Tag Archives: mechanical seals

Why are Mechanical Seals Still the Preferred Choice in the Process Industries?

The challenges facing process industries have changed although they continue to pump fluids, some hazardous or toxic. Safety and reliability are still of prime importance. However, operators increase speeds, pressures, flow rates and even the severity of the fluid characteristics (temperature, concentration, viscosity, etc.) while processing many batch operations. For the operators of petroleum refineries, gas processing facilities and petrochemical and chemical plants, safety means controlling and preventing loss of, or exposure to, the pumped fluids. Reliability means pumps that operate efficiently and economically, with less required maintenance.

picture of EagleBurgmann mechanical sealsA properly designed mechanical seal assures a pump operator of long-lasting, safe and reliable pump performance with a proven technology. Among multiple pieces of rotating equipment and a myriad of components, mechanical seals are proven to perform dependably under most types of operating conditions.

Pumps & Seals—A Good Fit

It is hard to believe that almost 30 years have passed since the mass promotion of sealless pump technology into the process industry. The new technology was promoted as the solution to all the issues and perceived limitations of mechanical seals. Some suggested that this alternative would eliminate the use of mechanical seals entirely.

However, not long after this promotion, end users learned that mechanical seals could meet or exceed legislated leakage and containment requirements. Further, pump manufacturers supported the technology by providing updated seal chambers to replace the old compression packing “stuffing boxes.”

Today’s seal chambers are designed specifically for mechanical seals, allowing for more robust technology in a cartridge platform, providing easier installation and creating an environment that allows the seals to function to their full potential.

Design Advancements

In the mid 1980s, new environmental regulations forced the industry not only to look at containment and emissions, but also at equipment reliability. The average mean time between repair (MTBR) for mechanical seals in a chemical plant was approximately 12 months. Today, the average MTBR is 30 months. Currently, the petroleum industry, subject to some of the most stringent emission levels, has an average MTBR of more than 60 months.

Mechanical seals maintained their reputation by demonstrating the ability to meet and even exceed the requirements of best available control technology (BACT). Further, they did so while remaining an economical and energy efficient technology available to meet emission and environmental regulations.

Computer programs allow seals to be modeled and prototyped prior to manufacturing to confirm how they will handle specific operating conditions before being installed in the field. Seal manufacturing design capabilities and the technology of seal face materials has progressed to the point that they can be developed for a one-to-one fit for a process application.

Today’s computer modeling programs and technology allow the use of 3-D design review, finite element analysis (FEA), computational fluid dynamics (CFD), rigid body analysis and thermal imaging diagnostic programs that were not readily available in the past or were too costly for frequent use with earlier 2-D drafting. These advancements in modeling techniques have added to the design reliability of mechanical seals.

These programs and technologies have led the way to the design of standard cartridge seals with much more robust components. These included the removal of springs and dynamic O-rings from the process fluid and made flexible stator technology the design of choice. Continue reading Why are Mechanical Seals Still the Preferred Choice in the Process Industries?

Spring Types and Materials in Sealing Systems

Springs are an integral part of all sealing systems. A simple air cylinder has O-rings to seal in the air, and the O-ring exhibits spring-like qualities to ensure a good seal over a broad temperature range.

But what are the different types of springs and materials in sealing systems? And how do you choose the best for your application?

image of metal spring types

Metal Springs

Metal springs, such as the Cantilever and Canted Coil spring, are used to energize polymers such as Teflon and ultra high molecular weight polyethylene (UHMW) to allow sealing in a wide range of temperatures. Selecting the correct spring material is critical to the life of the seal.

Metal energized seals are often subjected to a wide variety of fluids and temperature ranges, which then requires the correct material choice for the life of the seal in the application.

One of the earliest metal springs was the flat band or marcel expander, often made from common materials like 300 series Stainless Steel or heat treated 17-7 Stainless Steel.

These materials are often chosen for their tensile strength. But due to the cost to manufacture and the high volumes of spring required, these two expanders were often relegated to industrial or aerospace hydraulic systems.

If system fluids were not compatible with Stainless Steel, customers generally went to a different sealing system to avoid the high cost of short runs in these styles of energizers.

