Surface Finishing Services

Norman Noble, Inc. utilizes specialized surface finishing processes during the manufacturing of medical devices & implants, aerospace components, and commercial parts.

 
     

     
Automated Pickling and Passivation Line    

An advancement in technology, Norman Noble’s automated pickling and passivation line improves productivity, product quality, product consistency, operational safety and reduces environmental costs compared to conventional systems that are manually controlled.

 

The automated pickle and passivation line is a fourteen tank system including loading conveyor, pickle and passivation
  sections each with their own rinse and dry tanks, and an unloading conveyor. It’s a fully automatic system with gantry-style tank to tank movement. Parts are processed according to a pre-set “recipe”. Key tank parameters are monitored through the programmable controller and include alarm functions. Materials processed for both passivation and pickling are 304 and 316 stainless steel, titanium, and nitinol.

 

     
Pickling   Passivation Line

Purpose:
Pickling is a treatment for metal surfaces that remove oxides, impurities, stains, rust or dross. Used for stainless steel, titanium, and nitinol.

Process:
This is accomplished by dissolving the stain or oxide, along with the base material. This generally leaves the grain boundaries of the material exposed, and a somewhat matte and uneven surface. Pickling can be used to slightly change the parts dimensions, or chemically machine .0000” to .002”.

Considerations:
Back figuring may be required if dimensional tolerances are relatively tight. Heavy etching can cause grain boundary ditching, which may be undesirable in designs that require a specific fatigue cycle life.

 

Pickling

 

Purpose:
Passivation treatments improve the surface condition of stainless steel by dissolving iron that has been imbedded or exposed in the surface during forming or machining. If allowed to remain, the iron can corrode and give the appearance of rust spots on the stainless steel. Our passivation line is capable of processing all 300 and 400 series Stainless Steels, 17-4 Stainless Steel, titanium, and NiTinol.

Our validated processes are certifiable to ASTM A967. Passivation treatments also improve the surface condition of nitinol and titanium by dissolving iron that has been imbedded or exposed in the surface during forming or machining, and allowing the Nitinol or titanium to grow a thicker protective oxide layer, providing the maximum corrosion resistance. In addition, NNI can also perform passivation per: AMS-QQ-P-35 (Replaced QQ-P-35), AMS 2700, ASTM A-380, ASTM B-254, MIL-S-5002, ASTM B600.

Process:
This is not a rust removal or coating process, but rather a deep cleaning with various concentrations of nitric acid and temperatures. NNI’s passivation solutions are replaced weekly and this level of diligence exceeds industry standards. The passivation is designed to maximize the inherent corrosion resistance of stainless steel, titanium, and nitinol parts post-machining.

Considerations:
A very clean, machined, polished or pickled stainless steel part automatically acquires some oxide film from exposure to oxygen in the atmosphere. While this natural passivation provides a thin protective oxide layer, it is not robust. Even if the parts are shiny and bright, stainless steel parts may still tarnish in a short time. This invisible oxide layer is found to be extremely thin, from 1 to 10 millionths of an inch. During the nitric acid passivation process, a nitric acid solution dissolves all contaminants, sulfides, and loose iron allowing the metal to grow a robust protective oxide film that completely covers all surfaces of the part to the maximum possible thickness
.
 
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CNC Micro Bead Blasting and Aluminum Oxide Blasting    
Purpose:
To provide desired surface texture and/or corner breaks, i.e., matte, rough, bright, removing slag or dross, oxide removal, and corner rounding.

Process:
Varieties of different abrasives and beads are available, and need to be chosen for the application. Abrasive blasting is accomplished by propelling a graded abrasive media into a stream of compressed air or nitrogen, and focused thru a nozzle at a fixed positioned in relationship to the part(s). The abrasive material is directed at a targeted area to accomplish a specific task. Spent media is continuously drawn out of the work chamber via a vacuum and then sent through a filtration area to a dust collection system. Bead Blasting is similar to abrasive blasting, except beads lightly peen, cold work, or plastic level the surface with graded beads consistent sizes. Machined parts, which can be small or intricate, are placed onto either a static or rotating fixture, the nozzle(s) are then positioned, and the parts are blasted with fixed parameters and CNC movement. Finished parts will be deburred, and have consistent texture.
 

Eight main parameters control most blasting processes:
1. Type and size of media
2. If abrasive is used once or for a period of time
3. Velocity of the air flow
4. Media flow rate
5. Stand-off or distance from nozzle to part(s)
6. Nozzle diameter
7. Operator or machine precision and repeatability
8. Scheduled equipment maintenance

 
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Electropolishing    

Purpose:
Metal removal, remove stress risers, corner rounding, edge sharpening, deburring, providing high luster, removing heat effected zones and micro-cracks, and often improves the products fatigue life.

