A Brief Insight into Electrochemistry

Join us for a short excursion into electrochemistry to better understand the fundamentals that make this process so important in surface technology.

Energy Source

Electrochemistry typically uses direct current sources for anodic oxidation. These are characterized by a positive and a negative terminal. At the negative terminal, an excess of negatively charged electrons is present. Nature tends to equalize this charge difference (also known as electrical voltage or potential difference). Humans have learned to route this equalization through lamps, motors, or heating elements to obtain light, mechanical energy, or heat. Nature has also made it possible to use charge equalization in surface technology: through electrochemical reactions.

Electrodes

Electrically conductive connections between the poles of the DC source and two spatially separated metal objects turn these objects into electrodes. The electrode connected to the negative pole is called the cathode, while the one connected to the positive pole is the anode. In anodic oxidation, the anode is the workpiece that is to receive an oxide layer. To build this layer, an electrolyte is required that surrounds the anode and at least wets the cathode.

Electrolyte

The electrolyte for anodizing consists of bases (alkalis), acids, or salts dissolved in water. These substances consist of electrically positive and negative ions. In water, the ions are separated and freely mobile. At first glance, it seems as if the electrolyte could conduct electricity. On closer inspection, however, the ions migrate to the electrode with the opposite electrical charge, where they accept or release electrons. In doing so, the ions equalize their own charge and undergo chemical transformation.

Chemical Reactions

In chemistry, reactions in which electrons are accepted are called reductions. These reactions occur at the cathode, where there is an excess of electrons. During anodizing, hydrogen gas is typically formed at this electrode.

At the anode, where electrons are lacking, ions release electrons. This  process is known as oxidation. In anodizing, oxygen acts as the electron acceptor and bonds with the electrode material to form a metal oxide.

What Exactly Is Anodizing? Process Sequence of Anodizing

Pretreatment as a Prerequisite for Defect-Free Layer Formation

A uniform oxide layer can only form on metallically clean surfaces. Thorough surface pretreatment is therefore essential. Surface technology provides mechanical and chemical methods that remove all types of contamination from materials.

Mechanical surface treatments remove stubborn contaminants and corrosion products. They also create a defined surface structure—such as glossy or matte—and can eliminate scratches or defects. Mechanical pretreatment typically involves brushing, blasting, grinding, or polishing.

Chemical pretreatment primarily removes contamination from previous process steps, such as oils and greases used as corrosion protection or cooling and forming lubricants from manufacturing. Common steps include alkaline degreasing and pickling in acidic or alkaline baths to remove remaining contaminants and natural oxide films.

Sequence of Anodizing

Individual workpieces are mounted on racks and immersed in the electrolyte bath. Alternatively, sheet metal wound into coils can be drawn through the bath and rewound after anodizing. A conductive connection to the positive pole of the DC source ensures that the workpiece becomes the anode. The container material often serves as the cathode; if that is not possible, cathodes are mounted on the side walls of the tank and connected to the negative pole.

Once the power source is switched on, the ions begin to migrate. Initially, a  thin, electrically insulating metal oxide layer  forms on the workpiece or semi-finished product. Because the anode continues to attract negative ions, these ions accumulate in front of the layer. The voltage rises until it reaches a value that allows the ions to penetrate the layer and reach the base metal to form new metal oxide. This process often produces visible sparks. Oxidation continues at the base metal, forming a porous layer with countless microscopic channels. The structure of the oxide layer can be varied widely  by adjusting the electrolyte composition, current intensity, and temperature.

Post-Treatment to Seal Pores and Add Color

The porous structure of the fresh metal oxide layer is ideal for absorbing dyes. However, if you choose to dye the freshly formed metal oxide layer, the pores must be sealed. This step is usually performed in a hot-water bath. At 208.6 °F (97 °C), the metal oxide reacts with water (hydration). This increases the volume of the layer and compresses the pores. This densification process is known as sealing. As an alternative, surface technology also offers pore filling using waxes.

Applications of Anodizing

Anodizing is well suited for producing corrosion- and wear-resistant oxide layers on light metals. This is primarily due to the properties of the oxides. The process is primarily used for aluminum, titanium, and magnesium. Attempting to anodize stainless steel would fail because its corrosion protection is provided by a very thin oxide film formed by chromium in the alloy reacting with oxygen in the air.

Anodizing Aluminum

Anodizing aluminum is the most widespread and best-studied variant of anodizing. It has acquired its own name: *Eloxal*. Aluminum is used in aerospace, automotive engineering, machinery, equipment manufacturing, construction, and architecture.

Anodizing Titanium

Titanium is an ideal material for aerospace and aviation due to its low density, high mechanical strength, and excellent heat resistance. These properties, combined with outstanding chemical resistance, make anodized titanium valuable for the chemical industry and medical technology.

Anodizing Magnesium

Because magnesium is extremely lightweight yet strong, it is gaining interest in the automotive and equipment manufacturing sectors. However, anodizing magnesium is challenging due to its high reactivity. It requires special approaches both in preparation and during anodic oxidation.

Der Beitrag Surface Treatment by Anodizing erschien zuerst auf Kluthe Magazine.

Work hardening occurs when metallic materials are deformed below their recrystallization temperature. Discover how mechanical properties of metals change during forming processes, which industries benefit from increased material strength, and  the additional hardening methods  used in  various manufacturing processes.

Cold Forming

Cold forming is ideal for mass production due to its ability to achieve high material throughput in a short amount of time. Additional advantages include material integrity, efficient material utilization, and relatively low energy consumption. Metals can be shaped into almost any form using intense mechanical forces. These new contours are created with tools that shape the material according to design specifications.

Despite the high processing speeds, pressures, and temperature increases used in the process, forming lubricants ensure that tools maintain a cost-effective lifespan. Kluthe offers a wide range of friction-reducing products, including Hakuform, Hakuforge, and carrier coatings like Decorrdal zinc phosphating, which are specifically adapted to different manufacturing conditions.

Work Hardening

A key side effect of cold forming is work hardening, which enhances the mechanical properties of manufactured components, allowing them to withstand high operational loads. In most manufacturing processes, increasing material strength is a desired outcome, especially in cold rolling, tube drawing, wire drawing, and other bulk cold forming techniques.

