Learn how to use mesh and frame management to streamline changeovers and ensure that screens are always ready when needed.
The diversity of screen sizes, mesh counts, and quantities of frames in the typical shop never ceases to amaze me. Yet, the screenmakers constantly complain that they lack enough frames or they're out of the mesh they need for the jobs on the schedule. It occurred to me this area has not been addressed, and badly needs attention.
To balance the capacity of the screen department, a number of variables need to be considered. These include standardization of mesh counts, selection of frame sizes, determination of minimum and maximum frame-inventory levels, and cycle requirement. Most shops are vaguely aware of these concepts, at least in the back of their minds, but no formal organization has been applied. This month we will have a primer on how these relationships work together so you can check your own situation an determine how efficient your shop is in this area.
Let's start with selection of mesh counts. My experience has been that most printers are using far too many mesh counts. UV printers have it the easiest. They can settle on two or three mesh-count/thread-diameter combinations and be very satisfied. The textile printers will need four or five under most normal conditions.
The most rational approach, and the one that has worked for me, is based on the premise that the mesh must pass ink in a uniform manner and the stencil must be able to maintain a specified level of detail. My goal is to find the relatioship where detail is maintained and ink passes with the least amount of added squeegee pressure. To do this, I balance the percentage of open area and thread diameter.
When you study manufacturers' mesh charts, you'll notice most mesh counts are woven with two, three, or even four different thread diameters. The older designations were S (thinnest diameter) , T (most common diameter for that mesh count) , M (medium diameter for a specific mesh count), and HD (heavy duty, thickest diameter for that mesh count). The thread diameter changes for each designation as the mesh count changes. So a 34-micron thread may be an S designation at 255 threads/in. or a T at 305 threads/in. This is all very confusing and makes little sense from an engineering perspective.
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