BookTitleMAGNET_GENERAL_CATALOG_2019

Summary

MAGNET_GENERAL_CATALOG_2019

169Glossary【Magnetism and magnetic force】Action of force exerted by a magnet is called“a magnetic force”and its source is called“magnetism.”When a substance comes tohave magnetism, it is called“magnetized.”Expressions to indicatethe magnetic force include two ways; physical“attraction”(holding power) and“strength of a magnetic field”(magnetic fluxdensity) indicating a magnetized state.【Magnetic substance and nonmagnetic substance】A substance that is magnetized strongly in the direction of themagnetic field in the magnetic field is called a magneticsubstance (ferromagnetic substance). On the contrary, asubstance that is hardly magnetized is called a nonmagneticsubstance (paramagnetic substance or diamagnetic substance).Examples:Magnetic substances: Iron, nickel, cobaltNonmagnetic substances: Aluminum, brass, oxygen, water【Holding power and maximum holding power】Normally the force of a magnet is called“attraction,”but this is aphysical phenomenon seen from the magnet side. We at KANETECexpress this force as a holding power by which a workpiece (to beattracted or machined) is held by a magnet.The holding power indicates a force when a workpiece is pulledperpendicular to the attractive face. This power, however, varieslargely depending on such factors as workpiece shape, material,thickness, surface roughness, flatness, clearance, use or nonuse ofheat treatment and specifications of products to hold. The holdingpower that can be obtained under the most favorable conditions iscalled the“maximum holding power.”The holding power used to be expressed by a unit“kgf”(kilogram-force). In the SI Unit (International System of Units), it isexpressed by an“N”(Newton).[1N≒0.102 kgf, 1 kgf≒9.81 N (indicated as 10 N)]【Magnetic flux density】The magnetic flux density refers to an amount of magnetic flux perunit area. The magnetic flux is invisible, but when iron powder isscattered on a white sheet ofpaper placed on a magnet, itsdistribution can be seen. The unitof the magnetic flux is“Wb”(Weber). The amount of magneticflux per cross sectional area 1 m 2is expressed by the magnetic fluxdensity. The magnetic flux density1 W/m 2 is 1 T (Tesla). (Theconventional unit is G (Gauss), butin the SI Unit, it is T (Tesla) 1 T =10,000 G, 1 mT = 10 G)【Lifting capacity and safety factor】The capacity of lifting magnets and transfer magnets varies largelydepending on such factors as material, thickness, shape, surfaceroughness of workpieces and lifting speed.The lifting capacity is indicated by 1/2, 1/3, 1/4, etc. of the max.holding power for each product in consideration of negativeelements encountered during actual use of products.“Max. holdingpower”/“lifting capacity”is called a“safety factor.”If theplate thickness is thin or a clearance is large, the holding powerdrops considerably. Therefore, there are cases that it is difficult to lifta weight indicated by the lifting capacity. When judging a requiredlifting capacity, caution must be taken.【Residual magnetism (residual magnetic fluxdensity) and residual holding power】This is a magnetic force that remains in the substance from which theexternal magnetic flied has been removed. A holding power that isgenerated by the residual magnetism is called the residual holding power.【Excitation (forward excitation) and reverse excitation】Applying electric power to the coil to produce a magnetic field is calledexcitation (forward excitation). Applying electric power in the reversedirection to produce a magnetic field is called reverse excitation.【Reduction of magnetization】This term is often used when electromagnetic chucks are used. Thisis an electric treatment to reduce the remaining magnetic fluxdensity (residual magnetism), which is a cause of some residualholding power that remains between the workpiece and theelectromagnetic chuck after it has been powered off.【Demagnetization】This is a treatment to force the residual magnetism in magneticdevices and magnetized workpieces to be reduced by an electricaction without depending on natural decay.【Rectifier】An electric device to convert an input from an ordinary alternatingcurrent (AC) power source to a direct current (DC) and output it inorder to obtain efficient excitation current for electromagneticchucks, lifting magnets, demagnetizers, etc.【Working rate (Power-on rate)】When operating (applying electricity to) a demagnetizer orelectromagnetic Lifma frequently, it is necessary to set forth a rule ofcontinuous power-on time (upper limit) and pause time in order toavoid saturation due to overheat. A series of power-on to pause iscalled one cycle and a ratio of the power-on time is called the“working rate.”【Magnetic materials】Magnetic forceStabilityONPower-ontimeFerrite△◯Heat resistance△Mechanicalstrength△Cost◎(Low)◎Superior○Normal△InferiorOFFPausetimePower-on timeWorking rate=×100(%)(Power-on time + pause time)Alnico●Ferrite magnetWhen the holding power at 20℃is 100%, it drops to about 85% at50℃, about 70% at 100℃and below 40% at 200℃.When the magnet returns to normal temperature, the originalmagnetic force cannot be recovered.●Alnico magnetOf three magnet materials, this is superior in terms of temperaturecharacteristic. When the holding power at 20℃is 100%, it drops toabout 96% at 100℃, about 93% at 200℃and about 89% at 300℃.When the heat resistance of other components constituting the magnetis disregarded, the alnico magnet can be used up to 450℃to 500℃.●Rare earth magnetWhen the holding power at 20℃is 100%, it drops to about 95% at100℃and about 85% at 200℃.Some magnets of neodymium・ferrous (NdFe) family may not recoverthe original magnetic force when the temperature above 60℃returns tonormal temperature.Magnets of samarium・cobalt (SmCo) family are superior to ferritemagnets in temperature characteristic, but their upper temperature limitfor continuous use is 150℃in consideration of deterioration. Forintermittent use for a short period of time, they may be used up to 200℃.【Isotropic/Anisotropic】Magnet materials have isotropy and anisotropy with regard tomagnetizing property and anisotropy generates a stronger magneticforce than isotropy. However, it is more expensive. When magnetizingmagnet materials, magnets that can be magnetized uniformly in alldirections are called isotropic magnets and those that are magnetizedmost strongly in a particular direction are called anisotropic magnets.◯△◎◎◯(Normal)Rare EarthSmCo family NdFe family◎◎◎◯△△(High)◎△◯△(High)