Dr. Anderson's sage advice still rings true today with this flashback to 2003.
The Pros and Cons of Modern Stretching Methods
Screen printers take a variety of approaches to mesh tensioning. Some methods are driven by fast-turnaround demands, others by application requirements. This discussion considers the most used methods for producing screens on both rigid and retensionable frames and highlights the benefits and drawbacks of each. It also suggests how you can combine the best attributes of several stretching techniques to minimize the possibility of tension loss on your printing screens.
Rigid-frame screens (also known as fixed-frame screens) are the most common worldwide. Producing these screens involves stretching the mesh, then attaching it to a rigid frame. With this screen type, any tension loss the mesh experiences after it is attached to the frame is permanent for the life of the screen.
Types of stretching devices Tensioning mesh for rigid frames requires a tensioning system that is independent of the frame. Your choice include mechanical or pneumatic tensioning units that rely on some form of clamp system to grip each side of the mesh. On mechanical systems, mesh tension is typically increased manually with cranks or levers that stretch the screen along two axes. Pneumatic systems also tension mesh along two axes simultaneously. But these systems use pneumatic pistons, rather than operator force, to stretch the screen. The pulling action of the pneumatic clamps may be triggered and controlled by a human operator or completely automated with the use of a computer-based control system.
Mechanical systems tend to be simpler, with fewer moving parts, than pneumatic systems. As a result, they cost less than pneumatic stretchers, but are also less controllable and more dependent on operator skills. Pneumatic systems rely on very accurate pressure controls that allow for consistent and repeatable tension levels. But these features lead to substantially higher price tags for pneumatic units. If your budget allows it, the pneumatic systems are the preferable option.
Number of clamps How tension forces are applied is not the only aspect of stretching equipment to consider. You also have to think about the number of clamps the system uses to attach to the edges of the mesh. The ideal stretching system would pull each mesh thread individually to ensure correct tension. Obviously, physical limitations make this impractical, if not impossible, to achieve with a stretching device. So how many clamps should be used?
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