Category Archives: Aluminium

Aluminium is a silvery-white lightweight material that makes up for more than 8% of the earth’s core mass. It is the 13th element of the periodic table. and is the third common element on earth other than silicon and oxygen. Aluminum is available in the form of aluminium sulphates. Aluminium is used in enormous applications ranging from small cans to aircraft parts. It is the most unique material on earth.The Properties of Aluminium play an important role in its transformation to one of the most significant and versatile materials on earth. The properties of aluminium are acquired from its ability to form aluminium alloys on combining with chemical elements.

Aluminium, architectural finishes

Powder coating process – An amazing paint alternative

September 2, 2020 Vinod Gopinath 2 Comments

The powder coating process is a method of spraying electrostatically charged dry powder over the material surface. The powder coating process is also known as the electrostatic spray deposition process. The dry powder constitutes a combination of finely ground pigments and resins. Powder coating was introduced in the late 1980 s and is being extensively used in the industrial, commercial, and household applications. This process provides a smooth, durable, decorative, and a corrosion-resistant coating.

Difference between Powder coating process and Polyester Powder coating

A lot of confusion is prevailing between the terms, “Powder Coating” and “Polyester powder” coating. Powder coating is the method of application of electrostatically charged dry powder to the material to be coated. Powder coating can be applied on any surface. However, the powder coating ingredients differs with material types and the environment where it is used. The most popular powder coating types are Epoxy Powder Coating, Polyester Powder Coating, and Hybrid Powder Coatings.

Polyester powder coatings preferred in applications are classified into TGIC Polyester coating and Urethane polyester coating. For aluminium extrusions, TGIC Polyester coating is preferred due to there low temperature curing properties.

Also read : Aluminium Anodising Process -A remarkable Finish Coating

Powder coating process

Powder coating process is broadly classified into three important stages.

Surface preparation
Powder coating process
Curing process

Surface Preparation

The durability and serviceability of a coating depend on the quality of surface preparation. Surface preparation is essential to remove the dirt, grease, and other impurities from the material surface. The cleaning process includes various stages of cleaning, rinsing, etching, blasting, and drying, etc. The surface preparation stages are as follows.

Chemical cleaning
Conversion coating

Chemical cleaning

The chemical cleaning process uses mild alkalies(caustic soda), acids, and detergents for cleaning. The cleaning process is followed by rinsing with hot water, steam, detergent, etc. However, the type of acid/alkali cleaners depends on the material type to be coated. For example, aluminium is sensitive to acid attacks and requires mild alkaline cleaners. Rinsing with nitric acid done on anodised surfaces.
On completion of the cleaning process, the surface feels smooth and free from grease, oil, impurities, etc

b) Conversion coating

A conversion coating is applied on the surface to enable strong adhesion with powder coating. The chemical solutions for conversion coating are selected based on the type of material to be coated. For aluminium surfaces, the conversion coating is applied for a surface with strong adhesive nature and to arrest the progress of oxidation before powder coating.

For aluminium surfaces, conversion coating uses chromatic or phosphate solutions. In mild steel Zinc phosphate/ iron phosphate solutions are used. After completing the conversion coating, the coated material is cleaned in rinsing tanks. The final rinse is done using simonized water. The rinsing process removes chemical salts and other residues from the surface of the material that can trigger corrosion and can affect the coating adhesion properties.

On completion of the conversion coating, the material is dried in a drying oven to remove any possible moisture before application of the coating.

Powder coating process-Types

Once the drying process is over, the clean and dry material from the drying oven is shifted to a powder coating booth for powder coating. The powder coating application is commonly done in two methods based on the type of material and environment where it is used.

Electrostatic deposition
Fludized bed powder coating

Electrostatic deposition

In Electrostatic spray deposition or ESD method of powder coating, the finely ground powder is sprayed by a gun to the material. The entire system constitutes a spray booth, a powder feeder, an electrostatic spray gun, and a power unit.
For the ESD process of powder coating, a finely ground resin and pigment powder are charged inside a gun. The material to be coated is grounded/earthed to provide an opposite charge. The electrically charged particles from the gun are sprayed on to the earthed material. The powder on leaving the gun gets attracted to the earthed parts due to electrostatic attraction. In this process, areas that are not even in line with the gun also get attracted to the material to be coated. The powder will continue to stick on the surface as long as it is grounded/earthed. The thickness of the coatings depends on the type of environment the part will be used in. Any powder left after the coating is reclaimed and reused.

