Author:Site Editor Publish Time: 2020-09-30 Origin:Site
Magnetic attraction refers to the weight of ferromagnetic material that a magnet can absorb, and it is affected by the performance, shape, size, and adsorption distance of the magnet.
The tensile strength of a magnet is usually measured with a tension meter. It is a very subjective measurement method, which is usually not accurate and will be affected by many external factors. Today, let's talk about several factors that affect the tensile strength of a magnet.
The first is the influence of the magnet's own material. The following is a comparison of the attractive force of different magnetic materials and their own weight.
The comparison of the required self-weight when attracting the same volume and weight of iron products, as can be seen from the figure, ferrite requires the largest self, so relatively speaking, its own magnetism is the weakest, which is what we commonly see the black magnet. Sintered NdFeB has the strongest magnetism. Generally white, because of its own hard and brittle characteristics, it usually has a coating. It is also mentioned in the previous article on the influence of temperature that in addition to considering the influence of temperature on NdFeB, the use environment also needs to consider the influence of factors such as temperature on the coating.
The material of the attracted object
Then we must first analyze the composition of the magnet. The composition of the magnet is atoms such as iron, cobalt, and nickel. The internal structure of the atoms is quite special and they have a magnetic moment. Among iron, cobalt, and nickel, there are many primary magnets with two opposite magnetic poles. When there is no external magnetic field, the arrangement of these primary magnets is disordered and their magnetism cancels each other out and does not show magnetism. When the iron is close to the magnet, these primary magnets are neatly arranged under the action of the magnet so that the end close to the magnet has a polarity opposite to that of the magnet and attracts each other. This shows that the iron can be magnetized by the magnet due to the existence of the original magnet. Metals such as copper and aluminum do not have the original magnet structure, so they cannot be attracted by magnets.
Relative contact area
Area refers to the area through which the magnetic flux passes. For example, the area corresponding to the magnet and the iron. If the area of the magnet is large but the area of the iron is small, then the magnetic density on the surface of the iron will be larger, and the magnetic density on the surface of the magnet will be relatively small. The product, the magnetic flux, is equal. The larger the contact area, the smaller the magnetic force required, that is, the greater the suction force.
Surface condition and finish
When the magnet is attracted to the magnetic substance, there will be a gap on the contact surface. The size of the gap is affected by the surface condition and smoothness of the two contacting surfaces. Similarly, the adsorption capacity of the magnet is also affected by the contact area. The larger the contact area, the stronger the attraction. At present, there is no mathematical formula to calculate the attractive force of a magnet, but we can measure the magnetic attractive force through a magnetic attractive force measuring device (usually to measure the tensile force of the magnet and then convert it to weight), as shown in the figure below. The attractive force of the magnet will gradually decrease as the distance of the adsorbed object increases.
The Curie temperature of ferrite is 465℃, the Curie temperature of neodymium iron boron is 310℃, the Curie temperature of alnico is 800℃, and the Curie temperature of samarium cobalt is between 700-800℃, so NdFeB Boron has the worst temperature stability, but the highest performance. It is called "magnet king". The production of magnetic materials has two processes: sintering and bonding. The bonding will not have high magnetic properties due to the addition of a binder, but the product accuracy is relatively high. high. Therefore, when choosing a magnet, you can choose a ferrite magnet if the magnet is delicate, and the price is cheap. If high magnetic force is required, neodymium iron boron magnets is generally selected for the working temperature, but in an environment above 200 degrees Celsius, Samarium Cobalt magnets is the strongest magnet.
At this time, a reference object such as an iron block is needed. One end of the iron block is attracted to the magnet, and the other is hung on the dynamometer.
Pull the dynamometer forcefully to ‘vertical to the ground’ and read the measured force F at the ‘instant’ when the two magnets are separated.
Comparing the three values of pull force, the larger value means that the pull force of the magnet is stronger.