friction secures dowel pins:
Trib-joins are made with Trib-Tools,
which release trace amounts of friction enhancing chemical onto a surface as
they gently abrade the surface. This treatment typically quadruples the retention strength of
a dowel pin. Trib-joins tend to gain strength over time due to natural diffusion whereas adhesives tend to lose
Interference fitted pins are retained by dry friction between faces held in contact by elastic deformation of the pin or the material into which it is forced. Real contact can be as little as 1% of the overlap areas due to micro roughness. By treating the pin with a Trib-Tool the contacting asperities are enlarged and strengthened by permanent inter-metallic cold pressure welds interspersed with strong shear resisting mechanical interlocks formed as welds progressively break and reform when the pin is inserted.
Trib-Joining (Solid Phase Cold welding) a pin into a bore requires some parts of their surfaces be in good rubbing contact, but the quality of drilled holes is often poor, they being rough, tapered and out of round, with variation of size. This leads to a common misconception that Trib-joins cannot be made in poorly made bores. Very satisfactory Trib-joins are routinely made in drilled holes by either allowing the pin to size the bore as it is inserted or allowing the pin to deform and adopt the form of the bore. Typical pin sections are shown below - many of which are intended to deform upon insertion.
The round form (1) is a precision shaft or dowel. The pre-fit condition for a parallel dowel is ISO.H7/p6. Trib-joins also improve the retention of tapered dowels. Solid round dowels enlarge the bore as they are forced in. The lobed solid dowel (2) can be used in open tolerance drilled bores providing the pins major diameter is slightly greater than the worst case bore diameter so it always enlarges part of the bore as it is inserted. The net bore enlargement is minimised as material is pulled into the recesses thus making it very well suited to high density pinning of textile rolls. The spiral (3), wrapped pin or spring pin (4) and grooved pin (5) are all designed to deform when forced into regular drilled holes. The spline (6) tends to cut groves into a bore as it is forced in.
Trib-joins are safer than adhesives for securing press-fit pins because adhesives are limited by the shear strength of their cured plastic interlayer. They are also vulnerable because the thermal expansion of the plastic layer is almost ten times the rate of steel ! This leads to progressive join degradation over life if subjected to thermal cycling.
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