畢業(yè)論文-45噸移動破碎站液壓傳動開式油箱設計說明書.docx

四川理工學院課程設計（論文）四川理工學院課程設計45噸移動破碎站液壓傳動開式油箱設計學 生： 學 號：專 業(yè)：材料成型及控制班 級：指導教師： 四川理工學院機械工程學院二O一二年十二月四川理工學院課程設計（論文）摘要使用開式油箱的設計的一般方法，依靠派克油箱附件，并結和設計要求。通過油箱容積的計算，油箱結構設計，以及各相關配件的選用完成廠方需要。關鍵詞：液壓系統(tǒng)；開式油箱；設計；派克附件；ABSTRACTThe general method of using the design of the open tank, relying the Parker tank attachment, and the junction and design requirements. Through the calculation of the fuel tank capacity fuel tank structure design, as well as a selection of accessories to complete the factory needs.Keywords: Hydraulic system;open the fuel tank; design; Parker Annex目錄緒論1第一章 開式油箱的結構特點2第二章 開式油箱容積的確定3第三章 油箱結構的設計43.1油箱結構設計要點及需要注意的事項43.2油箱結構的詳細設計53.2.1油箱長、寬、高的確定53.2.2.壁板厚度的確定53.2.3.油箱腳的設計53.2.4油箱頂蓋設計63.2.5吊耳設計63.2.6隔板設計63.2.7油箱底板設計63.2.8油箱清洗孔設計63.2.9箱體法蘭設計63.2.10后處理7第四章 油箱配件的計算與選用84.1濾油器84.1.1濾油器的作用84.1.2濾油器的性能指標84.1.3濾油器的計算及選擇84.2.1吸油過濾器94.2.2過濾器流量的選擇104.2.3過濾器的壓力104.2.4.過濾器的定型104.2液位/溫度計144.3浮子開關154.4加熱器的選擇174.4.1油的加熱及加熱器的發(fā)熱能力174.4.2電加熱器的計算17參 考 文 獻19致 謝20附錄A：液壓油箱配件明細表21緒論45噸移動破碎站是一種多地域、多適用性的機械，主要功能是在移動中實現(xiàn)破碎功能，節(jié)約勞動成本，提高勞動效率。該機械的液壓油缸設計，主要參數為每分鐘額定液壓油流量為500L/min，油箱設計為長方體型，長度方向不超過2.2m，寬度方向不超過1.0m，高度方向不超過1.2m，油液工作環(huán)境為低壓系統(tǒng)。采用較為成熟的液壓油箱設計理念，以保證設計能夠達到實際生產需要，。由于本次設計時間較為緊迫，設計中仍有部分較為不完善之處，待實際安裝、選配是修改。望老師指正。23第一章 開式油箱的結構特點油箱在液壓系統(tǒng)中除了儲油外，還起著散熱、分離油液中的氣泡、沉淀雜質等作用。油箱中安裝有很多輔件，如冷卻器、加熱器、空氣過濾器及液位計等。根據油箱內液面是否與外液面相通，可將液壓油箱分為開式和閉式兩種油箱。開式油箱的結構特點是有箱體為封閉式容積，箱內液面與大氣相通，為防止油液被大氣污染，在油箱頂部設置空氣濾清器并兼做注油口。閉式油箱一般用于壓力油箱，內充一定壓力的惰性氣體，充氣壓力可達0.05MPa。如果按油箱的形狀來分，還可分為矩形油箱和圓罐形油箱。矩形油箱制造容易，箱上易于安放液壓器件，所以被廣泛采用；圓罐形油箱強度高，重量輕，易于清掃，但制造較難，占地空間較大，在大型冶金設備中經常采用。第二章 開式油箱容積的確定油箱容積的經驗公式為 V=aQV式中QV液壓泵每分鐘排出油的體積，m3/min a經驗系數，見表1系統(tǒng)類型行走機械低壓系統(tǒng)高壓系統(tǒng)鍛壓系統(tǒng)治煉機械a12245761210根據設計要求，本次設計為行走機械故a取2，液壓泵每分鐘排出油的體積為0.5m3/min，故：V=aQV=3x0.5=1m3四川理工學院課程設計（論文）第三章 油箱結構的設計液壓油箱主要包括液面指示器、空氣濾清器、上蓋、隔板、放油塞。要求比較高的油箱還要求有加熱器、冷卻器和油溫測量裝置等。圖1 油箱結構示意圖1.油面指示器 2.空氣濾清器 3.上蓋 4.隔板 5.放油塞3.1油箱結構設計要點及需要注意的事項（1）. 油箱一般為長六面體，其長、寬、高可依主機總體布置決定，約在1:1:11:2:3之間，中、小型油箱用鋼板焊接而成，大型油箱需用角鋼為骨架，然后再焊上鋼板而成。（2）. 壁板的厚度應考慮油箱容積的大小，在條件允許的條件下，應盡量選薄些，以減輕油箱容量的重量；當油箱容量為100L以內時，其壁厚應為3mm；容量為100320L時，其壁厚為34mm；容量大于320L時，壁厚可達46mm。（3）. 油箱底腳高度一般在150mm以上，以便散熱、搬移和放油，其壁厚應為箱體壁厚的23倍。（4）. 若液壓泵及電機需要安裝在油箱頂蓋上時，為避免振動，油箱頂蓋板的厚度應為側板厚度的3倍左右。郵箱頂蓋板必須用螺釘與箱體內所焊的角鋼固定連接。頂蓋可以是整體的，也可以分為幾塊，分別安裝閥板和電機、液壓泵等。（5）. 體積大的油箱適當部位應安設吊耳，以便起吊裝運。（6）. 油箱內常設23快隔板，將會由去與吸油區(qū)分開，這樣有利于散熱、雜質的沉淀及氣體的排出。隔板高度為油液面的2/33/4。（7）. 