O-Rings cover a wide range of temperatures, and fluids, but generally not both. If there are multiple fluids involved, O-Rings often fail to provide compatibility over a range of fluids.

The use of Cantilever, Canted Coil or Helical coiled spring allowed for long runs and lower costs. The most common spring material is Stainless Steel, but these styles of spring lend themselves to materials that have a wide range of chemical and temperature range while maintaining tensile strength.

Alternative Spring Materials

Some of the more common alternative materials are Hastelloy and Elgiloy. While 17-7 is available, it’s seldom used because Elgiloy (while more expensive per pound) is often run at a higher volume, bringing the overall cost down making 17-7 less attractive due to cost.

Another style metal spring for polymers is the Garter spring. Garter springs are normally run on a per job basis, but because it’s made from wire, it can easily be wound from any material like Elgiloy or Stainless.

Garter springs are often used in rubber style lip seals, but we often find them coupled with polymer-style seals.

Mechanical Seals

Mechanical face seals typically marry a material with the fluids the seal will be running in. Mechanical seals have the overall body and internal springs made from specific materials capable of handling variations in temperature and fluids.

PEEK in Seals

Polymers are thought of as seal materials, but PEEK has been used as a spring in polymer-style seals. PEEK can be wound into helical style springs, and also formed into cantilever springs. As a Helical style, it can be wound into a diameter to energize Teflon or rubber lip seals.

If you consider radiation service, a PEEK spring makes an excellent choice keeping metals out of the seal.

How to Choose the Right Spring Material

While there are a variety of metals, often economics determine the practicality of specialty metals.

A consideration is reviewing the hardware used in the application as to what spring material is acceptable in an application. We often review what the customer is using in the rest of the service for determining a spring material.

Temperature is often a key factor in determining materials for spring. Elgiloy tends to do an excellent job in maintaining tensile strength at elevated temperatures.


The original article can be found on Eclipse Engineering’s website and was written by Cliff Goldstein.

Gallagher Fluid Seals is an authorized distributor of Eclipse engineering. For more information about choosing the right spring material for your application, contact our engineering department today.

DiamondFace by EagleBurgmann – Innovative Sealing Technology

What is DiamondFace Technology?

DiamondFace is an innovative microcrystalline diamond coating for mechanical seals. It is extremely hard and offers high wear protection, excellent heat conductivity, maximum chemical resistance and low friction. The coating adhesion also exceeds all known practical requirements. This increases the service life of mechanical seals several times over, the maintenance intervals are extended accordingly and the life cycle costs are greatly reduced.

DiamondFace Technology BenefitThe diamond thin-layer technology was developed in 2007 by EagleBurgmann together with the Fraunhofer Institute for Surface Engineering and Thin Films (IST), the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), Fraunhofer Institute for Mechanics of Materials (IWM), the Condias GmbH, and the Forschungszentrum Jülich. EagleBurgmann has established DiamondFace for mechanical seals as a series-produced product – the very first on the market.

The technology behind it is a microcrystalline diamond layer up to 15 μm thick which is applied to the seal face under vacuum at temperatures of 2,000 °C (3,632 °F) by chemical vapor deposition (CVD). The properties of this diamond layer are where you benefit. Primarily from its extreme hardness and robustness.

Increased Service Life of Mechanical Seals
Mechanical seals are a factor that has a decisive effect on the cost-effectiveness of your operation because their wear determines the productivity of the entire system, whether it is a pump, agitator or compressor. What causes damage to the seal faces? One reason is dry running which is often unavoidable due to insufficient lubrication or when gas-lubricated seal faces get in contact. The resulting temperature rise causes the seal to wear. And ultimately results in system downtimes.

EagleBurgmann has solved this problem which directly affects the success of your plant. Thanks to DiamondFace, the service life of mechanical seals is increased several times over, the maintenance intervals are extended accordingly and the life cycle costs are greatly reduced. The advantages for the operator are clear: Continue reading DiamondFace by EagleBurgmann – Innovative Sealing Technology

The Complete Guide for Mechanical Seals & API 682 4th Edition Piping Plans

Mechanical Seals & API 682 4th Edition

A sealing system, consisting of a mechanical seal and an associated supply system that is balanced by individual applications, is the utmost guarantee for a reliable sealing point and uninterrupted pump service. The performance of the seal is greatly influenced by the environment around the seal faces, making the provision of suitable, clean fluids as well as a moderate temperature an essential topic.

