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FLEXO Magazine : Maxcess University Special
2 FLEXO FLEXO SUPPLEMENT/MAXCESS UNIVERSITY www.flexomag.com EDUCATION & What does it cost when your web wanders and misaligns, producing bad print registration on your material? Is the end product something you can sell? As a flexo- graphic printer, you will want to control what you can for web lateral position accuracy. Your web, paper or film, needs to be properly aligned prior to entering the first print station. ENTER WEB GUIDING. The most common question suppliers of web guides receive is, "How accurate is your web guide?" There is an equation that web guide manufacturers use to answer this question. More impor- tantly, there are critical elements that you need to know before determining the potential accuracy of your web. Why ask the question? Accuracy for the printer means consis- tency in the lateral web position at the first print station. Actual web guide accuracy is measured at the guide sensor, or the first idler roller, downstream from the sensor. Other variables may influence the web position after it leaves the guide zone. It is not the accuracy in the lab at the guide manufacturer's plant that is important. It is the accuracy on your press, with your operation and your web that counts. CAUSES OF MISALIGNMENT How does the web factor into web-guide accuracy? Leaving aside proper tension control and substrate specific factors, such as surface coefficient of friction, there are two primary characteris- tics of web behavior that influence accuracy: error magnitude and web lateral velocity. Magnitude is the easy component to consider.How far off the desired position is the web as it enters the guide zone? All guides are designed to correct a web that is off-center from either side of centerline. This amount of correction is primarily a factor of the stroke of the guide actuator. On a flexo press, that is typically +/- 1.5 in. to +/- 3 in. If the entering web error magnitude is more than the guide actua- tor stroke, the guide will go as far as it can, but will not be able to fully correct the error. Obviously, it is important to select the guide stroke to match the worst case web-error magnitude. The second important characteristic of the web's error is its lateral velocity. Lateral velocity has three components: 1. The magnitude of the shift. 2. The web length of the lateral shift. 3. The web process speed. Factoring the Web Accuracy of Alignment Means Considering Many Things By Mike Flannigan Calculating lateral velocity. TRAINING
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