For manufacturers working with stainless steel medical device parts, corrosion resistance is not just a finishing detail. It is part of product performance, quality control, and customer confidence.

Small stainless steel parts such as cannulas, surgical tubes, guide components, fittings, and machined instruments may look clean after fabrication. But the surface can still contain free iron from machining, handling, or manufacturing.

If that free iron remains, the part may be more vulnerable to rust, staining, or corrosion.

That is where citric acid passivation becomes an important final step.

In this example, a growing medical device component manufacturer needed a better way to manage stainless steel passivation. The company had been outsourcing the work, but higher production volume made outside processing harder to control.

The goal was simple: bring citric acid passivation in-house, improve process control, and reduce delays without adding unnecessary chemical handling challenges.

The Problem: Outsourced Passivation Was Slowing Down Production

For years, the manufacturer sent stainless steel parts to an outside vendor for passivation. That worked when production volume was lower.

As demand increased, the process became harder to manage.

Parts had to be packaged, shipped, processed, returned, inspected, and released back into production. A delayed batch could slow down customer orders. A failed test could create rework. A rush order depended on the vendor’s schedule.

The company needed better control over lead times, documentation, quality testing, and production flow.

They did not just need passivation. They needed a controlled passivation process that fit their own manufacturing schedule.

Why Citric Acid Passivation Made Sense

Historically, many manufacturers used nitric acid passivation for stainless steel. Nitric acid can be effective, but it also brings more safety, ventilation, handling, and disposal concerns.

For this application, citric acid passivation was a better fit.

Citric acid passivation removes free iron from the stainless steel surface and helps support the formation of a protective passive oxide layer. That improves corrosion resistance while offering a safer and more practical alternative to nitric acid for many stainless steel applications.

For this medical device manufacturer, the value was clear:

• More control over production timing
• Reduced dependence on outside vendors
• Better lot visibility
• Safer chemistry compared with nitric acid
• A process that can support ASTM A967 or AMS 2700 requirements when properly validated

Citric acid passivation was not just a chemistry change. It was a way to bring an important quality step back under internal control.

The Solution: An In-House Citric Acid Passivation Process

The manufacturer implemented a controlled in-house process for stainless steel parts using an ultrasonic automated passivation system.

Instead of moving parts from tank to tank, the system moved the fluids through a single automated process chamber. A typical process included:

• Alkaline cleaning to remove oils, debris, and manufacturing residue
• Water rinsing, often with DI or RO water
• Citric acid passivation to remove free iron from the stainless steel surface
• Additional 2 rinses to remove remaining chemistry
• Drying before inspection or packaging
• Lot-based testing based on the required specification

The cleaning step was critical. Citric acid passivation is not a replacement for cleaning. If oils, grease, fingerprints, or shop soils remain on the part, they can interfere with the passivation process.

Many manufacturers use citric acid chemistries such as CitriSurf® for this type of work. Best Technology offers CitriSurf® as an option for stainless steel citric acid passivation, along with the equipment needed to build a complete process.

How It Worked in Production

In production, operators loaded stainless steel parts into a basket or fixture inside the process chamber. The parts stayed in place while the system automatically moved cleaning, rinse, and passivation fluids through the chamber.

The parts were cleaned first, then rinsed. After cleaning, the system introduced the citric acid passivation solution. During this stage, the citric acid removed free iron from the stainless steel surface, helping the part develop a more corrosion-resistant passive layer.

After passivation, the parts were rinsed twice, dried, and prepared for inspection.

The biggest difference was control. Instead of waiting on an outside vendor, the manufacturer could process parts according to its own production schedule. Quality could document the process, verify results, and respond faster if a customer requirement changed.

For customers, that meant more reliable delivery of corrosion-resistant stainless steel components.

Testing After Passivation

After passivation, the manufacturer tested parts based on the applicable requirement.

Common testing methods include:

• Copper sulfate testing
• Salt spray testing
• High humidity testing
• Water immersion testing
• Free iron testing

The right test depends on the stainless steel grade, part application, and customer specification.

By defining the acceptance criteria before launching the in-house process, the manufacturer made passivation easier to document and easier to defend during quality review.

