High-performance thermoplastic for sensor bodies

Quantum Analytical Instruments has specified Victrex Peek polymer for the sensor housing and structural components of analytical sensors for process measurement

Quantum Analytical Instruments, a subsidiary of Racine Federated, located in Racine, Wisconsin, USA, have specified Victrex Peek polymer, for the sensor housing and structural components of analytical sensors to be used in a broad range of process measurement applications.

Quantum Analytical's new line of sensors is designed for continuous monitoring of pH, Oxidation-Reduction Potential (ORP), Conductivity and Dissolved Oxygen in all industrial process control, as well as municipal and environmental monitoring applications.

Victrex Peek polymer, a high-performance engineering thermoplastic, was chosen because of its outstanding combination of properties.

"Peek polymer is the one material that can be used across the board in the harshest environments," says William J.

Popp, Manager of Marketing and New Business Development at Quantum Analytical.

"Its unique combination of mechanical and chemical properties allows us to offer one product that can be used in both acidic and caustic applications, ranging from potable water and chemical feed to wastewater and food processing." Chemical resistance is a major property requirement for the sensor body and structural components.

"Traditional sensors commonly use materials such as LCP and PPS," explains Popp.

"However, each of these materials has a limited chemical resistance.

For example, LCP can withstand chemical attack in acidic applications, but this material is dissolved in hot, caustic applications.

Conversely, PPS is usually the material of choice for sensors used in caustic environments but it is not recommended for acidic applications.

Many times a customer has both acidic and caustic processes in the same plant which means the customer must carry two different types of sensors.

More importantly, the customer must take great care not to install the wrong sensor in each of the process lines.

But because of its superior chemical resistance, the sensors made of Peek polymer can be used in either application, thereby eliminating the need for multiple sensor types and preventing sensor misapplication." Another important feature of Peek polymer is its outstanding mechanical strength.

Sensors are frequently used in process applications with high-suspended solids concentrations.

A sensor operating in this type of environment requires very high mechanical strength because the housing is continuously being impacted by some type of solid.

The mechanical strength of other polymers, such as LCP, comes from the polymer's chemistry at the surface of the part.

Any abrasion by suspended solid or machining of the part can weaken the material structure.

The mechanical strength of Peek polymer, however, is derived from the polymer's internal chemistry.

Peek polymer can be abraded or modified without appreciable loss of its mechanical strength.

Temperature stability is also an important factor.

In certain applications there are large temperature transients which are a normal part of the process application.

The temperature of the process may start out at, or below, room temperature, but is then heated and cooled as part of the manufacturing process.

Over time, the sensor is subjected to repeated temperature cycles.

When a sensor is constructed of many different materials, changes in temperature cause the parts to expand and contract at different rates, or not return to their original dimensions.

This means that the integrity of the sensor seals tends to degrade over repeated temperature cycles, which can open a leak path into the sensor and render it non-functional.

"But because the housing and structural components in our new line of sensors are made with Peek polymer," says Popp, "they have the same coefficient of thermal expansion.

The parts expand and contract at the same rate so the integrity of the sensor seals is not compromised over repeated temperature cycles." An additional feature of the Quantum Analytical sensors is the encapsulation of the internal electronic components.

A critical requirement for this feature is the ability of the encapsulant to adhere to the surface of the housing and structural components.

When an encapsulant will not adhere to the sensor housing, the process fluid can leak into the sensor and short out the critical components.

"We tested several materials including PTFE and PVDF which are used in some sensors, but the non-stick nature of the material would prevent adhesion to the encapsulant.

One of the biggest advantages of using Peek polymer is its ability to adhere to the encapsulant, thus affording added protection against leakage," explains Popp.

A unique feature of the Quantum Analytical new sensor line is the cord grip, an integral part of the back seal of the sensor, which is custom made of Peek polymer.

According to Popp.

"We engineered this new line of sensors from the ground up to ensure that the integrity of the seals on the front of the sensor was just as good as the integrity of the seals on the back.

Our goal at Quantum Analytical Instruments is to provide the customer with a family of sensors that offers uncompromising integrity, thereby lowering their cost of maintenance and cost of ownership.

We believe that the advanced polymer technology of Peek polymer has helped us achieve this goal.".

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