Aluminum Dip Brazing: Strong, Efficient, and Cost-Effective Joining

Dip brazing offers numerous benefits. Each project requires little to no equipment, keeping tooling costs low and allowing for easy configuration changes with common fixtures. The process creates sturdy, leak-proof, EMI-shielded joints, improving overall strength. This method also ensures higher quality at a lower cost by brazing many smaller parts simultaneously. Aluminum dip brazing produces joints with better conductivity than adhesive or mechanical attachments. It brazes all joints of a component simultaneously, producing durable components quickly and evenly.

What is Dip Brazing?

Dip brazing is a metal fabrication process that joins metal surfaces by immersing a pre-assembled component containing braze alloy into a molten bath of the flux. This process uses capillary action to draw the molten braze alloy between the tightly fitted parts, forming a strong and permanent thermal and mechanical bond when it cools.

Why Use Dip Brazing?

Dip brazing efficiently joins metal surfaces across multiple planes in a single 60-second operation, simplifying assembly compared to the multi-step process of welding, which requires careful structural planning and additional time.

In contrast, vacuum brazing effectively joins components in the same plane, such as liquid cold plates and tube-and-fin heat exchangers but lacks dip brazing’s versatility across different planes. Welding, which handles complex structural requirements and provides higher joint strength, uses a fluxless process. Dip brazing efficiently handles multiple component planes in one operation, providing a balanced alternative to welding and vacuum brazing in liquid cooling systems.

When Not to Use Dip Brazing?

Liquid cooling applications or sensitive applications that demand meticulous cleaning are better suited to vacuum brazing or welding. Dip brazing can leave flux reside in smaller cavities that may be difficult to flush out in complex assemblies, which pose risks for sensitive electronics.

What Products and Applications Use Dip Brazing?

Dip brazing is a critical manufacturing process for a variety of products and applications that need high durability and reliability. Dip brazing creates robust and reliable joints essential to maximize performance and longevity across industries such as aerospace, defense, automotive, and electronics. Its versatility and reliability make it indispensable to fabricate intricate metal assemblies and components quickly with high reliability.

Chassis and Enclosures:

In the aerospace sector, dip brazing provides the structural integrity needed for aircraft frames and components. Dip brazing makes these assemblies better able to endure rigorous environmental conditions while ensuring optimal performance and safety.

In electronics applications, manufacturers use dip brazing to produce equipment enclosures. Devices such as communication systems, radar equipment, and power electronics rely on dip brazed enclosures for EMI shielding and structural stability.

The automotive industry uses dip brazing to fabricate chassis components and enclosures. This process ensures the durability and performance of vehicle frames, heat exchangers, and battery enclosures under demanding conditions.

Machined Components:

Dip brazing enhances the efficiency and durability of heat exchangers in HVAC systems, automotive cooling systems, and industrial machinery by creating robust joints for optimal heat transfer. Manufacturers utilize dip brazing for precision instruments that require exact alignment and structural integrity, such as optical mounts, sensor housings, and medical equipment parts. Power transmission equipment, including gearboxes, couplings, and shaft assemblies, rely on dip brazing for durable and reliable joints, ensuring smooth operation and longevity in critical systems.

Common Dip Brazing Materials

While Boyd only uses aluminum-based alloys, dip brazing relies on a selection of common materials tailored to ensure strong, reliable joints across various metal compositions. Among the critical components of the dip brazing process are base metals and brazing alloys.

Base Metals:

Aluminum Alloys: Ideal for aluminum and its alloys due to compatibility and low melting temperatures.

Boyd only specializes in aluminum alloy dip brazing.

Copper Alloys: Suitable for brazing copper, brass, and bronze components. Steel: Used for a variety of applications requiring robust, durable joints.

Stainless Steel: Offers corrosion resistance and strength, commonly brazed for critical applications.

Nickel Alloys: Suitable for high-temperature materials such as stainless steel and nickel alloys.

Titanium Alloys: Used in aerospace and other industries where lightweight, high-strength joints are required.

Magnesium Alloys: Commonly brazed for applications requiring lightweight components.

Brazing Alloys:

Aluminum-Based Alloys: Specifically designed for brazing aluminum and its alloys, featuring low melting temperatures and excellent compatibility.

Since Boyd only does aluminum dip brazing, we only use aluminum dip brazing alloys.

Silver-Based Alloys: Versatile and widely used for joining steel, stainless steel, copper, and brass components.

Copper-Based Alloys: Often chosen for brazing copper, brass, and bronze components, offering good strength and conductivity.

Nickel-Based Alloys: Suitable for joining high-temperature materials such as stainless steel and nickel alloys, providing strong and durable joints.

Fluxes:

Boyd’s large-scale dip brazing installation maintains only a single flux chloride-based flux. Other dip brazing installations can use different fluxes, based upon the parent and braze alloys.

Borax-Based Fluxes: Commonly used for aluminum and aluminum alloys, facilitating the removal of oxides and ensuring good wetting of the brazing alloy.

Fluoride-Based Fluxes: Effective for brazing stainless steel and other high-temperature alloys, aiding in the removal of surface contaminants and promoting proper alloy flow.

Chloride-Based Fluxes: Suitable for brazing copper and brass components, assisting in the removal of oxides and ensuring strong, clean joints.

These materials are carefully selected based on factors such as base metal compatibility, operating conditions, and specific application requirements, ensuring optimal performance and reliability in dip brazing processes.

Dip Brazing Process

The dip brazing process consists of a series of meticulous steps aimed at achieving strong, reliable bonds between metal components. Each step contributes to ensuring the quality and integrity of the final assembly. From surface preparation to cleaning, we carefully orchestrate every stage to facilitate the flow of molten brazing alloy and create robust joints.

1. Prepare the Assembly: Remove grease, oil, oxides, and scale from the component surfaces to ensure proper wetting of the alloy.
2. Select and Position Brazing Filler Metal: Choose the appropriate brazing filler metal, ensuring it contacts all the metals being joined.
3. Fixture the Assembly: Use fixtures to hold the assembled parts in place during brazing, using rods, hooks, or baskets.
4. Preheat the Assembly: Heat up the assembled components to just below the melting point of the filler metal to minimize furnace time and ensure uniform heating.
5. Perform Brazing: Move assembly from preheat and immerse it in the dip brazing furnace for a specific duration, allowing the brazing alloy to flow through the joint by capillary action.
6. Quench the Assembly: After brazing, rapidly cool the parts to a lower temperature to anneal the assembly and set the material’s mechanical properties. Boyd can use air, mist, or immersion to quench dip brazed assemblies.
7. Clean the Assembly: Remove flux residue from the components using chemical cleaning methods to ensure a clean finished assembly.
8. Age the Assembly: The part is artificially aged in an oven to lock in the mechanical properties set during the quench operation.

Key Considerations for Dip Brazing

For successful dip brazing, several key considerations must be addressed to ensure strong, reliable joints. This process involves immersing metals in a molten flux bath and requires meticulous planning. Attention to material compatibility, surface preparation, joint design, fixture design, brazing alloy selection, temperature control, flux selection, cooling and quenching, and quality control is crucial.

Material Compatibility: Ensure the materials being joined are compatible with both the brazing process and the brazing alloy. Consider the melting points, thermal expansion coefficients, and chemical compositions of the base metals and the brazing filler.

Surface Preparation: Proper cleaning and surface preparation are crucial for successful brazing. Remove any contaminants, such as oils, oxides, or coatings, from the surfaces to be joined to promote good wetting and adhesion of the brazing alloy.

Joint Design: Design the joint to facilitate capillary action and ensure the proper flow of the brazing alloy. Tight fits, appropriate gap sizes, and joint geometry promote capillary flow for stronger and more reliable joints.

Fixture Design: Use fixtures to hold the parts in the correct position during brazing and prevent distortion or misalignment. Design fixtures to withstand the thermal stresses of the brazing process and provide adequate support for the parts.

Brazing Alloy Selection: Choose the right brazing alloy to achieve the desired properties in the joint. Consider factors such as melting temperature, fluidity, strength, corrosion resistance, and compatibility with the base metals.

Temperature Control: Maintaining precise control over the brazing temperature ensures proper wetting and bonding of the brazing alloy without overheating the base metals. Ensure temperature uniformity throughout the assembly to prevent localized overheating or underheating.

Flux Selection: Select the appropriate flux for the application based on materials and brazing alloys. Ensure the flix bath is uniformly heated to the required temperature based on the materials being brazed.

Cooling and Quenching: Control cooling and quenching after brazing solidifies the brazing alloy, preventing the formation of undesirable metallurgical phases. Use controlled cooling rates to minimize residual stresses in the joint and reduce the risk of distortion.

Quality Control and Inspection: Regular inspection of the brazed joints for defects such as incomplete penetration, voids, cracks, or excess filler metal is crucial to ensure the quality and integrity of the assembly. Employing non-destructive testing methods such as visual inspection, leak testing, dye penetrant testing, or X-ray inspection as part of the quality control process.

Each of these factors plays a vital role in achieving the desired results and maintaining the structural integrity of the assembled components.

Why Use Boyd for Dip Brazing

Boyd’s total process control and breadth of experience enables us to meet demanding customer drawings and tolerances. Our expertise allows us to design dip braze assemblies, knowing how the material will react to each step of the manufacturing process. We can mitigate process-induced warping and distortion at each point through our deep skill and knowledge of the dip braze process to meet final dimensional requirements. And anything that we can’t adjust in the brazing process, we can machine in secondary operations on-site.

Boyd has been dip brazing complex assemblies for decades, making us an ideal partner when designing and fabricating your next project. We strive for excellence in each step of the dip brazing process and meticulously examine each detail of your application to ensure we produce a product that meets your requirements. Learn more about our chassis and enclosures or contact us today about your latest project.

From enhancing the visual characteristics of a part to shielding it from environmental damage, protective coatings have become a vital part of metal fabrication and finishing. While there are several different ways to apply a coating to metal, one of the most efficient and commonly used methods is roll coating.

