a study on volumetric magnetic susceptibility of weight due to its ...

IMEKO 2010 TC3, TC5 and TC22 ConferencesMetrology in Modern ContextNovember 22−25, 2010, Pattaya, Chonburi, ThailandA STUDY ON VOLUMETRIC MAGNETIC SUSCEPTIBILITY OF WEIGHTDUE TO ITS MANUFACTURING PROCESSRungsiya Sukhon 1 , Rattapon Kongchana 2Kusuma Khongsiri 3 ,Baramee Puntaratronnugoon 4 , Veera Tulasombut 51 National Institute of Metrology Thailand, Pathumthani, Thailand, rungsiya@nimt.or.th2 National Institute of Metrology Thailand, Pathumthani, Thailand, rattapon@nimt.or.th3 Faculty of Engineering, Srinakharinwirot University, Nakhonnayok, Thailand, kidcat_11@hotmail.com4 Faculty of Engineering, Srinakharinwirot University, Nakhonnayok, Thailand, lightingassassin@hotmail.com5 National Institute of Metrology Thailand, Pathumthani, Thailand, veera@nimt.or.thAbstract − The OIML R 111-1 requirements onmagnetic properties such as the volumetric magneticsusceptibility ( χ ) and the magnetization of weights used inlegal metrology. So far, these requirements cannot met byweights produced locally in Thailand. This research,therefore, aims to <strong>study</strong> manufacturing processes that mayinfluence the magnetic properties. In order to reduce themagnetic susceptibility of the weights. Preliminary resultsshow that the magnetic properties are stainless steel typedependent. Moreover, controlling process such as cutting,turning with lathe, grinding and heat treatment process canreduce the volume magnetic susceptibility of weights.Keywords : weight, magnetic susceptibility,manufacturing process1. INTRODUCTIONMagnetic force can adversely affect the weighingprocess, since without systematic investigation, thesespurious forces cannot be distinguished from gravitationalforces in the determination of mass. Magnetic force canarise from the mutual interaction of two mass standard, aswell as between a mass standard, the mass comparator beingused for the weighing, and other magnetic objects in thevicinity.[1]At present, weights manufactured in Thailand can not bein line with the specified limitation of OIML R111-1. Themain obstacle due to the manufactory process was coveredby the condition of magnetism which both the limits ofpolarization and magnetic susceptibility for E2 weightswhich nominal weight ≥ 20 g must be less than 2 µT and0.07, respectively. However, those measured values werestill higher than the requirement. Eventhough, the austeniticstainless such as 304 or 316L were chosen as the material ofthe manufactured weight. In order to improve thetechnology in the standard weight manufacture, the <strong>study</strong> onthe volumetric magnetic susceptibility of weight due to itsmanufacturing process was done.The most variable of weight manufactured, OIMLR1111-1 for class E2 is magnetic permeability which isconfined mainly to ferromagnetic and ferromagneticmaterials. Ferromagnetism exists is a number of metalsincluding iron, many forms of steel, nickel and cobalt. Asimilar phenomenon occurs in certain non-metals known asferrites, which are said to be ferrimagnetic. These materials,which can be magnetized, are characterized by variations ofmagnetic permeability with magnetic field strength,generally in a nonlinear manner and giving rise tohysteresis.[2].2. INFORMATION BACKGROUNDThe magnetic properties of material are affected bycomposition, methods and physical condition.Ferromagnetic materials are strongly attracted to apermanent magnet and may also be magnetized to act as apermanent magnet. [3]Magnetic permeability is the abilityof a material to carry magnetism, indicated by the degree towhich it is attracted to a magnet. Stainless steels are highalloysteels that have superior corrosion resistance thanother steels because they contain large amounts ofchromium. Stainless steels can contain anywhere from 4-30percent chromium, however most contain around 10 percent.All stainless steels, with the exception of the austeniticgroup, are strongly attracted to a magnet.Austenitic Grades - All austenitic grades have very lowmagnetic permeabilities and hence show almost no responseto a magnet when in the annealed condition; the situation is,however, far less clear when these steels have been coldworked by wire drawing, rolling or even centreless grinding,shot blasting or heavy polishing. After substantial coldworking Grade 304 may exhibit quite strong response to amagnet, whereas Grades 310 and 316 will in most instancesstill be almost totally non-responsive. The change inmagnetic response is due to atomic lattice straining andformation of martensite. In general, the higher the nickel tochromium ratio the more stable is the austenitic structureand the less magnetic response that will be induced by coldwork.