Powder coated materials — **POWDER COATED MATERIALS**

Fluidized bed powder coating process

In the Electrostatic deposition process, the powder coating material is electrostatically sprayed and adhered to the surface. But in the case of fluidized bed powder coating, preheated parts are dipped to the powder material within a fluidized bed. There is also an alternative option called electrostatic fluidized bed powder coating, which generates a cloud of electrically charged powder particles above the fluidized bed through which the part to be coated is passed.

Curing of coated materials

The coated materials are co to an oven, where the painting process gets completed by ‘curing’ the particles.
The oven heats the metal to about 200°C. The high temperature first fuses and melts the powder particles, allowing them to flow together to form a film and then cures the resin system in the film to form a smooth surface.
Other additives within the powder formulation make them anchored to the conversion coating, developing a cohesive structure.
After the curing oven, sections are transported to a cooling station, inspected, packed, and dispatched.

Advantages of powder coatings process over liquid coatings

The wet painting system was the most common and traditional coating method. In this method, water-based or solvent-based paint is sprayed or painted to the material surface. Many concerns or issues associated with liquid paints are eliminated or minimised with the powder coating process. The advantages of powder coating over wet paint are listed below.

Resistance to corrosion and chemicals

Powder coatings are more durable and more resistant to corrosion, chemicals, weather, etc than liquid coatings. Powder coating provides wear, scratch-free, and abrasion-resistant coatings in comparison with liquid paints. The application process of powder coating is thermal bonding which provides a uniform, smooth, and even coating. The colours always look fresh and bright and give a refreshing look than liquid paints.

Color choice

Powder coatings offer an unlimited range of colours, finishes, textures, which is not achievable through any type of conventional liquid coating method. Powder coating can match the colour scheme of any object/structure. The enormous choice of colours and textures ranging from matt, glossy, and textured to metallic finishes makes powder coating one of the most preferred coating choices. Powder coating can be used as a protective coating as well as decorative applications.

Durability of powder coating

Powder coatings are long-lasting and durable than any other liquid coatings. Powder coatings offer high resistance to impact, moisture, chemicals, wear, and abrasion compared to any other liquid coatings. They can also protect the materials against possible scratches occurring during the fabrication and fixing of the material and can be used in high traffic areas.

Environmental friendly

The liquid coatings emit VOC s (volatile organic compounds) due to the presence of solvents and cause serious environmental issues. Powder coating is free of any solvents and does not emit any VOCs and is thereby considered a green product. Moreover, the powder coating process does not create any hazardous waste that needs disposal. Any waste powder left after the coating is reclaimed and used. Powder coating is considered an environmentally friendly alternative to liquid coatings and thereby extensively used for green building-related projects.

Operational cost of powder coating

Powder coating is an economic option when compared with other organic finishes/ liquid painting methods. The powder coating application can be done with minimal training and supervision and thereby can reduce costs related to labour and operations. Powders left after the coating is recycled and reused. Fewer energy costs, reduced disposal costs, and low reject costs makes powder coating an economical option. Powder coating also has a longer life span when compared to other coatings and this can be another value addition in terms of money.

Safety

Liquid paints are flammable, carcinogenic, and full of volatile organic compounds and are harmful to the environment as well as the workers involved in the process, if not handled properly. Powder coating consists of solids and no solvents and hence is not harmful to persons handling it. Moreover, powder coatings possess good fire rating qualities in comparison with other liquid coatings.

Disadvantages of powder coating process

Thin coatings are difficult to produce

Powder coatings are 100% solid and because of this, even with a minimum amount of application, the initial thickness is formed. Moreover, it does not contain any volatile organic compounds. This makes it impossible to have thicknesses of less than 25 microns. Whereas in liquid paint, we have paint thinner and it is possible to have a lower percentage of solids, the film thickness can even be limited to 10 microns.

