by Ron Kosmalski
Clean Air Technology, Inc.
The health care community is a significant consumer of plastic products and components. Products ranging from syringes and IV bags to medical grade tubing and implantable devices now rely on injection molders to meet demand.
Manufacturers hoping to enter that arena already may have mastered product quality and production efficiency targets, but frequently are challenged with another set of performance goals ... meeting air cleanliness standards.
Understanding cleanroom classifications
By definition, a cleanroom is a pre-defined room or area where the volume of particulates as small as 0.5 microns in size is reduced through filtration and air exchanges. Instrumentation is used to sample volumes of air within the environment to qualify clean classifications as defined by global ISO standards. Control of temperature, humidity and pressure are additional environmental parameters frequently measured within cleanrooms.
The cleanliness classifications are well-documented and based on identification of six categories of sizes, ranging from sub-micron sized particles of 0.1 and up to 5 microns in size. A micron is one millionth of a meter. We are unable to see anything this small without the aid of microscopes, but if we could set particles that are one micron in size side-by-side, we would need 25,400 of them to span one inch. The cross section of a typical strand of hair is 35 to 40 microns in size, so when sub-micron-sized particles need to be controlled, High Efficiency Particulate Arrestance (HEPA) filters are required. There are plenty of other acronyms used, but the point is: this is a special, clean environment. These lightweight particles easily are suspended and influenced by air currents. Particle counters with laser light beams are used to qualify the ISO-clean manufacturing environment by identification of the quantity of particles present in a sampled volume of air. These are documented as the quantity found in a cubic meter of air within the environment.
Designing a cleanroom to meet an ISO-8 level means enough air needs to be delivered through enough filters to reduce the particle count to 832,000 one-micron-sized particles in a cubic meter of air (a sample equivalent to approximately 35 cubic feet).
Some plastic products can be terminally sterilized after manufacturing, but others are unable to withstand the sterilization methods effectively and must be produced in clean environments. Cleanrooms are not a substitute for sterilization, but they complement the process by reducing particulates that accumulate on the product or package surface.
If the product that warrants the ISO-classified environment can be produced in its entirety within a single line or similarly confined area, a cleanroom envelope can be built around that line. If this is not practical due to the multiple processing requirements of a product, the feasibility of upgrading the entire production environment may need to be evaluated.
Designing a cleanroom
Aside from the cost for the project, key considerations when planning a cleanroom are cleanliness and environmental goals, opportunities for effective air distribution and supporting infrastructure.
1. Environmental goals
Unless defined by the end user or final product packager, the actual cleanroom classification selected by the manufacturer may be determined by the nature of the product, the manufacturing process itself and the potential for effective sterilization. At the minimum, molding production facilities designed and built today will meet an ISO-9 air cleanliness classification.
Areas where specific molding operations take place frequently are designed to meet an ISO-8 or ISO-7 classification. If a particular material is adversely affected by sterilization procedures or if downstream assembly adds to the complexity, a more critical manufacturing environment meeting ISO-6 or ISO-5 cleanliness levels may be specified.
Temperature and humidity levels within the manufacturing environment should be identified as part of the cleanroom design. Medical grade component manufacturers should be able to obtain qualification data from the end user and, once identified, the air system can be designed to meet the specific temperature, humidity and filtration goals.
2. Effective air distribution
Cleanrooms are defined areas where increased air exchanges and high-efficiency filters combine to reduce airborne contamination within the designated space. Dedicated air handling systems and HEPA filtration components are used for this purpose.
The nature of molding operations combines electrical, pneumatic and mechanical functions that generate particulates and turbulence. The cleanroom or designated clean area should be designed to bathe the product and process in HEPA-filtered airflow and to reduce the opportunities for turbulence.
Effective removal of the particle-laden air steam is equally as important as directing the airflow onto the critical zone. This can be accomplished by utilizing low-wall air return ducts adjacent to the injection molding machine. Making provisions for the specially conditioned clean airflow to find a route away from the critical zone will help minimize the time these lightweight contaminants will be exposed to the product. This "conditioned" air can be returned to the cleanroom air handler for efficient operation. The physical dynamics of the recirculating air system need to be considered, along with the support utilities and material handling requirements of the process line.
An air return plenum is a key design element in building an effective recirculating airflow system. The plenum is a double-sided space that can be sealed to serve as a duct or airway within the room or space adjacent to the clean zone.
In existing facilities, adding/building plenums above and near the process line may be too complicated to achieve. Injection molding lines require numerous utility/service connections for electrical, chilled water supply/return, compressed air, etc. These frequently are routed through the facility and then dropped vertically to the molding machine. In addition, overhead cranes frequently traverse the manufacturing floor, compounding the issues in determining a layout for the ideal air distribution network. Depending on the logistics, it may be impractical to locate an air return plenum above, below or around this collection of service utilities and equipment, so dedicated low-wall air return ducts need to be routed throughout the space.
All of these factors need to be addressed when developing the floor plan for an injection molding facility.
3. Supporting infrastructure
New construction simplifies planning for the cleanroom. A reduced environmental envelope can be considered if planning a new facility, and a favorable location for the cleanroom can be chosen to take advantage of the proximity to the building’s mechanical and/or electrical rooms and platforms. Process equipment layout can be orientated to enable the use of portable cranes and hoists for die changes and other service requirements, and utility distribution can be routed to enable space for the air supply and return system ductwork.
The area for the clean operations should be away from material handling and high traffic aisles and also away from doors that frequently are opening to the outside. Cleanrooms should be located where a level, cured floor can receive a high-quality sealer and coating to ensure the surface cannot degrade and contribute particulates to the environment.
Existing facilities with molding operations rarely afford space for optimal air flow and distribution. Portable air projectors or scrubbers can be added to improve the air quality by reducing the particulate concentrations of the air near specific machines or operations, and emphasis must be placed on cleaning and turbulence. Machine surfaces near the platens should be cleaned, and utility lines with related fittings, gages and support members should be cleaned and maintained. Material handling equipment and personnel activities adjacent to the molding operation should be minimized or altered where possible to reduce disruptive air flow patterns nearby, and the floor should be effectively sealed.
Planning a cleanroom
Is extra cooling needed? Is humidity control a factor? How clean do we need to be? What level of gowning will be sufficient? How can we get from where we are to where we need to be?
The answers to those questions can help you proceed down the right path. Find the answers by doing your research, asking your customer and contacting industry experts for their insights and recommendations. You may be able to consider something as simple as a portable softwall cleanroom or air projector, or you may need something as complex as a dedicated multi-suite manufacturing environment with independent temperature, humidity and pressurization controls.
When in doubt, lay it out. Just like measuring furniture or appliances when renovating a room in our house, making a floor plan is the best start for any cleanroom project. The first priority always is safety. Ensure there are adequate paths or provisions for personnel egress if they need to make an emergency exit. Ensure there is adequate room for personnel to perform the loading, staging, retrieval and cartage of materials or other process-driven functions that require human interface.
Then, add the support services that make the production process possible. Determine the route for utilities, cranes or other lifting mechanisms, material carts, totes and relevant transfer components. Consider options that can enable a clear path for air supply and return requirements.
Include additional space adjacent to the cleanroom for the air handling system, and designate additional space for housekeeping supplies or potential gown-up/staging requirements.
Finally, enlist the services of a qualified and experienced cleanroom design/fabricator. Every sheet metal and air conditioning contractor will convince you that they can make this work, but due to the complexities involved, rely on the expertise of the companies that do this for a living. Work with a company that has fabrication capabilities to help make your investment a success from the start.