Multi-cavity mold with a knife pressure-box for a thermoforming machine used in the process of high-volume, continuous thermoforming of thin-gauge plastic products

Abstract

A multi-cavity mould (1) comprising:—an upper tool (11) and a lower tool (12) arranged in a cooperating manner; characterized in that the upper tool (11) comprises a knife pressure box (13) comprising:—a horizontal top plate (131);—first and second end plates (132) and first and second side plates (133) extending orthogonally downwardly from a lower surface of the plate (131); the plates (132, 133) are connected such that the plate (131) and the plates (132, 133) form a downwardly open rectangular parallelepiped enclosure; the plates (132, 133) are made from tool steel with a thickness (t) from 6.35-10 mm and a cutting surface (130) defined along an orthogonally downwardly projecting end of plates (132, 133) wherein—the surface (130) has a substantially V-shaped profile comprising a micro flat face (M) with a width from 0.02-0.1 mm and is positioned such that when the pressure box (13) is pressed against the sheet (3), the surface (130) partially penetrates the sheet (3) in order to form a seal around the pressure box (13) by pressing a zone of the sheet (3) which was partially trimmed and situated inside the enclosure against the surface (130).

1 . A multi-cavity mould ( 1 ) for a thermoforming machine used in the process of high-volume, continuous thermoforming of a plurality of thin-gauge plastic products ( 2 ) from a preheated thin-gauge thermoplastic sheet ( 3 ) comprising:
 an upper tool ( 11 ) and a lower tool ( 12 ) arranged in a cooperating manner; the lower tool ( 12 ) comprising:
 a plurality of cavities ( 8 ) for receiving cavity moulds ( 8 ′) and 
 a plurality of base plates ( 91 ) from which a plurality of supporting blocks ( 92 ) extend perpendicularly over a predetermined total height (a), situated between adjacent cavities ( 8 ) and 
   the upper tool ( 11 ) comprising:
 a top base plate ( 4 ) and 
 a plurality of plug moulds ( 5 ) arranged in an x-z array and connected in a translational manner to said top base plate ( 4 ) by means of driving rods ( 6 ) such that said plug moulds ( 5 ) are movable in a direction (y) perpendicular to a transport direction (x) of said preheated thin-gauge thermoplastic sheet ( 3 ) 
   
       characterized in that 
       said upper tool ( 11 ) further comprises a knife pressure box ( 13 ) comprising:
 a horizontal top plate ( 131 ) connected to said top base plate ( 4 ); 
 first and second vertical end plates ( 132 ) extending orthogonally downwardly from a lower surface of said horizontal top plate ( 131 ), 
 first and second vertical side plates ( 133 ) extending orthogonally downwardly from said lower surface of said horizontal top plate ( 131 ) wherein 
 
       the first and second end plates ( 132 ) and the first and second side plates ( 133 ) are connected such that the horizontal top plate ( 131 ), the first and second end plates ( 132 ) and the first and second side plates ( 133 ) form a downwardly open rectangular parallelepiped enclosure; 
       the first and second end plates ( 132 ) and the first and second side plates ( 133 ) are made from tool steel with a thickness (t) measured from 6.35 mm to 10 mm and have a cutting surface ( 130 ) defined along an orthogonally downwardly projecting end of said end and side plates ( 132 ,  133 ) wherein
 said cutting surface ( 130 ) has a substantially V-shaped profile comprising a micro flat face (M) with a width from 0.02 mm to 0.1 mm and is positioned such that when said knife pressure box ( 13 ) is pressed against the preheated thin-gauge thermoplastic sheet ( 3 ), the cutting surface ( 130 ) partially penetrates the preheated thin-gauge thermoplastic sheet ( 3 ) in order to form a seal around the knife pressure box ( 13 ) by pressing a zone of said thermoplastic sheet ( 3 ) which was partially trimmed and which is situated inside the rectangular parallelepiped enclosure against the cutting surface ( 130 ). 
 
     
     
         2 . A multi-cavity mould ( 1 ) according to  claim 1 , wherein each supporting block ( 92 ) which is situated below said cutting surface ( 130 ) of said end and side plates ( 132 ,  133 ) has a top zone ( 92   d ) made from hardened tool steel. 
     
     
         3 . A multi-cavity mould ( 1 ) according to  claim 1 , wherein said cutting surface ( 130 ) further comprises:
 an interior primary face (P 1 ) which forms a first cutting angle (δ) with a plane perpendicular to said horizontal top plate ( 131 ), measuring from 10° to 35°;   an exterior primary face (P 2 ) which forms a second cutting angle (γ) with a plane perpendicular to said horizontal top plate ( 131 ), measuring from 25° to 60° wherein each of said primary faces (P 1 , P 2 ) extend upwardly towards said horizontal top plate ( 131 ) from one longitudinal end edge of said micro flat face (M);   an interior secondary face (S 1 ) which forms a third cutting angle (α) with a plane perpendicular to said horizontal top plate ( 131 ), measuring from 0° to 10°;   an exterior secondary face (S 2 ) which forms a fourth cutting angle (β) with a plane perpendicular to said horizontal top plate ( 131 ), measuring from 15° to 35° and complying with the following condition:   
       when α=0°, β measures from 25° to 35° and 
       wherein each of said secondary faces (S 1 , S 2 ) extend upwardly towards said horizontal top plate ( 131 ) in continuation of said corresponding primary faces (P 1 , P 2 ). 
     
     
         4 . A multi-cavity mould ( 1 ) according to  claim 1  wherein the first and second end plates ( 132 ) and the first and second side plates ( 133 ) have an equal thickness (t). 
     
