Insulation parts
Slot Liners for Electric Motor Stators
Slot liners separate the winding from the core and prevent flashovers in the stator slot.
Slot liners are mainly used in the stators of electric motors and generators. Made from flexible sheet insulation, they line the slot of the lamination stack precisely. Without this separating layer the winding copper would touch the earthed iron core, making safe motor operation impossible.
Continuous progress in sheet insulation materials allows ever thinner liners. That frees up space for the winding, raises the fill factor and enables more powerful motors within the same envelope. Choosing the right material thickness is therefore always a trade-off between electrical safety and maximum fill factor.
We supply customers in e-mobility, wind power and mechanical engineering with high-quality, complex slot liners, from samples to high-volume production.
Designs and materials
Slot liners, also called slot cell insulation, are available with or without a cuff. The cuff prevents the liner from slipping during winding and its geometry secures the required creepage distance in the motor. For skewed stators we produce special slot linings, optionally reinforced with adhesive tape or with additional cut-outs.
Depending on the required thermal class we typically use NPN laminate and DMD laminate for classes F and B, Nomex 410 aramid paper for class H or NKN laminate for the highest thermal demands. The right choice depends on thermal class, slot geometry and the impregnation process. We are happy to advise.
Manufacturing at Hauler & Hermann
We have been producing slot liners in Filderstadt since 1961. We build our slot liner machines ourselves and equip them with a control system developed in-house, so we can adapt production to new geometries quickly instead of waiting for machine suppliers.
Our goal is an individual fit to your lamination stack: the liner should sit in the slot like a second skin. On request we 3D print your slot geometry and verify the fit on the physical model. Our engineers document fit, geometry and tolerances in technical drawings created in our in-house CAD department. Prototypes are available from a quantity of 1, and new projects including tooling are implemented within a few weeks. Production is certified to DIN EN ISO 9001 and DIN EN ISO 14001.
Applications and industries
Our slot liners are found in traction motors for e-mobility, wind power generators, industrial motors and special motors in small volumes. See our application areas for an overview. To close the slot after winding we supply matching slot wedges, and phase separators for the end winding.
Selection criteria for purchasing and design
Five points make an enquiry meaningful: the required thermal class of the insulation system, the material thickness in relation to the targeted fill factor, the cuff geometry with regard to creepage distance, the slot geometry including any skew, and the quantities from sample to series.
The fastest route is to send us a drawing or a lamination stack. If no drawing exists yet, we create one after fitting the part. Simply send us your requirements via our contact form.
Product view
Isometric view, various shapes, variable lengths
Frequently asked questions
What does a slot liner do in an electric motor?
The slot liner electrically separates the live winding from the stator core. It prevents flashovers and short circuits in the slot, making it a safety-relevant component of every electric motor and generator.
What does a slot liner with or without cuff mean?
The cuff is a folded edge at the end of the liner. It keeps the liner in place during winding and secures the required creepage distance between winding and core. Whether a cuff is needed depends on the winding method and the motor's insulation concept.
Which materials are suitable for slot liners?
Common choices are flexible sheet insulation and laminates such as NPN, DMD or NKN as well as Nomex aramid paper. The selection depends on the motor's thermal class, the slot geometry and the impregnation process. Hauler & Hermann processes materials of thermal classes B to C.
Does Hauler & Hermann make slot liners for skewed stators?
Yes. For skewed stators we produce special slot linings that follow the skew exactly. On request we reinforce the liner with adhesive tape or add extra cut-outs.
What is the minimum order quantity for slot liners?
Prototypes are available from a quantity of 1. From samples and small series for special motors to high-volume production, all quantities are possible. The tooling is made in our own tool shop within a few weeks.
More Products
Slot Wedges and Slot Closures
Slot wedges close the slots in rotor or stator after winding and are also called slot caps.
Learn more →
Phase Separators
Phase separators are stamped from flexible insulation and usually have rounded outer geometries.
Learn more →
NPN Laminate of Nomex and Polyester Film
NPN is a three-layer laminate of Nomex, polyester film and Nomex.
Learn more →Do you have a specific requirement?
Talk to us. We will find the right insulation solution.