FIGURES 1 AND 2. Replace complex traditional hydraulic valve controls (left) with a smart hydraulic system (right), which allows simple keypad entry of both pressure and flow and accepts digital or analog signals from a PLC.
Hydraulic technology has been doing useful work for centuries, but rising energy costs as well as environmental and health concerns have, in more recent times, motivated improvements in designs that represent a paradigm shift in applied technology. Most beneficially applied to cyclical loads like forging presses and manipulators, the designs are founded upon hydraulic power systems that combine mathematical modeling, proprietary software, a computerized drive controller, motor starter, electric motor and a fixed-displacement pump.
“SMART” HYDRAULIC POWER SYSTEMS
By placing intelligence in the drive, smart hydraulic power systems replace much of the hardware found in mature technology systems, including power-factor correction capacitors, motor starters, flow and pressure-control valves, valve control cards, variable-displacement pressure-compensated pumps, pump off-loading circuits, oil coolers, etc. (Figures 1 & 2). They precisely regulate the pressure and flow from a fixed-displacement pump to match the press cycle in a manner similar to operating a light dimmer switch.Smart hydraulic power systems control pressure and flow without the problems of pressure ripple, spikes or droops typical of conventional technology. System faults, such as a sudden drop in pressure as a result of a burst pipe, are detected immediately by the drive, which will shut down the pump instantaneously to minimize oil spillage.
Smart hydraulic power also brings many other important benefits. To explain these, let’s look at a typical application.
FIGURE 3. 2,500-ton closed-die press
CASE IN POINT - 2,500-TON CLOSED-DIE PRESS
Consolidated Industries (Cheshire, Conn.) is a producer of closed-die forgings for the aerospace industry. As part of its operation, the company uses a 2,500-ton press (Figure 3) that was originally powered by three 150kW Vickers PVA120 pumps running at 1,200rpm. After many years of service, the press’ hydraulic system was in need of replacement due to fair wear and tear that was causing excessive downtime, loss of system pressure and consequent product quality issues.Figure 4 shows the power drawn by one of the three original hydraulic pump motors and the motor power factor measured over three consecutive forging cycles. The power readings taken from the original system showed that the press stroked approximately once every minute, with each press stroke having a total duration of approximately 12 seconds.
The duty cycle of all forging presses creates an intermittent and cyclical demand for both hydraulic flow and pressure as each workpiece is successively loaded, forged and removed. “Work” is only done when both flow and pressure occur simultaneously, such as during the “forge” and “ram return” operations. On a large hydraulic forge, useful work is typically only performed for about 12 – 20% of the cycle time. With traditional hydraulic systems, the motor and pump continue turning – consuming power – but doing no useful work for the portion of the time that the press is unloaded. Traditional systems suffer the disadvantage that the drive motors and pumps do not stop during those periods of each cycle when the forge is not moving.
The original system on this press had high power consumption, a poor power factor and high maximum demand, resulting in higher utility costs. The hydraulic oil temperature during normal operation exceeded 54°C, indicating large energy losses over the downstream circuit control valves. Oil-cooling facilities were installed to prevent excessive oil temperatures, oil degradation and frequent oil replacement. The cooling circuit motors, pumps and fans consumed a significant amount of energy and were very noisy, contributing significantly to an ambient sound level of 102dBA.
The original hydraulic system used circuit hardware to control pressure and flow. Pressure spikes occurred during each press cycle due to sudden valve operation as the pumps were loaded and unloaded, causing the hydraulic pipe work to “jump” around. Consequently, pipeline bursts and leaks due to fatigue failure were of concern. Continuous service, adjustment and cleaning increased costs. Press outages due to repair and maintenance were giving management a headache.
For these reasons, company management decided to retrofit a UNiGY “smart” hydraulic power system (Figure 5) onto the press. The expectation was that replacing the conventional technology would provide significant energy savings, better control, quieter operation and lower lifetime cost of ownership.
The smart system allows presetting of the press operating force by simple keypad entry on the new computerized drive controller. Signals from the existing press control system (previously used to load and off-load the hydraulic pumps) are connected to the drive controller and used to request flow from the system. Analyzing the thousands of readings per second taken from the motor, the controller monitors and controls the pump performance with incredible speed and accuracy, providing performance enhancements that could not be matched by traditional fluid power systems.
The following direct benefits were realized by retrofitting a smart hydraulic power system to the forging press:
- Proportional, shock, pressure reduction and flow control valves were eliminated.
- Step changes in flow and sudden ram stops and starts were accommodated without the large pressure spikes or droops previously encountered.
- Enormous energy savings occurred – electric power consumption reduced more than 69%.
- The power factor improved to near unity and motor start in-rush current was eliminated by the built-in “soft-start” facility.
- The original oil cooling system became redundant because heat losses from the original oil storage reservoir were sufficient to dissipate the small amount of heat generated as energy was dissipated over the remaining directional control valves in the circuit.
