I. Processing flow of convex gemstones
Generally, semi-transparent and opaque materials are selected for convex cut gems, which mainly show color, luster and special optical effects (such as cat's eye effect and starlight effect). ) gems can fully make up for the shortcomings of gems in fire color, transparency and flaws. There is a wide range of materials for convex gemstones, and there is generally no specific requirement. Commonly used gems are: jade, ruby, sapphire, opal, golden emerald, garnet, agate and so on. The processing flow is as follows:
Blanking → ring → rod loading → preforming → fine grinding → polishing → post-treatment.
(1) unloading
Blanking includes drawing lines and blanking:
1. Draw a line.
There is no need to draw lines for precious gemstone rough stones with smaller particles, because this kind of gemstone rough stones can generally enter the next process (ring type) by slightly removing the leftover materials on the trimming saw.
In order to make full use of large pieces of raw materials and to be accurate and convenient, lines should be drawn. Line drawing is to draw the waist shape of convex gem on the plate with a brush. The brush used for drawing lines is a pointed brass rod or aluminum rod with a length of 10 ~ 15 cm. Colored pencils are also ok.
In order to accurately draw the waist shape according to certain specifications, templates are usually used (as shown in figure 1 1-4- 1). Templates are mostly made of plastic, plexiglass or stainless steel. There are many holes with different shapes and sizes designed according to production requirements on the template. When drawing lines, align the selected holes on the template with the raw materials of gems, and draw a waist-shaped outline with a brush. The finer the painting, the better.
Figure 1 1-4- 1 template
Step 2 make disappear
The method of blanking is sawing, that is, sawing along the drawn outline with a trimming saw, leaving a margin of about 2 ~ 4 mm to avoid unnecessary losses caused by embrittlement of gems and cracks extending into the outline during cutting.
When cutting, use a trimming saw. The operation steps are as follows: (1) Clean the stone table, turn on the cooling water, and cool the saw blade to prevent the raw material and the saw blade from overheating during friction.
(2) Hold the raw material in your hand and push it into the saw blade evenly. To control the feeding pressure, it is generally better to feed the plate smoothly without sparks or with small sparks. Generally, at the beginning of feeding, the speed will slow down. After the raw materials enter a section, the speed should be increased linearly, but you can't suddenly exert yourself. When cutting through, slow down to avoid cracking.
(3) Repeat the above steps, and cut off the excess amount other than drawing lines. As shown in figure 1 1-4-2.
(2) Ring shape
Ring is to circle the waist of the blank with a grinding wheel. Generally, a grinding wheel with a diameter of > > 250mm is used for the ring, and 80 # ~ 100 # silicon carbide is used as the abrasive. The specific steps are as follows:
(1) Turn on the cooling water and the wheel mill.
(2) The bottom of the blank is upward, hold it firmly by hand, and smooth the edges and corners of the blank. The shape of the circle should be smooth, natural and arc-shaped, equidistant from the drawn outline, with a margin of about 0.5 ~ 1 mm, and the waist surface of the circle should be perpendicular to the bottom surface (see figure 1 1-4-3).
(3) After looping, in order to prevent the edge of the bottom surface from cracking due to sharpness, a small inclined plane can be ground on the edge of the bottom surface to make the included angle with the bottom surface be 40 ~ 45. At this time, one side of the small inclined plane can coincide with the contour line, but the contour line should not be ground.
Figure 1 1-4-2 Blank shape during blanking
Figure 1 1-4-3 Top view of blank
(3) on the pole
Before preforming, the ring blank should be placed on the rod. The upper pole is to glue the gem blank and the wooden stick together with glue. For experienced jewelers, you can preform the blank directly, but for beginners, you need to wear it, because it can not only fix the gem, but also avoid hurting your hands.
The wooden stick is generally 100 ~ 150 mm long, with a round head and a diameter of about 6 ~ 12 mm, and is made of brass, iron or hardwood. The specific rod assembling steps are as follows:
(1) Clean the rough stones and stick them with alcohol (a few stones with unstable chemical properties can only be cleaned with tap water).
(2) Break the glue, put it in a beaker and heat it with an alcohol lamp until it melts.
(3) Immerse the bonded end of the stick in the molten glue to a depth of about 10mm, pause for a moment, let the glue completely soak the stick, and then take it out for later use.
(4) Clamp the gem blank with tweezers and heat it on an alcohol lamp to make the blank heated evenly and avoid cracking. For gems that are afraid of heat, they can be heated with asbestos mesh at regular intervals.
(5) Stick the bottom surface of the blank with adhesive. When the glue is not completely hardened, straighten the blank by hand so that the bottom surface of the blank is vertically attached to the rod, and then naturally cool.
