Turbopump seals undergo final inspectionsin a clean room.
Eagle Industry is a manufacturer that focuses primarily on mechanical—in other words, metal—seals. Compared to rubber seals, mechanical seals are characterized by the ability to tolerate harsh temperature environments (in terms of very high and very low temperatures). A manufacturer of rubber-based oil seals, Nippon Oil Seal Industry Co., Ltd., (currently known as “NOK”, also a manufacturer of flexible circuits) began developing mechanical seals in 1956. In 1964, Nippon Sealol was established through a merger with the American seal manufacturer Sealol. The mechanical seal division of this company was spun off and became the corporate predecessor of Eagle Industry. This company changed its name into what it is known as today in 1978 and subsequently severed capital ties with the United States. It is now a corporate member of the NOK Group.
The biggest clients of this company can be found in the automotive industry. The company supplies mechanical seals, bellows, valves, and other parts for engines, vehicular air-conditioning systems, and elsewhere and accounts for 65 percent of the global market for water pump seals, 70 percent of the global market for control valves, and 90 percent of the global market for lip seals. The company occupies an indispensable position in different industries in terms of its role in supplying gas seals for large compressors and mechanical seals for process pumps in the petrochemical industry, seals used in gas and steam turbines for electric generators in the energy industry, vacuum seals for the semiconductor industry, and screw-shaft seals for ships. Eagle Industry accounts for 70 percent of the total domestic market for mechanical seals.
At the same time, brush seals used in jet engines and other seals used with terrestrial gas turbines account for nearly half of the sales earned by the Aerospace Business Unit. Even then, seals for jet engines are supplied for 100 percent of engines domestically produced for the Ministry of Defense. All turbopump seals for domestic rockets are produced by this company.
The Aerospace Business Unit is located at the company’s Saitama site in Sakado City, Saitama Prefecture. With the exception of bellows and certain other products, everything from the development of technologies to the design and product manufacturing steps is carried out at this site. Out of 242 total employees at the company’s Saitama site, 114 are employees in the Aerospace Business Unit. In addition, sales teams affiliated with the Aerospace Business Unit and consisting of several employees each are permanently stationed in Tokyo, Nagoya, and Kobe.
Space parts are built through the heavy use of general-purpose machine tools. Since the quantities manufactured are low, however, the same item is never produced on the same machine for very long. Instead, the items manufactured are changed frequently. Another significant feature is the implementation of an exceedingly strict quality control system, part of which involves inspections of all items manufactured. In particular, for the turbopump seals in rocket engines where dust avoidance is an issue of paramount concern, cleaning, final inspections, and retention are carried out in a dedicated clean room.
|Saitama business site (Sakado City, Saitama Prefecture)
Okayama business site (Takahashi City, Okayama Prefecture)
|Various mechanical seals, actuator/valve products, metal bellows, and more
|Main Astronautics Equipment Produced
|Mechanical seals used with the turbopump for the engine powering the H-I, H-II, and H-IIA/B liquid rockets and static seals used with high-pressure piping and fuel tanks br>Nickel hydride battery cases (pressure vessel) and terminals for Kodama, a data relay satellite, Kiku No. 8, an engineering test satellite br>Bellows accumulators used in Kibo, Japan’s science module attached to the ISS (International Space Station), and more
We supply the mechanical seals used inJapanese liquid rocket engines.
Head of the Engineering Department of the Aerospace Business Unit
Your company is a manufacturer specializing in mechanical seals. Could you first describe what exactly constitutes a mechanical seal?
When a machine that handles liquids or gases is under pressure, it will leak if there are any gaps. Since leaks are problematic in most cases, it is necessary to block the gaps at such sites to prevent leakage. Machines also feature rotating parts. The screw shaft on a ship is a good example of this. The ship will sink if water leakage occurs. That said, however, filling in the gap on a rotating shaft will cause it to stop turning. Even if the shaft can be allowed to turn with the use of gland packing, the shaft will eventually wear out. The seal is the part that is designed to prevent wear and leaks at such sites. Generally, rubber seals are referred to as lip seals while metal seals are referred to as mechanical seals. Parts that prevent leaks by being inserted into piping seams and tightened are called gaskets or static seals.
