Urania

Temperature

The temperature "profile" that a pouch is subjected to as it traverses through the sealing system results in the sealing or fusing together of the poly or poly lined side surfaces of the pouch. The critical components of the profile are temperature of the heating bars, speed at which the pouch travels through the heating bars (belt speed), and force applied to the pouch from the heating bars. The temperature of the heating bars on a Urania sealing system is precisely monitored and controlled using the latest heating control technology. Two loop P.I.D. temperature controllers with auto tuning capabilities are standard. Additional thermocouples (one per heating bar, two total) are installed for use as a manual or automatic monitoring device. Temperature control functionality and programmability is accessible with the H.M.I. on the control panel. This accessibility is protected at important levels with a key switch and/or password combination.

During sealing, heater bar temperature is controlled within a programmable "window." The range of this window is determined by the customer. This determination of an acceptable seal is usually the result of burst or pull strength tests. Once the acceptable temperature window is determined and programmed, any pouch traversing the heater bars will be rejected by belt reversal if the temperature is not within the window.

Force Limits and Alarms

The Urania 3500P and 4000P heat sealers are capable of detecting foreign objects and creases in the seal area. This is accomplished using a specially designed load cell controller and load cell to constantly monitor the force being applied to the heated sealing bars. The force applied to the sealing bars when all conditions are acceptable for sealing, but no pouches are traversing through the sealer, is the "static force."

The high force limit is set in proportion to the total thickness of the pouch material being sealed. This limit is determined by sealing a sample pouch and monitoring the force deviation caused by the pouch traveling through the heating bars. This increase in force is referred to as "delta." For example, if the static force is 6.00 pounds and force increases to 6.30 pounds during sealing, the delta is .30 pounds. A typical set point for high force limit would be 150% of the delta plus the static force value. In this example, that would be 1.5 x .30 + 6.00 = 6.45 pounds.

During proper operation of the sealer, a pouch entering the heater bars would result in a force of 6.30 pounds being exerted on the heater bars. When the pouch exits the heater bar, the force would return to its "static" value of 6.00 pounds.

If a crease occurred in the sealing area, it would be four layers of material and exhibit a force of approximately 6.60 pounds. This would exceed the upper limit of 6.45 pounds and result in a high force alarm and rejection of the offending pouch.

The low (LO) force limit is typically set at .1 pounds below the static force level. Therefore, if the static force is 6.00 pounds, the low force limit should be set at 5.90 pounds. The low force limit is useful in determining a less than normal force applied to the heater bars which may be caused by an open sealer handle or loose or malfunctioning component.

Belt Speed Errors

The sealing belt drive system on the Urania sealers is composed of an inverter duty rated AC motor controlled by a pulse width modulated (PWM) compact inverter. The overall drive speed is monitored and controlled by the PLC. The speed is constantly being monitored and updated to maintain the pre-programmed setting. A speed error will occur if for any reason, the actual monitored speed varies greater than +/- 2% of the set speed. Since speed is a critical factor in maintaining a uniform sealing "profile," variations greater than 2% cannot be tolerated. If a speed error occurs, the sealing belts will reverse and expel the potentially faulty pouch. After the speed has recovered to an acceptable level, depressing the reset button will allow the belts to proceed in the forward direction. Soon after, the chime tone and HMI will notify the operator that it is ready to begin sealing pouches again.