The benefits of work hardening can be seen in everyday American products, from the stronger aluminum used in MacBook laptop bodies, to the durable stainless steel in kitchen appliances like KitchenAid mixers, and even the paperclips on your desk. However, in some cases, increased strength can hinder further processing. When needed, the material can be annealed (recrystallized) to restore its original mechanical properties. This step is essential when multiple forming stages are required to achieve the final shape, such as in multi-stage drawn tubes, cold-headed parts made from drawn wire, or bulk cold-formed components. Intermediate annealing helps regain the necessary material properties.

Metal Deformability and Crystal Structure

Lattice Structure

The deformability of metals can be attributed to their crystal structure. As the melt solidifies, particles (atoms, ions) initially arrange themselves at randomly distributed locations to form regularly structured crystal lattices. While the melt becomes solid, more and more particles attach to the lattice (crystal growth). Occasionally, irregularities occur, which in materials science are referred to as lattice defects. Simple defects include:

• Foreign atoms – take the place of a particle and distort the lattice due to their different size.
• Vacancies – individual particles are missing in the lattice.
• Interstitial atoms – additionally embedded in the lattice.

Dislocations in the Lattice

Dislocations in the crystal lattices significantly influence  material behavior during cold forming. Materials science distinguishes between edge dislocations and screw dislocations. Edge dislocations  occur due to the addition of half-planes within a crystal,  causing neighboring planes, which normally run parallel,  to deviate sideways. Planes running perpendicular to the half-plane maintain their position. Screw dislocations, on the other hand, occur when lattice regions assume an oblique course to bridge missing  components, forming a spiral pattern throughout the crystal lattice.

Influence of Dislocations on Cold Forming

Dislocations weaken atomic bonds, allowing materials to deform. When external forces are applied, dislocations move through the lattice, enabling the metal to take its intended shape. However, as new dislocations accumulate, they begin to interfere with each other, increasing resistance to further deformation. This effect, known as work hardening, gradually strengthens the material.

Recrystallization

Lattice structures are in constant motion, vibrating around their ideal positions, a motion directly correlated with temperature. When the temperature surpasses a critical threshold, the thermal energy allows atomic rearrangement, eliminating many dislocations and restoring the lattice. This temperature is known as the recrystallization temperature, typically around 40-50% of a material’s absolute melting temperature. Some metals, such as zinc (787°F / 418°C), lead (622°F / 328°C), and tin (450°F / 232°C), cannot undergo work hardening because their structures automatically realign after deformation.

Additional Hardening Methods

Grain Refinement

As molten metal solidifies, its crystal grains grow until they meet neighboring grains, forming grain boundaries. Since adjacent grains have different lattice orientations, grain boundaries resist deformation, increasing material strength. Grain refinement enhances strength by controlling cooling rates and introducing crystallization nuclei, increasing the number of grain formation sites. The result is a finer grain structure with more grain boundaries, boosting strength while preserving toughness—unlike work hardening, which increases brittleness.

Precipitation Hardening

Most metals used in industry are alloys, composed of multiple chemical elements. For example, steel is an alloy of iron and carbon, with additional elements enhancing corrosion resistance and mechanical properties. Since different elements exhibit varying solubility in metal lattices, precipitation hardening involves heating the alloy to dissolve alloying elements uniformly, followed by rapid quenching. This process creates supersaturated crystals containing more foreign atoms than the lattice can accommodate. Over time, excess atoms migrate out of the lattice, forming precipitates at grain boundaries, restricting dislocation movement, and increasing strength.

Solid Solution Hardening

Most pure metals are too soft for industrial applications. Alloying elements can be introduced to increase strength by occupying lattice positions (substitutional hardening) or embedding between lattice atoms (interstitial hardening). These additional elements distort the lattice, making it harder for dislocations to move.

Industrial Applications for Work Hardening

Work hardening plays a crucial role in many cold forming processes, improving the mechanical properties of manufactured parts. Modern forming simulations allow precise control of work hardening levels, optimizing manufacturing processes for specific performance requirements.

This effect is particularly beneficial in bulk cold forming, where components such as transmission parts for Ford F-150 trucks, aerospace fasteners for Boeing aircraft, and high-load components in American automotive and defense industries are produced in large volumes within short cycles. Work hardening also benefits wires, tubes, and structural profiles used in construction and steel fabrication.

Work hardening processes have been central to manufacturing in America’s industrial heartland, from Steel Belt manufacturers to aerospace suppliers in Washington state and automotive parts makers in the Southeast. These advanced metallurgical techniques support over 500,000 American manufacturing jobs and contribute significantly to the $2.3 trillion U.S. manufacturing sector.

Der Beitrag Work Hardening Explained erschien zuerst auf Kluthe Magazine.

Application of DIN EN ISO 9227 (Corrosion tests in artificial atmospheres – Salt spray tests)

Corrosion preventatives enable the use of base metals in a wide variety of components. Its effectiveness determines the service life of machines and systems, vehicles, and structures. Manufacturers of such products expect their suppliers to deliver parts that meet defined quality standards. To verify this quality, clear specifications and criteria are required. These are often summarized in the internal standards of major manufacturers. Within this framework, a salt spray test in accordance with DIN EN ISO 9227 may be required. Alternatively, this requirement  may be agreed upon contractually. The standard specifies how the test apparatus must be designed, which substances are used, and under what conditions the test is completed . All other specifications are defined by the company requesting the test from its suppliers. This includes the nature and size of the test specimens, specimen preparation, test duration, and the required results.

Artificial, corrosion-promoting atmosphere

The salt spray test is conducted in a chamber that is continuously supplied with a finely atomized salt solution via nozzles. The standard specifies three variants of the salt solution, each producing a different level of corrosive attack. The neutral salt spray test (NSS test) uses a 5% aqueous sodium chloride solution. A slightly more aggressive method is the acetic acid salt spray test (AASS test), in which acetic acid is added to the sodium chloride solution. The third variant is the copper-accelerated acetic acid salt spray test (CASS test). In this case, the solution contains sodium chloride, acetic acid, and copper(II) chloride dihydrate. DIN EN ISO 9227 specifies in detail how these solutions  should be prepared. It also defines required spray volumes, pH values, and temperatures to be used during testing. These specifications, in turn, dictate chamber equipment requirements for heating, dosing, measurement, and control.