油箱頂蓋板頂蓋板上應設通氣孔，使液面與大氣相通。通氣孔處應設空氣濾清器，它既能過濾空氣，又可利用其下面的濾網作加油時的過濾裝置。（8）. 油箱底板應適當傾斜，并在最低位置處放置放油塞或放油閥。在相壁易見位置設置液面指示器。在油箱側壁應開設用于安裝、清洗、維護的窗口，平時可用密封墊及蓋板封死，需要時打開。（9）. 泵吸油管口所裝濾油器底面與油箱底面應保持一定距離，其側面離箱壁的距離應大于3倍管徑，濾油器底面距離油箱底板應大于2倍管徑，距離最低液面應大于70mm，以使油液能從濾油器的四周、上下面進入濾油器?；赜凸芸谒b的濾油器底面距離最低液面應大于200mm，距離油箱底板距離應大于23倍管徑，其側面離箱壁的距離也應大于3倍管徑，避免飛濺起泡?；赜凸芸趹谐?50斜口，以增大出油口面積，其斜口應面向箱壁以利于散熱、減緩流速和沉淀雜質。閥的泄漏油管應在油的液面以上，不宜插入油液中，以免增加漏油腔的背壓。各進、回油管口通過頂蓋的孔，均須裝密封圈，以防止油液污染。（10）. 油箱的內壁必須進行加工處理。新油箱必須經噴丸、酸洗和表面清洗，其內壁可涂一層與油液相容的塑料薄膜或耐油涂料。3.2油箱結構的詳細設計3.2.1油箱長、寬、高的確定根據3.1.1的要求及1000L的油箱容量，當油箱液面達到油箱高度的83%時設定油箱長x寬x高為2000x500x1200。3.2.2.壁板厚度的確定因為本次設計油箱容量為1000L大于320L，所以壁板厚度選為6mm。3.2.3.油箱腳的設計此次油箱設計由于安裝高度的限制及安裝方式的限制，油箱腳不需直接承受油箱重量，只起固定作用，故確定選用14號槽鋼，所以腳高為140mm，厚度為6mm。不需要3.2.4油箱頂蓋設計結合油箱配件的選用，為頂置式，故頂該該厚度適當選大一些為20mm，大于設計標準壁板厚度的三倍。為方便安裝及其整體性能，頂蓋為整體式。3.2.5吊耳設計在四個對角部分分別設置1個安裝、轉運用吊耳。由于油箱整體質量較輕約為0.4噸左右。故選用M36的吊環(huán)螺釘。3.2.6隔板設計由于油箱長度為2000mm并參照設計標準，在油箱長度方向設置兩塊隔板，厚度與壁板厚度相同為6mm，高度為700mm3.2.7油箱底板設計為了能在最低液面放置放油塞，且便于清洗油箱和散熱，故將油箱底板設置為斜面。又因為油箱安裝位置及油箱總體結構的限定，故使油箱底板向中間傾斜，斜度為1:5。為了防止油箱底板承受壓力變形故在其下面增加一#的加強筋。3.2.8油箱清洗孔設計此次設計隔板為長度方向設計，故油箱的清洗不是很容易，但是由于油箱安防空間的限制，及后面配件安放位置的限制。綜合考慮各種因素，還是在兩塊隔板中間的壁板中心位置上開設清洗孔，并焊接法蘭，加密封墊圈，用螺栓將清洗蓋板連接上，封死清洗孔防止漏油。3.2.9箱體法蘭設計此次箱體為焊接而成，蓋板的固定及箱體的密封，需用螺栓連接，故需要設置蓋板連接法蘭。由于不沒有承受背壓故厚度選為與壁板厚度相同6mm。3.2.10后處理 油箱用噴丸、酸洗和表面清洗，其內壁可涂一層與油液相容的塑料薄膜或耐油涂料。第四章 油箱配件的計算與選用一般根據液壓系統(tǒng)的的具體要求配置油箱附件。合理選用附件，可使油箱充分發(fā)揮作用。油箱附件包括吸油過濾器、回油過濾器、注油器/空氣濾清器、液壓位/計、浮子開關、加熱器。4.1濾油器4.1.1濾油器的作用在液壓系統(tǒng)中，為了保證油液的干凈清潔，必須安裝濾油器以濾去油液中的雜質。油液中的雜質是有外界的灰塵、臟物、裝置時原件及油管中的殘留物和油液由于氧化變質析出物等混入油液中而產生的。這些雜質會引起相對運動零件的的表面劃傷、磨損以致卡死，堵塞管道小孔以及節(jié)流閥口，并影響機床的工作性能，導致系統(tǒng)不能正常工作。同時隨著液壓元件精度的提高，對油液清潔度的要求也越來越高。因此必須對液壓油中的雜質和污染物的顆粒進行清理，目前，控制液壓油潔凈程度的最有效的方法就是才有濾油器。濾油器的主要功用就是對液壓油進行過濾，控制油的潔凈程度。4.1.2濾油器的性能指標濾油器的主要主要性能參數主要是過濾精度、通流能力、工作壓力、壓力損失。濾油器的設計主要是根據工作壓力和過濾精度的要求選擇濾芯材料和流量要求來計算過濾面積。4.1.3濾油器的計算及選擇選擇過濾器應考慮如下幾個方面：（1）. 根據使用目的選擇過濾器的種類，根據安裝位置情況選擇過濾器的安裝形式。（2）. 過濾器應具有足夠的通油能力，并且壓力損失要小。（3）. 過濾精度應滿足液壓系統(tǒng)或元件所需清潔度要求。（4）. 濾芯使用的濾材應滿足所使用工作介質的要求，并且有足夠的強度。（5）. 過濾器的強度及壓力損失時選擇時的重點考慮因素，安裝過濾器后會對系統(tǒng)造成局部壓降或長生背壓。（6）. 濾芯的更換及清洗方便。（7）. 應根據系統(tǒng)需要考慮選擇合適的濾芯保護附件（如帶旁通閥的定壓開啟裝置及濾芯污染情況指示器的或信號器等）。（8）. 結構盡量簡單合理、緊湊、安裝形式合理。（9）. 價格低廉。選用過濾器的通油能力時，一般應大于實際通過流量的2倍以下，過濾器的通油能力可按下式計算。qv=KApx10-6式中 qv過濾器通油能力，m3/s；液壓油的動力粘度，Pas；A有效過濾面積，cm3；p壓力差，Pa；K濾芯通油能力系數，網式濾芯K=0.34；線隙式濾芯K=0.17；紙濾芯K=0.006；燒結式濾芯K=1.04D2x10-3，式中D為粒子的平均直徑，單位為m，為濾芯的壁厚，單位為m。4.2.1吸油過濾器1.過濾器精度的選擇吸油過濾器主要是對泵起保護作用，由表4-1可知其過濾器為粗過濾器過濾精度為100m?