Selecting the right size and material of your fasteners is essential for proper fitting and performance. The galvanic corrosion effect of different metals need to be taken into consideration when choosing the fastener as it might cause corrosion and reducing the life span of your products. Here are some pointers on how to choose the proper rivet, rivet nut and rivet stud for your projects. For repair situations, please follow the manufacturer’s guideline for the required fasteners.
Material Selection - What is Galvanic corrosion?
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte. -source Wikipedia
What does this mean in plain English?
The simplified explanation would be that whenever two different types of metal are fastened together, due to the composition of the metals and the interaction of the metals, one metal would corrode faster than if the same metals are fastened together.
How does this effect rivet/rivet nut/rivet stud selection?
Whenever possible, it is best to use the fastener of the same material as the metal that you are fastening. If this is not possible, a barrier should be created between the two metals to prevent the galvanic corrosion.
What barrier could I use?
In some application, epoxy glue, rubber washer, paint or other non-conductive materials are used for barrier.
This only applies to corrosive metals such as steel right ?
No, this happens even if you join seemingly non-corrosive metals such as Aluminum and Stainless together. If you fasten two aluminum plates with a stainless rivet, the aluminum plate around the fastened joint would actually corrode and the fastened joint would eventually fail due to the enlarged hole.
Is this all I need to know?
No, this is just a quick overview of galvanic effect. For repairs, it is best to follow the manufacturer’s guideline for proper fastener selection. For manufacturer, it is best to choose the fasteners with the same metal as the structure/project or use a barrier between any two dissimilar metals. For more details please check out these sources for more information.
Once the proper material has been determined, here are a few things to consider regarding the selection of the rivet.
- For new fastening joint, consider the available area for fastening and choose the rivet based on the required grip range, sheer strength and tensile strength that fits within your available fastening area.
- For repair, choose a rivet that meets the manufacturer’s required strength and that is designed for the rivet hole available. A size larger rivet is often required as the hole might have been enlarged to due to vibration/corrosion
Grip ranges refers to the optimal thickness of material that the rivet is designed for in order to achieve the specified sheer and tension strength. Using the rivet outside the specified grip range might cause unexpected failure.
Shear strength refers to the amount of force that the rivet can handle before failure. It is best to choose a fastener that has larger shear strength than you require.
Tensile strength refers to how much force the rivet can handle before it is pulled apart. It is best to choose a fastener that has larger tensile strength than you require.
Rivet Nut/Stud Selection
Once the proper material has been determined, here are a few things to consider regarding the selection of the rivet nut and rivet stud.
- Choose the appropriate rivet nut/stud for the required bolt sizes indicated by the manufacturer or application.
- Please note that the bolt size would also affect the hole size as each rivet nut/stud has its own hole size requirement.
This value refers to how much the rivet nut/stud could handle before the possibility of the rivet nut/stud to start spinning.
- The shear strength of the rivet nut is determined by the bolts installed into the fastened rivet nut as the installed bolt would become the integral part of the fastened system. As a result, the shear strength is typically determined by the bolt used in the final assembly.
- For rivet stud, the bolt shear strength is according to the grade/size of the equivalent bolt.
Pull-Out (Tensile) Force
- This is the amount of force that would result in failure of the installed rivet nut with bolt fastened.
- The force that the installed rivet stud could handle axially before failure.
- It is similar to the force that would cause the thread to strip on standard bolt and nut installations.
- Rivet nut and rivet studs are typically used to provide threads to thin metal materials or when threads are required where back side access is prohibited.