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Metal Finishing (Metal Fabrication)

January 8, 2019

 

If you have a product or are designing one then understanding the importance of the finish of your product is very important. Most people think that finishing is only for the visual look, but it affects much more than just how the product looks. Deciding on the finish for your part shouldn’t be at the end of the project, but done while you are designing that individual part. This is because the finishing also affects the mechanical part of the product as well, such as reducing the amount of friction. The main benefits of metal finishing are:
 

  • Improving corrosion resistance

  • Improving the strength of wear resistance

  • Serving as a primer for paint adhesion

  • Making the surface electrically conductive

  • Reduce friction

  • Improving the overall appearance

 

There is not one finish that can provide all of these benefits. However, there are two steps that when put together can improve both the appearance and the chemical side of your product. These two processes are the preparation and the finishing. The preparation is exactly what it sounds like, preparing the part to have the finish. The finishing process is the final finish coat that will be seen and often the reliability of this depends on the preparation step.

 

 

Metal Preparation

After the fabrication process is completed, there are some steps that are needed to prepare the part for the final finish or coating. During the preparation process, there are a number of steps that will compete the following:
 

  • Avoid corrosion

  • Helps the coating stick to the part

  • Add a texture

  • Clean the part for the final finish

 

The most common preparation steps to ready the part for the final finish are:

 

Sandblasting

This process is when the surface of a part is blasted by sand or abrasive grit with high pressure. Sandblasting is a quick process as it covers a large surface in a short amount of time. There are many different sizes of sand that can be used and those will affect the final quality and the texture of the product.

 

For production, you put the part inside an enclosed box and mask off the areas that you don’t want the sand, such as threads or holes. You then turn on the machine and the sand sprays onto and sticks to the part. The main reasons to use sandblasting is that it covers up minor defects such as scratches, adds texture, improves anti-corrosion and more. It can also help to clean the part from oils and contaminants picked up during the fabrication and welding processes, but usually, another secondary process is needed to truly clean the part. Lastly, if you have a part with a coating that you wish to remove, then sandblasting is the ideal solution.

 

Polishing

This step is used to clean and smooth the surface of a part. While sandblasting can add some texture to the part, polishing will make the part very smooth and can add more of a shine to the final finish. Polishing doesn’t add any chemicals by making the part more resistant to corrosion. It is simply just a machine with a cloth on a wheel that will be used to buff the surface. A polishing finish, it’s used mostly to provide a glossy and decorative finish.

 

Pretreatment

This process is used mostly for the parts that will be powder coated. During the pretreatment process, there are multiple steps to get the part ready for powder coating. These steps are the following:

 

  • Degreasing - This is the removal of oil and grease from the surface of the part.

  • Derusting - This is the removal of rust that is on the outside of the part. This will remove rust but is not necessarily the best means to prevent rust from forming again. This is used mostly for steel parts instead of aluminum.

  • Phosphate - This process is used to improve the corrosion resistance of the part. Another benefit is to improve the powder adhesion to the part. The two most common types are zinc and iron. Zinc phosphate provides a more robust finish which is ideal for parts that will be used in coastal areas or will come in contact with water. Iron phosphate, on the other hand, is a little simpler but doesn’t provide the protection that zinc phosphate provides. Both iron and zinc are used for steel. For aluminum, chromium phosphate is more popular.

 

Types of Finishes

After the pretreatment and preparation are completed, you can proceed to the final coat. Not all finishes are made the same and not all can be used after every single manufacturing process. For example, some parts that are processed by milling and turning can’t have the same finish as a part that was die cast. It’s best to consult a professional, or just ask EPower Corp for recommendations and guidance.

 

There are many different types of finishes that can be applied to metal parts as outlined below:

 

Anodizing

This process is only used for aluminum and cannot be used for other materials. This process is used when the natural coat on the outside surface changes to a tightly adhering layer. This coat is beneficial for a number of reasons:

 

  • Improves corrosion resistance

  • Is offered in a variety of colors

  • Increases the hardness

  • Increases wear resistance

 

Powder Coating

The process for powder coating is nice because the unused powder is recyclable. As you can guess, it’s a powder that is sprayed onto the part and then goes through a curing process. There are a number of benefits for using powder rather than liquid paint:

 

  • Improved durability

  • Color is uniform

  • Greater impact resistance

  • Extra corrosion resistance

 

Brushed Metal Finish

This process is used to mostly remove flaws from the surface of the part by applying a wire brush, belt, or wheel to the part’s surface. The final look consists of parallel lines that smooth out the surface of the part.

 

Hot Blackening

This process is most commonly used to provide a black matte finish on automobile parts, firearms, and tools in which a protective dark coating is needed. For this process, a thin black oxide coating is applied to the surface of the part.

 

Conclusion

Knowing the processes of metal preparation and finishing is important to understanding how the final product will look and perform. Not fully understanding how these processes work can lead to rusted parts, finishes that fade, or aren’t uniform and look inferior. For the ideal results, it’s always best to consult a professional who is familiar with the entire design, development and manufacturing process. Take a look at more metal finishing articles or contact us directly for a free consultation.

 

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