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，寿命短
1 light band = 0.0003 mm 1光带=0.0003mm
没有润滑干运转导致过热
Without Lubrication, Faces Run Dry And Overheat
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
密封腔
机械密封
什么是机械密封？
What is a mechanical seal?
two flat sliding surfaces, which maintain a close running clearance while separated by a fluid film
rotating seal unit
stationary seal unit
机械密封的结构
机械密封的基本组成
1
Loose ring set screwed to the shaft 动环靠紧钉螺钉传动与轴一起旋转
机械密封的基本组成
2
Wear here will create leakage 端面磨损会产生泄漏
推进式/非推进式 Pusher vs. Non-Pusher
Pusher 推进式
vs.
Non-Pusher 非推进式
O-ring secondary seal must slide along shaft as seal 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
Magnified Surface A 放大面
Separation 分离面 Lubricant 润滑剂 Heat 热量
Magnified Surface B 放大面
流体在两个面之间充当润滑剂的过程
Process Fluid Acts as Lubricant Between Faces
Pump Housing 泵腔 Process Fluid 工艺流体
• maximum temperature ~ +260°C
推进式密封：卡滞 Pusher Seal: Hang-up
An external quench will prevent hang-up 外部冲洗可 以避免卡滞
Product leakage solidifies / crystallises / polymerises Prevents o-ring 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
Gland 密封端盖
Primary Ring 补偿环
Mating Ring 非补偿环
Invisible Leakage: 不可见泄漏 Fluid Evaporates Upon Reaching Atmosphere 微量的泄漏在大气侧蒸发
主密封－平面Primary Seal – Face Flatness
二次密封：推进式
Advantages
Secondary Seal: Pusher
• sudden failure very unlikely • higher pressure capability - face not stressed
• wide choice of materials for all components
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
The liquid film between the primary ring & mating ring is only 0.5 - 3.0 microns thick There are three main sealing areas :• Primary Seal - Primary Ring & Mating Ring • Secondary Seal - Primary Ring & Shaft
Has three main parts :• Primary 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
主密封－膜厚度Primary Seal – Film Thickness
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
Fluid film thickness is very important膜厚很重要 • too 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
Mating Ring 非补偿环
Shaft轴
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 5. Auxiliary components to complete seal
FLUID PRESSURE
fluid film (3 - 5 microns)
主密封 Primary Seal
Face or Primary Ring Seat or Mating Ring
Springs
- Higher pressure on outside diameter - Higher pressure holds faces closed - Fluid is forced between faces to lubricate - Springs keep faces closed when no pressure
二次密封：推进式
Secondary Seal: Pusher
Positive drive
Optimised cooling flow
Compact multiple springs
Optimised face design
Typical pusher seal - low emission duties 典型的推进式密封
主密封－膜厚度Primary Seal – Film Thickness
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
机械密封的基本组成
Recirculation for cooling 冷却循环
4
Gasket or O-ring 垫片或O型圈
Secondary Seal 二次密封
Pr密封
机械密封的基本组成
Spring or Spring Force 弹簧
• 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
• field repairable Disadvantages
• hang-up (not likely where o-ring is well isolated)