When you need to choose the right scale for your clean room environment, you must know where you are installing and define an exact standard.
Ingolf Popel Sartorius Group
Ingolf Popel joined Sartorius in 1989 and has held various positions. His professional background includes experience in marketing, product, direct sales management and indirect investment product sales management. His current position is Senior Sales Manager, responsible for the entire product line of industrial scales and scales worldwide. In this role, his main focus is on the pharmaceutical industry and emerging regions such as China, including Asia/Pacific and the Americas. He holds a bachelor's degree in business economics.
What type of clean room do you classify?
A clean room is an environment where only low levels of contaminants are present, including airborne microorganisms, dust and chemical vapors present in the environment. The clean area is filtered through a HEPA or ULPA filter and the channels are sealed by an airtight chamber. Dust suits, gloves, masks and hair nets must be worn to enter the clean room to prevent particles from spreading. And people can release 5 million particles larger than 0.3 microns per minute! Equipment used in cleanrooms must also limit the amount of particulates released into the air, including industrial scales, balances and filling weighing systems.
In Tables 1, 2 and 3, the clean room standard US FED STD 209E is categorized by the maximum number of particles present per cubic foot (but this standard expired in November 2001 and was replaced by the ISO 14644-1 standard) (1).
Once the number of cleanrooms is determined by the number of particles allowed (eg Class 100, ISO Class 5), appropriate weighing equipment can be selected to meet current environmental requirements, based primarily on the material structure of the equipment and Whether there are movable parts, such as lifting plate system, need to be easy to move.
Table 1: US FED STD 209E
Table 2 ISO14644-1 standard
Table 3 Clean room level control
What are the basic statutory requirements for weighing in clean rooms ?
According to the GMP guidelines, the weighing equipment used must have the appropriate range and accuracy level (3.40 EU GMP guidelines). These devices must be calibrated periodically and calibration records must be saved (3.41 EU GMP Guide). Since weighing is important for subsequent processing and product quality, the equipment is periodically verified based on the amount of application workload. This requires a specific process definition through a standard operating procedure (SOP). For each weighing range, the allowable error limit must be defined, that is, the maximum allowable error from the nominal value, and the corresponding measurement uncertainty. (For error determination see the guide for chapter 41 of USP 25)
Another requirement for scales installed in cleanrooms is to understand the actual accuracy requirements. At present, there are several major manufacturers' scales that can meet the requirements of high precision, but when industrial scales must not only meet high precision, but also must face strict cleaning requirements, the real problem arises. According to the European GMP guidelines, weighing equipment must be cleaned after each weighing procedure is completed to avoid the transfer of impurities to the next process. Cleaning must include the bottom of the scale or the foundation pit, as this is often susceptible to contamination. area.
So when you enter the clean room again, please pay attention to the scales, balances or load cells you use – you can usually find them under the mix or storage tank – please check them out, whether they are made of stainless steel And easy to clean? Do they have many dead ends or gaps that may leave dirt? The answer is usually: these are made of stainless steel, but it looks very difficult to clean. Because the fact is that most scales are not designed for a clean environment, even if they meet the guidelines described above to some extent. So now the manufacturer of the scale is working on a special solution for the clean room environment.
What is the design and structure of a scale suitable for use in a clean room?
Stainless steel frame
Most weighing equipment does not have any problems in the 100,000 and 10,000 cleanrooms, but higher grades require better stainless steel (meaning better polishing and smaller surface finish) And easier to clean.
The pharmaceutical and medical technology industries have stricter hygiene requirements. More and more companies are beginning to trust the electro-polished stainless steel surface that is smooth and easy to keep clean. The electropolished surface meets the most stringent hygiene requirements because of its smooth surface, which is not easily retained by microorganisms or residues. In addition, it has good corrosion resistance and can withstand the strongest cleaning agents used in aseptic environments. Austenitic stainless steel is the material of choice for contact with the surface of the product in the pharmaceutical industry.
Stainless steel grade and performance
Stainless steel has certain corrosion resistance to chemicals, aqueous solutions, etc. Most grades of stainless steel contain 12% chromium and up to 1.2% carbon. The metal surface of the highly corrosion-resistant stainless steel has a protective layer that is resistant to chemical reactions. The protective layer consists of metal oxides or hydroxides, is rich in chromium, has a thickness of only a few angstroms, and the protective layer contains metals and corroded media. Separated. The stainless steel protective layer is not stable. After a period of time, the components and structures will reach a certain balance with the surrounding medium. Therefore, once the protective layer is formed, it is impossible to diffuse into another medium. And if the protection layer is destroyed, it usually reorganizes automatically. If a medium does not form a sufficient protective layer, or if the existing protective layer is penetrated or completely destroyed by a chemical, corrosion damage may follow.
Chromium is the decisive alloy for measuring the strength of a stainless steel protective layer. If the chromium content is greater than 12%, it will prevent rust under normal atmospheric corrosion. A further increase in chromium content, or the addition of molybdenum or other alloying elements, will enhance the corrosion resistance of the stainless steel to accommodate a more corrosive environment. Only alloy additions dissolved in the metal can form passivation, which is why the best corrosion resistance comes from the base layer because they do not require isolation and do not deplete chromium and molybdenum due to precipitation or action between the metals.