Are they used to prevent rotary shaft leaks?
That’s correct. A mechanical seal works by joining the rotary side and the stationary side together. The tiny gap between the two is sealed. This gap is filled with a liquid film about 0.5 to 2.5 μm thick. This helps to control leaks without seizures or the development of abrasions. Such control represents the technological edge that provides us with our lifeline. Since metal mechanical seals can be used despite high temperature and low temperature, they are used in settings that are subject to harsh environmental conditions. Indeed, they are often used in rocket engines, which are particularly unforgiving when it comes to such parts.
Precisely for what part of a rocket engine are your seals used?
No matter how you slice it, they are used with the turbopump. Given that the area around the shaft of the turbopump of a rocket engine is subject to high pressures, high speeds, and—what’s more—the harsh conditions of both extremely low temperatures and high temperatures, exceedingly advanced technologies are required.
In 1964, Japan began research on liquid rocket engines. Research on turbopumps for supercharging fuel was commenced by a consortium consisting of NAL (National Aerospace Laboratory; currently integrated with JAXA), Mitsubishi Heavy Industries, and Ishikawajima-Harima Heavy Industries (currently known as “IHI”). In 1967, development of turbopump seals began. Since we were adopting technology for welded bellows seals to accommodate high-speed rotations from the United States at the time, we were asked to design and supply such seals as the only seal manufacturer capable of providing such seals.
In 1974, we started developing a liquid hydrogen seal ahead of the development of the LE-5, the first fully domestic rocket engine in our country’s history. This marked the beginning of an era in which we were truly challenged for the first time. The first seal that we provided for an experimental research project by Professor Yukio Miyakawa of NAL leaked so much that we were rebuked for not having provided a real seal. It was only years later that we realized that the professor’s request corresponded to an exceedingly high level and that our seal, which was described as something that leaked profusely, was actually at the same level as that which had been prescribed by NASA (National Aeronautics and Space Administration). Nevertheless, we devised a structure that would ensure that the sealing surface would undergo virtually no deformation to achieve a level of leakage two orders of magnitude less than that achieved by NASA.
In this way, we have consistently supplied mechanical seals for Japanese liquid rocket engines ranging from the MB-3 first-stage engine for the N series and H-1 rockets to the LE-7A first-stage engine and LE-5B second-stage engine for the present-day H-IIA/B rockets. Development work continued unabated throughout this period. While the MB-3 engine was designed by the American company Rocketdyne, it was upgraded for domestic production in Japan. This upgraded design was regarded favorably enough by industry observers that Japanese seals ended up being sold to the Americans.
The hydrogen seal that we thought was completed later failed by leaking a large amount of hydrogen as a result of vibrations affecting the sealing surface. This was caused by the fact that the viscosity of liquid hydrogen is only about the same as that of air. Faced with this predicament, we devised a new control structure to perfect a hydrogen seal that we can boast of to the world. The structure for minimizing the deformation of the sealing surface and the structure for controlling vibrations have been refined and applied to the development of the latest seals.
If you possess such advanced technologies, would you say that you are receiving inquiries from overseas rocket manufacturers as well?
Yes, and we are considering overseas expansion. NASA is currently developing the SLS, a new manned rocket. The American company Rocketdyne is developing the J-2X engine for the second-stage engine of this rocket. We are supplying the mechanical seals for the turbopump incorporated into the J-2X. A big factor behind this arrangement was the participation of engineers who can recall what we went through for the MB-3. All of this was made possible thanks to the support of various players both in Japan and overseas.
What other products for space has your company shipped?
In the 1990s, we teamed with Toshiba to develop nickel hydride battery cases for mounting on satellites. Since we possess the technology to weld thin metal sheets of a fraction of a millimeter thick with a high degree of precision, we harnessed this technology to the fullest extent possible.
How is the technology for welding thin sheets connected to mechanical seals?