This guiding booklet provides a condensed overview of all piping plans established by the API 682 4th edition guidelines. Each illustrated piping plan is briefly described, and a recommendation that considers the media characteristics in terms of the relevant application and corresponding configurations is given to help you reliably select your sealing system. Furthermore, the content of this booklet has been enriched by providing clues – so-called ‘remarks and checkpoints’ – where EagleBurgmann shares the experiences gained from multiple equipped plants.

Sealing solutions to meet any requirement

Several factors play a major role when choosing the product, the product type, the materials used and how it is operated: process conditions at the sealing location, operating conditions and the medium to be sealed.

No matter what requirements our customers have, EagleBurgmann understands how these factors affect functionality and economic viability, and they translate this expertise into outstanding long-term, reliable sealing solutions. EagleBurgmann has all the expertise needed to manage and support the entire development, life and service cycle of its sealing solutions.

Plan 75 Piping Plan Example

EagleBurgmann and API 682

EagleBurgmann offers customers the widest product portfolio of seals and seal supply systems according to API 682 4th edition. The configurations listed for each individual piping plan are to be understood as recommendations including possible utilizations which may also be applied.

EagleBurgmann Profile

EagleBurgmann is one of the internationally leading companies for industrial sealing technology. Their products are used wherever safety and reliability are important: in the oil and gas industry, refining technology, the petrochemical, chemical and pharmaceutical industries, food processing, power, water, mining, pulp & paper and many others. More than 6,000 employees contribute their ideas, solutions and commitment towards ensuring that customers all over the world can rely on their seals and services. More than 21,000 EagleBurgmann API-seals and systems are installed world-wide.

The New Generation of Elastomer Bellows Seals: eMG and eMG1

Innovation in Detail: eMG and eMG1

Picture of eMG and eMG1With the latest generation of pump seals, eMG1 and eMG, EagleBurgmann has launched a further development of the million-fold proven MG1 on the market which can be used to seal, among other things, chemical pumps, water and waste water pumps, circulating pumps, and submersible motor pumps in numerous industrial sectors.

The eMG1 is 100 % compatible with the well-known MG1 standard seal. It has been innovated in detail and functionally expanded. The optimized geometry of this elastomer bellows seal was tested in long-term applications on EagleBurgmann test facilities and in practical use. A vastly reduced outer diameter of the bellows support now allows direct support by a retaining ring or with the use of much smaller spacer rings. The optimized bellows shape improves the automatic alignment of the bellows on the shaft and minimizes stick-slip effects. The characteristic innovative element is the profiled PEEK-PTFE disk which ensures consistent centering across the entire pressure operating range, exhibits outstanding sliding properties and safeguards the automatic alignment of the elastomer bellows in operation through continuous self-cleaning. The eMG1 is available in numerous material combinations. The program now includes the new face material eSiC-Q7, a powerful silicon carbide optimized towards friction and wear with hydrodynamic properties.

The eMG is identical in construction with the eMG1, but has a 20 % shorter installation length. This provides manufacturers with new opportunities in pump construction: e.g., a more compact design due to shorter shafts with the associated material savings and increased efficiency. The rotating unit is extremely space-saving. The computed pre-modelled bellows design and the spring assembly have no excess lengths and the outer diameter of the bellows support was reduced to a minimum. The standard stationary seat of the eMG is also the short-installation type G6 ring. Synthetic resin impregnated carbon graphite) (B) and the optimized silicon carbide eSIC-Q7 are the standard materials.

Features of the eMG1and eMG1:

  • For plain shafts
  • Elastomer bellows rotating
  • Unbalanced
  • Independent of direction of rotation
  • Single and dual seal

Advantages at a glance:

  • 100 % compatible with MG1 (eMG1)
  • 20 % shorter installation length (eMG)
  • Smaller outer diameter of bellows support enables direct retaining ring support, or smaller spacer rings
  • Optimal alignment characteristic through self-cleaning of disk/shaft
  • Improved centering across entire pressure operating range
  • Special bellows design protects the shaft across the entire seal length and the seal face during assembly
  • Dimensional adjustments and additional stationary seat geometries possible
Innovative face material: eSiC

The eMG1 and eMG can be supplied in numerous material combinations. The program now includes the new optimized face material eSic-Q7 series. A powerful face material optimized towards friction and wear with hydrodynamic properties.