Arrangement of test specimens in the chamber

To obtain reproducible results, the test specimens in a salt spray test must be exposed solely to the  corrosive action of the artificial atmosphere. Other influences, such as contact with other metals or standing moisture on the surfaces, must be excluded. For this reason, there are precise requirements regarding the materials used for the chamber and the racks holding the test specimens. The positioning of the specimens can also influence the results of the salt spray test. The following rules apply:

• as few contact points as possible between the test specimen and the rack or suspension
• no contact between different test specimens
• arrangement of the test specimens at an angle of 20° from the vertical so that condensate separating from the mist can drain freely
• condensate must not drip onto other test specimens

Evaluation and documentation of salt spray test results

The customer specifies which variant of the salt solution is to be used, how long the coating or surface pretreatment of the workpieces must withstand the defined conditions, and which surface changes are permissible. In addition, the customer determines the required characteristics of the test specimens.

After completion of the test period, the specimens tested in the salt spray test are rinsed with distilled water and dried. This is followed by a visual inspection for surface changes. If the salt solution penetrates the conversion coating formed during surface pretreatment, corrosion products form on the base material. This occurs at points where the layer is damaged or contains contaminants. This is evident from blistering under paint and coating layers or from the color and extent of corrosion products. Rust on iron is typically reddish-brown, while zinc forms white, spot-like corrosion products.

It is often of interest to determine how far paints and coatings used for corrosion protection can be undermined by aggressive media in damaged areas. In such cases, the coating is simply scratched, either randomly or according to a defined pattern, before the salt spray test. After the test, it is determined whether and to what extent the coating has detached at the scratched areas.

All observations are carefully documented together with the test duration, the measurement data from the salt spray test, and a description of the test setup, are  recorded in a test report. The observations are then compared with the customer’s requirements. If the changes fall within the specified tolerance range, the test is considered passed.

Informative value of salt spray test results

The salt spray test provides results that can only be used to assess the quality of a surface coating. It allows comparable coating systems on identical base materials to be evaluated. The conditions of salt spray testing differ significantly from the real environmental conditions that corrosion protection must withstand in actual use. For this reason, the test can only provide indirect indications of the corrosion behavior of the tested components. In simplified terms: the coating is acceptable, has proven itself in practice, and therefore also protects against corrosion. This applies primarily to organic coatings such as paints and lacquers, as well as to anodically produced oxide layers (e.g., anodized aluminum). By contrast, the informative value is limited for metallic coatings applied by electroplating or hot-dip galvanizing.

Der Beitrag What Is the Salt Spray Test? erschien zuerst auf Kluthe Magazine.

A Look into the History of Thread Manufacturing

The earliest known references to tools for thread production can be found in the notes of the universal scholar Leonardo da Vinci (1452–1519). Whether they were actually used for this purpose can no longer be determined.

The first primitive machine for cutting screw threads was built in 1568 in France. Seventy-three years later, Henry Hindley of York (1701–1771), a renowned clockmaker and mechanic, improved the design and helped establish screw-cutting for practical use. In Germany, screw forges began to appear toward the end of the 17th century, particularly in Westphalia and the Rhineland, though screws were still largely made by hand.

The idea of standardizing came from British engineer Joseph Whitworth (1803–1887). In 1841, he introduced the Whitworth thread, based on the English inch unit, laying the foundation for modern screw connections. Standardization made screws interchangeable and enabled mass production.

Toward the late 19th century, the first attempts were made to form threads by mass production processes, though this was initially limited to hot forming. American William Keane had already considered thread rolling (a form of cold forming) around 1835, but the steel available at the time splintered during cold working. Only after more ductile steels were introduced did the process gain momentum.

Today, several processes for production are established,  categorized into cutting and non-cutting methods.

Thread Forming with Cutting Processes

The starting material for cutting processes is usually free-machining steel, which offers particularly good machinability. If preformed blanks are further processed by grinding or turning into precision or necked screws, quenched and tempered steels may also be considered.

Cutting / Tapping

A distinction is made here between internal and external cutting. Internal versions are primarily produced using taps. The first step is to drill a core hole with a standard drill bit. The profile is then cut into this bore with a tap. External versions are cut onto a bolt-shaped blank using a die.

Turning

In this process, a cutting tool is used in a longitudinal turning operation. The profile and positioning of the tool are selected according to the desired shape. In multi-stage production, the cutting tip of the tool is applied repeatedly at the same point on the workpiece. The feed corresponds to the pitch. This method can be used to produce both external and internal forms.

Chasing

Thread chasing makes it possible to manufacture economically on lathes and automatic machines. The tools used for this are available as shank, square, and disk chasers for both internal and external use. They are available as single-tooth and multi-tooth versions.

Milling

Thread milling requires machine tools capable of performing movements along the x, y, and z axes simultaneously. This process is mainly used when there are high demands for process reliability and quality. Thread mills are considered problem solvers for special applications. They are rarely used in mass production.

Whirling

Thread whirling is the method of choice where the length is large in relation to the diameter. Also known as thread peeling, this process allows even difficult-to-machine materials to be processed with low tolerances. It is often used to manufacture bone screws from stainless steels or titanium.

Grinding

Thread grinding is primarily used to manufacture threading tools for internal forms. However, it can also be used to produce rolling dies for external ones. One of the biggest advantages of this process is the extremely  high-profile accuracy achieved  by using ceramic-bonded grinding wheels.

EDM (Electrical Discharge Machining)

EDM is mainly used for producing internal shapes in difficult-to-machine materials. The tool electrode, made of brass, copper, or steel, corresponds to the profile and is driven into a pre-drilled core hole in the workpiece.

Thread Forming with Non-Cutting Processes

In non-cutting production, a distinction is made between hot forming (smaller batch sizes, large fasteners) and cold forming (larger batch sizes). All standardized screws and nuts today are produced by non-cutting methods. For safety components, non-cutting forming is often even required. Non-cutting methods bring several advantages:

• no interruption of the grain flow in the material
• lower stress concentration
• faster production
• no chip formation
• fewer cutting errors
• and a smoother surface structure

Rolling

Thread rolling is  often used in screw production. The tools used for this are pressed onto the workpiece with high pressure, resulting in permanent plastic deformation.

For forming to work, the material must be cold-formable. For pointed types, the elongation at break should be at least five percent. The upper tensile strength limit is about 246,000 psi (1700 N/mm²). Typical materials for fasteners with rolled profiles are:

• free-machining and construction steels,
• high-alloy, corrosion- and acid-resistant steels,
• aluminum and copper wrought alloys with a copper content of at least 60 percent.

