The extruded fin is formed from an outer aluminum tube with a large wall thickness (muff), which is aligned over an inner base tube. The two tubes are pushed through three arbors with rotating discs that literally squeeze or extrude the aluminum fins up and out of the muff material in a spiral shape in one operation. The resultant fin typically has a base or root thickness of .035", average fin thickness .016" and a tip of .009", with an overall height of 16mm (5/8"). The root thickness serves to form an uninterrupted bond over the entire tube length.
McElroy disc technology now makes it possible to fin thinner muff thus offering significant material savings. Recommended standard muff wall is .176" as opposed to industry practice of .183"-.210" In addition, the same growth factor can be used for pitches from 8 - 11 FPI, allowing for standardization on one muff thickness and eliminating the need to stock multiple muff wall thicknesses. The same discs can be used to produce 5/8" (15,9mm) or 1/2" (12,7 mm) high fin.
Model B produces a 5/8" high fin on tube sizes from 25mm to 1.5" ( 38.1mm). The Model B Extruded Finning Machine is now capable of 7/16" high integral copper fin at 7 to 10 FPI within the tube size range of the machine (25mm and 1.5"). Each machine is configured for the specific production requirements of the end user.