Roll coating is the process of applying a base, intermediate, and/or topcoat coating to a flat substrate with a series of rollers. But how exactly does roll coating work?

What is the Process Behind Roll Coating?

Roll coating is a process that uses three rollers to apply a coating to a flat substrate: a soft application roll, a highly polished steel roll, and a metering (or doctor) roll. First, the substrate travels between the soft application roll and the steel roll. The application roll picks up the coating as it rotates and transfers the coating to the flat sheet of metal as it passes through. The metal sheets are then transferred to an oven where the coatings are baked and cured.

Roll coating offers a few benefits over other metal coating technologies. It’s critical to uniformly deposit the exact thickness when applying a coating to a flat metal substrate. With roll coating, the amount and viscosity of the liquid deposited on the substrate can be precisely controlled by the metering roll. The closer the metering roll is to the application roll, the thinner the coating, and vice versa. This makes roll coating one of the most precise coating methods currently available.

Another reason why roll coating is so frequently employed is that its deposition time tends to be faster than other coating technologies, such as spray application or screen printing. In addition, the coatings used can help protect metal from harsh environments while enhancing ink adhesion prior to any embossing or other finishing steps.

What Makes Roll Coating at Boyd Unique?

To meet a variety of project needs, Boyd has two types of roll coaters; one that does direct roll coating, and the other that can do both direct and reverse. Reverse roll coating works similarly as direct coating, but the application roll rotates in the opposite direction of the substrate’s travel. Reverse roll coating can apply a thicker coating than direct due to the different travel direction. This additional coating thickness is useful when the design requires a greater depth of color and environmental durability.

Boyd’s coating family includes acrylic, polyester, and urethane coatings, each offering a different level of thickness, malleability, and resilience against heat and UV radiation. Each coating employed at Boyd is custom formulated by our material scientists to meet a wide array of project needs.

At Boyd, we have years of experience using roll coating for products in a variety of industries, such as automotive, appliance, and personal care. To learn more about Boyd’s custom roll coatings and how they can help your next project, schedule a consultation with our experts.

Embedded systems are becoming more complex, processing and analyzing a growing number of sensors and signals. The result of this increased computing is often higher and more concentrated electronic heat loads.

How to Design a Liquid Cooling System for High-Performance System Thermal Management

Because excessive heat compromises the reliability of a system, air cooling is no longer adequate for some applications. Many engineers are turning to liquid cooling to remove the heat.

The complexities of designing a liquid cooling system can be intimidating for those unfamiliar with this set of technologies. Although selecting thermal components for a liquid cooling loop is relatively straightforward, there are other considerations or nuances that can be overlooked. These include materials compatibility, corrosion prevention, condensation control, the position of the liquid cooling loop, use of standard versus custom parts, joints, fittings, connectors, and maintenance and service.

A liquid cooling loop typically consists of a liquid cold plate, pump, heat exchanger, and pipes or hoses (Figure 1). The board generates waste heat, which is transferred from the board to the thermally conductive plate, and then to the liquid coolant that flows through the cold plate. Typically, the fluid path matches hot spots on the board. The heated coolant is then pumped through the heat exchanger, where heat is moved from the coolant to either ambient air, or, in the case of a liquid-to-liquid heat exchanger, to another liquid coolant. The cooled coolant then flows through pipes or hoses back to the cold plate, completing the cooling loop. Under normal operation, liquid coolant continuously flows through the liquid cooling loop to keep the board cool.

Material Compatibility

Since all materials and the fluid in the liquid cooling loop need to work together as a system, they need to be compatible with one another and should be selected together. Copper works well for most applications, since it has excellent thermal conductivity and is compatible with most non-corrosive fluids. Aluminum is compatible with fluids such as polyalphaolefin (PAO), oil, ethylene glycol and water solutions (EGW), as well as Fluorinert™, an electrically insulating inert perfluorocarbon fluid manufactured by 3M and used in many electronics cooling applications. Stainless steel is compatible with most fluids, including corrosive fluids such as deionized water. Several different fluids are compatible with various standard cold plate and heat exchanger materials (Figure 2).

Figure 2: Various fluids are compatible with a variety of standard cold plate and heat exchanger materials

Most liquid coolants also need a small percent of additives to inhibit corrosion and to lubricate the pump. However, it is important to note that corrosion inhibitors can be rendered ineffective by incompatible materials elsewhere in the system, so this must be evaluated as well. Biocides, algaecides, and pH adjustments may also be helpful in maintaining your system, depending on which liquid coolant is selected.

Corrosion Prevention

Corrosion can cause problems two different ways. Not only can material corrode away, which leads to leaks, but the corroded material can be deposited elsewhere in the system and block fluid passages or filters. This can produce a pressure drop that causes reduced coolant flow. In addition, if the deposition occurs on active heat transfer surfaces, the extra thermal resistance caused by fouling can make temperatures rise.

