Aluminium is widely used in applications such as beverage cans, flexible packaging, construction, transportation and household goods. Its properties, such as lightness, high thermal and electrical conductivity, good weldability, excellent formability and high recyclability, make this metal highly attractive and environmentally sustainable.

To meet the metallurgical and dimensional requirements of customers, especially regarding flatness, its production demands high-tech equipment and superior quality inputs. In hot rolling, an oil-in-water emulsion is used as a lubricant; in cold rolling, high-purity rolling oil is employed. In both processes, alcohol- and acid-based additives are added, essential for operational stability and the final quality surface of the material.

Rising rejections: When white stains became a production concern

Historically, the rolling of sheets intended for the manufacture of beverage cans had exceptional performance, with very low internal rejection rates. However, a progressive increase in these rejections was observed, accompanied by customer complaints. The problem evolved until it reached approximately 200 tonnes of internal scrap per month, associated with the appearance of a white stain.

To investigate the root cause, a multidisciplinary group was created, composed of process engineers, cold rolling and finishing machine operators, as well as an analyst from the metallographic laboratory (SEM/EDS).

Understanding the white stain: Appearance, spread & impact

The defect manifested as a white stain located on the side of the sheet (Figure 1). In most cases, the width of the stain was approximately 30 mm, which allowed for its natural elimination during trimming. In more critical cases, however, the width could reach values between 150 and 200 mm.

The stain appeared right at the beginning of the trimming process and extended for several meters along the coil, becoming consistently noticeable after the second rolling pass, with greater intensity on the upper face.

The phenomenon occurred in both wide and narrow materials, but was limited to a specific combination of thickness, alloy and temper defined by the process route.

SEM/EDS analyses revealed a transversal surface break in the affected region, suggesting that a residue was compressed during the second rolling pass, altering the hydrodynamic conditions of the rolling. A higher concentration of oxygen and carbon was also observed in the region of the defect, compared to other regions.

To eliminate the defect, it was necessary to scrap parts of the coil, resulting in losses ranging from 50 to 500 kg per coil. The plant has three rolling mills, A, B and C and the problem was identified exclusively in materials processed in rolling mill B.

Figure 1 – The stain on the surface of the sheet

From inspection to insight: How the defect was traced

To help in identifying the root cause, the cause-and-effect diagram (Ishikawa) was used, encompassing machine, method, manpower, environment, measurement and material. Based on this analysis, inspection, cleaning and process adjustment actions were established, aimed at both immediate containment and detailed investigation.

Also read: When stamping goes wrong: Investigating “Broken Surface” defects in aluminium cookers

During the inspections, it was observed that one of the rolling mill oil tanks had an excessive accumulation of a white, gelatinous residue (Figure 2). Samples were collected and analysed, revealing a composition consisting mainly of oxygen and carbon.

Figure 2 – White gelatinous residue

The team collected oil samples from various points in the rolling mill. Initially, they assessed the formation of residues on the surface of the samples. Subsequently, they were analysed by gas chromatography to identify additives, in addition to tests for moisture, acidity, viscosity and turbidity.

Temporary monitoring was established in the laboratory, in which oil samples were applied to aluminium sheets and kept for 24 hours to check for residue formation. After a few days of monitoring, it was found that the oil from rolling mill B left residues in different quantities.

During this period, it was also observed that the type of rolling oil was changed, along with adjustments to the parameters of the distillation unit, which decreased the efficiency of removing certain residues.

Another critical factor was the alteration of the filtration system in rolling mill B, implemented with the aim of increasing productivity, which ended up eliminating the component responsible for retaining chemical contaminants, including esters.

The root cause explained: Ester build-up & rolling impact

The reaction between alcohol and acid produces esters, which are normally removed during oil distillation. However, after oil replacement and improper adjustment of distillation parameters, some of these esters were no longer removed.

The oil filtration system is composed of several elements, but two of them are fundamental:

• One intended for the removal of solids;

• Another is responsible for retaining chemical contaminants, including esters.

With the removal of the chemical component from the filter and the lower distillation efficiency, there was an accumulation of ester in the system.

