MACHINERY | SLITTERS & REWINDERS
Above: Mondon’s
FTW3200-Dual is designed for winding agricultural film
The FTW3200-Dual ensures a constant speed and eliminates the damages of over-tension in the product. Each winder is controlled separately in roll diameter and tension. The equipment includes a global touchscreen for machine supervision.
Better flatness Reifenhäuser says that its Evolution Ultra Flat haul-off system allows the production of films with improved flatness – to ensure better printability and lamination capability. The company says that blown film producers have struggled for years with wave phenomena, and surfaces not being perfectly flat. Stiffer films containing HDPE or PP are particularly affected by these problems – which also often occur in the production of barrier films, said Reifenhäuser. The company says that the secret behind the
Evo Ultra Flat film flattening system is its position within the process: ordinarily, flattening systems have been arranged just in front of the winder. However, Evo Ultra Flat is installed exactly where optimum processing conditions are available for flattening the web – which means upstream, between the haul-off nip roll assembly and turner bar system. This arrangement offers several advantages: the film still has a temperature above 50°C, so is not fully crystallised; stretching the film is easier while it is still flexible; and the process is more energy efficient than similar systems used at the end of the process.
Other benefits include low investment cost, and high functionality and flexibility. Four heating-cool- ing rolls and two nip rolls designed for independ- ent speed and temperature control allow produc- ers to obtain the desired flattening effect. In this way, it is possible to obtain optimum results with different raw materials and film thicknesses. In addition, sagging of the web can be reduced by a targeted control of the rolls. Overall, flatness of lamination and barrier films can be improved by up to 40%, while sagging of the web can be reduced by up to 90%, says the company.
34 FILM & SHEET EXTRUSION | April 2018
Cutting edge Atlas Converting Equipment, a leading supplier of slitter rewinders, says that excessive overlap of the top knife is the most common type of shear knife set-up error. According to Dave Rumson, who has written a series of white papers for Atlas on the subject, there are six significant ways in which excessive overlap can lead to slitting defects and poor finished roll quality: n increased web travel chord; n cut point location change; n wider knife-to-web contact; n increased knife side load contact friction; n longer slit edge knife face rubbing; and n slowing of top knife rotation. In the first of the white papers, Rumson address- es the issue of increased web travel chord. The cut point is where the web meets the top
and bottom knives – which are in contact with each other. To create the cut point, the knives must line up: the bottom of the upper knife must be below the top of the lower knife. To do this, the knife holder overlap stroke is set to the side of the bottom knife, before the 90° knife travel engage- ment stroke is activated. With a tangential web path, a slitting system designer has the top knife contacting the bottom knife very close to the bottom knife apex. It is very important that the web be supported by the bottom knife at the cut point location, says Rumson. “For this reason, the bottom knife should intrude the web to push it slightly above the tangential web path line,” he said. To ensure that this is done properly, the top knife is usually set at an angle to the web path direction (known variously as the shear angle, cant angle, or toe in). The required amount of knife angle misalignment varies according to the material, but is usually 0.25-1.0°. When shear knives fracture the web, one side of
the fracture follows the web path while the other side of the fracture is directed away from the web path by the amount of top knife shear angle. The travel chord is the length the web is in contact with the top knife face – which usually has a bevelled shape. Knife diameters are also important, and will create different web-to-knife contact lengths.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.davis-standard.com �
www.goebel-ims.com �
www.sml.at �
www.mondon.com �
www.reifenhauser.com �
www.atlasconverting.com
www.filmandsheet.com
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