Vacuum Packing Machine for Semiconductors

it expands because your vacuum s**ks. Buy a good machine if you want vacuum.

A better description might help, but it sounds as though your observation is the result of an intentional leak in the plastic packaging. When first exposed to the vacuum environment, pressure inside the package is greater than the pressure outside the package and it expands. Further pumping results in low pressure inside and outside. At this point the package should look like it did prior to pumping. After the package is sealed and exposed to atmosphere the outside pressure will be 14.7 psi greater than the inside pressure, and the package will shrink. To test for this theory, puncture a sealed package and see if it expands.

Thanks ,Welderman

Your answer was so meaningful .I got the point.

Apologies for my explanation. I don't want to discuss the vacuum itself but the way you get to it. There are different types of machines, some work with folded foil made of PE or more technical extrusions made of PE and PP, other work with a hose type film. The first type is called a L sealer and has 2 sealing elements - often a flat hot wire covered with a teflon sheet that presses down onto a seat (like a stamp) The first seal has to be made to start and to have 1 side sealed. The machine has a vacuum pump and a pipe reaching towards the material to seal. This pipe goes pretty close to the pack to be sealed, in between the layers of PE. The operator brings down the cover with the hot wires, that are still cold. The vacuum pump sucks as far as you want and within its vacuum range. The cover has a soft rubber that pushes the film around the pipe to minimize the leaks while vacuum is applied. For technical reasons the wires need some distance from the goods, especially when the package is high or thick. The wires, in front of the tube (tube cannot be in the sealed foil section) are heated with electricity (timed) and seal the package in two directions. What you see is the relaxation of the foil, because the cut and seal needed leverage. The hose type works similar but is more difficult because the suction pipe needs a different location ( and this system has loss of foil too) With the L type the excess cut foil stays together, with the foil type the beginning has to be removed if cut. Sometimes and for tight packages the sealed product is sent through an oven with belt. The foils shrinks to a preset value. These systems can reach a close vacuum when a good pump is applied and the time is sufficient. The leak between the pipe and the foil needs to be minimal.