After the first rolling pass, some of the oil with residue is carried to the coil. Since ester has high viscosity, its presence alters the hydrodynamic regime in the second rolling pass, causing transverse break of the sheet surface and resulting in the white stain.

Corrective actions: Restoring oil quality & filtration efficiency

• Adjustment of the operating parameters of the distillation unit

• Reinstallation of the filtration system component responsible for removing esters from the rolling oil

Also read: Why & how to stop water stains in aluminium coils: A breakthrough solving the problem with a real case

The post Aluminium coil surface defects: Investigating white stain formation & causes appeared first on AL Circle Blog.

Aluminium is a light, malleable metal with excellent heat conduction capacity, characteristics that make it ideal for kitchen utensils, especially for those looking for practicality in daily use. Its high thermal conductivity, low cost, lightness, recyclability, mechanical and corrosion resistance, as well as ease of cleaning and long durability, make it an extremely attractive material for the household utensils sector.

The production of these utensils can occur through different processes, such as stamping or casting. In the specific case of pressure cookers, manufacturing is carried out by deep drawing using a die and punch, a relatively simple process. However, strict control of process variables is essential to guarantee the final quality of the product and its performance in use. Critical factors include: Blank holder pressure, tool clearance, tool alignment, lubricant viscosity, lubricant quantity applied and aluminium alloy.

A manufacturing issue begins to surface

A household utensils manufacturer uses an Al-Mn alloy in the production of pressure cookers, achieving high levels of efficiency, productivity and quality. At a certain point, however, the customer began to report a failure in the upper region of the product shortly after the first stamping stage, characterised as a “Broken Surface”.

We visited the customer to investigate the root cause of the complaint. During the follow-up process, we identified the use of a high-viscosity lubricant with added zinc stearate to increase lubricity. We observed other critical points: Variation in the amount of zinc stearate added by each operator and inconsistency in the amount of lubricant applied to the surface of the aluminium disc. The problem was more common in batches with thicknesses at the upper limit of the specification. Furthermore, it was found that the annealing was performed using two different routes, one using an inert atmosphere and the other not.

Examining the “Broken Surface” defect in detail

The surface defect known as “Broken Surface” had been requiring frequent operational interventions on the pressure cooker production line. The defect appeared in the upper region of the pan, right after the first forming stage, approximately 170 mm from the bottom, in random positions relative to the circumference.

SEM/EDS analysis revealed the presence of cracks on the aluminium surface, with varying depths. However, optical microscopy evaluation did not identify internal discontinuities, such as inclusions, mechanical damage or incrustations that could be related to the origin of the defect. Although the company manufactures various household utensils, the problem was observed exclusively in the pressure cooker line.

The defect presented three levels of criticality:

A – Very surface

B – Moderate

C – Severe

To reduce the impact on production, the client established the following approval criteria:

A – Approved

B – Approved with restrictions

C – Rejected

Figure 1: The lines represented the defects on pressure cooker

Testing the variables: A doe-driven investigation

To identify the root cause of the problem, a multidisciplinary group was formed, composed of representatives from the aluminium supplier and the client. From the supplier’s side, process engineers from the cold rolling and the finishing line participated, as well as a Black Belt engineer. From the client’s side, the team included process, quality and production engineers.

Based on the Six Sigma methodology, the development and execution of a Design of Experiments (DOE) was defined, a tool that allows for the systematic evaluation of the effects of the variables involved and their interactions.

The DOE was developed with 2 levels and 3 factors, totalling 8 tests.

The higher viscosity lubricant corresponds to the product currently used, already additivities with a standard amount of zinc stearate. The lower viscosity lubricant, in turn, is a commercially available alternative for this application.

The variable “thickness” was adopted as a reference to evaluate the tool clearance output (low thickness indicating greater tool clearance output; high thickness indicating less tool clearance output). It is important to highlight that no adjustments were made to the tool set during the tests.

After the experimental steps were completed, the pans were evaluated by the group members according to the previously established criteria.

Key findings from the stamping trials

To achieve criterion A, the combination of thinner thickness and lower viscosity lubricant showed the best product performance.

