在使用過程中，大多數大冶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，大冶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。大冶機械密封端(duan)面(mian)(mian)摩擦(ca)(ca)(ca)的工(gong)況一般分為：流體(ti)摩擦(ca)(ca)(ca)、混(hun)合摩擦(ca)(ca)(ca)和邊界摩擦(ca)(ca)(ca)三類(lei)，但不能長時間(jian)干摩擦(ca)(ca)(ca)。干摩擦(ca)(ca)(ca)狀態(tai)時，兩端(duan)面(mian)(mian)間(jian)的固體(ti)表(biao)面(mian)(mian)微凸體(ti)將直接接觸(chu)而引起(qi)劇烈的磨(mo)損(sun)(sun)。磨(mo)損(sun)(sun)時一方面(mian)(mian)會(hui)使摩擦(ca)(ca)(ca)表(biao)面(mian)(mian)物質(zhi)喪失或遷移，導致表(biao)面(mian)(mian)損(sun)(sun)壞；另(ling)一方面(mian)(mian)會(hui)產生大(da)量的摩擦(ca)(ca)(ca)熱直至燒毀密封。在(zai)無流體(ti)介質(zhi)的工(gong)況下，如何減少(shao)磨(mo)損(sun)(sun)降低摩擦(ca)(ca)(ca)熱，那就要依靠干磨(mo)密封了(le)。

　　干磨(mo)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)屬于(yu)浮動(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)的一種，常(chang)(chang)用材質(zhi)為(wei)(wei)耐磨(mo)碳(tan)精，結構包括環(huan)(huan)行(xing)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體和環(huan)(huan)行(xing)軸套，密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體內(nei)有(you)環(huan)(huan)行(xing)槽(cao)，槽(cao)內(nei)至少裝有(you)二個截(jie)面(mian)(mian)為(wei)(wei)矩形(xing)的環(huan)(huan)行(xing)石墨(mo)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)，石墨(mo)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)的內(nei)徑與(yu)(yu)環(huan)(huan)行(xing)軸套之間有(you)0.01-0.04的間隙(xi)，軸套外(wai)表面(mian)(mian)涂有(you)耐磨(mo)涂層(ceng)，涂層(ceng)材料(liao)一般為(wei)(wei)三氧(yang)化二鋁(lv)或三氧(yang)化二鉻。干磨(mo)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)有(you)時需(xu)要增加(jia)隔離氣，通常(chang)(chang)使(shi)用氮(dan)氣，氮(dan)氣耗量能控制在25-40。主(zhu)要應用于(yu)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)易燃(ran)有(you)毒介質(zhi)，由于(yu)操作維修簡(jian)單(dan)，密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)性好(hao)，不需(xu)要復(fu)雜(za)的潤滑(hua)冷卻(que)系統，可(ke)以干運行(xing)，得到廣泛的應用。干磨(mo)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)包括有(you)外(wai)罩(zhao)及(ji)架設(she)于(yu)外(wai)罩(zhao)上(shang)且可(ke)呈相對(dui)旋轉及(ji)貼合(he)的動(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)及(ji)靜密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)，靜密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)與(yu)(yu)外(wai)罩(zhao)固定連接，靜密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)及(ji)動(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)上(shang)分開設(she)有(you)供旋轉軸安裝的通孔，且動(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)與(yu)(yu)靜密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)貼合(he)的端(duan)面(mian)(mian)分別為(wei)(wei)動(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)(mian)及(ji)靜密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)(mian)，外(wai)罩(zhao)上(shang)設(she)有(you)促使(shi)動(dong)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)與(yu)(yu)靜密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)緊密(mi)(mi)(mi)(mi)(mi)(mi)(mi)貼合(he)的彈性抵壓(ya)件。除了要保持(chi)密(mi)(mi)(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)(mian)平行(xing)之外(wai)，主(zhu)要是摩擦副的材料(liao)問題。

　　摩(mo)擦材(cai)料應具備下列條件：

　　(1)機(ji)械(xie)強度高，能耐(nai)壓(ya)和耐(nai)壓(ya)力變形；

　　(2)具有耐干磨性(xing)(xing)，耐高載荷性(xing)(xing)，自潤(run)滑性(xing)(xing)好(hao)；

　　(3)配(pei)對(dui)材料的(de)磨(mo)合性(xing)好，無過(guo)大的(de)磨(mo)損和對(dui)偶(ou)腐蝕；

　　(4)耐磨性(xing)好，摩擦材料雖然是易損件，起到保護制(zhi)動(dong)(dong)或傳動(dong)(dong)裝(zhuang)置的(de)作用(yong)，但要求(qiu)具(ju)有一(yi)定的(de)耐磨性(xing)，使用(yong)壽命盡量要長，刮(gua)傷、腐蝕和粘(zhan)附對偶，都(dou)會造成(cheng)制(zhi)動(dong)(dong)或傳動(dong)(dong)的(de)震動(dong)(dong)和不穩定；

　　(5)導(dao)熱(re)(re)性(xing)(xing)(xing)和散(san)(san)熱(re)(re)性(xing)(xing)(xing)好，導(dao)熱(re)(re)性(xing)(xing)(xing)是傳導(dao)熱(re)(re)量的(de)能力(li)大(da)小，即包(bao)括吸熱(re)(re)，也(ye)(ye)包(bao)括散(san)(san)熱(re)(re)，所以，導(dao)熱(re)(re)性(xing)(xing)(xing)好的(de)必然(ran)散(san)(san)熱(re)(re)性(xing)(xing)(xing)也(ye)(ye)好；

　　(6)抗(kang)熱(re)裂性好，根(gen)本(ben)解決(jue)抗(kang)熱(re)裂性問題(ti)可能(neng)需要改變(bian)封孔(kong)方(fang)法；

　　(7)耐腐(fu)蝕(shi)性強，一些有(you)(you)色金(jin)屬合(he)金(jin)能將良好(hao)的摩(mo)擦學特性與有(you)(you)些流體的耐腐(fu)蝕(shi)性結合(he)；

　　(8)線膨脹系數小，熱膨脹會造(zao)成摩擦材料與摩擦對偶之間的間隙過小，發生拖摩，損毀制動、傳(chuan)動裝置。