The casting of valve body is an important part of valve manufacturing process, and the quality of valve casting determines the quality of valve. The following introduces several common casting methods in valve industry:
Sand casting:
Sand mold casting commonly used in valve industry can be divided into wet sand, dry sand, sodium silicate sand and furan resin self hardening sand according to different binders.
(1) Green sand is a molding process with bentonite as binder.
Its characteristics are: the sand mold does not need to be dried, does not need to be hardened, the sand mold has a certain wet strength, the sand core and shell have good resiliency, which is convenient for the cleaning of casting. High efficiency of molding production, short production cycle, low material cost, easy to organize assembly line production.
Its disadvantages are: the casting is easy to produce defects such as porosity, sand inclusion and sand sticking, and the quality of the casting, especially the internal quality, is not ideal.
The ratio and properties of green sand for steel castings are as follows:
| Serial number | mixture ratio% | performance | purpose | ||||||||
| New sand | Old sand | Bentonite | sodium carbonate | dextrin | pulp | water content
% |
Air permeability
AFS |
Wet compression strength
KPa |
|||
| Grain size group | Amount added | ||||||||||
| 1 | 10 | 100 | 9/11 | 0.2 | 0.2/0.4 | 3.8/4.3 | 100/200 | 56/77 | Sand for small steel castings | ||
| 2 | 15 | 50 | 50 | 3 | 0.4 | 0.6/1.2 | 4/4.7 | 100 | 50/75 | Sand for machine molding | |
(2) Dry molding sand is a molding process with clay as binder. Adding a little bentonite can improve its wet strength.
Its characteristics are: the sand mold needs to be dried, it has good air permeability, it is not easy to produce defects such as sand washing, sand sticking and air holes, and the internal quality of the casting is good.
Its disadvantages are: the need for sand drying equipment, production cycle is long.
Post time: Feb-03-2021
