Duplex Center Rewinding Technology

Duplex Center Differential Rewinding Technology

SP Ultraflex Systems Ltd. manufactures Secondary Slitting and Rewinding Machines of the extensively proven Duplex Center Differential Rewinding type

Types of Secondary Slitting and Rewinding Machines

There are broadly two types of Secondary Slitting and Rewinding Machines, differentiated by the Rewinding techniques employed :

Duplex Center Rewinding
Duplex Center-Surface Rewinding

To understand the above techniques, it is necessary to understand the terms "Duplex", "Center rewinding" and "Surface Rewinding".

The term Duplex Rewinding implies the use of two shafts for Rewinding the slit substrate. This ensures a positive separation between adjacent slit reels, which are wound alternately on the two shafts.

In Center Rewinding, the winding force is derived solely from the rewind shafts and is transmitted to the web through the core and layers of material which have already been rewound. The Rewind shaft is usually driven by a motor.

In Surface Rewinding, the web is driven by the winding drum which is always in contact with the outer layer of the material being rewound. Here, it is the winding drum which is driven, also by a motor in most cases.

As is clear by the above definitions, in the case of Center-Surface Rewinding, the winding force is derived from both the Rewind shaft and the contact with the winding drum. Here, both the Rewind shaft and the winding drum are driven by through a clutch mechanism and motor respectively.

The machines using Center-Surface Rewinding technology are simple in construction with a minimal role of electronics and have offered invaluable service to the Flexible Packaging and Converting industry in its nascent stages.

Center-Surface Rewinding technology was commonly used because of its ability to produce large diameter slit reels tight enough to handle the rigors of transportation to the customer. Since the winding drum is not required to transmit increasing torque with the build up in reel diameter, tightness was achieved without the need for complicated drives and controls.

Limitations of Center-Surface Rewinding Technology

Center-Surface Rewinding technology is not suitable for delicate substrates which can easily get damaged or blocked due to the contact pressure with the winding drum.
It is difficult to overcome problems arising from the differences in adjacent reel diameters due to thickness variations which are very common in most Flexible packaging substrates, especially composite structures / laminates, use of which is on the rise.
• In the Rewind section, the two Rewind shafts are mounted on a pair of levers pivoted on either side of the winding drum and pressured against the drum through pneumatic cylinders. A fall out of this construction is the increased time and effort for changeover between sets.

Over a period of time, center winding evolved to overcome the limitations of center-surface winding by the use of better technology and refinement of the following features :

Advantages of Duplex Center Differential Rewinding Technology over Center-Surface Rewinding

Variable speed motors for the rewind shafts and differential winding to compensate for web thickness variations by allowing each coil to rotate at the rpm suited to its diameter
Automatic Rewind diameter sensing device to provide the feedback necessary to reduce the motor RPM while increasing the differential torque with increasing reel diameter. This provides the range of torque necessary to produce Rewind reels of a large diameter. The provision for taper setting allows the operator to decide the rate at which the torque is increased, depending on the material characteristics
Pneumatically pressured lay on rolls enable the user to produce Rewind reels of the correct tightness by varying the contact pressure. The lay on assembly may be by-passed in case of special applications such as hot melt coated substrates. The possibility of segmented rolls with a separate roll against each coil further improves the edge finish which is very critical in the context of industry standards which are continuously on the rise.
Cantilevered construction of the Rewind shafts, Quick locks / Differential shafts / Laser core positioning, clamping bars and a Pneumatically retractable slide door have drastically reduced the changeover time between sets which is an issue of concern since on a high speed Slitter, about 30 to 50 percent of the Machine time is used up in changeovers.
The vertical arrangement of the two Rewind shafts makes possible various web configurations by changing the position of the Unwind. A careful comparison between the alternate configurations will enable the customer to identify the configuration best suited for the application.

Considering the Technology, Versatility and Configuration options offered by the Duplex Center Differential Rewinding Machine, It is no surprise that these Machines find much wider use for Secondary Slitting and Rewinding applications.