LL-Fin or Overlapped Footed Fin
This McElroy patented fin represents a natural evolution from the Wrap-On Fin. This fin is often referred to as a double-L (LL) fin and is often sold in place of extruded finned tubes.
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 actually "preform" the foot to allow the fins to fit together, on the axial surface of the tube, for continuous contact with the base tube. The double foot seals the base tube from atmospheric corrosion and offers a coverage of double the stock thickness (.032"), i.e. .016" fin stock X 2. |
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Fin Height hardware is specific for fin height, FPI, and stock thickness. Most double -L hardware is not interchangeable with Wrap-On or Imbedded fin height hardware.
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Fin Materials:
Aluminum, Copper |
Maximum Fin Height:
1" (25.4mm) on 1.5" Tube (38.1mm) and larger. |
Tube Materials:
No theoretical Limits. |
Fin Stock Thickness:
Varies based upon tube OD, but typically .016" (.4mm). Copper stock thickness can be reduced by 10%. Maximum aluminum fin stock thickness .030" (.76mm) |
Production Rate:
for Aluminum Fin X 10 FPI on 1" Tube X 40'L: 450-500' per hour ( 85% efficiency) |
Type of Service:
Light to Medium Duty |
Typical Acceptable Tube Wall Operating Temperature:
US 350 degrees F/ 176 degrees C. Europe 195 degrees F/ 90 degrees C. |
Advantages:
Improved corrosion protection of base tube over L-footed fin. Less material per foot of tube than extruded fin. Corrosion resistant aluminum alloys possible for this fin to enhance performance. Less material per foot tube than extruded fin. |
Disadvantages:
Requires more material per foot of tube than the Imbedded or I - Fin (Edgewound) or Wrap-On Fin. Care in production must be exercised to insure the proper nesting of the fin foot.
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Wrap On Footed and Overlapped Footed Fintube Height Range Chart
(Aluminum 1100-00 or Copper(102 Oxygen Free) |
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Tube Size |
Min. Tube Wall |
Fin Height Range |
FPI Range |
| 9/16 " or 14.29mm |
24 Ga (.022) (.558mm) |
1/4" (6.35mm)
to 13/32 (10.32mm) |
10 - 12 FPI |
| 5/8" or 15.88mm |
23 Ga (.025) (.635mm) |
1/4" (6.35mm)
to 9/16" (14.29mm) |
8 - 12 FPI |
| 3/4" or 19.05mm |
22 Ga (.028) (.711mm) |
1/4" (6.35mm)
to 5/8" (15.88mm) |
7 - 12 FPI |
| 1" or 25.40mm |
20 Ga (.035) (.888mm) |
1/4" ( 6.35mm)
to 8.07" (20.50mm) |
5 - 12 FPI |
| 1.25" or 31.75mm |
19 Ga (.042) (1.07mm) |
1/4" (6.35mm)
to .807" (20.50mm) |
4 -12 FPI |
| 1.5" or 38.10mm |
18 Ga (.049) (1.24mm) |
1/4" (6.35mm)
to 1" (25.40mm) |
4 - 12 FPI |
| 2.0" or 50.80mm |
16 Ga (.065) (1.65mm) |
1/4" (6.35mm)
to 1" (25.40mm) |
4 - 12 FPI |
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