Hard Anodise (MIL-A-8625, Type III, Class 1 or 2)
Hard Anodising is a process of converting aluminium into aluminium oxide. When this is performed in a tightly controlled environment the result is a crystal lattice structure 35 – 75 microns thick with a surface hardness of approximately 60 to 68 Rockwell C (800 to 1000 V.P.N). Thickness, hardness and colour of the coating will vary dependent on the type of alloy composition. This should be considered when discussing your requirements with our technical staff or at the design phase prior to manufacture.
Over a number of years now, Electromold have assisted in the development of many components within the areas of Motorsport, Medical/Surgical and General Engineering. Whether you are manufacturing from a blue print or in the early design phase the following points should be considered, please don't hesitate in contacting Electromold's technical staff for assistance.
- Choice of Aluminium: Alloys containing a high percentage of copper (2011) should be avoided at all costs. Hard Anodise is performed under extreme voltages and will attack and remove the copper from the alloy. The result from this attack can be as little as a microscopic etch or complete destruction of your component(s).
- Sharp Edges: Due to the characteristics of the crystal lattice structure it is important to remove all edge burrs after machining. As this coating is not ductile, chipping may occur if these burrs/sharp edges are not removed.
- Coating Thickness: As anodising is a conversion process, the coating thickness is measured across the crystal lattice structure not as dimensional growth. Dimensional change will occur based on material choice/selection. A rough rule of thumb used within the industry is 50% internal growth and 50% external growth (dimensional). This rule only applies on certain materials such as 2024 and 7075. As there are so many materials available today, the above stated percentages will vary so please consult our technical staff for choice of material grade and machining tolerances.
- Corrosion Protection: Once again, this is dependent on choice of material. Maximum corrosion protection is achieved at a coating thickness of approximately 35 Microns. This is further improved by sealing the crystal structure.
- Breakthrough Voltage: Hard Anodise has a resistance up to a maximum of 1000 volts, this is calculated at 7 to 10 volts/um.
- Wear Resistance: Optimum material to achieve maximum wear resistance is 6000 series aluminium. However as its tensile strength is low, no matter what coating thickness we apply might not be suitable for your application. Coating thicknesses for wear protection would be recommended at no less than 45 microns. Electromold Australia have achieved coating thicknesses up to 140 microns, to achieve this is also dependent on your choice of material.
- Sealed/Unsealed: To achieve maximum wear resistance it is best practice to leave the coating unsealed. Although by leaving the coating unsealed to enhance its wear resistance it is important to understand the environment the component will be subjected too, as this unsealed condition may be detrimental to the life of the item due to corrosion.
- Colour: This is totally reliant on material grade based on reasons stated above. The typical colour achieved is olive green to a dark olive brown. Some alloys can be dyed black if required.
Hard Anodised surfaces have many benefits. If weight is a factor then aluminium can replace the more conventional steels previously used, aluminium components that are subjected to a high corrosion environment such as marine applications will out perform that of steels using conventionally coated. By using lighter weight materials such as aluminium in lieu of ferrous materials will also reduce machining costs considerably.
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Areas where Hard Anodising is currently benefiting:
- Marine Research
- Mining/Petroleum Industries
- Printing Industry
- Paper Milling
- General Engineering
- Bio Chemical / Laboratory Equipment
- Food Processing / Confectionary Industry
Benefits of Hard Anodising are:
- Can increase corrosion protection up to 2000 hours Salt Spray Testing (depending on grade of Aluminium used)
- Better wear properties than that of Hard Chrome
- Brake through voltage 7 to 10 volts/um
- Can be honed or ground to achieve tight tolerances and surface finishes.
- Improved wear resistance (Tabor tested monthly using a CS17 wheels and a 1000g load with a wear index result of less than 1.5mg/1000 cycles)
- Food grade safe (FDA Approval)
- Improves Loctite bond strength
- Left unsealed to retain oils for lubricity
- Can be used to re-gain dimensional size
When requesting Hard Anodise please state the following:
Critical dimensions (Pre / Post Plating)
Grade of Aluminium used or proposing to use
Colour requirements (refer above)
Any standard or specification that is referenced on the manufacturing drawing
Part dimensions and production quantities
Whether a Certificate of Conformance is required
Recommended grades of Aluminium:
7075 – T6
6061 – T6
5083, 1100 – H18
5052 – H30
3003 – H11
2024 – T3
If you require any further information regarding this process or any of Electromold Australia's plating processes, please contact us on +61 3 9464 0922 and one of our technical staff will be able to assist you.
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