畢業(yè)論文-山西下合煤業(yè)有限公司礦井采區(qū)設(shè)計(jì)

m3的移動(dòng)儲(chǔ)水箱中，注水泵從水箱中吸水加壓向煤層注水。二、預(yù)防井下火災(zāi)的措施①加強(qiáng)電氣設(shè)備管理，嚴(yán)禁明火作業(yè)，防止外源火災(zāi)發(fā)生。②井下設(shè)消防灑水系統(tǒng)。③及時(shí)清除易燃物品，嚴(yán)禁坑木等易燃物品雜亂無(wú)章堆放。④清掃浮煤，及時(shí)封閉采空區(qū)，廢棄巷道避免風(fēng)流通過(guò)。⑤井下人員按規(guī)定配備自救器。⑥井下設(shè)有消防材料庫(kù)，并有足夠的消防材料，消防材料庫(kù)設(shè)備明細(xì)見表。⑦井下使用阻燃膠帶、風(fēng)筒和不延燃電纜。⑧膠帶輸送機(jī)巷安設(shè)自動(dòng)報(bào)警滅火裝置。井下消防材料庫(kù)備用品表第六章工作面采煤、裝煤、運(yùn)煤方式及設(shè)備選型第一節(jié)采煤機(jī)的選型與計(jì)算1、按采煤機(jī)工作面生產(chǎn)能力計(jì)算公式如下：Q采=60MBV采γ式中：Q采——采煤機(jī)工作面實(shí)際生產(chǎn)能力，t/h；M——采高，15號(hào)煤平均厚度3.37m；B——截深，0.6m；V采——給定條件下采煤機(jī)牽引速度，1.89m/min；投產(chǎn)時(shí)工作面的循環(huán)進(jìn)度0.6m，日循環(huán)次數(shù)6次，日循環(huán)進(jìn)度為3.60m。每天三班生產(chǎn)一班檢修，每班2個(gè)循環(huán)。則最大班6小時(shí)循環(huán)2次，割2刀（工作面長(zhǎng)170m）。取50%的開機(jī)率，則工作面割煤速度為170m÷180min÷50%=1.89m/min。γ——煤的實(shí)體視密度，為1.41t/m3；Q=60×3.37×0.6×1.89×1.41=323.31t/h2、按單位能耗計(jì)算采煤機(jī)裝機(jī)功率為：N=60Kb·B·H·Vave·Hw式中：N——采煤機(jī)裝機(jī)功率，kW；Kb——備用系數(shù)，取1.2；B——采煤機(jī)截深，0.6m；H——采煤機(jī)割煤高度，取15號(hào)平均厚度3.37m；Hw——采煤機(jī)割煤?jiǎn)挝槐饶芎模磳?shí)測(cè)統(tǒng)計(jì)資料Hw=0.65-0.85kWh/m3，根據(jù)該礦煤層煤質(zhì)、裂隙發(fā)育等的特點(diǎn)，取Hw=0.85kWh/m3；Vave——采煤機(jī)平均割煤速度，15號(hào)煤1.89m/min；N=60Kb·B·H·Vave·Hw=60×1.2×0.6×3.37×1.89×0.85=249.8kW15號(hào)煤層平均厚度為3.37m，最大厚度為3.80m，煤層結(jié)構(gòu)較簡(jiǎn)單，故15號(hào)煤滾筒直徑取2000mm。根據(jù)以上計(jì)算結(jié)果并結(jié)合煤層厚度、結(jié)構(gòu)以及結(jié)合采煤機(jī)生產(chǎn)廠家的產(chǎn)品系列型號(hào)的特點(diǎn)，15號(hào)煤回采工作面選用MG200/490—W型采煤機(jī)。采煤機(jī)技術(shù)參數(shù)見表6—1—1。表6—1—1采煤機(jī)技術(shù)特征表型號(hào)采高(m)電機(jī)功率(kW)滾筒直徑(mm/個(gè))截深(mm)牽引速度(m/min)牽引方式重量(t)備注MG200/490—W2.0—3.84902000/26300～5.4電牽引24第二節(jié)工作面刮板輸送機(jī)的選型與計(jì)算工作面刮板輸送機(jī)選型需滿足三個(gè)方面要求：一是運(yùn)輸能力與采煤機(jī)生產(chǎn)能力相適應(yīng)；二是外型尺寸和牽引方式與采煤機(jī)相匹配；三是運(yùn)輸機(jī)長(zhǎng)度與工作面長(zhǎng)度相一致。根據(jù)環(huán)節(jié)能力配套并考慮1.20富裕系數(shù)，刮板輸送機(jī)的運(yùn)量應(yīng)達(dá)到323.31×1.2=387.97t/h；考慮上述因素，綜采工作面刮板輸送機(jī)選用SGB764/264型可彎曲刮板輸送機(jī)，刮板輸送機(jī)主要技術(shù)參數(shù)見表4—1—2。表6—2—1刮板輸送機(jī)技術(shù)特征表型號(hào)機(jī)長(zhǎng)(m)輸送能力(t/h)刮板鏈速(m/s)中部槽(mm)電機(jī)功率(kW)電壓等級(jí)(V)備注SGB764/2641706001.001500×764×2222×1321140第三節(jié)轉(zhuǎn)載機(jī)、順槽帶式輸送機(jī)順槽轉(zhuǎn)載機(jī)轉(zhuǎn)載能力要求與工作面的生產(chǎn)能力相適應(yīng)，并要求與工作面刮板輸送機(jī)和順槽可伸縮膠帶輸送機(jī)相配套，綜采工作面選用SZZ764/160型轉(zhuǎn)載機(jī)、DSJ100/45/2×132型膠帶輸送機(jī)。