Joint Reconstruction, Part 6 – Shot Blasting for Surface Finishing, Coating Preparation, and Increased Component Life Span

Like mass finishing, shot blasting is an exceptionally versatile surface treatment technology. Its applications range from general cleaning after casting and forging to shot peening and, even, cosmetic blasting for placing a fine, matte finish on the work pieces.

For shot blasting of orthopedic implants Rosler Metal Finishing recommends mainly air and occasionally wet blasting systems. The blast media is accelerated by compressed air and thrown at the work pieces through a blast nozzle, creating an extremely precise blast pattern compared to turbine blasting. Another advantage of air blasting is that it can be used with metallic, mineral as well as organic blast media.

These attributes and many more make this surface finishing method particularly useful in the medical industry. 

Examples of Shot

Blasting

The most common shot blasting tasks for joint

reconstruction implants include:

Acetabular cups in need of shot blasting to texture the surface for better coating adhesion

• Surface cleaning after casting and forging.
• Surface texturing as preparation for coating.
• Cosmetic blasting.
• Preliminary surface smoothing of additive manufacturing implants.
• Shot peening.

Increased Life with Shot

Peening

Shot peening is a process

specially developed to improve the properties of components which are exposed

to changing strains. In this process, the surface of the work piece is bombarded

with a stream of blast media. Each pellet forms a little dimple on the surface

to create a compressive stress. As a result, extension of the fatigue life,

increased load bearing, and higher wear resistance are created.

Rosler shot peening schematic

Joints are a prime example of

components which must retain their strength over a long period of time.

Typically, joint implants such as hip stems, femorals, and tibia plates are

shot peened.

Gentle Shot Blasting

with Wet Blasting

The wet blasting method can be used for surface improvement, cleaning, preparation, decoating, preparation for initial coating, deflashing, and shot peening. This water-based method uses abrasives known as a slurry and is particularly suited for the finishing of delicate, precision-produced parts such as endoprosthetics.

The concentration of the slurry can

easily be adjusted for different surface effects. Acceleration of the slurry is

achieved using a special pump and compressed air.

Advantages of wet blasting include:

Tibia plate stem after wet blasting to remove leveling lines

• No dust.
• Very gentle to aggressive blasting capabilities.
• No metal or media impregnation in the work pieces.
• No heat warping of thin parts.
• Cleaning effect even without chemicals.
• Very fine, textured finishes.

Commonly Used Machines

Implants must always be individually attached to

or placed on work piece fixtures to prevent any contact between the work pieces,

which may cause nicking or denting, during the entire shot blasting process.

Satellite Table Machines

Rosler satellite table shot machine with fully automated work piece handling

These blast machines are equipped with a rotary table containing 4-12 independently rotating satellite stations. The work pieces—for example, hip stems and tibia plates—are attached individually or in groups to the satellites. Each satellite then passes through one or multiple blast stations equipped with several blast nozzles.

Swing Table Machines

Rosler RWT swingle table machine

Equipped with a round table, these blast machines

feature two rotating satellite workstations, one in the blast zone and one in

the load/unload zone. This allows loading/unloading one set of work pieces

while another set is shot blasted. A 180° table rotation of the satellite

station in the blast zone moves work pieces to the load/unload station and vice

versa.

Automatic Loading & Unloading

For small production volumes manual work piece

handling may be sufficient, but, for high-volume production, full automation of

the work piece loading/unloading function may be more efficient and economical.

Shot blast machines can be upgraded to any degree of automation requested.

The Rosler Way

Whatever your shot blasting needs are for joint reconstruction implants, Rosler Metal Finishing can help you find a better way and achieve the exact finish needed every time. Contact us today to discuss your unique challenges.

The complete Joint Reconstruction Series includes:

• Part 1 – Expertise for Endoprosthetics.
• Part 2 – Material Standards.
• Part 3 – Finishing Standards.
• Part 4 – Comparing Surface Finishing Methods.
• Part 5 – Mass Finishing for Smooth, Polished Surfaces.
• Part 6 – Shot Blasting for Surface Finishing, Coating Preparation, and Increased Component Life Span.

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