How to Avoid Tubular Rivet Problems
We have discussed loose rivets, which can be either solid, tubular or semi-tubular. When deciding on which fastener to use, it completely depends on stress and shearing. For strength and durability, solid rivets work the best, such as semi-tubular rivets. Therefore, tubular rivets are the best choice for light-duty applications.
Solid rivets, such as tubular and semi-tubular rivets are often used where an extreme application of high joint strength is required, like aircraft landing gear, automobile brake shoes, or mining and construction equipment. Also, they are ideal for light-load products that have very few strength requirements, such as electronic components.
There is another type, known as plastic rivets that have gained some popularity for applications that do not require high strength. They are typically more expensive than the steel ones and are used to join plastic to plastic, plastic to metal or fiberglass to fiberglass. They are ideal for nonconductive applications or noncorrosive environments.
Advantages and Disadvantages
The main benefits for semi-tubular in mild steel are high assembly speed, low install cost, high joint strength, and easy inspection.
When selecting a proper rivet, the first step is to evaluate the joint forces mainly shear and pull apart. And the only way to be sure is to assemble the parts in the lab and returning them to the customer for product testing.
Shear failure can occur in two ways and can be prevented by selecting the correct rivet diameter. This is done when either the shank may shear or the material may give way, elongating the rivet hole. To withstand the shear forces, the diameter to stack-up thickness should be in the ratio between 1:1 to 1:3 for metal parts and 1:1 for plastic parts. A shear failure is also caused by the rivet placement to the edge of the workpiece. If the rivet is too close to the edge, the material can tear away the clearance hole. To avoid this, the placement should be twice the diameter from the edge.
When axial forces down the shank that break the clinch or draws the rivet through the material, a pull-apart failure occurs. The most common form of this failure is the rolling back or stripping of the clinched end. In this case, the material’s resistance to pull-apart forces should be proportional to the material thickness, the circumference of the clinch and rivet heads, and the shear strength of the material should be perpendicular to its surface plane. Therefore, product testing is recommended to determine the required head diameter and clinch allowance.
Semi-tubular rivets have a hole in the end which is the wall of the semi-tube that is curled over to form the clinch. Ideally, the rivet hole diameter should be 70 to 80% of the rivet diameter, which means, the greater the percentage the thinner the tubular wall.
Having discussed all this, assembling products with low-cost semi-tubular rivets makes a good financial sense, as it increases throughout, improves quality, reduces scrap, and maximizes profits.