Ningbo GRJ Precision Investment Casting

• 
  Silica sol investment casting pipe fitting, stainless steel. The picture shows the part after acid wash before machining processes.
• 
  Various stainless steel silica sol investment casting parts made my Ningbo GRJ. The picture shows the parts after acid wash, before machining processes.

Silica Sol Investment Casting Processes in Ningbo GRJ

• 
  Investment casting master die and wax patterns. A set of master die usually comprises two half shell and usually a core to make more complicated casting parts. For short run casting project, the master die is made with aluminum material to save the cost. For long run casting project, the master die is made with steel to endure repeated assembly and disassembly when each wax pattern is produced.
• 
  Pictures of wax pattern and the stainless steel casting parts made with them. The wax pattern are color coded for different performance. For large casting parts, yellow color wax, which is more rigid, is used. For small casting parts, relatively soft green wax is used to make the pattern.

• 
  Wax injection production line: wax patterns are made from these pressure injection machines.
• 
  Wax are injected to the assembled master die, and then the master die is disassembled to take out the wax pattern.

• 
  Multiple wax patterns are assembled through welding to make a wax pattern cluster. This way, multiple casting parts can be formed in a single casting process.
• 
  Close-up picture of a wax pattern cluster with a sprue tree welded, hanging on a rack, ready to be cleaned and coated with silica powder.

• 
  Wax pattern clusters hanging on a rack for easy transportation for further processing
• 
  Water and acid pool that are used to clean the wax patters before coating

• 
  Worker dips wax pattern clusters to a container that filled with mixture of silica sol and zircon powder, to form a thin layer of coating.
• 
  Worker is stuccoing the silica sol coated wax pattern cluster in a container that blows up slurry fine zircon powder, to increase the coating thickness

• 
  A container that store silica sol, a silica acid solution that contains colloid silicon dioxide. It is used as a glue to bond the zircon powder / sand to form the investment casting shell.
• 
  Bags of zircon powder (zirconium silicate) used as the main filler material to form the investment shell for the casting.

• 
  The coated wax pattern cluster is hanging for drying and hardening for 24 - 48 hours before another coating process. Usually a investment casting shell mold will need to be coated for 4 layers to satisfy the needed strength requirement. That means it takes at least 5 to 8 days to made a investment shell mold.
• 
  Coated wax pattern clusters are hanged on rack and stored in a well ventilated climate-control room to let the shell dried and hardened. Record sheet is attached on each rack to record the ready time and number of layers applied.

• 
  Wax pattern clusters that have the third layer of coating applied. Fine zircon powder is applied for the first layer. For the second, third and fourth layer, the grain size of zircon increases. Larger grain zircon provides needed structure support and strength to the investment shell mold. Depending on the size of the casting part, the thickness of the investment shell is usually between 5 to 15 mm.
• 
  Above wax pattern clusters are coated with the 4th layer of zircon sand. The last coating layer application gives the investment casting shell a rough and coarse texture looking because large gain size zircon sand is used to provide the needed support and strength. When completely dried, the shell is ready for lost wax process.

• 
  Once the investment molds are fully cured, they can be put in this furnace to melt out the wax using high temperature steam.
• 
  After after lost wax process, the mold are put into very high temperature oven for a burnout, which remove any moisture and residual wax.

• 
  After burnout, the investment mold is inspected and ready for the melting metal pouring process.
• 
  Temporary storage of investment casting molds

• 
  Induction ovens for melting metal for casting, oven capacity 300kg
• 
  Melting stainless steel is poured into the empty investment mold shell.

• 
  After pouring, the investment mold that filled with melting metal is set on these sand box to allow slow cooling. Once cured, the investment mold shell is hammered to release casting part.
• 
  Investment casting parts attaced on the sprue formed and the mold shell is hammered off. The sprue will be cut off, and the casting parts will be acid washed later.

• 
  Container the evaporate moisture from the used wax.
• 
  Recycled wax is prepared for re-use.

• 
  A spark optical emission spectrometer is used to give on site analysis on the metal material for the casting.
• 
  Samples taken from induction oven for spectrometer analysis. Samples are picked up for each oven on production.

• 
  Yujie hold a large investment casting parts, a stainless valve body.
• 
  Yujie visiting the factory. In the picture are the factory owner Mr. Yuan, production foreman and Yujie