Design guide for using air cylinders in clean rooms｜From countermeasures to exhaust

Here.Automatic machines operating in a clean room　Used inAir CylinderIt is a note about.

Air cylinders are the most common mechanical element among machine designers, but when designing automatic machines for clean rooms, we are particularly concerned about the selection and use of air cylinders.　While the convenience of air cylinders is universally acknowledged, the risk of particle generation, especially in terms of exhaust treatment and specific measures to deal with dust emissions, is always a headache.

Although many information sites introduce individual countermeasures, we have felt that there is little information that systematically links and explains the root causes of contamination, specific product selection, and even the design concept of the entire equipment.　　This article is organized to link such fragmented knowledge and provide an understanding of the overall picture.　　First, it establishes a basic knowledge of the sources of contamination in clean rooms and air cylinders, and then proceeds from there to specific countermeasures.　　Finally, it covers the differences between alternative technologies, such as electric actuators, and design considerations that extend to the entire system, so that readers can make the best choice with confidence.With links to the relevant products as much as possible.　I will proceed.

Basics of Cleanroom Air Cylinder Countermeasures

ISO standard for cleanliness of clean rooms

Design of equipment for clean rooms　In embarking on theThe first thing to understand is the level of cleanliness required for the spaceIt is.

The ISO standard (ISO 14644-1) is the global indicator of this cleanliness and determines the design prerequisites.　　This standard grades cleanliness from "ISO Class 1" to "ISO Class 9" based on the number of particles of a specific size present in a given amount of air.

The smaller the class number, the cleaner the environment, i.e., less dusty.　For example, ISO class 3 to 5 is required for state-of-the-art semiconductor manufacturing plants, while class 5 to 8 is required for precision equipment and pharmaceutical plants.Of particular note to the machine designer is the fact that this cleanliness class must be maintained "in operation," that is, with the equipment actually in operation.

Even if the equipment is clean when it is stopped, it is useless if it emits particles as soon as it starts moving.　　Therefore,Designers must always assume that the equipment will be "in operation" and take measures to ensure that it will meet the required ISO class.

Two pathways for air cylinders to become a source of contamination

The reason why the use of air cylinders in cleanrooms is prudent is that they have two major pathways through which contaminants can be released into the environment.

Understanding these two pathways separately is the first step in developing effective countermeasures.The first path is "internal dusting" caused by mechanical wear inside the cylinder.

In air cylinders, the packing (sealing material) used to maintain airtightness rubs against metal parts as the piston rod moves back and forth at high speed.　　This friction gradually wears down the packing made of nitrile rubber and other materials, causing it to peel off in the form of fine particles.　　These particles may be released with the exhaust air to the outside.

The second path is "external emissions" caused by the power source, the compressed air itself.　　Typical compressed air supplied to a factory may contain various contaminants, such as oil mist mixed with compressor lubricant, rust and wear powder in the piping, and dust in the atmosphere sucked in by the compressor.　　Air containing these contaminants is supplied to the cylinder,Emissions from the exhaust port contaminate the clean room.The first is the

Quality control of supply air as a source of pollution

In considering contamination control measures for air cylinders,The most radical and effective approach is to clean one of the sources of contamination: the supply air itself.

This is, so to speak, source control for contamination control and is the basis for all countermeasures.　　The use of specially controlled "clean dry air (CDA)" is standard at sites where extremely high cleanliness is required, such as in the semiconductor industry.

ISO 853-1, the international standard for compressed air quality, defines cleanliness grades for three elements: solid particles, moisture, and oil.　　For clean room applications, the goal is to achieve Class 0 or Class 1, the cleanest grade in this standard.　　A CDA supply system to achieve this typically consists of the following equipment

• Oil-free compressorsOil contamination: Eliminates the root cause of oil contamination by eliminating the use of lubricating oil in the compression chamber.
• air dryer: Refrigeration or adsorption dryers remove moisture from compressed air and prevent condensation.
• multistage filter: A combination of pre-filters and mist separators removes fine oil mist and solid particles step by step.

The machine designer is responsible for clearly stating the required compressed air quality in the equipment specifications.　　This makes air quality part of the equipment installation requirements and ensures clean performance.

Selection of low-dust cylinders to reduce internal dust generation

Even if the air supply is clean, the risk of contamination remains if the cylinder itself generates particles.　　As a second measure, it is important to select a product designed to minimize dust generation inside the cylinder, or "internal dust generation.Air cylinders marketed for clean room use are equipped with various innovations to control dust emissions.

