法兰密封面常见的几种形式

2019-10-05 剑气书生 真空技术网整理

  中、低压法兰常(chang)用密封面形(xing)式有平面、凹凸面及(ji)榫槽面三种。

1、平面法兰

  该种(zhong)法兰的密封(feng)面是(shi)一光滑平面,有(you)时也在密封(feng)面上车有(you)二条界面为三角形的同(tong)心圆沟槽(俗称水线)。如图3-1(a)所示。

平面法兰的密封面

  适(shi)用(yong)于(yu)平(ping)面(mian)法兰(lan)的(de)垫(dian)(dian)片(pian)有各种非金属平(ping)垫(dian)(dian)片(pian)、包覆(fu)垫(dian)(dian)、金属包垫(dian)(dian)、缠(chan)绕式(shi)垫(dian)(dian)片(pian)(可同时带内(nei)(nei)环或(huo)外(wai)(wai)(wai)环或(huo)内(nei)(nei)外(wai)(wai)(wai)环)。由于(yu)结构(gou)简单(dan)、加工方(fang)便,便于(yu)防(fang)腐衬里的(de)施工,故可在(zai)公称压力(li)p<2.45MPa时使(shi)用(yong)。在(zai)0.588MPa压力(li)以下(xia)、温度(du)不高的(de)场(chang)所尤为(wei)适(shi)宜(yi),但这(zhei)种密(mi)封面(mian)与垫(dian)(dian)片(pian)接触面(mian)积较大(特别(bie)是管道用(yong)宽面(mian)法兰(lan)),所需压紧力(li)大,安(an)装时垫(dian)(dian)片(pian)不宜(yi)定位(wei)。预紧后,垫(dian)(dian)片(pian)易向两侧伸展或(huo)移动。故如(ru)(ru)聚四氟乙烯等摩(mo)擦(ca)系(xi)数较小的(de)垫(dian)(dian)片(pian),不宜(yi)采用(yong)该种密(mi)封面(mian)。另外(wai)(wai)(wai),如(ru)(ru)使(shi)用(yong)缠(chan)绕垫(dian)(dian)片(pian),为(wei)了(le)重(zhong)复利用(yong)垫(dian)(dian)片(pian),密(mi)封面(mian)上不车制三角槽。

2、凹凸面法兰

  该法(fa)兰密(mi)封面(mian)由(you)一(yi)凹(ao)面(mian)和一(yi)凸面(mian)组合而(er)成,垫(dian)(dian)片放置在凹(ao)面(mian)内,如图3-1(b)所示。其(qi)适用(yong)的(de)垫(dian)(dian)片有(you):各种非金属(shu)平垫(dian)(dian)、包覆垫(dian)(dian)、金属(shu)包垫(dian)(dian)、缠绕垫(dian)(dian)片(基本型或带内环(huan)的(de))、金属(shu)波(bo)形垫(dian)(dian)、金属(shu)平垫(dian)(dian)、金属(shu)齿形垫(dian)(dian)。