(4) Preform (Figure 1 1-4-4)
Preforming is to polish the shape of a gem with a grinding wheel. The tool used for preforming is a wheel mill, which has two silicon carbide grinding wheels with different thicknesses. The diameter of the coarse grinding wheel is about 300 ~ 400 mm, and the abrasive particle size is 80 # ~ 100 #. The diameter of the fine grinding wheel is 200 ~ 300mm, and the abrasive particle size is 180 # ~ 220 #. The main function of the coarse grinding wheel is to grind off the allowance of the blank, and the function of the fine grinding wheel is to further trim and remove the prefabricated allowance, scratches and microcracks left by the coarse grinding wheel, so as to improve the smoothness of the blank surface. Through preforming, the blank basically obtains the convex shape in the design, and the specific steps are as follows:
(1) Turn on the cooling water and grinding wheel, and wait until the grinding wheel rotates smoothly.
(2) Grind the top of the blank into an inclined plane with a hand-held stick, and the edge of the inclined plane should not exceed the bottom surface and the edge of the small inclined plane (circular polished small inclined plane), and it is best to leave a margin. When grinding the inclined plane, the force should be even, and the sticky rod should be rotated continuously to make the inclined plane become an endless belt as much as possible, and the included angle between the endless belt and the vertical plane is about 10 ~ 15.
(3) After grinding the first round belt, the second round belt is ground to the top, and the third and fourth round belts are ground to the top accordingly, and so on, so that the top surface of the blank is closer and closer to the smoother surface from the stepped surface.
(4) Use a fine grinding wheel to clean the blank to prevent coarse particles from being brought to the fine grinding wheel. Then according to the above steps, until the extra amount of the gem blank is polished and the smoothness is good.
Figure 1 1-4-4 Preforming Process
(5) fine grinding
The function of fine grinding is to improve the smoothness of gem blank and further improve the modeling accuracy.
The tools used for fine grinding mainly include wheel mill, belt mill and disc refiner. The same feature of them is that the grinding disc is covered with a layer of elastic material. When the grinding disc is pressed by the gem blank, it will automatically produce a yield surface to wrap the blank, that is, the elastic surface of the grinding disc and the arc surface of the gem blank are spherical grinding surfaces. It is precisely because of the existence of this yield surface that the contact with the gem is increased, and the grinding force of this yield surface is much softer than that of the grinding wheel, thus greatly improving the smoothness of the gem blank.
1. Grinding wheel grinding
The grinding wheel used for fine grinding is similar to the grinding wheel in appearance. Its base body is made of metal or wooden wheel, and its outer ring is bonded to the base body with rubber sleeve. The thickness of rubber is about10 ~15mm, and it contains diamond powder. This rubber grinding wheel is suitable for grinding rubies and sapphires with high hardness. Its outer ring can also be replaced by leather, and the abrasive used is 240 # or 280 # silicon carbide.
2. Sand belt polishing
It is very effective to use belt mill for fine grinding. When the convex surface of the gem is pressed against the abrasive belt, the abrasive belt will produce a yield surface, which will wrap the gem and increase the grinding area of the gem.
Step 3: Grinding with a millstone
Disc grinding is a common fine grinding method. Its matrix is mostly metal or hardwood, and its disk surface is slightly convex. Stick a piece of felt or soft foam with a thickness of 5 ~ 10 mm on it, and use tweed or canvas as the outermost layer, or use a belt. The abrasive is 220 # ~ 280 # silicon carbide or 280 # and W40 diamond powder.
(6) polishing
The polishing process of gems includes plane polishing process, curved surface polishing process and rolling polishing process. Due to the different compositions and properties of gemstones, the polishing discs and polishing materials used in polishing are also different (table 1 1-4- 1). The main polishing materials are: iron, copper, tin, aluminum, lead, zinc, bakelite, plexiglass, leather and wood. Main polishing materials: diamond, silica, alumina, chromium oxide, tin oxide and other fine powders.
The polishing process and equipment of convex gemstones are similar to fine grinding. If the polishing tool is made of wooden pallet, it is necessary to cover its surface with elastic materials, such as felt, leather, woolen cloth and canvas. To produce a yield surface. The specific operation steps are as follows:
(1) Clean the gem blank and polish the CD.
(2) Turn on the polishing machine, and use a brush to apply a little polishing agent to the polishing disc (polishing agent is to add water or other dispersants to the polishing powder to make it paste), and the amount applied at one time should not be too much.
(3) When polishing, it is necessary to start from the edge of the blank, and then gradually transition to the top, with uniform force to make the polished arc surface smooth, and check the polishing situation at any time.
Table 1 1-4- 1 Table of polishing discs and polishing agents used for different gemstones
(7) Post-treatment
After polishing a gem blank, the following post-treatments are usually performed:
(1) Glue removal: heat the gem, stick it with an alcohol lamp to melt the glue, and take it out.
(2) Cleaning: put the gem and the stick with a small amount of glue into alcohol respectively. After the glue is dissolved, take them out and clean them with clear water.
(3) Bottom surface treatment: use 220 # fine sandpaper or sand table to smooth the bottom surface. If the transparency of the gem is good, the bottom surface needs polishing.
(4) Waxing: cleaning, drying and waxing the gemstone with the treated bottom surface to fill microcracks and increase the surface smoothness of the gemstone.