After the study was completed, the tool set was removed from the press to make the necessary adjustments, and under these new conditions, the process resumed its standards of excellence.

No correlation was observed with the annealing furnace atmosphere.

Conclusion

When a high-viscosity lubricant is used with low tool clearance, a flow restriction occurs between the metal and the tooling. During stamping, this condition increases the pressure on the aluminium surface, increasing the likelihood of defects.

Also read: Aluminium in women’s accessories: Sustainability, comfort and innovation

The post When stamping goes wrong: Investigating “Broken Surface” defects in aluminium cookers appeared first on AL Circle Blog.

Aluminium has established itself as one of the most promising materials for the development of women’s accessories. Previously restricted to construction and packaging, aluminium has emerged as an attractive choice for earrings, necklaces, bracelets and chokers. Its combination of lightness, strength, versatile aesthetics, and strong sustainable appeal sets it apart from traditional metals like brass and copper. Furthermore, its hypoallergenic properties and excellent formability expand design possibilities, meeting the comfort, safety and style demands of modern consumers.

Technical characteristics of aluminium

• Lightweight: Due to its low density, aluminium ensures that accessories such as large earrings, bulky bracelets, and structured necklaces remain comfortable even during prolonged wear.
• Malleability: Enables complex designs without compromising structural integrity.
• Corrosion resistance: A naturally formed oxide layer protects the surface, enhancing durability.
• Recyclability: Aluminium can be recycled endlessly without loss of quality, requiring minimal energy input.

Environmental benefits and sustainability

• Lower environmental impact: Recycling aluminium consumes up to 95% less energy compared to primary extraction.
• Circular economy contribution: Reuse reduces solid waste and preserves natural resources.
• Reduced carbon footprint: Its lightness minimises transportation costs and emissions.

Comfort and practicality

• Effortless daily wear: Lightweight accessories prevent discomfort, particularly in earrings and chokers.
• Hypoallergenic properties: Aluminium is less likely to trigger allergic reactions, making it suitable for sensitive skin.
• Low maintenance: Resistance to oxidation helps accessories retain their shine with minimal care.

Innovation in design and production

The adoption of aluminium in women’s accessories marks a creative departure from conventional materials. Innovation is evident in several areas:

• Advanced manufacturing: Techniques such as laser cutting, 3D printing, and anodising enable complex geometries, unique textures and personalised finishes.
• Design: Aluminium’s malleability supports generative design, resulting in collections with organic, dynamic forms.
• Mass customisation: Ease of handling allows brands to deliver exclusivity at scale, catering to individual identity.
• Collaborative development: Partnerships among designers, engineers, artists, and material scientists foster collections that merge fashion, technology and sustainability.

Aesthetics and versatility

• Diverse Finishes: Anodising, polishing, and painting provide a broad palette of colours and textures.
• Creative Freedom: Designers can experiment with geometric, organic, or minimalist styles.
• Material Integration: Pairing aluminium with leather, fabric, or gemstones expands aesthetic possibilities.

Conclusion

Aluminium is establishing itself as a strategic material in the new generation of women’s accessories, combining innovation, sustainability and comfort. Beyond meeting the aesthetic demands of the market, it contributes to more responsible practices in fashion. With advancements in production technologies and the creativity of designers, aluminium is becoming a key player in contemporary, intelligent and environmentally conscious collections.

Featured image source: Armadillo Jewellery

The post Aluminium in women’s accessories: Sustainability, comfort and innovation appeared first on AL Circle Blog.

Aluminium foil is extensively used in the packaging industry due to the outstanding properties of the metal. Its primary role is to serve as a barrier against oxygen, light, moisture and microorganisms, thereby protecting food and pharmaceuticals from degradation.

The explosion of thin aluminium foil coils is associated with the entrapment of gas or water vapour, which occurs due to a rise in the metal’s temperature. This temperature increase is triggered by an exothermic reaction between the aluminium surface and water.

Exploring the root cause

The topic discussed here is rare but extremely important due to its relation to security. It is essential to highlight that this phenomenon occurs exclusively in thin aluminium foil coils, specifically those with widths greater than 450 mm and a particular temper.

