Diametric interference

A typical anode for practical use would be in the order of 25 to 48 mm in diameter, with hard platinum alloy pins of 0-50 mm diameter by 10 mm length, spaced every 150 to 300 mm and progressively positioned around the circumferenceThe pins are a press fit into holes in the lead or lead alloy (approximately 01 mm diametric interference) and lie flush with the surface. The lead is peened around the pins to improve the mechanical and electrical contact. 

The maximum allowable diametral interference between a shaft and a hub for press-fitting assembly is a function of part geometry, stress, modulus of elasticity of shaft and hub, and Poisson s ratio for shaft and hub materials. When the shaft and hub are made of the same material, the moduli of elasticity are the same and Poisson s ratio is the same for the shaft and hub, simplifying the equation for maximum diametral interference. Calculating diametral interference is simplified when the shaft is made of high-modulus material. 

Combinations of plastic and/or metal can be satisfactorily assembled using the press fit technique, provided correct diametral interferences are determined during design. 

Holding strength over an extended period of time is of prime importance and is governed by the creep characteristics of the material. Creep reduces effective diametral interference. Thus the effective pressure is reduced, resulting in a loss of holding power. Since this is a known phenomenon for most materials, it is impractical to... 

The relationship of maximum stress, caused by press fitting a shaft or insert in a plastic hub, to diametral interference (AD) is expressed as ... 

A line-to-line condition should be maintained prior to expanding the insert. The total diametral expansion of the insert into the material should not exceed the recommended diametral interference for press-fits. A complete analysis of the insert should be made to determine its total expansion prior to selecting the proper hole size. Material thickness around the insert should not be less than 0.9 times the final outer radius of the insert. ... 

The fuel assemblies must maintain their integrity throughout the duration of their operation in the reactor core. The fuel must not melt, the cladding must not fail and the structure must not deform to the extent that it interferes with the functioning of other components within the reactor. These requirements determine the pellet size and density, the clad-pellet diametral gap, the gas plenum size and the helium pre-pressurisation level. 

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