Low weight loss magnets are a type of neodymium magnet with strong corrosion resistance.Neodymium magnets are chemically active and have many tiny gaps in their internal structure, making them very susceptible to corrosion in air.Corrosion has a huge impact on magnets, and the magnetic properties of neodymium magnets gradually decrease and eventually disappear as the degree of corrosion increases.
Therefore, in order to ensure the normal operation of machines using neodymium magnets, we usually use metal or epoxy coatings to protect neodymium magnets from corrosion.
However, the plating also brings new problems.Magnets can be corroded and aged during electroplating due to acid washing and temperature rise.The plating increases the distance between the magnet and other objects, and the magnetic field intensity gradually decreases as the distance increases.This leads to a decrease in the performance of motors or other devices using plated magnets.
In addition, some magnetic components require glue to bond multiple magnets together, and the plating affects the strength of the bond between the magnets.Therefore, more and more customers prefer to use unplated magnets.
By adjusting the composition of raw materials and using special production processes, we have manufactured low weight loss magnets with high corrosion resistance even without a coating.
1. Weight loss test
Weight loss test is used to test the corrosion resistance of uncoated neodymium magnets.The test sample is exposed to high temperature, high pressure, and high humidity conditions.Weight loss refers to the mass loss per unit surface area of the magnet’s orientation plane due to corrosion, with the unit being mg/cm2.
The weight loss test can be conducted through two methods: PCT and Hast. PCT (Pressure Cooker Test) and HAST (High Accelerated Stress Test) are commonly used high-pressure aging test methods to evaluate the reliability of electronic components, equipment, or materials in high temperature and humidity environments.
Their differences are mainly reflected in the following aspects:
①Type of experiment:
PCT is a saturation experiment in which temperature, humidity, and pressure rise or fall simultaneously, used to quickly expose product defects and weaknesses and test the sealing performance of magnetic materials.
Hast is a non-saturated experiment in which temperature, humidity, and pressure can be adjusted according to needs, used to test the service life of magnetic materials, also known as accelerated aging testing.
PCT are usually conducted at a high temperature of 121°C, with a humidity of 100% and a pressure of 2 atmospheres.
The temperature of the HAST is generally between 100°C and 130°C, with a humidity of 85% to 100%, and the pressure is usually higher than 2 atmospheres.
The duration of the PCT is generally 96 to 1000 hours.
The duration of the HAST is usually relatively short, typically ranging from 48 to 168 hours.
④Different experimental equipment:
PCT and Hast require the use of dedicated experimental chambers.
2. Low weight loss magnet standard
As the weight loss test progresses, the surface of the neodymium magnet will slowly lose weight due to corrosion.When the weight loss reaches a critical point, the weight loss rate of the neodymium magnet will rapidly accelerate, with the critical point being approximately 5mg/cm2.
So, when we produce low weight loss magnets, we hope to control the weight loss below the critical point for as long as possible during the test.
When traditional magnets deform due to weight loss, low weight loss magnets can still maintain their original shape.
Different countries and regions have their own unique standards for defining low-weight magnets.Here are the definitions of the United States and the European Union.They are completely different in testing methods and qualification requirements.When you need to buy or sell low-weight magnets, you need to consider the definition of product standards in different regions.
1. US Standard: PCT ,temperature(121℃±1℃), 2 atm, 95%RH, for 96 hours, weight loss less than 5-10mg/cm2.
2. EU Standard: HAST ,temperature(130℃±2℃), 3 atm, 95%RH, for 168 hours, weight loss less than 2-5mg/cm2.
3.Application of low weight loss magnet
In addition to meeting the market demand for uncoated magnets, low weight loss magnets can also be coated.This dual protection further improves the reliability and service life of the product, making it suitable for high-end motor and equipment requirements.It is widely used in aerospace, wind power, radar, and military equipment.
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