Adoption of special materials and lubricants

Special wear-resistant materials are used for packing to reduce the generation of wear powder due to sliding.　　Also, the grease sealed for lubrication is made of a special material with low dust generation and evaporation resistance.

For example, SMC has a fluorinated grease in its standard clean series, while Koganei has a lineup of clean system equipment that uses highly safe NSF H1 grade grease, which is also intended for the food and medical fields.

Reference: Non-contact technology for ultimate low dust emission

For special applications that require the ultimate in low dust emission, there are also technologies that do not allow physical contact between sliding parts. This is not a common option, but knowledge of it will broaden the scope of your design.

For example,Air bearing cylinderis supported by levitating the piston rod with compressed air pressure, so mechanical friction does not occur in principle.　　This fundamentally eliminates the generation of particles due to wear.　　However, the cost tends to be high due to its special structure, and it is considered as an option when performance rather than cost is the top priority.

Cleanroom air cylinder exhaust and product selection

Exhaust treatment with exhaust filter and vacuum suction

Even if the supply air is cleaned and a low-dust cylinder is selected, it is difficult to completely eliminate dust emissions.　　The last resort, then, is exhaust treatment technology to prevent particles from being released into the clean room should they occur.　　There are multiple approaches to this, ranging from passive filtering to active suction.

Method 1: Direct exhaust with high-performance exhaust filter

This is the easiest way to install a high-performance filter directly into the exhaust port of the cylinder.　　For example,CKD's FAC series　Clean exhaust filters such as the "Clean Exhaust Filter" have a special structure called a hollow-fiber membrane and have extremely high performance, removing particles as fine as 0.01 μm at 99.991 TP3T or higher.

This allows exhaust air to be discharged directly into the clean room, which has the great advantage of greatly simplifying the exhaust piping design.

Method 2: Forced evacuation by vacuum suction

The most reliable and advanced method is vacuum suction from the sliding parts. This type of cylinder has a dedicated suction port (relief port) near the rod packing. By connecting this port to a vacuum source such as a vacuum pump or ejector, the air around the sliding portion of the rod is constantly sucked.

This allows particles generated by packing wear to be captured and removed directly at the source before they mix with exhaust air and are released to the outside.SMC's 11-series　and ... andCKD's P53 series　These are typical products that use this vacuum suction structure.

Comparison of clean products from three major manufacturers

When using air cylinders in cleanrooms, understanding the features of the solutions offered by each of the major pneumatic equipment manufacturers and selecting the best product for your project requirements is key. Here we compare the approaches of three companies, SMC, CKD, and Koganei.

Like this,SMC has a product lineup that can flexibly meet diverse needs, CKD has advanced technology that solves specific issues, and Koganei has system-wide cleanliness assurance and suitability for specific industries.are available.　　Designers must comprehensively consider the equipment's application, cleanliness requirements, cost, and ease of maintenance to select the most appropriate manufacturer and product series.

Clean handling of air cylinder peripheral equipment

While cleanliness measures for the air cylinder itself are important, they are not the only way to complete the system. The peripheral equipment used to drive the cylinder can also be a source of dust in a clean room, so it is essential to take measures for the entire system.

Solenoid Valves and Speed Controllers

Solenoid valves (solenoid valves) that control the movement of air cylinders can also be a source of contamination because they have exhaust ports.　　Therefore,Solenoid valve with clean specifications　exists and requires the same exhaust treatment as cylinders. Generally, the exhaust from multiple solenoid valves is collected in a manifold for centralized exhaust.

It also adjusts the speed of the cylinderSpeed controller for clean　Also, measures such as installing a clean exhaust filter in the exhaust port are required.

Fittings and Tubing

Depending on the material, fittings and tubes used to deliver compressed air may also generate particles due to wear and deterioration.　　For clean room applications, tubes and tubes made of fluoroplastic (PFA, PTFE, etc.), which generate less dust,Stainless steel fittings　are often chosen.

Another point to consider is that anti-static specification tubes are used in semiconductor plants as a countermeasure against static electricity.

Floating joints and sensor switches

The floating joint attached to the end of the cylinder rod is an important component that absorbs misalignment with the drive object.

If left unchecked, excessive force will be applied to the rod and packing, causing abnormal wear and increasing dust generation.　　Proper use of floating joints indirectly contributes to extending cylinder life and maintaining clean performance.　　Also, a sensor switch (auto switch) detects the position of the cylinder,It is necessary to check that cable sheathing and other materials conform to clean room standards.

