List of Alloys & profiles

List of Alloys & profiles

Coiled or Spiral Elements

Wire elements formed into a coil allow a suitable length of wire to be accommodated in a relatively short space, and also absorb the effects of thermal expansion.  When forming the coil care must be taken not to damage the wire by nicking or abrasion.  Cleanliness of the element is also important. The maximum and minimum recommended ratios of inside-coil diameter to wire diameter are 6:1 and 3:1.  The length of the close wound coil may be found using the table or equation below.

Where:

dWire diameter (mm)
DInside-Coil diameter (mm)
LLength of wire (m)
xLength of close wound coil (mm)
9 Coiled or Spiral Elements
spiral 1 Coiled or Spiral Elements

Length of close wound coil (mm) per 1 metre length of wire
Inside Coil Diameter :

Wire Diameter
SWG
Wire Diameter
in
Wire Diameter
mm
3mm4mm5mm6mm7mm8mm9mm10mm
10.1283.25166143125112101928478
11.1162.9515813511810594867972
12.1042.641491271109787797267
13.0922.341391171018980726660
14.0802.03129107928172645954
15.0721.83121100857466595449
16.0641.6311292786860544945
17.0561.4210283706154484340
18.0481.229274625447423835
19.0401.028164544640363229
20.036.917459494237332927
21.032.816854453833292624
22.028.716148403429262321
23.024.615442352925232018
24.022.565039322724211917
25.020.514636292522191715
26.018464233272320171514
27.0164.423930242118161413
28.0148.383527221916141312
29.0136.353325211715131211
30.0124.313023191614121110
31.0116.29282218151311109
32.0108.2727201714121198
33.0100.2525191513111098

When this close wound coil is stretched the stretch should be about 3:1 as closer winding will result in hotter coils.

Apart from accidental damage the service life of a heating element may be shortened by localised burn-outs (hot spots).  This may be caused by change to the wire’s cross section (e.g. nicks, stretching, kinks), or by shielding an area where the element cannot dissipate its heat freely, or by poor supporting points or terminations.

spiral 2 Coiled or Spiral Elements