  与平面(mian)(mian)法(fa)(fa)兰(lan)相比(bi)(bi),凹凸面(mian)(mian)法(fa)(fa)兰(lan)中垫片(pian)不(bu)易被挤出(chu),装配(pei)时便于(yu)(yu)对中,工作(zuo)压(ya)(ya)力(li)范围(wei)比(bi)(bi)平面(mian)(mian)法(fa)(fa)兰(lan)宽,用(yong)于(yu)(yu)密封要(yao)求较(jiao)严的场合(he)。但对于(yu)(yu)操作(zuo)温度(du)高(gao),封口直径(jing)(jing)大的设(she)备(bei),使(shi)(shi)用(yong)该种密封面(mian)(mian)时,垫片(pian)仍存在被挤出(chu)的可能。例如某换热(re)器,压(ya)(ya)力(li)2.45MPa,温度(du)250℃,使(shi)(shi)用(yong)纯(chun)铝平垫片(pian)。根据(ju)表2-2提供的数据(ju),纯(chun)铝最高(gao)使(shi)(shi)用(yong)温度(du)为425℃,其密封应该可靠。事实上(shang),换热(re)器投入(ru)运转不(bu)久就出(chu)现(xian)(xian)泄漏,二次(ci)紧固(gu)后也仅(jin)维持(chi)一段时间(jian)。经停车(che)检查,发现(xian)(xian)垫片(pian)内径(jing)(jing)发生显着变形。其原因是(shi)纯(chun)铝的塑性良(liang)好,250℃时的屈服强(qiang)度(du)约是(shi)常温下(xia)的15%,延(yan)(yan)伸(shen)率(lv)高(gao)达(da)4~5倍,这就是(shi)说在高(gao)温下(xia)铝垫的压(ya)(ya)延(yan)(yan)、蠕变现(xian)(xian)象严重。因此垫片(pian)和法(fa)(fa)兰(lan)面(mian)(mian)之(zhi)间(jian)无法(fa)(fa)保持(chi)所需要(yao)的密封比(bi)(bi)压(ya)(ya),故必须(xu)更换垫片(pian)材质或采用(yong)榫(sun)槽(cao)面(mian)(mian)法(fa)(fa)兰(lan)以及带有(you)两道止(zhi)口的凹凸面(mian)(mian)法(fa)(fa)兰(lan)(如高(gao)压(ya)(ya)密封中,金属平垫所采用(yong)的法(fa)(fa)兰(lan)面(mian)(mian)结(jie)构)予(yu)以解决。

3、榫槽面法兰

  该法兰密(mi)(mi)(mi)封面(mian)(mian)(mian)由(you)一(yi)榫槽面(mian)(mian)(mian)和一(yi)槽面(mian)(mian)(mian)配合组成(cheng),垫(dian)(dian)片(pian)(pian)置于(yu)(yu)槽内,如(ru)图3-1(c)所示。适用垫(dian)(dian)片(pian)(pian)有:金(jin)属及(ji)非金(jin)属平垫(dian)(dian)、金(jin)属包垫(dian)(dian)、缠绕(rao)垫(dian)(dian)(基本型(xing))等。与凹凸(tu)面(mian)(mian)(mian)法兰一(yi)样(yang),榫槽面(mian)(mian)(mian)法兰在槽中(zhong)不(bu)会被挤(ji)出,压(ya)紧面(mian)(mian)(mian)积最小(xiao)(xiao)(只有平面(mian)(mian)(mian)法兰和凹凸(tu)面(mian)(mian)(mian)法兰的52~68%),垫(dian)(dian)片(pian)(pian)受力(li)均匀。由(you)于(yu)(yu)垫(dian)(dian)片(pian)(pian)与介(jie)质不(bu)直(zhi)接接触,介(jie)质腐蚀(shi)影(ying)响(xiang)和压(ya)力(li)机制的渗(shen)透影(ying)响(xiang)最小(xiao)(xiao),可(ke)用于(yu)(yu)高压(ya)、易燃、易爆(bao)、有毒介(jie)质等密(mi)(mi)(mi)封要求严(yan)格(ge)的场(chang)合。这种密(mi)(mi)(mi)封面(mian)(mian)(mian)垫(dian)(dian)片(pian)(pian)安装时对(dui)中(zhong)性(xing)好,该密(mi)(mi)(mi)封面(mian)(mian)(mian)加工和垫(dian)(dian)片(pian)(pian)更换较为困(kun)难。

4、其他密封面型式的法兰

  除(chu)以上三种密封面(mian)型式以外,还有采(cai)用(yong)梯(ti)形(xing)(xing)槽密封面(mian),以及配用(yong)O形(xing)(xing)环、透镜(jing)垫时的特(te)殊(shu)密封面(mian)型式。见图(tu)3-2。

  图3-2(a)为采用橡胶O形(xing)圈和金属中空O形(xing)环的密封(feng)面形(xing)式。

  图3-2(b)为(wei)梯形槽密封面,可配金(jin)属八角垫和椭(tuo)圆垫。

  图(tu)3-2(c)为透镜垫密封结构(gou),它用于高压管道的连接。

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