Wrap-On Fin

The Wrap-On (W/O) Fin or “L” footed fin is characterized as an L fin and is widely used throughout the world. This fin is considered an interference fit type fin and is limited to light duty. 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 L foot. The foot of the fin is formed by pulling the strip through a two stage preformer set. The first stage rolls the fin to a 45-degree foot and the second stage rolls it to a true 90-degree foot. The tooling controls the fin height as specified. As a result of this, each combination of FPI (pitch) and fin strip thickness requires a specific strip width.

Fin strip width can be calculated with the simple formula for Wrap-on fins: Fin Tip Thickness is also predictable by the following formula:

The toe of the fin points upstream. This makes it possible for the incoming fin, as it enters the “nip” of the pan and spindle roll to press and form the toe of the previous fin flat against the tube, providing for maximum contact with the tube surface.

Fin height hardware will work with a range of tube sizes as shown on General Fintube Information (GFTI) -1B on 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 to the tip. This makes it possible to calculate the weight of fin strip per foot of tube with the following formula: