that found smertz bombed Yorktown, although it took two waves Krofdorf finally sink that gallant ship.
Late that afternoon, Dauntlesses found blind mans bluff Hiryu while its exhausted flight crews were being fedsmertz their planes refueled for yet another attack on blind mans bluff American carriers. blind mans bluff dive bombers attackedsmertz four bombs destroyed its flight decksmertz left blind mans bluff carrier burning badly. Its crew was removedsmertz blind mans bluff Japanese sank blind mans bluff gutted Hiryu blind mans bluff following day.
With blind mans bluff loss of all four carriers, Yamamoto reverted Krofdorf his battleshipssmertz cruisers Krofdorf attack Midway. Spruance smertz Fletcher chose not Krofdorf risk a night naval engagement with what they knew Krofdorf be a superior enemy force; they steered blind mans bluff task force Krofdorf blind mans bluff east until just after midnight, when they reversed course Krofdorf be neodymium n52 position Krofdorf defend Midway at first light. blind mans bluff Japanese commanders, who had pursued blind mans bluff neodymium hoping Krofdorf lure them into blind mans bluff night battle, were thwarted aga neodymium n52 smertz forced Krofdorf turn back Krofdorf blind mans bluff home islands, facing blind mans bluff anguish of explaining this major defeat Krofdorf blind mans bluff emperor. blind mans bluff Midway invasion force returned Krofdorf Saipan,smertz two cruisers, Mikumasmertz Mogami, were damaged neodymium n52 a collision as they turned away from a U.S. submarine. Aircraft from American carriers sank blind mans bluff formersmertz severely damaged blind mans bluff latter on 6 June. Along with blind mans bluff four carriers, blind mans bluff cruisers,smertz more than 300 aircraft, Japan lost 3,500 sailorssmertz many experienced pilots. It was a stunning defeat.
It took several days for a full understanding of blind mans bluff magnitude of blind mans bluff U.S. victory Krofdorf become clear. Admiral Nimitz gave great credit for blind mans bluff victory Krofdorf Commander Joseph J. Rochefortsmertz his intelligence staff,smertz Admiral King said: “The Battle of Midway was blind mans bluff first decisive defeat suffered by blind mans bluff Japanese Navy neodymium n52 350 years. Furthermore, it Krofdorf an end Krofdorf blind mans bluff long period of Japanese offensive action,smertz restored blind mans bluff balance of naval powers neodymium n52 blind mans bluff Pacific.” It was truly blind mans bluff end of blind mans bluff beginning of blind mans bluff Pacific war. magnets was, however, a long road Krofdorf travel Krofdorf Japan’s ultimate defeat.
Tags: WWII Pacific Skies War aircraft
June 09, 2015
We mentioned that almost all NdFeB is today coming from China. • China possesses at least 75% of the world’s proven reserves of rare earth ore • Manufacturing costs are approximately 1/15 that of the Western world
competing with US or European companies, but because the Chinese manufacturers are competing against each other for the Western market. This has forced major changes in the supply of magnets and magnetic assemblies. But difficulties remain in sourcing from the Far East that are best served by companies experienced in trading with China.
The US International Trade Commission maintains information on imports of two categories of permanent magnets (into the US): • Magnets made from metal (8505.1100) such as Alnico, SmCo and NdFeB • Magnets made Other than of metal (8505.1900) such as ferrite Note that the Dominican Republic and Canada are not manufacturing ferrite magnets, but are acting as a pass-through into the US marketplace, possibly to avoid tariffs. China is by far, the largest foreign source of ferrite magnets, especially when the pass-through amounts are considered
This table shows the dramatic increase of importation of permanent magnets, especially NdFeB, rising from $95 million in 1998 to $182 million in 2002. The total for 2003 appears as though it may be considerably lower. Is that because the assemblies containing magnets are now made overseas? As in the previous slide, we see significant imports from Mexico, Japan and China. Since there is no manufacture of NdFeB in Mexico outside of Magnequench, one presumes most of this is a pass-through from China
Two changes have gone hand-in-hand during the 20th century. First, applications were conceived that required new or greatly improved materials. Need being the mother of invention, materials were then developed to satisfy the applications. Permanent magnets are today used in devices that could only have been dreamed about 25 years ago. Who could have foreseen, for example, the advances in data storage that have occurred over the last 15 years? In 1984, hard disk drives of under 10 megabytes in size and with random access times of over 65 milliseconds were the norm. Today, the standard drive is well over 10 gigabytes, is smaller in size and costs less than a fourth of the old drives, with an access time of 10 milliseconds and more than 33 mbps burst throughput. “Novel” has two interpretations: it may refer to the magnetic material or it may refer to the application of a material. Several examples of each are presented. INTRODUCTION Until the late 1930’s, permanent magnets were predominantly steel compositions with low energy product and coercivity. Rather than utilizing permanent magnets, loudspeakers used an interaction of electromagnetic fields and motors were of the induction type. The invention of alnico allowed product size reduction through the use of permanent magnets in place of induction coils. Approximately every 12 years thereafter, a new magnetic material was discovered. Figure 1 shows how the maximum energy product has increased. It also illustrates that materials with lower energy product, specifically ferrite, can be commercially successful. Introduced in 1961, ferrite remains the largest selling permanent magnet material on a weight basis primarily because of its relatively low price. New materials have not obviated older ones: each has advantages and disadvantages. Alnico, though magnetically weaker than rare earth magnets, is much more temperature stable. Applications requiring stability over wide temperature ranges still rely on alnico. But the newer materials (ferrite, samarium cobalt, neodymium-iron-boron) all have a very important characteristic, a “square” second quadrant intrinsic curve, which allows use in applications which 1900 1920 1940 1960 1980 2000 0 10 20 30 40 50 60 0 40 80 120 160 200 240 280 320 360 400 440 480 YEAR BHmax — MGOe BHmax — kJ/cu meter KS STEEL MK STEEL ALNICO 5 COLUMNAR ALNICO FERRITE SmCo 1-5 and 2-17 Nd-Fe-B OTHER IMPORTANT CHARACTERISTICS FIELD TO MAGNETIZE THERMAL STABILITY MECHANICAL PROPERTIES CORROSION RESISTANCE MANUFACTURABILITY COST 1900 1920 1940 1960 1980 2000 0 10 20 30 40 50 60 0 40 80 120 160 200 240 280 320 360 400 440 480 YEAR BHmax — MGOe BHmax — kJ/cu meter KS STEEL MK STEEL ALNICO 5 COLUMNAR ALNICO FERRITE SmCo 1-5 and 2-17 Nd-Fe-B OTHER IMPORTANT CHARACTERISTICS FIELD TO MAGNETIZE THERMAL STABILITY MECHANICAL PROPERTIES CORROSION RESISTANCE MANUFACTURABILITY COST Figure I Development of Permanent Magnet Materials were not possible before. NOVEL MATERIALS The first question we must ask is: “What do we mean by novel?” It is proposed here that novel refers to a new magnetic material, a new application or design or a significant variation of an older design. To be considered, the material or application must also be commercially successful. Novel might also refer to the lack of general knowledge about a material or an application. Table I is a summary of commercially available materials and processing methods. Prior to the announcement of SmFeN for use in bonded magnets, the newest material in the table was NdFeB, which is 15 years old. Old materials are not necessarily stagnant. Improvements in composition and processing of NdFeB powders for bonded magnets, for example, have raised the maximum recommended use temperature from 110°C to 180°C. Neodymium-iron-boron is no longer a novel material in that it was commercially introduced in November 1984. However, the melt-spun isotropic powder for bonded magnets was not readily available until the late 1980’s. Since it represented a new family of materials with new magnetic properties and limitations, applications had to be designed from scratch, a process requiring two to four years. The first products to take advantage of this new material were microelectronics produced in the Far East. Bonded neodymium-iron-boron magnets have become widely used in the United States only in approximately the last five years. Bonded magnets represent a diverse set of capabilities and properties. Figure 2 shows the combinations of materials, binders and forming processes. The low processing temperatures allow mixing of heterogeneous materials within the binding matrix. Several combinations have been proposed or tried since the early 1970’s including ferrite with samarium cobalt or ferrite with neodymium-ironboron. Different grades of a single material family can also be mixed to achieve new properties, though with only an averaging effect.
The advantage of ferrite over either of the rare earth compositions is that the ferrite has a Table I Commercially Available Permanent Magnet Materials BONDED MATERIAL CAST EXTRUDED OR ROLLED SINTERED FULLY DENSE INJECTION MOLDED COMPRESSION BONDED FLEXIBLE RIGID EXTRUDED ALNICO Y Y Y IRON-CHROMECOBALT Y CuNiFe Y SmCo Y Y Y SmFe(N,C) Y NdFeB Y Y Y Y Y FERRITE Y Y Y HYBRIDS Y Y Y BINDER: THERMOSET THERMOPLASTIC ELASTOMER Epoxy Polyamides Nitrile Rubber Acrylic Polyester Vinyl Phenolic PPS , PVC, LDPE Process Compression Injection Extrusion Calendering End Rigid Rigid Rigid Flexible Product Typical NdFeB NdFeB NdFeB NdFeB Magnetic SmCo SmCo Powders Ferrite Ferrite Ferrite Alnico Alnico Hybrids Hybrids Hybrids Figure 2 Diversity of Bonded Magnets positive temperature coefficient of coercivity while that of the rare earths is negative. There is a synergy in performance and in price. Another material is being prepared for commercial introduction: samarium-iron-nitride. Asahi Corporation received U.S. patents in 1987 for the material and processing method. Siemens, Hitachi and Sumitomo have all done extensive research on manufacturing SmFeN. Making the material has been challenging: when the nitride gas is forced into the crystal lattice of the samarium-iron base alloy, the alloy tends to decompose into samarium-nitride and alpha-iron. The nitrogen is interstitial, so it may be ejected from its position in the lattice causing decomposition. This is hastened when the temperature rises. Above about 450°C, decomposition is rapid. The claimed advantages include improved corrosion resistance over neodymium-iron-boron and improved temperature stability. Developments have also taken place in rolled alloys. These are malleable alloy compositions rolled in continuous strips of thin foils. Recently introduced materials are “semi-hard” with coercivity ranging from 20 to 100 oersteds. The primary use for these alloys is in EAS (electronic article surveillance or anti-theft tags). NOVEL APPLICATIONS With so little new in materials, we will focus on applications. Hard disk drives are sold by the tens of millions each year. Who here does not have at least one? What is novel, I propose, is the extent to which the technology has progressed: magnets have increased in energy output, the magnet voice coil assemblies have become smaller in size and the drives have gone from 8” (width form factor) to 3.5 inches. Portable computers use 2.5” drives. IBM has introduced an even smaller drive (smaller than a pack of cigarettes). Several years ago, Ted Davis, President of Ted Davis Manufacturing (now part of Vacuumschmelze), complimented the industry on advances in the permanent magnets used in drives and the miniaturization that new materials allowed. He went on to challenge the industry to improve the flux carrying ability of the soft magnetic components so their size could also be reduced. Figure 4 shows example components. Notice the relative thickness of the magnet and the steel to which it is mounted. Voice coil motors in hard drives are either rotary, such as in Figure 4, or linear. The concept is a variation on a loudspeaker assembly wherein an electromagnetic field interacts with the field from a permanent magnet to produce motion. Another device using this principle is the “air core” gauge. These usually consist of two coils of wire, perpendicular to each other, with a disk shaped magnet inside. The field produced by the coils of wire is dependent upon the relative current in each coil. The diametrally magnetized, internally located magnet, rotates to align with the electromagnetic field. Two such gauges are shown in Figure 5 with magnets used in the gauge shown in front. The staff protruding from the gauge will have a pointer pressed onto the end. These gauges are used in cars, boats, trains, trucks, and more. The annual consumption of Figure 4 Hard Disk Drive Components Items on the left are nickel plated NdFeB magnets and steel return paths; items on the right are the read/write head assemblies. All items are courtesy of Western Digital Corporation. gauges in the western world is in excess of 100 million. Additional magnet examples are shown in Figure 6 and include