1. SCOPE
This manual outlines the components, safety information, recommended maintenance for LACO Technologies Vacuum Degassing Systems.
Following these recommended procedures will ensure that your degassing system is performing at its highest level. This manual also
includes product information for degassing systems, including accessories, options, and spare parts.
1.1 MAKEUP OF A DEGASSING SYSTEM
A typical vacuum degassing systems includes a vacuum chamber connected to a vacuum pump for removing trapped gases from
compounds. With the appropriate vacuum pump degas chambers are used to reduce the pressure above the surface of the material and
permit escape and subsequent removal of entrapped air and other gases that could induce failure of the fi nal product. Degas chambers and
pumps are available with several options and accessories for a complete vacuum degas system to meet your requirements.
2. SAFETY
2.1 VACUUM PUMP SAFETY
A complete manual will be provided for the vacuum pump and should be referred to for safety issues relating to the specifi c vacuum pump
purchased.
2.2 VACUUM CHAMBER SAFETY
All degassing chambers are designed for holding full vacuum, but any defects, cracks or severe wear should be reported to LACO for
advisement. Vacuum chambers are not designed for pressure applications. If slight pressure is needed (5 psi or less) the chamber must be
provided with necessary clamps and pressure safety relief valves.
3. COMPONENTS
A vacuum degassing system comprises of two main items; a vacuum chamber and vacuum pump. Several accessories and options can be
added to customize the degassing system. Systems are available in modular confi gurations or as complete setups mounted onto carts or
stands.
3.1 VACUUM CHAMBERS
The most common vacuum degassing chamber is a cylindrical vessel, fi tted with a vacuum control valve, vacuum release valve, vacuum
dial gauge, “L” type gasket and a clear acrylic or metal lid.
The cost of cylindrical vacuum chambers tend to increase far more with increases in diameter than length. Horizontal chambers will also be
more than corresponding vertical chamber due to the need for cradle supports and lid hinging. This orientation is preferred if the product is
easier to load and monitor. A common option for horizontal chambers include shelf support rails and removable shelves. Vacuum degas
chambers are most commonly made from 304 stainless steel however LACO off ers vertical chambers also in aluminum and clear acrylic for
full viewing.
To select a chamber for your purpose, ensure that your container will fit into the chamber with suffi cient space to allow for expansion of the
liquid to be degassed. Initially, fi ll your container one quarter with mixture, experience will show the limit of mixture level permissible.
3.2 VACUUM PUMP AND HOSE
Based on the application the vacuum pump can be the greatest cost and the most critical component for successful degassing. Choices range
from dry membrane pumps capable of vacuum levels down to 60 Torr or 27 inHG for single stage models and 7 Torr or 29 inHG for two
stage models.
These dry pumps have pumping speeds or cfm values ranging from 1 to7 cfm. For higher vacuum levels and cfm values, oil sealed rotary
vane vacuum pumps are used. Single stage models are capable of vacuum down to 0.5 Torr and cfm from 1 to 100 cfm. Two stage models
are capable of vacuum down to 0.005 Torr or 5 millitorr and range in cfm from 2 to 50 cfm.
When selecting a pump it is necessary fully degas the mixture before it even begins to gel or set. Knowing the pot life of the material will
help in selecting the right speed or cfm of pump. The manufacturer of the material may recommend a vacuum level based on the properties
of the material. If you are unsure of the vacuum level requirement it is always easier to have more vacuum than less.
3.3 COMMON ACCESSORIES
Vacuum traps protect the vacuum pump from contaminates during thedegassing process and also prevent backstreaming of pump oil into
the vacuum lines or chamber.
Digital vacuum gauges with units in torr or millitorr to accurately monitor and repeat the process at the same vacuum level.
Chamber mixers with rotary shaft feedthroughs
Chamber internal platen heaters
Heating blankets can be fi tted around the vacuum chamber to achieve higher wall temperatures. Heaters are NOT suitable for use with
clear acrylic doors.
Electrical and thermocouple feedthroughs
Liquid feedthroughs and valves
4. BASIC
OPERATION
Degassing of a liquid mixture is the removal of air bubbles which become entrapped in the mixture when mixing the components. See
Appendix A for a complete discussion on vacuum degassing. The following is a quick review of procedures for removal of air bubbles from
resin mixes, RTV silicone and similar liquids.
1. Close the vacuum valve connected to the vacuum pump and switch the vacuum pump ON and allow to warm up.
2. Open the vacuum release or vent valve and remove the chamber lid.
3. Mix the materials to be degassed in a suitable container not more that
1/3 to 1/2 full and place this container in the chamber.
4. Replace the lid, making sure it fully covers the gasket on the vacuum chamber.
5. Close the vacuum release valve.
6. Open the vacuum valve.
7. Watch the mixture and the vacuum gauge. When the chamber is undergoing the evacuation the mixture will begin to rise, slowly at first.
At nearly full vacuum the mixture will have swollen up to fi ll themixing vessel, air bubbles will appear and burst at the mixture surface.
After a few seconds, this mixture will collapse to near its originalvolume. Occasional bubbles will appear at the surface.
8. If the mixture rises too fast and is likely to overfl ow the container thenmomentarily reduce the vacuum by opening and closing the
vacuum release valve or closing the vacuum valve. Repeat if necessary.
9. Wait for about 30 seconds after the collapse and close the vacuum valve.
(NOTE One can also monitor the time and vacuum level on the vacuum gauge as well as the material, to determine the length of time to
hold it under vacuum. The length of time to degas is highly dependent on the product and the particular application. Often an absolute
pressure vacuum gauge is used to monitor the vacuum level of the system and determine if gases or solvents are evolving from the product.
The vacuum chambers are equipped with a relative 0-30 in HG vacuum gauge, which is mainly used to determine a rough vacuum level.
For more accurate measurement and control of the process, contact LACO about an absolute vacuum gauge.)
10. Open the vacuum release valve and remove the lid.
11. Fill the mold(s) carefully to minimize trapped air.
12. If necessary, place the mold(s) into the vacuum chamber.
13. Repeat stages above as necessary.
14. Some bubble may appear at the mixture surface and burst.
15. Continue degassing for about 30 seconds at full vacuum.
16. Repeat steps 10, 11, 12.
