Rosson offers advice on tracking your tension culprit.
I'm often confronted with the question, "What causes screens to lose tension?" While this question appears simple, the answer is not. The truth is that a variety of factors contribute to tension loss. More importantly, several of these factors can occur simultaneously, obscuring the reason for the drop in tension. In the following pages, I'll identify the material and screenmaking problems that most often lead to reduced screen tension and shed some light on how you can anticipate and minimize tension loss on your screens.
Tension loss: Source vs. cause
Low screen tension is a leading reason for poor image quality in screen-printed work. Common problems associated with low-tension screens include improper flooding, poor snap-off during printing, an uneven printed ink film, and image flaws such as smears and loss of detail. Maintaining a high and consistent tension level among screens used on a multicolor job (e.g., process-color work) is also important, otherwise you risk misregistered colors, moiré, mesh marks, and related image defects.
You can trace all screen-tension loss to two primary sources and numerous secondary causes. Note the distinction I've made between the words "source" and "cause." Every printing screen consists of only two principal physical elements: the frame and the mesh fabric. In every case, tension loss stems from one or both of these sources. External factors that lead to weakening or failure of either of these two elements are considered causes.
For example, if a truck ran over your frame, the frame might become too weak to hold screen tension. In this scenario, physical damage to the frame is the cause of tension loss, while the frame itself is the source of the problem.
The most widely used frame material is wood. A well-designed and constructed wood frame will yield an entirely satisfactory print. But wood frames are more likely to cause problems than metal frames.
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