其主要技術(shù)參數(shù)見表6—3—1、6—3—2、6—3—3.表6—3—1橋式轉(zhuǎn)載機(jī)技術(shù)特征表型號(hào)機(jī)長(zhǎng)(m)輸送能力(t/h)刮板鏈速(m/s)電機(jī)功率(kW)電壓等級(jí)(V)備注SZZ764/160508001.28160660/1140表6—3—2破碎機(jī)技術(shù)特征表型號(hào)破碎能力（t/h）最大給料尺寸（mm）最大排料尺寸（mm）電機(jī)功率（kW）電壓等級(jí)（V）備注PCM110800700×700300551140表6—3—3順槽帶式輸送機(jī)技術(shù)特征表型號(hào)運(yùn)輸能力(t/h)運(yùn)距(m)速度(m/s)電機(jī)功率(kW)電壓等級(jí)(V)備注DSJ100/45/2×1324507642.52×132660/1140第四節(jié)乳化液泵站、噴霧泵站工作面液壓支架對(duì)乳化液泵站要求MRBZ200/31.5型乳化液泵站其主要技術(shù)參數(shù)見表6—4—1：表6—4—1乳化液泵站的技術(shù)特征表型號(hào)額定壓力（MPa）公稱流量（L/min）配套電機(jī)外型尺寸長(zhǎng)×寬×高（mm）重量（kg）液箱容積（L）功率（kW）曲軸轉(zhuǎn)速(r/min）MRBZ200/31.531.52001255632360×960×10303000150根據(jù)所選采煤機(jī)配套噴霧泵站要求選ZPB200／5.5型噴霧泵站，其主要技術(shù)參數(shù)見表6—4—2。表6—4—2噴霧泵站技術(shù)特征表型號(hào)工作壓力（MPa）公稱流量（L/min）電動(dòng)機(jī)備注功率（kw）電壓（v）轉(zhuǎn)速（r/mim）ZPB200／5.55.5200226601485第五節(jié)支護(hù)設(shè)備選型和計(jì)算工作面頂板管理方式為全部垮落法。（1）確定支架的工作阻力或支護(hù)強(qiáng)度時(shí)，一般考慮垮落帶巖層變形破壞時(shí)對(duì)支架的影響。（2）按實(shí)測(cè)的支架外載荷有關(guān)數(shù)據(jù)，利用回歸分析計(jì)算支架的支護(hù)強(qiáng)度時(shí)，先求出支護(hù)強(qiáng)度的折算系數(shù)n。來(lái)壓前：n1=7.46M—0.829（R=0.94，S=0.13）來(lái)壓時(shí)：n2=9.768M—0.769（R=0.98，S=0.06）（3）按上述頂板來(lái)壓時(shí)載荷折算系數(shù)回歸公式，得出計(jì)算，支架額定支護(hù)強(qiáng)度qH（kN/m2）的公式qH=9.768K.M0.21.γ=9.768×1.3×3.800.21×26=437.00（kN/m2）437.00÷0.75=582.67（kN/m2）P=LBqH=5.3×1.4×582.67=4323.41（kN）式中：K——備用系數(shù)，K=1.3。支架阻力的實(shí)際利用系數(shù)為75%；M——煤層厚度，m；15號(hào)煤最大厚度為3.80m。γ——頂板巖石容重，kN/m3。根據(jù)液壓支架工作阻力計(jì)算數(shù)據(jù)，結(jié)合煤層賦存情況及煤層厚度，及選用的采煤方法，工作面支護(hù)選用ZZ5200/19/42型液壓支架，支架支護(hù)高度1.9—4.2m，工作阻力為5200kN。工作面過(guò)渡支架選用ZZG5200/19/42型液壓支架，支架支護(hù)高度1.9—4.2m，工作阻力為5200kN。回采工作面端頭采用單體液壓支柱四對(duì)八梁支護(hù)，采用DZ31.5配HDL-3500型π型鋼梁支護(hù)。運(yùn)輸順槽超前支護(hù)采用DZ31.5配HDL—4500型π型鋼梁進(jìn)行支護(hù)；回風(fēng)順槽超前支護(hù)采用DZ31.5配HDL—3500型π型鋼梁進(jìn)行支護(hù)，超前支護(hù)距離暫按20m考慮。表6-5-1ZZ5200/19/42型液壓支架技術(shù)特征表型號(hào)支架寬度（mm）支架高度（mm）工作阻力(kN)支架中心距(mm)架型操作方式重量（t）ZZ5200/19/4213501900-420052001350掩護(hù)式鄰架18.6表6-5-2回采工作面采、裝、運(yùn)設(shè)備配備表設(shè)備名稱設(shè)備型號(hào)功率(kW)單位總數(shù)量其中備用雙滾筒采煤機(jī)MG200/490—W490臺(tái)1可彎曲刮板輸送機(jī)SGB764/2642×132臺(tái)1液壓支架ZZ5200/19/42架14725過(guò)渡液壓支架ZZG5200/19/42架51單體液壓支柱DZ31.5根16433π型鋼梁HDL-3500根427π型鋼梁HDL-4500根427刮板轉(zhuǎn)載機(jī)SZZ764/160160臺(tái)1破碎機(jī)PCM110110臺(tái)1可伸縮膠帶輸送機(jī)DSJ100/45/2×1322×132臺(tái)1乳化液泵站MRBZ200/31.5125臺(tái)1兩泵一箱噴霧泵站ZPB200／5.522臺(tái)1回柱絞車JH-811臺(tái)2探水鉆MAZ-20011臺(tái)1煤層注水泵7BZ-45/13022臺(tái)1雖然支架工作阻力核算，滿足設(shè)計(jì)要求。