Volume 50, Issue 6 - June 2015

Guestbook

Coming Clean
How to Evaluate Glass Cleanroom Design

by Mike Hallahan

Determining the value of a properly designed glass cleanroom involves weighing the expected quality of the glass being processed against the industry standards that a customer or product may demand. As an example, most industry standards for insulating glass fabrication do not require cleanroom-level production. With laminated, digitally printed or solar glass, however, it’s imperative.

When deciding to construct a fully functional glass cleanroom, fabricators should consider their exact processing needs as well as the level of room control needed.

Here’s a look at several areas to consider when reviewing return on investment of a properly designed cleanroom.
Expectations and

Industry Class Levels


Both the glass manufacturer and end product user should determine what the cleanroom must provide. A room constructed without proper control methods will eventually not live up to either’s expectations. Laminating with polyvinyl butyral or Ionoplast interlayers, for example, requires specific moisture-control levels in both lay-up and storage due to their hygroscopic properties. Uncontrolled moisture levels will affect lamination-adhesion qualities. Cleanrooms are designed to prevent contamination between interlayers during laminated glass fabrication, as well as unwanted surface debris during digital ink printing. A perfectly produced product will lose all its value to highly visible contaminations.

In order to prevent unacceptable contaminations, the class level of the room is an important decision. Class levels normally are rated by two industry standards. The standards that represent graduated levels of cleanliness are ISO 14644-1 and FED STD 209E (numerical class levels). ISO levels are rated from 1 to 9 and numerical class levels are rated from 1 to 100,000. Both rating systems share a common linkage in defining air qualities by the amount of airborne particulates within a cubic area of measured airspace. In relation to the most accepted and recommended levels for the glass industry, the levels should be at a minimum equivalent to ISO 8 or Class 100,000 (see chart below.)

ISO 14644-1 Cleanroom Standards
Class Maximum Particles/m3 FED STD 209E Equivalent
≥0.1 μm ≥0.2 μm ≥0.3 μm ≥0.5 μm ≥1 μm ≥5 μm
ISO 1 10 2.37 1.02 0.35 0.083 0.0029  
ISO 2 100 23.7 10.2 3.5 0.83 0.029  
ISO 3 1,000 237 102 35 8.3 0.29 Class 1
ISO 4 10,000 2,370 1,020 352 83 2.9 Class 10
ISO 5 100,000 23,700 10,200 3,520 832 29 Class 100
ISO 6 1.0x10^6 237,000 102,000 35,200 8,320 293 Class 1,000
ISO 7 1.0x10^7 2.37x10^6 1,020,000 352,000 83,200 2,930 Class 10,000
ISO 8 1.0x10^8 2.37x10^7 1.02x10^7 3,520,000 832,000 29,300 Class 100,000
ISO 9 1.0x10^9 2.37x10^8 1.02x10^8 35,200,000 8,320,000 293,000 Room Air
In relation to the most accepted and recommended levels for the glass industry, cleanroom levels should be at least equivalent to ISO 8 or Class 100,000.



Layout, Plant Flow and
Raw Material Storage


When considering the prime location for a new glass cleanroom, the plant processing flow should be factored into the decision. Glass product entry into and exit from the cleanroom building should be considered in the scheme of process flow as well. This helps ensure effective distribution from one processing area to the next. Knowing which pre-cut glass products will need to be sent to the cleanroom and where they will travel next can be helpful to efficient plant production.

The actual floor plan is another preemptive decision. For starters, clean glass from an appropriate glass washer should enter the cleanroom directly through a slot in the wall. This will ensure that the clean and statically controlled glass will have the shortest distance and exposure time prior to laminating lay-up or ink printing.

The size of the work area and internal processing equipment also needs to be justified to determine the room’s actual footprint size. A well-planned cleanroom will support a built-in construction feature to include an overhead lifting device for large glass processing. There may also be a need for a removable wall portal to bring in existing and future processing equipment. Raw materials may require a connected cold storage area for laminating moisture- and temperature-sensitive interlayers. This area should be isolated from the working area but still accessible for deliveries and stocking. A separate entry and gowning room should be designed with an airlock system to help prevent the migration of outside contamination into the working areas.

The Four Factors

There are four major factors when considering clean room controls:

• Positive pressure flow;

• Temperature and humidity controls and

• Regulation of airborne particulate counts.

One of the most important decisions to make when purchasing or constructing a cleanroom is the room’s overall integrity. In order to obtain the highest level of finished product and a room that can operate on the most cost-effective energy-saving design, the building shell must be airtight, insulated and strategically outfitted with a properly engineered HVAC system. This will have a major impact on conserving energy and operational costs. Improper design of the building’s structure and environmental control system will have a long-term negative effect.
Positive pressure is a critical function of the air-delivery system. The room’s internal air pressure should have an attenuating measurement of pressure level from the working area to entry and storage areas, and eventually the outside ambient air. The circulated air should have the proper air exchanges per hour as defined by the classification of room standards. It should be filtered to equivalent levels to control airborne debris. The working climate levels should be maintained to the glass and/or material supplier’s recommendations.


Knowing which pre-cut glass products will need to be sent to the cleanroom and where they will travel next can be helpful to efficient plant production.


Monitoring and Maintaining


A cleanroom is no different than any other controlled system when it comes to maintaining an expected set level of proper processing conditions. From time to time, equipment mechanical breakdowns or power outages will happen. A real-time monitoring system is important to track temperature fluctuations and humidity levels as well as the increase of airborne contaminations. Reports can be logged to identify out-of-control events and provide automatic notification of what happened, and when, by way of various methods of communications such as e-mail, text or mobile contact. This can minimize product quality loss.

Cleanrooms can also incorporate monitoring and programmable controls that adjust environmental levels to save energy during specific times, such as production schedules, seasonal climate conditions or changing product needs. No matter how well a cleanroom facility is functioning, there will always come a time when room conditions will degrade. Human interactions will eventually change the level of cleanliness in a room; therefore, a meticulous system of periodic micro-cleaning is important to maintain acceptable levels. Proficient cleaning should remove the contaminants and not just push them around. As an example, a cleanroom rated at class 100,000 levels can drop to a level of 10,000 just by a well-scheduled cleaning program. Having the room cleaned and then evaluated by a professional company using the correct measurement equipment is important.

Expansion for Future Needs

A modular-design cleanroom using prefabricated wall systems and bolt-together wall connections will allow for future building modifications as production or processes require. As with any changing business, the ability to adjust to needs can be an important factor in a long-term business plan. As an example, most nailed-together wall constructions cannot be reconfigured easily.

The glass industry and associated glass products have been evolving rapidly. The need for environmentally controlled production areas will likely increase as the techniques of producing high-tech glass products continue to grow. Preparing a glass production facility with a high-quality cleanroom will help progressive companies quickly enter new areas of advanced glass production.

the author

Mike Hallahan is an independent glass consultant and also a glass support specialist with Joe’s Refrigeration/Cleanroom Solutions Inc., based in Withee, Wis.


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