Scaling the Process with High-Volume Automation

For this manufacturer, bringing citric acid passivation in-house solved the immediate problem. It reduced outside dependency and improved control over quality, documentation, and delivery.

As production volume grows, part size and handling requirements become just as important as the passivation chemistry itself. Smaller automated passivation systems can work well for smaller parts and lower-volume applications, but larger parts may require a different equipment approach.

For higher-volume production or larger stainless steel components, a rail-guided gantry automation system can move baskets or racks through cleaning, rinsing, passivation, rinsing, and drying stages with less manual handling. This helps manufacturers process heavier, larger, or more frequent loads while keeping the sequence controlled and repeatable.

That consistency matters when passivation becomes a regular production requirement instead of an occasional finishing step. For manufacturers with growing demand, rail-mounted gantry automation can provide a scalable path for bringing larger stainless steel passivation work in-house.

The Result: Better Control Over Passivation and Delivery

By bringing citric acid passivation in-house, the manufacturer gained better control over quality, scheduling, and customer delivery.

The company reduced dependence on outside processing, improved lot visibility, and created a repeatable process for stainless steel parts that required corrosion resistance.

For the manufacturer, the benefit was a safer, more controlled, and more scalable passivation process.

For customers, the benefit was simple: properly passivated stainless steel components delivered with fewer delays.

Is Citric Acid Passivation Right for Your Stainless Steel Parts?

Citric acid passivation can be a strong fit for stainless steel parts that require improved corrosion resistance after machining, polishing, welding, grinding, or other fabrication steps.

Best Technology helps manufacturers evaluate the full process, including cleaning, rinsing, citric acid chemistry, testing, equipment layout, and automation options.

Citric acid passivation chemistries such as CitriSurf® are also available through Best Technology for manufacturers looking to build or improve their in-house process.

Not sure where to begin? Our team at Best Technology can help you evaluate your application and plan the right automation solution—from selecting the system to putting it into operation. We’ll work with you to determine how automated finishing equipment can improve your passivation processes.

Call (612) 392-2414 or contact us to get started.

CitriSurf® is a registered trademark of Stellar Solutions, Inc. McHenry IL USA.

Best Technology offers BestSolv® Engineered Fluids for carrier fluid applications involving lubricant deposition, silicone transport, latent fingerprint processing, coatings, corrosion inhibitors, and other specialty chemical processes. These fluids may also support manufacturers and laboratories replacing discontinued 3M Novec carrier solvents.

What Is a Carrier Fluid?

A carrier fluid is a solvent or engineered fluid used to temporarily transport another material during a manufacturing, laboratory, or specialty chemical process. The carried material may be a lubricant, silicone, fluoropolymer, coating, corrosion inhibitor, fragrance, active chemical, heat transfer additive, or other process material.

The carrier fluid helps the active material move, spread, or penetrate more effectively. After the material has been delivered, the carrier fluid evaporates cleanly and leaves the intended material behind.

In lubricant deposition, a carrier fluid can thin the lubricant, help it reach small features, and then evaporate after application. This can support a more uniform deposit with less unwanted residue.

Carrier fluids are also commonly referred to as carrier solvents, especially when replacing legacy 3M Novec products used in established formulations.

Carrier Fluid Advantages in Precision Applications

In precision applications, carrier fluids are often selected to support controlled delivery of the active material. The goal is not only to move the chemistry across the surface, but to help it deposit evenly, reach small features, and evaporate cleanly after application.

Carrier fluid advantages include:

• Improve flow and surface coverage
• Carry materials into small features, gaps, or crevices
• Support thin, uniform deposition
• Reduce uneven coating, pooling, or beading
• Evaporate cleanly after the active material is delivered
• Minimize unwanted residue
• Support replacement of discontinued carrier solvents

These advantages are relevant across electronics, aerospace, automotive, medical device manufacturing, forensic science, and precision industrial manufacturing. Final selection should be confirmed through application-specific testing with the actual material, substrate, and process conditions.

Carrier Fluids, Wetting, and Uniform Surface Coverage

Carrier fluid selection often depends on wetting behavior, or how well the fluid spreads across and maintains contact with the surface. Poor wetting can contribute to beading, gaps, or uneven coverage.

