News

If you are a converter of paper, film, foil, textile or nonwoven webs, you are, most likely, familiar with unwind and rewind stands used in the converting process. There may come a time when you are considering replacing the existing unwind or rewind section of your converting process. This may be because you are looking to increase capacity, improve quality and performance or possibly to accommodate changes to your web. Whatever your motivation, the task of acquiring an unwind or rewind stand to accommodate your requirements may seem overwhelming. You may be asking yourself, where to start.

Budget: Understanding your budget and conveying that information to a potential supplier can save a lot of time. This information is important when considering the type of roll stand and many of the available options, like web guide, core holding, shaft support, tension control and anti-wrinkle requirement.

Double E Group Simple, Cantilevered Unwind Station

Lead time requirement: Most roll stands are custom engineered, designed and manufactured around customer operating specifications. This process may take considerable time, so understanding your requirement for delivery window will, often times, assist with equipment specification. Which leads me to the next bit of information any machinery manufacturer will require.

Double E Group Shafted Unwind Stand

Your operating specifications: This roll stand will most likely be manufactured to unwind or rewind specific size rolls at specific rates into a converting process requiring specific values. The information an equipment manufacturer will require includes these operating specifications:

• Machine - type of converting process
• Material(s) - type of webs to unwound or rewound
• Material thickness range - thinnest to thickest
• Core size
• Maximum roll diameter
• Web width range - narrowest to widest
• Web tension range in pounds per linear inch (PLI) - minimum to maximum
• Running speed range (usually in feet per minute, in the US) - minimum to maximum
• Maximum roll weight

A word about operating specifications: DO NOT over specify range. Price, design and operation will all be dictated by accommodating your operating specifications. Over specifying can lead to overpriced, over complicated and difficult to attain design parameters. Also, keep in mind 0 FPM or 0 PLI are not valid low-end speed and tension specifications.

Does your roll stand require web guide?

Most unwind stands require web a web guide system. There are a couple of ways to web guide unwind stands.

• Move the roll of material as it is being unwound. This type of web guide is more compact and potentially simpler than an intermediate guide system. However, it will induce more stress on your web when moving the roll laterally, during the web guiding operation than an intermediate guide.

Simple Unwind Stand with Roll Shifting Web Guide System
 

• Intermediate guide will move one layer of the web as it is unwound (instead of moving the whole roll of material). This type of web guide system induces the least amount of stress on the web.

Dual Station Unwind Stand with Intermediate Web Guide System

Some rewind applications will benefit with the use of an automatic web guide system.

• Moving the rewind stand laterally is actually considered a chasing operation. Instead of positioning the web where it needs to be - you will chase the rewind to where the web is going, as it is being rewound.
• Intermediate guiding onto the rewind is true web guiding, not chasing.

What type of tension control?

• Manual (really no tension control): This is manual control of a torque output device; brake, clutch or drive. Keep in mind unwind and rewind zone tension is directly affected by roll radius. Tension will change, proportionally to roll radius change as unwind rolls get smaller and rewind rolls build. Torque adjustments will, most likely, need to be completed as the unwind or rewind is running.
• Open loop tension control is an excellent upgrade to manual control. Open loop tension controls will sense roll radius change to adjust a torque output device.
• Closed loop dancer or load-cell control will measure web tension in the unwind or rewind tension zone and will adjust torque output of a brake, clutch or drive, automatically.
• These are the BASICS. Please understand there are whole classes and many documents dedicated to web tension and tension control. This is a white paper discussing the mechanical basics: https://www.converteraccessory.com/whitepages/tcpaper1.pdf

Shaftless roll stands support the core and roll with struts that supply torque to the core and roll from the ends.

Double E Group Shaftless Unwind Technology

Shafted roll stands include a center shaft, usually an air shaft that supports the full core and roll width.

Example of Core Shafts

Double E Group Multi-Station, Shafted Unwind Stand

Double E Group Heavy Duty Shafted Unwind Stand

Consider cantilevered for narrow width:

Double E Group Cantilevered Unwind / Rewind System

These are just some starting points when considering a new, custom engineered and manufactured roll stand for your application. As you discuss your needs with an equipment manufacturer, more information will come to light as available designs and technology are discussed and pondered.

This bi-weekly newsletter is brought to you by Double E Group.

Web Handling & Converting Industry Specialists | Double E Group