Creasing device and corresponding method

Abstract

A creasing device ( 10 ) for a work unit ( 11 ) of a machine ( 12 ) for at least creasing and possibly cutting a sheet made of a relatively rigid material, such as corrugated cardboard for packaging, fed in a determinate work direction (F), comprises a first creasing member ( 32 ) mounted rotatable with its first axis of rotation transverse to the work direction (F). The device ( 10 ) also comprises pre-creasing means ( 41 ) disposed upstream of the first creasing member ( 32 ) in the work direction (F), and configured to carry out a pre-creasing which progressively deforms the material of the sheet to be worked before it is subjected to the creasing operation proper.

1 . A creasing device for a longitudinal work unit of a machine for creasing and possibly cutting a sheet made of a relatively rigid material, such as corrugated cardboard for packaging, fed in a determinate work direction, comprising a first creasing member mounted rotatable with its first axis of rotation transverse to the work direction, wherein it also comprises pre-creasing means disposed upstream of the first creasing member in the work direction, and configured to carry out a pre-creasing which progressively deforms the material of the sheet to be worked before it is subjected to the creasing operation proper, the pre-creasing means being configured to define a lead-in surface inclined toward the first creasing member with respect to the sheet, which is suitable to progressively compress the sheet toward the first creasing member, wherein the lead-in surface is shaped with a profile having a desired geometry, which simulates and on the whole reproduces a segment of a creasing tool of greater sizes than those of the first creasing member. 
     
     
         2 . The device as in  claim 1 , wherein the pre-creasing means comprise a second pre-creasing member upstream of the first creasing member in the work direction. 
     
     
         3 . The device as in  claim 2 , wherein the first creasing member is a first creasing disc and the second pre-creasing member is a second pre-creasing disc. 
     
     
         4 . The device as in  claim 3 , wherein said first creasing disc has a diameter greater than the second pre-creasing disc and the axis of rotation of the first creasing disc is aligned and parallel on the same plane to the axis of rotation of the second pre-creasing disc, at the same height with respect to the lying plane of the sheet which is worked. 
     
     
         5 . The device as in  claim 2 , comprising a support element able to pivot and support both the first creasing member and also the second pre-creasing member, comprising a first portion which supports and pivots the first creasing member and a second portion, extended in the sense upstream of the first creasing member in the work direction, in order to support and pivot the second pre-creasing member. 
     
     
         6 . The device as in  claim 1 , wherein the lead-in surface connects the first creasing member to the second pre-creasing member along a trajectory which is suitable to achieve the desired and progressive linear compression of the material of the sheet. 
     
     
         7 . The device as in  claim 1 , wherein the distance between the axes of rotation of the first creasing member and the second pre-creasing member, together with the ratio between the diameters thereof, is correlated to the desired conformation which is to be obtained for the lead-in surface. 
     
     
         8 . The device as in  claim 1 , wherein the first creasing member and the second pre-creasing member are idle and a transmission element is provided which winds around the first creasing member and the second pre-creasing member, able to rotate following interaction with the advancing sheet, a segment of said transmission element which, gradually rotating, finds itself facing toward the sheet to be worked and comprised between the first creasing member and the second pre-creasing member, achieving said lead-in surface. 
     
     
         9 . The device as in  claim 1 , wherein the first creasing member and the second pre-creasing member are motorized independently, said lead-in surface being formed by an element shaped with a desired shape to determine the progressive pre-creasing effect, disposed fixed between the first creasing member and the second pre-creasing member on the side which faces onto the sheet to be worked. 
     
     
         10 . A machine for at least creasing and possibly cutting a sheet made of a relatively rigid material, such as corrugated cardboard for packaging, comprising a creasing device as in  claim 1 . 
     
     
         11 . A method for creasing a sheet made of a relatively rigid material, such as corrugated cardboard for packaging, wherein the method provides to carry out a pre-creasing operation which progressively deforms the material of the sheet to be worked, before it is subjected to the creasing operation proper, using pre-creasing means to define a lead-in surface inclined with respect to the sheet toward a creasing member used for creasing, the lead-in surface progressively compressing the sheet toward the first creasing member, wherein the lead-in surface is shaped with a profile having a desired geometry, which simulates and on the whole reproduces a segment of a creasing tool of greater sizes than those of the creasing member.