Read on to find out more about the latest technologies available for this screen-printing specialty.
By Harald Gavin
Highly motorized, servo-based screen-printing machines can accommodate automatic format changeovers and provide pre-set parameters to reduce setup times. Innovative solutions are now available to help reduce the time it takes to set up mechanically driven machines as well.
An excenter drive for the screen carriages of a press with rotary indexing table reduces setup times and gives screen printers another feature that improves the press's printing capabilities. Screen carriages of a multicolor high-speed machine are usually driven by gear trains that are linked to the fixtures' rotations. A gear wheel mechanically synchronizes the horizontal speed of its associated screen carriage with the surface speed of the rotating item. When the print job requires a machine setup for a different diameter, then this gear wheel has to be changed at each printing station to be used for the print job.
But now, an excenter drive on a screen-printing machine with a rotary indexing table makes it possible to change the movements of the screen carriages at all printing stations with a single adjustment of the drive (Figure 6). This reduces the time required for changing, saves gear wheels, and removes the limitations of fixed gear ratios. The drive can be adjusted for different item diameters in increments of 0.004 in. If necessary, adjustments can even be made to slightly stretch or compress the printed image.
When the excenter drive is controlled by a servomotor, then the drive can actuate either the screen carriages or the squeegee heads. The screen carriages move when printing onto cylindrical containers; the squeegees move when printing onto square bottles or onto flat sides of oval bottles.
Servomotors significantly shorten changeover times. Each servomotor electronically receives the parameters for the next product, each fixture is moved to the correct angle, and no gear change is required at the printing stations.
The sophistication of servo drives is not visible to operators. A servo-based screen-printing machine is controlled by an industrial programmable controller that is linked to a touchscreen. The screen provides a graphical user interface and intuitive user guidance. During machine setup for a new job, an operator can input item dimensions at the touchscreen or the system can read data from a specifically formatted CAD file. The control system automatically adjusts the print movements for the new item; changing of gear wheels is not required.
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