Basic Mechanical Seals 密封基础知识
JC Tianjin Training
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What is a mechanical seal?
什么是机械密封？
two flat sliding surfaces, which maintain a close running clearance while separated by a fluid film
Must be:
present - beware dry running谨防干运转
Stable稳定

谨防磨损征兆 clean - beware abrasive wear symptoms reasonable viscosity合理的黏度 temperature controlled受控的温度 acceptable pressure允许的压力
Advantages 优点
sudden failure very unlikely 几乎不会突发意外事故 higher pressure capability - face not stressed
耐压性能高-应力变形小
wide choice of materials for all components
As the face moves forward to take up wear, the o-ring moves forward with the face, pushed by the hydraulic and spring pressures
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Secondary Seal: Pusher 二次密封：推进式
Sintered silicon carbide 无压烧结碳化硅 (277) Reaction silicon carbide 反应烧结碳化硅（088） Sintered silicon carbide with controlled porosity 微孔碳化硅 （584）

Tungsten Carbide 碳化钨
Secondary Seal
Tertiary Seal
Primary Seal
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Complete Seal一个完整密
封的例子
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定位螺丝
基础机械密封
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Wear here will create leakage 这里的磨损将导致泄漏
O-ring prevents leakage through the bore
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Basic Mechanical Seal
基础机械密封
Heat generated here 此处生热 Leak path
Gland 密封端盖
Primary Ring 补偿环
Mating Ring 配合环
Invisible Leakage: 不可见泄漏 Fluid Evaporates Upon Reaching Atmosphere 微量的泄漏在大气侧蒸发
Faces Run Dry And Overheat 没有润滑干运转导致过热
两个光滑平面之间维持着一个由流体膜隔开的微小间隙
rotating seal unit
stationary seal unit
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Seal 机械密封必须有的特征


Small axial clearance 小的轴向间隙 Self adjusting 自调节
Shaft Movement 轴的运动

O Ring O型圈
Pusher vs. Non-Pusher 推进式/非推进式
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
Tungsten Carbide 碳化钨 Cobalt bonded 钴基碳化钨（025） Nickel bonded 镍基碳化钨（005）
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Secondary Seal 二次密封
Three basic forms
三种基本形式
o-rings o型圈
Two groups
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Basic Mechanical Seal
基础机械密封
Spring or Spring Force
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Seat or Mating Ring
Face or Primary Ring
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Basic Mechanical Seal
基础机械密封
SPRING OR
SPRING FORCE Recirculation for cooling Gasket or O-ring SEAT
Pusher推进式
Sliding滑移
o-rings wedges
Non-pusher
Wedges 楔形环
Bellows 波纹管 Elastomer 橡胶的 Metal 金属的
Formed 成型的 edge welded 焊接的
非推进式
Bellows风箱
PTFE
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The Sealing Interface 密封面

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
Gland Packing v. Mechanical Seals 盘根和机械密封
不像一个机械密封而 不可见泄漏、机械密封


更像一个限制装置,需 要泄漏否则将会灼伤. 会磨损轴或轴套 高功耗用来克服磨擦 产品损失 需要大量的水 安装,维修和盘根调整 需要停车时间 泄漏导致设备破坏和
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Primary Seal – Face Flatness 主密封——平面
If faces not flat, contact generates heat Excessive wear - short life 1 light band = 0.0000116 inch or 0.0003 mm
Long-life 很长的寿命 Easy maintenance 容易检修 Low cost 低成本
Basic Mechanical Seal
基础机械密封
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Loose ring set screwed to the shaft 把一个有间隙的环用顶丝固定在轴上
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Basic Mechanical Seal
所有成分的材料选择广泛
field repairable可修复的
Disadvantages 缺点
静止件之间形成很薄的液膜
SPRING FORCE
FLUID PRESSURE
fluid film (3 - 5 microns)
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FILM REACTION
Primary Seal – Film Thickness 主密封——膜厚度
Faces lapped flat to within 1 - 3 light bands.
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Large component 大零件
Spring ensures automatic adjustment 弹簧确保自动调整
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Basic Mechanical Seal
基础机械密封
Recirculation for cooling
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Gasket or O-ring 垫片或者O型圈
Secondary Seal Tertiary Seal Primary Seal 三次密封 二次密封 主密封
resin impregnated 树脂浸渍 （171） antimony impregnated 金属锑浸渍 （218）

Carbon converted to Silicon Carbide 硅化石墨（121）
CVR 化学汽相反应硅化石墨 CVD 化学汽相沉积硅化石墨

Solid Silicon Carbide 碳化硅
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Elements 二次密封
Elastomeric Bellows 橡胶波纹管 Half Convolution 半波
Teflon Bellows 聚四氟乙烯 波纹管
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
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
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
Secondary Seal: Pusher 二次密封：推进式
O-Ring O型圈
Mating Ring 配合环
Shaft轴