High-speed doors serve cleanroom applications
08/01/2007
New high-speed doors minimize potential contamination and maximize production efficiency
By Matjaz Sentjurc and Vladimir “Benny” Bernard, Efafl ex-CZ s.r.o.
Beginning about 35 years ago, manufacturers began to recognize that to achieve greater productivity, they would need faster, more efficient internal factory transportation and logistics systems. The result was the development of all kinds of new, fast forklifts, cranes, conveyors, and other means of transport. But there remained a weak point—facility doors. Even when operated automatically, access doors were slow to open, and transport vehicles were held up waiting for them, wasting valuable time.
In addition, the slow-operating doors also had a negative impact on the factory environment, particularly for doors opening to the outside. In winter, conditions could not only become very unpleasant for workers, but also cause potential damage to manufacturing materials from continuous temperature and humidity change.
To solve these problems designers developed a new type of fast-opening industrial door—doors that opened and closed so fast that their operation was transparent to transport operations. Similar principles are now being applied to cleanroom doors and pass-throughs with the goal to both minimize potential opportunities for contamination as well as maximize production efficiency.
From high-speed industrial to cleanroom doors
In general operation, cleanrooms are just like other industrial rooms, but with special demands for contamination controlled production—whether pharmaceutical, electronic, fine mechanical, or other products. As such, the requirements driving door and pass-through design are also similar.
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For example, in many highly automated semiconductor fabs, where the processing and transfer of materials is completely automatic, including the use of automatic guided vehicles (AGVs), fast-moving cleanroom doors can significantly reduce the time of processing and transfer of materials and even increase the cleanliness class of the room.
Not all the principles guiding the design and implementation of fast-opening industrial doors apply to cleanroom doors, but there are many common requirements. For example, one of the challenges that needed to be addressed in the development of the high-speed industrial door—the sheer size of the door leaf being operated—must also be addressed for cleanroom doors.
The door must be able to handle both the rapid acceleration of a large-mass door leaf as well as the very rapid deceleration needed to stop it at both full open and close. This requires large and highly stable drive units and components, but by meeting this operational requirement, designers have also achieved significant durability improvements and increased the average life expectancy of the doors. Today, fast-opening industrial doors have top speeds of more than 4 meters per second and a life expectancy of up to 1 million operations.
Safety is another common consideration for door designers as both personnel and equipment must be protected from possible collision with the fast-moving door leaf. Hence, several safety systems have been adopted such as contact edge, light barrier, light wall, light grid, etc.
Sophisticated control units have also been developed using sensors and computer systems to send, receive, and process impulses from different opening devices (activators), other doors, conveyor systems, and other control units. In the event of power failure or other emergency, backup mechanical counterbalance systems have also been developed to ensure doors can be opened without an external power source.
Special requirements
There are also special demands for high-speed doors intended for cleanroom applications. For example, in cleanrooms, multiple doors are usually arranged and installed in an airlock configuration with control units programmed to ensure that one or more doors remains closed at all times. These airlocks can be relatively large with standard doors for transport of large equipment and personnel or small access ports or cabins for passing materials and product.
The basic cleanliness requirements and criteria for designing and manufacturing high-speed doors for cleanroom applications include the following:
Air tightness. Each cleanroom or clean area is continuously refreshed with clean air, so the room maintains either a constant positive or negative pressure. The amount of air to be delivered into the cleanroom depends on the tightness of the entire room. High-speed industrial doors are therefore of great importance, since they are the only element in the cleanroom (sometimes in addition to a personnel pass-through) that is not permanently fixed.
Even if it is accepted that the cleanroom door is not completely tight, it is important to know how large the leakage factor is. Sometimes, a small, controlled air leakage can be welcome, but this should be known in order to most efficiently design the HVAC system and ensure that the room’s required pressure differential is maintained.
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Particle sources. A high-speed door—including its frame, drive unit, and the door leaf itself, which regularly opens and closes—must be designed so it will not produce any particles. The door’s components must therefore also be constructed from suitable materials.
Surfaces. Horizontal surfaces should be avoided in the design of the door s components, as these can provide places where particles can accumulate. All sources of potential electrostatic charge must also be eliminated.
Cleaning. The surfaces of door components should be at and very smooth, without any corners or crevices. This helps ensure regular effective cleaning of the door. Manual activators, if used, are also specially designed to meet this requirement. All metal parts are made of stainless steel. Frames can also be constructed of powdered galvanized steel and door leaves from eloxed aluminium, acrylic glass in aluminum frames, or laminate, depending on the door type.
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Because not all cleanrooms are the same, there are also different types of fast-moving cleanroom doors for different applications. Table 1 on page 35 lists some common important considerations.
International manufacturing and safety standards
To ensure commonality in product manufacturing and safety standards an important consideration especially in the European market, where every country has its own laws, standards, and demands the guidelines and standards in Table 2 have been applied to the design, production, and installation of fast-opening industrial doors.
Finally, anyone operating a cleanroom should certainly be familiar with U.S. Federal Standard 209 cleanroom classification criteria and standards and the follow-on ISO 14644-1 document, which combines the best features of the different base documents available from Europe, Japan, and the U.S.
Matjaz Sentjurc is project manager and Vladimir “Benny” Bernard is sales manager at Efafl ex-CZ s.r.o., a German-based manufacturer of high-speed spiral, roll-up, and folding doors for indoor applications and inlet/outlet bays in various facilities. Bernard can be reached at benny.bernard@efafl ex.cz.