；赜瓦^濾器精度主要按照液壓元件對油液潔凈度來選擇，由表4-1可知其過濾器為普通過濾器過濾精度為10100m。注油器/空氣過濾器防止油液被空氣污染且防止注油時污染物進入郵箱，注油/空氣過濾器的精度應不低于40m，由由表4-1可知其過濾器為粗過濾器過濾精度為100m。名稱用途精度類別濾材形式效果油過濾器保護液壓泵粗過濾器網式、線隙式濾芯粗過濾器：能濾掉100m以上的顆?；赜瓦^濾器降低油液污染程度普通過濾器紙質、纖維濾芯空氣過濾器防止污物隨空氣侵入普通過濾器多沉疊加式濾芯普通過濾器：能濾掉10-100m的顆粒注油過濾器防止注油時侵入污染物粗過濾器網式濾芯表4-1 過濾器的名稱、用途、類別、形式以及效果4.2.2過濾器流量的選擇吸油過濾器的流量不應大于實際通過流量的2倍，所以取1.5倍為650L/min；回油過濾器的流量須與最大回油量相同，故應為500L/min；注油口的流量應大于20/min其容量應是泵容量的2倍。4.2.3過濾器的壓力本次設計為低壓設計，故不需特別考慮壓力類型。4.2.4.過濾器的定型圖4-1 低壓過濾器型號1).吸油過濾器型號由圖4-1選擇吸油過濾器ATZ系列（如圖4-2），ATZ系列技術參數如圖4-3，液壓系統(tǒng)為兩個主泵一個輔泵， 主泵吸油口為ATZ-300過濾器（流量為300L/min），查圖4-4選擇標準產品為ATZ210QBPXR481；輔泵由于流量較小故選用一個ATZ-120過濾器（流量為120L/min），查圖4-5選擇標準產品為ATZ110QBPXG241。這里我們特別要求選用過濾材質為40m金屬不銹鋼，增加過濾器的通透能力，也可以更換降低過濾精度，達到設計要求的100m。圖4-2 ATZ-300、ATZ-120安裝尺寸圖4-3ATZ系列性能圖4-4 標準產品表2).回油過濾器型號由圖4-1選擇回油過濾器TP、&系列，TP、&系列技術參數如圖4-5，液壓系統(tǒng)為一個主回油管，一個輔回油管，主回油管選用TP過濾器（如圖46），查圖4-7選擇標準產品為TPR650-2G11/2PXWL8-20B15MM（流量為650L/min）;輔回油管同樣選用TP過濾器（如圖4-6），查圖4-7選擇標準產品為TPR120-2G11/4PXWL3-20B15MM（流量為120L/min）。圖4-5TP、&系列技術參數4-6 安裝尺寸圖4-7 標準產品表3).注油/呼吸器型號圖4-7 呼吸器、加油器列表本次設計采用注油器與加油器為一個配件，由圖4-7選用IP65等級加油/呼吸器（如圖4-9圖1），其具體性能參數如圖4-8，查圖4-9選擇標準產品為AB98810011。圖4-8 單孔或六孔安裝技術參數 圖4-9 IP65加油呼吸器6孔安裝帶伸縮濾網安裝圖1和標準產品表圖24.2液位/溫度計計算可知最低液面離最高液面的距離為500mm，故需要選用中心距位500mm的液位/溫度計，由圖4-10選擇液位/液溫計（如圖4-12），其性能參數如圖4-11，可知其中心距位255mm，所以需要選用兩個同等型號的液位/溫度計組合使用，查圖4-13選擇液位/溫度計規(guī)格為FL69321。圖4-11 液位液溫計圖4-10 流體液位指示器圖4-12 液位/液溫計安裝尺寸圖4-13 標準產品表4.3浮子開關在注油的時候，油液超過油箱的最高液面高度，易增加油箱的背壓，損壞液壓元件和油箱。增設浮子開關在得到信號后，開關打開使多余的液壓油從油箱中排除，起到保護油箱的作用。由圖4-10選擇FL系列可調浮控開關（如圖4-15），其性能參數如圖4-14，查圖4-16選擇標準產品為FL050010R。4-14 典型技術參數圖4-15 FL系列可調浮控開關安裝尺寸圖4-16 FL系列可調浮控開關標準產品表4.4加熱器的選擇4.4.1油的加熱及加熱器的發(fā)熱能力液壓系統(tǒng)中的油溫，一般應控制在3050范圍內。最高不應高于70，最低不應低于15。油溫過高，將使油液迅速老化變質，同時使油液的粘度降低，造成元件內泄漏量的增加，系統(tǒng)的效率降低；油溫谷底，使油液的粘度過大，造成泵的吸油困難。油溫的過高、過低都會引發(fā)系統(tǒng)工作不正常，為了保證油液能在正常的范圍內工作，需對系統(tǒng)油液溫度進行必要的控制，既采用加熱或冷卻方式。油液的加熱可以采用電加熱或蒸汽加熱等方式，為了避免油液過熱變質，一般加熱管表面溫度不允許超過120，電加熱管表面功率密度不應超過3W/cm2。加熱器的發(fā)熱能力俺下式估算：NCrVQT式中 N加熱器發(fā)熱能力，W; C油的比熱，去C=16802094J/(kg)；r油的密度，取r=900kg/m；V油箱內油液體積，m；Q油加熱后溫升，；T加熱時間，s。4.4.2電加熱器的計算電加熱器的功率：P=N/式中，為熱效率，取=0.60.8。液壓系統(tǒng)中裝設電加熱器后，可以較方便地實現(xiàn)液壓系統(tǒng)油溫的自動控制。計算如4-2表擬在30min內加熱40，由表4-3選取6個GYY2-220/8型加熱器(功率為8KW)。表4-2 不同加熱時間和不同加熱溫度所需加熱器功率油 功率（kw）液升高溫度，升溫時間，min1020304050601027.613.89.26.9kw5.52kw4.62055.227.618.413.811.49.23082.841.427.620.716.5613.840110.455.236.827.622.0818.4表4-3 GYY型電加熱器的型號和技術參數型號功率/KWA/mm侵入油中長度/mm電壓/VGYY2-220/11307230220GYY2-220/22507430GYY2-220/33707630GYY2-220/44922845GYY2-220/55697620GYY2-220/66807730GYY2-220/881007930注：生產廠為上海電熱電器廠、沈陽電熱元件廠參 考 文 獻1 王守城，段俊勇.