Method and apparatus for forming joints in thermoplastic strip

Apparatus for forming a joint in a strip of thermal plastic material having a notch, defined by laterally opposed notch walls, formed therein, comprising:

• a pair of opposed jaws mounted for substantially rectilinear movement inwardly toward and outwardly, away from each other;
• means for holding the strip between the jaws, with the notch substantially axially centered therebetween, whereby inward movement of the jaws toward each other compresses the strip portions adjacent the notch and causes the walls defining the notch to move together;
• a thin heated blade arranged in a plane centrally between the jaws and aligned with the axis of the notch, said blade having opposed, generally parallel faces, and being movable in a direction generally perpendicular to the axis of movement of each of the jaws, and means for reciprocating the blade inwardly to a position between the jaws and outwardly to a position remote from the jaws for withdrawing the blade;
• and
• means for (a) moving the jaws to engage the strip portions adjacent the notch and to press the notch walls against the opposite generally parallel faces of the heated blade for momentarily heating such walls, and (b) thereafter moving the jaws further toward one another after withdrawal of the heated blade to compress and hold the walls of the notch together until the faces thereof are joined.