Depending on the application, a filter system is used either for emulsions or oil. In terms of specific weight and viscosity, emulsions, i.e., mixtures of mineral oil and water are similar to a mixture of water and chemicals, while cooling and cutting oil is of higher viscosity and lower weight. The pumps and filters must always be designed specifically for the application.
In the case of the pumps, this applies both to the hydraulic components and the seals. This is especially relevant in selecting seals, as due attention must be paid to several important factors, such as the type of material being machined and, above all, the size and concentration of the chips in the CL to be filtered. The normal chip load range is approximately around 100 mg/l and particle sizes are below 50 µm. “However,” as Michael Pfeiffer explains, “the centrifugal pumps we use are among the most robust components in the entire CL cycle.”
That is a positive point for both the engineering contractor and the user, because a single VL filter system includes three or four centrifugal pumps. A self-priming centrifugal pump, such as the KSB Etaprime with a mechanical seal, transfers the chip-laden CL from the machine tool”s sludge tank to the filter. At various points around the system, KSB Etanorm pumps handle partial flows of CL and ultimately, the cleansed CL is transferred back to the supply tank by a KSB Etabloc pump. This pump is also ideal for moving the CL from the supply tank to the machine tool.
Trend toward higher energy efficiency
The potential and relevance of energy efficiency are best explained by the largest central filter system to have been built by Knoll Maschinenbau. It serves around 50 machine tools that together require up to 14,000 l/min of emulsion and four VLX vacuum filter systems remove all the metal particles from the fluid down to a size of 30 µm. Each of these four VLX systems has a capacity of 5,000 l/min, so one system is redundant and serves as a backup. The same applies to one of the three KSB pumps in the closed circular supply line.
The decisive efficiency aspect is that the pumps have frequency-controlled motors and therefore only consume the exact amount of electricity they need at their respective operating point along the system curve. For each individual VLX filter system, Knoll has calculated annual energy savings of up to 60,000 kWh.
Pumps adjusted to their individual operating point
The frequency-controlled pumps in the closed circular line account for a major share of the savings on energy. For KSB, it is matter of principle for the pumps to be adjusted to their optimum operating points. In this respect it is essential to take the impeller diameter into account in the energy consumption calculation. The pump specialist must ensure that the impeller diameter exactly matches the operating point required.
In order to account for all relevant circumstances, KSB has developed the EasySelect pump configurator, a software and database that can be used by its partners. This ensures that such application-specific criteria as pumped fluid, operating point, cost of energy, NPSH (Net Positive Suction Head), shutoff head, purchase cost and volume flow to allow for future applications are accounted for in pump selection. For the users, this means that they get exactly the optimal hydraulic system they need for their respective requirements. Motor efficiency also has a positive impact, if only to a linear degree.
Energy efficiency, explains Michael Pfeiffer, is equally relevant to small scale applications: “Demand-driven control is not just a question of absolute power. It can be worthwhile for pump ratings as low as 4 kW. It all depends on the operating conditions, e.g., on changes in volume flow or on the size of the tank. Pumps serving small vessels have to cut in and out frequently, so a frequency inverter can control the pump”s output as a function of the fill level. That saves a lot of electricity,” he says.
Today”s trend toward energy-saving solutions is buoyed by a number of factors: frequency inverters have become much less expensive, and manufacturers like KSB have increased the energy efficiency of their pumps. In addition, users are attaching more importance to a holistic approach to purchase and operating costs (total cost of ownership) and life cycle costs. Lastly, cost considerations have been joined by enlightened attitudes to the use of energy and resources in general. All in all, this is reason enough for manufacturers like Knoll and KSB to dedicate even more time and energy to the subject of energy efficiency.
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