Moulding unit for a plant for blow-moulding plastic containers, particularly bottles
A plant for blow-moulding plastic containers ( 2 ), particularly bottles, from respective parisons ( 3 ) comprises at least one moulding unit ( 15 ) composed of two half-moulds ( 17 a , 17 b ), each mobile relative to the other half-mould ( 17 a , 17 b ) between a position of opening and a position of closing at least two cavities ( 19 ) for blow-moulding containers ( 2 ); the two half-moulds ( 17 a , 17 b ) being oriented in such a way that they close in a closing plane ( 20 ) that is substantially tangent to the feed path (P) of the moulding unit ( 15 ).
1. A moulding unit for a plant for blow-moulding plastic containers ( 2 ), particularly bottles, from respective parisons ( 3 ), the moulding unit being movable along an annular path (P) and comprising two half-moulds ( 17 a , 17 b ) positioned one on the inside and the other on the outside of the path (P), the half-mould ( 17 b ) on the outside being movable about a substantially vertical pivot axis ( 18 ) relative to the half-mould ( 17 a ) on the inside between a position of opening and a position of closing at least two cavities ( 19 ) for blow-moulding respective containers ( 2 );
the two half-moulds ( 17 a , 17 b ) defining a closing plane ( 20 ) that is substantially tangent to the path (P), wherein both half-moulds ( 17 a , 17 b ) are movable away from each other through different angles between respective open and closed positions, the angle of movement of the half-mould ( 17 b ) on the outside towards the outside of the path (P) being greater than the angle of movement of the half-mould ( 17 a ) on the inside towards the inside of the path (P),
wherein the half-mould ( 17 a ) on the inside of the path (P), in the respective open position, is rotated a predetermined angle apart from a position of finished blow moulded articles, inwardly with respect to said closing plane ( 20 ) that is substantially tangent to the path (P).
2. The moulding unit according to claim 1 , comprising a closing element ( 501 ) that is vertically movable between a raised position where it is partly inserted between the half-moulds ( 17 a , 17 b ) in the closed position to form a mould bottom wall, and a lowered position where it does not impinge on the half-moulds ( 17 a , 17 b ) so that the container ( 2 ) can be extracted from the mould after blow-moulding.
3. The moulding unit according to claim 2 , wherein the closing element ( 17 a , 17 b ) comprises an upper portion ( 503 ) shaped in such a way as to impinge on an edge of an opening formed at the bottom of the half-moulds ( 17 a , 17 b ) when they are in the closed position.
4. The moulding unit according to claim 3 , wherein the upper portion ( 503 ) of the closing element ( 501 ) forms an annular surface ( 504 ) shaped to match portions ( 505 ) of the inside surface of the half-moulds ( 17 a , 17 b ), said matching surfaces being designed to hermetically seal the opening at the bottom of the half-moulds ( 17 a , 17 b ) when they are in the closed position.
5. The moulding unit according to claim 4 , wherein said surfaces ( 504 , 505 ) have at least one downwardly converging, tapered portion.
6. The moulding unit according to claim 1 , comprising a mould ( 16 ) defining two moulding cavities ( 19 ).
7. A blow-moulding machine comprising a carousel and a plurality of moulding units associated with the carousel, wherein said moulding units are moulding units according to claim 1 .
8. The moulding unit according to claim 1 , wherein the two half-moulds ( 17 a , 17 b ) have corresponding contact surfaces, said contact surfaces being in contact with each other to define the closing plane in the closing position, wherein the half-mould ( 17 a ) on the inside of the path (P), in the respective open position, has its contact surface rotated inwardly, with respect to the closing plane ( 20 ) tangent to the path (P), of the angle of movement of said half-mould ( 17 a ) on the inside of the path (P), relative to the direction of rotation of the mould along the path (P).
9. The moulding unit according to claim 1 , wherein the moulding unit comprises a vertical shaft defining said pivot axis ( 18 ), and wherein the two half-moulds ( 17 a , 17 b ) have corresponding ends configured to partially embrace said shaft, whereby each one of the two half-moulds ( 17 a , 17 b ) is hinged to said shaft.
10. The moulding unit according to claim 9 , wherein said ends of the two half-moulds ( 17 a , 17 b ) have corresponding fingers embracing the shaft and aligned in an alternating fashion along the vertical length of the shaft.