- Noise levels were reduced more than 12dBA. There is no longer any cooling-fan noise to contend with, and the hydraulic pumps only turn when the forge is moving, generating much less noise.
- Because they turn much less, motor- and pump-maintenance have been greatly reduced.
- Electronic control of the press performance enables forging operations to be performed with greater precision and consistency and have reduced scrap and rework costs.
FIGURE 4. Energy readings before and after fitting a smart drive system demonstrate remarkable energy savings.
THERE ARE COMPELLING REASONS TO CHANGE…
Forging companies differentiate themselves in the market by offering not only “competitive advantage” but also “repetitive advantage.” These advantages are not maintained by standing still. The old adage, “A company either advances or goes backwards – but it is never static,” remains true. These imperatives continuously confront leading forging producers with compelling reasons for change, i.e., to improve health, safety and environmental factors, to reduce the cost of production and to assure product quality.Take the U.K. as a case in point with other markets influenced proportionately. Seventy percent of electricity in the U.K. is generated from gas. Consequently, electricity prices rose dramatically in recent years. Gas and electricity prices are forecast to increase further. If the cost of power alone is not a sufficiently compelling reason to reduce consumption, then the environmental effects of carbon emissions are. Governments currently offer highly beneficial incentives to industrial companies that invest in energy-saving technology.
In the U.K., the Carbon Trust provides interest-free loans for energy-saving retrofits. Most, if not all, of these loans can be repaid from the electricity savings a smart hydraulic power system achieves as a retrofit replacement of a traditional hydraulic system. In the U.S., different states have different schemes that are often much more attractive than that of the U.K.’s Carbon Trust.
Press control systems have evolved. They continue to be a hot topic among hydraulic press users looking for new capabilities, automatic setup and user-friendly operation through a touch-screen control. The latest generation of programmable logic computer (PLC) controls, coupled with fast, efficient computerized fluid management, is a potent combination in improving hydraulic press performance, generating valuable management information and providing system diagnostics. Better performance comes from faster hydraulic response time, higher press speeds and improved repeatability.
Traditional designs of hydraulic presses were prone to leaks. Smart hydraulic technology, by reducing the number of potential leakage sites and pressure spikes that eventually lead to leaks, improves the working environment significantly. Modern hydraulic systems have fewer pipes. Fluid management is through ported manifolds and the connection points – areas that can leak – are much reduced. The fluid is contained within machined-steel blocks.
As was experienced with the application at Consolidated Industries, UNiGY smart hydraulic power systems will typically consume up to 69% less energy and greatly reduce apparent power draw relative to traditional hydraulic systems. The savings may seem incredible, but they’re true. On any hydraulic press operation these savings fall directly to the bottom line as profit, an effect that can be sufficiently compelling.
The next major incentive is “control.” The computers that are integrated within our smart hydraulic drive-system platforms monitor, analyze and control based upon system readings taken thousands of times per second. Their software programs make repeated decisions correctly and quickly. The improved speed, repeatability and reliability of digital hydraulic control are compelling because they translate consistently into much better forging quality.
Because smart hydraulic power systems only turn motor/pump sets during the few seconds of each cycle requiring flow, their motors and pumps run for far less time. This translates into much less wear and tear, hence much fewer press outages for maintenance and repairs. So, compelling savings accrue from major reductions in lost production, maintenance labor, parts replacement, spares inventories and from operating in a manner that incrementally improves forging-shop health and safety.
We can fall behind our competitors and gradually lose market share, or we can continuously invest in the best technology to ensure that we are working smarter and achieving lower operating costs. Companies are thus compelled to use highly efficient, digitally controlled, minimal maintenance, and clean and quiet technology. Otherwise, even in the medium-term, they will not achieve the lowest life cycle cost of ownership.
FIGURE 5. UNiGY hydraulic power system schematic
…AND COMPELLING REASONS TO RESIST IT.
If these are the compelling reasons for change, then what drives resistance to change?Firstly, replacement of the hydraulic power system on a forging press represents considerable downtime.
Secondly, some individuals, when faced with new technology, are inclined to wait and see before they buy it. Some will want to be in the vanguard. But the truth is that more of us fall into the former than the latter category. Resistance to change is the conservative characteristic of many of us.
Thirdly, forging companies have not, historically, considered specific energy consumption when buying a press, so no one has left themselves open to criticism by ignoring this criterion.
Finally, the press operator often is only interested to know that the hydraulic power system will provide sufficient ram speed and force. How this is achieved is often a bit of a mystery that’s better left to the experts. Hydraulic component suppliers and press design engineers have invested a great deal of their time and ingenuity in devising ways around the shortcomings of traditional hydraulic equipment. The range and complexity of traditional pumps, control valves and hydraulic circuits are testimony to many years of dedication from engineers who find it hard to accept that their technology is archaic.
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