Super High temperature resistance heating alloy wire-Surface load
If the FeCrAl resistance heating alloy wire equips regular cross sectional shape like a round wire, it becomes easy to show the load to the heating material. Although for a band wire, it is viable to decrease the surface load content to zero when the thickness is decreased for a particular cross section area. In this situation, the lifetime of the heating material is not large even after the reduction of load value. For instance, if the heating material's thickness is reduced less than its minimum limit, the area exposed to the environment increases and aluminum replacement from the internal surface is hindered, causing issues in the maintenance of properties of the security layer and thus decreases the life. Particularly it is not essential to decrease the thickness of heating alloys than a fix limit, if the heating material is needed to use in the elevated temperature furnaces or carburizing conditions. if band wires are used in the elevated temperature furnaces or carburizing conditions, the heating material's life improves in several cases with the increased thickness of band wire while compromising with the surface load content. In this case, the user needs to consider the current density, not the surface load content to find the loads on the heating wire.
Generally the heat produced by the heating material is directly proportion to the square of current supplied to the resistance heating wireso it is feasible to show the loads to the heating material in the current passing through per unit area of the heating material that is called current density. It is another essential factor to find the loads on the heating wire. While designing the wire such as band wires, it is practically to keep the crucial significance on current density instead of surface load content and place another significance on the surface load. The following table describes the furnace temperature and highest value of current density.
Relationship between furnace temperature and current density
Furnace temperature, oC
Band thickness, mm
Current density
1300
2.9 or higher
2.3 or less
1200
2.6 or higher
2.7 or less
1100
2.3 or higher
3 or less
1000
2 or higher
3.5 or less
800
1.6 or higher
4 or less
Relation between resistance heating wire temperature and current
Pyromax-D
Wire type, mm
Heating element temperature, oC
200
400
600
800
1000
1200
1300
7
45.5
93.3
143
206
289
385
438
6
37.7
76.4
117
165
231
307
351
5.5
33.6
67.3
103
146
204
271
310
5.0
29.5
59.7
90.7
128
179
235
270
4.5
25.4
51.8
78.7
111
154
202
231
4
21.4
44
67
93.9
130
170
195
3.5
17.9
36.6
55.9
78.2
109
141
160
3.0
14.6
29.6
45.6
63.6
87.7
113
129
2.5
11.4
23.1
35.4
49.8
68.3
87.7
99.6
2
8.39
17.2
26.1
36.6
50
64
72.7
1.8
7.27
14.9
22.6
31.7
43.2
55.3
62.5
1.6
6.19
12.6
19.3
26.9
36.7
46.8
52.8
1.4
5.16
10.5
16.1
22.4
30.3
38.7
43.7
1.2
4.17
8.58
13.1
18.2
24.6
31.3
35.3
1
3.29
6.73
10.2
14.4
19.1
24.1
27.2
0.8
2.45
4.97
7.57
10.5
14.0
17.7
19.9
0.6
1.66
3.36
5.14
7.11
9.39
11.8
13.2
0.4
0.96
1.96
2.98
4.14
5.37
6.72
7.48
0.2
0.38
0.78
1.17
1.62
2.07
2.48
2.77
___________
Relation between resistance heating wire temperature and current
Pyromax-N1
Wire type
Heating temperature, oC
Mm
200
400
600
800
1000
1200
1300
7
54.7
116
184
270
365
473
6
43.4
93.2
146
214
289
375
5.5
38.6
82.5
128
187
254
329
5.0
33.5
71.9
112
163
220
285
4.5
29
62.2
95.6
139
188
244
4
24.5
52.8
80.3
117
158
204
3.5
20.3
43.7
65.9
95.4
129
166
3.0
16.3
35.1
52.5
76
103
133
2.5
12.7
27
40
57.8
78.9
101
2
9.37
19.6
28.8
41.5
57.2
72.8
1.8
8.16
17.1
24.8
35.6
49.1
62.2
1.6
6.91
14.5
21
29
41.5
52.3
1.4
5.76
12
17.3
25
34.1
43
1.2
4.74
9.70
13.8
20.1
27.2
34.2
1
3.67
7.52
10.6
15.3
20.8
26.1
0.8
2.73
5.59
7.79
11.1
15.2
19.4
0.6
1.90
3.89
5.29
7.35
10.3
13.2
0.4
1.10
2.36
3.11
4.25
5.99
7.58
Forging and welding of resistance heating elements
Pyromax has excellent mechanical features and it can be forged and machined conveniently. Although, the FeCrAl resistance heating materials Pyromax-C and Pyromax D have nominally lesser tenacity as compare to standard steel alloys just like on other resistance heating materials. Moreover, if these are heated at the elevated temperature for long time, these certainly become brittle while cold processing. Consider the expansion of heating material while deciding the configuration of heating material. It should be able to move freely on its supports. Care should be taken to thermal distortion at the elevated temperature.