Failure of coating on exposed to atmosphere

On exposure to extreme atmospheric conditions like sunlight, heat, humidity, etc powder coating tends to fail, crack, and peel off. Hence not preferred for external applications involving exposure to extreme atmospheric conditions.

Color change after application

The production process and blending of powder coatings are carried out in a molten form. Hence it is not possible to change the color after production. Whereas in liquid paint we can change the color in all the stages, even when applying the paint, by adding stainers and pigments.

Size of coating material

The spray equipment and method of application of powder coatings confine the coating application to spray chambers only. Substrates must be charged and on completion of the coating. The materials have to be transferred to an oven where the curing process involving a temperature up to 200 degrees is done. Considering these conditions, it is not possible to coat and cure large substrates.

Oven curing

Powder coatings only dry and cure in temperatures above 180 degrees. Whereas liquid paints are varied and could dry up even in room temperature.

Control of material quantity and smoothness

Powder coating offers less control over the speed and amount of powder coating applied. The smoothness of the coating cannot be controlled as it is happening inside the oven.

Start up costs

The start up costs are high for powder coatings. Requires skilled workers for coating and operation of the plant.

After considering the limitations and advantages of powder coatings, and the selected product to be coated, you can evaluate whether coating metals with liquid paint or powder is more suitable.

Uses of powder coating process

Powder coating process is being used for a wide range of applications ranging from household , commercial, industrial ,automobile sectors.

Appliances

Powder coating is used for appliances like stoves, refrigerators, washers, dryers, dishwashers, air conditioners, water heaters, microwave ovens, and many other areas.

Automotive

Powder coating is used often in the automotive industry for engine parts and componets. It is also used by major auto brands as a clear top coat for increasing protection

Commercial Buildings and Offices

Powder coating is used for doors, windows, partions, roofing, cladding etc for residential buildings, commercial buiding etc.

Everywhere you look there are various building and highway projects which use powder coating as well – guardrails, light poles, fencing, posts, and signs are a few examples.

Normal Daily Products

Many daily products are being powder coated to increase the quality of finishes. These products include antennas, lighting fixtures, and electrical elements. Farm equipment and tractors use powder coating. Fitness industries use powder coating on golf cards, golf clubs, ski poles, bicycles, snowmobiles, and other different types of exercise equipment.

Powder coating is also used for supermarkets, stores, malls etc . Every where around us we can see a material using powder coating.

Video : Difference between Anodising and Powder coating

DIFFERENCE BETWEEN ALUMINIUM ANODISING AND POWDER COATING

Aluminium

Aluminium Anodising – A remarkable finish coating

August 27, 2020 Vinod Gopinath 3 Comments

Aluminium Anodising is an electrochemical process done on aluminium to increase the thickness of thin natural oxide coating and thereby enhance its corrosion properties. In our previous article Properties of Aluminium, the reasons behind applying a coating are described in detail. The anodic layer is non-conductive and acts as an insulation against electricity, sound, and heat. Aluminium anodising can increase the aesthetic look, absorb wear and tear and provide requisite durability against possible scratches occurred during handling, fabrication, and erection.

What is Aluminium Anodising ?

Anodising is an electrochemical process that transforms the metal surface into a decorative, durable, and anti corrosive anodic oxide finish. The Anodising process is conducted by passing an electric current through an electrolyte with aluminium to be coated as an anode. The oxygen ions released from the electrolyte get deposited on the surface of the object/anode. Oxygen reacts with aluminium to produce aluminium oxide. The thickness of Anodising ranges from 4 microns to 30 microns or some times more.

Aluminium Anodising Process

The process of anodising is divided into stages depending upon t

Pre-treatment

The products to be anodised are cleaned in acid or alkali solutions to remove the dirt, grease, and other impurities from the surface. The pre-treatment method depends on the types of finish to be applied. The material is de-oxidised in an acidic solution to remove the natural oxide film.