In practice this means up to 50 % longer operating periods, expanded emergency running properties and reduced power consumption. Long-term tests performed at the customer‘s site confirm the efficiency.

picture of emg1 bellows sealThe Compatible One: eMG1

The latest eMG1 generation sets new standards again: an optimized seal design and innovative details guarantee maximum safety and reliability.

The new eMG1 is 100 % compatible with the proven MG1 and can be replaced one-to-one. This permits immediate use of all the advantages. Customized dimensional adjustments and additional stationary seat geometries are possible as option.

The Compact One: eMG

picture of emg bellows seal

The new eMG is unbeatable when it comes to compact seal installation spaces of pumps with consistent requirements. Even with a reduced installation length of 20 %, it has the same technical features as the eMG1.

The short installation length also opens new perspectives in the construction of new pumps. Standard seat of the eMG is type G6 – also very short in lengths.

Customized dimensional adjustments and additional stationary seat geometries are possible as option.

Operating range

  • Shaft diameter: d1 = 15 … 100 mm (0.59″ … 3.94″)
  • Pressure: p1 = 16 bar (230 PSI), vacuum … 0.5 bar (7.25 PSI), up to 1 bar (14.5 PSI) with seat locking
  • Temperature: t = -20 °C … +140 °C (-4 °F … +284 °F)
  • Sliding velocity: vg = 10 m/s (33 ft/s)
  • Admissible axial movement: ±2.0 mm

To Learn More about the eMG series of elastomer bellows seals, contact us today at 1-800-822-4063 or click the button below.

Contact Gallagher

Upgrade from Pump Packing to Mechanical Seals

Mechanical sealing conserves water, improves energy efficiency, and minimizes environmental impact

The environmental performance of products and processes in all industrial sectors increasingly is cause for critical inspection, with sustainability, conservation of natural resources, and reduced environmental contamination concerns influencing equipment design and selection.

Many industrial processes can be addressed to improve sustainability and minimize environmental impact, while at the same time maintaining or reducing operating costs. Implementing energy-efficient and environmentally friendly processes and technologies should be embraced as a priority at the component, process, and system levels.

One aspect of these processes is mission-critical rotating equipment, and specifically centrifugal pumps, which represent a significant proportion of the equipment found in industrial operations. One vital component of a centrifugal pump is the seal around the rotating shaft that passes through a stationary pressure casing or housing. The seal contains the liquid or gas from escaping to the environment.

Sealing systems help maintain acceptable pump efficiency, reliability, energy consumption, water usage, and emissions control. These factors can materially facilitate achieving total-life cycle cost-reduction and sustainability objectives. Sealing performance can be improved for centrifugal pump applications by upgrading from traditional compression packing to mechanical seal technology.

When sealing a centrifugal pump, the objective is to allow the rotating shaft to enter the wet area of the pump without large volumes of pressurized fluid escaping. The pump discharge pressure forces the fluid back behind the impeller, where it is induced to exit by way of the rotating drive shaft. To minimize leakage, a seal is needed between the shaft and pump housing to contain the pressure of the process being pumped and withstand friction caused by shaft rotation.

Compression packing is the traditional means to seal centrifugal pumps, going back more than 100 years. Also referred to as gland packing, it is a braided, rope-like, and lubricated material packed around the shaft in rings, physically stuffing the gap between the shaft and the pump housing, within a stuffing box.

Water leakage and consumption

Charred packingFor compression packing to work, some leakage must be maintained to lubricate and cool the packing material. Therefore, packing rings allow for an adjustable, close-clearance leak path parallel to the shaft axis. As the packing is used, however, some of the lubricant that is embedded into the packing is lost, reducing the packing ring’s volume. The pressure squeezing the rings together is also reduced, increasing leakage.

