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» Process & Capabilities

Anodized Aluminium Castings

"VJP has setup a new anodizing plant to accomplish customer orders on time. This page provides the details of the anodizing plant at VJP and also the process details for technical understanding."

Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than bare metal. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light. Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors. Anodizing most closely resembles standard electroplating. When a reactive metal is suspended in an electrolytic bath as an anode and current is passed through the bath oxygen is produced at the anode surface. This oxygen reacts with the metal to form a thin oxide film that generates colors. The transparent oxide increases in thickness in relation to the amount of voltage applied. At any given voltage the oxide will grow to a specific thickness (i.e. color) and stop, having reached a stage where current will no longer pass.

Sulphuric Anodizing

Sulfuric anodize, commonly referred to as Type II anodizing, is formed by using an electrolytic solution of sulfuric acid at room temperature and a current density of 15 to 22 Amps per square foot. The process will run for 30 to 60 minutes depending on the alloy used. This will produce a generally clear coating, depending on sealing, a minimum of 8ìm thick. One third of the coating
square foot. The process will run for 30 to 60 minutes depending on the alloy used. This will produce a generally clear coating, depending on sealing, a minimum of 8ìm thick. One third of the coating

Value Additions
  • Can handle large size parts
  • Sizes of 4.5mx2 m.
  • Coloring.
  • Integrated paint shop.

Plant and Machinery

VEE J PEE’s anodizing plant has a built in area of 5000 sq ft. This would be operated as a separate plant away from foundry premises.

The list of equipments and corresponding specifications are given below.

  • Cleaning Tanks-16x3x6 ft
  • Anodizing bath-16x3x6 ft
  • Rectifier 1000 Amps, 32 volt
  • Cooling Plant
  • Double handed buffing machine
  • Dyeing tanks
Plant and Machinery
Plant and Machinery
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Process Procedure

Anodizing process undergoes pre-treatment, rinsing, etching, desmutting, anodizing, coloring and sealing. Aluminum anodizing is the electrochemical process by which aluminum is converted into aluminum oxide on the surface of a part. The process of anodizing is rather simple. It consists of an anodizing solution typically made up of sulfuric acid. A cathode is connected to the negative terminal of a voltage source and placed in the solution. An aluminum component is connected to the positive terminal of the voltage source and also place in the solution. When the circuit is turned on the oxygen in the anodizing solution will be liberated from the water molecules and combine with the aluminum on the part forming an aluminum oxide coating. Conditions such as electrolyte concentration, acidity, solution temperature, and current must be controlled to allow the formation of a consistent oxide layer. Harder, thicker films tend to be produced by more dilute solutions at lower temperatures with higher voltages and currents. The film thickness can range from under 0.5 micrometers for bright decorative work up to 150 micrometers for architectural applications.

Key Benefits
  • Corrosion Resistance
  • Increased Emissivity
  • Decorative Colors
  • Excellent Dyability


The most common anodizing processes, sulfuric acid on aluminium, produce a porous surface which can accept dyes easily. The number of dye colors is almost endless; however, the colors produced tend to vary according to the base alloy. Dyed anodizing is usually sealed to reduce or eliminate dye bleed out.

Alternatively, metal can be electrolytically deposited in the pores of the anodic coating to provide colors that are more lightfast. Metal dye colors range from pale champagne to black. Bronze shades are commonly used for architectural use. Alternatively the color may be produced integral to the film. Splash effects are created by dying the unsealed porous surface in lighter colors and then splashing darker color dyes onto the surface. Aqueous and solvent based dye mixtures may also be alternately applied since the colored dyes will resist each other and leave spotted effects.

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Anodizing is an environmentally safe electrochemical process that converts the aluminum metal surface into a porous aluminum oxide, ultimately creating an end product whose finish is more durable and weather-resistant. Anodized products and components are used in thousands of commercial, industrial and consumer applications. Structural Building exteriors, roofing, window frames, and door handles.

Microwaves, Refrigerators, Dryers and grills.

Transportation Car parts, Boats, Aerospace Vehicles

Integrated Facilities

  • Grid blasting – 4x2 m (max size)
  • Welding – Aluminium TIG welding
  • Cutting Machine
  • Portable grinder
  • Handling equipment and Packing facility

Anodized Aluminium castings Advantages:

  • Anodized aluminum can replace stainless steel in certain applications owing to lesser weights which makes it easy to handle, bringing down overall material used and consequently the shipping costs.
  • Corrosion resistance of aluminium castings improves a lot with anodizing. Hard anodizing is used in marine applications.
  • Anodizing is one of the more environmentally-friendly metal finishing processes
  • Anodizing is said to impart anti-galling properties on threaded components.
  • The aluminium oxide coating is grown from and into the surface of the aluminium. Because of this it is not prone to peeling or cracking like organic coatings such as paint.
  • Aluminium oxide also possesses excellent thermal and electrical insulation qualities.
  • Coating thickness is very less ( between 15 microns to 50 microns depending on the requirement) but strength is high. With less coating thickness the dimensions of the part does not change considerably and can be generally maintained within tolerance.
  • Painting done on anodized surface have very less peeling-off characteristics compared to the painting done on the raw casting surface. Most aluminium aircraft parts including major components are anodised before assembly and painting.
  • Hard anodizing of aluminium castings will give black color surface, which can be used as an alternate for black painting.
  • Anodized surfaces are highly resistant to scratches and wear.

Please note: Anodizing of aluminium alloy castings is different from anodizing pure aluminium (parts that have more than 98% aluminium content like extrusions, bars) The color of the casting changes due to the presence of alloying elements like Silicon. This color change is not seen on pure aluminium.

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