1. The structure of compressed packing喝現

Most compressed fillers use asbestos f黑弟ibers as the base material 制訊because of the properties of asbes東弟tos. It is basically not affected 開下by most media, tempera個她ture and time, and is a good heat con白物ductor.
(1) The disadvantage of 飛拿asbestos is poor lubricity, so lubrican問吧ts that do not hinder the perf那線ormance of asbestos must be added, su場來ch as graphite powder an市工d mica powder. Since this mixture is 醫也still permeable, liquid lubricant 水物must be added.
(2) PTFE has the smallest shrinkage ra為報te, the lowest shrinkag你小e rate, and has the characterist低遠ics of a small friction coeffici見新ent. It has high corrosion res如錢istance for most corrosive media. T看上he working temperature of the 見民PTFE filler at the filler; between -150村要-260℃. In this temperature 店師range, it is a high-performance, multi學黑-purpose valve stem packi但男ng.
(3) Flexible graphite has the charact舞報eristics of high temp門討erature resistance. It also has a low樹分 friction coefficient and 吃長is resistant to most corrosive media.身票 The working temperature at妹術 the packing can reach 600℃. Theref亮間ore, the valves at high temperature in 術多power stations, petrochemical depar來多tments, etc. use flexible graphite話事 filler.

2. The corrosion of the filler to t火女he stainless steel valve stem

Stainless steel valve s風慢tems, especially those made of chromi務飛um 13 series steel, are厭了 often corroded on the s司作urface in contact with the packing. Thi能飛s kind of corrosion ofte錯友n occurs in the storage stage before u身刀se, because the filler is saturated w也體ith water after the hydrostatic test. 你議If it is put into use immediatel女筆y after the hydraulic t生森est, it will not corrode. Theoretical我路ly speaking, the corrosion of the stain內亮less steel valve stem in the wet p木房acking is due to the fact that the 科內surface of the valve stem surro讀文unded by the packing is in a deoxidiz要朋ed environment. This environment 光站affects the activation and passi跳街vation properties of met唱關als. Many small anodes are produc媽會ed on the oxygen-deficient sensi志車tive points on the surface of th一下e stainless steel oxidati現票on protection layer. Together 新的with the large amount也美 of residual passive metal that has 水看an anodic effect, these anodes cause 和他the metal to function as a gal們空vanic cell. Graphite, whic習廠h is usually used in the filler, acts海美 as an anode material on the cathod照草e field of the valve s業離tem steel to enhance the curre報畫nt intensity of the 開吃galvanic cell, there有冷by greatly intensifying輛要 the corrosion of the 熱科original corrosion poi飛服nt.