Foil thickness plays a significant role: in intermediate and thick foils, there is sufficient space between the wraps to allow trapped gases or water vapour to escape. However, in thin foils, the minimal spacing between wraps restricts this release, increasing the risk of accumulation. Temper is another key factor influencing the oxidation process.

The mechanism

When a thin aluminium foil coil remains submerged in water for an extended period, water infiltrates between the wraps, triggering a corrosion process. This reaction is exothermic, producing heat and releasing hydrogen gas. The chemical interaction between aluminium and water results in the formation of hydrated aluminium oxide and hydrogen.

2Al+3H₂O = Al₂O₃ (H₂O) + 3H₂

When the coil temperature exceeds 100°C, water vapour begins to form. It is estimated that the vapour pressure inside the coil can reach up to 7 bar. The internal pressure responsible for the coil’s rupture (explosion) is linked to the entrapment of hydrogen and/or water vapour.

The explosion process typically starts with the gradual heating of a wet coil. As the temperature rises, water vapour begins to escape from the sides of the coil. Just moments before the explosion, the release of vapour becomes more intense, accompanied by a distinctive sound similar to boiling water on a hot surface.

The explosion emits a dry noise (bang), throws aluminium foil a distance away and can even deform the coil’s spool. The event is marked by a single loud bang, without any burning or visible light emission (flash). Typically, the explosion propagates from the centre of the coil outward. An explosion caused by hydrogen oxidation can generally be ruled out if there is no presence of a spark or flame.

Also read: From Turkey to China: Which companies are leading global aluminium foil production?

Coils with widths greater than 450 mm are more prone to this phenomenon due to the difficulty in releasing gases generated during the process. Additionally, the flatness of the material contributes to gas retention. A flatter foil increases the likelihood of gas being trapped within the coil.

Aluminium foil coils must not be exposed to environments with excessive moisture, such as flooded areas. If a coil becomes submerged, it is recommended to isolate the material in a dry, well-ventilated area for at least 48 hours.

When insulating coils, priority should be given to the thinnest and widest ones, as these present the greatest risk. Wet coils stored in wooden packaging should also be isolated, since the force of an explosion can break the packaging.

Recommendations

It is essential to maintain a safe distance from coils that emit noise or release water vapour, as these are signs of a possible explosion. If a rise in coil temperature is observed, actively cool the coil using a fan and isolate the surrounding area for a minimum of 48 hours. Whenever feasible, cut the coils to eliminate the possibility of trapping pressurised gases.

Also read: Why & how to stop water stains in aluminium coils: A breakthrough solving the problem with a real case

The post Explosion of thin-thickness foil aluminium coil when submerged in water appeared first on AL Circle Blog.

Aluminium is a highly reactive metal that oxidises readily. Because of its strong affinity for oxygen, it quickly forms a thin, adherent and impermeable layer of aluminium oxide (Al₂O₃), which serves as a protective barrier against corrosion. However, when this layer is broken, corrosion can begin either in a localised area or on the entire surface.

One of the most common forms of aluminium corrosion is crevice corrosion. This occurs when water becomes trapped in tight spaces, such as between overlapping aluminium surfaces or between aluminium and another material, creating an environment conducive to corrosion. As a result, aluminium coils are particularly vulnerable to crevice corrosion, commonly referred to as “water stain”, when exposed to conditions that allow water ingress or condensation of water vapour. This can happen during transportation or even while in storage.

Image used for representational purpose

Water stains affecting aluminium coils

Although “water stain” is a common term in the aluminium industry, it actually refers to crevice corrosion. This phenomenon occurs when water becomes trapped between the layers of the coil, triggering oxidation. The chemical reaction involves aluminium interacting with water to form hydrated oxide and hydrogen gas:

A few years ago, in São Paulo state of Brazil, we experienced a severe drought, with very little rainfall and extremely high temperatures. During this period, we noticed a significant increase in internal rejections of aluminium coils due to water stains, which led us to initiate a study to identify the root cause of the issue.