但實(shí)際生產(chǎn)中仍不可掉以輕心，礦方應(yīng)按照規(guī)程要求配備相應(yīng)的礦山壓力觀測(cè)設(shè)備，隨時(shí)監(jiān)控礦山壓力的變化情況，壓力大時(shí)配備足夠單體柱加強(qiáng)支護(hù)，確保安全的情況下，方可進(jìn)行生產(chǎn)。第六節(jié)采區(qū)電氣設(shè)備的選型一、采區(qū)高、低壓配電系統(tǒng)井下中央變電所分別向回采工作面移動(dòng)變電站、回采工作面運(yùn)輸順槽移動(dòng)變電站、回采工作面回風(fēng)順槽移動(dòng)變電站、順槽掘進(jìn)面移動(dòng)變電站、二采區(qū)軌道巷掘進(jìn)面移動(dòng)變電站提供1回10kV電源。回采工作面移動(dòng)變電站選用一臺(tái)KBSGZY-800/10，10/1.2kV，800kVA型礦用隔爆型移動(dòng)變電站為回采工作面采煤機(jī)及刮板輸送機(jī)供電，負(fù)荷率為79％。工作面運(yùn)輸順槽移動(dòng)變電站選用一臺(tái)KBSGZY-315/10，10/0.69kV，315kVA型礦用隔爆型移動(dòng)變電站為運(yùn)輸順槽的設(shè)備供電，負(fù)荷率為60％。工作面回風(fēng)順槽移動(dòng)變電站選用一臺(tái)KBSGZY-200/10，10/0.69kV，200kVA型礦用隔爆型移動(dòng)變電站為回風(fēng)順槽的設(shè)備供電，負(fù)荷率為84％?；仫L(fēng)順槽掘進(jìn)工作面移動(dòng)變電站選用一臺(tái)KBSGZY-400/10，10/0.69kV，400kVA型礦用隔爆型移動(dòng)變電站為膠帶順槽掘進(jìn)的設(shè)備供電，負(fù)荷率為81％。二采區(qū)軌道巷掘進(jìn)工作面移動(dòng)變電站選用一臺(tái)KBSGZY-400/10，10/0.69kV，400kVA型礦用隔爆型移動(dòng)變電站為軌道順槽掘進(jìn)的設(shè)備供電，負(fù)荷率為81％。在井下中央變電所設(shè)置2臺(tái)KBSG-100/1010/0.69kV100kVA型干式變壓器為2個(gè)掘進(jìn)工作面局部通風(fēng)機(jī)供電，負(fù)荷率55％，保障率100%。井下40kW及以上用電設(shè)備的控制開關(guān)選用QBZ礦用隔爆型真空起動(dòng)器；40kW以下設(shè)備選用QBD型礦用隔爆磁力起動(dòng)器；煤電鉆選用ZBM-4.0型礦用隔爆電鉆變壓器綜合保護(hù)裝置以127V供電。井下中央變電所的高壓饋電線上，裝設(shè)選擇性的單相接地保護(hù)裝置，供移動(dòng)變電站的高壓饋電線上，必須裝設(shè)有選擇性動(dòng)作于跳閘的單相接地保護(hù)裝置。井下低壓饋電線上裝設(shè)帶有漏電閉鎖裝置。井下供配電電壓為10kV、1140V、660V。煤電鉆及照明燈具電壓127V，由電鉆或照明變壓器綜合裝置供給。二、井下電纜、照明選型井下10kV供電電纜選用MYPTJ—6/10型礦用金屬屏蔽橡套軟電纜；井下供電電纜選用MYP—0.66/1.14型礦用橡套軟電纜；采煤機(jī)采用專用電纜；煤電鉆選用MZ—0.3/0.5型礦用電鉆軟電纜；井下照明選用MYQ—0.3/0.5型礦用輕型橡套軟電纜。膠帶大巷、軌道大巷、工作面膠帶順槽及主要機(jī)電硐室設(shè)固定照明。固定照明電壓127V，選用DGS—13/127礦用隔爆型節(jié)能燈具。燈具電源由BZX—4.0660/127V照明變壓器綜合裝置供電。照明干線選用MYQ—0.3/0.53×4礦用輕型橡套軟電纜。三、井下接地井下主、副水倉(cāng)中各埋設(shè)一塊2000mm×400mm×5mm鋼板作為井下主接地極，各配電點(diǎn)處設(shè)局部接地極，通過(guò)電纜的接地芯線及鎧裝電纜金屬外皮相互連接，構(gòu)成井下總接地網(wǎng)，網(wǎng)上任一保護(hù)接地點(diǎn)測(cè)得的接地電阻值不超過(guò)2Ω。每一個(gè)移動(dòng)式和手持式電氣設(shè)備至局部接地極之間的保護(hù)接地連接導(dǎo)線的電阻值不超過(guò)1Ω。