NMN laminate is a three-layer insulation composite of two outer Nomex aramid-paper plies and a core of Mylar, a biaxially oriented polyester film. The three webs are bonded across their full surface. The abbreviation names the layer order: Nomex, Mylar, Nomex. The composite combines the heat resistance of the aramid paper with the high dielectric strength of the polyester film and serves mainly as slot, layer and phase insulation in electric motors, generators and dry-type transformers.
What NMN laminate is
NMN belongs to the family of flexible laminate composites that place a thin, mechanically sensitive film substrate between two robust paper plies. The aramid paper protects the film from tearing and abrasion while it is pulled into the slot and carries the thermal class. The film core delivers most of the electrical strength. On its own the thin Nomex would be strong but costly in the required thickness, and the bare polyester film would be too heat-sensitive and too easily damaged. The composite solves both. Which composite types exist alongside this layered composite, and why CFRP is not an insulating material despite its fibre reinforcement, is explained in the article on composite materials.
The three webs are held together by an adhesive that must also hold the thermal class, usually a heat-resistant acrylic or epoxy-based glue; the article on laminating film covers the adhesive types. The adhesive layer is the weakest point in the build-up, so the bond decides delamination and service life. A good composite cannot be split by hand and shows no open gap between paper and film at the cut.
NMN laminate from GOBA: supply forms, thicknesses and enquiry
GOBA supplies NMN laminate from a single piece, as material or as a finished part to your drawing.
- Supply forms
- Roll and slit roll, Sheet and board, Cut-to-size, Die-cut part to drawing, Formed part (folded, embossed or bent)
- Thicknesses
- To your specification. GOBA processes materials from 7 µm to 3 mm.
- Versions
- Nomex, polyester film, Nomex in various build-ups and thickness ratios. With a polyimide core as NKN.
- Slit rolls
- Widths from 5 to 1,600 mm, tolerance ±0.1 mm, cores of 25, 55, 76 or 152 mm
- Die-cut and formed parts
- Material thickness 0.023 to 3.0 mm, dimensions up to 1,000 × 2,000 mm
- Quantity
- From 1 piece, from sample to series
- Lead time
- Two weeks at most when the material is in stock
What we need for your quotation
- Drawing or dimensions
- Quantity
- Material and thickness
For rolls also width, length, core diameter, core material (for example plastic) and tolerances.
Layer build-up and variants
The composite is described by the ratio of the three individual thicknesses, given in millimetres for Nomex, polyester film, Nomex. Common total thicknesses run between roughly 0.15 and 0.50 mm. A typical build-up is 0.05 / 0.10 / 0.05, a thinner one 0.03 / 0.05 / 0.03. Symmetrical build-ups with equal outer plies are the rule, because the material then does not curl during stamping and folding.
- Thin build-ups from around 0.15 mm for the layer insulation of small windings.
- Medium build-ups of 0.20 to 0.30 mm for classic slot insulation.
- Thick build-ups up to 0.50 mm for slot closure and mechanically stressed points.
The outer plies are usually calendered Nomex 410. The core is a polyester film, or in special cases a polyethylene naphthalate film when a higher continuous temperature is needed.
Properties and thermal class
NMN reaches thermal class F, meaning 155 degrees continuous temperature. The Nomex alone withstands more, the polyester core is the limit. Anyone who needs thermal class H at 180 degrees moves to a build-up with a more heat-resistant film or to a pure aramid-aramid composite. The dielectric strength of a medium build-up ranges, depending on thickness, from 8 to over 15 kV measured in the composite. Add good tear strength, edge stability during insertion and resistance to the impregnating varnishes and resins common in motor building.
The aramid outer ply brings two advantages that count in service. It absorbs little moisture and keeps its insulating effect even in a humid environment, and it ages thermally slowly, which is why NMN still has reserve at the upper edge of thermal class F. In handling the material is dimensionally stable and can be folded without the edge cracking. Unlike pure Nomex, the composite absorbs little resin because of the film core, which matters for resin-heavy windings.
How NMN differs from DMD
DMD laminate is the cheaper relative. Instead of Nomex it uses polyester fleece as the outer ply, the core stays polyester film: Dacron, Mylar, Dacron. DMD also reaches thermal class F but is more absorbent and takes up resin better. NMN scores with the higher mechanical strength of the aramid paper and more reserve against thermal ageing. As a rule of thumb: for price-sensitive standard series motors DMD is the default, for more heavily loaded drives, traction motors and transformers, where the slot is tight and edge stress is high, we recommend NMN.
Applications
In the motor NMN handles three classic tasks. As slot insulation it lines the stator slot and separates the winding from the core stack. As layer insulation it separates the turn layers inside the coil. As phase insulation it sits between the windings of different phases. Details on material selection for these tasks are in the article on insulation paper for electric motors. Outside the motor NMN appears in dry-type transformers, in generators and as general barrier insulation where heat and mechanical load meet.
The choice of thickness follows the task. For slot insulation it depends on the voltage and the space in the slot, because every tenth of a millimetre of insulation is missing from the copper fill factor. For layer insulation what counts is mostly the dielectric strength between two turn layers, and thin build-ups often suffice. For slot closure and mechanically loaded cover strips the thicker variant is used, because that is where the force acts during insertion and in service. If in doubt, state voltage, slot dimensions and thermal class, then the build-up can be laid out cleanly.
Cutting and stamping at GOBA
NMN comes as roll stock and is slit, stamped and converted at our plant. The edge is what matters in cutting: a clean cut keeps the outer ply from lifting off the core. We slit slot strips to tight width tolerance, stamp slot-closure wedges and phase papers and fold cuffs where the slot geometry calls for it.
- Roll slitting in widths from a few millimetres, with a clean, delamination-free edge.
- Stamped parts for slot closure, phase and cover insulation to your drawing.
- Cuffs and folded formed parts for the stator slot.
GOBA Takeaway
NMN laminate is the more robust choice when the slot is tight, the edge suffers during insertion or the thermal reserve counts. For price-sensitive series motors DMD often suffices, for traction, generators and transformers we advise NMN. GOBA has been slitting and stamping NMN for decades and advises on the choice of build-up and thickness ratio. Send us your drawing through our insulation and molded parts, or ask for the matching insulation materials directly. You will receive a technical quote.
