Plastics are widely used as packaging materials, insulators, components in various machines and devices, and as coating agents. Unfortunately, their widespread use has led to increasing environmental concerns as they are now frequently found in the environment.  Recycling offers a potential solution—but not all chemical recycling methods are equally environmentally friendly. The following provides an overview of chemical processes used to recover value from plastic waste.

Type and Composition of Plastic Waste

The choice of recycling method depends on the physical characteristics of the material and the degree of contamination or  interaction with other substances. Plastics fall into three main categories: thermoplastics, thermosets, and elastomers. Thermoplastics, such as PVC, polyethylene, and polypropylene, soften when heated and can be reshaped and reused once cooled.

These materials can only be recycled by chemically breaking down the molecular bonds in their polymer chains. This process known as solvolysis. Elastomers, which behave like rubber, also decompose at high temperatures. However, they can still be recycled in shredded form, for example, as filler in bitumen applications.

The degree of mixing significantly affects the recycling process. Homogeneous plastic waste is easiest to recycle. When different types of plastics are mixed, combined with other materials, or contaminated, extensive sorting and separation steps are often necessary—especially in the case of collected packaging waste, composites, and coated components. Surface coatings, commonly used to enhance the performance of plastic parts, often interfere with recycling and must be removed in advance.

Types of Recovery Processes

There are three main categories of recovery for plastics within sustainable chemical practices: mechanical recycling, chemical (feedstock) recycling, and energy recovery.

• Mechanical recycling preserves the base material. The plastic is cleaned and reprocessed—using dry, wet, or solvent-based techniques—so that it can be reused. These methods are primarily physical and mechanical.
• Chemical recycling (also called feedstock recycling) uses chemical reactions to break down plastics into raw materials, which can then be used to make new products.
• Energy recovery is not considered a recycling method in the strict sense of chemistry. In this process, plastic waste is incinerated to generate energy.

Chemical Recycling Methods

The most common chemical recycling methods are liquefaction (oil recovery), solvolysis, gasification, and pyrolysis. These often require pre-treatment steps to remove contaminants, such as separating multi-layer materials (e.g., beverage cartons, coated films) or stripping surface coatings. Eco-friendly paint stripping agents are available for these tasks.

Liquefaction (Oil Recovery)

In this process, plastics are converted into oily substances through thermal or catalytic reactions, which requires well-sorted plastic waste. The reaction typically occurs in stirred tank reactors at temperatures up to 750°F (400°C). As the plastic liquefies, gaseous by-products and wax-like residues are separated from the resulting oil.

After purification and distillation, the recovered oil can be used as diesel fuel or as a chemical feedstock.

Solvolysis

Solvolysis breaks down the polymer chains in plastics using special solvents. The reaction may be aided by elevated temperatures and is primarily used for recycling thermosets. It yields the original building blocks of the plastic, which are then separated from the solvent.

The solvents are usually reused in a closed-loop system. Depending on the input material, valuable raw components can be recovered from the decomposed polymers.

Gasification

Gasification is conducted at temperatures of up to 2,900°F (1,600°C) and pressures up to 2,175 psi (150 bar) with limited oxygen supply. This oxygen does not support combustion but facilitates the reaction between carbon and oxygen. The process produces a synthetic gas (syngas) composed of carbon monoxide and hydrogen. Before further use, impurities must be removed. Syngas serves as a raw material for a wide range of chemical products, including GTL (gas-to-liquid) oil, which is used in surface treatment applications.

Pyrolysis

Pyrolysis involves the thermal decomposition of plastic waste in the absence of oxygen at temperatures between 300–1,300°F (150–700°C). One of the oldest known pyrolysis methods is the production of charcoal in kilns. Modern pyrolysis of plastics yields solid, liquid, and gaseous products, which can be processed into valuable chemical precursors.

Comparing Recycling Methods

Chemical plastic recycling requires a high amount of energy as well as extensive pre- and post-treatment steps involving additional auxiliary substances. For this reason, material recycling—which reuses materials without chemical changes—is given priority. When this is not feasible, energy recovery is often the more sustainable option. Under certain conditions, however, chemical recycling methods can still be advantageous. They allow harmful substances to be removed from the material cycle and can supply the chemical industry with valuable raw materials.

This is especially true when larger quantities of homogeneous plastic waste from one or similarly composed materials are available. Research is actively working to improve plastic recycling methods, gradually making this form of plastic recovery more prominent in the future.

Regulatory Considerations

This is particularly true when large quantities of homogeneous plastic waste are available from a single or similar source. In the United States, recycling operations must comply with EPA regulations under the Resource Conservation and Recovery Act (RCRA), which governs how facilities manage hazardous and non-hazardous solid waste. Ongoing research is actively improving chemical recycling methods, making them an increasingly viable part of future waste management strategies.