Sufficient material thickness is required to form in this way. This depends partly on the material itself and partly on the type and depth of the desired profile.

Pressing / Flow Forming

Thread forming by pressing is another process which is used to produce round profiles in sheet metal. A rotating roller is inserted into a pre-drilled core hole while another roller is applied from the outside. The contour is formed in this stepwise process by displacing the material.

What Role Do Cutting and Forming Lubricants Play in Thread Production?

No matter the method—rolling, cutting, chasing, or milling—threads cannot be produced reliably without lubricants. Especially in cutting, the need for lubrication is often underestimated, which frequently results in significantly shortened tool life. Lubricants lower the temperature and reduce friction between the workpiece and the tool, which in turn reduces wear.

Lubricants are indispensable in non-cutting forming, as sliding occurs between the workpiece surface and the tool. Forming lubricants (generally non-water-miscible) ensure that production runs smoothly. They prevent material build-up, which could cause rough surfaces or even tool breakage. In addition, they help dissipate the heat generated during forming. Residual lubricants remaining on the workpiece provide a degree of corrosion protection but often need to be removed before further processing steps.

Der Beitrag Thread Forms – Rolling, Pressing, and Cutting erschien zuerst auf Kluthe Magazine.

Surface Coating with Electroplating

Electroplating uses electrical currents to deposit metal uniformly on workpiece surfaces. The resulting metal layer typically serves to protect against mechanical wear, as corrosion preventative, and/or improve electrical conductivity. Additionally, electroplating can simplify further processing or achieve aesthetic changes.

This technique is frequently applied to steel or stainless-steel components, employing metals with properties suited to the application, such as:

• Copper
• Zinc
• Tin
• Brass
• Nickel
• Silver
• Gold.

Electroplating is not limited to metallic objects; it can also be applied to materials like plastics, ceramics, and glass. . These materials are pre-treated with conductive coatings, chemically applied metal layers, or metal seeds to enable electroplating. Common coating materials used in this process include chrome, copper, zinc, and nickel.

Surface Modification with Anodizing

Eloxal is the abbreviation for ‘electrolytic oxidation of aluminum’. The term itself indicates that only aluminum can be anodized.  This lightweight metal naturally forms a thin but dense oxide layer under oxygen exposure, providing some resistance to corrosion. However, natural protection is limited, especially in the presence of substances like salt or sulfur  dioxide and does not prevent wear.

Anodizing enhances the aluminum’s surface by creating a nearly pore-free dielectric barrier layer, topped with a finely porous, honeycomb-like outer layer. While natural oxide layers are only a few nanometers thick, anodized layers can reach up to 25 micrometers, making aluminum components suitable for harsh industrial conditions and marine environments. The porous structure also allows aluminum to be dyed, particularly when using pure aluminum alloys with a magnesium content below 4%.

Electroplating Process Steps

Depending on the size of the workpiece and specific requirements, different electroplating techniques can be employed. For oversized components that cannot be treated in an electroplating bath, alternatives like dip plating or brush plating are used. In brush plating, the electrolyte is applied under voltage with a sponge.

Other techniques include:

• Barrel plating
• Chemical plating
• Strip plating

The electroplating process generally follows three main steps:

1. Pretreatment

Mechanical and chemical processes remove oils, greases, rust, scale, chips, and grinding dust from the workpiece surface. Multiple rinsing steps follow to ensure a completely clean surface. The pretreatment is completed with several rinsing processes that ensure an absolutely clean surface.

2. Coating

The workpiece is immersed in an electrolyte solution containing the desired metal. Connected to a DC power source, the workpiece acts as the cathode, while the metal anode serves as the source of positive ions. When the current flows, metal ions from the anode deposit onto the workpiece. The duration in the bath and the current strength  determines the thickness of the coating.

3. Post-Treatment

After electroplating, the workpiece is rinsed and dried. Additional steps, such as passivation or chromating (e.g., for zinc-plated steel), may be  added.

Anodizing Process Steps

Unlike electroplating, anodizing does not add a coating but transforms the surface layer of aluminum. The anodizing process involves four steps,  followed by coloring as an optional fifth step.

1. Pretreatment

As with electroplating, this step ensures a grease- and dust-free surface. For components with high aesthetic demands, chemical pretreatment can smooth surface irregularities through pickling.

2. Anodic Oxidation

Aluminum parts are submerged in an electrolyte solution (sulfuric or oxalic acid) with the workpiece connected as the anode to a DC power source. Lead or titanium plates, unaffected by the electrolyte, are used as cathodes. When  the current flows, water at the cathode decomposes, releasing hydrogen, while oxygen reacts with the aluminum to form the oxide layer. The longer the process, the thicker the protective layer, forming capillary-like pores.

3. Coloring (Optional)

The pores created during anodic oxidation can absorb dyes. Since the color embeds within the pores rather than sitting on the surface, it is highly durable and  abrasion resistant.

4. Sealing

After anodizing, the open pores are sealed by boiling the aluminum in demineralized water. This causes the aluminum oxide to react with water, forming aluminum oxide hydroxide. The pores swell from the edges toward the center, closing completely.

Pros and Cons of Electroplating

Electroplating is a cost-effective method offering extensive coating options. It provides excellent corrosion protection and enhances the visual appeal of workpieces. However, the process generates precipitation sludge containing concentrated chemicals, which must be disposed of properly to prevent environmental harm.

Pros and Cons of Anodizing

Like electroplating, anodizing creates a durable, corrosion-resistant surface. Anodized aluminum can achieve hardness levels between 200 and 400 HV, and even up to 600 HV with hard anodizing. The process also allows for vibrant, long-lasting coloring. However, anodizing is limited to aluminum components.

Anodized aluminum’s non-conductive protective layer cannot be easily re-anodized without first removing the oxide layer through pickling. This can alter the dimensions of precision components, potentially rendering them non-compliant with specifications.

Der Beitrag Electroplating and Anodizing: Key Differences erschien zuerst auf Kluthe Magazine.

Wear occurs whenever materials degrade through use. Abrasion is a specific form of wear that results from what is known as micro-cutting. High abrasiveness significantly reduces the service life of machine parts, places undue stress on materials, and leads to shorter maintenance intervals. To prevent this, here’s what matters most.

What Does “Abrasive” Mean?

The term abrasion comes from Latin and literally means “scraping off.” It describes the removal of material through grinding or rubbing. Materials experts refer to a substance as abrasive when it causes a grinding or rubbing effect that results in smoothing, cleaning, or wearing away of metals or other materials. In practical terms, this often applies to abrasives used to grind or polish surfaces. However, lubricants such as oils or greases can also develop unwanted abrasive effects, which must be avoided during machine operation. This kind of wear increases strain on individual machine parts and often results in expensive maintenance. By simply switching to a different lubricant, such wear can often be reduced. The choice of the right cooling lubricant or forming lubricant has a significant impact on the service life of moving parts. Abrasive, as well as adhesive wear, is one of the leading causes of failure in machines with moving components.

What Happens When a Lubricant Becomes Abrasive?

Lubricants can contain hard particles that impair their lubricating properties. Low-quality oils or greases, especially those used over prolonged periods, tend to form clumps that interfere with lubrication. When such particles—or microscopic surface roughness—penetrate the outer layer of a material, abrasion occurs. Under the microscope, characteristic signs of micro-cutting can be seen, such as tiny scratches or grooves. This is also referred to as furrow wear. It occurs gradually and often goes unnoticed at first.

Much like a cave carved by water and wind over millennia, abrasive wear can take time to become noticeable. Highly stressed machine components like gears, roller bearings, or needle bearings are  significantly affected. Choosing an appropriate lubricant is essential for maximizing the lifespan of interacting parts. Even hardened machine components such as gears or bushings are subject to abrasion. However, using high-grade lubricants can significantly extend service life and reduce maintenance and repair costs.

When Does Abrasive Wear Occur?

There are several common causes of abrasion-related wear. It typically occurs during machine startup or under sudden load changes. At low speeds, lubricants often fail to form a protective layer between components. This is especially true in sump-lubricated systems, which only function effectively once the gearbox is running. Not all gears are fully submerged in oil; only once the parts are in motion does the lubricant spread across all gears, shafts, and related components. Until the machine reaches  an effective operating speed, the oil’s viscosity is not enough to prevent abrasion.

When Is a Lubricant Abrasive? Viscosity Matters

The viscosity of a fluid determines how thick or thin it is. Simply put, viscosity indicates how readily a fluid flows. This allows for a direct comparison of different liquids and their lubrication properties. Using a lubricant with too low a viscosity can lead to excessive wear. If the oil is too thin, it cannot form a sufficient separation layer between moving components. Even when gears appear to mesh perfectly, a proper lubricant ensures that the metal surfaces do not  rub directly against each other. A thin oil or grease layer protects the material and prevents premature degradation.

Abrasive wear can be significantly reduced by using additives in oils. These additives help protect surfaces in boundary lubrication situations—especially when the oil film begins to break down. High operating temperatures can also reduce an oil’s viscosity. When separation between moving parts is inadequate and the lubricant behaves abrasively, anti-wear additives offer critical short-term protection.

Abrasive Wear Caused by Particles in Lubricants

Another common occurrence—even in already lubricated machine parts—is the presence of hard particles in oil or grease. These microscopic particles are roughly the same size as the lubrication film intended to protect the metal surface. Because of their size, they can enter the narrow gap between moving parts and can compromise the lubricant’s effectiveness.

Detecting Abrasive Wear

To determine whether a machine is suffering from abrasive wear, a visual inspection is the first step—but microscopic damage is usually invisible to the naked eye. In such cases, an oil analysis provides clarity. This test can detect foreign particles in the lubricant and indicate whether it is time to change the oil.

Preventing Abrasive Wear

Even during the design phase of a machine, abrasive wear can be minimized by selecting appropriate material pairings. Combining metals with plastics, ceramics, or other materials can reduce surface abrasiveness significantly.

Oils should also be filtered before being filled into the system. Continuous filtration during machine operation is also highly recommended. Oil change intervals must be strictly followed, and only certified, high-quality lubricants suitable for the machine’s operational loads should be used. New equipment should undergo system flushing before commissioning to remove foreign materials and even the smallest particles. Seals and access points should remain closed to prevent contaminants from entering the system.

Der Beitrag Abrasive Wear erschien zuerst auf Kluthe Magazine.

Manganese phosphating is a conversion coating process used primarily on low-alloy ferrous parts. It provides excellent corrosion resistance and reduces friction and wear in sliding or rotating applications. This guide explains how manganese phosphate conversion coatings are formed and how they affect the properties of treated parts. These coatings provide excellent corrosion protection and are especially valued for their wear resistance in sliding applications.

Manganese Phosphating Process: How the Layers Form

The main steps in manganese phosphating are:

• Cleaning and degreasing
• Pickling to remove rust and scale
• Activating the surfaces
• Forming the manganese phosphate layer
• Post-treatment through oiling or coating

Cleaning and Degreasing

Cleaning and degreasing are the first step in any surface treatment process. Workpieces often have accumulated cooling lubricant or corrosion prevention residues that can interfere with the chemicals used to build the manganese phosphate layer. The type of cleaner depends on the contamination: alkaline cleaners work well for heavy, greasy deposits, while milder neutral cleaners can handle light residues. After cleaning, a thorough cascade rinse removes any leftover cleaning solution. In this step, the parts pass through a series of rinse tanks while deionized water flows in the opposite direction, allowing the rinse water to be reused for mixing fresh cleaning solutions.

Pickling to Remove Rust and Scale

Heat treatments and welding often leave rust or scale on metal surfaces. Storing parts for extended periods can also lead to rust spots. Since conversion coatings rely on chemical reactions, these contaminants must be removed. Pickling is only necessary if such impurities are present and it is typically done with an inorganic acid that dissolves rust and scale. After pickling, parts go through a multi-stage cascade rinse.

Activating the Surfaces

Before manganese phosphating, the surfaces must be activated. As salts of phosphoric acid, phosphate coatings naturally form a crystalline structure. The activation solution creates nucleation sites where the manganese phosphate crystals can start to grow. These crystals expand until they meet and cover the entire surface. The number and distribution of nucleation sites determine how large the crystals become in the next step. Choosing the right activation agent helps tailor the coating structure for the intended application.

Forming the Manganese Phosphate Layer

This conversion coating takes place in immersion tanks using a solution of diluted phosphoric acid, Mn²⁺ ions (manganese), and other additives. Bath temperatures for this process are typically around 185 °F (85 °C), with immersion times ranging from 5 to 20 minutes. A multi-stage cascade rinse and drying process completes the phosphating. To keep the concentration of process chemicals within the required limits, the bath must be monitored. Dosing pumps replenish chemicals as needed, and any water lost due to evaporation is replaced with rinse water from the final cascade rinse. Sludge generated during phosphating should be continuously removed using a sloped tank bottom to avoid the need for frequent draining and cleaning.

