Showing posts with label vacuum. Show all posts
Showing posts with label vacuum. Show all posts

Monday, April 16, 2018

Vacuum Forming

So illustrating the power of vacuum in the previous post, the two pictures of the crushed rail tanker show the negative effects of such power but there are also many positive uses for vacuum as well. I mentioned woodworking glue-ups before. This application is more suited to industrial applications, with large glue-up assemblies, using large industrial vacuum systems. I have seen small shops set up for this but, it is less common.

More common for the home hobbyist is plastic vacuum forming, especially for the model maker, though a large variety of items can be produced. I have two books on plastic vacuum forming, both written for the home hobbyist.

The first "A Plastic Vacuum Forming Machine" is the more advanced of the two and will take you through a complete build of a advanced machine capable of large work. Written and built by Vincent Gingery in 1999, it follows in the footsteps of his other well documented builds.



Heres a picture of one successful builders machine.


The second book "Do It Yourself Vacuum Forming" is much lower tech. and aimed at the novice interested in making model parts and other small items. No large expense here, Douglas Walsh the author, shows you how to set up with common items at low expense. Written in 1990 you will find easy clear instructions.





A Short Primer On Vacuum

Most processes operate on the principle of pressure, steam, air, hydraulics, IC engines and even explosives. This results in vacuum being a less understood concept. Air has volume and because of gravity has weight. The total weight of air from the earths surface to the edge of space acting on the earths surface at sea level is 14.7 psi (pounds per square inch). A press. gauge calibrated to 0, in the vacuum of space, when brought to earth would read 14.7 psi. Ok so thats easy. The important number here is 14.7 psi that is the maximum amount of press that can be exerted on the exterior surface of a vessel that has been evacuated to a perfect vacuum. Doesn't sound like much right. As in the example below a 3"X 4.5" pop can, has a surface area of around 56.5 sq. in. X 14.7 psi = 830.5 . So if you evacuate the air from the can, or condense the steam as the case may be, thats 830.5 lbs. acting on the surface of that can to crush it. In real life it will be a bit less since perfect vacuums are harder to develop but thats still an awesome amount of power exerted by nothing more than the weight of air.

I could go on but thats the basics. Vacuum has and is being used to do work. As shown below, the earliest steam engines operated on the principles of vacuum not press, and vacuum is often used as a  clamp for glued assemblies. When overlooked, vacuum has also caused much damage as pictured in the second example below.

As an operating engineer my background is right but I always did better doing than teaching so here is a excerpt from "Mechanical Movements" on the early development of the steam pumping engine using vacuum.



And here is an example of what can happen if you don't understand or disregard vacuum and how it is developed. Pictures and commentary are on the Metalworking.com Drop Box Files site.