Etching

Etching involves the removal of some parts of aluminium from the surface. This can be done using alkali or acid according to the finish coat type and texture.
For satin finishes and precision parts light etching is done using alkali where minimum etching is done just enough to remove the natural oxide film. The alkaline solution used for light etching is Sodium Hydroxide.
For non-precision parts and architectural extrusions, minor scratches and dye markings will be visible. Hence etching is done by treating in a concentrated mixture of phosphoric and nitric acids.

Brightening

Brightening is a micro level treatment done on the aluminium surface by chemical or eletrochemical means. This is done to level up the undulations. This provides a high lustre on the surface for receiving the coatings

Aluminium Anodising

The aluminium part to be anodised is submerged in an electrolyte solution. The electrolyte used in this process is sulphuric acid.
The positive charge is applied to the submerged aluminium which acts as an anode and negative charge is applied to the plates suspended in the electrolyte. High voltage direct current is passed through the electrolyte constituting positive and negative ions. The electric current in the circuit causes positive ions to get attracted to the negative plates, and negative ions to flock to the positive aluminium anode.

**Anodising aluminium in an electrolyte**

Formation of barrier layer

The aluminium combines with the negatively charged oxygen ions to create aluminium oxide. This process develops a metal oxide film on the surface of aluminium that is treated. The layer quality can be adjusted with the concentration of solution and temperature.This is called a barrier layer, a defence against further chemical reactions at those spots.

As current continues to be applied, the relatively weak and reactive areas of the pores will continue to penetrate deeper into the substrate, forming a series of column-like hollow structures. At this point the surface is porous and attracts dirt and other substances. Colour can be added at this stage.

**SEQUENCE OF PORES FORMATION DURING ANODISING**

For typical non-hard coatings, the depth can be up to 10 microns. Once this level is reached, and if no colour is needed, the process is stopped.

Sealing process

The final stage is sealing of pores and the process involves in dipping in a de-ionised water rinsing.

The coating can withstand chemical attack, scratch resistant and have a hardness index of 9 out of 10 in Mohs Hardness scale , means second only to diamond.

Application of colour

As mentioned above the barrier layer is porous like what is shown in the figure. At this stage we can go application of colour. The pigments fills the porous.

The pigment fills all the empty pores up to the surface, where it’s then permanently sealed off. That’s why anodised colours are so durable – they can’t be scratched off from the surface because in fact the colours are deep down and can only be removed by grinding away the substrate.

COLOUR/PIGMENT FILLING IN PORES — **COLOUR/PIGMENT FILLING IN THE PORES**

After colouring, anodised aluminium has a characteristic “metallic” look. This is caused because of the roughness left after a uniform electro-chemical etching. The deeper the pores, the rougher the surface will be but the colours will also be that much more durable.

Technique of colour anodising

There are several techniques for colour anodising aluminium. One technique is electrolytic colouring, which involves immersing the anodised aluminium in an inorganic metal salt bath. An electric current is applied to this bath as the metal salts oxidise in the aluminium’s pores. Depending on the chemical conditions of the bath and the length of time immersed, the aluminium colour will vary. Popular anodised colour finishes include gold, black, stainless, clear, brown, bronze, and nickel.

Advantages of aluminium anodising

Anodised aluminium possesses a lot of advantages over any other type of coatings. What is unique, is that no additional layer is applied to the aluminium during anodising. Anodising creates a layer that is built up from the existing aluminium. The oxide layer is fully integrated into the material.

a) Appearance of aluminium anodising

Anodising protects the natural feel and appearance of aluminium with its aesthetically pleasing looks. Anodised look feels better than a painted artificial look.

b) Resistance to corrosion & wear

Anodising increases corrosion resistance and the material retains its appearance for a longer period. Anodising creates a hard, wear-resistant layer which protects the underlying aluminium. Anodised aluminium is used in high traffic areas subjected to excessive wear and abrasion. It can also be used in areas exposed to sunlight, humidity, heat, etc without any effect on the coating.

c) Increase life span of aluminium anodising

Anodising is a very old and proven process. Anodised materials have a greater life span when compared with any other coating material.