Periodic adjustment of the packing follower brings the pressure back into specification and controls the excess leakage. In today’s world, however, this maintenance is not always being done at required intervals or adjusted correctly. As the number of centrifugal pumps incorporating the use of compression packing decreases, training for and understanding of packing maintenance has waned.

Consequently, under-tightening and over-tightening of packing rings is a prevalent and growing misapplication of centrifugal pump maintenance, with critical consequences to both water consumption and energy draw.

Under-tightening results in too much leakage. Already, when properly adjusted, packing leakage can amount to gallons of liquid leaked per minute. This can be either aqueous solutions comprised of varied benign or caustic chemical compositions, or particles in suspension or slurry, depending on the process.

The heavier the suspension or slurry content in the pumped liquid, the more water is needed to get packing to work reliably. Typically, a clean external flush is piped into the stuffing box through a lantern ring, which keeps the packing lubricated and cool while flushing abrasives and chemicals.

Normally, some portion of the leakage is released continually into the atmosphere. Under-tightening of the packing rings and use of external flushes increase this atmospheric release proportionately, along with environmental impact potential. Continue reading Upgrade from Pump Packing to Mechanical Seals

Your Seal Pump Just Failed and Production is at a Stop… Now What?

Can your Facility Afford Extra Downtime?

Introducing the new CartexExpress Rapid Ship Program!

CartexExpress

Fast delivery for Cartex mechanical seals is available (if necessary) when an order is received by 12pm CST.


Not familiar with Cartex by EagleBurgmann?

Cartex Mechanical Seals are engineered to provide the extra margin of performance.

EagleBurgmann’s mechanical seals are designed with greater attention to functional details like tighter tolerances for more accurate seal operation, greater axial movement to handle pump shaft movement, seal parts with robust cross sections for optimal seal stability in operation, and castings that meet ASTM A 351/351M standards for proven quality.

cartex mechanical sealHighlights and Advantages of Cartex

  • Ideal for use in ANSI process pumps
  • Universally applicable for packings conversions, retrofits or original equipment
  • Ideal seal for standardizations
  • No dimensional modification of the seal chamber necessary, small radial installation height
  • No damage to the shaft by dynamically loaded o-ring
  • Extended service life
  • Installation faults are avoided, cost-effective
  • No damage caused by dirt entered during assembly
  • Straight-forward and easy installation due to pre-assembled unit (reduced downtimes)

Recommended Applications

Cartex Seals are designed with greater attention to functional details like tighter tolerances for more accurate seal operation, greater axial movement to handle pump shaft movement, seal parts with robust cross sections for optimal seal stability in operation and castings that meet ASTM A 351/351M standards for proven quality.

  • Process, petrochemical, chemical, pharmaceutical, power plant, pulp and paper, water and waste water, mining, food and beverage, universally applicable, ANSI process pumps

Cartex Seal High-Performance Materials

cartex materials


So, Which Cartex Seals are Included in the Express Program?

  • Single seals
    • -ASTN and -ABTN
  • Dual seals
    • -ASDN and -ABDN

cartex express single and dual seals

Comparison With Competition: Part vs Part

Cartex seal faces, o-rings, drive pins and spring are more robust and
specifically engineered for superior strength, heat removal and maximum reliability and performance vs. competing modular seals.

  • Robust engineered design – Less sensitive
  • Fewer o-rings and components – Reduced possible leakage paths
  • High-performance pumping feature – Lower operating temperatures

cartex vs modular


So the next time your production is suddenly at a stop or you have unplanned issues and need a mechanical seal fast – contact Gallagher Fluid Seals and ask about the CartexExpress program.

Contact Gallagher

Gallagher to Partner with EagleBurgmann

Gallagher Fluid Seals, Inc. Awarded Exclusive Distribution Rights with EagleBurgmann

Partnership will expand Gallagher’s OEM and MRO business into the mechanical sealing industry

Gallagher Fluid Seals, Inc. has exciting news for its customers. EagleBurgmann, a leading provider of industrial sealing technology, has awarded Gallagher Fluid Seals with exclusive distribution rights in the Northeast and Mid-Atlantic territory of the United States. The territory includes Maine, Vermont, Massachusetts, Connecticut, New Hampshire, Rhode Island, New York, New Jersey, Pennsylvania, Delaware, Maryland, Washington D.C., and Virginia.

picture of gallagher and eagleburgmann map

2019 marks 63-years in business for Gallagher. As the global sealing landscape has continued to evolve since 1956, so has Gallagher. New technology brings new sealing challenges, and that has allowed the expansion of new areas of expertise and growth – enter mechanical sealing.

