G-Fin or Imbedded Fin
This fin is characterized by the fact that the fin is curled into a groove in the tube wall and securely locked into the tube wall in a subsequent rotation. The grooved fin cannot expand away from the base tube and therefore there is negligible loss of the fin bond during the cycling process. In fact, as the temperature rises, the fin material expands into the tube wall. |
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The McElroy plow system for imbedding fins, is fixed on the overarm and plows the metal much as a farmer's plow would do. The metal rises high on each side of the tool one-half pitch upstream of the finning head rollers. This positions an open groove for the fin as it is curled. The fin is loosely curled into the groove until it completes another half revolution. Due to the additional raised metal, backfilling and locking requires only flat rollers to secure the fin in the groove. Standard groove depth is controlled by the overarm at .012" deep into the wall. A pull test device and procedure has been developed within the industry to verify fin bond quality.
Alternative tooling is available to produce imbedded fin tubes with a groove depth of .008" allowing for the application of fins to thinner wall tubes. |
Fin Materials:
Aluminum, Copper, Carbon Steel, Stainless Steel, Pre-Galvanized Carbon Steel |
Maximum Fin Height:
Aluminum & Copper .807" (20.5mm) on 1" tube (25.4mm) and larger. Carbon Steel 5/8" on 1" tube and ¾" on 2" Tube. Stainless Steel 3/8" on 1" and larger tubes. Special tooling is availablefor1.04" (26.4mm) high fin or 1.5" OD tube. |
Tube Materials:
Carbon steel, copper alloys, stainless steel, aluminum, CuNi, Monel, Incoloy, Inconel, Titanium, Sandvick 2205. Consult McElroy for specific alloy recommendations and minimum tube wall. RcB 90 or less recommended for stainless steel and alloy tubes. Dovetail rollers required for applications of aluminum on aluminum, copper on copper, and steel and stainless steel fin on various tube materials. |
Fin Stock Thickness:
Varies based upon tube OD, but typically .016" (.4mm) aluminum. Copper stock thickness can be reduced by 10%. Maximum aluminum fin stock thickness .030" (.76mm). Maximum carbon steel thickness .022". Maximum stainless steel thickness .015". |
Production Rate:
for Aluminum Fin x 10 FPI on 1" Tube X 40'L = 350-400' per hour. (85% efficiency) |
Type of Service:
High temperature, fin material is limiting factor. |
Typical Acceptable Tube Wall Operating Temperature:
Aluminum US 650 degrees F/ 343 degrees C. European practices are the same. CS fin 1850 degrees F/ 450 degrees C. Stainless steel 1000 degrees F/ 540 degrees C. |
Advantages:
Mechanical bond with negligible deterioration of fin bond during cooler cycling. Requires less material per foot of tube than W/O, W/O Knurled or Overlapped Footed Fin. Production speeds of the fin may be comparable to the W/O type fins. Newer aluminum alloys have helped to improve corrosive resistance of the fin stock. |
Disadvantages:
Thicker tube walls required for groove depth. Corrosion resistance is not perfect and the base tube is penetrable unless protected by coatings.
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Imbedded & Edgewound 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 |
18 Ga (.049) (1.24mm) |
1/4" (6.35mm) to 13/32 (10.32mm) |
10 - 13 FPI |
| 5/8" or 15.88mm |
.054 (1.37mm) |
1/4" (6.35mm) to 9/16" (14.29mm) |
8 - 13 FPI |
| 3/4" or 19.05mm |
.060 (1.52mm) |
1/4" (6.35mm) to 5/8" (15.88mm) |
7 - 13 FPI |
| 1" or 25.40mm |
15 Ga (.072) (1.83mm) |
1/4" ( 6.35mm) to .807" (20.50mm) |
5 - 13 FPI |
| 1.25" or 31.75mm |
14 Ga (.083) (2.11mm) |
1/4" (6.35mm) to .807" (20.50mm) |
5 - 13 FPI |
| 1.5" or 38.10mm |
13 Ga (.095) (2.41mm) |
1/4" (6.35mm) to .1.04" (26.4mm) |
5 - 13 FPI |
| 2.0" or 50.80mm |
11 Ga (.120) (3.05mm) |
1/4" (6.35mm) to .807" (20.50mm) |
5 - 13 FPI |
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Imbedded & Edgewound Fintube Height Range Chart
(Carbon Steel Fin Stock 1008/1010-5) |
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Tube Size |
Min. Tube Wall |
Max. Fin Height Range |
FPI Range |
| 5/8" or 15.88mm |
.054 (1.37mm) |
3/8" (9.52mm) X .015" (.381mm) |
7 - 10 FPI |
| 3/4" or 19.05mm |
.060 (1.52mm) |
1/2" (12.69mm) X .016" (.381mm) |
7 - 10 FPI |
| 1" or 25.40mm |
15 Ga (.072) (1.83mm) |
5/8" (15.88mm) X .020" (.508mm) |
7 - 10 FPI |
| 1.25" or 31.75mm |
14 Ga (.083) (2.11mm) |
5/8" (15.88mm) X .020" (.508mm) |
7 - 10 FPI |
| 1.5" or 38.10mm |
13 Ga (.095) (2.41mm) |
5/8" (15.88mm) X .020" (.508mm) |
7 - 10 FPI |
| 2.0" or 50.80mm |
11 Ga (.120) (3.05mm) |
3/4" (19.04mm) X .020" (.508mm) |
7 - 10 FPI |
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Imbedded Fintube Height Range Chart
(Stainless Steel Stock 304 Alloy) |
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Tube Size |
Min. Tube Wall |
Max. Fin Height Range |
FPI Range |
| 5/8" or 15.88mm |
16 Ga .065 (1.65mm) |
5/16" (7.90mm) X .020" (.508mm) |
9 FPI |
| 3/4" or 19.05mm |
15 Ga .075 (1.83mm) |
5/16" (7.90mm) X .016" (.406mm) |
9 FPI |
| 1" or 25.40mm |
14 Ga .083 (2.11m) |
3/8" (9.52mm) X .015" (.381mm) |
9 FPI |
| 1.25" or 31.75mm |
13 Ga .095 (2.41mm) |
3/8" (9.52mm) X .015" (.381mm) |
9 FPI |
| 1.5" or 38.10mm |
12 Ga .109 (2.77mm) |
3/8" (9.52mm) X .015" (.381mm) |
9 FPI |
| 2.0" or 50.80mm |
10 Ga. 134 (3.40mm) |
3/8" (9.52mm) X .015" (.381mm) |
9 FPI |
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