2Al+3H₂O ->  Al₂O₃ (H₂O) + 3H₂

To investigate the problem, we created a task force including process engineering and operations teams from both hot and cold rolling areas. There were differing opinions, with some suggesting that the issue might originate from the hot rolling process, which uses an emulsion as a coolant. This emulsion, a mixture of water and oil, was suspected of possibly being transferred to the coil surface at the exit of the rolling mill, contributing to the staining.

Exploring the root cause

The initial investigation was carried out at the laboratory. Aluminium sheets were heated to temperatures above 300°C and upon removal from the oven, an emulsion was applied to some of the sheets, which were then overlapped. Once the sheets cooled to room temperature, we observed only oil stains since water evaporates at 100°C. This finding allowed us to narrow the focus of our study to the cold rolling process.

To structure the investigation, we employed two analytical tools: the “Is/Is Not” matrix and the Ishikawa (fishbone) diagram.

The “Is/Is Not” matrix helped determine whether the issue affected all coils or only some of them. The product line is divided into two segments, A and B. Based on rejection data analysis, we found that the problem was concentrated in segment B. As a result, segment A was excluded from the scope of the study.

Next, we used the Ishikawa diagram to generate hypotheses and outline a detailed action plan.

Recognising the Stain Patterns

• The defect was observed on one or both edges of the sheet, but was not observed in the central area.
• The stain was not observed along the entire length of the coil, but only on part of it.
• The stain was typically located about 200 mm from the edge, differing from rain-induced stains, which usually begin at the edge.
• The stain exhibited a distinct pattern: Some were isolated away from the edge, while others showed a “trail” leading toward the side, likely influenced by the hot band profile.

Image used for representational purpose

Exploring other approaches

Although several actions had already been taken, they did not yield the expected results. This led us to pursue a different approach: exploring existing literature for deeper insights.

It is well established that water staining can occur when coils are stored near doors and become wet during heavy rainfall or due to leaks in the warehouse roof. It can also happen during transportation by dry cargo, especially when using damaged tarpaulins or poorly maintained trucks.

Given the severity of the drought, we were compelled to think outside the box and consider alternative causes. In our literature review, we found not only the commonly known sources of water staining but also an important additional factor: The formation of a dew point as a potential cause.

Armed with this information, we set out to understand the underlying mechanism that could be occurring during coil storage.

Role of dew point in aluminium coil corrosion

Air contains water in the form of vapour, creating an invisible mixture. Relative humidity represents the ratio between the actual amount of water vapour in the air and the maximum amount the air can hold at a given temperature. As air temperature increases, its capacity to hold water vapour also rises.

The dew point is the temperature at which water vapour begins to condense into liquid. It is determined by both the ambient temperature and the relative humidity. Using these two parameters, the dew point can be calculated.

With this understanding, we began investigating the coil storage area. We identified three types of cooling methods in use: Natural cooling, Forced cooling with a fan and Forced cooling using external air

Next, we conducted field measurements using a pyrometer and a thermo-hygrometer to record coil surface temperature, ambient temperature and relative humidity.

When natural or fan-assisted cooling is applied, the coil temperature tends to follow the ambient temperature. However, with external air cooling, coils can reach significantly lower temperatures. Depending on the relative humidity, this may lead to condensation of water vapour.

For instance, if the ambient temperature is 29°C and the relative humidity is 75%, the dew point is 24°C. Any coil with a temperature below this threshold will cause water vapour to condense on its surface.

During our measurements, we observed that coils cooled with external air reached temperatures as low as 20°C. Another critical factor is the storage of hot coils adjacent to cold ones, which can also promote condensation.

In one case, we found two coils stored side by side, one at 24°C and the other at 220°C. Upon inspecting the cooler coil, we discovered water trapped between its wraps.

Conclusions

• No water staining was observed on the coils of segment A, because they are laminated at temperatures ranging from 30°C to 40°C.
• The internal rejection rates increased due to a reduction in spacing between stored coils.
• Once the root cause was identified, the recommended corrective action was to cool segment B coils either by cooling naturally or by using fans.
• This measure led to a dramatic reduction in rejection rates, never before reached.

Another real story: Odisha’s first 200 KLD ZLD plant: how Aditya Aluminium is redefining water conservation

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