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机械密封基础知识(一)


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 sea

l?

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

O-ring prevents leakage through the bore O型圈防止通过间隙泄漏

机械密封的基本组成
Heat generated here Leak path

3
Large component

Spring ensures automatic adjustment 弹簧确保动环能够自动补偿

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

Primary Seal 主密封

Tertiary Seal 三次密封

机械密封的基本组成
Spring or Spring Force 弹簧

5
Seat or Mating Ring 静环或非补偿环

Face or Primary Ring 动环或补偿环

机械密封的基本组成
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 O-Ring O型圈

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

辅助密封

机械密封的结构
—主密封

主密封 Primary Seal
a thin film of liquid forms the primary (dynamic) seal between the rotating and stationary elements FILM REACTION

SPRING FORCE

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

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

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

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

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

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

Pump Housing 泵腔 No Fluid Or Dry Running 没有流体或者干运转 Gland 密封端盖

Primary Ring 补偿环

Mating Ring 非补偿环

稳定液膜

Stable Fluid Film

主密封-总结
? A mechanical seal is self-adjusting for wear

? 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
? 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

? 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

? Two groups ? Pusher推进式 ? sliding o-rings ? Wedges 楔形环 ? Non-pusher非推进式 ? bellows

? PTFE

二次密封元件Secondary Sealing Elements
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

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

二次密封:推进式

Secondary Seal: Pusher

As the face moves forward to take up wear, the o-ring moves forward with the face, pushed by the hydraulic and spring pressures

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

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
? 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 ~ +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

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 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
No contact here

Elastomer Bellows grips shaft tightly

二次密封:金属波纹管Secondary Seal: Metal Bellows

static o-ring 静止O型圈

二次密封:PTFE波纹管Secondary Seal: PTFE Bellows

Type 10T

Type 10R

机械密封的结构
—三次密封

三次密封 Tertiary Seal

三次密封 Tertiary Seal
? Prevents leakage round mating ring 偿环周围泄漏 ? Sometimes also prevents mating ring rotation 还起防转的作用 有时 防止通过非补

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 fibre

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 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 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

驱动机构的类型Types of Drive Mechanisms

?

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

Dent Drive 凹轮驱动

Key Drive 键驱动

Set Screw Drive 定位螺丝驱动

Pin Drive 销驱动

Snap Ring Drive 卡环驱动

Slot and Ear 缝和支耳

Elastomer Drive 橡胶驱动

Spring Drive 弹簧驱动

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

Carbon 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-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

B≥1为非平衡型机械密封,B<1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

Balance diameter 平衡直径

平衡比

Balance Ratio

Pressure = 10 kg/cm2 125% 0.8 cm2 1 cm2

50% 10

0

125% - 50% = 75% (7.5 bar)

75%

50% 10

0

75% - 50% = 25% (2.5 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。


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