Datasheet

Kanthal Appliance Alloys Handbook 71
10
Example:
According to section 2
ρ = 1.35 Ω mm
2
/m = (812 Ω/cmf) for
Kanthal D
P = 1000 W
p = 8 W/cm
2
(51.6 W/in
2
)
R = 40 Ω
According to equation [13]:
metric
imperial
B) Strip :
C) Ribbon:
Since ribbons are made by flattening round
wires, the cross-sectional area is somewhat
smaller depending on size, than equation
[14] indicates. As a rule of thumb, a factor
0.92 is used.
d = 3
812 ·1000
15.28 · 10
6
= 0.022 inch
d = 3
4 1.35 ·1000
π
2
8 · 40
= 0.55 mm·
L
10
·
4
π
2
·
51.6
· 40
·
L
=
[14]
q = b · t
[15]
q = 0.92 · b · t
Lately, investigations have shown that a
more correct way of expressing the cross-
sectional area of ribbon is:
(Equation [15] is, however, used throughout
this Handbook).
Definition:
Coil pitch, s [mm] or [in]
A round wire is often wound as a coil. For
calculating coil pitch, s, the equation [16]
applies:
[16]
+ 1 =
π · (D – d)
s
L
L
e
2
➔
π · (D – d)
s =
– 1
L
L
e
2
metric
imperial
[16’]
π · (D – d)
s =
– 1
L · 1000
L
e
2
When the pitch, s, is small relatively to coil
diameter, D, and wire diameter, d.
Than , so that equation [16]
can be simplified to:
s
π
(D – d)
<< L
d = 3
[13]
4
π
2
ρ · P
·
p · R
20
L
10
·
[mm]
d = 3
[13]
4
π
2
ρ · P
·
p · R
20
L
15.28 · 10
6
· [in]
[15’]
q = 0.985 –
2
t
2 · b
· b · t
2
[16’]
π · (D – d)
s =
– 1
L · 12
L
e
2