在使用過程中，大多數金牛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，金牛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。金牛機械密封端(duan)面摩(mo)(mo)擦(ca)的工(gong)況一(yi)般分(fen)為：流(liu)體摩(mo)(mo)擦(ca)、混合摩(mo)(mo)擦(ca)和(he)邊(bian)界(jie)摩(mo)(mo)擦(ca)三類，但不能長(chang)時間干(gan)摩(mo)(mo)擦(ca)。干(gan)摩(mo)(mo)擦(ca)狀(zhuang)態時，兩(liang)端(duan)面間的固體表面微(wei)凸體將直(zhi)接接觸(chu)而引起劇烈的磨(mo)損。磨(mo)損時一(yi)方(fang)面會(hui)使摩(mo)(mo)擦(ca)表面物質(zhi)喪(sang)失或(huo)遷移(yi)，導(dao)致(zhi)表面損壞(huai)；另一(yi)方(fang)面會(hui)產(chan)生大量的摩(mo)(mo)擦(ca)熱直(zhi)至燒毀密封(feng)(feng)。在無流(liu)體介(jie)質(zhi)的工(gong)況下，如何減少磨(mo)損降低摩(mo)(mo)擦(ca)熱，那(nei)就要依(yi)靠干(gan)磨(mo)密封(feng)(feng)了。

　　干磨密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)屬于浮動(dong)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)的(de)(de)一種，常用材質(zhi)為(wei)(wei)耐磨碳精，結構(gou)包括環(huan)(huan)(huan)(huan)行(xing)(xing)(xing)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體和環(huan)(huan)(huan)(huan)行(xing)(xing)(xing)軸套(tao)，密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體內(nei)有環(huan)(huan)(huan)(huan)行(xing)(xing)(xing)槽，槽內(nei)至少裝(zhuang)有二個截面為(wei)(wei)矩形的(de)(de)環(huan)(huan)(huan)(huan)行(xing)(xing)(xing)石(shi)墨(mo)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)，石(shi)墨(mo)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)的(de)(de)內(nei)徑與環(huan)(huan)(huan)(huan)行(xing)(xing)(xing)軸套(tao)之間(jian)(jian)有0.01-0.04的(de)(de)間(jian)(jian)隙，軸套(tao)外(wai)(wai)表面涂(tu)有耐磨涂(tu)層，涂(tu)層材料一般為(wei)(wei)三(san)氧(yang)化(hua)二鋁或三(san)氧(yang)化(hua)二鉻。干磨密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)有時需(xu)要增加隔離氣，通常使(shi)用氮氣，氮氣耗量能控制在(zai)25-40。主(zhu)要應(ying)用于密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)易(yi)燃有毒介質(zhi)，由(you)于操作維修簡單，密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)性(xing)好，不需(xu)要復(fu)雜的(de)(de)潤滑冷卻系統(tong)，可以(yi)干運行(xing)(xing)(xing)，得到廣泛的(de)(de)應(ying)用。干磨密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)包括有外(wai)(wai)罩(zhao)及(ji)架(jia)設(she)(she)于外(wai)(wai)罩(zhao)上(shang)且(qie)(qie)可呈相對旋(xuan)轉(zhuan)及(ji)貼(tie)合的(de)(de)動(dong)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)及(ji)靜(jing)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)，靜(jing)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)與外(wai)(wai)罩(zhao)固定連接(jie)，靜(jing)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)及(ji)動(dong)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)上(shang)分(fen)開設(she)(she)有供旋(xuan)轉(zhuan)軸安裝(zhuang)的(de)(de)通孔，且(qie)(qie)動(dong)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)與靜(jing)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)貼(tie)合的(de)(de)端面分(fen)別為(wei)(wei)動(dong)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面及(ji)靜(jing)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面，外(wai)(wai)罩(zhao)上(shang)設(she)(she)有促使(shi)動(dong)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)與靜(jing)密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)(huan)緊(jin)密(mi)(mi)(mi)(mi)(mi)貼(tie)合的(de)(de)彈性(xing)抵壓件。除了要保持密(mi)(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面平(ping)行(xing)(xing)(xing)之外(wai)(wai)，主(zhu)要是摩擦副的(de)(de)材料問題。

　　摩擦(ca)材料應具備下列條件：

　　(1)機械強度(du)高，能耐(nai)壓(ya)和耐(nai)壓(ya)力變(bian)形；

　　(2)具有耐干(gan)磨性(xing)，耐高載(zai)荷性(xing)，自潤滑性(xing)好；

　　(3)配對材料的磨合性好(hao)，無過大的磨損和對偶腐(fu)蝕；

　　(4)耐(nai)磨性(xing)好，摩(mo)擦材(cai)料雖(sui)然是易損件，起到保護制(zhi)動(dong)(dong)(dong)或(huo)傳動(dong)(dong)(dong)裝置(zhi)的作(zuo)用，但要(yao)求具有一定的耐(nai)磨性(xing)，使用壽命盡量要(yao)長，刮(gua)傷、腐蝕(shi)和粘附對偶，都會造成制(zhi)動(dong)(dong)(dong)或(huo)傳動(dong)(dong)(dong)的震(zhen)動(dong)(dong)(dong)和不穩定；

　　(5)導熱(re)(re)(re)性(xing)(xing)和(he)散(san)熱(re)(re)(re)性(xing)(xing)好(hao)，導熱(re)(re)(re)性(xing)(xing)是傳導熱(re)(re)(re)量的能力大小(xiao)，即包括(kuo)吸熱(re)(re)(re)，也包括(kuo)散(san)熱(re)(re)(re)，所以(yi)，導熱(re)(re)(re)性(xing)(xing)好(hao)的必然(ran)散(san)熱(re)(re)(re)性(xing)(xing)也好(hao)；

　　(6)抗熱(re)裂性(xing)好(hao)，根本解(jie)決抗熱(re)裂性(xing)問(wen)題可能(neng)需要(yao)改變封孔方法；

　　(7)耐腐蝕性(xing)強，一些有色金屬合金能將良好的摩擦學(xue)特性(xing)與有些流體的耐腐蝕性(xing)結合；

　　(8)線膨脹系數小，熱膨脹會(hui)造成摩(mo)擦材料與摩(mo)擦對偶之(zhi)間(jian)的間(jian)隙過(guo)小，發生(sheng)拖摩(mo)，損毀制動、傳動裝置。