Vacuum coating is vital in various industries, including glass coating and solar cell production. Efficient substrate feeding and removal from the coating chamber is crucial for productivity, and cycle times are key factors. Flowserve’s latest screw booster technology targets these times and has the potential to double system productivity.
Limitations of Roots-type blowers
Dry-screw and oil-sealed vacuum pumps can compress gas flows down to near-vacuum pressure, but single-stage pumps require high power consumption for high vacuum requirements at low suction pressures. Multistage systems are more practical and commonly used in vacuum-coating processes, but the traditional combination of Roots-type blowers and oil-sealed or dry-backing pumps struggles to meet today’s demands for faster pump-down of load lock chambers.
Roots-type blowers are vacuum pumps designed to function as boosters in order to achieve high capacities at low pressures, typically below 10 mbar (0.15 psi). Their operation is limited, however, by the maximum difference allowed between their suction and discharge pressures. Since the full capacity of a Rootstype blower is only available at low pressure, the suction capacity of such a system declines significantly as the pressure rises. As a result, these pumps are not suitable for compression directly against atmospheric pressure.
The SIHI Boost principle
Flowserve SIHI Boost dry-running vacuum pump systems, introduced in 2013, were developed specifically to meet the requirements of industrial applications in the medium and fine vacuum pressure ranges.
SIHI Boost pumps have a larger stepdown ratio (up to 100:1) than other booster units in the industry, yet they deliver faster vessel evacuation. Traditional Roots-type blowers have a maximum pumping speed ratio of 10:1 with the backing pump under ideal conditions, and the step-down ratio is typically no greater than 3:1 or 5:1. The unique design of SIHI Boost pumps allows them to harvest kinetic energy stored in the spindles, resulting in faster pumping and using less electricity. The unit’s twin screws and symmetrical spindles produce an even distribution of forces and compression to both ends of the booster.
Electronically synchronized spindles
SIHI Boost pumps use electronically synchronized spindles instead of oil-lubricated gearboxes, resulting in quiet and vibration-free operation, eliminating the need for oil lubrication and costly mechanical seals, and extending component life. The elimination of the gearbox also removes the need for gear oil maintenance, reducing costs and labor.
Overall, these innovations allow for faster evacuation to deep vacuum levels with less power, a smaller footprint, and quieter, safer and cleaner operation. A single SIHI Boost unit can replace multiple Roots-type blowers and interstage cooling units while delivering superior performance, even with smaller backing pumps.
Repurposing a traditional concept
By combining a SIHI Boost pump with a liquid-ring vacuum pump (LRVP), the risk of process buildup is eliminated. The LRVP acts like a scrubber to wash out particles from process carryover, providing a pre-cleaned discharge flow. This dual-stage system solution offers unique features including the ability to handle gases, condensable vapors and/or solid carryover; optimization of process and load lock applications; entirely oil-free operation; easy maintenance; high reliability; and low noise and vibration.
Since the achievable vacuum of LRVPs is limited to a pressure level above 100 mbar abs (1.45 psi abs), combining them with Roots-type blowers is not an option in coating applications.
The SIHI Boost design remains unique in the industry, delivering significant competitive advantages traditional Roots-type blowers simply cannot provide. SIHI Boost pumps can compress easily to a pressure level of 100 mbar abs (1.45 psi abs), ideally to combine it with LRVPs.
Now Flowserve is taking the LRVP technology to an even higher level with the SIHI Boost UltraPLUS dry-running vacuum pump, which more than doubles the evacuation speed of the pump — without increasing the unit’s footprint.
The SIHI Boost UltraPLUS vacuum pump was designed to increase the continuous output of the original SIHI Boost units, requiring several changes to achieve this outcome, including optimization of gap, temperature distribution, and adaptation of integrated motors.
Measurements and simulation were used to qualify the new product for different volumes and backing pump combinations, leading to optimized cooling, material changes, and gap distribution modifications to address thermal deformations during operation.
Together, these improvements dramatically increased the machine’s performance, enabling the original SIHI Boost vacuum pump’s continuous power limit of 12.5 kW to be more than doubled to 28 kW in SIHI Boost UltraPLUS pumps. All this was realized without changing the size of the casing or modifying the drive electronics.
Coating line use case
The screw blower technology offers significant advantages for vacuum coating and lock processes by combining fast pump-down time with optimized re-acceleration time. Replacing existing Roots blowers with screw blower units can result in 20–50% shorter pump-down times and 50% lower energy consumption in final pressure operation compared to standard vacuum systems.
The new screw blower series doubles the value of the technology, retaining all the benefits of oil-free operation and full electronic synchronization while reducing re-acceleration time by up to 50% without increasing the unit’s footprint. This technology can enable existing coating lines to achieve the fastest pump-down time for load locks to date.
The innovative design of SIHI Boost UltraPLUS dry-running vacuum pumps literally doubles the value of a technology that was already unrivaled in the industry. The new pump design retains all the advantages of the original SIHI Boost pumps, including oil-free operation and full electronic synchronization, while cutting re-acceleration time up to 50% or more — without increasing the footprint of the unit. Simply by replacing the obsolete technology of Roots-type blowers, SIHI Boost UltraPLUS pumps can enable existing equipment to achieve the industry’s fastest load lock cycle times to date.
About the Author
This article was written by Stefan Laehn, Global Product Line Leader – Vacuum Pumps, Compressors and Systems at Flowserve Corp.
This article first appeared in the May/June 2023 issue of World Pumps magazine. To read the full issue, click here.