efficient sealing of cooling water in mixing, milling and calendering operations. (process machinery).

by:Lepu     2019-11-09
In the rubber industry, precise control of temperature is an important part of the mixing, grinding and pressing operations to ensure the quality of production.
In the early days of the industry, the production manager used a crude oil concept called overflow boxes to control the temperature of the rollers.
In this method, water is injected into the roller using the inlet pipe through the journal end (figure 1).
Then, the water overflow is allowed to be exported to the drain outlet through the same log end.
Unfortunately, this approach is not able to maintain the surface roller temperature required for emerging industries. [
Figure 1 slightly]
In the 1900 s, a breakthrough called a rotary joint enabled the industry to use a closed pressurized system to accurately adjust the temperature.
The rotary joint also allows the use of steam as a heat source.
Before mixing, grinding or pressing, the steam is injected into the roller chamber to increase the temperature of the rubber.
Rotary Joint: from rope filler to carbon graphite seal, the first rotary joint is a simple packing gland consisting of rope filler compressed into the chamber, fixed by a spring or gland nut
A major drawback of these basic joints is the need for constant adjustment of wear and tear.
If the seal is too loose, the joint will leak.
If excessive tightening, the packaging material will be destroyed quickly due to overheating caused by friction.
Introduction of a new material
Carbon Graphite-
Led the development of the next generation of rotary joints in the 1940 s.
This new technology is called a pressure joint because it uses the pressure of the fluid rather than a mechanical device to create a tight seal and prevent leakage.
Unlike softer graphite materials, the new grade of carbon graphite can withstand high fluid pressure and provide excellent wear properties.
Carbon Graphite is also chemically compatible with many fluids, so its application in the rubber industry is diverse.
The base pressure rotary joint of the pressure rotary joint consists of one or two carbon bearings, a carbon graphite seal on a spherical sealing surface, and a spring that remains sealed at zero pressure (figure 2). [
Figure 2:
The spherical seal allows the fixing of the seal or the dislocation of the seat.
Carbon bearings require a running gap between the bearing and the rotary joint sleeve.
Due to this gap, the sealing seat contained in the housing is not perpendicular to the rotating center line and cannot be precisely aligned with the sealing surface.
The spherical surface of the seal, similar to the ball-
Socket arrangement, sliding to each other, to maintain full contact with the seat.
The balance ratio of most pressure rotary joints is 3. 0 or higher.
The sealing balance ratio is determined by taking the closing or clamping area and dividing it by the sealing surface or the opening area (figure 3).
As the fluid pressure increases, the sealing force increases dramatically, resulting in a torque curve that is highly dependent on the pressure (figure 4).
In order to prevent the hose from failing, a twist bar must be installed between the rotating joints to transfer the force from the hose. [
Figure 3, 4 slightly]
Since the fluid pressure is used to motivate the seal, the rotary pressure joint is self-
Wear adjustment.
However, the closure of the sealing surface is inconsistent.
At low fluid pressure, most of the closing force is provided by the spring, and it is not uncommon for a slight drop of water.
Conversely, high fluid pressure creates a high closing force, which increases friction and wear.
This wear is exacerbated by high-speed rotation.
The spherical sealing surface is made of two materials.
Common materials such as cast iron, bronze and steel can be processed economically and are suitable for steam, heat transfer and clean water applications.
In contaminated water applications, rust and scale can cause wear of softer materials, and it is recommended to use harder materials, which must be spherical grinding, which is an expensive operation.
Pressure rotary joints are designed for applications that require positive sealing between a fixed pipe and a continuous rotating machine.
Specific examples include heat transfer applications for steam and thermal fluid systems.
Dimensions of the rotary joint from 1/2 to 4, pressure to 250 psi, speed to 400 rpm, temperature to 600 [degrees]F.
The base mechanical rotary joint of the rotary joint consists of two seals, one is rotating and the other is stationary.
Fixed seals are fixed in place by pin or plane to prevent them from rotating, but at the same time allow the seals to move along the center line in an axial direction (figure 6).
The spring keeps the sealing surface in contact, o-
When the fixed seal slides in the axial direction, the ring seal prevents leakage. [
Figure 6 slightly]
There are three different types of rotary joints and rotary joints.
