Greatest boon for metal industry: High-frequency grinding

February 17, 2014 8:30 am

 Huge savings in production can boost your company growth sooner than you expect
In electrical engineering, frequencies above 10 kHz are described as high frequency. For power tools, this is commonly used to describe all frequencies above the standard mains frequency of 50/60 Hz. Modern high-frequency power tools usually operate at a frequency of 300 Hz. Achieving this level requires special frequency converters that bring the power up to the higher frequency. These frequency converters are connected to the national lighting current or three-phase grid.
Why is the current from the socket at a higher frequency? One reason is the need for enhanced performance. By increasing the frequency, one can achieve a higher speed.
Peak performance, robust technologyFEIN high-frequency power tools prove their superiority in many sectors of trade and industry where continuous peak performance is demanded of tools. Compared to both compressed air tools and power tools with universal motors, they possess a wide variety of design-related advantages offering enormous potential for cost reduction.
Permanent peak performance in continuous operation is only possible if the high-frequency power tools are designed structurally as well as a qualitatively to meet peak requirements. FEIN, precision, renowned for its attention to every last detail, is an ideal prerequisite for the manufacture of such machines.
Savings of €500 per day at 15 workstationsIn terms of energy, capital expenditure and maintenance costs, high-frequency power tools are considerably more economical than comparable tools driven by compressed air. In addition, when grinding, they facilitate higher efficiency. This was the conclusion of a study carried out by a university of technology comparing the capability and economic efficiency of both types of drive.
Use of high-frequency power tools means up to …90 per cent less energy costs70 per cent less capital expenditure75 per cent less maintenance costs50 per cent less consumption of grinding discs10 per cent more material removal, i.e. higher labour productivity.
90 per cent less energy costsFor 15 workstations on two-shift operation a cost saving of around € 90,500 p.a. can he achieved
In the current distribution system for high-frequency power tools there are virtually no energy losses, whereas with compressed air systems energy losses occur during the compression of the air due to the compression heat. What‘s more, in practice a 10-20 per cent higher energy requirement can be expected due to leakage – in badly maintained systems even up to 30 per cent or more. The performance of the compressed air motors also changes with the condition of their components which are subject to a process of wear and tear (for example cylinder, rotor, starting discs, blades). This results in continuous losses in performance which in turn manifest themselves in decreasing efficiency and rising energy consumption. On the other hand, the performance of the robust induction motors is always constant – irrespective of wear and tear.
70 per cent less capital expenditure for new plantA cost saving of € 50,000 can be achieved in the purchase and installation of a plant designed for 15 grinders, not including machinesFor a new compressed air plant of this magnitude, costs of around € 60,000 can be expected for the peripheral equipment (compressor, air vessel, air drier, pipe network including installation and maintenance units). For the peripheral equipment of an equivalent high-frequency plant (converter, switch cabinets, cable network including installation and sockets) costs of only around € 6,000 will be incurred.Purchase and energy costs: Amortisation period for a high-frequency plant.
75 per cent less maintenance costsIn a plant with 15 workstations, this means a cost saving of at least € 1,500 p.a.The costs for the maintenance of the compressor drive in compressed air plants, including the line systems plus connection and maintenance work, amount to about € 2,000 p.a. These costs were estimated by scientists of a university of technology for a compressed air reference plant. By contrast frequency converters, apart from the maintenance of the ball bearings (approximately every 20,000 operating hours), require practically no servicing.
Higher efficiencyUp to 50 per cent lower consumption of grinding discs alone can lead to a cost saving of around € 35,000 p.a. with 15 workstations on two-shift operations. To this can be added the material removal which is approx. 100 per cent higher. Even under load, high-frequency grinders operate with optimum circumferential speed for the grinding discs. It can be seen clearly from the motor characteristics that compressed air tools record a speed drop of up to 50 per cent, whereas high-frequency power tools show only an insignificant speed drop when the power curve is rising. This constancy of speed results in higher grinding performance and lower grinding disc wear.
Uses of high frequencyLonger service life, minimum maintenance costThe induction motors of high-frequency power tools with short-circuit rotors have no current transmission components (such as commutators or carbon brushes) which are subject to wear and tear. For cooling they do not require draw-through ventilation and can therefore be designed with surface ventilation and as such are fully enclosed.
Accordingly, the motors are completely protected from dust. High-frequency tools are constructed in an uncomplicated fashion, enabling servicing to be carried out simply by a specialist with savings in time and cost. Frequency converters, apart from the maintenance of the ball bearings (approximately every 20,000 operating hours), require practically no servicing.
Where size is identical, power increases with frequencyThe more power is built into a power tool, the bigger and therefore heavier and more unwieldy it usually becomes. With a higher frequency; however, a higher speed is attained and with this the output power of the motor increases — without an increase in weight and size. Thus, as a result of an increase in frequency from 50 Hz to 300 Hz, you get six times more power at the same size and same weight. At 300 Hz, moreover, the power weight ratio reaches an optimum level.
High level of safetyHigh frequency makes a contribution to enhanced electrical safety. High frequency power tools are operated using a frequency converter. The voltage in this HF network is substantially below that of the public network. The maximum voltage occurring against earth is only 0.58 of the rated voltage. With a rated voltage of 200V at 300 Hz, for example, that is only 116V.
Furthermore, high-frequency power tools are designed to be in protection category I, i.e. special protection in case of fault caused by the earthed conductor connecting with the metal housing. The fault current is immediately diverted against earth. The earthing resistance is smaller than 2 ohms. Additional safety is offered by fault current safety switches (FI safety switches). Safety disconnection only has to be performed in urgent cases.
At a glanceGrinding with high frequency instead of compressed air High-frequency power tools are used in industrial manufacture  for grinding, cutting and polishing, in short, anywhere where compressed air grinders have previously been used and cost aspects play a role.