A total of 34 high temperature inductive sensors from Ipf electronic are currently capturing metal objects in the 40-meter-long curing oven of the automobile manufacturer without contact. The new high-temperature sensors were implemented as cylindrical devices with an M50 thread to ensure the required switching distance of up to 25 mm in the drying oven.
Cathodic dip painting (KTL), also called cathaphoresis, is an electrochemical process with which workpieces can be coated with very high quality. After coating, the workpieces are placed in a baking oven. If there is no drip station in front of the baking process, the excess coating evaporates suddenly in the oven. The hot, humid climate inside the furnace therefore places very special demands on inductive position and proximity switches.
The KTL has long been a tried and tested method for coating and thus for corrosion protection of vehicle parts. The parts to be coated or painted are immersed in an electrically conductive immersion bath, a direct voltage being applied between the parts and a counter electrode. This DC field allows water-soluble binders to precipitate on the surface of the workpieces connected as cathodes. The result is a closed, as well as very adherent coating. The KTL is therefore particularly well suited for the coating of very complex structures, for example with cavities or corners that are difficult to access.
Humid, hot climate
In the KTL system of a leading automobile manufacturer, inductive proximity switches in a baking oven are to interrogate positions, for example from a lifting device. For technical reasons, no draining station can be integrated in the system between the dip coating and the baking oven. The coated parts therefore go directly into the furnace, with the excess paint evaporating abruptly when the workpieces are moved in, precipitating as condensate on the top of the furnace and then dripping onto the system components. The inductive proximity switches not only have to be extremely tight so that no condensate can penetrate them, they also have to withstand the high temperatures of up to +205 ° C in the baking oven.
Silicone-free solution well above IP 68
The condensate in the stoving oven has significantly higher creep properties than water, which requires the sensors to be extremely tight, far beyond IP68. But not only in terms of tightness and temperature resistance, no off-the-shelf sensor solution came into question and therefore presented ipf electronic gmbh from Lüdenscheid with very special challenges. The new development was not allowed to contain silicone, since the outgassing of this material can deposit on the coated parts and thus lead to burn-in errors.
Absolutely leakproof even when the temperature changes
Through the use of special seals and sealing systems, it was finally possible to develop an absolutely tight and completely silicone-free high-temperature sensor that not only reliably prevents the condensate from penetrating, but also withstands the high furnace temperatures with its maximum temperature resistance of +230 ° C. Even more: Even if the kiln has to be opened due to inspections and its internal temperature drops to the ambient temperature of the hall, the sensor remains sealed during this temperature change.
Pluggable system facilitates exchange
However, the car manufacturer's wish list for the special properties of the sensor included not only extreme temperature resistance and absolute tightness as well as the absence of silicone, but also a solution that guarantees quick replacement if the device is mechanically damaged. For this reason, the sensor specialist from Lüdenscheid implemented a plug-in system that still guarantees a high level of tightness.
Variable, also in the cable length
Sensor systems that are used in particular in such demanding applications are usually designed in two parts, with the sensor head at the query position, here inside the oven, and the evaluation unit outside the baking oven. With conventional solutions, the cable length between the sensor head and amplifier is fixed and therefore cannot be changed. The Ipf electronic solution, on the other hand, has a variable cable length that can be flexibly adapted even when the system is installed on site.