Lost wax casting now known precision investment casting precision casting , cutting or no cutting is a precision casting process less precision casting industry is a superior technology, which is widely used that it applies not only to the high melting point metal various alloy precision casting and production

The casting dimensional accuracy, surface quality than other methods to high precision casting , precision casting methods and even other difficult to cast complex , high temperature processing is not easy to cast , may adopt precision investment casting precision casting to cast our country is on century began the fifties and sixties the melting mold

Casting used in industrial production and subsequently this advanced precision casting process has been tremendous development , have been widely used in the aerospace, automotive , machine tools , ships, internal combustion engines, gas turbines, telecommunications equipment, weapons , medical equipment and tools and other manufacturing industries used, but also for

Nowadays manufacturing arts and crafts , jewelry processing precious metals using this method is completely based on personal experience on the following brief look at jewelry casting technology.

Lost wax casting technique in the production of jewelry processing
Lost wax casting process flow is : suppress plastic mold - a plastic mold - Note Wax - Dressing wax - wax tree - filling plaster cylinder - vacuum plaster - plaster natural clotting - Baking plaster - melting , casting - fried plaster - washing, pickling, cleaning - are described below for each cut of rough work

Sequence
1 . Pressed plastic mold
Caulking mode sounds simple, but there are many details which must pay attention to the first box must be clean and raw film die , die before you die should be possible to clean the box clean, wash your hands and the table operator ; secondly to ensure that no adhesion between the original and the rubber

To do this , you should give priority to the use of silver version , if it is silvered copperplate etching should be carried out after the die , because it is easy copperplate together with rubber adhesive ; once again is to pay attention to determine the appropriate depending on the circumstances sulfide temperature and time - both of which not only the basic character

One aggregate function , but also the thickness of the plastic mold , and the length , the complexity of the original , but is usually about the die temperature to 150 ℃, if the thickness of the plastic molding layer 3 ( about 10mm), the curing time is generally 20 to 25 minutes , if the 4-layer ( about 13mm) vulcanization time

For 30 to 35 minutes ...... and so on, while the complexity of the curing temperature also has a relationship with the original : If the original is a complex , fine style , you should reduce the curing temperature and longer curing time , whereas if the temperature is too high , it will affect in order to ensure the effect of die plastic mold

You can use a considerable period, they should have enough to make plastic mold thickness, a plastic mold least 3 layers should also be used to suppress the gum after gum layers should make good the original plastic mold die box slightly larger than the whole , that long width slightly larger ( can be forced into the die box ) , plastic mold thickness pressure

After the frame is slightly higher than the frame into the die plane about 2mm
2 . Open plastic mold
Open plastic mold factory in jewelry is a demanding technique because a plastic mold directly affects the quality wax and metal blanks , but also directly affect the life of plastic mold skilled master mold out of plastic mold after injection wax basically no deformation, fracture , Phi

Wind phenomenon, the basic need repair wax, wax welding , can save a lot of finishing work , get higher productivity
Plastic mold usually legs positioning method , that is, out of the plastic mold with four legs fixed mutual agreement , part of the legs are straight line between the cut , there is also a general curve mold cutting sequence ( in open ring plastic mold, for example ) as follows :
1 ) when the pressure off the plastic mold is cooled to not hot, cut with scissors flash, use needle-nose pliers to take the drain block , got me to focus shell
2 ) The plastic mold upward vertical outlet from the outlet side of the knife along the sides of the center line of plastic mold cutting depth of 2 ~ 4mm ( can be adjusted according to the size of the plastic mold ) , cut the plastic mold sides
3 ) from the first cutting knife at the first pin the first two straight cut edges , depth of 2 ~ 4mm, and then tugged straight edge has been cut , cut a 45 ° oblique direction , forming a triangle shape of the foot then cuts plastic mold halves should have a corresponding male and female three

Angular legs mutual agreement
4 ) Use the procedure in the previous step , followed by the remaining three legs cut out
5 ) opened the first cut legs , cut with a razor blade smoothly inward along the midline , while cutting out the side pulled plastic mold , quick to reach the outlet line to be careful with the tip gently pick open plastic mold , exposing outlet and then cut along one end ring ring ring outer ring until the ring flower head

And inserts the mouth
Cut 6 ) flower head , which is a plastic mold of the more difficult and complex steps if the main stone inlay mouth is prong setting , cut flower heads should axis incision along the flower heads one of the two claws , and then to spend the other end side of the ring outer end face cutting, cutting into the outlet position until then had plastic mold