液壓元件及選用M.北京：化學工業(yè)出版社，2007.42 韓桂華.液壓系統(tǒng)設計技巧與禁忌M.北京：化學工業(yè)出版社，2011.33 張利平.液壓傳動設計指南M.北京：化學工業(yè)出版社，2009.94 建公.液壓與氣壓傳動M.成都：西南交通大學出版社，2011.8致 謝感謝這些天來胡老師給予的無微不至指導和關心，才能順利完成這次課程設計。附錄A：液壓油箱配件明細表名稱公司型號、規(guī)格、數量主要性能指標吸油過濾器派克ATZ系列ATZ210QBPXR4812300L/min10mATZ110QBPXG2411120 L/min10m回油過濾器TP、&系列TPR650-2D11/2PXWL8-20B15MM1650L/min10mTPR120-2G11/4PWL3-20B15MM1120L/min10m注油/呼吸器AB988100111L/minm液位/溫度計FL693211中心距254mm浮子開關FL系列可調浮控開端FL050010R1加熱器上海電氣廠、沈陽電熱元件廠GYYZ-220/86功率8kw電壓220V請刪除以下內容，O(_)O謝謝！The origin of taxation in the United States can be traced to the time when the colonists were heavily taxed by Great Britain on everything from tea to legal and business documents that were required by the Stamp Tax. The colonists disdain for this taxation without representation (so-called because the colonies had no voice in the establishment of the taxes) gave rise to revolts such as the Boston Tea Party. However, even after the Revolutionary War and the adoption of the U.S. Constitution, the main source of revenue for the newly created states was money received from customs and excise taxes on items such as carriages, sugar, whiskey, and snuff. Income tax first appeared in the United States in 1862, during the Civil War. At that time only about one percent of the population was required to pay the tax. A flat-rate income tax was imposed in 1867. The income tax was repealed in its entirety in 1872. Income tax was a rallying point for the Populist party in 1892, and had enough support two years later that Congress passed the Income Tax Act of 1894. The tax at that time was two percent on individual incomes in excess of $4,000, which meant that it reached only the wealthiest members of the population. The Supreme Court struck down the tax, holding that it violated the constitutional requirement that direct taxes be apportioned among the states by population (pollock v. farmers loan & trust, 158 U.S. 601, 15 S. Ct. 912, 39 L. Ed. 1108 1895). After many years of debate and compromise, the sixteenth amendment to the Constitution was ratified in 1913, providing Congress with the power to lay and collect taxes on income without apportionment among the states. The objectives of the income tax were the