Advancements in Metal Finishing Technologies
Metal finishing usually involves coating to enhance the surface, referred to as the substrate in metal finishing. Surface improvement technologies can include polishing, cleaning, and electroplating, where metal ions are deposited onto the substrate using an electrical current. Various industries utilize a range of metal finishing methods, including anodization, bead blasting, passivation, powder coating, and vibratory tumbling. While effective, these methods have limitations such as water use, chemical impact, and specific material restrictions. Innovative metal finishing technologies aim to enhance effectiveness, affordability, and sustainability.
- Citric acid passivation
- Cold spray technology
- Electroless plating
- Environmentally friendly electroplating
- Graphene plating
- Hydrophilic and hydrophobic coatings
- Laser substrate texturing
- Nanotech coatings
- Supercritical carbon dioxide cleaning
Let’s look at the advantages and applications of these metal finishing technologies.
Citric Acid Passivation
Typically used with stainless steel and sometimes titanium, this method creates a corrosion-resistant layer by drawing out iron from the base material to form a protective coating. While passivation has been in use for some time, traditional techniques often involve nitric acid for finishing metals. Recent advancements in metal finishing technologies have focused on more eco-friendly passivation methods.
Because of this increasing focus on sustainability, citric acid passivation has become more popular. This metal finishing technique involves making a uniform solution from citric acid and water, which is then heated. Parts are then added to the solution and completely immersed for a specific period to achieve the desired finish. The oxidation layer produced by citric acid passivation can benefit components of all sizes, making it a more flexible metal finishing technology.
Primary advantages of using citric acid passivation include:
- Capable of meeting modern standards for metal finishing, including copper sulfate, high humidity, immersion, and salt spray tests.
- Enables a more rapid removal of free iron from substrate.
- Generates no corrosive or toxic fumes and is much less hazardous for workers than nitric acid.
- Only removes iron, thus preserving other alloys within a metal.
- Produces outstanding results regardless of the stainless steel grade.
- Safer for the environment as it requires no special disposal methods.
Citric acid passivation is usually used when parts or products require greater corrosion resistance. Passivated parts are used in aerospace, automotive, chemical processing, defense, food and beverage, medical, water treatment and other industries where corrosive conditions are common.
Cold Spray Technology
This method uses compressed gas to deposit a metallic coating onto the substrate for finishing parts and products made from metal. Finishing technologies like cold spray coating require no heat input; instead, they accelerate particles to high velocities that collide with the component’s surface to form a thick layer. This method allows dissimilar materials to be bonded while also enabling the repair of worn or damaged components without changing their material properties. Cold spray coatings adhere well to metals and alloys, offering advantages over conventional metal finishing technologies.
Primary advantages of using cold spray coatings include:
- Causes no thermal distortion or other substrate damage as the process uses no heat.
- Creates a uniform and dense coating that’s very durable and able to withstand rigorous conditions.
- Establishes a strong mechanical bond between coating and metal substrate.
- Requires no curing or post-processing so is among the more cost-effective metal finishing technologies.
- Suits the coating and repairing of heat sensitive materials.
Due to these advantages and their versatility, cold spray coating methods can be used when other metal finishing technologies aren’t suitable. The aerospace sector uses this finishing technique to repair damaged parts without adding weight. Automotive manufacturers use the method for various parts of vehicle bodies and motors to augment corrosion resistance and toughness. Cold spray techniques can also be used for repairing and maintaining military equipment, while these methods are used for coating fragile parts in the electronics industry. The versatility of this method means it’s likely to find uses in other sectors as well.
Electroless Plating
Electroless plating offers substantial advantages over conventional electroplating methods. Unlike other metal finishing technologies that involve electroplating, this method uses less water and fewer chemicals. Electroless plating also makes coatings more uniform in thickness and allows these finishes to be applied to substrates not made from conductive materials. Electroless plating has become one of the more promising modern metal finishing technologies because it reduces exposure to dangerous materials and doesn’t require expensive infrastructure.
Primary advantages of using electroless plating include:
- Allows for even distribution of coatings.
- Needs no external source of power.
- Permits precision control over the thickness of coatings.
- Requires no electric current so eliminates the chance of electrodes burning.
- Works well for components with intricate geometries.
The aerospace, automotive, and electronics industries can all benefit from electroless plating. To resist extreme temperatures, protect against corrosive conditions, and augment robustness, the aerospace sector uses this technique to coat vital components. Auto manufacturers use them to protect parts like bearings, gears, and pistons against corrosion, while they can additionally be used for ornamental trim on vehicles. Circuit board manufacturers also use electroless plating to coat conductive materials with wafer-thin layers to improve conductivity. Because of its effectiveness and versatility, electroless plating has become one of these industries’ more favored metal finishing technologies.
Graphene Plating
While nanotech coatings, described later, are considered one of the more innovative metal finishing technologies in recent years, one specific type of coating has shown extraordinary characteristics. Graphene plating consists of carbon atoms in a singular layer, making this coating the thinnest material ever made by humans. Incredibly conductive of heat and electricity and two hundred times stronger than steel, it’s also watertight, transparent, flexible, and chemical resistant.
