What is a laminated core?


Sheathed magnetic cores made of electrical sheet laminations.

A stack of stacked and tightly connected laminations is called a laminated core, or stator– or rotor core. To produce these packets, also known as cores or magnetic cores, individual laminations of sheet metal are stacked on top of each other, precisely aligned and baked into a packet, or joined by another packaging step. These stacks of laminations are also referred to as lamination stacks or simply as a stack of laminations.

Stacked laminations are used as magnetic cores in electrical machines and are, among other things, a component of every electric motor, including, for example, electric cars.

Electrical steel strip is used for manufacturing the individual sheets in laminated cores. Electrical steel strip or electrical sheet is an iron-silicon alloy with special magnetic properties that are particularly suitable for use in electric motors. Due to these special properties, the targeted use of laminations made of electrical steel sheet for the production of magnetic or iron cores leads to a significantly improved energy efficiency or high efficiency of electrical systems and thus to a sustainable and optimal use of the required resources.

Structure of a laminated core package

Sheet metal packages for motors in the form of stator (also stator) and rotor are made of layered individual laminations of electrical steel insulated from each other. The laminations usually have a material thickness between 0.10 and 1.00 mm, with the most common thicknesses of 0.35 mm, 0.50 mm and 0.65 mm having established themselves as the standard. Insulation between the sheets is achieved by a specific coating that prevents electrical contact between the individual sheets.

These coatings are often only a few micrometers thick. The individual laminations are stamped or laser cut, with the stamping process being suitable for high-volume production and laser cutting offering flexibility for prototyping and small- and medium-scale production. However, laser cutting also has several other specific advantages over punching; for example, virtually no structural changes occur at the edges of the individual layers during laser cutting compared with punching.

The individual sheets are then firmly joined together. With punching, this step can already take place in the punching tool. This is also referred to as punch packaging. Laser-cut lamellae are precisely aligned with a corresponding device, stacked on top of each other and glued (adhesive stacking) or baked (baked varnish process). The baked varnish process but also adhesive stacking lead to complete insulation of the individual sheets and thus to lower eddy current losses.

The full-surface bonding of the layers also suppresses unwanted vibrations. TEPROSA relies on laser cutting of the sheet and packaging of the packages using the baked varnish process. The magnetic cores for electric motors that we manufacture in this way are free of short circuits and have optimum magnetic properties due to the gentle manufacturing process.

Coating of the laminations in the laminated cores

To prevent short circuits between laminations in electrical laminations packages and thereby reduce eddy currents, various coatings are applied to the strip. The coating thicknesses vary from 1 to 4 µm. Depending on the processing technology and subsequent application, coatings exist for better corrosion protection, improved insulation of the individual layers, heat resistance, improved punching properties or weldability.

  • Coating C3 – coating for improving the lubricating effect. Relevant, for example, for the stamping process.
  • Coating C4 – Coating to improve corrosion protection and insulation resistance.
  • Coating C5 – Coating to optimize the temperature resistance. Relevant, for example, for stress-relief annealing after the stamping process.
  • Coating C6 – Coating for a particularly high insulation resistance.
  • Baking varnish – baking varnish process; coating as a bonding technology for sheet metal packages.

The baking varnish process

Baking varnish is a special connection technology for sheet metal packages. Electrical steel strip with baking varnish coating is baked at elevated temperature after cutting the individual lamellae to form a sheet bundle. The result is a flat, strong connection of the individual sheets with complete insulation. Packages manufactured in this way exhibit high dimensional precision and perfect magnetic properties.

Advantages of the baked enamel process:

  • Precision – Laminations coated with baking varnish are baked over the entire surface. Thus, even filigree lamellae can be precisely assembled.
  • Design freedom – The bonding enables an optimal design of the lamellae / sheet packages, since no package nubs or weld seams must be considered.
  • Isolation – In contrast to other stacking techniques, no short circuits occur during stacking.
  • Magnetic properties – With no other manufacturing technology do the specific properties of the electrical steel strip remain as unaffected as with the baked enamel process.
  • Jointing – Due to the full-surface connection of the individual lamellae, vibrations are reduced.
  • Heat conductivity – Electrical sheet packs with baked enamel coating exhibit improved heat conductivity.
  • Stability – Due to the full-surface connection, baked enamel packages are very stable and robust.

Materials/materials for magnetic cores

The electrical steel used for baked enamel packages is made of iron-silicon alloy and is basically classified into two types: isotropic or non-grain oriented and anisotropic or grain oriented electrical steel.

The magnetic properties of isotropic electrical steel are largely uniform and therefore almost independent of the direction of magnetization. This isotropy arises due to a non-ordered distribution of the position of iron elementary cells in the electrical steel.

Homogeneity of magnetic properties is important for all rotating machines, such as electric motors or generators. Minor inhomogeneities (anisotropies), which are unavoidable in the manufacturing process of electrical steel, can be compensated by using special technologies in the construction of electrical machines.

The starting material is manufactured as finally annealed and coated cold-rolled strip. It has special physical properties and is one of the soft magnetic materials.

Your supplier for laminated cores

TEPROSA GmbH has specialized for many years in the production of sophisticated, precisely fitting laminated cores of exceptionally high quality. In the area of electrical sheet, we manufacture individual sheet laminations for stator and rotor, as well as entire sheet packages (stator- or rotor cores) from various electrical steel grades.

We process non-grain oriented electrical steel for electric motors, generators and other electrical machines, such as small transformers. We rely on baked enamel technology for the packaging of individual laminations. Alternatives are welding or bolting of laminations.

As a long-standing supplier to various OEMs, the quality of our work is particularly important to us. Therefore, we work according to uniform processes and thus ensure consistent quality and complete traceability of each individual production step.

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We are experts in manufacturing electrical sheets and sheet packages for electric motors. But we can do even more! In addition to the production of sheet metal packages, we also offer the following services:

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Paul-Ecke-Str. 6
39114 Magdeburg

Tel 0391 598184 70