equitable distribution of the tax burden and the raising of revenue. Since 1913 the U.S. income tax system has become very complex. In 1913 the income tax laws were contained in eighteen pages of legislation; the explanation of the tax reform act of 1986 was more than thirteen hundred pages long (Pub. L. 99-514, Oct. 22, 1986, 100 Stat. 2085). Commerce Clearing House, a publisher of tax information, released a version of the Internal Revenue Code in the early 1990s that was four times thicker than its version in 1953. Changes to the tax laws often reflect the times. The flat tax of 1913 was later replaced with a graduated tax. After the United States entered world war i, the War Revenue Act of 1917 imposed a maximum tax rate for individuals of 67 percent, compared with a rate of 13 percent in 1916. In 1924 Secretary of the Treasury Andrew W. Mellon, speaking to Congress about the high level of taxation, stated, The present system is a failure. It was an emergency measure, adopted under the pressure of war necessity and not to be counted upon as a permanent part of our revenue structure. The high rates put pressure on taxpayers to reduce their taxable income, tend to destroy individual initiative and enterprise, and seriously impede the development of productive business. Ways will always be found to avoid taxes so destructive in their nature, and the only way to save the situation is to put the taxes on a reasonable basis that will permit business to go on and industry to develop. Consequently, the Revenue Act of 1924 reduced the maximum individual tax rate to 43 percent (Revenue Acts, June 2, 1924, ch. 234, 43 Stat. 253). In 1926 the rate was further reduced to 25 percent. The Revenue Act of 1932 was the first tax law passed during the Great Depression (Revenue Acts, June 6, 1932, ch. 209, 47 Stat. 169). It increased the individual maximum rate from 25 to 63 percent, and reduced personal exemptions from $1,500 to $1,000 for single persons, and from $3,500 to $2,500 for married couples. The national industrial recovery act of 1933 (NIRA), part of President franklin d. roosevelts new deal, imposed a five percent excise tax on dividend receipts, imposed a capital stock tax and an excess profits tax, and suspended all deductions for losses (June 16, 1933, ch. 90, 48 Stat. 195). The repeal in 1933 of the eighteenth amendment, which