1、2007新进员工技术培训资料之三,机械密封基础知识（一）,主要内容,机械密封的典型结构、组成部分 机械密封的布置方式,离心泵结构,rotating seal unit,two flat sliding surfaces, which maintain a close running clearance while separated by a fluid film,stationary seal unit,什么是机械密封？ What is a mechanical seal?,机械密封的结构,机械密封的基本组成,Loose ring set screwed to the shaft 动环靠紧钉
2、螺钉传动与轴一起旋转,1,机械密封的基本组成,O-ring prevents leakage through the bore O型圈防止通过间隙泄漏,2,机械密封的基本组成,Spring ensures automatic adjustment 弹簧确保动环能够自动补偿,3,机械密封的基本组成,4,机械密封的基本组成,5,机械密封的基本组成,O-Ring O型圈,Shaft轴,Mating Ring 非补偿环,Primary Ring补偿环,Snap Ring卡环,Anti-X Ring 挡环,O-Ring O型圈,Disk推环,Springs弹簧,Retainer传动套,Set Screw
3、定位螺丝,机械密封的基本组成：小结,机械密封由以下部分组成： 1. A wearable, stationary, primary sealing element一个耐磨,静止的密封件 2. A wearable, rotating, primary sealing element一个耐磨,旋转的密封件 3. A secondary sealing element二次密封 4. A mechanical loading device to press primary sealing elements 1 and 2 against one another, and使件1和件2相互贴合的机械装置
4、 5. Auxiliary components to complete seal辅助密封,机械密封的结构主密封,主密封 Primary Seal,SPRING FORCEFLUID PRESSURE,fluid film (3 - 5 microns),a thin film of liquid forms the primary (dynamic) seal between the rotating and stationary elements,FILM REACTION,主密封 Primary Seal,- Higher pressure on outside diameter - H
5、igher pressure holds faces closed - Fluid is forced between faces to lubricate - Springs keep faces closed when no pressure,Faces lapped flat to within 1 - 3 light bands. 密封面研磨后平面度1-3个光带,主密封膜厚度Primary Seal Film Thickness,主密封膜厚度Primary Seal Film Thickness,Fluid film thickness is very important膜厚很重要 t
6、oo thin - wear, causing early seal failure 太薄磨损，早期失效 too thick - visible leakage 太厚泄漏量大 Must be:必须： present - beware dry running 存在避免干运转 stable 稳定 clean - beware abrasive wear symptoms 干净避免磨粒磨损 reasonable viscosity 合理的黏度 temperature controlled 控制温度 acceptable pressure 压力可以接受,主密封膜厚度Primary Seal Film
7、Thickness,Lubricant 润滑剂,Separation分离面,Magnified Surface A 放大面,Magnified Surface B 放大面,Heat 热量,密封面 The Sealing Interface,Lubrication Purpose: 润滑目的 Separate surfaces 分离两个面 Prevent contact of high surface points 防止出现面接触 Reduce friction/heat generation 减少摩擦/生热,流体在两个面之间充当润滑剂的过程 Process Fluid Acts as Lubr
8、icant Between Faces,Gland 密封端盖,Pump Housing 泵腔,Process Fluid 工艺流体,Invisible Leakage: 不可见泄漏 Fluid Evaporates Upon Reaching Atmosphere 微量的泄漏在大气侧蒸发,Primary Ring 补偿环,Mating Ring 非补偿环,主密封平面Primary Seal Face Flatness,If faces not flat, contact generates heat Excessive wear - short life 如果密封面不平，摩擦生热，过度磨损，寿
9、命短,1 light band = 0.0003 mm 1光带=0.0003mm,Gland 密封端盖,Pump Housing 泵腔,No Fluid Or Dry Running 没有流体或者干运转,Primary Ring 补偿环,Mating Ring 非补偿环,没有润滑干运转导致过热 Without Lubrication, Faces Run Dry And Overheat,稳定液膜 Stable Fluid Film,主密封总结,A mechanical seal is self-adjusting for wear Has three main parts :- Primar