Wetting vs. Viscosity

Viscosity describes how thick or resistant to flow a liquid is. Wetting describes how well that liquid spreads and stays in contact with a surface. A carrier fluid may need to reduce the effective viscosity of the active material, but it also needs to help that material spread evenly over the part surface. This is why product selection and application testing are important.

The right carrier fluid can help create a thin, uniform layer instead of an uneven deposit.

Common Carrier Fluid Applications

Carrier fluids are used across multiple applications where controlled material delivery is required. BestSolv® fluids may be used in applications involving lubricant deposition, silicone delivery, coatings, corrosion inhibitors, latent fingerprint processing, and specialty chemical transport.

Lubricant Deposition

Lubricant deposition is one of the clearest carrier fluid applications. In this process, the carrier fluid temporarily thins or transports the lubricant so it can flow across the surface, reach tight areas, and penetrate small features. After application, the carrier fluid evaporates and leaves the lubricant behind.

BestSolv® 7300 is commonly associated with lubricant deposition applications where clean evaporation, material transport, and controlled deposition are important.

This type of application can be relevant for precision parts, mechanical components, electronics, aerospace parts, and other assemblies where controlled lubrication is required without excessive residue.

Silicone Carrier Applications

Carrier fluids can also be used to transport silicones in applications where controlled spreading or deposition is required. In these processes, the carrier fluid helps move the silicone into place and supports more uniform application.

BestSolv® 71DA is frequently associated with silicone carrier applications. Because material behavior can vary depending on the silicone formulation, application testing is recommended before full process implementation.

Coatings, Corrosion Inhibitors, and Specialty Additives

Carrier fluids may also be used to help apply thin coatings, corrosion inhibitors, fluoropolymers, heat transfer additives, and other specialty materials. The carrier fluid helps transport the active ingredient, supports spreading, and then evaporates after the material has been delivered.

These applications often depend heavily on the chemistry being carried. A carrier fluid that performs well with one material may not perform the same way with another. Solubility, stability, surface wetting, evaporation profile, and residue requirements all need to be considered.

Latent Fingerprint Processing

Carrier fluids are also used in forensic latent fingerprint processing. In these applications, the fluid helps carry fingerprint development chemistry across evidence surfaces while supporting clean evaporation and consistent results.

BestSolv® 7100 and BestSolv® Sierra have both been used in latent fingerprint processing applications. BestSolv® 7100 is especially important for users replacing 3M Novec 7100, while BestSolv® Sierra has also shown strong performance in specific latent fingerprint formulations.

Adhesives and Thin-Film Applications

Carrier fluids may be used in adhesive or thin-film applications where the active material needs to be thinned, transported, or spread more evenly before the carrier evaporates. In these cases, the carrier fluid can help improve flow, penetration, and surface coverage.

Because adhesive and thin-film applications vary widely, product selection should be based on the exact adhesive chemistry, required deposit thickness, substrate material, and evaporation needs.

BestSolv® Carrier Fluid Options

Best Technology offers several BestSolv® fluids that may be evaluated for carrier fluid or carrier solvent applications. Selection depends on the material being carried, substrate compatibility, evaporation requirements, and whether the process is replacing an existing 3M Novec carrier solvent.

BestSolv® 7100

BestSolv® 7100 is an important option for customers replacing 3M Novec 7100 in carrier solvent applications. If a process has already used Novec 7100 successfully, BestSolv® 7100 is often the recommended starting point for maintaining similar carrier fluid performance.

BestSolv® 7200

BestSolv® 7200 may be used in applications requiring a carrier fluid with clean evaporation and compatibility with precision chemical processes. It can be considered where the process requires controlled delivery of an active material and where the fluid’s physical properties align with the application.

BestSolv® 7300

BestSolv® 7300 is commonly associated with lubricant deposition. It can help carry and thin lubricant materials so they flow more effectively into small areas before the carrier fluid evaporates.

BestSolv® Sierra

BestSolv® Sierra may be suitable for select carrier fluid applications, including latent fingerprint processing. It has been used successfully in certain forensic formulations.

However, Sierra should not be positioned as a universal carrier fluid for every application. Because it is a shorter-chain molecule, some materials may not mix uniformly and may separate depending on the formulation. For customers who have previously used Novec 7100 successfully, BestSolv® 7100 remains the preferred starting point.

