Folding carton gluing machines process carton blanks from a die cutter by folding and gluing them into finished folding cartons. At branded goods or pharmaceutical companies, the folding cartons are later erected and filled in automatic packing machines. Many cartons require various folds in and across the machine's running direction before glue is applied. This prepares them for trouble-free erection.

Speed and precision required

Gluing machines reach speeds of more than 700 m/min and can glue well over 40,000 folding boxes per hour, depending on the size of the packaging. "It is therefore no easy task to apply the adhesive in the right place and in the right quantity," explains Marco Ahler, Technical Manager at Baumer hhs.

Baumer hhs systems ensure millimeter-precise gluing without contact with the blank, even at the highest production speeds. The closed system minimizes cleaning and set-up times. It glues continuously from machine standstill to maximum speed without waste. A modular system consisting of a high-pressure adhesive supply, fast-switching and wear-free electromagnetic application valves and a user-friendly control unit that enables application changes at the touch of a button is used for this purpose.

Power like an eight-cylinder

At the heart of this gluing process is the DPP double piston pump. This pump must provide a defined pressure for the adhesive application. The adhesive application is controlled by air pressure. The pump consists of two single-acting piston pumps, each of which only sucks in liquid on the upstroke and displaces it from the glue cylinder on the downstroke. "You could describe it as a two-cylinder engine with the behavior of an eight-cylinder engine," says Ahler with pride.

The air pressure on the input side is converted into a largely fluctuation-free fluid pressure according to the transmission ratio of the feed pump. This allows the delivery rate to be quickly regulated and adjusted. A pressure sensor on the output side of the DPP pump measures the fluid pressure. A closed-loop control of the pump ensures that automatic readjustment takes place if the actual pressure deviates from the set value.

This is particularly advantageous when the fluid is removed discontinuously. Tests show that the spontaneous pressure drop of the DPP pump when opening a tapping valve is 25 to 50 % lower than with a pump with a downstream material pressure regulator and is intercepted significantly faster and more reliably by the control system. In addition: Critical fluids are less stressed and largely retain their original consistency.

Precision with proportional valve

The DPP piston pump regulates the air inlet pressure instead of the fluid pressure and thus sets the desired fluid pressure. The precise proportional pressure control valve VPPM from Festo controls the air volume on the input side. Its large linear pressure control range is between 0.06 and 6 bar. For a feed pump with a transmission ratio of 8:1, this results in a corresponding, safe fluid pressure control range of 8 to 40 bar. The control starts at 2 bar with minimal loss of control quality.

The advantage of regulating the inlet pressure instead of regulating the fluid pressure on the outlet side is that only as much compressed air is used as the current operating conditions require. The compressed air consumption is proportional to the material pressure. This significantly reduces operating costs on average, especially if the maximum delivery pressure is only rarely required. For Baumer hhs, the matter is clear: "Our designer of the double-piston pump, Maren Pyttel, told me that we could make a lot of changes to the design, but the proportional valve from Festo had to remain part of the pump," explains Ahler.