Both galvanic corrosion and erosion-corrosion should be minimized in the liquid cooling loop. Galvanic corrosion occurs when dissimilar metals are in electrical contact with each other in the presence of an electrolyte such as a conductive liquid. Most water-based coolants are electrolytic to some degree. To prevent galvanic corrosion, either the loop should be designed with similar materials throughout the system, ideally with just one metal, or a non-conductive fluid should be used. The galvanic potentials of all materials in the system should be considered. This includes not only the primary thermal components, but also all connectors, fittings, valves, and junctions in the fluid path.

Erosion-corrosion is the acceleration in the rate of corrosion in metal due to the relative motion of a fluid and a metal surface. It is most often found in pipe bends & elbows, tube constrictions, and other structures that alter flow direction or velocity. Erosion-corrosion is most prevalent in soft alloys, such as copper and aluminum.

Some methods for minimizing erosion-corrosion include allowing bends to have larger angles, changing pipe diameters gradually rather than abruptly, and improving flow lines within the pipe by deburring, i.e., smoothing out irregularities. Other methods include reducing the amount of dissolved oxygen, changing the pH, and switching the pipe material to a different metal or alloy. See our application notes “Erosion-Corrosion in Cooling Systems” and “Avoiding Galvanic Corrosion” for more information on corrosion.

Condensation and Liquid Cooling Loop Design

In addition to minimizing corrosion, it’s important to minimize or prevent condensation. One of the risks of using coolants below ambient temperatures is that condensation may form on cool surfaces. This condensation can drip onto electronics or collect in the bottom of the system and cause corrosion. To avoid condensation, surface temperature can be maintained above the ambient dew point by either insulating these surfaces or using higher fluid temperatures. Boyd offers a variety of insulating materials like SOLIMIDE® Foam to maintain line temperatures and prevent condensation and potential damage.

In a properly designed and maintained liquid cooling loop, leaks are very unlikely. However, to minimize the effect of any potential leaks, the reservoir and liquid loop can be located below electronics that would short out if coolant or condensate dripped or sprayed on them. Other options include installing a liquid shield or barrier over the high-voltage portions of the electrical system.

When designing the liquid cooling loop, there is also the option of using standard or custom parts. There are advantages and disadvantages to each. Standards are readily available if replacements are needed. Custom parts, on the other hand, are optimized for the application’s size, performance, and device requirements. However, they will have longer lead times and may have a higher cost.

Joints, Fittings, and Connectors

The number of joints in the cold plate or heat exchanger is important. When there are more joints that must be brazed, there is a higher risk of leaks. It is important to ensure that the manufacturer is highly skilled at brazing, has proper test procedures in place, and eliminates any unnecessary braze points within a custom component.

To prevent leaks, the right fittings must be selected and properly used. For a leak-free joint, a beaded tube fitting mates with a hose that is secured with a clamp. Hard plumbing is generally preferable to hoses, but hoses may be used in environments where systems are exposed to shock or vibration. A unit with a straight tube fitting can be welded into the system or used with a self-locking, torque-free fitting. With a quick-disconnect coupler that isn’t drip-free, you’ll need to expect the occasional drop of fluid when connecting or disconnecting the fittings. For more information, please review our application note on “Choosing a Quick Disconnect Coupler”.

Another option is to use O-rings fittings that are manufactured to Society of Automotive Engineers (SAE) material specifications or those manufactured to military specifications. These fittings are available in various materials and sizes and provide a reliable leak-free seal. Boyd’s O-Ring portfolio and expertise can help ensure you select the right material, certifications, and size quickly to help prevent leaks within your system.

Maintenance and Service

Although maintenance and service may be the last thing engineers consider when designing a liquid cooling loop, including this consideration in the design process will help to reduce problems over the long term. Several different types of questions must be answered.

For example:

• Will the pump need lubrication over its life or is the coolant going to perform that function?
• Will the fluid reservoir need topping off?
• Which components are field-replaceable?
• What is the maintenance schedule?
• What is the required pump life?
• If pump replacement is needed, how does one charge the system and start the system up?

Other questions concern what the user must do to get the system working again.

• Does this require removing the electronics and cold plate, or just the electronics, and can both be easily removed and replaced merely by snapping in a new one?
• If the cold plate is replaced, will it be shipped with cooling fluid?
• Does the OEM ship the system or field-replaceable unit filled with fluid?
• If so, freezing of the fluid may be a concern, such as in aircraft cargo holds that get very cold.

These questions must be considered by members of both design, operations and maintenance teams. Involving all affected individuals in the decision will help to ensure smooth operations in the future.

Materials compatibility, corrosion prevention, condensation control, the position of the liquid cooling loop, standard versus custom parts, joints, fittings, connectors, hoses, and maintenance and service requirements all must be considered when designing either a modified standard or custom liquid cooling loop. When properly integrated into a system, liquid cooling can provide highly effective heat removal with low risk. Today, tens of thousands of cold plates and heat exchangers are liquid cooling electronics in some of the most demanding and high-performance applications.