BestSolv® 71DE

BestSolv® 71DE may be considered for specific carrier solvent applications where its chemistry aligns with the material being transported and the required process conditions. It should be evaluated based on the active material, surface requirements, and evaporation expectations.

BestSolv® 71DA

BestSolv® 71DA is frequently associated with silicone carrier applications. It can help transport silicone materials and support controlled application in suitable processes.

BestSolv® 72DE

BestSolv® 72DE may be considered for specialty carrier fluid applications where the process requires clean delivery, controlled evaporation, and compatibility with the active material being transported.

As with the other carrier fluid options, application testing is important to confirm solubility, mixing behavior, and final deposit quality.

PFAS-Free Carrier Fluid Option: BestSolv® Zeta

Some manufacturers are evaluating PFAS-free carrier fluid options due to regulatory pressure, customer requirements, or internal sustainability goals. BestSolv® Zeta may be considered where the chemistry and performance requirements are compatible.

BestSolv® Zeta should be evaluated based on the material being carried, the surface being treated, and the required evaporation and wetting behavior.

This is an important distinction: not every PFAS-free fluid will work in every carrier fluid application. The carrier fluid must still perform the technical job of transporting the active material, supporting uniform spreading, and evaporating cleanly without disrupting the final deposit.

For customers exploring PFAS-free carrier fluid options, Best Technology can help review the application and determine whether BestSolv® Zeta is an appropriate candidate for testing.

Choosing the Right Carrier Fluid

The best carrier fluid depends on the process. A fluid that works well for lubricant deposition may not be the right option for silicone, forensic chemistry, adhesives, or specialty coatings.

When selecting a carrier fluid, the following factors should be reviewed:

• The active material being carried
• The desired final deposit or coating
• Solubility and mixing behavior
• Wetting and surface coverage
• Evaporation rate
• Residue requirements
• Substrate compatibility
• Process temperature
• Regulatory requirements
• Whether the application is replacing a discontinued 3M Novec fluid
• Whether a PFAS-free option is required

For customers replacing 3M Novec 7100 in a known carrier solvent application, BestSolv® 7100 is often the recommended starting point. For lubricant deposition, BestSolv® 7300 may be a strong candidate. For silicone carrier applications, BestSolv® 71DA may be appropriate. For PFAS-free applications, BestSolv® Zeta may be evaluated.

Compatibility and Application Testing

Carrier fluid performance is highly application-specific. Even when two fluids appear similar on paper, they may behave differently with a specific lubricant, silicone, coating, or active ingredient.

Testing should evaluate:

• Whether the active material dissolves or disperses properly
• Whether the mixture remains uniform
• Whether separation occurs
• Whether the fluid wets the surface correctly
• Whether the final deposit is even and complete
• Whether the carrier evaporates cleanly
• Whether residue levels are acceptable
• Whether the substrate or part material is compatible

This is especially important when replacing an existing carrier solvent. A successful replacement should not only match broad chemistry requirements. It must also work with the actual formulation and process conditions.

Talk to Best Technology About Carrier Fluid Selection

Carrier fluid selection depends on the material being carried, the surface being treated, evaporation requirements, residue limits, and compatibility with the existing process.

Best Technology can review carrier fluid requirements and identify BestSolv® options that may be appropriate for testing. Final selection should be confirmed through application-specific evaluation with the actual formulation, substrate, and process conditions.

Contact Best Technology today to discuss your carrier fluid application and receive guidance on the right BestSolv® option for your process.

That is where the process begins. Whether you are setting up a new chem film line, expanding your current operation, or replacing outside processing with an in-house system, the right equipment sequence makes all the difference. Each stage of the process has a purpose, and each piece of equipment needs to work together to produce a consistent, specification-compliant finish.

At Best Technology, we design chem film and Alodine equipment around the actual process you need to run. That includes the tank sequence, rinse stages, handling method, ventilation, and support features required to keep the line running reliably. Below is a step-by-step look at how a chem film line is typically built.

Start with the Process You Need to Run

Before selecting tank sizes or support features, the first step is understanding which chem film process your line needs to support. The equipment configuration will depend on whether you are processing to MIL-DTL-5541 Type 1 or MIL-DTL-5541 Type 2.