EagleBurgmann has a wide array of product lines, including: mechanical seals, carbon floating ring seals, and magnetic couplings. Gallagher is focusing strictly on mechanical sealing products from EagleBurgmann, which include: Cartex Cartridge Seals, SeccoMix 1, H75VN, Splitex® Cartridge Split Seals, Unitex, MBS682 Metal Bellows Seal, and much more.

“We are thrilled to have this new partnership with EagleBurgmann,” says Chris Gallagher, CEO of Gallagher Fluid Seals. “EagleBurgmann’s gold-standard level of service, quality, and support will allow us to enter this new market both efficiently and effectively.”

With Gallagher account executives located throughout the Northeast & Mid-Atlantic, and a team of experienced full-time mechanical engineers on staff, customers can expect prompt service and custom sealing solutions if their application requires it.

This new partnership is an exciting start to 2019, and Gallagher will continue in its mission to work with customers whose sealing applications are critical to the performance of their equipment.

Want to speak with an engineer or account executive? Contact us today:

button saying contact gallager

 

 


About Gallagher Fluid Seals, Inc.

Gallagher Fluid Seals, Inc. is a global distributor and manufacturer of Fluid Sealing products. Gallagher represents the strongest seal manufacturers in the world, in addition to operating its own gasket fabrication facility. Gallagher serves both OEM & MRO customers through the development of technical solutions that solve sealing challenges.

Gallagher Fluid Seals currently operates 3 Facilities; its headquarters in King of Prussia Pennsylvania, and it’s 40,000 square foot gasket fabrication and sales office in East Longmeadow, Massachusetts, and the newly-acquired Quality Seals office in Bethel, Connecticut.

Contact:
Kevin Patton
Marketing & Communications Analyst
610-277-8200

 

About EagleBurgmann

EagleBurgmann is one of the leading providers of industrial sealing technology on the international stage. Their products and comprehensive services are used wherever the key requirements are reliability and safety.

Excellent quality, close proximity to their customers, great capacity for innovation and an extensive product portfolio for nearly all industrial processes and fields of application are what make them stand out.

Their portfolio includes mechanical seals and seal supply systems, magnetic couplings, carbon floating ring seals, expansion joints and gaskets, packings, special products and extensive services. Being part of the German Freudenberg and Japanese EKK group gives EagleBurgmann all the resources they need for a reliable partnership built on solid foundations. Worldwide.

Contact:
Ekaterina Shkarbul
Marketing Manager BA Americas

A Guide to Elastomer Technology in Mechanical Seals

Elastomer Technology in Mechanical Seals

Evaluate properties of rubber during installation and seal life.

Elastomers (or rubbers) are a ubiquitous family of materials whose use stretches across nearly the entire range of mechanical seal designs.  From plant-sourced natural rubber, so named by John Priestly in 1770 for its utility in rubbing away pencil graphite, to petroleum-sourced synthetic rubber first developed around the turn of the 20th century, the “elastomer” and their properties are familiar but should not be overlooked—especially when dealing with mechanical seals.

How Elastomers Work in Mechanical Seals

Rubber seals come in a variety of profiles—O-rings, cup gaskets, bellows diaphragms, sealing/wiper lips and many others. They are classified as either static or dynamic and create positive pressure
against surfaces to eliminate or control the leakage of liquids and/or gases while preventing the entrance of external contaminants such as dust and dirt. Static sealing occurs between adjacent surfaces with no relative motion, such as between the pump casing and cover. Due to frictional wear and heat generation, dynamic sealing is less straightforward, occurring between adjacent surfaces that are continuously or intermittently moving relative to another, such as between the pump casing and shaft.