had prohibited the manufacture and sale of alcohol, brought in an estimated $90 million in new liquor taxes in 1934. The social security act of 1935 provided for a wage tax, half to be paid by the employee and half by the employer, to establish a federal retirement fund (Old Age Pension Act, Aug. 14, 1935, ch. 531, 49 Stat. 620). The Wealth Tax Act, also known as the Revenue Act of 1935, increased the maximum tax rate to 79 percent, the Revenue Acts of 1940 and 1941 increased it to 81 percent, the Revenue Act of 1942 raised it to 88 percent, and the Individual Income Tax Act of 1944 raised the individual maximum rate to 94 percent. The post-World War II Revenue Act of 1945 reduced the individual maximum tax from 94 percent to 91 percent. The Revenue Act of 1950, during the korean war, reduced it to 84.4 percent, but it was raised the next year to 92 percent (Revenue Act of 1950, Sept. 23, 1950, ch. 994, Stat. 906). It remained at this level until 1964, when it was reduced to 70 percent. The Revenue Act of 1954 revised the Internal Revenue Code of 1939, making major changes that were beneficial to the taxpayer, including providing for child care deductions (later changed to credits), an increase in the charitable contribution limit, a tax credit against taxable retirement income, employee deductions for business expenses, and liberalized depreciation deductions. From 1954 to 1962, the Internal Revenue Code was amended by 183 separate acts. In 1974 the employee retirement income security act (ERISA) created protections for employees whose employers promised specified pensions or other retirement contributions (Pub. L. No. 93-406, Sept. 2, 1974, 88 Stat. 829). ERISA required that to be tax deductible, the employers plan contribution must meet certain minimum standards as to employee participation and vesting and employer funding. ERISA also approved the use of individual retirement accounts (IRAs) to encourage tax-deferred retirement savings by individuals. The Economic Recovery Tax Act of 1981 (ERTA) provided the largest tax cut up to that time, reducing the maximum individual rate from 70 percent to 50 percent (Pub. L. No. 97-34, Aug. 13, 1981, 95 Stat. 172). The most sweeping tax changes since world war ii were enacted in the Tax Reform Act of 1986. This bill was signed into law by President ronald reagan and was designed to