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1 min read

Q&A How does temperature impact the properties of PTFE materials?

By Dave Biering on February 28, 2017

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We are often asked about what can be expected when you use a Rulon bearing or any PTFE in high temperatures. Many things can occur, and it varies from material to material based on the use of different fillers. Let’s review:

PTFE is an odd material in that it is a thermoplastic material, but dressed in thermoset clothes. Once molded, the material can’t be remolded like other thermoplastics, so it acts like a thermoset. The other interesting feature of PTFE is that while it has an operating temperature range of -400 to +550°F, it actual starts to transition at around 78°F. This means that the material is “moving” with thermal changes, which is known as cold flow. The big feature of Rulon materials is that the additives used in the hundreds of different Rulon materials help to stabilize the PTFE components to resist cold flow.

So, what happens when these materials are taken to higher temperatures?

It again depends on the nature of the fillers used. As an example, virgin PTFE has a tensile strength of 4075 psi at room temperature, but at 500°F the tensile drops to just over 1000 psi.

As a comparison, a carbon graphite filled material has a tensile at room temperature of 3300 psi but 990 psi at 500°F. Elongation numbers will also be impacted. Virgin PTFE has an elongation of approximately 330% at room temperature but only 210% at 500°F. The carbon graphite is 240% at room temperature and 180% at 500°F.

Why is this information important?

It’s important in the design of seals, bearings and even structural components used at high temperatures. Add to this the thermal conductivity and thermal expansion of these different materials, and it’s clear how important it is to get the right information at the beginning of your design.

For assistance in making heads or tails of the world of PTFE components contact TriStar Engineering.

Bearing Selection: Get the Ultimate Plastic Bearing Design

Topics: PTFE
1 min read

PTFE and High-Radiation Environments: 5 Important Facts

By Dave Biering on January 31, 2017

PTFE and High-Radiation Environments

We’ve had many questions about the connection between PTFE materials and high-radiation environments. Often, when working in these conditions, engineers turn to fluoropolymers like Tefzel (ETFE) as a preferred material instead of PTFE. But before you make a final material decision, let’s review some key facts about PTFE in this environment.

PTFE has never been recognized for its performance in high radiation environments, as it tends to degrade. But it also can gain some favorable material properties in certain applications. Explore more on the crystallinity of PTFE.

Consider:

1. Threshold

When PTFE is exposed to radiation in air, it’s damage threshold is 2-7 x 104

2. Strength

At these exposure levels, PTFE will lose 50% of its tensile strength. At 7 x 104 it loses nearly all of its elongation, flex and impact properties.

3. Vacuum

When PTFE is exposed to radiation in vacuum, the properties are up to 10x better in terms of tensile, elongation, flex and impact values.

4. Applications

In space applications (which are in vacuum conditions), PTFE can survive service in satellites that may encounter radiation exposures in the Van Allen belt, which is about 10rads per hour. Depending on the other conditions, a PTFE component could survive 5-50 years in earth’s orbit.

5. Alternate materials

  • FEP, another type of fluoropolymer, has a radiation tolerance 10-100 times better than PTFE in air, so it’s an option in many earthbound radiation exposures. However, Tefzel would still be our material of choice.
  • Rulon materials are NASA-approved for satellite service in seals and bearings aboard geosynchronous satellites and deep space probes because the material does not outgas in vacuum and is more tolerant to radiation.

If you have applications where a fluoropolymer seal, bearing, gasket or structural component may be under consideration contact TriStar Engineering to discuss your options. We’ll help you compare materials for the best option.

Bearing Selection: Get the Ultimate Plastic Bearing Design

 

Topics: PTFE
1 min read

Chlorine, Corrosion and the PTFE Bearing Connection: A Case Study

By Dave Biering on November 29, 2016

Chlorine, Corrosion and the PTFE Bearing Connection: A Case Study

Our recent post on PTFE and Rulon in water applications generated some solid interest. Today I want to share a case study of how PTFE-based bearings have resisted corrosion in a submerged chlorine tank as a replacement for Torlon ― all despite the fact that PTFE is not generally recommended for chemical exposure.

Corrosion is the second-leading cause of bearing failure, following right behind lubrication. It manifests as flaking and peeling, pitting and rust. Some key sources of corrosion include hard gases and strong chemical forces, or even simple water spray.