10、y Ring (narrower running face) Mating Ring (wider running face - harder) Spring Force Usually the mating ring is stationary & the primary ring rotates with the shaft The liquid film between the primary ring & mating ring is only 0.5 - 3.0 microns thick There are three main sealing areas :- Primary S
11、eal - Primary Ring & Mating Ring Secondary Seal - Primary Ring & Shaft Tertiary Seal - Mating Ring & Housing,机械密封的结构二次密封,二次密封 Secondary Seal,二次密封 Secondary Seal,Three basic forms o-rings wedges bellows elastomer metal formed 冲压成型 edge welded 焊接 PTFE,Two groups Pusher推进式 sliding o-rings Wedges 楔形环 No
12、n-pusher非推进式 bellows,Teflon Bellows 聚四氟乙烯波纹管,Elastomeric Bellows 橡胶波纹管,Half Convolution 半波,Welded Metal Bellows 焊接金属波纹管,V Rings V型圈,U Cup 杯型,Wedge 楔形,Encapsulated O Ring 包覆 O型圈,O Ring O型圈,二次密封元件Secondary Sealing Elements,Pusher 推进式,Non-Pusher 非推进式,O-ring secondary seal must slide along shaft as seal
13、 face wears O型圈二次密封在密封面磨损的时候必须能够沿轴滑动,Bellows secondary seal expands to accommodate face wear. Bellows tail is stationary against shaft. 波纹管伸长能够补偿密封面磨损,波纹管尾部与轴保持静止,vs.,推进式/非推进式 Pusher vs. Non-Pusher,二次密封：推进式 Secondary Seal: Pusher,As the face moves forward to take up wear, the o-ring moves forward wi
14、th the face, pushed by the hydraulic and spring pressures,二次密封：推进式 Secondary Seal: Pusher,Typical pusher seal - low emission duties 典型的推进式密封,二次密封：推进式 Secondary Seal: Pusher,Advantages sudden failure very unlikely higher pressure capability - face not stressed wide choice of materials for all compone
15、nts field repairable Disadvantages hang-up (not likely where o-ring is well isolated) permanent set / pressure problems (cause hang-up) excellent shaft surface finish required maximum temperature +260C,推进式密封：卡滞 Pusher Seal: Hang-up,Product leakage solidifies / crystallises / polymerises Prevents o-r
16、ing pushing forward - leakage increases 泄漏的介质凝固/结晶/聚合阻止O型圈移动，造成泄漏增加,An external quench will prevent hang-up 外部冲洗可以避免卡滞,二次密封：O型圈 Secondary Seal: O-Ring,二次密封：楔形环 Secondary Seal: Wedge,二次密封：非推进式 Secondary Seal: Non-Pusher,Bellows flexes to take up wear, misalignment and axial play 波纹管伸缩弯曲，补偿磨损，不对中和轴向跳动
17、,Fine machined shaft surface required Do not use a good lubricant - never use silicon grease 对轴表面光洁度要求高，不能使用润滑剂,二次密封：波纹管 Secondary Seal: Bellows,二次密封：金属波纹管Secondary Seal: Metal Bellows,static o-ring 静止O型圈,Type 10T,Type 10R,二次密封：PTFE波纹管Secondary Seal: PTFE Bellows,机械密封的结构三次密封,三次密封 Tertiary Seal,三次密封
18、Tertiary Seal,Prevents leakage round mating ring 防止通过非补偿环周围泄漏 Sometimes also prevents mating ring rotation 有时还起防转的作用,三次密封 Tertiary Seal,Four basic types 4种基本形式 O-rings elastomers Seat Rings (square or rectangular section) PTFE graphite Cup Rings elastomers Gaskets or Flat Joints PTFE compressed fibr
