Surface Finishing

Summary

Abrasive Blasting equipment is widely used for Surface Preparation or Blast Cleaning applications on steel products as a pre-step prior to applying subsequent coatings. It can also be used to obtain a specific surface finish on corrosion-resistant materials that do not need protective coatings, such as stainless steel or plastic.

In some applications, surface finishing may refer to the process of removing all small pieces of unwanted material remaining after production processes (other than chemical or soluble contaminants) in order to obtain a finished product that is safe to use and handle – for example, a component of an industrial system. The look of the product itself is not very important, as long as it fulfills its task and is not hazardous for operators. 

In commercial and consumer applications, a finished product can be enhanced with an aesthetic finish that may be viewed as an added value for its users. For instance, the glossy finish of a laptop computer or the shiny look of cookware items.

What is Surface Finishing?

Surface finishing refers to a wide range of industrial processes meant to alter the surface of an object made of non-ferrous material, usually stainless steel, plastic, wood, aluminum, glass, composite material, and more. We do not consider coated surfaces here since they use a coating agent, which is not within the same composition of the substrate.

Finishing processes can be used to enhance the appearance of a manufactured item or to obtain specific properties: wear resistance, adhesion, wettability, solderability, electrical conductivity, hardness, friction, etc. In its most basic function, finishing could refer to the process of removing any unwanted material residues left from previous processes – such as welding residues, laser cutting imperfections, burrs, edges, etc.

Types of Metal Surface Finishes

There are many types of finishes available. Some of them are patented – which means the recipe and process for achieving it are fully documented and protected by an entity – while others can only be achieved on certain substrates.

Here are the main categories of specialty finishes:

  • Ground
  • Burnished
  • Brushed
  • Dull polished
  • Satin polished
  • Bright polished
  • Patterned
  • Corrugated
  • Matte finish
  • Blasted
  • Peening

Some aesthetic surface finishes can be achieved with techniques related to abrasive blasting. Here are some examples:

  • Wet Blast technique – water is added to the media mix to smoothen the impact on a surface – it is widely used to produce a brushed or polished finish on electronics, housing, and various consumer goods.
  • Shot Blasting techniques using glass beads or steel shot can be used to peen an object or give it a hammered finish.
  • Abrasive blasting techniques are used in the glass finishing process to create a frosty look.

Standards and Requirements

There are no standard specifications for surface finishes on metal parts as there are for Surface Cleaning or Surface Preparation. However, some finishes are specified in order to obtain consistency. Furthermore, some processes are patented by the O.E.M. and cannot be reproduced by other manufacturers for similar products.

The Canadian Association for Surface Finishing (CASF) and the National Association for Surface Finishing (NASF) are advocates of the surface finishing industry, and publish studies and guidelines to help manufacturers improve their processes. Professional associations – such as SAE Aerospace Standards, American National Standards Institute (ANSI), American Society of Mechanical Engineers (ASME), and ASTM International standards – may also publish standards or guidelines for certain finishes.

However, aesthetic finishes produced by Abrasive Blasting are not widely documented or regulated. The know-how behind those finishes relies on mechanical contractors or manufacturing engineers.

Abrasive Media Used in Surface Finishing

Spherical abrasive media like glass beads and steel shots are widely used for surface finishes. Very fine angular-type media can also produce interesting finishes on various metal, plastic, or glass substrates.

Surface finishes produced by abrasive blasting are usually performed at a relatively low pressure to avoid damaging the surface. The grit size tends to be very fine in order to evenly cover the surface and produce a fine polishing. Water is sometimes added to the mix to soften the impact on the surface.

Refer to the IST Media Selection Guide to choose the right media for your application.

Metal Surface Finishing Machines

Many different tools and machines can be used to obtain a proper metal finish. Some manual tools like sand paper or manual sanders with an abrasive belt can be used to remove cutting edges on metal parts. Polish machines are best when it comes to producing a fine polishing. However, no other finishing equipment is more efficient than abrasive blasting equipment where it can apply.

Metal finishing operations are mainly carried out in sandblast cabinets. Sandblast cabinets are convenient for delicate finishing processes, as they allow the operator to work freely behind a protective sight glass and close to the part. This type of equipment has a very small footprint in the shop and can be used for other types of surface treatment processes as well.

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