The Magic Milk Bottle

[The Milk Man]

Can anyone help me with this problem? I have a large glass bottle washer in the factory in which I work. The bottles are transported around the machine (upside down) in round metal carriers. As the bottles travel thorugh the machine they are subjected to a variety of treatments to enusre they are clean. After the treatments are complete the bottles enter a spray rinse section which uses a blend of hard and softwater to achive a hardness of around 120ppm. Once the bottles are finished in the rinse section the bottle carriers are turned 180 degrees and we rely upon gravity for the bottles to fall out.

 

If we drift away from this hard/soft water mix of 120ppm the bottles start to hang up inside of the carriers (its almost magic). There is nothing to hold the bottle up. Effectivly we have a standard british glass pint bottle hanging vertically in a metal cylinder. Only one part of the bottle is in contact with the metal tube (remember the metal tube is heavily covered in limescale). If we go to softwater (0-5ppm) the bottles do not fall out and if we go hard (240ppm max) the bottles do not fall out.

 

Can anyone explain what is happening here?

 

A caustic cleaning chemical is used further upstream from the rinse section and a surfactant is added to one of the wash tanks to prevent foaming. The tanks are also heated but the rinse water is at ambient temperature.

 

From what I have read and with limited brainpower I understand the following to be true.

 

The softwater has a low water tension and therefore high adhesive properties and the hard water has high water tension and low adhesive properties.

 

Help?

Edited November 18, 2009 by The Milk Man
spelling

[Spyman]

Well, I hardly know anything about "hard" water or chemicals, but it might be possible that the difference of hard/soft also affects the strength in surface tension of the rinsing water and the small amount of dishwashing liquid that is left in the cylinder from the cleaning process.

 

If the surface tension is strong and there is water left in the cylinder when the carries are turned, then the water could act as an seal between the bottle and the cylinder. When the bottles start to fall out a vacuum builds up in the end of the cylinder, which can be powerful enough to hold the bottles.

 

Magdeburg hemispheres

The Magdeburg hemispheres, around 50 cm (20 inches) in diameter, were designed to demonstrate the vacuum pump that von Guericke had invented. One of them had a tube connection to attach the pump, with a valve to close it off. When the air was sucked out from inside the hemispheres, and the valve was closed, the hose from the pump could be detached, and they were held firmly together by the air pressure of the surrounding atmosphere.

 

The force holding the hemispheres together was equal to the area bounded by the joint between the hemispheres, a circle with a diameter of 50 cm, multiplied by the difference in air pressure between the inside and the outside. It is unclear how good a vacuum von Guericke's pump was able to achieve, but if it was able to evacuate all of the air from the inside, the hemispheres would have been held together with a force of around 20 000 N (4 500 lbf), equivalent to lifting a car or small elephant; a dramatic demonstration of the pressure of the atmosphere.

http://en.wikipedia.org/wiki/Magdeburg_hemispheres

[Mr Skeptic]

Hm, letting your equipment get covered in limescale hardly seems like a good idea. Any strong enough acid will get rid of that. Eg warm vinegar, or fairly dilute HCl.

[Phi for All]

How practical would it be to cut out and glue some blocked surface rubber sheeting circles to the bottom of your carriers? The raised blocks break the surface tension so the bottles won't hang up. The rubber and the glue you use need to withstand the chemicals and the heat.

 

If rubber sheets/glue won't work, perhaps some kind of stainless steel bolt or screw can be added to the base of the carrier to raise the bottle off the base. It just needs to be raised enough to keep the bottles from resting flat against the base.

[SH3RL0CK]

Why not simply insert a stainless steel screen at the end of the tube? Then there will be less surface area contacting the bottle and (hopefully) the bottle will no longer stick in the tube.

[InigoMontoya]

I don't think the OP is looking for solutions. He's already got a working system (it ain't broke, don't fix it). He's just looking for an explanation as to WHY his system works like it works.

[Phi for All]

I don't think the OP is looking for solutions. He's already got a working system (it ain't broke, don't fix it). He's just looking for an explanation as to WHY his system works like it works.

I don't understand why you think an automated system where bottles stick in carriers designed to have them fall out is a "working system" that "ain't broke". The OP's first and last sentences ask for help with this problem.

[StringJunky]

If the bottom of the tubes are flat with no holes, what could be happening is the bottles and water start out hot and as they cool down a vacuum is formed inside the bottle with the water on the bottle rim acting as an air seal

 

If this is the cause then a hole or holes or irregular surface needs to be made in the bottom of the tube to allow equalization ie prevent a vacuum forming in the first place.