In the periodic table, Mn (atomic number 25) and iron (26) are next to each other. They share similar chemical properties, and their ions are almost identical in size. As a result, the metal surface easily forms mixed crystals that contain both Mn²⁺ and Fe²⁺ ions along with phosphate ions. These ions can combine in nearly any ratio. The crystal size depends on prior surface activation, while the final coating thickness is mainly determined by immersion time and bath conditions. Coating thickness can be controlled very precisely, typically ranging from 0.00008 to 0.0002 inches (2–5 µm), with thicker layers up to about 0.0012 inches (30 µm) possible.

Post-Treatment: Oiling or Coating

Thanks to their fine, porous structure, phosphate coatings based on manganese make an excellent base for subsequent painting or coating. This is why this method is often used as a pretreatment step before applying an organic coating to high-quality components. The coating’s structure also makes it highly receptive to oils and greases, which are used for additional corrosion protection. The parts are dipped in appropriate oil baths, and the protective agents penetrate and remain in the pores.

Typical Applications for Manganese Phosphating

These manganese based phosphate layers stand out for their wear resistance and ability to reduce friction in sliding contacts. For this reason, they are widely used on parts such as gears and plain bearings. For example, automotive camshafts and transmission gears often receive this type of coating to improve break-in wear resistance and ensure reliable operation under high loads. These benefits also apply to forming processes: when parts are to be further processed by deep drawing, wire drawing, or tube drawing, a phosphate layer containing manganese can reduce the required forming force, decrease tool wear, and minimize the risk of cold welding.

Additional features of these coatings include:

• Electrical insulation
• Temperature resistance of up to about 570 °F (300 °C)
• Attractive matte black-gray appearance
• Excellent dimensional stability
• Good flexibility
• Insoluble in water
• Resistant to solvents, fuels, and lubricants
• Strong adhesion
• Environmentally friendly

Typical uses for manganese phosphating range from fasteners and gears, to components for roller and plain bearings, all the way to parts used in valve manufacturing. Industries that rely on manganese phosphate coatings include automotive, general machinery, aerospace, and plant engineering.

In mechanical engineering and firearms manufacturing, black oxide finishing (also known as bluing) is still common. This conversion coating provides temporary corrosion protection and an attractive black finish. Bluing is done with highly concentrated salt solutions heated up to about 300 °F (150 °C), producing smooth layers up to 0.00004 inches (1 µm) thick. However, the strongly alkaline salts used for bluing are classified as hazardous materials. In many cases, the energy-intensive, environmentally taxing bluing process can be replaced with manganese phosphating, which generates less hazardous waste and is easier to manage under OSHA and EPA regulations.

Der Beitrag Surface Treatment with Manganese Phosphate Coatings erschien zuerst auf Kluthe Magazine.

EcoVadis SAS is a Paris-based company, established in 2007, that operates globally to assess sustainability practices within companies. The outcome is the EcoVadis Sustainability Rating. This rating allows participating companies to precisely determine their standing compared to others in their industry and identify areas for improvement. Learn here about how the service works and what the EcoVadis Rating truly entails.

Why EcoVadis Rating?

Many companies strive to improve sustainability for various reasons. For example, the chemical industry is interested in demonstrating to society how it increasingly minimizes the environmental impact of production through green chemistry, achieves social goals, and makes supply chains for raw materials in the chemical sector progressively more sustainable. A challenge in this area is defining measurable goals and indicators to track improvements and make comparisons. EcoVadis helps companies overcome these challenges by providing a reliable assessment and monitoring of their sustainability performance.

Questions that might influence the assessment include:

• Has the company calculated a CO2 balance?
• Does it set CO2 reduction targets?
• How does it  manage finite and critical resources?
• Is there a human rights officer?
• Is there a sustainable waste management and recycling program?
• How are gender equality and occupational safety ensured?
• Are there comprehensive employee training programs?
• Is the supply chain traceable?
• Does the company engage in social initiatives?

Service Management

To monitor a company’s sustainability and rate it through EcoVadis, reliable information on operational standards, treatment of employees, respect for human rights, and environmental protection along the supply chain is needed. The company uses diverse information sources, including client documents, third-party certificates, business partner data, and publicly available information. This data is stored in a secure cloud and protected from loss and unauthorized access, through processing via a SaaS platform. SaaS stands for Software-as-a-Service, a model widely used in customer relationship management (CRM) where it supports process optimization and profitability enhancement. A unique, specially developed methodology is available for sustainability assessment. This methodology enables a comprehensive rating of a company’s commitment to sustainable practices (Corporate Social Responsibility, CSR).

Methodology for EcoVadis Rating and Scorecard Creation

Alongside the EcoVadis Rating, which allows companies to compare their sustainability management with others in the same industry, EcoVadis creates a scorecard. This report details individual results and highlights areas for improvement. Built on international sustainability standards like the United Nations Global Compact, the Global Reporting Initiative, and ISO 26000, the EcoVadis methodology is based on seven core principles:

1. Assessments are conducted by highly qualified international experts.
2. Evaluation procedures are tailored to specific industries, company sizes, and countries.
3. Using all available sources ensures extensive stakeholder input for a reliable rating.
4. Modern Technology enables secure, confidential processes with accelerated processing times.
5. Documentation is transparent and traceable.
6. Evaluation is based on empirically derived and scientifically validated information.
7. Continuous improvement in assessment processes enhances methodological excellence.

The EcoVadis Sustainability Scorecard

The EcoVadis Sustainability Scorecard contains the assessment results, covering four areas that are also relevant to the chemical industry and promote sustainable chemistry:

• Environment
• Labor and human rights
• Ethics
• Sustainable procurement

Twenty-one indicators are available for evaluating individual performance. These indicators generate points that contribute to the company’s overall rating, allowing for easy comparison of sustainability performance across companies. Additionally, the point scores are used for the rating, which is linked to the awarding of recognition medals: Platinum (top 1%), Gold (top 5%), Silver (top 25%), and Bronze (top 50%). These medals can be used in corporate materials for promotional purposes.

Using the Scorecard in Business Relationships

The EcoVadis Scorecard can be requested by other companies to assess if a business partner meets high standards or presents CSR risks, impacting supplier selection. Clients may also require corrective measures from suppliers if needed. For instance, the chemical industry can only truly engage in green chemistry if raw material suppliers practice sustainable chemistry. A supplier’s scorecard provides reliable insight into the standards of its production processes.

Summary of the EcoVadis Rating Benefits

An established methodology with proven technology, quickly delivers a comprehensive assessment of a company’s sustainability, meeting environmental, sustainability, and legal requirements. Self-assessment questionnaires are tailored to company needs, while strengths and improvement areas are revealed through the EcoVadis Rating. Key performance indicators facilitate efficient, trackable improvements, and the scorecard information exchange between companies strengthens business networking.
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Der Beitrag What Does the EcoVadis Rating Indicate? erschien zuerst auf Kluthe Magazine.

QUALICOAT is the registered trademark of the Association for Quality Control in the Painting and Coating Industry, headquartered in Zurich, Switzerland. The trademark also serves as a quality label for surface pretreatment and finishing of aluminum components used in architectural applications. Detailed quality requirements must be met to receive the label, as defined in the QUALICOAT Standard. In this article, we explain  the performance that aluminum powder coatings must deliver to ensure a long service life without loss of quality.

Organization of quality assurance

The QUALICOAT product certification system has become firmly established worldwide for aluminum finishing quality assurance. The global organization consists of national and international associations that function as general licensees on behalf of the Zurich-based Association for Quality Control in the Painting and Coating Industry. These general licensees inspect both manufacturers of pretreatment chemicals and coating materials, as well as companies that apply finishes to aluminum components. When the QUALICOAT specifications are met, chemical manufacturers receive approval for their respective products. Coating contractors then earn facility licenses upon passing inspection.

Structure of the QUALICOAT Standard

The specifications for pretreatment chemicals, finishing materials, and application facilities are updated annually and published by the Executive Board of the Association for Quality Control in the Painting and Coating Industry under the title “Specifications for Obtaining the Quality Label for Coatings on Aluminum by Liquid and Powder Coating for Architectural Applications.”  Below is a brief description of each chapter of the standard.

Chapter 1

Chapter 1 of the specifications addresses general notes on the scope of application as well as general requirements for the aluminum alloys, coating materials, and pretreatment materials used. In addition, Chapter 1 includes the obligation for license holders of the quality label in surface technology to participate in QUALICOAT training programs, as well as important definitions of terms.

Chapter 2

This chapter describes the test methods for finished products and powder coating materials and defines the criteria for evaluating the test results. In most cases, these are based on international standards, which are summarized in Annex A9 of the specifications. The methods are supplemented by tests developed specifically for the QUALICOAT Standard.

Chapter 3

This chapter contains detailed operational guidelines for coating contractors. Among other things, it specifies exactly how surface pretreatment, the conversion process, finish application, and heat curing must be conducted. Contractors are required to perform certain inspections on the parts and to monitor equipment operating conditions. This requires a laboratory with a defined minimum level of equipment.

Chapter 4

This section describes the requirements that must be met for the approval of powder coating materials. Approval is granted for a specific production site if the manufacturer of the powder coating materials provides the required technical information on its products. In addition, the manufacturer must operate a test laboratory with a defined minimum level of equipment and have the specified tests carried out on test panels by an accredited laboratory. The final evaluation of the results is performed by the responsible general licensee or by QUALICOAT itself. For this purpose, the independent laboratory submits the test report. Approval must be renewed on a regular basis.

Chapter 5

This section outlines the procedure by which coating companies in surface technology obtain the license to use the quality label. This requires inspection of the technical equipment of each coating line, the laboratory, as well as the materials and finished products. The basis for reviewing operating procedures and technical equipment is the operating instructions set out in Chapter 3. Tests on finished products are carried out in accordance with the test methods specified in Chapter 2. Once a coater holds the license to use the quality label, two inspections are conducted per year. If the results comply with the QUALICOAT Standard, the license is renewed on a regular basis.

Chapter 6

Chapter 6 requires coating companies to carry out extensive internal inspections as well as to document the procedures performed and the results obtained. Inspections cover operating conditions in surface pretreatment, during conversion processes, and in metal coating, including curing conditions, as well as quality controls of finished products from surface technology.

Brief overview of the prescribed test methods in the QUALICOAT Standard

The specifications for procedures and evaluating results in the QUALICOAT Standard are extremely comprehensive. This ensures the quality of the finished products and  their long-term corrosion protection. The following tests are specified:

• Evaluation of the appearance of the visible surface
• Measurement of gloss according to customer requirements (matte, satin, or gloss)
• Determination of coating thickness (for QUALICOAT powder coating, depending on requirement class, between approximately 2.0 and 4.3 mils)
• Determination of adhesion of the powder coating to the surface using standardized adhesive tape (dry and wet adhesion)
• Indentation hardness test, cupping test, mandrel bend test, and impact test (after the specified mechanical load is applied, the finish must show no defects or cracks)
• Acetic acid salt spray test and exposure in cyclic condensation with sulfur dioxide–containing atmosphere (a scribe mark approximately 0.04 in. wide down to the metal may be undercut only up to the specified limit; no blistering; the tests provide information on the corrosion protection of the coating)
• Machu test (immersion in a solution with precisely defined composition, temperature, and exposure time; the previously applied scribe line may be undercut only up to the specified limit)
• Accelerated weathering test (after 1,000 hours, gloss loss and color change are evaluated)
• Weathering test (outdoor exposure is performed in Florida, USA, and lasts up to 10 years, depending on the class of the organic coating)
• Degree of crosslinking test (procedure to determine whether the properties of the finish change when exposed to an organic solvent)
• Resistance to mortar (mortar must be easily removable from powder-coated surfaces, subsequent color inspection)
• Resistance under constant condensation climate and resistance to boiling water (under defined conditions; for powder coatings, testing in a pressure steam cooker is also possible; application of a scribe pattern; testing with standardized adhesive tape; defects or delamination are not permitted; blistering and color change are subject to defined limits)
• Sawing, milling, and drilling of finished parts with sharp tools must not cause cracking or flaking
• Filiform corrosion test (on a scribed specimen, this thread-like form of underfilm corrosion is induced using hydrochloric acid; after a defined exposure time under specified conditions, the specimen is evaluated)
• Water spot test (evaluation of color change after exposure to fully deionized water at a temperature of 140 °F)
• Scratch and abrasion resistance test (using a Martindale tester; an abrasion pad passes over the surface under defined conditions for a specified period; gloss measurements are then carried out, and the gloss level is evaluated)

Conclusion: Quality in surface technology

Overall, it can be said that anyone purchasing coating products manufactured to the QUALICOAT Standard can rely on them meeting high quality requirements. Thanks to the strict testing criteria, such products in surface treatment meet fundamental requirements, which increasingly also include sustainability (green chemistry).