Written by Richard Goldman and Tracey Barber
Original Published in RTC magazine, July 2006

Visit our Liquid Heat Exchanger Section or Liquid Cooling System Section to learn more about Boyd’s full liquid loop solutions.

Key Factors that Determine the Cost of Fabricating Heat Exchangers

Manufacturing costs can be greatly impacted by demand, but this is not necessarily within the thermal or design engineers’ control. However, you can reduce costs by understanding how core and frame materials, interface tolerances, coatings, and other requirements can affect the cost of a heat exchanger. By involving your heat exchanger manufacturer early in the design process, you’ll be able to identify the manufacturing cost drivers and select the most cost effective design.

Core and Frame Materials

Core and frame material specifications can add significantly to the cost of a heat exchanger. The core, which may consist of tubes, fin, and/or sheet metal, can be manufactured using a variety of metals. The metals most commonly used in heat exchangers are copper, aluminum, and stainless steel. The cost of these metals has risen significantly over the past several years, making their percent of the total heat exchanger cost even greater. Since stainless steel is more expensive than copper or aluminum, it makes sense to opt for copper or aluminum unless your application requires stainless steel. Heat exchangers may also be manufactured using nickel, cupronickel, hastelloy®, inconel®, titanium, or other metals. However, these metals are not used as frequently due to their higher costs.

Usually the core’s materials are specified to ensure that fluid path metals are compatible with the coolant selected for the application. For example, stainless steel might be specified for use with deionized water, whereas cupronickel might be specified for use with saltwater. Heat exchanger core material may also be selected based on weight. Aluminum and titanium are preferential for military and aerospace applications since these metals are less dense.

Core costs can also vary based on the type of heat exchanger selected. Cost variations are due to the different amounts of materials required to make the specific heat exchanger as well as the amount of factory time required to manufacture the part. The least expensive type of heat exchanger to manufacture is a copper tube-fin heat exchanger. Stainless steel tube-fin heat exchangers are more expensive than copper because stainless steel is more expensive by weight, it requires more time to punch, and it must be welded. Like tube-fin heat exchangers, vacuum-brazed flat tube oil cooler heat exchangers are relatively easy to produce. Conversely, the most expensive type of heat exchanger to produce is a vacuum-brazed plate-fin heat exchanger.

Other heat exchanger specifications that can add cost are the materials and processes used to attach the heat exchanger’s frame to the core. Pop rivets are the least expensive option, followed by screws and then welding. Screws will provide a bit more strength than pop rivets. Flat tube heat exchanger frames are generally attached with rivets or welding. With welding, the result is an even stronger and more reliable part that is better able to handle shock and vibration. Welding is also preferable when space and weight are concerns, such as with plate-fin heat exchangers that are used in weight sensitive applications (e.g. airborne applications). Welding eliminates the need to use rivets, which can add weight. In addition, rivets may require a larger heat exchanger frame than welding does since the rivets need a wide section of metal to pass through and effectively hold the heat exchanger frame and core together. Due to additional factory time involved in the welding process, however, welding is more expensive than the other two methods.

Interface Tolerances for Installing Heat Exchangers

After core and frame materials, interface tolerance specifications for mounting and plumbing features are the next biggest cost drivers. For mounting features, the most cost effective approach is to design mounting features into individual sheet metal components. This will yield tolerances ranging from ± 0.03″ to ± 0.06″ ( ±0.076cm to ± 0.1.52 cm). If tighter tolerances are needed, the product will have to be machined during the final production stages, which will require additional machine time. The heat exchanger is also at risk of contamination from metal chips or coolant from machining, so extra care must be taken. This additional machining step can therefore add significantly to the cost.

Normal plumbing tolerances are ± 1/8″- ± 3/16″ (± 0.318 cm to ± 0.476 cm) for copper tube fin heat exchangers and ± 1/8″ (± 0.318 cm) for stainless steel and aluminum products. If tighter tolerances are required for plumbing, more expensive tooling and an increase in labor and inspection time will also be required. Off-the-shelf plumbing fittings are the least costly, however, they have looser tolerances. A beaded tube fitting that mates with a 3/8″ (0.953 cm) ID hose and is secured with a clamp does not require tight tolerances, so opting for this type of fitting may help to keep costs low. The most expensive fitting options are custom machined fittings.

Coatings for Heat Exchangers and Cold Plates

Finishes to Protect Thermal Management Solutions

Custom heat exchangers and cold plates are often coated for corrosion protection or for cosmetic purposes. Chemical conversion coating, anodization, e-coating, and painting are four coating options that will help to minimize corrosion and/or result in a more attractive component. One of the most widely used coating options is chemical conversion coating or chromate conversion coating, also known as “Chem Film” or alodine. Conversion coating helps to minimize surface oxidation and is often specified for military as well as commercial heat exchangers and cold plates. It also sometimes serves as a surface preparation for paint.

