind, should be done during the design stage of any product utilizing fasteners.
Corrosion occurs due to a chemical reaction involving the following elements: a positively charged electrode, a negatively charged electrode, and the presence of an electrolyte which provides a current for the reaction to flow, or breakdown of the fastener material. There are many different types of corrosion and preventing/limiting it will depend on the conditions the fastener will be exposed to. Some of the most common types of corrosion include:
- Uniform Corrosion – Most prevalent; occurs when fastener is not properly coated or plated. The fastener begins to rust and it is evenly distributed along the length of the fastener. It is very destructive and can make removing the fastener very difficult.
- Crevice Corrosion – Occurs within small cracks and crevices in the fastener that are not ventilated properly. Crevices retain moisture which then reacts with the metal and leads to corrosion.
- Galvanic Corrosion – Occurs when two different metals come into contact with each other in the presence of moisture. This can lead to damage to one or both metals involved.
- Stress Cracking Corrosion – Occurs when the fastener material is under too much tension, causing the fastener to weaken. Weakness can lead to cracking. If the fasteners are going to be under constant tension, then periodic inspection should be implemented.
- Pitting Corrosion – Occurs when tiny holes, almost impossible to detect, appear on fastener. This is most likely to occur in materials like Nickel or Chromium.
- Intergranular Corrosion – Occurs in Stainless Steel when it reaches extremely high temperatures, as it does in welding and hot-forming. To prevent this, the fasteners are dipped in cold water during the manufacturing process to cool them down.
Researching the materials your fasteners are made of during the design stage of your product is the best way to avoid corrosion. However, choosing non-corrosive metals, keeping surfaces free of water, limiting the use of washers/ensuring joint surfaces are smooth, using plastic washers when using two different metals, keeping surfaces clean, and treating the metal with grease/oil/paint (depending on the elements it will be exposed to) are also great ways to mitigate corrosion. Field has a team of engineering experts that are ready and willing to provide assistance to your design team. Let us focus on the “fastening” aspect of your products so you don’t have to!