The heat treatment process used to achieve the optimum material structure is described in the data sheet for some special materials. Stainless steel may be subject to local corrosion or other forms of corrosion due to surface wear, and in the environment of strong acid and alkali, mainly surface wear and corrosion (2)
When you enter the clean room again, please pay attention to the scale, balance or load cell you are using. –You can usuallyfind them undermixes orstoragetanks–Please check them, is it made of stainless steel and is easy to clean? Do they have many dead ends or gaps that may leave dirt? The answer is usually: these are made of stainless steel, but it looks very difficult to clean.
Figure 1 curve shows the arithmetic mean
Stainless steel weighing surface
It is essential that the surface of the device is easy to clean. All surfaces in contact with the product must be completely resistant to corrosion, not only to the product itself, but also to detergents and all other items used for cleaning, disinfecting and sterilizing equipment. Moreover, these surfaces must be made of a non-absorbent material and specify the allowable surface roughness. Surface characteristics must meet the specified average roughness (Ra) specification and must be free of defects such as holes, brush marks, grooves or cracks. For larger surfaces, Ra should be no greater than 0.8μ. The surface that does not touch the product must be smooth enough to ensure easy and thorough cleaning.
Ra is the average roughness of the steel above and below its surface, which is the arithmetic mean (AA) or centerline average. The average roughness is defined by the area between the rough outline and the average line; Figure 1 illustrates the mathematically representative meaning of this point (integration of the absolute value of the height above a given value). The following processes are commonly used to achieve lower surface roughness:
◆ Sandblasting – Abrasives for non-alloyed metals cannot be used to polish stainless steel because the iron particles after rubbing may cause stainless steel to rust. To avoid rust and corrosion, we must ensure that the polish used in stainless steel does not contain iron and sulfur.
â—† Electrolytic polishing - Electrolytic polishing, also known as chemical polishing, is an ideal method for mechanical parts that require polishing. For example, some have complex structures or thin walls, or the material is easily bent and deformed. During the electropolishing process, the portion to be polished is immersed in a special cylinder to make it an anode. The cathode metal immersed in the cylinder causes metal ions to migrate from the surface of the anode specimen while reducing the surface roughness of the material, greatly increasing the proportion of chromium on the surface. This in turn increases the corrosion resistance. The advantage of an ultra-smooth surface is obvious because it prevents crevice corrosion that may result from precipitation. Only a completely smooth, shiny surface can effectively resist corrosion that may originate from cracks or holes. The surface roughness of electrolytically polished stainless steel can be as low as 0.2 to 0.3 microns.
Figure 2a: Pharmaceutical line platform scale with pressure rise system in closed weighing position
Figure 2b: The pharmaceutical production line platform scale can be opened 90 degrees to facilitate the bottom of the cleaning scale
Mechanical Design
The use of stainless steel to design the weighing equipment structure is only one aspect of the clean room environment. Flat-panel scales used in daily weighing (such as loading and unloading scales) may only care about one thing - the price, which is a good idea when no precision requirements or hygienic cleaning are required; however, such a popular scale It should not be used in an environment that is clean or has strict hygiene requirements. In general, scales designed for clean room environments should also have the following common features:
â—†Open frame design for easy cleaning and disinfection
â—† Extremely limited corners and gaps to eliminate bacterial accumulation points â—† Large platforms must be equipped with pressure lifting devices to clean the bottom of the platform
Figure 2 shows an ultra-low table scale designed for a clean room environment. This is a complete electropolishing structure, arc chamfering and integrated pressure boosting system to meet the basic needs of a clean room.
Figure3: Stainless steel before and after polishing       Figure4:Combicsplatform scale with open design frame structure
to sum up
:
Choosing the right scale for a clean room environment is not as easy as it seems. At present, the primary factor is that investigations must be conducted to determine the weighing equipment, not only to meet your accuracy requirements, but also to meet strict cleaning requirements. Carefully check the scales used in your clean room and ask yourself the following questions: First, the resolution and range of the scale? Use the scale's maximum range divided by the resolution (readability). If this number is less than30,000, then you can replace it with a higher precision scale that is only slightly higher in price. Second, does the scale look easy to clean? Even if each scale looks easy to clean the surface, when you lift the weighing platform? Does it have an open frame design and whether there are many dead ends and gaps? Is the bottom of your flat scale uncleanable? If your scale is used in the health sector but it is not easy to clean, then it is time to consider replacement.
Before you purchase weighing equipment for the clean room, consult an expert in the weighing field. Most major manufacturers offer free phone calls or email consultations, and some offer free on-site consultations to customers.
Contact the author: ingolf.
Reference material
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2 Formore details on the corrosion resistance of stainless steel under different media, please refer to “Corrosion of stainless steelâ€, which can be downloaded from (click “English†and then “Products > Materialsâ€)
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