Leak Detection Systems - Extrusion Blow Molding

>> Friday, 1 April 2011

The leading container leak detection systems are manufactured as a complete functional package with self-calibrating microprocessor and adjustable stand-strand conveyor or indexing rotary table. Leak detection systems may be equipped with one or up to four leak detection heads and require specific adjustments depending on the container design and production rate requirements. Most systems are programmable allowing the fill value and inspection time to be tailored and can accommodate a wide range of container sizes. Additional programmable functions allow the inspection cycle to be adjusted to Trimmer speeds or Blow Molding machine cycle time. The systems include an LCD display that indicate accepted and rejected containers in total and accepted containers as a percentage.

Initial adjustment procedures include centering the leak detector nose cone assembly over the opening of the container, adjustment of the relative height of the nose cone assembly on the column stand and adjustment of the conveyor height.

Nose cones have two ports on them. One port is for the fill line and is used to fill the container with air. On certain nose cones, the two ports are different sizes. If the ports are different, the fill line should be connected to the larger of the two ports. The second port is for the sensing line. The sensing line is used to track the pressure in a container during the inspection cycle. This line is connected to the bottom of the control panel, which then goes to the pressure transducer on the printed circuit board.

Set-Up

1. Disconnect the air and turn the power off to the leak detector.
2. Remove the gasket from the nose cone.
3. Extend the cylinder to full stroke.
4. Raise or lower the nose cone assembly, so that the surface of the nose cone just meets the opening of the container.
5. Center the nose cone by moving the arm the desired direction.
6. Reconnect the air and turn the power on.

Note: The printed circuit board uses the input from the photo-eye to start the leak detector. The timing of the nose cone comes from the position of the photo-eye. The photo-eye needs to be positioned so that the nose cone comes down in the center of the container opening.

7. Run some containers past the leak detector. Adjust the photo-eye so when the leak detector is cycled the nose hits the center of the container opening.
8. After the timing is set, switch the leak detector to the maintenance mode. Run a couple of containers through the leak detector. Monitor the four test parameters found in the maintenance mode.

Note: After any adjustments are made, the leak detector should be put into the maintenance mode. The test parameters should be monitored to determine if the chances were correct.
8. After the timing is set, switch the leak detector to the maintenance mode. Run a couple of containers through the leak detector. Monitor the four test parameters found in the maintenance mode.

Note: After any adjustments are made, the leak detector should be put into the maintenance mode. The test parameters should be monitored to determine if the chances were correct.


Sequence Of Operations

The following is the sequence of operations for a Single Head Inline Leak Detector. Special applications may cause slight variations from this description. The steps are as follows:

1. A container enters the leak detection area and breaks the photo-eye beam.
2. After the printed circuit board receives the cycle start input from the photo-eye, the fill and nose cone solenoids will energize. The fill solenoid will stay energized until the starting pressure is reached or the Max. Fill Time has elapsed. The nose cone solenoid will stay energized for the total leak test period.

Note: If the inline system is equipped with an index cylinder it will be programmed slightly different. The cycle start signal will energize the index/brake solenoid first. This is so the index cylinder can extend and stop the container before the nose cone meets the container opening. This output is controlled by a programmable timer and is referred to as the Stop Lead Time. After the index/brake solenoid times out, the fill and nose cone solenoids will energize as stated before.

3. As long as the preprogrammed Fill Value was reached, the leak detector will complete its test cycle. If the Fill Value was not reached, the leak test cycle will be aborted and a No Fill condition will occur. This may be do to a large air leak in the system or a large hole in the container. If no leak can be found, the Max. Fill Time may need to be increased.
4. After the pressure in the container has reached its Fill Value, there is a short delay . This delay is to allow for the valve response and to let the air settle in the container before the leak test takes place. If an air flow is present during the leak test, a false pressure loss will be measured. If this pressure is great enough to make the loss negative, the container will be rejected. This delay is typically set a t .050 msec. And can be increased or decreased to meet the particular needs of the container being leak tested.
5. Next, the microprocessor takes a pressure measurement, waits for a period of time, and then takes another pressure measurement. The period between the two pressure measurements is called the Check Time. This time determines how small of a hole the Leak Detector can detect. The longer the time is between the two measurements means the more air pressure that will be lost. It should be noted that the longer Check Time is, the larger the normal Loss will be on a good container. This is due to system air leakage. If the Check Time is increased significantly, the Initial Average Loss will have to be increased also. The Initial Average Loss should be equal to the average loss of several containers. The difference in PSI between the two pressure measurements is displayed as the Loss. If the Loss is smaller in value than that of the Loss Limit, the container is considered good. This container will then advance, allowing another container to enter the test area. If the Loss is greater than the Loss Limit, the container will be failed. At this point, the eject contact will close and the eject solenoid will be energized. The bad container will be ejected of the conveyor by the means of a blow-off or a pusher. The eject solenoid will stay energized until the Blow-Off Time has elapsed.

Note: The blow-off has to be completed before the next container enters the leak detection area.
The Blow-Off Time should be programmed as short as possible, so that this can be accomplished.

Test Conditions

The leak detector has 3 possible test conditions:

1. PASS (good container) - When the loss of the container being tested is lower than that of the Loss Limit (LMT), the test condition will become pass. The eject contact will stay in its de- energized state.

2. FAIL (bad container) - When the loss of the container being leak tested exceeds the value of the Loss Limit (LMT), the test condition will become a fail. The eject contact will go to its energized state. It will stay energized until the Blow-Off Time has elapsed. The Blow-Off Time can be increased of decreased by the use of a hand held programmer.

3. NO FILL (bad container) - A no fill condition is the same as a fail and the container will be rejected. This condition may be the result of either a large air leak of the absence of a container.

6 komentarze:

Sneha Sharma 27 November 2011 at 21:17  

Thanks for sharing the post!This will prove helpful to us as we here at Bergen Systems provide the clients with helium leak detection system.

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