Insulating materials for coil insulation
Insulation material for coil electrical isolation
As mentioned in the induction furnace coil section, insulation material provided by our company is from a wide spectrum of composite compounds and grades. Here the properties and application is discussed more in detail.
Coil supports
Also called traverse or ruler, fixing the distance between coil turns and coil diameter during time is of composite insulation material which is a compound of fiberglass and resin epoxy having various properties according to the grades of the used fiberglass and resin like high electrical resistance to guarantee coil turns isolation, tensile and flexural strength to bear forces and tensions caused by electromagnetic fields and extremely low moist absorbing to maintain the properties.
Composite type |
cried NEMA3 |
|
resin (filler) |
A/D-48.50 | electrical strength Sudden/ gradual |
CW/LW |
CW/LW | working temperature Mechanical/ electric |
Flame class |
|
KV | KV/mm | Mpas | Mpas | °C | UL94 | % | ||||
Fiberglass | G-10 |
Woven glass fibers | Normal epoxy |
45/40 |
27.5/17.7 |
245/275 |
345/415 | 140/130 |
H-B |
0.25 |
G-11 | High temperature epoxy |
| ||||||||
FR-4 | Fireproof epoxy | 140/130 |
V-1 | |||||||
FR-5 | High temperature and fireproof epoxy |
180/170 | ||||||||
GPO-3 | Random glass fibers |
| 40/15 | 11.8 | 55/55 | 125/125 | 140/120 | V-0 | 0.60 | |
bone fiber | CE/LE | Linen fibers | Phenolic | 23/2.5 | 19.6/11.8 | 62/48.5 | 96.5/115 | 125/115 | H-B | 2.20 |
Support drilling is done precisely using computer design plans by CNC machine.
All types of supports discussed in different grades can be supplied by Araz Trans company both raw and cut and perforated.
Special epoxy-based varnish
This liquid insulator is based on epoxy produced by Elantas, Italy and with easy usage (spraying) and desirable properties is very common among manufacturers. This single-material liquid is sprayed by air pressure pistol easily dried at environment temperature (air-dried) or outdoor space in half an hour at most ready to operate. This insulation liquid is used quite easily against to compound insulation liquids including base and hardener. The only point to consider is mixing with proper solvent up to maximum 3%.
Below table summarizes properties of the mentioned epoxy-based insulation liquid:
| measurement standard |
|
| |
Density ( at 23°C) | DIN 51757 | gr/lit | 960-1000 | |
| at 23°C |
|
| ≤ 5 |
|
| |||
Electrical Strength | after water immersion |
IEC 60464-2 |
KV/mm | ≥ 140 |
at temperature above 23°C | ≥ 100 | |||
| touch-dry |
|
| 15-20 min |
non Slip mood | 2 h | |||
|
| |||
Drying time at 80°C | touch-dry |
|
min & h | 3-5 min |
non Slip mood | 15 min | |||
fully dried | 2 h | |||
Electrostatic insulation powder
As mentioned in the coil section, electrostatic insulating powder used by Araz Trans Co. is introduced by Inductoterm company commercially called Inductoflex2M. The most outstanding characteristics of this epoxy-based insulation is durability against cracks and peeling duo to tension on the coil turns. High heat resistance, good electrical insulation and even adhesiveness to the surface while dispersed are other properties of the material. It can solely help insulate the coil and under standard conditions no liquid or tape insulations are demanded. The only problem to apply this insulation is the lack of equipments to do the process which are the special tool to disperse and the coil-sized stabilizing furnace.
Below table presents various characteristics of the Inductoflex2M
quantity | measurement standard |
| amount |
Color | —– | —– | dark blue |
Layer thickness | —– | mm | 0.25-0.30 |
Density ( at 23°C) | ISO 8130-2 | gr/cm3 | 1.25-1.30 |
Electrical Strength | IEC 60243-1 | KV/mm | ≥ 30 |
Preheating temperature object | —– | °C | 200-220 |
|
|
| 200 °C 3-8 min |
Insulating tapes for coil isolation
Araz Trans uses various kinds of insulation tapes for coils relative to costumer demands and operation conditions. Below a brief discription is presented:
Fiberglass Tape:
This tape, also publicly called “silk tape”, is one of the most common types of insulating tapes for coils. Fiberglass tapes are composed of resin-less glass fiber strings. Not applying resin makes it more heat-withstanding up to 400-500 C degree.
The suggested wrapping overlap for silicon rubber tape is 50% (two-ply).
Silicon Rubber Tape:
This rubber-based tape, among all othe coil insulation tapes, is the least moist-absorbant. On the contrary, low isolation capability and heat resistance are the weak points for this tape.
The suggested wrapping overlap for silicon rubber tape is 50% (two-ply).
Nomex Tape:
Nomex is among meta-aramyd fibers with vast application for sensitive aims in sophisticated industry application. Against other usages in power industry (compounded with other insulating materials), for coil isolation according to urgent need to have flexibilty, it used solely which offers high electric isolation and low moist-absorbance but higher expenses.
The suggested wrapping overlap for silicon Nomex tape is 50% (two-ply).
Mica Tape:
Based on Maskovit or Phlogopite, mostly mixed with this fiberglass or Teflon layers. Having highest resistance against heat amongst other tapes for coil isolation, this type has low insulating characteristic and higher moist absorbance and hence decaying probability.
The suggested wrapping overlap for Mica tape is 50% (two-ply).
Kapton Tape:
Kapton tape, in comparison to other tape types, offer more reliability. High electrical isolation, almost no moist absorbance and relatively high heat resistance are the advantages of this tape. On the other hand, high isnulation expense is the most remarkable weakpoint for Kapton tape. Kapton tape is composed of thin poly-amid films with rough thickness of 25 to 50 micron.
The suggested wrapping overlap for 50 micron tape is 50% (two-ply) and for 25 micron is tape 75% (four-ply).
Below graph compares different insulation tapes from electric isolation level at operation temperature and the maximum tempered heat aspects:
Spacer (Segment)
For isolation aims, using insulating material in all electrified parts of the induction furnace is of high importance and inevitable. The slightest isolation issue in the electrical parts will lead in fault and melting interruption. One important isolation aspect is applying spacer or segment between coil turns. Aside from isolating turns, spacers help solidify the refractory. Spacers are made of Mika or fiberglass and are shaped in crescent or cubic form which are used in continuous and sectional way, respectively.
- Mika spacers are more heat-resistant in comparison to fiberglass ones and henceforth more expensive to use.
- Crescent spacers are more solid than the cubic ones.
- Continuous crescent spacers are machined and placed on top of each other in beehive form with definite overlap (0-50%). The more the overlap is, the solidity and reliability is higher but in return, moist will run out of refractory more slowly while sintering.