After being cut in half , but not able to remove the silver version
7 ) Cut left rabbet , plastic mold section to remove the silver version of the flower head
8 ) will open at the end is how easy to remove wax from the rubber mold
3 wax injection
Plastic mold injection can be performed after a good wax the wax injection operation should pay attention to the operating temperature of the wax , plastic mold clamping pressures and other factors
Wax injection machine and the temperature of the heater so that the liquid wax is able to reach and maintain a certain temperature is usually in the wax wax injection machine should be maintained at a temperature between 70 ~ 75 ℃, such a temperature to ensure the fluidity of molten wax if temperature is too low , easy to fill liquid wax wax , wax mold caused by incomplete

; Contrary wax temperature is too high , will lead to an overflow of liquid wax from plastic injection molding crevice or wax from the mouth of the overflow , easy to form flash or burn your fingers
Wax injection machine wax cylinder pressure is provided by an external pump, generally should be maintained at 0.5 ~ 0.7at ( or kgf/cm2) that is between 0.051 ~ 0.071Bar, can also be appropriate based on the volume of wax and complexity adjustment
4 finishing wax
Generally, after removing the wax wax injection will more or less have some problems , flying side , multiple edges , broken jaw , visible blisters, in part or whole structural deformation , the hole barrier, flower head lines are not clear these issues take sides , and so will spend the first casting constraints

Quality
5 kinds of wax tree
After finishing wax , wax tree species need to perform further operations
Wax tree basic requirement is to be arranged in an orderly wax , the key is not contact between the wax mold , both to maintain a certain gap , but also can be as much wax welded wax tree, that is to say , a tree wax trees to try to "grow" the largest number of wax models , has met the bulk

Production needs
6 plaster filling , vacuum
Will put stainless steel tube ( steel bell ) together with a wax tree with the chassis, on the outside surface of the steel bell parcel tape ( tape should last up along the steel bell about 2cm ) alternate choice of quality casting powder ( gold letters 3G licenses for example )
A ) mixing a gypsum slurry : at 38% - 40% of the powder ratio , the weighed powder into water, stirred for 2-3 minutes ; vacuum can be carried out for the first time ( 1 to 2 minutes )
2 ) Note gypsum : gypsum slurry pumping along the inner wall of the vacuum after the bell slowly into steel , gypsum slurry should not be poured directly wax tree, not seen until the gypsum slurry wax tree about 1cm, a second vacuum evacuated immediately 3 - 4 minutes completed, the natural stand for 1 - 2 hours to ensure the plaster

Solidification
7. Baked gypsum
Plaster mold baking is the most important process in general to ensure the normal casting , the mold 18K gold baking time is 6 to 12 hours, platinum mold baking time is 12 to 20 hours baking role are: dewaxing , dry and 18K gold casting insulation baking , for example, dewaxing

Temperature is 0 ~ 350 ℃, holding time 2 hours ; drying temperature of 350 ~ 700 ℃, holding time 2 to 3 hours ; casting insulation temperature 550 ~ 650 ℃, holding time of 1 to 2 hours
The roasting process is generally : the first resistance furnace preheated to the initial temperature, the plaster mold downwardly into the furnace outlet , so that the fluid exits the evaporator wax ; the constant temperature zone in the initial 1 hour , then 1 to 2 hour intervals gradually liters / cooling and heating thermostat attention ( or cooling ) rate should

The holding at 100 ~ 200 ℃ / hour, or excessive heating of the cast cracks easily formed , may cause serious damage or cast scrap , slow warming caused by genetic and easy drying wax or plaster mold is not completely affect the quality of the casting baking time depends mainly on the cast gold tree

The size and complexity can be adjusted according to the specific circumstances
The above operation if operating properly, would have led to the casting defects are mainly the following common phenomenon :
1 . Casting surface acupuncture or Bead causes and solutions :
1 ) slurry is too thick , gouache ratio should be adjusted appropriately
2 ) residual slurry bubble body should be fully exhausted
3 ) vacuum for too long
2 . Rough casting surface discoloration causes and solutions :
1 ) wax rough, high quality wax -type material
2 ) the lost wax temperature. Process too fast , lost wax temperature should not exceed 150 ℃
3 ) plaster model firing temperature is too high, the final firing temperature should not exceed 780 ℃
4 ) metal pouring temperature , the temperature of the molten metal to reduce
3 . Casting is not complete or have trachoma and piercing causes and solutions :
1 ) liquid metal temperature is too low to maintain appropriate casting temperature
2 ) mold firing incomplete , as recommended firing temperature curve
3 ) selection of metal material is not good enough
4 . Casting surface cracks or burrs , causes and solutions :
1 ) slurry is too thin , the proposed gouache than
2 ) Casting pressure is too high, the pressure is reduced to a reasonable