Stress Relieving - Any austenitic stainless steel which hasdeveloped magnetic response due to cold work can bereturned to a non-magnetic condition by stress relieving. Ingeneral this can be readily achieved by briefly heating toapproximately 700 - 800°C (this can be conveniently carriedout by careful use of an oxy-acetylene torch). However,unless the steel is a stabilised grade it could becomesensitised to carbide precipitation. Full solution treatment at1000 - 1150°C will remove all magnetic response withoutdanger of reduced corrosion resistance due to carbides. Ifmagnetic permeability is a factor of design or isincorporated into a specification, this should be clearlyindicated when purchasing the stainless steel from asupplier.Cold Working - Many cold drawn and/or polished artefact,weight, have a noticeable amount of magnetism as a resultof the previous cold work. This is particularly the case withgrades 304 and 303, and much less so for the higher nickelgrades such as 310 and 316. Even within the chemicallimitations of a single standard analysis range there can be apronounced variation in the rate of inducement of magneticresponse from cold work.Effect of cold work on- austenitic stainless steelsThe table1. shows the relative permeability of 304 and 316at a low magnetic field strength and various cold reductions.Highly alloyed austenitics including the high nitrogengrades do not develop low carbon martensite on cold workand so their relative permeability typically remains below1.02. The values may be compared with mild or carbon steelwhich has a ferritic structure and a relative permeability ofat least 200. The effect of composition and degree of coldwork (measured by the tensile strength) on the permeability,and hence the strength of any magnetic attraction, is plottedbelow fig below for a series of austenitic alloys. It showsthat increasing the nickel content reduces the effect of coldwork on magnetic properties, shows as Fig.1 below[3].Table 1. Relation of relative permeability of 304 and 316 at alow magnetic field strength and various cold reductions.Alloy304(Chromium 19%,nickel 10.7%)316(Chromium 17.5%,nickel 13.4%,molybdenum 2.4%)Cold reduction(% reduction inarea)RelativePermeability0 1.003713.8 1.004832.0 1.037165.0 1.54084.5 2.200 1.00320.8 1.00345.0 1.00460.8 1.006581.0 1.00703. EXPERIMENT AND RESULTSFirstly, we considered about the component of material.So, the OIML weight class E2 was analysed the compoundby Optical Emission Spectrometer. The result shows in table2.Table 2. The element compound of OIML weight class E2 inpercent of total weightElementWeight in %compoundC 0.010Si 0.496Mn 0.167P 0.019S 0.004Ni 25.512Cr 20.436Mo 3.266Cu 1.085Mo 3.266Ti 0.008Nb 0.014This result shows the largest element compound ofOIML weight class E2 is Nickel (Ni) and close up thespecification of stainless type SUS 809L[4]. Unfortunately,we can not find this type stainless steel in commercialThailand. Next step, the type and price of stainless steel inlocal are pick up, shows in table 3.Table 3. The price each type of stainless steel in Baht*(φ2.5 cm. X 6 m.)Type 904L 310S 304 316L 303price 41,910 11,500 5,900 9,000 8,500(*about 31 Baht = 1USD)Therefore, the Fig.2 shows the austenitic stainless suchas 304 and 316L were chosen as the material of themanufactured weight.