Primary advantages of using graphene plating include:
- Offers hydrophobic properties to metal substrates that cause water to slide easily off surfaces, due to its honeycomb structure and chemical makeup.
- Provides a lasting glossy finish that enhances appearance.
- Repels dust, dirt and other contaminants because of its antistatic nature.
- Replaces other types of coatings that don’t last as long.
Combining nanotechnology and the inherent properties of this thinnest of materials, graphene plating offers protection against abrasion and keeps contaminants off metal substrates. As such, it’s often applied to metal components, becoming an especially valuable material for flexible solar panels and other applications within the renewable energy sector. Passing along properties to the metals on which they’re overlaid, graphene plating helps resist corrosion from moisture, heat, and chemicals, which makes this finish ideal for medical devices, motor vehicles, and an array of industrial applications.
Green Electroplating
With its use of noxious solvents, conventional electroplating is among the most detrimental metal finishing technologies to the environment. The process also uses significant amounts of energy, with certain electroplating methods using large amounts of water. However, electroplating is becoming more sustainable due to widespread public trepidation about industrial effects on the natural world and strict environmental regulations. Yet green electroplating seeks to keep the many useful benefits these processes can provide with ways to reduce the amount of chemicals and water used, encouraging recycling and decreasing waste.
Some environmentally friendly approaches to electroplating include:
- Alternative metal finishing technologies that avoid using toxic substances to decrease damage to the environment, include the use of unconventional chemical interactions that include plating with gold, silver or zinc without the traditional use of cyanide in the process.
- Aluminum-based electroplating solutions have proven less harmful than materials commonly used cadmium or chrome, which are incredibly toxic; this method requires neither specialized equipment nor huge amounts of energy.
- Biodegradable chemicals are gradually replacing more toxic chemicals used in traditional electroplating processes for baths used in electroplating metal.
- Dry electroplating processes are being developed to avoid wet substrate metal finishing; technologies involving this dry process can reduce the need for harsh solvents, thus minimizing toxic waste.
- Pulse plating is one of the more innovative metal finishing technologies that, though not new, has become increasingly refined to make electroplating greener while also better controlling the accumulation of metal layers; this method also results in evener and smoother coatings, along with more efficient use of raw materials and energy.
- Renewable energy resources and energy-efficient operations are incorporated into metal finishing technologies like electroplating to reduce dependence on carbon-based fuels and make energy use more sustainable.
- Trivalent chromium used in plating systems to replace hexavalent chromium, a carcinogen, allows manufacturers to meet increasingly stringent regulatory requirements, such as the European Union’s regulation that mandates registration, evaluation, authorization, and restriction of chemicals, referred to as REACH.
- Water treatment innovations that include ion exchange systems, high-efficiency filtration, and reverse osmosis are being implemented in conjunction with metal finishing technologies like electroplating to reduce chemical and water consumption while reducing waste that can harm the environment.
For the foreseeable future, electroplating will be critical for contemporary manufacturing and metal finishing. Technologies that make electroplating more ecologically sound will continue to advance as regulations on these processes become ever stricter. Meanwhile, research continues to explore different metal finishing technologies to make electroplating greener.
Hydrophilic & Hydrophobic Coatings
These related yet distinct metal finishing technologies involve the pre-painting of substrates before fabrication to create a durable and even finish. Though used since the middle of the 20th century, promising innovations have increased the value of this technique for metal finishing. Nanotechnology, in particular, looks to augment these metal finishing technologies for water purification, self-cleaning, and anti-icing applications. Hydrophilic coatings attract and hold water to reduce friction, a property that improves lubrication and protects against corrosion, while hydrophobic coatings make water beads, swiftly repelling it.
Primary advantages of using hydrophilic coatings include:
- Enhances biocompatibility for medical applications.
- Helps reduce the need for water and chemical cleaning agents due to their self-cleaning characteristics.
- Improves performance and lifespan of products.
Primary advantages of using hydrophobic coatings include:
- Augments water-repellent qualities of fabrics and construction materials.
- Enables quicker and easier cleaning of surfaces.
- Reduces the need for maintenance by significantly moderating damage caused by water.
Both hydrophilic and hydrophobic metal finishing technologies continue to develop, with material scientists looking for formulations that offer greater durability and versatility while continually improving the environmental friendliness of both processes. Various industries are looking to hydrophilic coatings to augment efficiency in solar panels and other devices, driving greater industrial sustainability and enhancing recyclability, which is showing promise. Additionally, hydrophilic coatings are increasingly used in medical devices as their lubricating properties curtail the possibility of tissue damage. These coatings also protect against internal corrosion within water pipes by reducing friction.
Hydrophobic coatings are used by the construction and textile industries to increase the water-repellence of materials. In industrial settings, hydrophobic coatings reduce the need for maintenance, a particularly important requirement for the aerospace sector. The use of conventional paints often means aircraft must be frequently repainted due to damage by water, whereas hydrophobic coatings considerably diminish the need for such upkeep.