Comparison with electric actuators and their merits and demerits

When considering linear motion in clean rooms, electric actuators are always compared as an alternative technology to air cylinders.　　The choice between the two must be based on a proper understanding of the application requirements.

Advantages and disadvantages of air cylinders

The greatest advantage of air cylinders is that they are compact and lightweight, yet can generate a large thrust force, and the initial installation cost is relatively low.　　They are also characterized by their simple and robust structure, which makes them resistant to harsh environments.　　On the other hand,The biggest disadvantage is the risk of contamination, which has been detailed in this article.　　In addition, they are not good at precise stopping at arbitrary positions and fine control of speed and thrust.

Comparison with electric actuators

Generally, electric actuators are considered cleaner because there is no exhaust.　However, electric actuators may also generate dust due to wear of the drive mechanism, such as ball screws and linear guides, so it is equally important to select clean-compatible grade products.

The greatest strength of electric actuators lies in their ability to precisely control position, speed, acceleration/deceleration, and thrust.　This enables smooth motion with less impact and multi-point positioning. However, initial installation costs tend to be higher than those of air cylinders.

Ultimately, neither is better than the other, and it is crucial to use the right one in the right place.Air cylinders with countermeasures can be an excellent choice for clamping processes that require high thrust and simple reciprocating motion between two points, while electric actuators can be an excellent choice for precision multi-point positioning and transfer processes where shock is to be avoided.

Designed with downflow and surrounding environment in mind

In addition to the selection of individual components, the overall design concept of the equipment has a significant impact on clean performance.　　In particular, layout design that understands the unique air flow and environment of clean rooms and makes it an ally is very effective.

Overall equipment layout design

Most high-performance clean rooms use a "downflow" (vertical laminar flow) system, in which clean air flows in one direction from the ceiling filter to the floor.　　This airflow is responsible for quickly pushing particles generated in the room down to the floor and expelling them.The basic principle of design based on this principle is to place components that are sources of dust below the product (workpiece) whenever possible.

Air cylinders and motors.Layout of moving parts under the workpiece significantly reduces the risk of particle adhesion to the product.It can be done.

Material Selection and Static Control

Material selection for the equipment is also important.As a rule, it is recommended that stainless steel (SUS304 or SUS316) be used for exposed parts to prevent corrosion and rust.　　This is because rust is itself a significant source of particle contamination.　　In addition, in semiconductor plantsDestruction of products and adsorption of particles due to static electricity are problems　This is the case.　　Therefore,Anti-static measures, such as selecting conductive materials for equipment frames and covers and providing appropriate grounding, should be incorporated into the design.

Consideration for maintainability

Regular maintenance is essential for equipment in a clean room to maintain its cleanliness for a long period of time.　　It is important to keep in mind that the structure should be easily accessible from the design stage so that exhaust filters can be replaced, cylinders inspected, and cleaned easily.　　Complicated structures that are difficult to clean can accumulate dirt, which itself can become a new source of contamination.

How to Select the Best Cleanroom Air Cylinder

Based on what has been explained in this article, we will summarize the key points for selecting the best cleanroom air cylinder.

• First, check the cleanliness class (ISO standard) of the clean room to be designed.
• Assuming that cleanliness is maintained during "operation" when the equipment is actually in operation
• Understand that there are two contamination pathways: wear inside the cylinder and contamination of the supply air.
• The basic countermeasure is to use high-quality clean dry air (CDA) as the supply air
• Equipment specifications clearly state the required air quality (in accordance with ISO 8573-1)
• Select a cylinder body with wear-resistant packing and low-dust grease.
• Direct exhaust with a high-performance filter" and "vacuum suction" are effective exhaust countermeasures
• Direct exhaust filters can greatly simplify piping design
• Vacuum aspiration is the most reliable way to capture contamination at the source
• SMC offers a wide range of options to meet your requirement specifications
• CKD has strengths in specific technologies such as vacuum suction and exhaust filters
• Coganei is suitable for system-wide cleanliness and food and medical applications
• Unify not only cylinders but also peripheral equipment such as solenoid valves and fittings with clean specifications.
• Floating joints prevent misalignment and suppress abnormal packing wear
• Air cylinders are advantageous when cost and thrust density are important
• Consider electric actuators when precise positioning or speed control is required
• The ironclad rule is to place the dust emission source below the product in the equipment layout.
• The basic material is stainless steel to prevent rust, and anti-static measures are also taken into consideration.

That's it.