It is not always possible to predict all the load cases of the structural design with mechanical calculation and therefore it is…
Rotor balancing of agricultural machinery
On site and without disassembly, we balance rotary agricultural machines that have access to their own rotor: mulcher, combine harvester, band saws, mills, mixers. It often happens that the cause of the off-balanced operation of the rotary machine or increased vibrations is only the rotor imbalance and then it is not necessary to remove the bearings and shaft which significantly increases the cost of the process, but it can be balanced (achieve balancing of moments by adding weights in the plane of the bearings by welding). Precondition is that the rotor is not bent, that there are no cracks, ie that the bearings and the shaft are in the correct condition, otherwise balancing does not make sense before the mechanical repair. Working with the machine in a high vibration frequency mode it does not just damage the bearings and the shaft, even all other parts of the machine as well. If a crack has occurred somewhere, the consequences are only covered by welding, but the cause of the problem still remains, and the damage to the rotor parts can only become greater.
Testing of static and dynamic characteristics of structures
It is not always possible to predict all the load cases of the structural design with mechanical calculation and therefore it is not easy to have full knoledge of the permissible load capacity based on the characteristics of the material. By measuring physical quantities in situ at interesting cross sections, as well as subsequent analysis, we can get to know the basic construction characteristics, as well as predict the withstand limit loads. Loads can be static or dynamic. While static ones are more predictable with respect to constant forces, masses and loads and easier to measure (stress, pressure, static displacement, force and static moment), dynamic ones are often not (vibrational displacement, dynamic stress, resonant phenomena, forms of vibration). The dynamic impact itself is different, and it can be caused by machines and devices with constant dynamic forces and operating frequencies, but also by time changeable load levels such as climate (wind, sea) or traffic.
In cooperation with our partners and state-of-the-art equipment, we can provide periodic measurements but also continuous monitoring of the structure, and this is especially important in changing load conditions where loss or change of structural characteristics occurs more often. Before the measurement, we can determine together with the Client the interesting, ie the most unfavorable cases of load in operation, and make quality preparation and create a test plan. After measuring and analyzing the recorded quantities, we can compare the measured quantities with allowed ones in the mechanical calculation, but also predict the limit loadcases at which the structure is not safe.
Finally, we can also optimize the design of the structure, such as stiffening in critical sections or unloading (subtraction of mass), in order to improve and better distribute its static and dynamic properties.
FEM analysis – finite element method
Sometimes it is necessary during design phase to make a more detailed mechanical analysis of the loaded system with static and dynamic forces, in order to eliminate or at least reduce the possibility of the occurrence of impermissible values of physical quantities in operation. In cooperation with our partners, we can create several types of structure analysis of the system by the finite element method. It often happens in the exploitation and operation of the system that excessive loads or dynamic phenomena occur, which are difficult and expensive to solve by reconstruction. In the project phase, possible load cases can be predicted and by help of FEM analysis we can identify failures, points of impermissible or concentrated values which allow us to modify the design and optimize the structure.
Checking the influence of static loads, ie those that are not variable in the time domain, can give a solution in the form of: stress, reaction forces and moment, deformation, temperature in the structure. Dynamic analysis determines the influence of variable inertial forces in time or forced vibrations caused by installed or surrounding machines and devices, but we also determine possible resonant phenomena in the system, which is much more dangerous.It is very important to eliminate the possibility for a machine or device to excite the resonant frequency of the system structure in the project phase, because without sufficient damping faktor, a breakdown can occur.
Work environment testing
In cooperation with our partners, we perform testing of physical factors in the work environment, namely noise and vibration. Testing of the working environment is one of the tasks of safety at work, and if there is increased vibration or noise, the employer is obliged to do testing at that workplace and ensure the development of work processes. The assessment is performed by comparison with the allowed exposure values specified in the applicable standards after measurement analysis.
Noise and vibration not affect just on the working ability of the worker, but can also affect his health. Measurement and analysis can be performed not only in workplaces in the process industry but also in working vehicles, and workplaces that require the use of various self-propelled and hand tools. In cases where the test results do not satisfied the prescribed standards, by help of the analysis we can determine the failures and causes of increased values, such as: malfunction of the machine, devices and tools or inadequate system of workers protection. Based on this, we can propose measures to reduce the impact of certain health hazards in the work environment.