机械密封的腐蚀类型与防护方法
<P><FONT size=2> </FONT></P><P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT size=2>机械密封出现损坏的情况较多，常见的损坏形式主要有腐蚀损坏、热损坏和机械损坏。其中腐蚀损坏危害性较大，由于机械密封特殊的结构形式及工作环境和条件不同，腐蚀损坏的形态也多种多样。</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN lang=EN-US><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21.1pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><B style="mso-bidi-font-weight: normal"><FONT size=2><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">机械密封的腐蚀</SPAN><SPAN lang=EN-US><o:p></o:p></SPAN></FONT></B></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21.1pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><B style="mso-bidi-font-weight: normal"><SPAN lang=EN-US><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></B></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT size=2>一、金属环腐蚀</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN lang=EN-US><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT size=2>第一，表面均匀腐蚀。如果金属环表面接触腐蚀介质，而金属本身又不耐腐蚀，就会产生表面腐蚀，其现象是泄漏、早期磨损、破坏、发声等。金属表面均匀腐蚀有成膜和无膜两种形态，无膜的金属腐蚀很危险，腐蚀过程以一定的速度进行，这主要是选材错误造成的。成膜的腐蚀，其钝化膜通常具有保护作用的特性，但金属密封环所用的材料，如不锈钢、钴、铬合金等其表面的钝化膜在端面磨擦中破坏，在缺氧条件下新膜很难生成，使电偶腐蚀加剧。</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN lang=EN-US><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT size=2>第二，应力腐蚀破裂。金属在腐蚀和拉应力的同时作用下，首先在薄弱区产生裂缝，进而向纵深发展，产生破裂，称为应力腐蚀破裂，选用堆焊硬质合金及铸铁、碳化钨、碳化钛等密封环，容易出现应力腐蚀破裂。密封环裂纹一般是径向发散型的，可以是一条或多条。这些裂缝沟通了整个密封端面，加速了端面的磨损，使泄漏量增加。</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN lang=EN-US><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT size=2>二、非金属环腐蚀</FONT></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN lang=EN-US><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><FONT size=2><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">第一，石墨环腐蚀。用树脂浸渍的不透性石墨环，它的腐蚀有三个原因：一是当端面过热，温度大于</SPAN><SPAN lang=EN-US><FONT face="Times New Roman">180oC</FONT></SPAN><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">时，浸渍的树脂要折离石墨环，使环耐磨性下降；二是浸渍的树脂若选择不当，就会在介质中发生化学变化，也使耐磨性下降；三是树脂浸渍深度不够，当磨去浸渍层后，耐磨性下降。所以密封冷却系统的建立，选择耐蚀的浸渍树脂，采用高压浸渍，增加浸渍深度是非常必要的。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN lang=EN-US><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><FONT size=2><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">第二，石墨环的氧化。在氧化性的介质中，端面在干摩擦或冷却不良时，产生</SPAN><SPAN lang=EN-US><FONT face="Times New Roman">350</FONT></SPAN><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">～</SPAN><SPAN lang=EN-US><FONT face="Times New Roman">40o</FONT></SPAN><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">℃的温度能使石墨环与氧发生反应，产生</SPAN><SPAN lang=EN-US><FONT face="Times New Roman">CO</FONT></SPAN><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，气体，可使端面变粗糙，甚至破裂。非金属环在化学介质和应力的同时作用下，也会破裂。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><SPAN lang=EN-US><o:p><FONT face="Times New Roman" size=2> </FONT></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0cm 21pt 0pt 0cm; TEXT-INDENT: 21pt; mso-para-margin-right: 2.0gd; mso-char-indent-count: 2.0"><FONT size=2><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">第三，聚四氟乙烯</SPAN><SPAN lang=EN-US><FONT face="Times New Roman">(F4)</FONT></SPAN><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">密封环的腐蚀。</SPAN><SPAN lang=EN-US><FONT face="Times New Roman">F4</FONT></SPAN><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">填充如玻璃纤维、石墨粉、金属粉等以提高其耐温性、耐磨性。填充</SPAN><SPAN lang=EN-US><FONT face="Times New Roman">F4</FONT></SPAN><SPAN style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">环的腐蚀主要是指填充的选择性腐蚀、溶出或变质破坏。例如在氢氟酸中，玻璃纤维分子热腐蚀，所以填充何物应视具体情况而定。</SPAN></FONT></P>
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