In mechanical face seals, elastomers tend to take second chair because the primary seal—the dynamic seal between the housing and rotating shaft—is achieved by sliding contact between the pair of stiffer, lapped-flat sealing faces, one stationary in the housing and one rotating with the shaft. In many designs, rubber provides the secondary seal between each seal face and adjacent surface. One seal face is fixed and sealed statically using an O-ring or cup gasket. The other is spring-loaded and requires a semi-dynamic seal to accommodate some axial play, such as a dynamic O-ring in pusher-type mechanical face seals or elastomeric bellows in nonpusher ones. These semi-dynamic applications (involving flexing and sliding of the elastomer) can be critical for maintaining proper contact between the faces through face wear, shaft movement, etc.

Although the seal face pair tends to be the most critical design feature, mechanical face seals are  often used in the most demanding applications.

Rubber technology features prominently in radial lip seals, where typical applications have lower pressurevelocity (PV) values relative to those involving mechanical face seals. Still, the flexible elastomer lip must handle considerable relative motion in the form of shaft/bore rotation, reciprocation or a combination of both. In addition to standard designs and sizes, numerous customizations and proprietary approaches exist. The simplest designs rely on a single rubber lip’s inherent resiliency, although common enhancements include multiple sealing lips, a circumferential garter spring installed in a groove over the sealing lip to maintain contact with the shaft, and an auxiliary wiper lip or “excluder” to prevent abrasive dust or debris from compromising the primary sealing surface. For improving service life and performance in rotary applications, unidirectional or bidirectional hydrodynamic pumping aids can be added in the form of custom-shaped extrusions on the backside of the sealing lip to return leaked fluid to the sealing interface, increase lip lubrication and lower operating temperatures.

Diagram of secondary, dynamic elastomeric seals in mechanical face seals.

Benefits of Rubber

The definition of an elastomer provides initial insight into where rubber gets its resilient sealing quality: “a macromolecular material which, in the vulcanized state and at room temperature, can be stretched repeatedly to at least twice its original length and which, upon release of the stress, will immediately return to approximately its original length.”

When the rubber is squeezed by the adjacent surfaces of the clearance gap to be sealed, it has the characteristic
properties of malleably deforming and taking the shape of each  surface in response to the stress and applying a force back against the surfaces in its attempt to return to its original dimensions. Elastomers consist of large molecules called polymers (from the Greek “poly” meaning “many” and “meros” meaning “parts”), which are long chains of the same or different repeating units, called monomers, usually linked together by carbon-carbon bonds (the
most notable exception being silicone elastomers, which are linked by silicon-oxygen bonds). Soft and hard plastics are also composed of polymers. However, the regularity of the monomers in their polymer chains allows neighboring segments to align and form crystals, making the macromolecular plastic material rigid and inelastic.

One can prevent this crystallization by breaking up the regularity of the polymer chain, resulting usually in a viscous “gum” that is readily shaped into molds. At the molecular level, the polymer chains are similar to spaghetti-like strands flowing past each other.

During the process of vulcanization, Representatin of three polymer chains after formation of crosslinking via vulcanizationor curing, the viscous liquid is heated with sulfur or peroxides and other vulcanizing agents, and crosslinks form between polymer chains, tying them together with chemical bonds, converting the gum into an elastic, thermoset solid rubber that retains its shape after moderate deformation.

In addition to the selection and preparation of base polymer(s) and cure system ingredients, formulating the final rubber product, also known as compounding, involves five other broad categories of ingredients, which have percentage compositions expressed in parts per hundred rubber (phr). Fillers include various powders that thicken the polymer mixture, improve strength and resistance to abrasives, and reduce final cost. Plasticizers are oils and other liquid hydrocarbons that lower viscosity to ease processing, soften the final compound and in some cases improve low temperature performance. Process aids are specialized chemicals added in low concentrations to improve mixing, flow properties and final appearance.

Antidegradants protect the rubber from environmental attack. Finally, various miscellaneous ingredients may be added for special purposes, including foaming agents, dyes, fungicides, flame
retardants, abrasives, lubricants and electrically conductive particles. A simplified description of processing these ingredients includes mixing via tangential or intermeshing mixers, forming into desired shapes and vulcanizing into the final product.

Continue reading A Guide to Elastomer Technology in Mechanical Seals