China
Africa
Explore chapters and articles related to this topic
Principles of Energy Conversion
Published in Hamid A. Toliyat, Gerald B. Kliman, Handbook of Electric Motors, 2018
Hamid A. Toliyat, Gerald B. Kliman
In this configuration, the coil structure (armature) rotates in the air gap between the inner core and the permanent magnet. To find the operating point on the magnet B‒H curve, the permeance coefficient is calculated by dividing the magnet length by the air gap length, assuming that the air gap area equals the magnet area. By superimposing the load line based on the permeance coefficient on the B‒H curve for Alnico 5-7 as shown in Fig. 2.59, the operating point is found to be at 12 kilogauss. However, the coercive force at this load point is only 400 Oersteds, indicating a motor design that could result in demagnetization from severely high current pulses. To counteract this tendency, a pole piece is often bonded to the face of the magnet, and then machined to the diameter of the armature plus clearance. It short-circuits the circulating current flux from the high current pulses. With this configuration, the pulse current can typically be six times the rated current before demagnetization will occur. The pole piece also serves to concentrate the lines of flux coming from the face of the magnet, resulting in a higher flux density across the conductors. As a family, these motors are the most efficient dc machines available. Another characteristic associated with this type of motor is a low mechanical time constant, resulting from the small mass of the armature (no rotating Iron). Ironless armature motors also exhibit the lowest armature inductance, another factor that must be considered in stabilizing a servosystem using this type of motor.
CHAPTER 12 Diversity of Design
Published in Douglas Self, Audio Engineering Explained, 2012
There are many people who consider the metal magnets to be capable of better sonic performance than the ferrite magnets, citing better resolution of fine detail with materials such as Alnico and the neodymium alloys. It is hard to find evidence of tests which rigorously compare the differences in the magnetic materials only, because the required structural differences needed to get exactly the same magnetic field in the same gap can lead to other changes being necessary. Nevertheless, there is a tendency for many of the highest resolution devices to use metal magnets, and explanations have been put forward to suggest that the magnetic domain jumps which take place in non-conducting materials can give rise to effects not dissimilar to digital quantizing distortion. These jumps are smoothed out by large eddy currents flowing in the electrically conducting magnets. In some loudspeaker designs the central pole-piece of the magnetic assembly is fitted with a copper ring to provide a very low electrical resistance— less than that of steel — to effectively short out any flux-modulation currents.
40 K single-stage split-type Stirling cryocooler
Published in International Journal of Ambient Energy, 2022
Fayaz H. Kharadi, A. Karthikeyan, Bhojwani Virendra
The expander unit consists of a displacer (Figure 12) suspended on two stacks of flexure bearings and reciprocating inside the cryocylinder (Figure 13). The central hole of the main body (Figure 14) accommodating the displacer shaft separates the working space from the bounce space inside the end cover. Clearance of the order of 12–15 µm was kept between the displacer tube (pasted with Rulon) and cryocylinder to avoid working gas leaking to the expander bounce space. The nominal stroke of the displacer is 3 mm. The required drive was provided by a moving coil linear motor which consists of a top pole piece, bottom pole piece, coil former and magnet (Figure 15). Moving coil is physically connected to the shaft of the displacer. When ac supply is given to the coil former winding the displacer starts oscillating. The displacer is freely suspended on two stacks of flexure bearings. The displacer leads the piston and hence a phase difference is essential between the two. The flexure support ring (Figure 16) supports the stack of flexure bearings. A vacuum jacket with O ring (Figure 17) was used to create the vacuum at the copper tip to reduce the losses. Figure 18 shows the photochemically itched flexure bearings. The coil former (Figure 19) which gives the oscillating motion to the displacer through the shaft.
Simulation and Experimental Study on Pressure Transfer Mechanism in Multitooth Magnetic Fluid Seals
Published in Tribology Transactions, 2021
Hongming Zhou, Yibiao Chen, Yanjuan Zhang, Decai Li
The magnetic circuit consists of the pedestal, the pole piece, and the permanent magnet. The pedestal and the pole piece are made of 20Cr13 martensitic stainless steel with good magnetic permeability. The pole tooth is a rectangle with a width of 0.6 mm and a height of 3 mm. The magnet is made of NdFeB with an N35 grade. The connecting blocks are used to connect the pole pieces and pedestal. The material of the blocks is 304 stainless steel, whose permeability is approximately equal to vacuum permeability. The magnetic fluid is diester based and was synthesized at Beijing Jiaotong University.
The Pressure Loading Process among Stages of Magnetic Fluid Seal in Aqueous Environment
Published in Tribology Transactions, 2019
Zhongzhong Wang, Decai Li, Yanjuan Zhang, Yanan Gao, Hannah Rose Neumann
An MF seal is a noncontact seal and uses MF as a sealing medium. When responding to the magnetic field, several magnetic fluid “O” rings are formed, followed by an injection of MF into the gap of the magnetic circuit, which is composed of a high-performance permanent magnet, magnetically conductive pole piece, and rotating shaft. At this point, the MF will reach a balancing point between pressure differences and magnetic forces and will then continue to perform its sealing function. The principle factors of the MF sealing process are shown in Fig. 2.