The tightening torque is an inaccurate quantity! For safety-critical screw connections, trust the direct measurement of the preload force.
With our patented e-Bolt® solution for integrating preload force measurement into bolted connections, you can detect a loss of preload force at an early stage and thus prevent a possible failure of the connection! This helps to avoid bolt breakages and the resulting potential damage, accidents, and downtime. Checking the preload force is uncomplicated with the use of our e-Bolt® and can also be carried out by laymen.
The problem!
A large number of bolted joints, both in mechanical engineering and in structural engineering, are made using torque-controlled tightening methods. This procedure is simple and inexpensive, but very inaccurate! In this procedure, the applied tightening torque is converted to the resulting preload force via an assumed coefficient of friction. However, the coefficient of friction in the threads of the screw set and in the bearing surface of the nut or the screw head depends on many different influences and is subject to strong scattering.
Possible influencing variables include:
- Dry or lubricated thread or contact surfaces
- Contamination
- Surface roughness
- Corrosion
- Damage to the thread
- Damage to the screw connection (screw crack, plastic deformation)
It has been extensively documented that bolted joints pretensioned by applying a tightening torque show very large scattering regarding the resulting magnitude of the preload force. These are in the range of ± 25 % and can be significantly higher in the case of execution errors such as screw misalignment, cold welding (seizure) of the friction partners due to insufficient material hardness, etc. Direct measurement of the pretensioning force is therefore essential for the most precise pretensioning of a bolted joint!
The solution is our e-Bolt®!
The direct measurement of the preload force at the screw connection is possible with our e-Bolt® without additional sensors or measuring equipment. With our e-Bolt® we provide you with an intelligent component, the bolt or the nut, in combination with our radio-based reader. With this simple option, you can measure the preload force of bolted connections completely wirelessly and without contact in a matter of seconds. The e-Bolt® requires no power supply, it is completely self-sufficient and maintenance-free. The power supply for carrying out the preload force measurement and data transmission is provided by our Pocket Work, an easy-to-use handheld reader. On this, the preload force can be easily read off in kN; in addition, the e-Bolt® also measures the current temperature.
The technology!
e-Bolt®:
The e-Bolt® is based on commercially available standard hexagon nuts or hexagon bolts with a thread size of M10 (bolt) or M12 (nut), whereby the type and size of the nuts depends on the specific requirements of the customer. The nuts selected for the respective application are equipped by us with sensors and the latest RFID technology (Radio-Frequency-IDentification technology) and calibrated for the specific application with a tightening test bench. Since we only glue on the sensors and do not carry out any mechanical processing of the nut, the condition of the nut remains unchanged in terms of the requirements for load-bearing capacity and strength. Due to the calibration of the nuts to the respective application, we can respond very precisely to customer requirements and cover a wide range of applications. By using the latest RFID technology, the measurement of the preload force can be carried out completely wirelessly and without contact.
Pocket Work:
The Pocket Work is an RFID-based handheld reader that can be used to read the preload force of the e-Bolt® with just one touch of a button via radio contactless. The Pocket Work, in combination with the e-Bolt®, is the easiest way to perform quick and reliable checks of the preload force. For further documentation purposes or long-term monitoring, the measured values can also be transferred to a smartphone and visualised on a web platform. The individual measurement with the Pocket Work includes the current value of the preload force and the current temperature of the e-Bolt®.
Transducer:
For applications where the screw connections are difficult or impossible to access, we have developed the e-Bolt® Transducer. This small additional module is placed on the existing e-Bolt® connection and has the same RFID technology as our Pocket Work handheld reader. The read-out measurement data can be transferred to any devices, such as computers, smartphones or measuring stations, via the Bluetooth interface. Depending on the application, the battery-powered transducers are maintenance-free for up to several years.
