在使用過程中，大多數金鄉機械密封都屬于接觸式密封，其機理是靠動密封環與靜密封環的接觸端面在密封流體壓力和彈性元件壓緊力的作用下緊密貼合，并相對滑動而達到密封。工作時，金鄉機械密封端面上同時發生摩擦、滑動與磨損等現象，摩擦是它的基本特征。金鄉機械密封端面(mian)(mian)摩擦(ca)(ca)的工(gong)況(kuang)一(yi)(yi)般(ban)分為：流(liu)體(ti)(ti)摩擦(ca)(ca)、混合摩擦(ca)(ca)和邊界摩擦(ca)(ca)三類，但不能長時間干摩擦(ca)(ca)。干摩擦(ca)(ca)狀態時，兩(liang)端面(mian)(mian)間的固(gu)體(ti)(ti)表(biao)面(mian)(mian)微凸體(ti)(ti)將(jiang)直(zhi)接(jie)接(jie)觸而引(yin)起(qi)劇烈的磨(mo)損(sun)。磨(mo)損(sun)時一(yi)(yi)方(fang)面(mian)(mian)會使(shi)摩擦(ca)(ca)表(biao)面(mian)(mian)物(wu)質喪失或(huo)遷移，導(dao)致表(biao)面(mian)(mian)損(sun)壞；另一(yi)(yi)方(fang)面(mian)(mian)會產(chan)生大量的摩擦(ca)(ca)熱直(zhi)至燒毀密封。在無流(liu)體(ti)(ti)介質的工(gong)況(kuang)下(xia)，如(ru)何減(jian)少磨(mo)損(sun)降(jiang)低摩擦(ca)(ca)熱，那就要依靠(kao)干磨(mo)密封了。

　　干(gan)磨密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)屬于浮動(dong)(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)的一種，常用(yong)(yong)(yong)材(cai)(cai)質為耐(nai)磨碳(tan)精，結構包括環(huan)(huan)(huan)行(xing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體和環(huan)(huan)(huan)行(xing)軸套(tao)，密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體內(nei)有(you)(you)(you)環(huan)(huan)(huan)行(xing)槽，槽內(nei)至少裝(zhuang)(zhuang)有(you)(you)(you)二(er)個截(jie)面(mian)為矩形(xing)的環(huan)(huan)(huan)行(xing)石(shi)墨密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)，石(shi)墨密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)的內(nei)徑與(yu)環(huan)(huan)(huan)行(xing)軸套(tao)之(zhi)間有(you)(you)(you)0.01-0.04的間隙，軸套(tao)外(wai)表面(mian)涂有(you)(you)(you)耐(nai)磨涂層，涂層材(cai)(cai)料一般為三(san)氧化(hua)二(er)鋁或三(san)氧化(hua)二(er)鉻。干(gan)磨密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)有(you)(you)(you)時(shi)需要(yao)增加隔離氣(qi)，通常使用(yong)(yong)(yong)氮氣(qi)，氮氣(qi)耗(hao)量能控制在25-40。主(zhu)要(yao)應用(yong)(yong)(yong)于密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)易燃(ran)有(you)(you)(you)毒介質，由于操作維修簡(jian)單(dan)，密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)性(xing)好，不需要(yao)復雜的潤滑冷卻系統，可以干(gan)運行(xing)，得到廣泛(fan)的應用(yong)(yong)(yong)。干(gan)磨密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)包括有(you)(you)(you)外(wai)罩及(ji)架設于外(wai)罩上(shang)且可呈相對旋轉及(ji)貼合的動(dong)(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)及(ji)靜(jing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)，靜(jing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)與(yu)外(wai)罩固(gu)定連接，靜(jing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)及(ji)動(dong)(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)上(shang)分開設有(you)(you)(you)供旋轉軸安裝(zhuang)(zhuang)的通孔，且動(dong)(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)與(yu)靜(jing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)貼合的端面(mian)分別為動(dong)(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)及(ji)靜(jing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)，外(wai)罩上(shang)設有(you)(you)(you)促使動(dong)(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)與(yu)靜(jing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)緊密(mi)(mi)(mi)(mi)(mi)(mi)(mi)貼合的彈性(xing)抵壓件。除(chu)了要(yao)保持密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)平行(xing)之(zhi)外(wai)，主(zhu)要(yao)是摩擦副的材(cai)(cai)料問題。

　　摩擦材料應具備(bei)下列條件：

　　(1)機械強度高，能耐(nai)(nai)壓和耐(nai)(nai)壓力變形；

　　(2)具有耐(nai)干磨性，耐(nai)高載荷性，自潤滑(hua)性好；

　　(3)配對(dui)材料的磨(mo)合性好(hao)，無過大的磨(mo)損(sun)和對(dui)偶(ou)腐蝕；

　　(4)耐磨性好，摩擦(ca)材(cai)料雖然是(shi)易損件，起到(dao)保護制(zhi)動(dong)或(huo)(huo)傳動(dong)裝(zhuang)置的(de)(de)作用，但要(yao)求具有一定的(de)(de)耐磨性，使用壽命盡量要(yao)長，刮傷、腐蝕和粘附對偶，都會(hui)造成(cheng)制(zhi)動(dong)或(huo)(huo)傳動(dong)的(de)(de)震動(dong)和不穩定；

　　(5)導(dao)(dao)熱(re)(re)性和散(san)熱(re)(re)性好(hao)，導(dao)(dao)熱(re)(re)性是傳導(dao)(dao)熱(re)(re)量的(de)能力大(da)小，即包括吸熱(re)(re)，也包括散(san)熱(re)(re)，所以，導(dao)(dao)熱(re)(re)性好(hao)的(de)必然散(san)熱(re)(re)性也好(hao)；

　　(6)抗熱裂(lie)性好，根本解決抗熱裂(lie)性問題(ti)可能(neng)需(xu)要改變(bian)封孔方(fang)法；

　　(7)耐腐(fu)蝕性(xing)(xing)強(qiang)，一些有(you)色(se)金(jin)屬(shu)合金(jin)能將(jiang)良好的摩擦學(xue)特(te)性(xing)(xing)與有(you)些流體的耐腐(fu)蝕性(xing)(xing)結(jie)合；

　　(8)線膨脹系數小，熱膨脹會造成摩擦材料與摩擦對(dui)偶之間(jian)的間(jian)隙(xi)過小，發生(sheng)拖摩，損毀制動(dong)、傳動(dong)裝置。