Fins Per Inch

The Overlapped Footed Fin (OLFF) is characterized as a double LL fin and is widely used throughout the world as an alternative to the extruded fin. This fin is considered an interference fit type of fin and is used in corrosive applications where protection of the base tube is required. The double LL coverage of the base tube represents a double strip thickness coverage of the base tube. Typically, this fin is produced out of aluminum or copper fin strip. This fin type is not suitable for carbon steel or stainless steel fin materials as the material is too hard for the formation of the characteristic LL foot. The foot of the fin is formed by pulling the strip through a two stage preform roller set. By preforming the foot of the fin into a “joggle” or a one thickness offset, it is possible to take advantage of the ability to place the heel of one fin on the toe of the adjacent fin. The preformers preform the foot to allow the fins to fit together on the surface of the tube, for continuous contact with the base tube and forms a seal to protect the base tube from atmospheric corrosion.

Fin Tip Thickness is also predictable by the following formula:

Fin height hardware will work with a range of tube sizes as shown on GFTI-1B (page 92). This chart shows the principle of fin height, fin strip thickness and tube size. The zero pitch line of all of the McElroy fin types are basically at the surface of the tube. The fins are smooth with a uniform taper from the base of the tube to the tip of the fin. This makes it possible to calculate the weight of fin strip per foot of tube with the following formula: