This guide focuses on frame systems and procedures for affixing screen mesh to the frames and discusses the benefits and drawbacks of each.
Drawbar frames have several configurations for locking the fabric into the frame. One is a stretch-and-glue version, but most consist of either one to two plastic rods or a metal bar that slide into grooves or channels on the frame sides and lock the mesh in place. Which configuration to use depends mainly personal preference, but also on the mesh type and thread count you use. For instance, printers working with stainless-steel mesh tend to use the single plastic rod or metal bar locking mechanisms as opposed to the two-rod systems since these meshes are stiffer and the single-component locking systems are easier to work with. Locking the fabric in the frame uniformly is fairly critical to ensure a consistent stretch with drawbar systems.
The act of stretching screens on a drawbar frame usually consists of either turning a series of bolts along the side of the frame or using a special tool on the corners to draw the bar back mechanically. In the first scenario, depending on how much you turn each individual bolt along the frame, you can influence the fabric in that general area to compensate for any inconsistencies in the way the mesh was loaded. In the second situation, the construction of the frame may cause issues because as you tension the mesh, the dimensions of the frame will increase. This is not a problem in some applications, but it’s something to keep in mind if you’re considering this frame type.
Roller frames are clearly the most popular of the retensionable frames. Once again, some skill is required to use these frames, but once they are mastered, roller frames provide a quick and easy method of making a screen. The principle behind the roller frame is that the fabric is locked in the frame with either a plastic strip or two round plastic rods. Then the rollers are turned away from each other to increase the tension. Just like the drawbar frame, the fabric can be retensioned to a degree to compensate for tension lost during printing. Also, pneumatic tensioning systems are offered for roller frames to simplify tensioning even more.
With all retensionable frames, you have to take care when reclaiming and handling due to the fact that there are many pockets in which cleaning chemicals can collect, only to drip out at the worst possible time. The other common issue with these frames is that oily reclaimers and ink washes tend to get trapped in the locking channels and can sometimes lead to the fabric slipping out of the channels. Liquids also can leak into the hollow tubes. This problem is quite common when using a dip tank in the screen-cleaning area. Everything works fine until the frame is placed under vacuum in the exposure unit, which causes chemicals trapped inside the tubes to be pulled out and across the screen, ruining the emulsion.
Did you enjoy this article? Click here to subscribe to the magazine.