What is the purpose of this article?
Detail the Type-SR probe variants available with PTFE coating and their use cases.
What products are involved?
SRV - Inline Viscosity Meter and SRD - Inline Density and Viscosity Meter

Introduction

PTFE (Polytetrafluoroethylene) is a synthetic polymer widely known for its remarkable chemical resistance, high-temperature tolerance, and low friction properties. Commonly recognized by its brand name Teflon, PTFE is used in a variety of industries, including aerospace, automotive, electronics, and medical applications. Its non-stick qualities make it a popular material for cookware, while its electrical insulation and corrosion-resistant capabilities are essential in industrial settings. 

One of the most common uses of PTFE is as a coating or covering with the purpose of transmitting its properties onto a desired surface. In industry, equipment and machinery can often be coated with this material, gaining some of the aforementioned surface benefits.

When it comes to instrumentation, PTFE can be a key surface alternative, helping improve the operation of sensors and similar equipment. In this way, applying a PTFE coat can help reduce fouling by decreasing the chance of deposits forming around key sensor parts, which in turn, ensures consistent and accurate readings.


PTFE-Coated (Teflon Coated) viscosity and density sensors: (Left to right): SRV-TF-X1-34N, SRD-TF-X1-34N, SRV-TF-X1-12G, SRD-TF-X1-12G, SRV-TF-HD-X3-15T, SRD-TF-HD-X3-15T

Figure 1: PTFE-Coated (Teflon Coated) viscosity and density sensors: (Left to right): SRV-TF-X1-34N, SRD-TF-X1-34N, SRV-TF-X1-12G, SRD-TF-X1-12G, SRV-TF-HD-X3-15T, SRD-TF-HD-X3-15T


Currently Rheonics offers PTFE coating on the X1 (standard short threaded probe) and X3 (Tri-Clamp short probe) variant for Type-SR probes. The Type-SR-TF (TF: Teflon Coated) probes are intended for applications that are prone to the creation of deposits or fluid solidification around the probe.

When to use a PTFE-coated sensor

PTFE-coated sensors are used in environments that tend to create deposits, or when cleaning the sensor probe is difficult (Probes are made of 316L or C22. See Process Viscometer and Density Meter Chemical Compatibility). In such cases, PTFE-coated sensors may prevent or reduce the build-up of fouling layers or deposits which affect the sensor’s measurement, thus improving the reliability of the measurement and reducing maintenance requirements. Typical applications include:

  • Paints or varnishes

  • Slurries

  • Semiconductors

The main benefits introduced by Teflon-coated sensors across these industries include: 


High-Temperature Tolerance: Teflon can tolerate high temperatures without losing its properties, making it suitable for use in elevated temperatures, typical in many industrial processes.

Cleanability: Teflon surfaces are very easy to clean and have non-stick properties. This is important in industrial fabrication, where maintaining a clean environment is critical to avoid defects in the final products.


Coating limitations and considerations:

PTFE coatings are soft, delicate, and not guaranteed to be free of pin holes. They are susceptible to mechanical damage if surface forces exceed approx. 10 N/mm2, meaning the coating is typically damaged when sharp or edged impacts take place.

When working with PTFE-coated probes, it is important to assert that these do not guarantee chemical protection as any damage to the coating could create points of ingress for the fluid to contact the underlying material. Nonetheless, the PTFE coating provides no limitation when it comes to operating temperatures or material compatibility as long as these are within the limits of the probe.