PTFE-Carbon

Definition and Classification

PTFE-carbon (carbon-filled PTFE) is a PTFE compound — that is, a composite material made of polytetrafluoroethylene (PTFE) and a carbon filler. PTFE is very chemical-resistant and has a low friction coefficient, yet it is comparatively soft mechanically. In sealing technology, PTFE is therefore frequently “filled” in a targeted way, so that it remains more stable under pressure and motion.

Carbon fillers are used because they address typical weaknesses of pure PTFE. These include in particular creep (slow yielding under sustained load) and elevated wear in dynamic sealing points. In many material overviews, PTFE-carbon is also listed as a material for sliding elements and dynamic seals, because the tribological properties (friction and wear behavior) frequently turn out more favorable in practice than with unfilled PTFE.

Carbon vs. Carbon/Graphite: What Is Meant?

By “carbon”, what is usually meant in compounds is carbon as a filler. Carbon is frequently combined with graphite, because graphite acts as a solid lubricant. A solid lubricant reduces friction without liquid lubrication — for example with poor lubricant supply or with temporary dry running.

In data sheets and overviews, designations such as PTFE-carbon/graphite therefore appear. For selection, what matters is: whether and how much graphite is contained co-decides friction coefficient, wear, and behavior under boundary or dry friction.

Properties: What Improves Compared to Pure PTFE?

Pure PTFE offers very good chemical resistance and low friction but shows limits under load and motion. Carbon-filled PTFE aims to improve mechanics and tribology. In sealing technology, this is relevant when sealing or guide elements permanently take up pressure, see high speeds, or work with media that lubricate only weakly.

The specific parameters depend strongly on the recipe — that is, on filler type, filler content, and processing. Therefore, carbon-filled PTFE is a material family rather than a single, unambiguous material.

Creep / Cold Flow and Dimensional Stability

Creep (in practice often referred to as cold flow) means that PTFE deforms permanently under constant load over time. In seals, this can lead to a geometry yielding, gaps becoming larger, or contact pressure dropping. As a result, tightness and service life are affected, particularly in dynamic applications.

Carbon fillers reduce this time-dependent deformation behavior in many cases. As a result, shape remains more stable, which is a key selection reason particularly for guide and sealing elements under pressure.

Tribology (Friction, Wear) and Heat Dissipation

In a dynamic seal, friction — and thus heat — arises at the contact face. Wear arises through material loss and surface interactions, which depend strongly on mating surface and lubrication. Carbon fillers typically improve wear resistance and increase the mechanical load capacity in friction contact.

Graphite can additionally lower friction and wear when lubrication conditions are poor. This is particularly relevant when the medium has little lubrication effect or when temporary dry running cannot be reliably excluded. Carbon-filled compounds can also improve heat dissipation compared with pure PTFE, which can help at higher sliding speeds and in continuous operation.

Electrical Conductivity / Antistatic Behavior (Optional, Depending on Compound)

Carbon can change the electrical properties of PTFE. Depending on the recipe, a compound can be antistatic or in some cases even conductive, so that charges can be dissipated. This matters when electrostatic charging is problematic in the application.

Since the electrical effect depends strongly on filler content and filler form, the data sheet of the specific compound should always be consulted for this.

Typical Applications and Operating Limits in Sealing Technology

In sealing technology, PTFE-carbon/graphite is frequently used when components must simultaneously seal, guide, or slide, and pressure, speed, and temperature vary. Typical components are guide rings and guide bands as well as seal and slide rings. Support functions in sealing systems are also possible, provided the compound is designed for it.

The application limits are not generally applicable, because they depend on recipe, installation space, mating surface, and operating point. In practice, manufacturer-side PV limits (pressure × velocity), temperature ranges, and lubrication notes are therefore used.

Media and Lubrication Conditions

PTFE-carbon/graphite is frequently mentioned when the medium lubricates poorly — for example in water hydraulics, or when only limited lubrication is present in pneumatics. In oil hydraulics, the material can also be used when high pressure and sliding fractions occur and dimensional stability becomes important.

Under dry running, graphite frequently helps to stabilize friction. Nevertheless, dry running remains a design question, because temperature, mating surface, and contact pressure strongly determine wear.

Mating Surfaces and Friction Pairing

Friction and wear depend to a high degree on the friction pair — that is, on the interplay of the PTFE compound and the mating surface. Common mating partners are steel, hard-chrome-plated steel, and stainless steel. Decisive here are surface quality, hardness, and roughness, because they influence the transfer film and thereby the friction behavior.

Material Variants: Filler Content and Distinction from Other PTFE Compounds

Carbon-filled PTFE is not a single uniform material. Manufacturers vary filler content and combinations to target wear, creep behavior, friction coefficient, or electrical properties. In sealing technology, the material is often classified as a robust option for dynamic, pressure-loaded applications, while suitability must always be checked at the specific operating point.

Rough Orientation on Filler Content (Without Standard Values)

As a rough range, carbon fillers are frequently cited at around 5 to 30 wt.-%. As filler content rises, several properties change simultaneously — for example creep behavior, heat dissipation, and electrical effect. This coupling leads to trade-offs: a recipe that strongly reduces wear is not automatically the best choice for minimum friction or maximum tightness at very low contact pressures.

For sealing design, data sheets and application-near test values are therefore decisive, not only the filler fraction.

Comparison: Carbon vs. Glass Fiber / Bronze / MoS₂

With filled PTFE materials, the filler is an adjustment variable for the tribological and mechanical profile. A brief classification helps for pre-selection but does not replace testing on the specific system:

A brief comparison of medium, lubrication, mating surface, and PV requirement usually leads to the right variant faster than looking at individual parameters. For critical operating points, specialized material and sealing consultation is sensible.