quote== 有沒有可能拾音器線圈的磁性會消失呢 quote== 前面朋友提的問題應該是筆誤，拾音器的 "線圈" 並沒有磁性。Alnico 磁鐵 (除了鋁/鎳/鈷外還有"鐵") 除非遇到高溫或極大外力，一般使用並不會有衰減磁力問題。若想刻意衰減磁力，可以拿一個相反磁極的磁鐵輕輕拍、敲，或使用所謂的 "demagnetizer"。 下面文章偷自： http://www.duramag.com/rawmat/alnico_tech.htm ============================== Alnico Manufacturing Processes A cast alloy consisting primarily of iron, aluminum, nickel, cobalt, with minor amounts of other elements including copper and titanium. Produced by conventional foundry methods using resin bonded sand molds, Alnico is suitable for complex geometries and configurations not achievable with other magnet materials. These alloys can be tailored easily to obtain a variety of magnetic properties and characteristics. Specialized casting techniques are used to achieve the unique crystalline grain orientation found in the Alnico 5-7 grade. Properties are optimized during a heat treatment process which is unique to Alnico. The direction of orientation for most Alnico material is determined during this process which involves heating the casting above its Curie temperature then cooling at a controlled rate in the presence of a directionalized electromagnetic field. The actual shape of the magnetic field as well as its intensity can be optimized during this process. Magnets which have been processed in this fashion are anisotropic in nature and exhibit a preferred direction of orientation. Unoriented materials (Alnico 2) are available for those applications which require the specialized magnetizing capabilities of a non-aligned material. Final shaping of the Alnico materials is achieved by abrasive grinding and cutting where close tolerances are required, otherwise it is desirable to use the part with as cast features. Magnetizing Requirements and Recommendations The lower coercivity of Alnico makes magnetizing a simple matter in most cases. In order to optimize the performance of an Alnico magnet, it is advisable to magnetize the part after assembly with the other circuit components. This also helps control particle contamination, simplifies assembly operations, and allows for automation of the assembly process. Calibration of the magnet to achieve very precise levels of performance can also be accomplished after the magnetizing process is complete. Caution: Alnico magnets can be adversely effected by exposure to the repulsive forces generated by another magnetized magnet or by stray AC fields. (Care must be exercised when either of these conditions exists.) Temperature Characteristics of Alnico Materials Alnico offers the best temperature characteristics of any standard production magnet material available. It can be used for continuous duty applications where temperature extremes up to 930°F can be expected. Temperatures above 1022°F will result in permanent metallurgical changes which can only be recovered by reheat treating. Excursions to lower temperatures pose less of a problem for most Alnico applications, however each individual circuit should be examined carefully to determine the effects which may occur as a result of operating at those extremes. Duramag's Application Engineering staff can provide specific guidelines concerning the temperature characteristics for a given Alnico grade and make recommendations for their proper use. Physical Characteristics of Alnico Alnico materials are hard and brittle and are not suited to common drilling, tapping, or machining operations. Tolerances closer than as cast are achieved only by abrasive grinding and cutting. Due to its brittle nature, Alnico should not be used as a structural component in any device. Pole pieces or other components can be attached by using a structural adhesive for assembly purposes. In addition, Alnico lends itself to silver soldering operations in certain circumstances. Specific recommendations can be made by our Application and Engineering staff.
順便把 "Rare Earth" 也給搬過來.... http://www.duramag.com/rawmat/neo_tech.htm Neodymium Iron Boron Manufacturing Processes Neodymium Iron Boron and Samarium Cobalt are produced by compacting a finely milled metallic powder in the presence of an electromagnetic alignment field. Magnets produced in this manner are anisotropic, and will exhibit a preferred direction of orientation when magnetized. The "green" compacted part is sintered and heat treated in a controlled inert gas atmosphere to achieve full density and optimize the magnetic properties. Final shaping of the magnet is accomplished by grinding with diamon abrasives. Normally these magents are ground only on the pole faces, all other surfaces would exhibit as pressed dimensions and surface conditions. Temperature Characteristics If the Neodymium and Samarium Cobalt materials are required to operate at temperatures other than ambient, consideration must be given to the effect on the magnet's performance. Normally operating below 20°C causes no adverse effects, and in fact performance increases with decreasing temperatures. The Neodymium materials do exhibit a temporary, or reversible loss of flux with increasing temperatures. The severity of these losses and the possiblity of permanent, or irreversible losses must be considered when the design is being developed. The grade of material, temperature extremes, magnet geometry, and circuit configuration will all influence the ability of a given device to withstand adverse thermal conditions without experiencing unexpected losses. Please consult the individual product data sheets for specific temperature data, or consult our application engineering department for additional information. Physical Characteristics Neodymium magnets are stronger mechanically than most other permanent magnet materials. Even with this improved mechanical strength they should not be considered as structural components, and should be handled with some care to minimize any possible chipping or breakage. Minor imperfections such as chips, surface porosity, or other similar characteristics can occur with any permanent magnet material. These imperfections will not effect the magnet's performance, and should not be considered cause for rejection. Duramag will work with you to develop a mutually agreed upon visual inspection standard to insure that only acceptable physical characteristics are present in any parts we supply. The high iron content of Neodymium makes it prone to oxidation. Depending upon the environment in which the magnet is destined to operate, a variety of coatings or surface treatments may provide adequate protection from corrosion.
Ceramic 請看這裡： http://www.duramag.com/rawmat/ceramic_tech.htm Ceramic (Duramax) Manufacturing Processes Ceramic magnets are manufactured by calcining or presintering a mixture of iron oxide and strontium ferrite to produce a metallic oxide. A multiple stage milling operation reduces the calcined material to a small particle size; this finely milled water borne powder is then compacted in the presence of a magnetic alignment field to a "green" state. These compacted parts, which approximate the finished geometry, are then sintered at high temperatures to achieve the final fusion of the individual particles. Parts which have been produced in this manner are anisotropic and will exhibit a preferred direction of orientation when magnetized. Final shaping of this material is accomplished by grinding with diamond abrasives. Normally, ceramic magnets will not only be ground on the pole faces; all remaining surfaces will exhibit as sintered tolerances and physical characteristics. Temperature Characteristics of Ceramic Magnets If the Ceramic materials are required to operate at temperatures other than ambient, consideration must be given to the effects on the magnet's performance. Normally temperature ranges above ambient do not result in any permanent losses unless they approach the Curie point for that given grade of material. Elevated temperatures do have a temporary effect on the performance of the magnet and these losses must be considered when designing a particular circuit. Excursions below ambient temperatures may result in permanent losses if the circuit has not been designed to account for such extremes. The grade of material, temperature extremes, magnet geometry, and circuit configuration will all influence the ability of a given device to withstand adverse thermal conditions without permanent losses. Please consult the individual product data sheets for specific temperature data or consult our application engineering staff for additional information. Physical Characteristics of Ceramic Magnets The crystalline structure of the ferrite material makes drilling, threading or machining of the magnet impractical. The mechanical characteristics of this material prevent them from being utilized where impact or flexing may be experienced. As with most ceramics, the ferrite materials should not be exposed to heating or cooling rates greater than (200°F per hour). This will minimize the possible effects of thermal shock which can result in physical damage to the part. Imperfections such as chips, cracks, or similar characteristics are commonly found on sintered ferrite magnets. Duramag works with its customers to develop a mutually agreed upon visual inspection standard to insure that only acceptable physical characteristics are present in the final products supplied.