Elastomers
- February 07, 2019
Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.
Original content can be found on Parker’s Blog.
You’ve probably heard a bit about microwave absorbers and how they are used to reduce or absorb the energy that is present in a microwave. But what are they exactly? And how do they work? Go ahead, read on.
What are microwave absorbers?
Simply put, microwave absorbers are special materials, often elastomer or rubber based, which are designed to offer a user-friendly approach to the reduction of unwanted electromagnetic radiation from electronic equipment. They also work well to minimize cavity to cavity cross-coupling, and microwave cavity resonances. When comprised of a silicone elastomer matrix with ferrous filler material, microwave absorbers provide RF absorption performance over a broadband frequency range from 500 MHz to 18 GHz.
- January 31, 2019
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.
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, or 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. - August 21, 2018
Gallagher recently released our High Performance Elastomer Seals for the Instrumentation Industry White Paper. This was written by Russ Schnell, an Elastomer Consultant contracted by Gallagher Fluid Seals, and a former Senior Application Engineer with the Kalrez® perfluoroelastomer parts business at DuPont. This white paper is now available for download on our Resources page.
Below is the third and final section of the white paper, which will discuss the importance of proper seal and groove design.
Proper Seal & Groove Design
Proper seal design is a necessity for elastomer seals to perform reliably over the long term. Many of the instrument applications mentioned above use o-ring seals. The suggested compression for an elastomer o-ring seal to perform properly is typically a minimum of 16%, and a maximum of 30%. However, this range must also take into account the thermal expansion of an elastomer at elevated temperatures as well as any swell due to chemical exposure. Many of the elastomer seals used in instruments are small o-rings, which can create design issues. This is especially true for perfluoroelastomer parts which have a relatively high coefficient of thermal expansion (CTE). Fluoroelastomers have a lower CTE, making seal design easier at elevated temperatures.
- June 05, 2018
Gallagher Fluid Seals recently posted our new Fluoroelastomer Basics webinar on gallagherseals.com. This is the third and final section of our webinar, focusing on Considerations When Choosing a Fluoroelastomer. The full video is now available on our Resources page.
This video discusses considerations when choosing a fluoroelastomer, including temperature performance range, performance in harsh chemical exposure, and the need to take caution when using fluoroelastomer blends.
[embed]https://youtu.be/ETuFwz88SB0[/embed]
- May 01, 2018
Gallagher Fluid Seals recently posted our new Fluoroelastomer Basics webinar on gallagherseals.com. This is the second section of our webinar, focusing on Fluoroelastomer Materials. The full video is now available on our Resources page.
This section of the video discusses different fluoroelastomer materials, along with their mechanical and physical properties, and in which applications they're normally found.
[embed]https://youtu.be/pukqRYUXtbw[/embed]
- April 03, 2018
Gallagher recently published its Failure Modes of Elastomers in the Semiconductor Industry White Paper, now available for download on our site. This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the fourth and final section of our new white paper, discussing Volatiles (offgassing) and Particle Generation. To download the white paper in its entirety, visit our Resources Page, or click on the image to the right.
Failure Modes of Elastomers in the Semiconductor Industry
High performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.
- March 27, 2018
Gallagher Fluid Seals recently made our Fluoroelastomer Basics webinar available on the website.
This webinar will discuss:
- Differences between an elastomer and a fluoroelastomer
- The important role fluorine plays
- Types of fluoroelastomers and their features and benefits
- Material performance comparisons
- Chemical resistance of fluoroelastomers
- Temperature ratings of fluoroelastomers
- Considerations when choosing the right fluoroelastomer for your application
What is an Elastomer?
An elastomer is made up of long chain polymers which are connected by crosslinks. Crosslinks are analogous to springs and provide an "elastic" (recovery) nature to the material. The crosslinks are relatively stable, but can break down under extreme temperatures and pressures.
- March 13, 2018
Gallagher recently published its Failure Modes of Elastomers in the Semiconductor Industry White Paper, now available for download on our site. This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the third section of our new white paper, discussing O-Ring Stretch, Chemical Attack, Plasma Cracking, and Permeation. To download the entire white paper, visit our Resources Page, or click on the image to the right.
Failure Modes of Elastomers in the Semiconductor Industry
High performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.
- February 15, 2018
Gallagher recently published its Failure Modes for Elastomers in the Semiconductor Industry White Paper, now available for download on our site. This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the second section of our new white paper, discussing Loss of Sealing Force, and Extrusion. To download the white paper in its entirety, visit our Resources Page, or click on the image to the right.
Failure Modes of Elastomers in the Semiconductor Industry
High performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.
- February 06, 2018
Gallagher recently published its Failure Modes of Elastomers in the Semiconductor Industry White Paper, now available for download on our site. This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the first section of our new white paper, discussing groove design and seal leakage. To download the entire white paper, visit our Resources Page, or click on the image to the right.
Failure Modes for Elastomers in the Semiconductor Industry
High performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.