 The cartridges for fountain pens or ball point pens are filled in an automatic production process. Automatic filling requires a metering pump that can be controlled parallel to the machine operating cycle. Metering is required in short bursts and it must also be possible to flexibly adjust the stroke volume corresponding to the size of the receptacle to be filled. A critical point is the response time between the control signals at the pump and execution of the metering stroke. The task is to meter a precisely predefined quantity of coloured ink within 0.5 seconds. If metering does not take place within this timeframe, the component to be filled will no longer be in the correct position and the metered medium will not land in but rather next to the cartridge.
Mr. Rummer, product manager of ProMinent Dosiertechnik explains: "It all depends on providing the required quantity of ink in one stroke at the right time. For this purpose, it is necessary to correspondingly adapt the pressure stroke interval. This can be easily realised with the delta diaphragm metering pump. The controlled solenoid drive optoDrive® makes it possible to correspondingly vary the metering stroke and the outlet speed of the liquid at the injection point. Since our delta® pump can execute complete individual strokes, it is the ideal pump for filling and single-drop metering applications.
Depending on the type of pump, the stroke volume can be adjusted to between 0.2 and 4 ml. Even the smallest vessels can be filled with low viscosity media without spillage."
Controlled in sync with the machine operating cycle
ProMinent has perfected the process for filling felt pens and ink cartridges in cooperation with a special machine construction company in Winterbach, Germany. Robot-controlled filling needles that are moved by means of steel cables are used in the automatic filling process. The ink is injected simultaneously as the needle penetrates into the ink cartridge. The metering stroke starts on receiving the signal from the position sensor. The metering stroke time during cyclic operation is adapted by means of the stroke frequency of the pump to the penetration time of the filling needle. The penetration time corresponds to the pressure stroke interval and amounts 0.5 seconds for ink cartridges. A time of 0.1 second is required for the intake stroke. The sum of the intake stroke and the pressure stroke results in a clock cycle time of 0.6 seconds. Process specialists therefore set 100 strokes per minute for this application, thus achieving a pressure stroke interval of 0.5 seconds.
Summing up
Filling procedures that are performed in the "conventional" way, e.g. with stainless steel piston delivery units, are relatively inflexible, intricate and expensive. The use of the delta diaphragm metering pump with controlled magnetic drive makes it possible to achieve precision metering controlled in sync with the machine operating cycle. Without the need for additional accessories, fully automatic filling procedures can be executed cleanly, reliably and precisely while largely rendering additional operations to eliminate drips superfluous. |