Dukane SVB051 Manuel d'utilisateur télécharger pdf (Page 37)

Spin Welder User’s Manual Section 5 – Theory of Operation

Page 27

Page 26 Dukane Manual Part Number 403-547-03Dukane Manual Part Number 403-547-03

Spin Welding Process

The formal denition of spin welding is “An as-

sembly process in which thermoplastic parts with

rotationally–symmetric mating surfaces are joined

together under pressure using unidirectional circular

motion. The heat generated during the rotational

contact melts the plastic in the heat–affected zone

forming a weld upon cooling” Note that the parts

do not have to be circular, only the mating surfaces

to be welded have to be circular.

The spin welding process is divided into 5 distinct

phases as shown in Figure 5–1. In Phase I, the rota-

tional friction generates heat. Frictional heating is

intensied with both axial pressure and joint surface

velocity. In Phase II, the friction results in abrasive

forces which strip off surface roughness, generating

wear particles causing the surfaces of the polymer

to begin to melt. As the polymer reaches its crystal-

line melting point or glass transition temperature, it

enters Phase III. This is an unsteady state in which

the temperature quickly increases and viscous ow

is initiated resulting in a large increase in melt thick-

ness. This is accompanied by a sharp rise in the

melt (weld) penetration velocity. Once the melting

process is initiated, heat is then generated by internal

friction within the molten region. This continues in

Phase IV until a steady state equilibrium is reached

and the penetration velocity stalls. In Phase IV,

the heat loss through the wall and ash expelled

approaches the heat being generated. Here the tem-

perature of the molten layer remains relatively con-

stant. Because plastics are poor conductors of heat,

the surface heat is transferred slowly to the interior

and much of it remains localized. At this point, the

rotation is stopped and we enter Phase V where the

molten material is allowed to cool under pressure

for a short period called the Hold Time.

Figure 5–1 Penetration Depth and Velocity as a

Function of Time During the Five Phases

of Spin Welding.

Weld

Penetration

Depth

Weld

Penetration

Velocity

III III IV V

Frictional Heating

Wear Particles

Melting Transition

Steady State

Hold Time

1 2 ... 32 33 34 35 36 37 38 39 40 41 42 ... 111 112

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Dukane SVB051 Manuel d'utilisateur Page 37

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