The Vacuum Molding or V-Process
V-process molding takes advantage of an abundantly available, totally reliable and almost free natural phenomenon to bind molding sand in place… Atmospheric Pressure!
With V-process molding you eliminate many of the costs and problems associated with conventional green sand and no-bake molding.
Because the V-Process uses clean, dry unbonded sand, you can forget about mullers and mixers, and costly sand reclamation and reconditioning equipment. Most V-Process users require only sand cooling and transportation, dust collection and simple screening to remove tramp metals.
Molding equipment is simple too. It can be limited to as few as five items (a vacuum system, Film heater, vibrating table, pattern carrier and flasks) or automated for higher production. There is no need for heavy, noisy jolt squeeze equipment, ramming of slingers.
The molding media is clean and dry therefore shakeout equipment is usually nothing more than a grate to allow the sand to flow away from the casting and back into the sand system. Fume and odor control is unnecessary in most applications.
Low operating cost
You not only save on the cost of sand binders but all of the cost of sand mixing, testing and disposal/ reclamation. Even pattern life is extended because the sand never touches the pattern and it is never subjected to the rigors of a conventional molding machine. Finally, V-Process produces castings with fewer imperfections and less scrap.
Any shape or size can be produced in a V-Process mold, from thin walls to thick sections, or from castings weighing ounces to several tons. Sand thermal conductivity is lower and metal fluidity is improved. Solidification time is slower. In addition, zero draft designs are common, and can reduce clean up and rough machining operations. Fine surface finish and excellent dimensional accuracy are two if the key advantages of V-Process.
The V-Process Stages
1. Pattern (with vent holes) is placed on hollow carrier plate. A heater softens the .002″ or .005″ plastic film. Plastic had good elasticity and high plastic deformation ratio.
2. Softened film drapes over the pattern with 200 to 400 mm Hg vacuum acting through the pattern vents to draw it tightly around the pattern.
3. Flask is placed on the film-coated pattern. Flask walls are also a vacuum chamber with outlet shown at right.
4. Flask is filled with dry unbonded sand. Slight vibration compacts sand to maximum bulk density.
5. Sprue cup is formed and the mold surface leveled. The back of the mold is covered with unheaded plastic film.
6. Vacuum is applied to the flask. Atmospheric pressure then hardens the sand. When the vacuum is released on the pattern carrier plate, the mold strips easily.
7. Cope and drag assembly form a plastic lined cavity. During pouring, molds are kept under vacuum.
8. After cooling the vacuum is released and free-flowing sand drops away leaving a clean casting, with no sand lumps. Sand is cooled to re-use.
- Simplified sand control
- No sand reclamation
- No sand mixing
- No waste sand removal
- Inexpensive patterns
- Complete mold venting
- Reduced noise level
- Better general environment
- Reduced cleaning costs
- Reduced smoke and fumes
- Lower sand cost
- No shakeout
- No sand lumps
- Better finish on castings
- Better dimensional accuracy
- Less energy consumption
- Reduced pattern maintenance