為防止雷電侵入井下，引入井下的金屬部件均在井口處設(shè)可靠接地，且接地點(diǎn)不得少于兩處。第七章主要技術(shù)經(jīng)濟(jì)指標(biāo)礦井設(shè)計(jì)主要技術(shù)經(jīng)濟(jì)指標(biāo)順序指標(biāo)名稱單位指標(biāo)備注（1）（2）（3）（4）（5）井田范圍（1）東西長(zhǎng)（2）南北長(zhǎng)（3）井田面積kmkmkm3.1652.623.452.4煤層可采煤層數(shù)可采煤層總厚度首采煤層厚度m煤層傾角層mm°1層；15號(hào)煤3.373.3763.4資源/儲(chǔ)量保有地質(zhì)資源/儲(chǔ)量工業(yè)資源/儲(chǔ)量設(shè)計(jì)資源儲(chǔ)量設(shè)計(jì)可采儲(chǔ)量ktktktkt112401117398966981.644.1煤類15號(hào)煤PM5.4煤質(zhì)灰份（原煤/浮煤）硫份（原煤/浮煤）揮發(fā)份（原煤/浮煤）原煤發(fā)熱量％％％MJ/kg24.29%2.39%17.64%25.43礦井設(shè)計(jì)主要技術(shù)經(jīng)濟(jì)指標(biāo)順序指標(biāo)名稱單位指標(biāo)備注（1）（2）（3）（4）（5）66.16.2礦井設(shè)計(jì)生產(chǎn)能力年生產(chǎn)能力日生產(chǎn)能力kt/at/a900272777.1礦井服務(wù)年限設(shè)計(jì)生產(chǎn)年限a5.588.18.2礦井設(shè)計(jì)工作制度年工作制度日工作班數(shù)天班330“四六”制作業(yè)9.49.5井田開拓開拓方式水平數(shù)目水平標(biāo)高大巷主運(yùn)輸方式大巷輔助運(yùn)輸方式個(gè)m斜—立井混合開拓1+789膠帶調(diào)度絞車1010.4.210.4.3采區(qū)回采工作面?zhèn)€數(shù)掘進(jìn)工作面?zhèn)€數(shù)采煤方法主要采煤設(shè)備采煤機(jī)支架輸送機(jī)個(gè)個(gè)12綜采一次采全高M(jìn)G200/490-WZZ5200/19/42SGB764/2641111.1礦井主要設(shè)備主井提升設(shè)備DTL100/20/2×132輸送機(jī)礦井設(shè)計(jì)主要技術(shù)經(jīng)濟(jì)指標(biāo)順序指標(biāo)名稱單位指標(biāo)備注（1）（2）（3）（4）（5）11.211.311.411.5輔助提升設(shè)備主通風(fēng)設(shè)備主排水設(shè)備壓風(fēng)設(shè)備JK-2/31.5型提升機(jī)FBCDZ-8-№22BMD155-30LG132-8

請(qǐng)刪除以下內(nèi)容，O(∩_∩)O謝謝?。。heoriginoftaxationintheUnitedStatescanbetracedtothetimewhenthecolonistswereheavilytaxedbyGreatBritainoneverythingfromteatolegalandbusinessdocumentsthatwererequiredbytheStampTax.Thecolonists'disdainforthistaxationwithoutrepresentation(so-calledbecausethecolonieshadnovoiceintheestablishmentofthetaxes)gaverisetorevoltssuchastheBostonTeaParty.However,evenaftertheRevolutionaryWarandtheadoptionoftheU.S.Constitution,themainsourceofrevenueforthenewlycreatedstateswasmoneyreceivedfromcustomsandexcisetaxesonitemssuchascarriages,sugar,whiskey,andsnuff.IncometaxfirstappearedintheUnitedStatesin1862,duringtheCivilWar.Atthattimeonlyaboutonepercentofthepopulationwasrequiredtopaythetax.Aflat-rateincometaxwasimposedin1867.Theincometaxwasrepealedinitsentiretyin1872.IncometaxwasarallyingpointforthePopulistpartyin1892,andhadenoughsupporttwoyearslaterthatCongresspassedtheIncomeTaxActof1894.Thetaxatthattimewastwopercentonindividualincomesinexcessof$4,000,whichmeantthatitreachedonlythewealthiestmembersofthepopulation.TheSupremeCourtstruckdownthetax,holdingthatitviolatedtheconstitutionalrequirementthatdirecttaxesbeapportionedamongthestatesbypopulation(pollockv.farmers'loan&trust,158U.S.601,15S.Ct.912,39L.Ed.1108[1895]).Aftermanyyearsofdebateandcompromise,thesixteenthamendmenttotheConstitutionwasratifiedin1913,providingCongresswiththepowertolayandcollecttaxesonincomewithoutapportionmentamongthestates.Theobjectivesoftheincometaxweretheequitabledistributionofthetaxburdenandtheraisingofrevenue.Since1913theU.S.incometaxsystemhasbecomeverycomplex.In1913theincometaxlawswerecontainedineighteenpagesoflegislation;theexplanationofthetaxreformactof1986wasmorethanthirteenhundredpageslong(Pub.L.99-514,Oct.22,1986,100Stat.2085).CommerceClearingHouse,apublisheroftaxinformation,releasedaversionoftheInternalRevenueCodeintheearly1990sthatwasfourtimesthickerthanitsversionin1953.Changestothetaxlawsoftenreflectthetimes.Theflattaxof1913waslaterreplacedwithagraduatedtax.AftertheUnitedStatesenteredworldwari,theWarRevenueActof1917imposedamaximumtaxrateforindividualsof67percent,comparedwitharateof13percentin1916.In1924SecretaryoftheTreasuryAndrewW.Mellon,speakingtoCongressaboutthehighleveloftaxation,stated,Thepresentsystemisafailure.Itwasanemergencymeasure,adoptedunderthepressureofwarnecessityandnottobecounteduponasapermanentpartofourrevenuestructure….Thehighratesputpressureontaxpayerstoreducetheirtaxableincome,tendtodestroyindividualinitiativeandenterprise,andseriouslyimpedethedevelopmentofproductivebusiness….Wayswillalwaysbefoundtoavoidtaxessodestructiveintheirnature,andtheonlywaytosavethesituationistoputthetaxesonareasonablebasisthatwillpermitbusinesstogoonandindustrytodevelop.Consequently,theRevenueActof1924reducedthemaximumindividualtaxrateto43percent(RevenueActs,June2,1924,ch.234,43Stat.253).In1926theratewasfurtherreducedto25percent.TheRevenueActof1932wasthefirsttaxlawpassedduringtheGreatDepression(RevenueActs,June6,1932,ch.209,47Stat.169).Itincreasedtheindividualmaximumratefrom25to63percent,andreducedpersonalexemptionsfrom$1,500to$1,000forsinglepersons,andfrom$3,500to$2,500formarriedcouples.Thenationalindustrialrecoveryactof