The purpose of blasting is to achieve a specific material surface, or even sub-surface characteristic. The most common desired results are:
- Strength - Increase component cycle life & reduce fatigue
- Cleaning – Remove contaminates for following processes
- Adhesion – Provide a stronger bond to adhered materials
- Appearance - Produce a desired cosmetic surface
Peening is the process of impacting a surface area uniformally with small, round, and often heavier media, where that area receives a compressive stress. Media mass, blast force, distance and duration and coverage area are all calculated to produce the desired result, often a MIL-SPEC. Peening can be performed to increase tensile strength and improve part life, reducing failures caused by cyclic force loads in a high stress area of the part. In this case, the action reduces the local stress as a part flexes in normal operation. Peening can also produce a stronger surface for improved resistance to abrasion and wear. Typical medias used are cast carbon steel, cast stainless steel and glass shot. Peening is often used for automobile and aircraft parts, and the media can be delivered by all forms of blasting; Pressure, Suction, Wheel, Wet and Gravity.
Many manufacturing processes to produce parts leave them dirty and with rough edges. Often these parts have other treatments they must receive and need to be cleaned first. Some parts are blasted just to improve their appearance, as in used core castings, like brake calipers, being remanufactured. Many medias and most types of delivery except Gravity are used in blast cleaning.
Various surface fiinishes can be created by blasting. Achievable finishes range from a rough textured surface, to a matte finish, to satin smooth, to polished and shiny. For example, a titanium bone replacement implant may have a highly polished end for a joint but the opposite end will have deep and rough channels blast into it for strong bone attachment and growth. Media types used range from soft walnut shells media to aluminum oxide with sharp edges, and are delivered by most blast methods.
Surface preparation of various materials for additional finishes is nearly an industry in itself. Blasting can produce surfaces with vastly improved adhesion qualities by increasing surface area. From metal plating, to paints, powders, plasma treatment and a wide variety of other coatings, the surface must be pre-treated. The typical metal substrate specification is a "white metal finish", defined as a surface which, when viewed without magnification, will be free from oil, grease, dirt, mill scale, rust, paint or other coatings, and foreign matter, and which will exhibit a uniform metallic color. Again, the media and delivery are chosen to create a specific surface condition.
While not as popular as other surface applications, blast etching is a chemical free way to modify a surface in all unmasked areas. Decorative etching in glass is achieved by adhering a rubber template cut out in a design pattern, possibly with text. where the grit blasting only affects, or etches, the exposed glass. This is typically performed with a pressure or suction gun.