Used in rocket turbopumps and other components under conditions of high temperatures and extremely low temperatures, mechanical seals are referred to as welded bellows seals. Metal bellows capable of applying a seal load to the sealing surface to fully seal areas other than the sealing surface are used. Bellows are created by welding together exceedingly thin, donut-shaped metal sheets on an alternating basis between the inner and outer diameters. Since they can be flexibly bent, they are used to accommodate bends in the piping and to dampen vibrations. As metal bellows constitute a flagship product of our company, it is natural that we would possess the technology for skillfully welding thin sheets of metal.
In returning to the topic at hand, nickel hydride battery cases must be thin and lightweight and designed to tolerate internal pressure cycles generated with the charging and discharging of the battery. While our partner initially produced this case by press-working thick sheets and then making the result thinner by chemically dissolving the surface, the high costs of this approach prompted them to entrust the job to us.
By first finding a process manufacturer capable of deep-drawing numerous thin sheets at once and then welding together the resulting parts, we perfected a low-cost nickel hydride battery case that was sufficiently strong and reliable.
The development work we undertook at this time too did not go off without complications. As the internal gas pressure approached 10 MPa, the law governing pressurized gas became applicable. The fact that a special design was involved meant that we had to undergo a design review for a special license application. Analysis also revealed that our case lacked fatigue strength. The cause lay in the fact that, as the part holding the internal battery contacts was simultaneously joined to the welded parts of the case, rigidity would invariably rise and stress would concentrate against the thickness of the sheets making up the case. We devised a form for this part to ensure that the welded parts of the case would swell in a nearly uniform way in line with the increase in internal pressure and allow the generated stress to dissipate. These cases have been loaded onto satellites typical of satellites launched at the beginning of this century, including Kodama, a data relay satellite, and Kiku No. 8, an engineering test satellite. With this as our opening shot, we also went on to produce terminals for space batteries. Technology for joining ceramics to metal parts with a special method helped to achieve both pressure resistance and insulating strength. In addition to nickel hydride batteries, our terminals came to be adopted for an entire series of 13 Ah, 35 Ah, and 50 Ah nickel cadmium batteries produced by Sanyo Electric (now Panasonic) and have been mounted on many launched satellites. Since we have seen a recent shift to lithium-ion batteries as the leading choice for these types of applications, production of these terminals has ended.
We also developed and supplied a bellows-type accumulator for the environmental control system used in Kibo, Japan’s science module attached to the ISS (International Space Station). Each module attached to the ISS is maintained at a fixed temperature by circulating a refrigerant throughout the module. This device is designed to be inserted at a non-end point of refrigerant piping and to stop the expansion of this refrigerant caused by temperature changes with the use of metal bellows. This device is required not to get broken at least for ten years and the specifications required by NASA also applied because this device is connected to the manned ISS, and so development work for us was a truly difficult task. Because one of these devices must be fitted to the orbital exchange unit attached to Kibo’s external experimental platform, we expect that we will be receiving additional orders in the future.
What is your outlook for the future of the field of space?
Unfortunately, we can expect to post little in the way of sales in the field of space. Sales by the Aerospace Business Unit account for 4.6 percent of total sales by our company, but much of this is due to sales tied to jet engines for aircraft and terrestrial gas turbines. The field of space accounts for maybe one percent of total sales, if that. Nevertheless, space is a field that can allow us to obtain advanced technologies. For example, by developing parts for liquid hydrogen in the field of space, we were able to secure technology for minimizing as much as possible leaks of liquid hydrogen. If the use of liquid hydrogen by civilians increases in the future, major possibilities will emerge from this technology.
Significant contributions are also being made by our efforts to recruit personnel. We are a manufacturer specializing in rubber seals and a member of the NOK Group. The hiring of new graduates is carried out at the group level. Indeed, a majority of graduates with science- and technology-related degrees express a desire to work in the aerospace field. For this reason alone, we would like to see JAXA commit more funds to the development of basic elemental technologies. After passing through many hands, this will surely end up constituting a fundamental source of vitality underpinning the entire machine industry of Japan. (Honorific titles have been omitted.)