Orthopedic Implants, Part 6 – Shot Blasting Improves Longevity

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 orthopedic implants, Rosler recommends mainly air and occasionally wet blasting systems.  In each process, 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.

Air blasting and wet blasting schematics

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

Examples of Shot Blasting

Shot blasting is an impact system in which small metal or mineral pellets are thrown onto the surface of a work piece at speeds of 200-800 feet/second. The impact on the work piece surface produces the desired cleaning, peening, or texturing effect.

For medical applications, mainly air and wet blast systems are used which generally make a surface rougher. The smoothest finishes achieved with shot blasting are about Ra = 16-32 microinches (= 0.4 to 0.8 μm).

The most common shot blasting processes include:

• Surface cleaning to descale work pieces after forging, casting, or heat treatment. This process usually creates a rougher surface.
• Surface texturing as preparation for coating to allow for better adhesion of the coating material.
• Cosmetic blasting and texturing to place a very fine, matte, anti-glare finish on the work pieces.
• Preliminary surface smoothing of additively manufactured (3D printed) implants. While shot blasting normally makes a surface rougher, 3D printed parts have a very rough initial surface. Shot blasting provides a smoothing effect on these work pieces and is often used in preparation for mass finishing.
• Shot peening to induce a compressive stress in a work piece’s surface, making it more resistant to general wear and corrosion stress cracking.

Shot peening versus wet blasting in use

Shot Blasting 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.

A number of shot blasting machines can be utilized, each with its own benefits and areas of expertise.

Satellite Table Machines

• Used For: Hip stems, tibia plates, and other orthopedic implants
• Key Benefits: Prevention of contact between work pieces
• How It Works: These blast machines are equipped with a rotary ta­ble containing 4-12 independently rotating satellite stations. Work pieces are attached to the satellites, which then pass through one or multiple blast stations equipped with several blast nozzles.

Rosler's RWT 10-4S Blast chamber

Swing Table Machines

• Used For: Finishing of orthopedic implants
• Key Benefits: Efficiency, prevention of contact between work pieces
• How It Works: Blast machines are equipped with a round table with 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.

Rosler's RSKI 1400 SAT Nozzles

Robotic Blasting Systems

• Used For: Complex part geometries and large part variety
• Key Benefits: Repeatable and precise process
• How It Works: The robot holds either the part or the blast nozzles and follows the pre-programmed blast path to blast the part.

Most machines can be equipped with automated work piece loading and unloading to achieve high production volumes, improved efficiency and throughput, and additional cost efficiency.

Robotic blasting system

The Rosler Way

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

The complete Orthopedic Implant Series includes:

• Part 1 – “Surface Finishing Enhances Component Life, Function.”
• Part 2 – “Required Component Characteristics Define Finish.”
• Part 3 – “Materials Must Provide Strength, Safety.”
• Part 4 – “Finishers Meet Standards, Face New Challenges.”
• Part 5 – “Mass Finishing Offers Medical-Grade Polishing.”
• Part 6 – “Shot Blasting Improves Longevity.”
• Part 7 – "Processing Technology Evolves with Industry Advancements."