Generally the heat produced by the heating material is directly proportion to the square of current supplied to the resistance heating wireso it is feasible to show the loads to the heating material in the current passing through per unit area of the heating material that is called current density. It is another essential factor to find the loads on the heating wire. While designing the wire such as band wires, it is practically to keep the crucial significance on current density instead of surface load content and place another significance on the surface load. The following table describes the furnace temperature and highest value of current density.
Relationship between furnace temperature and current density
Furnace temperature, oC
Band thickness, mm
Current density
1300
2.9 or higher
2.3 or less
1200
2.6 or higher
2.7 or less
1100
2.3 or higher
3 or less
1000
2 or higher
3.5 or less
800
1.6 or higher
4 or less
Relation between resistance heating wire temperature and current
Pyromax-D
Wire type, mm
Heating element temperature, oC
200
400
600
800
1000
1200
1300
7
45.5
93.3
143
206
289
385
438
6
37.7
76.4
117
165
231
307
351
5.5
33.6
67.3
103
146
204
271
310
5.0
29.5
59.7
90.7
128
179
235
270
4.5
25.4
51.8
78.7
111
154
202
231
4
21.4
44
67
93.9
130
170
195
3.5
17.9
36.6
55.9
78.2
109
141
160
3.0
14.6
29.6
45.6
63.6
87.7
113
129
2.5
11.4
23.1
35.4
49.8
68.3
87.7
99.6
2
8.39
17.2
26.1
36.6
50
64
72.7
1.8
7.27
14.9
22.6
31.7
43.2
55.3
62.5
1.6
6.19
12.6
19.3
26.9
36.7
46.8
52.8
1.4
5.16
10.5
16.1
22.4
30.3
38.7
43.7
1.2
4.17
8.58
13.1
18.2
24.6
31.3
35.3
1
3.29
6.73
10.2
14.4
19.1
24.1
27.2
0.8
2.45
4.97
7.57
10.5
14.0
17.7
19.9
0.6
1.66
3.36
5.14
7.11
9.39
11.8
13.2
0.4
0.96
1.96
2.98
4.14
5.37
6.72
7.48
0.2
0.38
0.78
1.17
1.62
2.07
2.48
2.77
___________
Relation between resistance heating wire temperature and current
Pyromax-N1
Wire type
Heating temperature, oC
Mm
200
400
600
800
1000
1200
1300
7
54.7
116
184
270
365
473
6
43.4
93.2
146
214
289
375
5.5
38.6
82.5
128
187
254
329
5.0
33.5
71.9
112
163
220
285
4.5
29
62.2
95.6
139
188
244
4
24.5
52.8
80.3
117
158
204
3.5
20.3
43.7
65.9
95.4
129
166
3.0
16.3
35.1
52.5
76
103
133
2.5
12.7
27
40
57.8
78.9
101
2
9.37
19.6
28.8
41.5
57.2
72.8
1.8
8.16
17.1
24.8
35.6
49.1
62.2
1.6
6.91
14.5
21
29
41.5
52.3
1.4
5.76
12
17.3
25
34.1
43
1.2
4.74
9.70
13.8
20.1
27.2
34.2
1
3.67
7.52
10.6
15.3
20.8
26.1
0.8
2.73
5.59
7.79
11.1
15.2
19.4
0.6
1.90
3.89
5.29
7.35
10.3
13.2
0.4
1.10
2.36
3.11
4.25
5.99
7.58
Forging and welding of resistance heating elements
Pyromax has excellent mechanical features and it can be forged and machined conveniently. Although, the FeCrAl resistance heating materials Pyromax-C and Pyromax D have nominally lesser tenacity as compare to standard steel alloys just like on other resistance heating materials. Moreover, if these are heated at the elevated temperature for long time, these certainly become brittle while cold processing. Consider the expansion of heating material while deciding the configuration of heating material. It should be able to move freely on its supports. Care should be taken to thermal distortion at the elevated temperature.
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