破碎知識
時(shi)間(jian):2012-05-25 14:44:31 點擊數(shu):
對(dui)機(ji)械(xie)化施工(gong)企業來說,工(gong)程機(ji)械(xie)技術(shu)狀(zhuang)況的良好(hao)與否是企業能否正常(chang)生產的直接(jie)因素。液(ye)(ye)壓(ya)傳動的工(gong)程機(ji)械(xie)而言,液(ye)(ye)壓(ya)系(xi)統的正常(chang)運行(xing)是其良好(hao)技術(shu)狀(zhuang)況的一個(ge)主要標志(zhi)。合(he)格(ge)的液(ye)(ye)壓(ya)油是液(ye)(ye)壓(ya)系(xi)統可靠(kao)運行(xing)的保障,正確的維(wei)護是液(ye)(ye)壓(ya)系(xi)統可靠(kao)運行(xing)的根本。
1選擇適合的液壓油
液(ye)壓(ya)油(you)(you)(you)在液(ye)壓(ya)系(xi)統(tong)中起(qi)著(zhu)傳遞壓(ya)力、潤滑、冷(leng)卻、密封(feng)的(de)作用,液(ye)壓(ya)油(you)(you)(you)選擇(ze)不(bu)恰當是(shi)液(ye)壓(ya)系(xi)統(tong)早期故障和(he)耐久性(xing)下(xia)降的(de)主(zhu)要(yao)原因(yin)。應(ying)按隨機《使(shi)用說明書》中規(gui)定的(de)牌(pai)(pai)號(hao)選擇(ze)液(ye)壓(ya)油(you)(you)(you),特(te)殊情(qing)況需要(yao)使(shi)用代用油(you)(you)(you)時,應(ying)力求其(qi)性(xing)能與原牌(pai)(pai)號(hao)性(xing)能相(xiang)同。不(bu)同牌(pai)(pai)號(hao)的(de)液(ye)壓(ya)油(you)(you)(you)不(bu)能混(hun)合使(shi)用,以防液(ye)壓(ya)油(you)(you)(you)產生(sheng)化學反應(ying)、性(xing)能發(fa)生(sheng)變化。深褐色、乳(ru)白色、有異味的(de)液(ye)壓(ya)油(you)(you)(you)是(shi)變質油(you)(you)(you),不(bu)能使(shi)用空氣濾芯。
2防止(zhi)固體雜(za)質混入(ru)液壓系統
清潔的(de)液(ye)(ye)(ye)壓(ya)油(you)是液(ye)(ye)(ye)壓(ya)系(xi)統的(de)生命。液(ye)(ye)(ye)壓(ya)系(xi)統中有許多精(jing)密偶(ou)件(jian)(jian)(jian),有的(de)有阻尼(ni)小孔、有的(de)有縫(feng)隙等。若固體(ti)(ti)雜質(zhi)入(ru)侵將造成精(jing)密偶(ou)件(jian)(jian)(jian)拉傷、發卡、油(you)道堵塞等,危及液(ye)(ye)(ye)壓(ya)系(xi)統的(de)安全(quan)運(yun)行。一(yi)般固體(ti)(ti)雜質(zhi)入(ru)侵液(ye)(ye)(ye)壓(ya)系(xi)統的(de)途(tu)徑(jing)有:液(ye)(ye)(ye)壓(ya)油(you)不(bu)潔;加(jia)油(you)工(gong)具不(bu)潔;加(jia)油(you)和維修、保養(yang)不(bu)慎;液(ye)(ye)(ye)壓(ya)元件(jian)(jian)(jian)脫屑等。可以從(cong)以下幾(ji)個方面防(fang)止固體(ti)(ti)雜質(zhi)入(ru)侵系(xi)統:
2.1加油時
液壓油(you)必須過(guo)濾(lv)加(jia)(jia)注,加(jia)(jia)油(you)工具應可靠清潔。不能(neng)為了提高(gao)加(jia)(jia)油(you)速度而(er)去掉油(you)箱加(jia)(jia)油(you)口處的(de)過(guo)濾(lv)器。加(jia)(jia)油(you)人(ren)員應使用干凈(jing)的(de)手套和工作服,以防固(gu)體雜(za)質(zhi)和纖(xian)維雜(za)質(zhi)掉入油(you)中。
2.2保養時