First, the rotary joint uses a ball bearing to keep the seal aligned precisely.
Ball bearings provide rigidity and support the thrust load generated by fluid pressure.
In the rotary joint, the spherical seal is the sealing element and the thrust bearing.
The second difference between the two seals is that the mechanical seal can be designed below-
Balance, the balance ratio is less than 1. 0.
The fluid pressure can be balanced by changing the geometry of the seal (figure 7). [
Figure 7 Slightly]
Finally, the balance reduces the surface shrinkage and torque.
Therefore, unlike the pressure seal (rotary joints)
Mechanical Seal (rotary unions)
No twist bars are needed.
When designing mechanical seals, the goal is to use a combination of three elements
Balance ratio, contact force and sealing geometry-
Develop a thin layer of fluid on the entire sealing surface width.
This layer of fluid as a fluid bearing improves sealing performance by further reducing torque and lubrication of the sealing surface.
In fact, the film developed in the rotary joint can reduce the torque by 12 times compared to the rotary joint.
The fluid film that separates the sealing surface may be only a few million inches thick, making minor changes to the sealing geometry that is critical to the performance of the rotary adapter (figure 5).
Due to the increased service life by separating the sealing surface with enough fluid film, the mechanical seal can be made from a wider range of materials.
Sealing designers can choose from harder materials such as bronze, iron, and hard alloys, rather than being limited to carbon graphite, alumina, and carborama like pressure seals.
Mechanical rotary joint designed for water
Especially for applications involving high speed rotation and fluid pressure.
Dimensions of the rotary joint from 3/8 to 4, pressure to 150 psi, speed to 3,500 rpm, temperature to 225 [degrees]F.
The design factors of the rotating joint in order to maintain the necessary fluid film layer, the rotating joint is carefully manufactured into strict tolerances.
For example, the sealing surface is the surface and the overlapping plane. 000033\" (0. 8 microns)
Or three helium bands.
This precision produces a certain degree of flatness, making the rotary joint leak
It is very tight under high pressure and low pressure.
In addition to strict manufacturing tolerances, the mechanical sealing surface must be kept flat in a constantly changing working environment of temperature and pressure.
If the fluid film is disturbed, the seal will run dry and the wear rate will increase.
For materials with self
Lubrication performance-
Such as carbon graphite-
This is not a major problem.
However, drying with hard surface materials can lead to catastrophic results.
In terms of maintaining the flatness of the sealing surface, the hard surface material is the first choice.
This is because they all have high elastic coefficients (
Prevent deformation of sealing surface)
Low thermal expansion value (
Minimize thermal deflection).
More importantly, the hard surface material is able to resist the wear caused by contaminants in the water, which is the main source of wear of the rotating joint.
The flatness of the sealing surface can also be achieved through design.
Most rotary joints are designed for the internal pressure of the fluid pressure inside the mechanical seal.
This design creates pressure and temperature deflection in the counter
Clockwise.
If the sum of these deflections is large enough, the film will be eliminated and face contact will occur at the inner diameter of the surface.
Instead, mechanical seals can be designed for external pressure.
In this design, the seal is mounted on the shaft facing the opposite direction.
The pressure on the seal deflates in a clockwise direction, while the temperature deflates in the opposite directionclockwise.
These opposite forces minimize the deflection of the sealing surface and maintain the thickness of the fluid film.
Rotating joint or rotating joint: due to modern design tools such as the finite element geometry used to develop the geometry of the optimal sealing surface, select the correct seal, the mechanical rotary joint is more technically advanced than the rotary joint.
For applications with high speed and high pressure, the rotating joint is the obvious choice.
In the rubber industry, water systems may not be able to filter, and mechanical seals made of hard surface materials have excellent resistance to grinding elements in most water sources.
For many applications, however, engineers still prefer rotating joints.
There are a variety of rotary joints and rotary joints on the market today, and it is often difficult to choose.
It is better to call on the service of the sealing application engineer of the local supplier to help match the proper sealing with the application at hand.
By analyzing the application and then matching it with the best sealing design and material selection, maximum performance and sealing life can be achieved.
Due to the choice of the wrong seal, most complaints about the short life of the seal will appear.
Often, problems can be corrected with simple changes and the performance of the rotating joint can be improved.
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