Solvent-based or solventless varnish?

Solventless (100 % solids) polyester-imide or epoxy resins are now standard for trickle and VPI processes: better fill, less VOC and faster cure. Solvent-based varnishes are still used for simple dip processes.

How do I match varnish to the wire?

The varnish, wire enamel and other insulation must be tested together as an insulation system (UL 1446 or IEC 61857). Ask the varnish supplier which wire types and thermal class their system covers.

What should I check on incoming varnish?

Viscosity at the stated temperature, gel time, solids content and shelf life, plus a periodic bond-strength (helical coil) test.

Auxiliary material

Impregnating Varnish

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Process flow

Upstream manufacturing of this bought-in item is not covered yet; see the incoming inspection and approval tests.

Incoming inspection & approval tests

Viscosity, solids content, gel timeBatch incoming inspection
Bond strength (helical coil method)IEC 61033
Electric strengthIEC 60243-1
Thermal classIEC 60216

Buyer FAQ

Solvent-based or solventless varnish?: Solventless (100 % solids) polyester-imide or epoxy resins are now standard for trickle and VPI processes: better fill, less VOC and faster cure. Solvent-based varnishes are still used for simple dip processes.
How do I match varnish to the wire?: The varnish, wire enamel and other insulation must be tested together as an insulation system (UL 1446 or IEC 61857). Ask the varnish supplier which wire types and thermal class their system covers.
What should I check on incoming varnish?: Viscosity at the stated temperature, gel time, solids content and shelf life, plus a periodic bond-strength (helical coil) test.

Supply chain / regions

International varnish makers run Pearl River Delta offices and blending sites (Zhuhai), and Foshan and Zhuhai have domestic insulating-resin producers. Choose varnish and process together — the supplier's process support matters as much as the product.

Representative suppliers

Used in

57 mm Inner-rotor BLDC MotorImpregnating varnish · Specification: Polyesterimide or epoxy, class F / H, 1K
42 mm Two-phase Hybrid Stepper Motor (NEMA 17)Impregnating varnish · Specification: Class 155 or higher, compatible with the wire enamel
57 mm Two-phase Hybrid Stepper Motor (NEMA 23)Impregnating varnish · Specification: Class 155 or higher, compatible with the wire enamel
86 mm Two-phase Hybrid Stepper Motor (NEMA 34)Impregnating varnish · Specification: Class 155 / 180, suitable for dip or VPI, compatible with the wire enamel
57 mm Integrated BLDC Motor (built-in driver)Impregnating varnish · Specification: Polyesterimide or epoxy, class F / H, 1K
70 mm Outer-rotor BLDC MotorImpregnating varnish (optional) · Specification: Polyesterimide or epoxy, class F
AC Servo Motor (60–130 mm flange)Impregnating varnish / potting · Specification: Polyesterimide or epoxy, class F / H; or thermally conductive epoxy potting
Coreless Brushed DC Motor (16–22 mm)Coil impregnation epoxy · Specification: Low-viscosity heat-curing epoxy, Class F or higher
IEC Three-phase Induction Motor (frames 80–160, IE3)Impregnating varnish · Specification: Polyester / polyesterimide or solventless epoxy, class F / H