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CONCERNS AND SPECIFICATIONS FOR NICKEL PLATED SCREWS

2007

Maybe more important I need help with my only two weaknesses: I drink too much Mountain Dew, and eat too many chocolate chunk cookies. But I will save this problem for later.

I am a seasoned mechanical engineer working for the largest company in design and manufacture of exercise equipment. I love my work and the people. I have a great sense of humor so part of my job is to have fun, laugh, and help others enjoy being at work. I am passionate about producing high quality engineering drawings, and products. I often use Geometric Dimensioning and Tolerancing; it is a great tool. Some people may not use it for weldments but it has great application here too.

PROJECT:
I am researching the feasibility of replacing some stainless steel screws with nickel plated screws to keep a similar appearance while reducing cost. I need a few specifications that have been hard to find.

The ENVIRONMENT is typically a health club, but those near the ocean may necessitate better corrosion resistance.

SPECIFICATIONS WHERE I NEED SOME HELP TO FINALIZE:
SPECIFICATIONS FOR METRIC-LOW HEAD-SOCKET CAP SCREWS; NICKEL PLATED STEEL:
Metric class 8.8 - medium strength steel (comparable to SAE Grade 5 in strength). DIN 7984 / ISO 898
Rockwell hardness C22-C32 / Minimum Tensile Strength 116,000 psi.
Nickel Plate: NEED plating thickness for screws? And reference a standard? Need appropriate corrosion resistance.
NEED Post-Plate Bake requirements and reference a standard?
L.F. Screw Thread Specification: M � 10X � 1.5 � 6g � 6g After Plating. Is it common for medium thread fit to just use one 6g which is for the pitch tolerance?
o DEFINITIONS for those who have interest.
o M = metric
o 10 = nominal size in millimeters
o X = separator between size and pitch
o 1.5 = thread pitch�number of threads in millimeters
o Tolerance Class:
First 6 = PITCH diameter tolerance GRADE
First g = PITCH diameter tolerance POSITION
Second 6 = MAJOR diameter tolerance GRADE
Second g = MAJOR diameter tolerance POSITION
Grade 6 is for medium tolerance quality

What about tarnishing?
One resource stated nickel plating will tarnish unless chrome plated too. I need to keep just nickel for appearance.

I am researching using our existing stainless steel nuts so we will test for galling. Any concerns with galvanic corrosion? Some cleaners may get on the fasteners.

Thank you for taking the time to consider my questions.

Greg M Rice
design engineer - Minneapolis, MN, USA

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Greg
Have you considered
health club = sweaty hands + nickel = dermatitis

Geoff Smith
Hampshire, England
2007

Electrodeposited nickel coatings for fasteners are usually specified according to ASTM F871M-98 [withdrawn] which references the plating standard ASTM B456. This standard is for Cu+Ni+Cr or Ni+Cr coatings. The SC1 requirement is for 10 micrometers of Ni thickness. Tarnishing is improved by depositing Cr. ASTM B850-98 is the standard for referencing with regards to hydrogen embrittlement, but steels with a tensile strength < 1000 MPa (hardness < 320 HV or 32 HRC) do not require baking. Regarding thread fit, it is my experience that almost all fastener drawings specify only the pitch tolerance and not the major diameter tolerance. Galling is always a concern when stainless steel is involved, so use an appropriate lubricant during tightening. I doubt galvanic corrosion will be much of a concern as long as the joints are not constantly wet.

Toby Padfield
Automotive module supplier - Michigan
2007