Der Beitrag Plastic Recycling in Chemistry 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.

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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).

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What Are Emulsifiers?

Emulsifiers are included in the broader class of surfactants. These are chemical substances with a special molecular structure. Their molecules consist of a water-attracting (hydrophilic) end and an oil-attracting (lipophilic) end. The ratio between these two parts determines whether a surfactant is more soluble in water or in oil. This molecular structure causes the molecules to migrate to interfaces and align toward the phase they favor. An interface can be, for example, the surface of a liquid where it is exposed to the surrounding air.

Interfaces also occur between liquids that do not mix. The heavier liquid collects at the bottom (sedimentation), while the lighter liquid rises to the top (creaming). When surfactants are present in the mixture, they occupy the surface that separates the two phases. If the two phases are mixed by vigorous shaking or stirring, droplets form. The surface of a droplet represents another interface where surfactants accumulate. If this process results in a stable mixture, it is called an emulsion. In such a system, the surfactants function as emulsifiers.

A) Two immiscible liquids, not yet emulsified
B) A (temporary) emulsion of the two liquids
C) The unstable emulsion gradually separates
D) Only the surfactant (outline around the particles) ensures a stable emulsion

Requirements for Emulsifiers in Water-Miscible Metalworking Fluids

Chemical Stability of the Emulsifiers

Water-miscible metalworking fluids are concentrates whose main components are base oils. These oils act as lubricants. To ensure the lubricants disperse in water, the concentrates contain emulsifiers. In addition, the concentrates include various additives that further stabilize the emulsion, protect the materials against corrosion, inhibit microbial growth, and prevent excessive foam formation. Each component must retain its properties during storage and use. Only then can they perform their specific functions in the metalworking fluid. This requires that the components do not form chemical bonds either with one another or with water.

Adapting Emulsifiers to Water Hardness

Water-miscible metalworking fluids are emulsions composed of concentrates and water. For mixing, ordinary tap water is typically used, which always contains a certain amount of dissolved minerals—primarily magnesium salts, calcium salts, and carbonates. The amount of dissolved minerals determines the water hardness, expressed in degrees of German hardness (°dH), which roughly corresponds to grains per gallon (gpg).

If the hardness is below 5 °dH, the emulsions tend to foam excessively. If it exceeds 20 °dH, water-insoluble lime soaps may form and deposit on the surfaces of tools and workpieces. Choosing suitable emulsifiers for metalworking fluids can reduce these issues to some extent. However, it is generally more effective to adjust the water hardness itself—either by diluting the water with deionized water or by increasing the hardness with appropriate salts—to bring it into the optimal range.

Hydrophilic-Lipophilic Balance

The hydrophilic-lipophilic balance (HLB) is a scale used to classify surfactants according to their areas of application. Values range from 0 to 20, where 0 represents a completely oil-soluble, water-repelling substance and 20 represents a completely water-soluble, oil-repelling substance. Between these extremes, surfactants are arranged according to their solubility. The oil-to-water ratio in the emulsion determines the choice of suitable emulsifiers. In most cases, one component predominates (the continuous phase), while the other is dispersed within it in droplet form (the dispersed phase). Water-based metalworking fluids usually contain 5–10% concentrate, making water the continuous phase. For a stable metalworking fluid, emulsifiers are required that are equally or slightly more soluble in water than in oil. Their HLB values typically range between 8 and 18. The optimal emulsifier depends on which lubricants and other additives are included in the formulation of the metalworking fluid.

Influence of Droplet Size

Emulsion stability also depends on the droplet size within the dispersed phase. The smaller the diameter, the more stable the mixture. However, producing very small droplets requires significant effort. On the one hand, a large amount of mechanical energy is needed to continually reduce the droplet size. On the other hand, the total surface area increases, leading to higher consumption of emulsifiers. It should also be considered that an equilibrium forms between emulsifier molecules adsorbed onto the dispersed phase and those dissolved in the continuous phase. Consequently, more emulsifier is required than the droplet surfaces can actually accommodate.

Production of Metalworking Fluid Emulsions

Most metalworking fluids belong to the category of coarse-dispersed macroemulsions with droplet diameters greater than 1 µm (1 micrometer or 0.00004 in). Mixing is often performed with adjustable dosing devices connected to a  freshwater line. The core component of these devices is a Venturi nozzle. The free diameter of this nozzle narrows down to a throat and then widens again. Because the flow velocity of the water is very high at the narrowest point, the pressure drops significantly (according to Bernoulli’s principle). This pressure drop is sufficient to draw in the metalworking concentrate through a hose connected to the throat. As the concentrate is entrained by the flow, an emulsion with the desired droplet size distribution is formed.

Another common method is to add a metered amount of water to a container and then add the required quantity of concentrate. The liquids are first mixed slowly. Adequately small droplets can then be produced with the aid of a stirrer.

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Forming includes those manufacturing processes in which tools apply significant external forces to deliberately change the contours of materials. A prerequisite is the close interaction between material and tools, which enables force transmission while also allowing relative motion. The role of forming lubricants in this process, is to create these conditions. Here you can learn about the variety of forming processes and gain insight into how surface technology contributes to successful forming by providing optimal lubricants.

What Forming Processes Exist?

Classification According to DIN 8582

DIN 8582 is a German industrial standard that classifies forming processes based on the prevailing stress state in the material. While US manufacturers typically follow ASTM or ASME standards for materials and testing, DIN 8582 remains a widely referenced framework for categorizing forming methods internationally.

The effect of external forces depends on the amount of material being moved. Therefore, force is related to the cross-section of the workpiece affected by forming. The result is stress, expressed in psi or N/mm². The direction of the forces determines whether tensile, compressive, bending, or shear stresses occur. According to DIN 8582, the following forming processes are defined:

• Pressure forming (rolling, open-die forging, die forging, indentation, extrusion)
• Tensile-compression forming (drawing, deep drawing, flanging, metal spinning, buckling)
• Tensile forming (stretching, expanding, deepening)
• Bending forming (bending with linear or rotational tool movement)
• Shear forming (sliding, twisting)

Manufacturing also depends on how strong the required forces must be. These values depend on the workpiece temperature and the characteristics of the semi-finished products.

Classification According to Material Temperature

As temperature increases, material strength decreases, reducing the forces required for forming. However, high temperatures influence material’s structure and surface properties (eg., scale formation). Material structure can be restored through heat treatment, while surface treatment technology provides scale-removal methods. Classification by material temperature results in the following categories:

• Cold forming (at ~70 °F (20 °C); high forming forces; limited formability; good dimensional accuracy)
• Warm forming (e.g., steel at 1200–1650 °F (650–900 °C); medium forming forces, formability, and dimensional accuracy)
• Hot forming (e.g., steel at 1830–2280 °F (1000–1250 °C); low forming forces; very good formability; low dimensional accuracy)

Classification According to Semi-Finished Product Properties

Forming forces depend on whether all three spatial dimensions are affected or only the length and width. For sheet metal, thickness is negligible relative to length and width and changes only slightly during forming. Required forces are therefore lower than in forming processes that alter length, width, and thickness. Thus, sheet forming is distinguished from bulk forming.

Forming Processes from the Perspective of Manufacturing

In manufacturing, the finished product is the focus. This leads to naming conventions based on the final product (e.g., tube drawing, wire drawing, profile drawing, extrusion) and names indicating combinations (e.g., cold forming + bulk forming = cold bulk forming). Forming processes are also further specified; for example, stretch drawing is a type of deep drawing using simple tools.

Additional Steps Enable Forming

Manufacturing processes include additional steps such as heat treatment to establish or restore material properties and surface processing to prepare or finish semi-finished products. For example, surfaces must be descaled after hot forming. Surface processing also adjusts surface roughness to create optimal forming conditions. Successful cold bulk forming often requires specific conversion layers created through conversion processes.

Forming Lubricants – More Than Just Auxiliary Agents

Forming lubricants must fulfill numerous tasks:

• reduce friction and wear
• wet surfaces uniformly
• transfer forces
• cool tools and materials
• protect against corrosion
• suppress effects of contaminants

Their properties change with varying temperatures, forming speeds, and pressures. Lubricants must be tailored to each forming method. For example, oil suitable for thread rolling would evaporate at hot-forming temperatures of 1830–2280 °F (1000–1250 °C). A lubricant that performs well in sheet forming will fail under the extremely high pressures of cold bulk forming, such as tube drawing. Surface technology provides specialized lubricants for such conditions, including expander oils for enlarging large-diameter tubes.

As Varied as the Forming Processes, So Numerous are the Lubricants Used

Each forming process has an optimal lubricant, usually based on oil, grease, or solid lubricants. The selection depends primarily on forming temperature, while additives adjust the properties precisely to operating conditions.

Example: Hot and Warm Forming

Hot and warm forming commonly use mixtures of oil and graphite, oil and wax, and sometimes water. Water is an excellent coolant, as it absorbs large amounts of heat when evaporating. Emulsifiers and dispersing agents keep components evenly distributed. Additional additives support surface wetting, corrosion protection, and adhesion.

Example: Cold Bulk Forming

Cold bulk forming begins at ~70 °F (20 °C). Temperature rises significantly during the process, and high forces can cause cold welding between tool and material surfaces. Lubricants must therefore remain stable across wide temperature ranges and prevent direct surface contact. Normal forming oil is insufficient. Surface technology provides solutions such as phosphate layers, which separate tool and material. Reactive oils produce similar results: their additives chemically react with the material, forming a protective layer that prevents cold welding and increases process efficiency.

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