Should I choose aluminum alloy or stainless steel for ULPA outer frame?

The outer frame is often mentioned briefly in the selection discussion. After chatting about filter materials, grades, and sealing methods, I finally asked 'What material is used for the outer frame?'

But the choice of outer frame actually affects many things. It determines the weight, stiffness, corrosion resistance of the filter element, and the matching accuracy of the installation frame, and also affects the sealing reliability after long-term operation. Choosing aluminum alloy or stainless steel is not a question of 'which one is better', but a question of 'which one better suits this working condition'.

First look at the actual requirements of the environment for materials

Environment is the first filtering condition for selecting frame materials.

In places with high humidity and risk of condensation, aluminum alloys may oxidize or corrode in the long term if they are not surface treated. The moisture resistance of stainless steel is usually better, but it also depends on the grade - 304 and 316 have different corrosion resistance, and 316 is more stable in chlorine-containing or acidic environments.

If the air flow is likely to come into contact with acidic or alkaline gases, cleaning agents or disinfectants, the resistance of the material needs to be checked individually. The anodized layer of aluminum alloys is stable under most cleaning agents, but strong alkali or certain fluorine-containing cleaning agents may damage the oxide layer. Stainless steel is resistant to most cleaning agents, but chlorine-containing environments may cause pitting corrosion.

The key is not to ask 'whether aluminum alloy is corrosion-resistant', but to ask 'how does aluminum alloy or stainless steel perform in this specific medium and concentration'. This information comes from project working conditions and material data, and is not a general experience. involving The selection and material verification of ULPA ultra-high efficiency filters should be done under actual working conditions.

Weight and installation conditions tend to be more straightforward

Many projects choose aluminum alloy, not because it is more corrosion-resistant, but because it is lighter.

With the same external dimensions, the weight of the aluminum alloy frame is usually significantly lower than that of stainless steel. For ceiling installation For FFU fan filter units , the weight of the filter element will affect the load-bearing and installation operations of the ceiling structure. Device-side applications such as The EFU equipment-side fan filter unit has a compact internal space. Installation and replacement often require one-handed operation or adjustment in a small space. The light-weight filter element is more convenient to operate.

Stainless steel frames are heavier but generally have better stiffness and structural stability. If the rigidity of a large-sized filter element is insufficient, it may deform slightly due to its own weight or pressing force after installation, affecting the sealing surface fit. In this case, a stainless steel or structurally reinforced aluminum alloy solution may be more suitable.

There needs to be a balance between weight and stiffness. Lighter is not better, nor is stiffer better. It depends on the installation method, supporting structure and frequency of replacement. If the filter element position is changed frequently, lightweighting can reduce the operating burden; if the filter element size is large and the operation time is long, structural stability may be more critical.

Surface preparation and contamination control should also be checked

The surface treatment of the outer frame will affect pollution control in special processes.

Anodized aluminum alloy : There is an oxide film on the surface, usually without additional coating. The outgassing level is low in conventional clean environments, but may be affected in some highly corrosive media.

Stainless steel : The surface may be passivated or electrolytically polished. Electropolishing can reduce surface roughness and reduce particle adhesion, and is more common in semiconductor or pharmaceutical projects. However, the outgassing, corrosion resistance and cost of different treatment methods are different and need to be confirmed according to project requirements.

Coated or sprayed frames : less expensive, but the coating may peel or release organic matter. For projects with low outgassing or high cleanliness requirements, the suitability of the coating needs to be confirmed. For specific verification methods, please refer to the instructions related to low outgassing.

Material designation alone does not demonstrate the level of contamination control. 'Stainless steel' does not mean low outgassing, and 'aluminum alloy' does not mean no dust generation. Surface preparation, cleaning processes and packaging methods all play a role. involving When selecting a HEPA/ULPA air filter , the pollution control requirements should be checked together with the material and surface treatment.

Installation fit and long-term sealing

The dimensional accuracy and stiffness of the outer frame directly affect the sealing fit between the filter element and the installation frame.

Aluminum alloy has good processability and easy control of dimensional accuracy, but its stiffness is relatively low, and large-sized products may deform during transportation or compression. Stainless steel has good rigidity, but it is difficult to process. The flatness after welding or bending needs to be strictly controlled.

The liquid tank sealing structure requires high accuracy of the outer frame , and the cooperation between the blade edge and the tank body requires the outer frame to maintain a stable shape. Gasket sealing relies more on the uniformity of the pressing parts and the flatness of the outer frame. For specific seal verification methods, please refer to the relevant instructions.

After long-term operation, if the outer frame is corroded, deformed or the surface treatment is degraded, the sealing surface may fail. When selecting, in addition to looking at the initial state, the stability of the material within its design life must also be evaluated. When replacing the filter element in a pharmaceutical project, the condition of the outer frame is often one of the references for judging whether it can continue to be used.

Project judgment example

A certain pharmaceutical clean area needs to replace the ULPA filter. The original product uses a spray-coated carbon steel frame. After several years of operation, it will become rusty and the sealing surface will also be affected.

The project team considered two alternatives: anodized aluminum alloy and stainless steel 316L. When comparing, first look at the environment: the humidity in this area is high, so use chlorine-containing disinfectants when cleaning. The long-term performance of aluminum alloys in chlorine-containing environments needs to be confirmed; stainless steel 316L has better chlorine resistance, but its weight increases significantly.

Let’s look at the installation conditions: the filter element is located above the ceiling, and two people are required to replace it. As the weight increases, installation becomes more difficult. In terms of stiffness, both materials can meet sealing requirements at the same size.

Anodized aluminum alloy was ultimately chosen, but the supplier was required to provide resistance data to chlorine-containing cleaners and adjust cleaning methods in maintenance procedures to avoid prolonged exposure to high-concentration disinfectants. After replacement, regularly check the surface condition of the outer frame and include it in the annual maintenance plan.

This case shows that the choice of outer frame material is a balance between environment, installation and cost. No one material is suitable for all working conditions, the key is to look at the actual constraints. involving When selecting the ULPA ultra-high efficiency filter , the material plan can be checked based on the project conditions.

Selection and Acceptance Checklist

About Aili Industrial’s outer frame configuration package

The choice of outer frame material ultimately depends on the specific working conditions and installation conditions. Environment, cleaning method, replacement frequency, sealing structure, these information are determined, and the material plan has a basis.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. The sheet metal processing link can process outer frames of different materials and surface treatments according to project requirements. In the planning stage, the installation space, sealing method and cleaning requirements will be combined to help check the matching of materials and structures. When the filter is matched with FFU, EFU and other equipment, the outer frame interface and installation matching dimensions can also be confirmed uniformly.

When enquiring, provide the usage environment, cleaning methods, installation conditions and sealing requirements to help confirm the appropriate outer frame solution. Specific specifications are subject to the technical documents and drawings confirmed by the project.