d) Adhesion

Unlike paints and powder coatings, anodising is not a coating. Hence it may not fade or peel off when exposed to atmospheric conditions like sunlight, heat, moisture, etc.

e) Abrasion resistant

The aluminium oxide layer is one of the hardest material next to diamond. The anodic layer is capable of withstanding wear and abrasion in transportation, handling, and fabrication. Powder coatings are not as harder as anodised aluminium.

f) Environmental Friendly and VOC s

The process of anodising aluminium is an environmentally friendly metal coating technique. It does not emit any volatile organic compounds. (VOC s). The waste of aluminium anodising constitutes aluminium sulphate and aluminium hydroxide which are recycled and used in water treatment systems and cosmetics. Anodised aluminium can be used in green buildings.

**Anodised Aluminium used for Green Building**

g) Surface finish

Anodising creates a uniform and regular finish. The problem of orange peeling and high coating thickness may not occur in anodising. Anodising can be applied to modified materials also.

h) 100% Recyclable

Anodised Aluminium can be recycled and reused to any extend. The recycled product possesses the same quality as the virgin product. Coating removal is not necessary before recycling like other coating products.

i) Filiform corrosion

The diminishing of the internal layer between the aluminium surface and the coating doesn’t happen in anodising like other coatings.

J) Chalking

Chalking is the formation of fine powder on the surfaces of paint films due to weathering, whereas in aluminium no chalking will be formed. The colour , gloss, texture etc shall be retained in all atmospheric conditions.

Aluminium anodising – Applications

Anodised aluminium is used in a lot of applications.

a) Building and construction sector in the form or extrusions which are fabricated and erected for sky light,facades, green building, handrails,doors and windows etc.

b) Used for automobile, boat and aircraft parts

c) Food processing industry

d) Decorative works

e) Marine – Yacht masts, pontoons and decks etc

Demerits of Anodised aluminium

Aluminium anodising got limited colour selection because of the chemicals used in the anodising process. The available colours may not match with the colour scheme of structures.

Touch-up, repair and re coating of anodised product is not possible.

Anodising is vulnerable to lime and cement, Industrial acid, alkali pollutants etc. Anodised aluminium has to be protected while using in under construction buildings.

Anodising is costly than the other polyester coatings.

Anodising does not cover the welded joints.

Shade variation between batches usually happens in anodising.

Aluminium

Properties of Aluminium – The Most Unique Metal.

August 25, 2020 Vinod Gopinath 6 Comments

The Properties of Aluminium play an important role in its transformation to one of the most significant and versatile materials on earth. The properties of aluminium are acquired from its ability to form aluminium alloys on combining with chemical elements. These aluminium alloys got unique properties that can be customised for various applications. Aluminium sections are available in various forms that include aluminium square bars, aluminium plates, aluminium extrusions etc.

What is aluminium?

Aluminium Processed In Smelter — ALUMINIUM PROCESSED IN SMELTERS

Manufacturing process of aluminium

The primary raw material used for producing aluminium is Bauxite. Extracting a tonne of aluminium requires 5-6 tonnes of bauxite. Aluminum is manufactured in two phases: the Bayer process of refining the bauxite ore to produce aluminium oxide. Aluminium oxide is processed in smelters to produce aluminium. The process of extraction of aluminium from bauxite is known as electrolysis or electrolytic reduction.

Properties of aluminium.

Aluminum is one of the most commonly used building material. Aluminum is the preferred choice for a lot of applications because of its unique and valuable properties.

a) Light weight properties of aluminium

Aluminium is lightweight and is 1/3rd the weight of steel and is one of the lightest materials in the world. Even though aluminium is lightweight it is very strong and corrosion-resistant. Because of its lightweight properties, aluminium can reduce the dead loads on a structure and optimise the design. This optimisation can reduce costs in a lot of applications.

b) Corrosion Resistant properties of aluminium

Aluminum is corrosion-resistant, due to the formation of a thin oxide film on its surface. This film acts as a barrier and prevents corrosion.

