Richard H. Siderits MD
Christoper Sereni MSIII
Varun Singh - Investigational Pathology Team
Removing bubbles, when you're making blanks to be used for machining plastic parts or casting models from Room Temperature Vulcanization (RTV) silicone rubber is an important step. The bubbles leave behind void spaces that can spoil an otherwise flawless model or part.
A "degassing apparatus" or Vacuum "Desgasser" takes bubbles out of plastic resin or silicone rubber, before it sets. Commercial degassers can be expensive.
This project shows you how to make a small vacuum degassing apparatus for under 20 dollars.
The only thing that you need to use the apparatus is a standard air compressor.
Step 1: Parts List:
1. Plastic container for the vacuum chamber - from the "Dollar Store" (1 dollar).
2. Semi-rigid plastic hose and air-hose connectors - from the local hardware store (4 dollars).
3. Venturi-type vacuum pump* - from Harbor Freight (12 dollars).
4. Hot glue gun.
*Vacuum Pump specifications: A Venturi-type vacuum pump is connected to a compressor to supply the airflow that creates the vacuum.
Note: Air-Vacuum pump: Includes 1/2" ACME (R134a) connector. Vacuum level: 28.3" of mercury at sea level; Air consumption: 4.2 CFM; Air inlet: 1/4 NPT; Overall dimensions: 8-3/8" L x 5" W x 6-1/2" H
Weight: 1.75 lbs.
Step 2: Making the Vacuum Chamber: "Dollar Store Style"
The container that we'll use has to be sturdy enough so that it won't collapse when you pull a vacuum on it (I learned that the hard way) and it needs to be deep enough to hold the mold for the model that you are working with. The container in this image has strong corners, a strong rim and is deep enough to hold the small molds that we want to the pull bubbles out of (de-gas).
The short segment of hose has to be rigid enough so that it won't collapse under the vacuum. The quick connect for the other end is not necessary but you can get it at any hardware store. The threaded end is only threaded on one end, the other end of the connector has a bayonet tip that goes into the tube.
Step 3: Attaching the Vacuum Hose: Drill a Hole in the Side of the Container
Make a hole in the side of the container.
Instead of using a drill, you might consider heating the connector and melting your way through the plastic container. You might also heat the base end of a drill and melt it into the side of the plastic container. This will assure that the nozzle fits snugly.
When you have a hole in the side of the container, screw in the connector and then hot-glue or rubber cement the nozzle in place from the INSIDE.
This fitting has to be air-tight
Step 4: Two Part Plastic Resin Material:
Image 1: Example of two part plastic resin available through Micro-Mark or Room Temperature Vulcanization (RTV) silicone rubber two part mold mixture available from Polytek
Image 2: Example of a flawless, bubble free, plastic blank made by pouring the liquid two part plastic resin into a PVC pipe that the inner surfaces have been coated with a layer of Vaseline for release agent.
Image 3: Here is an example of a two part plastic resin "blank" that was degassed. The blank was then placed on a CNC milling machine to make models of various human hand bones. Most importantly there are no void spaces in the material.
Step 5: Another Good Vacuum Source
This small "Hand-vac" will pull enough of a vacuum to pull the bubbles out of most resins and RTV silicone molds and still costs under 20 dollars. Its also available from Harbor Freight.
Step 6: Disclaimer
Follow all safety guidelines, including but not limited to:
1. Using vacuum systems or compressors.
2. Power-tools that you never read the instructions for.
3. All tools that you never learned to use properly.
4. Anything that heats up, pinches, cuts, squeezes or causes traumatic, caustic or thermal injury.
We are sharing our experience, not telling you to do it.
If you choose to try this, then it is at your own risk!
No really, we're not kidding about this.
Step 7: Project Description
Facility: RWJUHH Exp Division and Center for Parabiotics Research
Section: Special Projects
Application: Part Manufacture for Scientific Apparatus
Technique: Rapid Prototyping in laboratory development
Title: "Making a Venturi Vacuum Degassing System"
Step 8: The End
Good Luck and Be Safe!