     
         5 . A multi-cavity mould ( 1 ) according to  claim 1 , wherein the first and second end plates ( 132 ) and the first and second side plates ( 133 ) are made from the same material, a high Carbon, high chromium cold work tool steel. 
     
     
         6 . A multi-cavity mould ( 1 ) according to  claim 2 , wherein said top zone ( 92   d ) of each supporting block ( 92 ) which is situated below said cutting surface ( 130 ) is made from a high Carbon, high chromium cold work tool steel. 
     
     
         7 . A multi-cavity mould ( 1 ) according to  claim 1 , wherein said horizontal top plate ( 131 ) is made from a medium carbon steel. 
     
     
         8 . A multi-cavity mould ( 1 ) according to  claim 2  wherein each supporting block ( 92 ) which is situated below said cutting surface ( 130 ) has a reduced width such that a distance measured between an exterior contour of the top zone ( 92   d ) of said supporting blocks ( 92 ) situated below said cutting surface ( 130 ) and an adjacent thermoformed product's trim contour is from 7.5 mm to 7.8 mm. 
     
     
         9 . A multi-cavity mould ( 1 ) according to  claim 1  wherein said cutting surface ( 130 ) is positioned such that during use it partially penetrates said preheated thin-gauge thermoplastic sheet ( 3 ) at a distance measured between said micro flat face (M) and an adjacent thermoformed product's trim contour from about 0.8 mm to 2 mm. 
     
     
         10 . A multi-cavity mould ( 1 ) according to  claim 1  wherein the first and second end plates ( 132 ) and the first and second side plates ( 133 ) are connected to the horizontal top plate ( 131 ) by fastening means ( 14 ). 
     
     
         11 . A multi-cavity mould ( 1 ) according to  claim 1  wherein said horizontal top plate ( 131 ) comprises a plurality of window cut-outs ( 51 ) arranged in an x-z array, said window cut-outs ( 51 ) being dimensioned and positioned such as, during use, each plug mould ( 5 ) of the plurality of plug moulds ( 5 ) passes through a corresponding window cut-out ( 51 ) of the plurality of window cut-outs ( 51 ). 
     
     
         12 . A multi-cavity mould ( 1 ) according to  claim 1 , wherein the upper tool ( 11 ) and the lower tool ( 12 ) are being operable to simultaneously form a plurality of thin-gauge plastic products ( 2 ) in corresponding cavity moulds ( 8 ′) arranged inside the cavities ( 8 ) of said lower tool ( 12 ) in an x-z array and wherein each of said supporting block ( 92 ) has a stepped profile comprising a first ( 92   a ), a second ( 92   b ), a third ( 92   c ) substantially rectangular shaped zones in a vertical cross section and said top zone ( 92   d ) having a substantially isosceles trapezoid shape in a vertical cross section with a common symmetry axis in a vertical cross section through a plane perpendicular to said base plate ( 91 ) wherein:
 said first zone ( 92   a ) extends perpendicularly from said base plate ( 91 ) over a distance (al) calculated as 17-50% of the total height (a) of said supporting block ( 92 ) and the width of the first zone ( 92   a ) is calculated as 24-60% of the total height (a) of said supporting block ( 92 ); 
 said second zone ( 92   b ) extends in continuation of said first zone ( 92   a ) over a distance (a 2 ) calculated as 45-65% of the total height (a) of said supporting block ( 92 ) and the width of the second zone ( 92   b ) is calculated as 7-16% of the total height (a) of said supporting block ( 92 ); 
 said third zone ( 92   c ) extends in continuation of said second zone ( 92   b ) over a distance (a 3 ) calculated as 9-12% of the total height (a) of said supporting block ( 92 ) and the width of the third zone ( 92   c ) is calculated as 5-10% of the total height (a) of said supporting block ( 92 ); 
 said substantially isosceles trapezoid shaped top zone ( 92   d ) extends in continuation of said third zone ( 92   c ) over a distance (a 4 ) calculated as 9-12% of the total height (a) of said supporting block ( 92 ), wherein the top zone ( 92   d ) has a bottom base in contact with and having the same width as the third zone ( 92   c ), a top base and two legs of equal length between the top and bottom bases and the width of the top base of said top zone ( 92   d ) is calculated as 2.5-5% of the total height (a) of said supporting block ( 92 ) and preferably both acute base angles of said top zone ( 92   d ) measure about 75° to about 89° and 
 
       wherein in said lower tool ( 12 ):
 the legs and top base of said top zone ( 92   d ) are spaced apart from a top part of adjacent cavity moulds ( 8 ′) at predetermined distances (d 1 , d 2 ) and 
 top rims of two adjacent cavity moulds ( 8 ′) extend over a part of the top base of the top zone ( 92   d ) of the supporting block ( 92 ) situated between them, leaving a middle portion of the top base uncovered, with a width (D) of about 1.5 mm to about 6 mm. 
 
     
     
         13 . A multi-cavity mould ( 1 ) according to  claim 12  wherein said width (D) of the middle portion is about 2 to 4 mm. 
     
     
         14 . A Form/Cut/Stack thermoforming apparatus comprising a multi-cavity mould ( 1 ) according to  claim 12  as a forming station wherein said substantially isosceles trapezoid shaped top zone ( 92   d ) and said third zone ( 92   c ) corresponding to each supporting block ( 92 ) which is situated below and inside the periphery of said rectangular parallelepiped enclosure are made from the same material, preferably an Aluminum alloy.