Method for making mushroom-type hook strap and mushroom-type hook strap made thereby
A method for making a mushroom-type hook strap for mechanical fasteners is disclosed. In a first stage of the method, a hook strap on which a plurality of hook preforms each having a substantially V-shaped free end are integrally molded. Then, in a second stage of the method, the V-shaped free end of each the hook preform is deformed into a polygonal head portion by two calendar rolls so as to form a mushroom-type hook strap that has a higher engaging percentage with the loop strap, has a longer lifetime, and is capable of providing a reliable and all-directional uniform fastening function.
1. A method for making a mushroom-type hook strap for mechanical fasteners, the method comprising the steps of:
providing a rotational molding roller, the molding roller having a plurality of substantially Y-shaped molding cavities formed in an outer periphery surface thereof and a cooling device provided therein, the Y-shaped molding cavities each having a stem adjacent and opening onto the outer periphery surface and a flared fork at an opposite end of the open stem pointing to an axis of the roller;
providing an extruder, the extruder having a extruding die disposed imminently close to the outer periphery surface of the rotational molding roller with a gap being formed therebetween;
feeding a thermoplastic material to the extruder and melting the thermoplastic material in the extruder to extrude the melted thermoplastic material through a channel within the extruder and extruding die and into the plurality of substantially Y-shaped molding cavities and onto the outer periphery surface of the rotational molding roller through the extruding die;
cooling the thermoplastic material on the outer periphery surface of the rotational molding roller from within the molding roller and within the substantially Y-shaped molding cavities with the cooling device to form a hook strap on which a plurality of Y-shaped hook preforms are molded, each said Y-shaped preform having a substantially flared V-shaped free end;
peeling off the hook strap from the molding roller; and
feeding the hook strap through a nip formed between a pair of calender rolls, wherein the calender roll that contacts the V-shaped free end of the hook preforms is heated to a temperature above a plastic deforming temperature of the thermoplastic material to deform the flared V-shaped free end of each hook preform into a single multifaceted head shape situated on top of an axis of a single stem and thereby forming a mushroom type hook having a single multifaceted head portion on the axis of the single stem,
the single multifaceted head portion providing protruding portions in substantially every direction for engaging fabric loops of a loop strap.
2. A method for making a mushroom-type hook strap for mechanical fasteners according to claim 1 , wherein a plane that contains the two intersected arms of the V-shaped free end of the hook preform is parallel to the direction that the hook strap is fed through the calender rolls.
3. A method for making a mushroom-type hook strap for mechanical fasteners according to claim 1 , wherein the gap between the extruding die and the outer periphery surface of the rotational molding roller can be adjusted by moving the extruding die relative to the molding roller.
4. A method for making a mushroom-type hook strap for mechanical fasteners according to claim 1 wherein the peeling off step is performed by a rotational stripping roll.
5. A method for making a mushroom-type hook strap for mechanical fasteners according to claim 1 further comprising the step of providing an auxiliary cooling device outside the molding roller to provide extra cooling to the outer periphery surface of the rotational molding roller.
6. A method for making a mushroom-type hook strap for mechanical fasteners according to claim 1 , comprising the additional step of
adjusting the nip formed between the calender rolls to be smaller than the sum of the thickness of the backing and the height of the preforms of the strap and substantially equal to the height of the stem portion of the preforms.
7. A method for making a mushroom-type hook strap for mechanical fasteners according to claim 1 , having substantially uniform engaging force in all directions.
8. A method for making a mushroom-type hook strap for mechanical fasteners according to claim 1 , wherein a surface of the single head portion is planar.
9. A method for making a mushroom-type, hook strap for mechanical fasteners according to claim 8 , wherein the single, planar head portion extends in a perpendicular direction to the axis of the stem.