c) Non magnetic properties of aluminium

Aluminum is non-magnetic and a very good conductor of heat and electricity. Because of these properties aluminium is used for power transmission cables, computer components, LED lights, etc

d) Flexibility in moulding and fabricating

Aluminum is processed in both cold and hot conditions. It can be easily pulled, moulded, rolled, and extruded very easily. Similarly, aluminium can be formed into thin sheets of even 4-micron thickness.
They can be welded and fabricated to any shape. Aluminum is used for making sophisticated aircraft parts to foils for wrapping. Considering the flexibility of fabrication into any shape aluminium forms an integral part of the construction sector for facades, skylights, green building structures, doors, and windows, etc

Aluminium Glass House — ALUMINIUM GLASS HOUSE

e) Aluminium alloys

Aluminum forms a huge variety of alloys in combination with a lot of chemical elements. Even the smallest change in the percentage of ingredients can change the metal properties. This gives the much-needed flexibility for usage in various conditions. Aluminum zinc alloy is used for making computer and mobile components, similarly aluminium with silicon is used for manufacturing alloy wheels and automobile components. A small percentage of elements can vary the properties to any extend.

f) No toxic and odourless

Aluminum is non-toxic and orders less. Hence it is used extensively in the food processing and beverage industries.

g) Strength at low temperatures

Aluminum can retain its strength even at very low temperatures wherein steel tends to get brittle in low temperatures.

h) Coating/painting

Aluminium can be coated/finished using any colour in line with the objects colour scheme.

i) Recyclable

Aluminum is a hundred percent recyclable. The recycled product has all the qualities of a virgin product.

j) Reflective properties of aluminium

Aluminum posses very good reflectivity. Hence it is used for roofing sheets and Light shades. Aluminum roofing can reflect heat and cools the ambient temperature.

Applications of aluminium in construction sector

Aluminum can be welded, fabricated, painted, and moulded into any shape and forms. They are lightweight and can be lifted and erected very easily. Because of these unique qualities, aluminium is one of the most versatile, significant, and cost-effective materials used in the construction sector. The most important use of aluminium is in the form of extrusions. Aluminium is also available in form of aluminium square bars, aluminium plates etc. Extrusions are fabricated/jointed to form doors, windows, and partitions, frames of facades, skylight structures, green buildings, aluminium structures, etc. Aluminum extrusions are coated/painted to match the colour scheme of the building/structure. Because of these qualities, aluminium is the most popular material used extensively in the construction sector.

Aluminium Extrusions For Various Uses — ALUMINIUM EXTRUSIONS FOR VARIOUS USES

Aluminium coatings

Aluminum itself is non-corrosive due to the formation of thin oxide films on the surface for protection from corrosion. Then why you need a coating for aluminum.

a) Enhance the look and appearance

Mill finished aluminium is dull in colour and may not always match with the building/structure’s colour scheme. On the application of the coating, the aluminium structures can match the colour scheme of buildings/structures. Designers/architects proposes the type of coating and colour to be applied after analysing the utilities, environment, and colour schemes. A coating matching with an appropriate colour scheme can enhance the appearance and look of structures/buildings.

b) Increase the Corrosion resistant properties

Most of the cases the oxide film on the surface of aluminium is sufficient to take care of corrosion. In some cases, the structures need an extra protection from corrosion. Similarly long exposure to moisture and water can damage the natural oxide film. The coatings can increase the thickness of oxide film and can provide an extra layer of protection which in turn enhance the protection against wear and tear, handling defects, and corrosion.

Aluminium Wall Cladding — ALUMINIUM CLADDING

c) Hardness of members

Coatings can increase the hardness of the materials and protect the material from excessive wear and abrasion encountered on transportation, loading, fabrication erection, etc. Coatings also protect the structures against possible wear and abrasion when used in high traffic areas.

d) Dye marks

Mill finished aluminium have dye marks. Coatings cover these dye marks and makes the surface look smooth and even.

e) Reflectivity

Coatings increase the reflectivity of aluminium and hence used for roofing sheets and light covers.

Coatings and treatments on aluminium

The most commonly used types of coatings are as follows. The type of coating basically depends on the choice of colour, hardness required, durability and area of application. The following are the the three different types of coatings commonly used for aluminium.