A Type 2 hex-free process is often more streamlined and may use fewer tanks, depending on whether the chemistry follows an acid clean or alkaline clean path. A Type 1 hexavalent chromium process typically requires more process stages, including added pretreatment and rinse steps.

That is why the system should always be built around the process first. Once the chemistry and process path are clear, the line can be configured correctly.

Video: What Is Chem Film?

What Equipment Is Required to Start a Chem Film Line?

At the most basic level, a chem film line needs a sequence of tanks and transfer steps that prepare the part, apply the conversion coating, and protect coating quality from one stage to the next.

1. Cleaning Tank

The first stage is the cleaning tank. This removes oils, residues, and contamination left behind from machining, handling, or prior manufacturing steps. Proper cleaning is critical because the chem film coating can only form consistently on a properly prepared surface.

Depending on the chemistry being used, this may be an acid clean or alkaline clean stage.

2. Rinse Tank

After cleaning, the part moves into a rinse tank. This stage removes carryover chemistry and helps protect the next tank in the sequence. Rinse stages are essential in chem film processing because poor rinsing can contaminate downstream tanks and affect finish quality.

Many systems use cascade counterflowing rinses to improve rinse performance and maintain cleaner water conditions.

3. Etching Stage or Deoxidizing

Depending on the process type, the line may need an etch stage, a deox stage, or both, each requiring its own rinse tank. These stages help prepare the aluminum surface so the conversion coating forms correctly.

For example:

• Type 1 systems typically include etch and deox stages
  
• Type 2 alkaline clean systems typically include a deox stage
  
• Type 2 acid clean systems may reduce the number of pretreatment stages

This is one of the reasons process type matters so much during line design.

4. Chem Film / Alodine Tank

This is the main process tank where the chromate conversion coating is applied. The aluminum part is immersed for a controlled period of time based on the chemistry, the part geometry, and the process requirements.

This stage is the heart of the line. Tank construction, dwell time, chemistry compatibility, and rinse performance all affect the final coating result.

5. Final Rinse Stages

After the chem film coating is applied, the line will require one or more final rinse stages to reduce residual chemistry and protect finish quality.

For applications that demand higher rinse quality, DI water rinses can also be integrated into the system.

Typical Chem Film Tank Sequences

The exact tank order depends on the chemistry and process you need to run.

Typical Type 2 Hex-Free Chem Film Line

A typical MIL-DTL-5541 Type 2 line using TCP-HF with an acid clean process may include:

• Acid Clean
  
• Rinse
  
• Trivalent chromium chem film coat
  
• Rinse
  
• Second Rinse

A Type 2 line using an alkaline clean process may include:

• Alkaline Clean
  
• Rinse
  
• Deox
  
• Rinse
  
• Trivalent chromium chem film coat
  
• Rinse
  
• Second Rinse

Typical Type 1 Hexavalent Chromium Line

A typical MIL-DTL-5541 Type 1 line may include:

• Clean
  
• Rinse
  
• Etch
  
• Rinse
  
• Deox
  
• Rinse
  
• Chem film coat
  
• Rinse
  
• Warm rinse

So before asking how large the system should be, the first question should really be: which process are you building for?

Video: Chem Film Type 1 and 2 Chromate Conversion Coating System

When needed, a chem film line can be designed to support both Type 1 and Type 2 chromate conversion coating processes. This allows manufacturers to run hexavalent and hex-free chem film processes within one equipment system, depending on the required specification, chemistry, and application. The tank sequence, rinse stages, controls, and handling method must be planned carefully so the system can support both process paths while maintaining consistency, safety, and coating quality.

Supporting Equipment That Helps the Line Run Properly

Once the required process tanks are defined, the next step is adding the support equipment that helps the line run safely, cleanly, and consistently.

Material Handling

Parts need to move through the process in a controlled and repeatable way. In smaller or lower-volume systems, that may be done manually. In larger systems, a more advanced transfer method may be used.

Lip Ventilation

Chem film lines can include lip ventilation so the system can connect to customer-supplied facility exhaust. This helps manage fumes and improve operator safety.

Drip Diverters

Drip diverters between tanks help contain chemistry when baskets or racks move from one tank to the next. This helps reduce drag-out and cross-contamination.

Containment Stand or Tray

Some systems are built with containment that can hold up to 110% of the volume of the largest tank. This helps protect the surrounding area in the event of a spill or overflow.

Tank Covers

Tank covers can be added to help control fumes, reduce evaporation, and support a cleaner operating environment.

Pumps, Circulation, and Monitoring

Depending on the application, the system may include:

• circulation pumps
  
• pH meters
  
• conductivity monitoring
  
• Air Sparger

DI Water Systems

For applications requiring higher rinse purity, the line can include DI rinse tanks or DI skids to support water quality throughout the process.

Required Equipment vs. Application-Driven Options

Every chem film line needs a solid process foundation. But not every line needs the exact same support features. Some items are fundamental to the process, while others depend on your quality requirements, part geometry, chemistry, and production goals.

Required Equipment

These are the core components most chem film lines need in order to run the process:

• Cleaning tank
  
• Rinse tanks
  
• Etch and deox stage, depending on process type
  
• Rinse stage
  
• Chem film coating tank
  
• Final rinse stage
  
• A method for moving parts through the line

Application-Driven or Optional Features

These features may be added depending on the process and production requirements:

• DI rinse tanks or DI skids
  
• Lip ventilation
  
• Drip diverters
  
• Tank covers
  
• Containment stands or trays
  
• pH and conductivity monitoring
  
• Circulation pumps
  
• Right-to-left or left-to-right custom line flow
  
• Added process control features for repeatability and documentation

This is where custom system design becomes important. The right line is not just about getting the process to run. It is about building the right level of control, cleanliness, and workflow for your application.

The System Should Fit Your Process, Parts, and Facility

Chem film lines are not one-size-fits-all. The right configuration depends on the parts you are processing, the chemistry you are using, the specifications you need to meet, and the space you have available in your facility.

Best Technology builds chem film systems to order with configurable features such as:

• tank sizes
  
• process flow orientation
  
• tank materials, often polypropylene
  
• rinse configurations
  
• ventilation and containment options
  
• manual or automated handling

A line can also be designed around your available floor space, including left-to-right or right-to-left process flow depending on how the system needs to fit into the room.

Manual Chem Film Lines and Automated Chem Film Systems

For many manufacturers, a manual chem film line is the right place to start. A manual system can provide the full process sequence needed for Type 1 or Type 2 conversion coating while allowing flexibility for a wide range of part sizes and production needs.

For higher-volume production, the process can also be automated.

Best Technology offers automated chem film systems with rail-mounted gantry crane automation that move loads through the tank line in a controlled, repeatable sequence. This helps improve throughput, reduce manual handling, and support more consistent coating quality across the process.

These automated systems can be designed for:

• Type 1 hexavalent processes
  
• Type 2 trivalent hex-free processes

Depending on the application, the system can also include PLC-controlled recipes, programmable dwell times, flowing rinse tanks, and optional monitoring for pH and conductivity.

So if you are planning your chem film line now, but expect production demands to grow, automation can be part of the design conversation from the beginning.

Build the Line Around the Process, Not Just the Tanks

A successful chem film line is more than a row of tanks. It is a complete process system designed to prepare the part correctly, manage chemistry from stage to stage, and support a consistent finish over time.

That is why the best place to start is with the process itself:

• What chemistry are you running?
  
• What process type are you supporting?
  
• What pretreatment stages are required?
  
• How will parts move through the line?
  
• What level of rinse quality, ventilation, and monitoring do you need?

Once those answers are defined, the right equipment configuration becomes much clearer.

How can you test your parts after the chem film process to verify they meet the MIL DTL 5541 requirements?

Best Technology’s Salt Fog Chamber and Humidity Test Chambers provide a controlled corrosion chamber environment for testing the corrosion resistance, durability, and long-term material performance of metal components, coatings, and finishes.

Ready to Start Your Chem Film Line?

If you are planning to set up a chem film or Alodine line, Best Technology can help you build the right system for your application. From manual tank lines to fully automated rail-mounted gantry systems, we design chem film equipment around your process requirements, part sizes, and production goals.

Talk to our team about your chem film application, and we will help you define the tank sequence, support equipment, and system configuration needed to get started.