Electrodeposition or E-Coat

A third coating method that provides corrosion protection is called an e-coat, also known as electrodeposition or electrocoating. A DC charge is applied to a metal part immersed in a bath of oppositely charged paint particles. The paint particles are drawn to the metal part and paint is deposited on the part, forming an even, continuous film over the entire surface. Of the four types of coatings described here, it is the most expensive type of corrosion protection.

Heat Exchanger Coatings

Another significant cost driver is heat exchanger coatings for corrosion protection or for cosmetic purposes. Coating for corrosion protection is most common on aluminum heat exchangers, since aluminum corrodes more easily than other metals. There are several types of heat exchanger coatings to minimize corrosion: chemical conversion coating, anodization, e-coating, and painting.

One of the most widely used coating options is chemical conversion coating or chromate conversion coating, also known as “Chem Film”, that minimizes surface oxidation. Most government and commercial heat exchanger engineering specifications require that aluminum be chemical conversion coated (per military standard MIL-DTL-5541F, previously MIL-C-5541E).

In addition to Chem Film, another option that can be used to protect aluminum is anodization. Anodizing minimizes corrosion and abrasion by modifying the crystal structure close to the metal surface. It produces a harder part with even greater corrosion protection. However, it is not a common coating and it’s more expensive than chemical conversion coating.

A third coating method that provides corrosion protection is called an e-coat, also known as electrodeposition or electrocoating. A DC charge is applied to a metal part immersed in a bath of oppositely charged paint particles. The paint particles are drawn to the metal part and paint is deposited on the part, forming an even, continuous film over the entire surface. It is the most expensive type of heat exchanger corrosion protection.

Heat exchangers may also be coated with paint for corrosion protection or cosmetic purposes. For example, copper heat exchangers are sometimes painted for aesthetics since uncoated copper may change color over time. For epoxy paint applications, the cost per heat exchanger can range from $10-$200 per heat exchanger. The cost of the paint application will depend not only on the coating itself, but also on the amount of surface area to be coated. Weigh the value of the added corrosion resistance or improved appearance against cost to determine to opt for coating or painting. How long do you want your heat exchanger to last? Will your heat exchanger be visible and how important to your end users is heat exchanger appearance? The appearance of a heat exchanger on equipment in a hospital is likely to be more important than the appearance of a heat exchanger on equipment in a factory.

Heat Exchanger Design and Manufacturing Partnerships

Working with a heat exchanger manufacturer early in the design stage or being flexible on a build to print design will allow for the greatest amount of cost savings. Although the biggest cost driver in heat exchanger manufacturing is annual demand, there are many other factors over which thermal and/or component engineers have some control. Ensure that there is a reason for every specification, as every specification may drive up cost. When core and frame materials, tolerances, and coating specification are outlined, it’s important to determine whether they are necessary for the application or not. In addition, it’s important to realize that there are many alternatives in heat exchanger design as well as the manufacturing processes used, both of which impact cost.

Pressure-sensitive adhesives (PSA) have made it possible to permanently adhere two dissimilar substrates together. While bonding two surfaces together, there are several factors that need to be considered including surface tension and texture of the substrate, bond strength, surface area, environmental conditions, design, and product application. However, one crucial factor that influences the selection of adhesive is the surface energy of a substrate. Surface energy is the excess energy that flows on the surface of the substrate and is measured in dynes/cm. The dyne level is the actual reading of the critical surface tension.

How Does the Surface Energy Influence Adhesive Selection?

Based on the surface energy, substrates can be broadly categorized into three groups – high surface energy (HSE), medium surface energy (MSE), and low surface energy (LSE). With high surface energy ranging from 250-1103 dynes/cm, metals like copper, aluminum, zinc, and stainless steel are some of the most popular HSE substrates. The surface energy takes a big dip to 38-50 dynes/cm for MSE substrates such as polycarbonate, polyester, nylon, acrylonitrile butadiene styrene (ABS), and acrylic. Finally, materials with surface energy below 37 dynes/cm fall into the category of LSE. The widely employed LSE substrates include polyethylene, polyvinyl alcohol (PVA), ethylene vinyl acetate (EVA), and polypropylene.

To understand the importance of surface energy in bonding substrates, let’s consider “wetting”. Wettability is the ability of an adhesive to spread on the surface, thereby increasing the contact area and creating a stronger bond. In most cases, when you pour water on a HSE metal such as copper, the water will quickly spread across the surface and form puddles. On the other hand, when you pour water on ABS, it will form small beads, thus preventing the surface from wetting. Simply put, HSE substrates aid the wetting of the adhesive, while LSE substrates avert the wetting. The surface energy of the substrate dictates the strength of attraction and therefore remains as one of the most critical aspects in bonding.

There is a wide variety of PSA solutions available, each of them offering a unique set of advantages and disadvantages. For example: 3M offers approximately 25 different PSA solutions, with 100MP, 200MP, 300MP and the 300LSE being the most dominantly utilized adhesives. While the high-performance acrylic adhesive family such as the 100MP and 200MP, strongly adheres to most HSE substrates, the 200MP is frequently preferred for MSE substrates, and 300LSE is usually chosen for both MSE and LSE substrates. It is the interplay of several factors that ultimately dictate the selection of the adhesive, thus the optimal solution varies from one application to the other.

With years of process innovation and material science experience, Boyd has the capabilities to not only tailor adhesives to match your unique application, but also address any other bonding needs and challenges. To learn more, schedule a consultation with our experts.

To maintain the visual and functional integrity of your metal automotive trim ornamentation, including sill plates, liftgates, center stacks, steering wheel badges, and door trim, it is essential to use coatings and/or screen printing inks having superior scuff resistance.

Currently, there are many scratch and mar tests that are known throughout the industry and are employed by accredited testing laboratories. While these tests accurately gauge some real world environmental forces to which your ornamentation application will be subjected, they fall short of capturing the effects of one significant key real world destructive force: scuffing.

Boyd’s Scuff Resistant Coating and Ink Families:

Therefore, to ensure that our customer’s products could maintain their beauty and functionality throughout their life cycle, Boyd’s in-house chemists formulated a proprietary anti-scuff family of custom coatings and inks identified. Coatings and inks in this family withstand the real-world harmful scuffing forces that automotive trim components encounter regularly throughout their lifetime to preserve the original aesthetic and functional needs of the component for a prolonged period. The coatings underwent a variety of qualitative and quantitative tests in order to prove the superior scuff-resistant properties of this additive. One such rigorous test subjected the coating samples to aggressively brushing the surface with steel wool as the abrasive material at selected weights in multiple directions, known as our steel wool abrasion test.

Boyd’s scuff-resistant coatings are a significant improvement to our existing coating chemistry. The improved coatings and inks still have the same solvent resistance, stain resistance, and formability. This breakthrough coating technology can be applied to either aluminum or stainless steel constructions with low to high gloss without having any aesthetic effects, while maintaining its performance benefits in a wide variety of severe environments, from high heat to extreme cold. Our steel wool abrasion test results showed that the average product will scuff when subjected to two to three double rubs of steel wool pads when under a downward pressure of 3000 grams. Coatings and inks with the new additive could exceed 100 contacts with the steel pad under the same conditions with little to no scuffing.

During our battery of tests, we were able to validate that this family of coatings meets the industry standard specifications for the following:

Adhesion:

• Humidity resistance (GM4465P) – a test where the sample is exposed to 100% relative humidity at 38°C (100.4°F) for a specified time.
• Impact cross-hatch tape pull (ASTM D-3281) – a one-pound ball or cone is dropped at a specified vertical distance to an area that had been cut with a knife or crosshatch tool. The sample is tested with adhesive tape for any coating removal.

Scratch and Mar:

• Taber abrasion (ASTM D4060-1) – test samples are placed on a Taber rotating plate with a grit wheel of a specified
  grade and are abraded for a number of cycle turns with a given weight applied on each grinding wheel. The samples
  are graded by number of cycles for wear through point of the coating.
• A new type of scratch and mar test using steel wool – this test uses 000 steel wool that is rubbed back and forth with
  the weight of 3,000 grams applied. The end point is measured by the number of “double rubs” the sample could
  sustain before the coating began to wear through.

Solvent Resistance (GM9509P):

• This is usually tested by using a solvent that is specified by the paint supplier (commonly MEK). A soft solvent-saturated cloth is rubbed back and forth on the sample a number of times using the firm downward pressure of a gloved finger. The number of “double rubs” specified for a “pass” varies, but it typically ranges from 10 to 50 rubs.

Improved Film Properties Including:

• High durability in all environments of radiation and moisture
• Increased resistance to abrasion, scratching, and marring
• Improved adhesion and film flexibility
• Better impact resistance
• No detectable effect on accelerated xenon-arc exposure, helping to protect the color or gloss level fading over time

Boyd has years of process innovation and material science experience in the automotive industry. Learn more about our eMobility capabilities.

When it comes to stainless steel, there are many colors and textures that can be added to enhance the visual and tactile attributes of a component. With an endless number of patterns and hues from which to choose, Boyd can support your development with virtually any desired combination.

Versatility of Stainless-Steel Finishes

In addition to creating textures mechanically, Boyd can also create textures organically to have linear, geometric and micro patterns. Linear patterns can be in the form of pinstripes with the lines varying in thickness for accent/highlight purposes, geometric patterns that are structured to have bold distinctive values or micro patterns that are subtle patterns of tightly aligned shapes and/or lines. Organic textures can also be natural patterns that look handcrafted, such as woodgrain. Textures can be created to be transparent, tinted, opaque, or colored, with high or low gloss values and varying tactile values. All textures can be combined with custom colors that which can be applied overall or selectively deposited.

Subtle Stainless Steel Finish

For subtle designs and harmony considerations, customers often lean towards choosing 430 stainless steel using a No. 4 brushed finish. This combination is often layered with black, silver, or grey tints and a fluid pattern such as a micro or organic texture. Muted tone finishes are typically seen in home appliance suites across multiple applications, such as on microwaves, dishwashers, washers, dryers, and refrigerators that are within view of one another.

