Silicon steel is electrical steel. It is mainly used as cores of various motors and transformers, magnetic switches, relays, magnetic barriers, ballasts and other electrical components. It is an important soft magnetic alloy material in power, electronics and military industries. There are two outstanding features in the current production of silicon steel sheets:
First, the requirements for the chemical composition of silicon steel are extremely strict and demanding.
Second, the production method has changed from hot rolling production before the 1960s to cold rolling production.
Silicon steel sheets are divided into oriented silicon steel and non-oriented silicon steel. There are different methods for controlling chemical composition. Grain-oriented silicon steel has extremely strict requirements on the content of conventional elements. At the same time, the beneficial inclusion elements added must be strictly controlled within a certain range. In this way, oriented silicon steel with high grain orientation, strong directionality, high magnetic induction and low iron loss can be obtained. Non-oriented silicon steel requires pure steel with ultra-low carbon, ultra-low sulfur, and high aluminum content to obtain isotropic non-oriented silicon steel with high magnetic induction and low iron loss.
Requirements for the performance of electrical steel plates
Motors, transformers and other electrical components are generally required to be highly efficient, consume less power, and be small in size.
and light weight. Electrical steel plates usually use iron loss and magnetic induction intensity as product magnetic protection.
Proof value. The performance requirements of electrical steel plates are as follows:
1. Good film processing performance
There is no unified test method for the punchability of electrical steel. The number of repeated bends of the finished product can be used as an indirect indicator to evaluate the punching performance. It can also be judged based on the wear of the mold, for example, the number of punched pieces with 0.025mm wear as the standard. For steel plates for micro motors, it can be judged by the actual number of punched pieces of high-speed punching until the punching burr reaches a height of 0.05mm.
2. The surface of the steel plate is smooth, flat and uniform in thickness. The surface of the electrical steel plate is required to be smooth, flat and thick.
The purpose of uniformity is mainly to improve the lamination coefficient of the core sheet. The punching coefficient refers to the ratio of the theoretical volume of a certain electrical steel plate lamination (calculated based on the lamination weight and density) to the actual volume measured under a certain pressure. The percentage represents the percentage of net metal in the core volume.
Lamination factor is a measure of how tight the core actually is.
The lamination coefficient is mainly related to the following factors:
1) Flatness of steel plate
2) Thickness deviation of steel plate
3) Surface insulation film and thickness uniformity
4) The thickness of the selected steel plate (the thicker the steel plate, the higher the lamination coefficient)
5) The degree of compression of the iron core during assembly.
3. The insulation film has good performance
In order to prevent short circuits between core laminations and increase eddy current losses, the surface of the electrical steel plate is coated with a semi-organic insulating film of inorganic salts + organic salts.
Requirements for insulating films:
1) Good heat resistance. (No damage during stress relief annealing at 750~800°C)
2) The insulation film is thin and has a uniform thickness of 1.5μm. At this time, the lamination coefficient is reduced by 0.5%~1.0%
3) The interlayer resistance is high. Generally it is 5~505.cm2/piece. Since oriented steel has two layers of insulating films, the interlayer resistance is in the range of 30~120 2.cm2/piece (suitable for large transformers and steam turbines)
4) Good adhesion. Will not fall off after punching or stress relief annealing
5) Good film processing performance. Organic or semi-organic coatings provide lubrication during film processing and significantly improve film processing properties.
6) Good internal corrosion and rust resistance. Does not react chemically with transformers or fleon.
7) Good welding performance. No air bubbles are produced in the weld seam during core welding.
The surface of hot-rolled silicon steel is generally not coated with insulating film. The user applies insulating paint after punching, but it has poor heat resistance and poor weldability. The insulation film is thicker (2~3 μm on each side), which reduces the lamination coefficient by 1%~2%