Challenge: Torlon bearing corrosion in a chlorine tank

As a general rule, we do not recommend PTFE for any type of chemical environment, since the chemicals can degrade bearing coatings. Our client shared how their Torlon polyamide-imide (PAI) components experienced surface deterioration from a combination of submerged chemical exposure and metal-to-metal contact. This application was for moving parts used in tanks filled with thousands of gallons of chlorine water. As the PAI bearing failed from chemical corrosion, they posed an expensive replacement challenge.

Solution: Rulon W2 performance improves when wet

Our engineering team tested the mechanical properties of the running hardware, and recommended Rulon W2 for its excellent wear life. Rulon is compatible with most water applications, including slurry, DI, fresh and salt water, plus chemical liquids with a full PH range. And unlike Torlon, Rulon does not absorb moisture to give longer wear. The material runs so well in fact, it’s DWGV-certified (European) for drinking water applications.

Our client now reports that Rulon W2 has provided several years of maintenance-free operation at a lower cost than Torlon. Explore the importance of sourcing genuine Rulon products.

Consider Rulon W2 for:

  • Zero moisture absorption
  • Limited regular maintenance
  • Value-driven replacement for PAI
  • Longer service life in wetted environments

Could Rulon W2 work in your submerged application? Connect with the Rulon Experts for a full comparison.

Topics: PTFE
1 min read

Ask the Expert: How Do PTFE and Rulon Bearing Materials Perform in Water? [Test Results]

By Dave Biering on October 25, 2016

Rulon W2

I’ve been getting a lot of questions recently about PTFE-based materials like Rulon for use in water applications. Generally, PTFE is not a good solution for water-lubricated applications. Today I want to share the results of some independent testing we conducted.

PTFE bearing materials, like Rulon, are not usually friends of water-lubricated applications. This is simply because the PTFE does not properly transfer to the mating metal hardware to reach the goal of producing a thin lubricating film. The water is, by itself, a lubricating film, but it isn’t very efficient and does not leave room for lubricant starvation. To confim the connection, we conducted some testing with an outside lab. The goal was to study some traditional, filled PTFE materials along with Rulon W2, which was developed specifically for applications in water lube systems.

The results were definitely telling:

Traditional Filled PTFE Materials vs. Rulon W2

Testing was done using standard ASTM thrust bearing tests at 10,000 PV, 100FPM and 100 psi load.

Further to this testing, one of our customers reported over 4 million rotary cycles on a water micro-turbine shaft bearing using the Rulon W2 and there was no measurable wear at the end of the test. Rulon W2 gives low friction and excellent wear as well as good thermal dissipation, plus it prevents shaft distress. The material actually has enhanced properties when wet.

The bottom line? When it comes to bearing applications in clean water or other clean-water based solutions, Rulon W2 is our go-to material! View the Rulon Comparison Chart to review other unique formulas.

Got a question you’d like to submit to the Bearing Experts?  Submit it here!

Rulon - Quality Assurance Begins With Precision Processing

Topics: PTFE
1 min read

Q&A - Can you review amorphous vs. crystalline polymers?

By Dave Biering on February 12, 2015

The key attributes of crystalline vs. amorphous polymersA recent customer visit found us reviewing the attributes of amorphous vs. crystalline polymers. I thought I’d share the information as a good refresher on polymers and PTFE. 

So what are the key attributes of crystalline vs. amorphous polymers?

Crystallinity is one of the key properties of all polymers. Crystalline polymers are nearly linear in structure, which tends to be flexible and fold up to form tightly and packed. Processing time and temperature greatly influence the degree of crystallinity. These polymers have a higher level of shrinkage, are generally opaque or translucent, possess excellent chemical resistance, low friction, and superior wear resistance.

Conversely, amorphous polymers have low shrinkage, good transparency, gradual softening when heated (no distinct melting point), average or poor chemical resistance, high friction, and low wear resistance.

Here are some common materials of each:

Crystalline polymers

  • Polyethylene
  • Polypropylene
  • Acetals
  • Nylons

Amorphous polymers 

  • Polystyrene
  • Polycarbonate
  • Acrylic
  • ABS
  • SAN
  • Polysulfone
Want to learn more? Check out how crystallinity can help you Recognize Quality in PTFE Materials or Ask an Engineer for assistance!
Topics: polymer bearings PTFE