The characteristic of thermosensitive ferrite is that its magnetism changes suddenly near the Curie point: when the temperature reaches the Curie point, its permeability and saturation magnetic flux density suddenly drop, and the ferromagnetism disappears; the temperature returns to the Curie point Below the point, its ferromagnetism is restored. Thermosensitive ferrite is a mixed sintered body of iron oxide and oxides of other transition metals.
This kind of element cooperates with a permanent magnet ring and a reed switch to form a reed switch. When the temperature changes up and down at the Curie point, the reed switch turns on and off, which can be used for automatic control and overheat protection. The raw material price of thermosensitive ferrite is low, the cost of the device is low, it is a kind of very promising thermosensitive element. Thermal ferrite sensors can be used for automatic control and overheat protection in electromechanical devices.
The main characteristics of thermal ferrite
Thermosensitive ferrite material is a kind of soft magnetic material, so it has the general characteristics of soft magnetic material, and has lower coercivity and remanence.
Under normal circumstances, we hope that the Curie temperature of soft ferrite is higher and the temperature coefficient is smaller, while the thermosensitive ferrite is different. It has special requirements for the Curie temperature and physical properties near the Curie temperature.
1. Thermosensitive materials require a stable and specific Curie temperature. For example, the thermal element that plays a protective role in a color video recorder needs a material with a Curie temperature of 40 ℃, a boiling water alarm needs a material with a Curie temperature of 95 ℃, and the automatic control of boiler water temperature needs a material with a Curie temperature of 120 ℃, etc. .
2. The temperature-sensitive material requires the Bi-T curve to drop rapidly when it is close to O, and the material is required to have a good consistency in this characteristic. As shown in the Bi-T curve in the following figure, this requirement for the heat-sensitive material in the overcurrent protection device More obvious.
3. In the process of designing the device, it is hoped that the initial permeability of the thermal ferrite will be higher. Generally above 800 is better.
4. The heat sensitivity of the material is better. Therefore, the thermal conductivity is required to be higher and the specific heat to be smaller, so that the sensitivity is high when used.
Thermal ferrite production
1. Raw materials: ferric oxide, zinc oxide, manganese carbonate, copper oxide.
2. Equipment: 30 kg ball mill, oven, flaking machine, vibrating particle screen, 10t automatic press, 5 kg balance electronics, box-type electric furnace.
3. Instrument: 4225 electric bridge, constant temperature bath.
The production adopts the general oxide ceramic technology, through the process of primary ball milling → drying → pre-sintering → secondary ball milling → drying → granulation → compression molding → sintering. The products are tested with 4225 electric bridges, constant temperature baths and self-made fixtures. 18 products can be tested at one time.
Thermal ferrite applications
The main advantages of thermal soft ferrite materials are oxidation resistance, corrosion resistance, resistance to aging, stable performance and low price.
The TRS series thermal switch is a new type of temperature sensor that uses ferrite soft magnetic thermal material and hard magnetic material, and a combination of reed tube. It has accurate action temperature, small recovery action temperature difference, fast speed, and long life. , Explosion-proof and other advantages. When the external temperature rises from low and crosses the Curie temperature, the magnetic permeability of the soft magnetic ring drops rapidly, and the magnetic flux density through the reed switch decreases, causing the state of the reed switch to change (the reed is on or off ); When the external temperature decreases from high to cross the Curie temperature, the magnetic permeability of the soft magnetic ring increases rapidly, and the magnetic flux density through the reed switch increases, causing the state of the reed switch to change (the reed is on or off Open), so as to realize its temperature control switch state. The thermal magnetic switch is an updated product of the temperature control switch such as bimetallic sheet and thermistor (NTC).
Countries in the world have widely used thermosensitive magnetic switches instead of bimetallic strips and thermistors. The thermal magnetic switch has excellent characteristics such as high temperature control accuracy, stable performance, reliability, durability and energy saving. It has been widely used in refrigerator defrosting, refrigeration and heat preservation, air conditioner temperature control, drinking water mechanism heating, temperature control, rice cookers Temperature limitation, heat preservation, temperature monitoring of solar power generation systems, heat preservation of gas boilers and automatic blowers, cold start, hot start and water temperature control of automobiles, temperature compensation of electronic components, air supply switching of cold rooms and greenhouses, video recorders and recorders Moisture-proof, insulation of nursery box, nursery room, washing equipment, color video recorder, constant temperature room, building fire spray, temperature control of internal combustion engine cooling water system, overheating (current) protection of various machinery and equipment such as power supply and compressor, automatic sales Temperature control and overheating protection of cargo planes, amplifiers, computers, gas stoves and box-shaped electric stoves, temperature alarms, prevention of condensation on the lens of photocopiers, etc.