拆(chai)卸(xie)液(ye)壓(ya)油(you)(you)箱(xiang)加(jia)油(you)(you)蓋、濾(lv)(lv)清(qing)(qing)(qing)(qing)(qing)器(qi)蓋、檢測(ce)孔、液(ye)壓(ya)油(you)(you)管(guan)等部(bu)(bu)位,造成系統油(you)(you)道暴露時要避開揚塵(chen),拆(chai)卸(xie)部(bu)(bu)位要先徹(che)底(di)清(qing)(qing)(qing)(qing)(qing)潔(jie)(jie)(jie)后(hou)才能(neng)打開。如拆(chai)卸(xie)液(ye)壓(ya)油(you)(you)箱(xiang)加(jia)油(you)(you)蓋時,先除(chu)去油(you)(you)箱(xiang)蓋四周的(de)泥土,擰松油(you)(you)箱(xiang)蓋后(hou),清(qing)(qing)(qing)(qing)(qing)除(chu)殘留在接合部(bu)(bu)位的(de)雜物(不能(neng)用(yong)水(shui)沖洗(xi)以免水(shui)滲入油(you)(you)箱(xiang)),確認(ren)清(qing)(qing)(qing)(qing)(qing)潔(jie)(jie)(jie)后(hou)才能(neng)打開油(you)(you)箱(xiang)蓋。如需(xu)使(shi)用(yong)擦(ca)拭(shi)材(cai)料和(he)鐵錘(chui)(chui)時,應選(xuan)擇不掉纖維雜質的(de)擦(ca)拭(shi)材(cai)料和(he)擊(ji)打面(mian)附著(zhu)橡膠的(de)專用(yong)鐵錘(chui)(chui)。液(ye)壓(ya)元件、液(ye)壓(ya)膠管(guan)要認(ren)真清(qing)(qing)(qing)(qing)(qing)洗(xi),用(yong)高壓(ya)風吹干后(hou)組裝(zhuang)(zhuang)(zhuang)。選(xuan)用(yong)包(bao)裝(zhuang)(zhuang)(zhuang)完(wan)好(hao)的(de)正品濾(lv)(lv)芯(xin)(內包(bao)裝(zhuang)(zhuang)(zhuang)損壞(huai),雖然濾(lv)(lv)芯(xin)完(wan)好(hao),也可能(neng)不潔(jie)(jie)(jie))。換(huan)油(you)(you)時同時清(qing)(qing)(qing)(qing)(qing)洗(xi)濾(lv)(lv)清(qing)(qing)(qing)(qing)(qing)器(qi),安裝(zhuang)(zhuang)(zhuang)濾(lv)(lv)芯(xin)前應用(yong)擦(ca)拭(shi)材(cai)料認(ren)真清(qing)(qing)(qing)(qing)(qing)潔(jie)(jie)(jie)濾(lv)(lv)清(qing)(qing)(qing)(qing)(qing)器(qi)殼內底(di)部(bu)(bu)污物。
2.3液壓系統(tong)的清洗
清(qing)(qing)洗油必須使用(yong)與系(xi)(xi)統所用(yong)牌號相同的液壓(ya)油,油溫(wen)在45~80℃之間,用(yong)大流(liu)量盡可能將(jiang)系(xi)(xi)統中(zhong)雜(za)質帶(dai)走。液壓(ya)系(xi)(xi)統要反復清(qing)(qing)洗三次(ci)以上,每次(ci)清(qing)(qing)洗完后,趁油熱時將(jiang)其全部放(fang)出系(xi)(xi)統。清(qing)(qing)洗完畢再清(qing)(qing)洗濾清(qing)(qing)器、更換新濾芯后加注新油。
3防止空氣(qi)和水入侵液(ye)壓系統
3.1防(fang)止空(kong)氣入侵液(ye)壓系統
在常壓(ya)(ya)常溫下液(ye)壓(ya)(ya)油(you)中(zhong)含有容積比為6~8%的空(kong)(kong)氣(qi),當壓(ya)(ya)力降(jiang)低時空(kong)(kong)氣(qi)會從油(you)中(zhong)游離(li)出(chu)(chu)來,氣(qi)泡破裂使(shi)液(ye)壓(ya)(ya)元(yuan)件(jian)“氣(qi)蝕”,產生噪聲。大量的空(kong)(kong)氣(qi)進入油(you)中(zhong)將使(shi)“氣(qi)蝕”現象加劇(ju),液(ye)壓(ya)(ya)油(you)壓(ya)(ya)縮性增大,工作不穩定,降(jiang)低工作效率,執行元(yuan)件(jian)出(chu)(chu)現工作“爬行”等(deng)不良后果。另外,空(kong)(kong)氣(qi)還會使(shi)液(ye)壓(ya)(ya)油(you)氧化,加速(su)油(you)的變(bian)質(zhi)。防(fang)止空(kong)(kong)氣(qi)入侵(qin)應注意(yi)以下幾點(dian):
1、維修和換油后要按隨機《使(shi)用(yong)說明書》規定排除系(xi)統中的空氣(qi),才能正(zheng)常(chang)作業(ye)。
2、液壓油(you)(you)泵的吸油(you)(you)管口不得(de)露出油(you)(you)面,吸油(you)(you)管路必須密(mi)封良好。
3、油(you)(you)(you)泵(beng)驅(qu)動軸的密封(feng)(feng)應(ying)良好,要注意更換該處油(you)(you)(you)封(feng)(feng)時應(ying)使用(yong)“雙唇”正品油(you)(you)(you)封(feng)(feng),不能用(yong)“單(dan)唇”油(you)(you)(you)封(feng)(feng)代替,因為“單(dan)唇”油(you)(you)(you)封(feng)(feng)只(zhi)能單(dan)向封(feng)(feng)油(you)(you)(you),不具備封(feng)(feng)氣(qi)的功(gong)能。本(ben)單(dan)位曾有一臺柳(liu)工ZL50裝載機(ji)大修后,液(ye)壓(ya)油(you)(you)(you)泵(beng)出現連續(xu)“氣(qi)蝕”噪聲(sheng)、油(you)(you)(you)箱(xiang)油(you)(you)(you)位自動升高等故(gu)障,經(jing)查(cha)詢(xun)液(ye)壓(ya)油(you)(you)(you)泵(beng)修理過(guo)程,發現即為液(ye)壓(ya)油(you)(you)(you)泵(beng)驅(qu)動軸的油(you)(you)(you)封(feng)(feng)誤(wu)用(yong)“單(dan)唇”油(you)(you)(you)封(feng)(feng)所致。
3.2防止水入侵液壓(ya)系統(tong)
油中含有過量水分,會使液壓(ya)元件(jian)銹蝕、油液乳化(hua)變(bian)質(zhi)、潤滑油膜強度降低,加速機械磨損。
除(chu)了維修保養時(shi)要(yao)(yao)防止水(shui)分(fen)入侵外(wai),還要(yao)(yao)注(zhu)意儲油桶(tong)不用時(shi),要(yao)(yao)擰緊(jin)蓋子,倒置(zhi)放置(zhi);含水(shui)量大(da)的油要(yao)(yao)經多次(ci)過(guo)濾(lv)(lv),每(mei)過(guo)濾(lv)(lv)一(yi)次(ci)要(yao)(yao)更換一(yi)次(ci)烘干的濾(lv)(lv)紙,在沒(mei)有(you)專(zhuan)用儀(yi)器檢測時(shi),可將油滴(di)到燒熱的鐵(tie)板(ban)上,沒(mei)有(you)蒸氣冒出并立即燃燒方能加注(zhu)。
4作業中注意事項
4.1機械(xie)作業要柔和平(ping)順(shun)
機(ji)(ji)(ji)(ji)械作(zuo)(zuo)(zuo)(zuo)業應避免(mian)粗暴(bao),否(fou)則必然產生沖(chong)(chong)擊(ji)(ji)負荷,使機(ji)(ji)(ji)(ji)械故障頻(pin)發,大(da)大(da)縮短使用(yong)壽命(ming)。作(zuo)(zuo)(zuo)(zuo)業時(shi)產生的(de)(de)(de)沖(chong)(chong)擊(ji)(ji)負荷,一(yi)(yi)方面使機(ji)(ji)(ji)(ji)械結構件(jian)早(zao)期(qi)磨(mo)損、斷裂、破(po)碎(sui),一(yi)(yi)方面使液(ye)壓(ya)(ya)(ya)系統中產生沖(chong)(chong)擊(ji)(ji)壓(ya)(ya)(ya)力,沖(chong)(chong)擊(ji)(ji)壓(ya)(ya)(ya)力又會(hui)使液(ye)壓(ya)(ya)(ya)元(yuan)件(jian)損壞(huai)、油(you)(you)(you)(you)封和高壓(ya)(ya)(ya)油(you)(you)(you)(you)管(guan)接(jie)頭(tou)與膠(jiao)管(guan)的(de)(de)(de)壓(ya)(ya)(ya)合處過(guo)(guo)早(zao)失效(xiao)漏油(you)(you)(you)(you)或爆管(guan)、溢流(liu)閥(fa)(fa)頻(pin)繁動(dong)(dong)作(zuo)(zuo)(zuo)(zuo)油(you)(you)(you)(you)溫上升。我(wo)單位(wei)曾(ceng)新購一(yi)(yi)臺(tai)UH171正鏟挖掘機(ji)(ji)(ji)(ji),作(zuo)(zuo)(zuo)(zuo)業中每(mei)(mei)隔4~6天斗門(men)(men)油(you)(you)(you)(you)管(guan)要(yao)(yao)漏油(you)(you)(you)(you)或爆裂,油(you)(you)(you)(you)管(guan)是隨(sui)機(ji)(ji)(ji)(ji)進口(kou)的(de)(de)(de)純正品(pin),經(jing)檢測沒有質量問(wen)題。通(tong)過(guo)(guo)現場(chang)觀察,發現為斗門(men)(men)開、閉(bi)時(shi)強烈(lie)撞擊(ji)(ji)限位(wei)塊、門(men)(men)框所致。要(yao)(yao)有效(xiao)地(di)避免(mian)產生沖(chong)(chong)擊(ji)(ji)負荷:必須嚴格執行(xing)操(cao)(cao)作(zuo)(zuo)(zuo)(zuo)規程;液(ye)壓(ya)(ya)(ya)閥(fa)(fa)開、閉(bi)不(bu)(bu)能(neng)(neng)過(guo)(guo)猛(meng)過(guo)(guo)快;避免(mian)使工(gong)作(zuo)(zuo)(zuo)(zuo)裝(zhuang)置構件(jian)運(yun)動(dong)(dong)到極限位(wei)置產生強烈(lie)撞擊(ji)(ji);沒有沖(chong)(chong)擊(ji)(ji)功(gong)能(neng)(neng)的(de)(de)(de)液(ye)壓(ya)(ya)(ya)設(she)(she)備(bei)不(bu)(bu)能(neng)(neng)用(yong)工(gong)作(zuo)(zuo)(zuo)(zuo)裝(zhuang)置(如挖掘機(ji)(ji)(ji)(ji)的(de)(de)(de)鏟斗)猛(meng)烈(lie)沖(chong)(chong)擊(ji)(ji)作(zuo)(zuo)(zuo)(zuo)業對(dui)象(xiang)以(yi)達到破(po)碎(sui)的(de)(de)(de)目(mu)的(de)(de)(de)。還(huan)有一(yi)(yi)個(ge)值(zhi)得注意的(de)(de)(de)問(wen)題:操(cao)(cao)作(zuo)(zuo)(zuo)(zuo)手(shou)要(yao)(yao)保持穩定。因(yin)為每(mei)(mei)臺(tai)設(she)(she)備(bei)操(cao)(cao)縱(zong)系統的(de)(de)(de)自由(you)間隙都有一(yi)(yi)定差異,連接(jie)部位(wei)的(de)(de)(de)磨(mo)損程度不(bu)(bu)同因(yin)而其間隙也不(bu)(bu)同,發動(dong)(dong)機(ji)(ji)(ji)(ji)及液(ye)壓(ya)(ya)(ya)系統出力的(de)(de)(de)大(da)小也不(bu)(bu)盡相同,這些因(yin)素賦予了設(she)(she)備(bei)的(de)(de)(de)個(ge)性。只有使用(yong)該設(she)(she)備(bei)的(de)(de)(de)操(cao)(cao)作(zuo)(zuo)(zuo)(zuo)手(shou)認(ren)真(zhen)摸索,修正自己的(de)(de)(de)操(cao)(cao)縱(zong)動(dong)(dong)作(zuo)(zuo)(zuo)(zuo)以(yi)適(shi)應設(she)(she)備(bei)的(de)(de)(de)個(ge)性,經(jing)過(guo)(guo)長期(qi)作(zuo)(zuo)(zuo)(zuo)業后(hou),才能(neng)(neng)養(yang)成符合設(she)(she)備(bei)個(ge)性的(de)(de)(de)良好操(cao)(cao)作(zuo)(zuo)(zuo)(zuo)習慣。一(yi)(yi)般機(ji)(ji)(ji)(ji)械行(xing)業堅持定人定機(ji)(ji)(ji)(ji)制度,這也是因(yin)素之一(yi)(yi)。
4.2要注意氣蝕和溢(yi)流(liu)噪聲
作(zuo)業(ye)中要時(shi)刻(ke)注意液(ye)壓泵(beng)和(he)溢流(liu)閥的聲音,如果(guo)液(ye)壓泵(beng)出現“氣(qi)蝕”噪聲,經排氣(qi)后不能消除(chu),應(ying)查明原因排除(chu)故(gu)障后才(cai)能使(shi)用。如果(guo)某執行元件(jian)在沒有(you)負荷時(shi)動(dong)作(zuo)緩慢(man),并伴有(you)溢流(liu)閥溢流(liu)聲響(xiang),應(ying)立即停(ting)機檢修。
4.3嚴(yan)格執(zhi)行交(jiao)接班制(zhi)度
交班(ban)司機停放機械(xie)時,要保(bao)證接(jie)班(ban)司機檢(jian)查時的(de)安全和(he)檢(jian)查到(dao)準確的(de)油(you)位(wei)。系統是(shi)否(fou)滲漏、連接(jie)是(shi)否(fou)松動、活塞(sai)桿和(he)液壓(ya)膠管(guan)是(shi)否(fou)撞傷、液壓(ya)泵的(de)低壓(ya)進油(you)管(guan)連接(jie)是(shi)否(fou)可(ke)靠、油(you)箱(xiang)油(you)位(wei)是(shi)否(fou)正(zheng)確等,是(shi)接(jie)班(ban)司機對液壓(ya)系統檢(jian)查的(de)。常壓(ya)式油(you)箱(xiang)還要檢(jian)查并(bing)清潔油(you)箱(xiang)通氣孔(kong),保(bao)持(chi)其暢(chang)通,以防氣孔(kong)堵塞(sai)造成油(you)箱(xiang)真空(kong),致使液壓(ya)油(you)泵吸(xi)油(you)困(kun)難(nan)而(er)損(sun)壞(huai)。
4.4保持(chi)適宜的油溫
液壓系(xi)統(tong)(tong)的工作(zuo)溫度一般控制(zhi)在30~80℃之間為(wei)宜(危險溫度≥100℃)。液壓系(xi)統(tong)(tong)的油(you)(you)溫過高會導致:油(you)(you)的粘(zhan)度降(jiang)低(di),容易引(yin)起(qi)泄漏,效(xiao)率(lv)下降(jiang);潤滑油(you)(you)膜強度降(jiang)低(di),加速(su)機械的磨(mo)損;生成碳(tan)化(hua)(hua)(hua)物和淤(yu)碴(cha);油(you)(you)液氧(yang)化(hua)(hua)(hua)加速(su)油(you)(you)質(zhi)惡(e)化(hua)(hua)(hua);油(you)(you)封、高壓膠管過早老化(hua)(hua)(hua)等。為(wei)了(le)避免溫度過高:不(bu)(bu)要(yao)長期過載;注意散(san)熱(re)(re)器散(san)熱(re)(re)片不(bu)(bu)要(yao)被油(you)(you)污染,以(yi)防塵土(tu)附著影響(xiang)散(san)熱(re)(re)效(xiao)果;保(bao)(bao)持(chi)(chi)足夠的油(you)(you)量以(yi)利于(yu)油(you)(you)的循環散(san)熱(re)(re);炎(yan)熱(re)(re)的夏季(ji)不(bu)(bu)要(yao)全天作(zuo)業,要(yao)避開中午(wu)高溫時(shi)(shi)(shi)間。油(you)(you)溫過低(di)時(shi)(shi)(shi),油(you)(you)的粘(zhan)度大(da),流動(dong)(dong)(dong)性差,阻力大(da),工作(zuo)效(xiao)率(lv)低(di);當(dang)油(you)(you)溫低(di)于(yu)20℃時(shi)(shi)(shi),急轉(zhuan)彎易損壞液壓馬達、閥(fa)、管道等。此時(shi)(shi)(shi)需要(yao)進行暖(nuan)機運(yun)轉(zhuan),起(qi)動(dong)(dong)(dong)發(fa)動(dong)(dong)(dong)機,空載怠速(su)運(yun)轉(zhuan)3~5min后,以(yi)中速(su)油(you)(you)門提高發(fa)動(dong)(dong)(dong)機轉(zhuan)速(su),操縱手柄(bing)使(shi)(shi)工作(zuo)裝(zhuang)置的任何一個動(dong)(dong)(dong)作(zuo)(如挖(wa)掘機張斗)極限位置,保(bao)(bao)持(chi)(chi)3~5min使(shi)(shi)液壓油(you)(you)通(tong)過溢(yi)流升(sheng)溫。如果油(you)(you)溫更(geng)低(di)則(ze)需要(yao)適當(dang)增(zeng)加暖(nuan)機運(yun)轉(zhuan)時(shi)(shi)(shi)間。
4.5液(ye)壓(ya)油箱氣壓(ya)和(he)油量的控(kong)制
壓力式油(you)(you)(you)箱在(zai)工(gong)作中(zhong)要(yao)隨(sui)時注意油(you)(you)(you)箱氣壓,其壓力必須保持在(zai)隨(sui)機《使用(yong)(yong)說明(ming)書(shu)》規(gui)定的范圍內(nei)。壓力過低,油(you)(you)(you)泵吸油(you)(you)(you)不足(zu)易損壞,壓力過高,會使液壓系(xi)統漏油(you)(you)(you),容易造(zao)成低壓油(you)(you)(you)路爆管(guan)。對維修和(he)換油(you)(you)(you)后的設備(bei),排盡(jin)系(xi)統中(zhong)的空(kong)氣后,要(yao)按隨(sui)機《使用(yong)(yong)說明(ming)書(shu)》規(gui)定的檢(jian)查(cha)油(you)(you)(you)位(wei)(wei)狀態,將機器(qi)停在(zai)平整的地方,發動機熄火(huo)15min后重新(xin)檢(jian)查(cha)油(you)(you)(you)位(wei)(wei),必要(yao)時予以補充。
4.6其他注意事項
作(zuo)業中(zhong)要防(fang)止飛落石(shi)塊打擊液(ye)壓油(you)缸(gang)、活(huo)塞(sai)(sai)桿(gan)、液(ye)壓油(you)管等部件。活(huo)塞(sai)(sai)桿(gan)上(shang)如果有小點擊傷,要及時用(yong)油(you)石(shi)將小點周圍棱邊磨(mo)(mo)去,以防(fang)破壞活(huo)塞(sai)(sai)桿(gan)的密封裝(zhuang)置,在(zai)(zai)不漏油(you)的情況下可繼續使用(yong)。連續停機在(zai)(zai)24h以上(shang)的設備,在(zai)(zai)啟動前,要向液(ye)壓泵(beng)中(zhong)注油(you),以防(fang)液(ye)壓泵(beng)干磨(mo)(mo)而(er)損壞。
5定期保養注意事項
目前有(you)(you)的工(gong)程機(ji)械液壓(ya)(ya)系統(tong)(tong)設(she)置(zhi)(zhi)(zhi)了(le)智(zhi)能裝置(zhi)(zhi)(zhi),該裝置(zhi)(zhi)(zhi)對(dui)液壓(ya)(ya)系統(tong)(tong)某(mou)些(xie)隱患有(you)(you)警示功能,但其監(jian)測范圍和程度有(you)(you)一定(ding)的局限性,所以液壓(ya)(ya)系統(tong)(tong)的檢查保養(yang)應將智(zhi)能裝置(zhi)(zhi)(zhi)監(jian)測結果與定(ding)期檢查保養(yang)相(xiang)結合(he)
5.1250h檢查(cha)保養(yang)
檢查濾清器濾網上的附著物,如金屬粉末過多,往往標志著油泵磨損或油缸拉缸,對此,必須確診并采取相應措施后才能開機。如發現濾網損壞、污垢積聚,要及時更換,必要時同時換油。
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