Der Beitrag The QUALICOAT Standard for Powder Coating erschien zuerst auf Kluthe Magazine.

Criteria for distinguishing types of metal corrosion

Corrosion damages the material. Without countermeasures, many metal products would have a very short service life. Suitable solutions for corrosion protection can only be identified if the causes and mechanisms of corrosion processes are  considered. Individual metals and alloys react differently to corrosive attack by environmental media. Both the chemical elements involved, and the material structure formed during solidification of the melt play a role in the type of corrosion. In addition, prior metal processing, and the design of the component influence corrosion behavior. Finally, differences arise in the way material degradation spreads, whether limited to the metal surface or extending into the depth of the material. Based on these criteria, distinct  types of metal corrosion are classified  to facilitate targeted prevention.

Types of corrosion based on reaction mechanisms

Formation of local galvanic cells

Understanding corrosion starts with the atomic structure of metals. Atoms are arranged in regular lattices. The outer electrons of the atomic shells are freely movable within these lattices. Their absence from individual atomic shells allows the positive charge of the atomic nuclei to dominate. Strictly speaking, these lattices consist of ions that respond to electric fields. When moisture is present, galvanic cells form. Such corrosion processes correspond in their processes to galvanic coating or the electrolysis of water. A small electric current causes metal ions to dissolve at locations where there is an electron deficiency (anode) and combine with oxygen from  moisture. At locations with an excess of electrons (cathode), gaseous hydrogen is produced, which immediately reacts with oxygen in the air to form water. The material areas in which these processes take place usually have only a very small spatial extent. This results in the term local galvanic cells.

Contact corrosion

When different metals come into contact with each other, an electrical potential difference can be observed between them. An electric field forms. When metals are arranged according to the magnitude of these potential differences, the electrochemical series results. Hydrogen is arbitrarily placed in the middle of this series. Metals that are more positive in the electric field are considered noble, while those that are more negative are considered base. The greater the distance between metals in the series, the greater the potential difference and thus the electric current that flows when a closed circuit is formed. This current consists of ions from the less noble metal, which detach from their lattice, migrate toward the more noble metal, and deposit there. These types of corrosion can be suppressed by using identical materials within a system or by careful electrical isolation.

Chemical oxidation

In addition to electrochemical processes, some types of corrosion are caused by direct chemical reactions. When certain dry gases, salts, bases, or acids make contact with metal surfaces, they form molecules whose stability is based on shared electrons. These corrosion processes are known as redox reactions. The metal receives electrons for shared use and is oxidized. The reaction partner provides these electrons and is reduced. These processes occur more intensely at high temperatures. Substances that can trigger such behavior include oxygen, hydrogen sulfide, ammonia, chlorine, and ammonium salts. These types of corrosion can be avoided through the use of resistant materials or suitable coatings.

Biocorrosion

Biocorrosion is another important type of metal corrosion. In this form of corrosion, the substances responsible for the corrosive attack originate from the metabolic processes of living organisms. Microorganisms, fungi, lichens, plants, and animals that colonize metal surfaces produce an almost inexhaustible range of organic substances that can form chemical compounds with metals. These include  various organic acids, such as formic acid, acetic acid, uric acid, and citric acid. In addition, metabolic by-products such as hydrogen sulfide and nitrogen oxides can form, which under certain conditions react with water to form sulfuric or nitric acid.

Types of metal corrosion based on propagation mechanisms

Uniform corrosion

In this type of corrosion, the electrochemical conversion of the material occurs evenly across the metal surface. Depending on the material used, thin passive layers quickly form under the influence of atmospheric oxygen and moisture, protecting the underlying material from further degradation. This is the case, for example, with chromium, tin, and stainless steel. However, the oxide layers on many iron-based materials are loose and porous. Without corrosion protection, material degradation continues until the material is completely consumed.

Pitting corrosion

Pitting corrosion is one of the electrochemical types of corrosion. It occurs primarily when passive layers on metal surfaces contain defects. Material degradation is intensified by the influence of chloride or bromide ions. These ions occupy the defects and prevent oxygen from reaching the surface, which would otherwise repair the passive layer. As a result, localized damage initially forms and continues to penetrate deeper into the base metal.

Crevice corrosion

If a metal structure contains narrow crevices, for example at overlapping edges, attached components, or interrupted weld seams, the concentration of surrounding substances inside the crevice differs from that outside. This concentration difference creates a potential difference similar to that between different metals. As a result, electrochemical reactions occur within the crevice.

Additional types of metal corrosion

Depending on material composition, microstructure, mechanical stresses during metal processing or operation, and operating temperature, numerous additional types of corrosion are distinguished. Examples include:

• Intergranular corrosion
• Stress corrosion cracking
• Corrosion fatigue
• Undercutting corrosion
• High-temperature corrosion
• Knife-line corrosion
• Erosion corrosion
• Stray current corrosion

Damage caused by these types of corrosion is primarily prevented through careful material selection and corrosion-resistant design.

Corrosion protection through substances and surface engineering processes

Corrosion inhibitors for protection during processing and transport

Corrosion inhibitors protect metal materials from corrosive attack during processing and transport. These substances are added to process fluids such as metalworking fluids or cleaning agents, or are included in packaging. Corrosion inhibitors work through two main mechanisms. Some protect metal surfaces by covering vulnerable areas of the material. Others react with corrosive media and thereby neutralize their effect.

Surface treatment to protect metal products from corrosion

The most common types of metal corrosion can be suppressed through appropriate coatings. For this purpose, a wide range of processes are used in surface treatment and surface pretreatment.

Examples include:

• Formation of conversion coatings (conversion processes)
• Painting
• Powder coating
• Electroplating
• Galvanizing

These coatings prevent environmental media from reacting with the metal surfaces.

Der Beitrag Types of Metal Corrosion erschien zuerst auf Kluthe Magazine.