Laser Texturing
This is a non-contact method for metal finishing. Technologies involving high-powered lasers have been used for metalworking since the 1960s, though this more modern technique is used for making precisely shaped textures and patterns on metal substrates. Using high-intensity beams of light, this technique involves applying a laser to a metal substrate, which causes intricate microstructures to form on the surface of the metal. This textures the substrate, augmenting adhesion and wear resistance properties while decreasing the friction coefficient. Unlike many conventional metal finishing technologies, laser texturing enables complete control over shapes and depth to allow greater complexity while only removing tiny amounts of material.
Primary advantages of using laser texturing include:
- Allows for better bonding between metal substrate and coating material.
- Augments biocompatibility for medical applications.
- Creates a textured surface to increase contact, lower friction coefficient and improve wear resistance.
- Enhances corrosion resistance through the laser-applied microstructures, which impede oxidization.
- Provides higher strength for critical components, allowing them to withstand harsh conditions.
The aerospace and automotive sectors rely on laser texturing for its adhesive qualities to ensure aircraft and vehicles are safer and more reliable. The auto industry uses it for engine components like cylinders, gears, and pistons to improve performance. In contrast, laser texturing is used for critical aircraft components that require significant strength and can withstand extreme conditions. Additionally, medical devices use laser texturing, improving the biocompatibility of medical implants while reducing friction for medical implements.
Nanotech Coatings
Modern metal finishing technologies often create extraordinarily thin coatings between 1 to 100 nanometers thick. Manufacturers use nanotech coatings to better control a metal’s properties with a negligible mass increase. Most nanotech coatings are made with a glass derivative made of silicon dioxide, though, as mentioned earlier, graphene can also be used. The coating itself is very flexible, so it doesn’t break easily, while it also evens out on its own during curing to form a level surface, which prevents the buildup of contaminants like water or dust. Certain nanotech coatings help provide metal substrates with hydrophilic or hydrophobic properties, while others can enhance antimicrobial and electrical conductivity properties.
Primary advantages of using nanotech coatings include:
- Creates a self-cleaning substrate that’s both easy to clean and resistant to staining.
- Filters out harmful ultraviolet radiation.
- Protects surfaces against corrosion indefinitely.
- Provides superior hardness to metal substrates, so works well for protecting delicate surfaces.
- Repels water away from transparent surfaces like windshields, while also protecting metal substrates against damage from water.
Metal finishing technologies involving nanotech coatings have an almost endless number of possible applications in a wide range of industries. Nanotech coatings are used in electronics to make transistors and for medical research and solar panels in the renewable energy sector. Coatings made from nanotech have also been touted for cleanup operations after oil spills and for spacecraft due to their extremely lightweight. These coatings can also be used for aircraft, air purifiers, battery systems, body armor, catalytic converters, eyeglasses, machine parts, smart fabrics, spacecraft, and other purposes.
Supercritical Carbon Dioxide Cleaning
Certain metal finishing technologies are used to clear the metal substrate of any residue left over after fabrication. This metal substrate cleaning process involves pressurizing this gas to a temperature at which carbon dioxide enters a physical state in which there’s no difference between its gaseous and liquid form. This supercritical state causes the carbon dioxide to act as a potent solvent that can penetrate areas that are difficult to access, making it one of the more environmentally friendly metal finishing technologies being developed.
Primary advantages of using supercritical carbon dioxide cleaning include:
- Due to its lack of toxicity, offers advantages over conventional methods that use aqueous or solvent-based cleaning solutions.
- Efficiently cleans metal in a less harmful and more ecologically sound manner.
- Leaves no residual contamination on metal substrate.
- Lowers possibility of corrosion or harm to fragile components, making it more suitable for cleaning certain implements or parts.
- Produces no harmful emissions or waste, while also being nonflammable.
Conventional metal finishing technologies for cleaning substrates benefit from supercritical carbon dioxide, with applications for the aerospace, electronics, and medical device industries. It’s used to clean fuel injectors, turbine blades, and other vital components on aircraft without resulting in damage or corrosion. This process also enables electronics manufacturers to clean printed circuit boards and other delicate components without leaving residue or causing damage. Additionally, medical devices often undergo sterilization using supercritical carbon dioxide cleaning because of the effectiveness of this method.
RP Abrasives: Green Metal Finishing Technologies
RP Abrasives strives to use the most environmentally friendly metal finishing technologies to protect ecosystems and the world in which we live. RPA takes great pride in using clean energy with an on-premises hydroelectric plant that produces renewable power for our facility and others in the area. RPA has also replaced high-performance fluorescent lights with energy-conserving LED lighting to further conserve. This also includes our use of citric acid passivation, along with other green metal finishing technologies.
RPA also offers specialized cleaning processes for aluminum, plastics, stainless steel, and titanium. At RPA, we seek to meet or exceed all customer expectations, including quality, responsiveness, and punctual delivery. Whether requiring a single prototype or a batch of a million components, RPA offers innovative metal finishing technologies and excellent customer service. To learn more about our products and services, contact the metal finishing professionals at RP Abrasives today.