Epoxy Coating Powders for Motor Armature Slot Insulation

Epoxy Coating Powders for Motor Armature Slot Insulation

One of the most pop­u­lar appli­ca­tions for Epoxy Coat­ing Pow­der is slot insu­la­tion for motor arma­tures. The main pur­pose of epoxy coat­ing pow­ders like the Lin­q­sol MCP-5000 and Lin­q­sol MCP-5260 is to cre­ate a bar­ri­er between steel lam­i­na­tion and the cop­per wiring. This process can be used for rotors inside a pow­er gen­er­a­tor, sta­tor, and arma­ture prod­ucts. The motors can be for the auto­mo­tive indus­try, or even pow­er tools and home appliances.

Slot Liners vs Epoxy Coating Powders

motor armature with slot liners

Anoth­er pop­u­lar method used for motor arma­ture insu­la­tion is using slot lin­ers and plas­tic cast­ings. With this method, slot liners/plastic cas­ings are insert­ed into the slot, pro­vid­ing the insu­la­tive bar­ri­er between the cop­per wind­ing and mag­net­ic core. A real-life exam­ple can be seen below:

Com­pared with slot lin­ers and plas­tic cast­ing meth­ods, epoxy coat­ing pow­ders own the advan­tages of effi­cien­cy and reli­a­bil­i­ty for mul­ti­ple reasons:

  1. They allow the use of up to 25% more cop­per wire than plas­tic slot lin­ers = increased effi­cien­cy by 15%-20%
space in epoxy coated motor armature versus slot lined motor armature

2. They pro­vide a more even and con­sis­tent dis­tri­b­u­tion = improved bal­ance effi­cien­cy and lifetime 

area where a motor armature gets epoxy coating powder

3. Since epoxy coat­ing pow­ders are 10x more ther­mal­ly con­duc­tive than air, they can dis­si­pate more heat from the motor = increased oper­at­ing lifetime

graph showing thermal conductivity of air versus epoxy coating powder

Selecting Epoxy Coating Powders for Motor Armatures

To select the best epoxy coat­ing pow­der for your motor arma­ture, some of the require­ments you need to take into con­sid­er­a­tion are:

  • Break­down Voltage
  • Class Rat­ing
  • Edge Cov­er­age

Breakdown Voltage

Break­down Volt­age — Break­down volt­age is an elec­tri­cal prop­er­ty that is thick­ness-depen­dent. It is the max­i­mum amount of volt­age that a dielec­tric mate­r­i­al can with­stand before break­ing down. The break­down volt­age is cal­cu­lat­ed by mul­ti­ply­ing the dielec­tric strength of the mate­r­i­al times the thick­ness of the film. The high­er dielec­tric strength will allow the mate­r­i­al to achieve the same result with less mate­r­i­al, trans­lat­ing into mate­r­i­al cost savings.

MCP-5000 has a break­down volt­age of 25,000 V/mm, and MCP-5260 has a break­down volt­age of 30,000 V/mm.


Class — Anoth­er essen­tial char­ac­ter­is­tic of epoxy coat­ing pow­ders for motor arma­tures is the class. Epoxy coat­ing pow­ders can be Class A (105°C), Class B (130°C), Class F (155°C), or H (180°C). The Class is cal­cu­lat­ed by look­ing at the max­i­mum (hot spot) tem­per­a­ture at which the insu­la­tion can be oper­at­ed and still have an aver­age life of 20,000 hours. To cal­cu­late the max­i­mum hot spot tem­per­a­ture, you take the ambi­ent tem­per­a­ture, add it to the motor tem­per­a­ture rise, and then add the hot spot allowance. For example, 

motor armature under infrared thermometer showing temperatures

Max­i­mum Hot Spot Temperature =

  • Ambi­ent Tem­per­a­ture: (57°C) +
  • Motor Tem­per­a­ture Rise (75°C) +
  • Hot Spot Allowance (5 — 15°C) (15°C)

142°C Max­i­mum Hot Spot Temperature

Motor Insu­la­tion Class Required: F

Insu­la­tion Sys­tem / ClassMax­i­mum Hot Spot Tem­per­a­ture (°C)
Table 1. Insu­la­tion Sys­tem and Cor­re­lat­ing Temperature

The Rule of Thumb is that a 10°C rise cuts the insu­la­tion’s use­ful life in half and a 10°C decrease dou­bles the insu­la­tion’s life.

Edge Coverage

Edge Cov­er­age - One of the most impor­tant qual­i­ties of an epoxy coat­ing pow­der for motor arma­tures is Edge Cov­er­age. Since the parts are com­plex, with many edges and curves, the coat­ing thick­ness on the sen­si­tive parts must be high. The coat­ing thick­ness must be high­er because the cop­per wires at the edges are like­ly to cut through the coat­ing pow­der, break­ing the insu­la­tion bar­ri­er and short­ing out the motor. That is why epoxy coat­ing pow­ders for motor arma­tures are specif­i­cal­ly designed to have a high­er edge cov­er­age. A min­i­mum 300–400um coat­ing thick­ness and 40% edge cov­er­age ratio are gen­er­al­ly required. If high edge cov­er­age is some­thing you are look­ing for Lin­q­sol MCP-5000 has an edge cov­er­age of 55%.

microscope image showing edge coverage for epoxy coating powders


To sum every­thing up, the choice between epoxy coat­ing pow­ders and alter­na­tive meth­ods, such as slot lin­ers and plas­tic cast­ings, for motor arma­ture insu­la­tion is a cru­cial deci­sion that sig­nif­i­cant­ly impacts motor per­for­mance. Epoxy coat­ing pow­ders, like Lin­q­sol MCP-5000 and Lin­q­sol MCP-5260, offer effi­cien­cy and reli­a­bil­i­ty advan­tages by allow­ing increased cop­per wire usage and ensur­ing even dis­tri­b­u­tion. Fur­ther­more, their supe­ri­or heat dis­si­pa­tion prop­er­ties con­tribute to extend­ed motor lifespans. 

The selec­tion process should con­sid­er fac­tors such as break­down volt­age and class rat­ing, where high­er break­down volt­age trans­lates to poten­tial mate­r­i­al cost sav­ings, and the class rat­ing deter­mines the insu­la­tion’s oper­a­tional tem­per­a­ture lim­its. Ulti­mate­ly, care­ful­ly con­sid­er­ing these fac­tors is essen­tial to opti­mize motor effi­cien­cy, lifes­pan, and over­all per­for­mance in var­i­ous indus­tri­al applications.

Fac­ing chal­lenges in prod­uct selec­tion or encoun­ter­ing dif­fi­cul­ties with your appli­ca­tion? Let our team of Coat­ings Experts be your guide. Con­tact us today, and we’ll nav­i­gate the com­plex­i­ties with you to find the per­fect solu­tion for your unique needs.

About Kalliope Zembillas

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