Process:
The NNI electropolishing (EP) process utilizes various engineered blends of acids that are designed to dissolve the components of the part’s material, when the part is connected to a positive electrical charge, placed in a bath of engineered acids, in the presence of a negatively charged counterpart, miracles can happen. The part then becomes the anode, the counterpart becomes the cathode. Ions flow from the part to the cathode, in a somewhat disproportionate manner. The irregularities such as corners, burrs, and protrusions become high current density areas, these polish the fastest. Low areas or middle areas polish slower. ID’s will only polish if there is exposure to a cathode.

During polishing, the acids become saturated with the dissolved metals and metal salts from the parts that have been polished. During repeated use, the solution approaches its equilibrium point and then begins precipitating out additional metals and salts to the bottom of the EP system as sludge. The majority of the metal in the solution plates to the cathode.

 

Considerations:

  • Oxygen is liberated at the anode, and hydrogen is liberated at the cathode. Therefore, electropolishing will not cause hydrogen embrittlement of the parts.
  • Electropolishing can improve fatigue life by removing cold working stresses, or heat effected zones on the cut surfaces, smoothing stress risers, removing micro-cracks, and rounding corners.
  • NNI can also modify the electropolishing effect to sharpen edges and points.
  • The electropolishing effect when done properly, can improve a finish typically 2 fold, or more if tolerances allow. i.e., a 8Ra will be reduced to a 4Ra.
  • Proper electropolishing can greatly reduce the possibility of bacterial growth on critical surfaces.
  • An area to attach the rack should be identified prior to RFQ.
  • Typically, part designers target .0008” to .0010” inch removal per surface, if maximum fatigue life of the product is a concern.
  • Parts typically need to be back figured by NNI engineering to allow for the material that the customer’s design requirement needs to be removed.
 
Electropolishing
 
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High Energy Finishing and Dry Tumbling    

Purpose:
To remove burrs, and/or add luster.

Process:
Machined parts are placed in a hexagonal, sealed barrel, with media, water, and soap. The barrel is then placed into a turret with 4 other containers. This process is similar to a carnival ride.

Rotation of the large turret creates a centrifugal force on the media and parts inside each barrel. This force compacts the load into a tight mass causing the media and parts to slide against each other, removing burrs and creating desired finishes. This action also reduces the cycle time needed to complete the finishing of the parts by up to a factor of 30 over conventional vibratory and barrel tumbling. Results with this centrifugal barrel finishing are consistent and predictable, every time.

Considerations:
The expected Fatigue life of the parts must be considered prior to exposure to High Energy Finishing.

 
 
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Vibratory Finishing    

Purpose:
To remove burrs, and/or add luster.

Process:
This is similar to High Energy Finishing, but with much less energy. This process uses cyclic vibration causing rotation to move the media around and thru the parts. This can be performed wet or dry.

Considerations:
The expected Fatigue life of the parts must be considered prior to exposure to Vibratory finishing.

  Vibratory Finishing
 
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Microburnishing    

Microburnishing is like using a wire brush, but without a handle.

Purpose:
To level burrs, and/or add luster.

Process:
Variously shaped smooth metal media is rubbed on the metal surfaces. This process flattens the high spots by causing a plastic deformation flow of the metal surfaces and corners. Typically the corners will only slightly round, and exhibit displaced material compressed on the edge. Passivation is recommended post burnishing, to remove loose iron. Very little material is removed, in normal use, only a few ten thousandths of an inch off corners. This process will not remove heat affected zones. Burnishing economically improves the surface finish, and provides some work hardening of the surfaces.

  Microburnishing
 
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Automated Microtube Flushing    

Purpose:
Cleaning and removal of dross from the inside of Stainless Steels and Nitinol Tubes.

Process:
Proprietary. NNI custom built this machine to wash, descale, flush clean, and dry small tubes up to 5’ long, and ID’s as small as .0050”.

  • High powered (13,000 psi) acid flushing system.
  • Capable of processing hypotubing with a minimum diameter of .004” ID and maximum length of 69”.

Processes all types of metals including stainless steel, nitinol, and cobalt chrome.
  Automated Microtube Flushing
 
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Micro-Abrasive Blasting for PEEK Implants    

Purpose:
Norman Noble Inc.’s proprietary micro-abrasive blasting equipment can be used to deburr PEEK implants.  Though PEEK’s biocompatibility and chemical resistant nature make it an ideal choice for medical implants, it creates challenges to the manufacturing process.  Machining typically generates burrs that are cumbersome to remove manually.  Norman Noble’s validated Micro-abrasive blasting can be used to eliminate this laborious process.  The fine abrasive stream quickly strips off the burs without damaging the delicate features machined into the parts.

 
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Additional information about Medical Coatings and Plating Specifications is available at www.electrohio.com, including: