Letter 40060

Interference of phosphating layer with press fit

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I have an application where a phosphated sintered female part namely Hub (density 6.5~7.0 g/cc) is press fit with a steel shaft. The design interference is 0.060mm to 0.100mm (0.0024" -0.0039"). Recently I had lot of failures where hubs slipped off from the press fit under working condition. We have specified phosphating layer in the bore to an extent of 0.005 to 0.012 mm (0.00019" - 0.00047"). My query is whether the presence of such phosphated layer in the interference will weaken the joint or not?

G. MURALIDHARAN
Auto ancillary - Chennai, Tamilnadu, India

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Most likely the cause may be an over etch during the pre-cleaning or an over exposure to the phosphating solution of the parts.

Guillermo Marrufo
Monterrey, NL, Mexico

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My thought would be that the interference fit is crushing the phosphate to a fine powder which can work out and also act as a lubricant.

James Watts
- FL

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Thanks for the responses. I am glad that I could move a step or two forward with these inputs.

G.Muralidharan
- Chennai, Tamilnadu, India