Method of operating a two-shot injection-molding machine

A method of operating a two-shot injection-molding machine to produce composite brushes each having a set of bristles of a relatively flexible modified rubber with a tendency to cling to a mold cavity during an extended hardening period and further having a handle of a relatively rigid and more rapidly hardening plastic material joined to said set of bristles, comprising the steps of:

• (a) injecting said modified rubber into a first cavity formed at one station of the machine between a primary mold portion and a secondary mold portion juxtaposed with each other, said first cavity including a multiplicity of elongate cells in said primary mold portion and an adjoining clearance in said secondary mold portion to produce a set of bristles integral with a common backing layer;
• (b) retaining said bristles in said cells on said primary mold portion while removing said secondary mold portion therefrom to expose a major surface of said backing layer while letting same cool together with said bristles;
• (c) juxtaposing a tertiary mold portion at another station of the machine with said primary mold portion to form a second cavity bounded by said major surface of the backing layer;
• (d) injecting said relatively rigid plastic material into said second cavity to produce a handle adhering to said backing layer along said major surface;
• (e) allowing said handle to cool with further cooling of said backing layer and said bristles;
• (f) thereafter separating said tertiary mold portion from said primary mold portion;
• and
• (g) gradually pulling said handle away from said primary mold portion at a controlled rate slow enough to maintain the coherence of the entire brush so molded.

A method of operating a two-shot injection-molding machine to produce composite articles each having one part of a relatively flexible modified rubber with a tendency to cling to a mold cavity during an extended hardening period and further having another part of a relatively rigid and more rapidly hardening plastic material adjoining said one part, the machine being provided with a multi-sided turret sequentially rotatable through a plurality of angular positions between two platens which are relatively displaceable in each turret position within a respective molding cycle between a mold-open position and a mold-closed position, comprising the steps of:

• (a) injecting said modified rubber into a first cavity formed in a first angular turret position between a primary mold portion on a side of said turret and a secondary mold portion on one of said platens juxtaposed therewith in a mold-closed position of a first molding cycle thereby producing a first workpiece section;
• (b) retaining said first workpiece section on said primary mold portion while removing said secondary mold portion therefrom in a mold-opening stroke of said first molding cycle to expose a major surface of said first workpiece section;
• (c) letting said first workpiece section cool in a second angular turret position during a second molding cycle concurrently with a duplication of steps (a) and (b) on another turret side;
• (d) juxtaposing a tertiary mold portion on the other of said platens in a mold-closed position of a third molding cycle with said primary mold portion in a third angular turret position to form a second cavity bounded by said major surface of the first workpiece section;
• (e) injecting said relatively rigid plastic material into said second cavity to produce a second workpiece section, adhering to said first workpiece section along said major surface, during the third molding cycle concurrently with a duplication of steps (a) and (b) on a further turret side;
• (f) allowing said second workpiece section to cool with further cooling of said first workpiece section;
• (g) thereafter separating said tertiary mold portion from said primary mold portion in a mold-opening stroke of said third molding cycle;
• and
• (h) gradually pulling said second workpiece section away from said primary mold portion at a controlled rate slow enough to maintain the coherence of the entire workpiece.

A method of operating a two-shot injection-molding machine to produce composite brushes each having a set of bristles of a relatively flexible modified rubber with a tendency to cling to a mold cavity during an extended hardening period and further having a handle of a relatively rigid and more rapidly hardening plastic material joined to said set of bristles, the machine being provided with a multi-sided turret sequentially rotatable through a plurality of angular positions between two platens which are relatively displaceable in each turret position within a respective molding cycle between a mold-open position and a mold-closed position, comprising the steps of:

• (a) injecting said modified rubber into a first cavity formed in a first angular turret position between a primary mold portion on a side of said turret and a secondary mold portion on one of said platens juxtaposed therewith in a mold-closed position of a first molding cycle, said first cavity including a multiplicity of elongate cells in said primary mold portion and an adjoining clearance in said secondary mold portion to produce a set of bristles integral with a common backing layer;
• (b) retaining said bristles in said cells on said primary mold portion while removing said secondary mold portion therefrom in a mold-opening stroke of said first molding cycle to expose a major surface of said backing layer;
• (c) letting said bristles and said backing layer cool in a second angular turret position during a second molding cycle concurrently with a duplication of steps (a) and (b) on another turret side;
• (d) juxtaposing a tertiary mold portion on the other of said platens in a mold-closed position of a third molding cycle with said primary mold portion in a third angular turret position to form a second cavity bounded by said major surface of the backing layer;
• (e) injecting said relatively rigid plastic material into said second cavity to produce a handle, adhering to said backing layer along said major surface, during the third molding cycle concurrently with a duplication of steps (a) and (b) on a further turret side;
• (f) allowing said handle to cool with further cooling of said backing layer and bristles;
• (g) thereafter separating said tertiary mold portion from said primary mold portion in a mold-opening stroke of said third molding cycle;
• and
• (h) gradually pulling said handle away from said primary mold portion at a controlled rate slow enough to maintain the coherence of the entire brush so molded.