Modern, Brilliant Stainless Steel Finish

For a modern look, customers frequently choose a higher gloss for a more brilliant finish. An example of this this would be 430 stainless steel with a No. 8 BA (bright annealed) polish. This finish is known for its blue hue, reflectivity, and lack of visual grain structure. Customers typically combine this finish with white or black coloring and/or geometric texture accents. Applying the brush in multiple directions can add gradation and tactile value to the geometric pattern. Colors applied selectively can be used to offset sections of a pattern. Boyd provides a variety of options for different looks and finishes to enhance the look of stainless steel applications. To learn more about our metal decoration and fabrication capabilities, reach out to our experts.

Boyd offers a wide variety of stainless-steel decorating capabilities including custom coatings, printed graphical images and patterns, and mechanical finishes. Of these options, one of the most popular metal decoration capabilities is adding a brushed mechanical finish. Brushed finishes distort the light reflection pattern on a part, and in turn can heighten visual contrast, increasing the perceived value of the part to which it is affixed.

What Are Brushed Mechanical Finishes?

Brushed metal finishes are produced by mechanically polishing or wearing away the outer surface of the metal. Brush finishes can be applied overall or selectively, in one or multiple directions. To create a selective mechanical brush or a spun finish, a screen-printed resist ink is applied to the metals’ surface prior to it being subjected to the mechanical brushing wheel. In doing so, the area protected by the resist ink will maintain its original brilliance, as it will not come in contact with the brushing wheel. Brushed metal finishes for both stainless steel and aluminum can be linear or oscillating (overlapping).

Wet Number Four Stainless Steel Finish

Of the many options, the most common finish used is a wet number four polish. The uneven brush strokes of a number four polish/brush highlight the metal’s brilliance on stainless steel without being too reflective. It provides a uniform look from the elongated brush pattern, and can withstand everyday wear by scuffing, scratching, and fingerprints. Common applications for a number four brush finish include automotive trim such as sill plates and arm rest trim, in addition to a number of home appliance uses.

Bright Annealed Stainless Steel Finish

By contrast, a BA (bright annealed) finish is a high-luster, brilliant chrome finish that is used frequently in the automotive industry for decorative parts. While various levels of reflectivity are achievable, the number eight BA finish is the most reflective. This finish is created by treating the surface with a series of fine abrasives, then buffing the surface to create a mirror like appearance. The buffing improves the corrosion resistance of the number eight finish, as it polishes away any minor surface imperfections where particles may stick and initiate the corrosion process. With its corrosion resistant properties, the number eight finish is commonly used for exterior applications requiring brilliant, highly reflective surfaces.

While these are two of the most popular options, this is far from a full list of metal finish options. Mechanical brush finishes can also be combined with a number of different colors, textures, and metals to add even more visual contrast to a part. To learn more about stainless steel options at Boyd, visit our blogs on Stainless Steel Alloys or Stainless Steel: Colors and Textures. To discuss your own custom metal finishing needs, reach out to our experts.

While stainless steel is a durable material for many applications, not all steel alloys are created equal. As one of the most common materials for parts used in extreme environments, stainless steel has applications in industries ranging from automotive to home appliance. With extensive experience working with and fabricating stainless steel components, Boyd can help customers choose the correct stainless steel alloy for their application.

Which Stainless Steel Is Right For Your Project?

Each stainless steel alloy is unique in element composition and elongation, resulting in differing performance capabilities, visual characteristics, cost profiles, and elongation ratios. Elongation is the amount of expansion a metal under stress can endure given its original length. The two most common alloys employed in automotive and major appliance parts are the 300 and 400 series.

Stainless Steel 300 Series

With superior elongation, the stainless steel 300 series is non-magnetic and employed where severe metal forming is required. Prevalent in the automotive industry, the 300 series is also known for extreme corrosion resistance, crack resistance, and non-yellowing when subjected to high temperatures. The automotive industry favors the 300 series for sill plates, liftgate trim, and other vehicle accents that are exposed to rugged environments. For its durability under high temperatures, the 300 series is used in many stovetop ranges for the home appliance industry as well.

Stainless Steel 400 Series

By contrast, the stainless steel 400 series is magnetic and has a smooth surface finish that is ideal for home appliance products, but can be more susceptible to corrosion than the 300 series (as it contains less chromium and nickel). Due to this, the 400 series is more cost effective than the 300 series. The 400 series is the alloy of choice for cost-sensitive appliance applications, such as dish washers and refrigerators. While these two are commonly used, this is far from an exhaustive list of steel alloys. In addition to help selecting the right stainless steel alloy, Boyd can provide customers with industry-leading metal decoration capabilities including selective mechanical finishing on stainless steel. Boyd’s mechanical metal finishing capabilities include but are not limited to brushing, spinning, and tooled patterns. In addition to mechanical finishing, Boyd offers a number of finishing options including premium coatings and inks. Boyd has years of material science and process innovation experience. For more information about some of our metal decoration capabilities, visit our Scuff-Resistant Coatings Blog or schedule a consultation with our experts