1933(NIRA),partofPresidentfranklind.roosevelt'snewdeal,imposedafivepercentexcisetaxondividendreceipts,imposedacapitalstocktaxandanexcessprofitstax,andsuspendedalldeductionsforlosses(June16,1933,ch.90,48Stat.195).Therepealin1933oftheeighteenthamendment,whichhadprohibitedthemanufactureandsaleofalcohol,broughtinanestimated$90millioninnewliquortaxesin1934.Thesocialsecurityactof1935providedforawagetax,halftobepaidbytheemployeeandhalfbytheemployer,toestablishafederalretirementfund(OldAgePensionAct,Aug.14,1935,ch.531,49Stat.620).TheWealthTaxAct,alsoknownastheRevenueActof1935,increasedthemaximumtaxrateto79percent,theRevenueActsof1940and1941increaseditto81percent,theRevenueActof1942raiseditto88percent,andtheIndividualIncomeTaxActof1944raisedtheindividualmaximumrateto94percent.Thepost-WorldWarIIRevenueActof1945reducedtheindividualmaximumtaxfrom94percentto91percent.TheRevenueActof1950,duringthekoreanwar,reduceditto84.4percent,butitwasraisedthenextyearto92percent(RevenueActof1950,Sept.23,1950,ch.994,Stat.906).Itremainedatthisleveluntil1964,whenitwasreducedto70percent.TheRevenueActof1954revisedtheInternalRevenueCodeof1939,makingmajorchangesthatwerebeneficialtothetaxpayer,includingprovidingforchildcaredeductions(laterchangedtocredits),anincreaseinthecharitablecontributionlimit,ataxcreditagainsttaxableretirementincome,employeedeductionsforbusinessexpenses,andliberalizeddepreciationdeductions.From1954to1962,theInternalRevenueCodewasamendedby183separateacts.In1974theemployeeretirementincomesecurityact(ERISA)createdprotectionsforemployeeswhoseemployerspromisedspecifiedpensionsorotherretirementcontributions(Pub.L.No.93-406,Sept.2,1974,88Stat.829).ERISArequiredthattobetaxdeductible,theemployer'splancontributionmustmeetcertainminimumstandardsastoemployeeparticipationandvestingandemployerfunding.ERISAalsoapprovedtheuseofindividualretirementaccounts(IRAs)toencouragetax-deferredretirementsavingsbyindividuals.TheEconomicRecoveryTaxActof1981(ERTA)providedthelargesttaxcutuptothattime,reducingthemaximumindividualratefrom70percentto50percent(Pub.L.No.97-34,Aug.13,1981,95Stat.172).ThemostsweepingtaxchangessinceworldwariiwereenactedintheTaxReformActof1986.ThisbillwassignedintolawbyPresidentronaldreaganandwasdesignedtoequalizethetaxtreatmentofvariousassets,eliminatetaxshelters,andlowermarginalrates.Conservativeswantedtheacttoprovideasingle,lowtaxratethatcouldbeappliedtoeveryone.Althoughthissingle,flatratewasnotincludedinthefinalbill,taxrateswerereducedto15percentonthefirst$17,850ofincomeforsinglesand$29,750formarriedcouples,andsetat28to33percentonremainingincome.Manydeductionswererepealed,suchasadeductionavailabletotwo-incomemarriedcouplesthathadbeenusedtoavoidthe"marriagepenalty"(agreatertaxliabilityincurredwhentwopersonsfiledtheirincometaxreturnasamarriedcoupleratherthanasindividuals).Althoughthepersonalexemptionexclusionwasincreased,anexemptionforelderlyandblindpersonswhoitemizedeductionswasrepealed.Inaddition,aspecialcapitalgainsratewasrepealed,aswasaninvestmenttaxcreditthathadbeenintroducedin1962byPresidentjohnf.kennedy.TheOmnibusBudgetReconciliationActof1993,thefirstbudgetandtaxactenactedduringtheClintonadministration,wasvigorouslydebated,andpassedwithonlytheminimumnumberofnecessaryvotes.Thislawprovidedforincometaxratesof15,28,31,36,and39.6percentonvaryinglevelsofincomeandforthetaxationofsocialsecurityincomeifthetaxpayerreceivesotherincomeoveracertainlevel.In2001CongressenactedamajorincometaxcutattheurgingofPresidentgeorgew.bush.Overthecourseof11yearsthelawreducesmarginalincometaxratesacrossalllevelsofincome.The36percentratewillbeloweredto33percent,the31percentrateto28percent,the28percentrateto25percent.Inaddition,anewbottom10percentratewascreated.Sincetheearly1980s,aflat-ratetaxsystemratherthanthegraduatedbracketedmethodhasbeenproposed.(Thegraduatedbracketedmethodistheonethathasbeenusedsincegraduatedtaxeswereintroduced:thepercentageoftaxdiffersbasedontheamountoftaxableincome.)Theflat-ratesystemwouldimposeonerate,suchas20percent,onallincomeandwouldeliminatespecialdeductions,credits,andexclusions.Despitefirmsupportbysome,theflat-ratetaxhasnotbeenadoptedintheUnitedStates.Regardlessofthechangesmadebylegislatorssince1913,thebasicformulaforcomputingtheamountoftaxowedhasremainedbasicallythesame.Todeterminetheamountofincometaxowed,certaindeductionsaretakenfromanindividual'sgrossincometoarriveatanadjustedgross