The results measurement of comparing the volumemagnetic suscepability at maximum magnetic field is788.25 A.m -1 before and after process of cutting, turningwith lathe for both type stainless shows in table 4 below.Table 4. The results of volume magnetic suscepabilityat maximum magnetic field is 788.25 A.m -1Fig.2 shows the rod of austenitic stainless 304 and 316LThen, Cutting both rod and mark point of each pieceswith the control process with fix the feed at 224cycle/minute, compare with cooling water, as Fig.3 andexcept cooling water, as Fig.4Type316L304Process cuttingand turning withlatheCondition S/NCoolingwaterexceptCoolingwaterexceptVolume magnetic suscepabilityat Maximum magnetic field = 788.25 A.m -1BeforeprocessAfterprocess%DeviationA10 0.101 0.125 23.76 3.6A11 0.119 0.170 42.86 6.4A12 0.117 0.156 33.33 5.0A13 0.100 0.128 28.00 4.2A14 0.089 0.108 21.35 3.2% UncertaintyU c (k=2)A15 0.089 0.110 23.60 3.5B10 0.109 0.124 13.76 2.1B11 0.119 0.161 35.29 5.3B12 0.122 0.142 16.39 2.5B13 0.129 0.157 21.71 3.3B14 0.117 0.156 33.33 5.0B15 0.100 0.175 75.00 11.3Regarding to the tooling machine maintenance andresults from table4 , so our team decide to use cooling waterin fix the condition process shows as Fig.5.Fig.3 shows cutting process with cooling waterFig.4 shows cutting process without cooling waterThe magnetic properties results use the BIPMsusceptometer that was set up at NIMT mass laboratory formeasurement of Volume magnetic susceptibility on thesesample. Regarding to the theory, measurement procedureand uncertainty calculation from [1] and [5]. The masscomparator is Mettler Toledo UMT5 with a capacity 5.1 gand readability 0.1 µg. The rare-earth magnet is material ofNd Fe and B, diameter 4.8 mm, height 5.1 mm, magneticmoment 0.085 Am 2 and relative magnetic permeability is1.00506 at 99.97 kA/m of magnetic field strength.Fig.5 shows using cooling waterNext, <strong>study</strong>ing about heat treatment process attemperature 768, 850 and 1100 o C shows as Fig 6 and stop hotby dipping water shows as Fig 7. The results shows in table5.Then, the final adjust weight by polishing process is pick upto <strong>study</strong> for improvement the manufacturing process ofweight shows as Fig 8 and the results of volume magneticsuscepability in table 6.

Fig.6 shows heat treatment processFig.8 shows polishing processTable 6. The results of volume magnetic suscepabilitybefore and after final polishing processType316L304Volume magnetic suscepabilityat Maximum magnetic field = 788.25 A.m -1S/NBefore After % % Uncertaintyprocess process deviation U c (k=2)A10 0.125 0.106 -15.20 2.3A11 0.170 0.124 -27.06 4.1A12 0.156 0.113 -27.56 4.1B10 0.124 0.118 -4.84 0.7B11 0.161 0.128 -20.50 3.1B12 0.142 0.101 -28.87 4.3Type316L304Fig.7 shows dipping water to stop hotTable 5. The results of volume magnetic suscepabilitybefore and after the heat treatment processHeat treatmentprocessTemperature( o C)76885011007688501100Volume magnetic suscepability atMaximum magnetic field = 788.25 A.m -1S/N Before After %deviation% U c(k=2)A7 0.105 0.060 -42.86 6.4A8 0.083 0.043 -48.19 7.2A9 0.104 0.060 -42.31 6.3A1 0.100 0.044 -56.00 8.4A2 0.085 0.043 -49.41 7.4A3 0.104 0.040 -61.54 9.2A4 0.094 0.176 87.23 13.1A5 0.099 0.170 71.72 10.8A6 0.094 0.173 84.04 12.6B7 0.143 0.068 -52.45 7.9B8 0.101 0.058 -42.57 6.4B9 0.138 0.064 -53.62 8.0B1 0.100 0.047 -53.00 8.0B2 0.097 0.046 -52.58 7.9B3 0.106 0.046 -56.60 8.5B4 0.094 0.172 82.98 12.4B5 0.096 0.164 70.83 10.6B6 0.091 0.152 67.03 10.14. CONCLUSIONSThe process of manufacturing weight in Thailand mayinfluence the magnetic properties. In order to reduce themagnetic susceptibility of the weights to meet OIMLR111-1 technical requirement about magnetism.Preliminary results show that the magnetic properties arestainless steel type dependent. The results of comparisonbetween 304 and 316 austenitic stainless steels show thethe volume magnetic suscepability change during themanufacturing process such as cutting, turning with lathe,grinding and heat treatment process.REFERENCES[1] OIML R 111-1 : International RecommendationWeights of classes E1, E2, F1, F2, M1, M1-2, M2, M2-3 and M3 Part 1 ; Metrological and Technicalrequirements requirements , pp.33, 2004.[2] Jack Blitz, Electrical and Magnetic Methods ofNondestructive Testing, Adam Hilger, New York, pp35-37 1991.[3] Australian Stainless Steel Development AssociationACN 061 226 051 Website www.assda.asn.au[4] Report of support technology development projects ofthe Thai industry , NIMT, Office of National Scienceand Technology (ITAP) and Thai Scale companyLimited, 2009.[5] R. Davis and M. Glaser, “Magnetic properties ofweights, their measurements and magnetic interactionsbetween weights and balances”, Metrologia, vol. 40,nº. 3, pp. 339-355, December 2003.