在使用過程中，大多數大英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，大英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。大英機械密封端面(mian)(mian)摩(mo)(mo)(mo)(mo)擦(ca)(ca)的工況一般分為：流(liu)體摩(mo)(mo)(mo)(mo)擦(ca)(ca)、混(hun)合摩(mo)(mo)(mo)(mo)擦(ca)(ca)和邊界摩(mo)(mo)(mo)(mo)擦(ca)(ca)三類，但不能(neng)長時(shi)間干摩(mo)(mo)(mo)(mo)擦(ca)(ca)。干摩(mo)(mo)(mo)(mo)擦(ca)(ca)狀態時(shi)，兩端面(mian)(mian)間的固(gu)體表面(mian)(mian)微凸(tu)體將(jiang)直(zhi)接接觸而(er)引起劇烈的磨(mo)損(sun)(sun)。磨(mo)損(sun)(sun)時(shi)一方面(mian)(mian)會使摩(mo)(mo)(mo)(mo)擦(ca)(ca)表面(mian)(mian)物質(zhi)喪失或遷移，導致表面(mian)(mian)損(sun)(sun)壞；另(ling)一方面(mian)(mian)會產生(sheng)大量的摩(mo)(mo)(mo)(mo)擦(ca)(ca)熱直(zhi)至燒毀密(mi)封。在無(wu)流(liu)體介質(zhi)的工況下，如何(he)減少磨(mo)損(sun)(sun)降低摩(mo)(mo)(mo)(mo)擦(ca)(ca)熱，那就要(yao)依靠干磨(mo)密(mi)封了。

　　干(gan)(gan)磨(mo)(mo)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)屬于浮動(dong)(dong)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)的(de)(de)一種，常(chang)用(yong)材質為耐(nai)磨(mo)(mo)碳精，結構包括環(huan)(huan)(huan)行(xing)(xing)(xing)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體(ti)(ti)和環(huan)(huan)(huan)行(xing)(xing)(xing)軸套，密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)腔體(ti)(ti)內(nei)有(you)(you)環(huan)(huan)(huan)行(xing)(xing)(xing)槽，槽內(nei)至少(shao)裝有(you)(you)二(er)個截面(mian)(mian)(mian)(mian)為矩(ju)形(xing)的(de)(de)環(huan)(huan)(huan)行(xing)(xing)(xing)石墨(mo)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)，石墨(mo)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)的(de)(de)內(nei)徑與(yu)環(huan)(huan)(huan)行(xing)(xing)(xing)軸套之間有(you)(you)0.01-0.04的(de)(de)間隙(xi)，軸套外(wai)(wai)(wai)表面(mian)(mian)(mian)(mian)涂(tu)有(you)(you)耐(nai)磨(mo)(mo)涂(tu)層，涂(tu)層材料一般為三氧(yang)化(hua)二(er)鋁或三氧(yang)化(hua)二(er)鉻。干(gan)(gan)磨(mo)(mo)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)有(you)(you)時需要(yao)增加隔離氣(qi)，通(tong)常(chang)使(shi)用(yong)氮(dan)氣(qi)，氮(dan)氣(qi)耗(hao)量能控制在25-40。主要(yao)應(ying)用(yong)于密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)易(yi)燃有(you)(you)毒介質，由于操(cao)作維修簡(jian)單，密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)性好(hao)，不需要(yao)復雜的(de)(de)潤滑冷卻系(xi)統，可(ke)以干(gan)(gan)運行(xing)(xing)(xing)，得(de)到廣泛的(de)(de)應(ying)用(yong)。干(gan)(gan)磨(mo)(mo)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)包括有(you)(you)外(wai)(wai)(wai)罩(zhao)(zhao)及(ji)(ji)(ji)架(jia)設(she)于外(wai)(wai)(wai)罩(zhao)(zhao)上(shang)(shang)且(qie)可(ke)呈相對旋(xuan)轉(zhuan)及(ji)(ji)(ji)貼(tie)(tie)合(he)的(de)(de)動(dong)(dong)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)及(ji)(ji)(ji)靜(jing)(jing)(jing)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)，靜(jing)(jing)(jing)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)與(yu)外(wai)(wai)(wai)罩(zhao)(zhao)固定連接，靜(jing)(jing)(jing)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)及(ji)(ji)(ji)動(dong)(dong)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)上(shang)(shang)分開設(she)有(you)(you)供旋(xuan)轉(zhuan)軸安(an)裝的(de)(de)通(tong)孔，且(qie)動(dong)(dong)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)與(yu)靜(jing)(jing)(jing)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)貼(tie)(tie)合(he)的(de)(de)端面(mian)(mian)(mian)(mian)分別為動(dong)(dong)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)(mian)(mian)(mian)及(ji)(ji)(ji)靜(jing)(jing)(jing)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)(mian)(mian)(mian)，外(wai)(wai)(wai)罩(zhao)(zhao)上(shang)(shang)設(she)有(you)(you)促使(shi)動(dong)(dong)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)與(yu)靜(jing)(jing)(jing)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)環(huan)(huan)(huan)緊密(mi)(mi)(mi)(mi)貼(tie)(tie)合(he)的(de)(de)彈性抵壓件(jian)。除了(le)要(yao)保持密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)(feng)(feng)(feng)(feng)面(mian)(mian)(mian)(mian)平行(xing)(xing)(xing)之外(wai)(wai)(wai)，主要(yao)是(shi)摩(mo)擦(ca)副的(de)(de)材料問(wen)題。

　　摩擦材料應具備下列條件：

　　(1)機械強(qiang)度高，能耐壓和耐壓力變(bian)形；

　　(2)具(ju)有耐干磨性，耐高載(zai)荷性，自潤滑性好；

　　(3)配對材料的磨合性好，無過(guo)大(da)的磨損和對偶腐蝕；

　　(4)耐磨性好(hao)，摩擦材料雖然(ran)是易損(sun)件，起(qi)到保護制(zhi)動(dong)(dong)或傳動(dong)(dong)裝(zhuang)置的作用，但要(yao)求(qiu)具有(you)一(yi)定的耐磨性，使(shi)用壽命盡量要(yao)長(chang)，刮傷、腐蝕(shi)和粘附對偶，都會造成制(zhi)動(dong)(dong)或傳動(dong)(dong)的震(zhen)動(dong)(dong)和不(bu)穩定；

　　(5)導(dao)熱(re)(re)(re)性和散熱(re)(re)(re)性好(hao)，導(dao)熱(re)(re)(re)性是傳導(dao)熱(re)(re)(re)量的能力大(da)小，即包(bao)(bao)括吸熱(re)(re)(re)，也(ye)包(bao)(bao)括散熱(re)(re)(re)，所以，導(dao)熱(re)(re)(re)性好(hao)的必然(ran)散熱(re)(re)(re)性也(ye)好(hao)；

　　(6)抗(kang)熱(re)裂性好，根(gen)本解決抗(kang)熱(re)裂性問題(ti)可能需要改變(bian)封(feng)孔方法；

　　(7)耐(nai)腐(fu)蝕性(xing)強，一些(xie)有色金屬合金能將良好(hao)的摩擦學特性(xing)與(yu)有些(xie)流(liu)體的耐(nai)腐(fu)蝕性(xing)結合；

　　(8)線(xian)膨(peng)脹(zhang)系數(shu)小(xiao)，熱膨(peng)脹(zhang)會造成摩擦材料與摩擦對偶之間的(de)間隙過小(xiao)，發生拖摩，損毀(hui)制動、傳動裝置。