Measuring forces and torques on rotating components is often a major challenge, especially when high speeds or environmental influences occur simultaneously. Measuring inside a hollow shaft is a very good alternative to established external strain gauge application. We describe the basics of strain gauges, advantages and disadvantages, and the possibility of cost-effectively measuring in the bore using new technologies.
In industrial drives in mechanical engineering, many rotating components are made of pipes or hollow shafts. The measurement data from these components is of crucial relevance, as these are dynamically stressed machine elements such as couplings, screw spindles, and cardan shafts.
Strain gauge application as a simple & smart solution
Stress detection is possible through the application of strain gauges (SGs). These can be bonded to the component using cold- or heat-curing adhesives and provide precise data, which can be further processed in a measuring amplifier thanks to the linear relationship between component and strain gauge elongation. This makes strain gauges an intelligent and simple solution.
Disadvantages of classic strain gauge application
However, classic strain gauge application has a decisive disadvantage: Harsh environmental conditions usually prevail on dynamic machine elements. Lubricating oils, dirt, but also mechanical influences during assembly make the application of strain gauges difficult and usually prevent their use. Furthermore, high centrifugal forces act on electronics and cables on rotating shafts.
Strain gauges inside the components
One solution is to place the strain gauges inside the pipes or hollow shafts. The machine element thus protects the sensor from environmental influences, and centrifugal forces are reduced by decreasing the distance to the axis of rotation.
As with external strain gauge application, a pair of strain gauges must be positioned and bonded very precisely. However, the necessary preparation of the bonding point, the application of contact pressure, and especially the soldering is hardly possible inside pipes and hollow shafts.
For diameters that are too small (<70 mm), the application of strain gauges on the inside is almost impossible, as this can only be done with great effort and with the help of special tools using a prepared strain gauge. Economic efficiency is rarely achieved in these cases.
Precise measurement data from inside the component
However, the advantages of internal application cannot be denied. Usually, the outer surfaces of the machine elements are also active surfaces and therefore cannot be used. This creates the first opportunity to obtain precise and direct measurement data. In addition, the lower centrifugal forces and protection from environmental influences offer great benefits for many companies. This benefit lies primarily in improved process monitoring.
coreIN – the integrated sensor solution
The integrated sensor solution from core sensing offers the possibility of correctly and easily detecting the load in the component for both small and large internal diameters. In the diameter range from 14 mm (special sizes on request), we offer sensor elements that can be integrated into the interior of the pipe and safely and reliably detect the loads there.
Further information on coreIN can be found here:
Alternatively, we are also able to apply strain gauges from the inside or outside. Both with cold and hot application.
Simply contact us!
