Whilst many conventional flow sensors are unable to cope with the conditions in high temperature applications, FlexFlow thermal flow sensors from Baumer have proved they are more than up to the job


hen things start getting hot, conventional flow sensors often

reach their limits, for example in heat treatment applications such as high strength ceramics manufacture and cooling circuits in sintering furnaces. When temperatures rise above 100°C, most sensors are unable to cope, can fail after a short period of time and frequently have to be replaced. Thankfully, flow and temperature sensors specifically designed for high-temperature applications, such as the range of FlexFlow thermal flow sensors from BAUMER, are now available. FlexFlow sensors function reliably even

at process temperatures up to +150°C and also have the ability to handle transient temperature peaks so their performance is unaffected. Since they have no moving mechanical parts, they are virtually maintenance-free and ensure smooth operation of systems, reliably monitoring flow and speed in high temperature applications. In sintering furnaces, powdery

substances are mixed together and then combined with each other, either by compression or heating. Once the powder masses are formed in this way, the cohesion of the particles is possible and after the preformed mixture has been prepressed in this way, it’s then compressed and hardened by applying heat treatment below melting point. It’s only through this temperature treatment that the product of the sintering process achieves the essential properties required for the eventual application, such as hardness, strength or temperature conductivity. Typical high temperature applications

include the production of high-strength ceramics and metal materials with complex geometrical shapes, such as cutting inserts for tool manufacture (Pic 1), components for motors and transformers and also grinders for coffee machines. Things can certainly heat up in these applications. For example, in silicate ceramics manufacture, temperatures during sintering can range from 800°C to 1400°C, and in technical ceramics up to 2500°C. Furthermore, in sintering furnaces and

other high temperature applications, procedures can be complex and the demands on systems can be challenging with processes tending to be energy-


intensive and therefore expensive (Pic 2). Sintering must take place smoothly over hours or even days under defined conditions, otherwise the consequences would be waste (along with the associated costs) as sintering ovens are generally operating at optimum levels. The cooling of the connections of the

heating elements is a critical point for reliable functioning so it’s important that breakdowns don’t occur. Water cooling is usually the preferred method and cooling circuits must be constantly monitored during operation. For example, on the basis of the flow rate and temperature of the coolant, sensors in the return flow recognise whether the pumps are working reliably and whether sufficient coolant is flushing the heating element connections. However, the choice of suitable sensors

for this application depends on a number of factors. Coolant temperatures frequently exceeding 100°C are a problem for many sensors and if 20 or 30 or more sensors have to be replaced in large sintering furnaces at regular intervals, the additional costs can be considerable. Thermal flow sensors work according to

the calorimetric measuring principle which is based on the physical laws of thermal conduction and thermal transfer in liquids and gases. A body with a higher temperature releases energy into its environment in the form of heat. The amount of this energy release depends on the temperature difference and the mass flow. A heated sensor is cooled by the

Pic 2: In sintering furnaces and other high temperature

applications, procedures can be complex and the demands on systems can be challenging with processes tending to be energy-intensive and therefore expensive

Pic 3: FlexFlow sensors with the tapered seal connection are usually the preferred option in sintering furnaces

Pic 1: Typical high temperature applications include the production of high-strength ceramics and metal materials with complex geometrical shapes, such as cutting inserts for tool manufacture

liquid flowing around it and the degree of cooling is directly dependent on the mass flowing past it. In addition to the flow rate, the media temperature can also be recorded and monitored with one sensor. This reduces the number of measuring points and minimises the effort required for installation, service and storage. In addition to sensors being able to

withstand high process temperatures there are also other requirements, such as ease of installation. Baumer FlexFlow thermal sensors are also able to meet these requirements. Thanks to their symmetrical, centered design, the sensors can be easily installed in the process regardless of the installation position and orientation, helping to ensure precise measurements and process safety. They are available with different process connections and rod lengths from 16mm to 200mm so are suitable for a variety of applications. In sintering furnaces, the version with the tapered seal connection is usually the preferred option (Pic 3). The metallic seal combined with an additional plastic O-ring seal is pressure resistant up to 100 bar, is easy to install in the pipe and, should the situation arise. It’s also quick and easy to replace. Thermal flow sensors by Baumer are

suitable for flow rates of 10 to 400 cm/s and temperatures of between -25 and +150°C so are suitable for cooling systems that operate at high temperatures. They are available either as analogue versions (4-20 mA) or with user-adjustable outputs using IO-Link. The versions with analogue outputs have proved successful in cooling systems of sintering furnaces and are tamper-proof. For applications with frequently

changing batches or different process steps, the IO interface is the best option as it allows for simultaneous parameterisation of several sensors. This simplifies switching point adjustment and saves time. All data can be recorded and managed centrally in the control system, which helps with the overall configuration of the system.



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