equalize the tax treatment of various assets, eliminate tax shelters, and lower marginal rates. Conservatives wanted the act to provide a single, low tax rate that could be applied to everyone. Although this single, flat rate was not included in the final bill, tax rates were reduced to 15 percent on the first $17,850 of income for singles and $29,750 for married couples, and set at 28 to 33 percent on remaining income. Many deductions were repealed, such as a deduction available to two-income married couples that had been used to avoid the marriage penalty (a greater tax liability incurred when two persons filed their income tax return as a married couple rather than as individuals). Although the personal exemption exclusion was increased, an exemption for elderly and blind persons who itemize deductions was repealed. In addition, a special capital gains rate was repealed, as was an investment tax credit that had been introduced in 1962 by President john f. kennedy. The Omnibus Budget Reconciliation Act of 1993, the first budget and tax act enacted during the Clinton administration, was vigorously debated, and passed with only the minimum number of necessary votes. This law provided for income tax rates of 15, 28, 31, 36, and 39.6 percent on varying levels of income and for the taxation of social security income if the taxpayer receives other income over a certain level. In 2001 Congress enacted a major income tax cut at the urging of President george w. bush. Over the course of 11 years the law reduces marginal income tax rates across all levels of income. The 36 percent rate will be lowered to 33 percent, the 31 percent rate to 28 percent, the 28 percent rate to 25 percent. In addition, a new bottom 10 percent rate was created. Since the early 1980s, a flat-rate tax system rather than the graduated bracketed method has been proposed. (The graduated bracketed method is the one that has been used since graduated taxes were introduced: the percentage of tax differs based on the amount of taxable income.) The flat-rate system would impose one rate, such as 20 percent, on all income and would eliminate special deductions, credits, and exclusions. Despite firm support by some, the flat-rate tax has not been adopted in the United States. Regardless of the changes made by legislators since 1913, the basic formula for computing the am