19、e,三次密封：O型圈 Tertiary Seal: O-ring,三次密封：O型圈 Tertiary Seal: O-ring,三次密封：O型圈 Tertiary Seal: O-ring,三次密封：方形环Tertiary Seal: Seat Ring,三次密封：杯形环 Tertiary Seal: Cup Rubber,三次密封：垫片Tertiary Seal: Gasket,三次密封：垫片Tertiary Seal: Gasket,三次密封：端盖Tertiary Seal: Cover/Gland Plate,机械密封的结构弹簧,设计特点 Design Features,Springs
20、弹簧 Provide The Initial Closing Force提供初始闭合力 Are Very Important At Low Pressures低压下很重要 Are Not So Important At High Pressures高压下不重要,设计特点 Design Features,Springs 弹簧 Single 单弹簧 Multiple 多弹簧 Bellows 波纹管 Wave 波形,设计特点 Design Features,Springs 弹簧 High Speed Seals Use Stationary Springs (5000 ft/min Typical
21、Break Point) 高速机械密封使用静止弹簧(5000ft/min 典型的分界点),机械密封的结构传动机构,Drive Mechanism 驱动机构 Must Transmit Torque 必须能够传递转距 Must Allow Axial Movement (Primary Ring) 必须能够使动环轴向运动,驱动机构的类型Types of Drive Mechanisms,Pin Drive 销驱动,Dent Drive 凹轮驱动,Slot and Ear 缝和支耳,Spring Drive弹簧驱动,Set Screw Drive 定位螺丝驱动,Snap Ring Drive 卡环
22、驱动,Elastomer Drive 橡胶驱动,Key Drive 键驱动,驱动机构的类型Types of Drive Mechanisms,机械密封的主要材料,主密封材料 Primary Seal Materials,Face (Primary Ring-Narrow) Materials Carbon-graphite 碳石墨 resin impregnated 浸树脂 antimony impregnated浸锑 Carbon converted to Silicon Carbide resin impregnated,主密封材料 Primary Seal Materials,Carbo
23、n converted to Silicon Carbide,主密封材料 Primary Seal Materials,Seat (Mating Ring) Materials Ni-resist high nickel cast iron; austenitic cast iron高镍铸铁，奥氏体铸铁 Ceramic 陶瓷材料 99.7% aluminium oxide氧化铝,主密封材料 Primary Seal Materials,ceramic mating ring,主密封材料 Primary Seal Materials,Seat (Mating Ring) Materials Ni
24、-resist high nickel cast iron; austenitic cast iron Ceramic 99.7% aluminium oxide,Silicon Carbide 碳化硅 pure sintered or reaction bonded无压烧结或反应烧结 Tungsten Carbide 碳化钨 cobalt or nickel-bonded 钴基或镍基,平衡比,平衡比 Balance Ratio,平衡比也称为面积比，指的是机械密封的流体压力作用的有效面积与密封面名义接触面积之比。平衡比的大小反映机械密封的流体压力作用载荷的大小。平衡比B=Af/Ah,B1为非平
25、衡型机械密封，B1为平衡型机械密封。,平衡比 Balance Ratio,平衡比 Balance Ratio,平衡比 Balance Ratio,平衡比 Balance Ratio,平衡比 Balance Ratio,Balance Ratio 平衡比,平衡比 Balance Ratio,1 cm2,0.8 cm2,Pressure = 10 kg/cm2,125%,10,0,50%,125% - 50% = 75% (7.5 bar),平衡比 Balance Ratio,Metal bellows Seals are INHERENTLY balanced 金属波纹管密封固有的平衡型密封,平
26、衡比平衡型机械密封的优点,Reduced heat generation 减少热量生成 ideal for unstable and low SG fluids 对不稳定的和低密度的液体是比较理想的 less heat to be dissipated - less cooling required 产生的热量少，需要冷却的也少 Reduced wear rate 降低磨损速度 longer life 延长使用周期 Reduced power required to drive the seal降低能耗 lower running costs 减少运行成本 Increased pressure range for the seal 增大密封压力范围 this simple modification allows much higher pressures to be sealed 这些简单的改变允许大的压力,思考题,1。指出典型机械密封的构成？ 2。机械密封有几个密封点？ 3。说出密封面润滑的目的。 4。说出密封面流体膜厚与泄漏量的关系。 5。指出旋转式弹簧与静止式弹簧的使用场合。 6。指出密封面硬环与软环常用材料。 7。说出对机械密封驱动机构的要求，指出常用的两种驱动机构形式。 8。指出二次密封和三次密封O形圈的区别。 9。解释机械密封中平衡比的概念。,