Second, the processing flow of faceted gemstones
Generally, multi-faceted cutting is used for gemstones with good transparency. The processing technology of faceted cutting is much more complicated than convex cutting, and its processing flow is as follows:
Blanking → rod loading → ring grinding → crown grinding → rod loading → grinding pavilion → grinding pavilion → post-treatment.
1. Exempted
Usually, the original stone is divided into small pieces by chopping and sawing, and the datum plane (table top) is processed by rough grinding, and the defective part is removed by rough grinding or fine grinding.
Climb the pole
The datum plane of the gem is close to the vertical plane of the bonding frame, and the pavilion of the gem is bonded to the processing rod with adhesive. The bonding end of the bonding rod has various shapes (figure 1 1-4-5) so as to bond different cut gems. The specific steps of rod installation are as follows:
Figure 1 1-4-5 Types of stickers
(1) Clean the surface of the wooden stick and the gem blank.
(2) Preheat the rod, and then preheat the gem blank, so that the gem is evenly heated.
(3) Stick the wooden stick of the gem blank and the pavilion together, and correct the angle when the glue is not completely solidified. The center line of the blank is required to coincide with the axis of the bar, and the datum plane is perpendicular to the bar.
3. Ring shape
Circle the basic cambered surface of the waist and crown of the gem, and the abrasive particle size used in the ring is 180 # ~ 220 #. When winding the waist shape, it is necessary to ensure that the axis of the bar is parallel to the grinding surface, so as to ensure that the top surface of the blank is vertical to the waist surface. When winding the basic cambered surface of the crown, the radian should be small, that is, the included angle between the cambered surface and the stick should be small, and the curvature of the cambered surface should be consistent (Figure 1 1-4-6), otherwise it will affect the grinding of the facets of the crown.
4. Crown grinding
Crown grinding should be carried out on gem carving and grinding machine. There are two kinds of stone carving mills: octagonal hand carving mill and manipulator carving mill. The diameter of the grinding disc used by engraving and milling machine is generally 150mm, and the abrasive particle size is generally 600 mesh. The grinding sequence is table top, crown main facet, star facet and upper waist surface. The specific steps are as follows (take the octagonal hand carving workshop as an example):
(1) Turn on the grinder and cooling water.
(2) Install the sticky stick with the blank on the 45 block, then install the 45 block on the gemstone carving and milling machine, so that the table top faces down and is parallel to the grinding table top, and then grind the gemstone table top flat (Figure 1 1-4-7).
(3) Remove the 45 stop, directly install the stick with blank on the octagonal hand carving grinder, adjust the main platform to make the gem contact with the grinding disc at 40 (the crown angle is 40), and adjust the octagonal hand to the hole position 1. By rotating the eight sides of the octagonal hand on the platform, the eight main facets of the crown can be ground, and the main facets must be the same size and diameter as the watch.
Figure 1 1-4-6 Ring shape of jewel crown
Figure 1 1-4-7 Grinding 45 pieces of crown countertops.
1-45; 2- stick; 3- Gemstone blank; 4- millstone; 5- fixture; 6- bracket
(4) Lift the main platform so that the blank forms an angle of 25 with the grinding disc, adjust the octagonal hand to the position of 2 holes, and through the rotation of the octagonal edge, eight star facets can be ground. At this time, the facet and main surface of the star are just two squares.
(5) Lower the main platform so that the blank forms an angle of 46 with the grinding disc, adjust the octagonal hand to the 3-hole position, and grind the eight waist surfaces on the left side of the crown through the rotation of the eight sides (as shown in figure 1 1-4-8).
Figure 1 1-4-8 Grinding Steps of Round Drill Crown
(6) Keep the platform still, adjust the octagonal hand to the position of 4 holes, and polish the 8 waist faces on the right side of the crown through the rotation of eight faces.
Polishing crown
When polishing, replace the grinding disc, install the polishing disc, and then apply the polishing agent.
The order of polishing is: first, polish 8 star facets, then polish 8 main facets, then polish 16 upper waist facet, and finally polish the desktop.
Problems that should be paid attention to when grinding are:
(1) The polishing angle should be consistent with the grinding angle, otherwise there will be redundant facets.
(2) The polishing surface and polishing agent should be kept clean, and there should be no rough abrasive residue, otherwise the polishing effect will not be achieved, but scratches will be left on the gem surface.
6. Turn the upper rod of the gem (Figure 1 1-4-9)
Figure 1 1-4-9 Sticker changing rod
1-flat head bar; 2- paste blank; 3- adhesive; 4- Bonded frame
After the crown is polished, put the gem blank on an alcohol lamp to heat it, then take it off, turn it over, and stick the crown on a flat-headed stick.
7. Polishing the pavilion
The polishing method of the pavilion is basically similar to the crown except that there is no countertop, and the specific steps are as follows:
(1) Install the adhesive rod on the octagonal hand, adjust the host platform, make the blank form a 40-degree angle with the grinding disc, select the 1 hole position of the octagonal hand, and grind eight main faces through the rotation of eight faces.
(2) Lower the main platform so that the blank forms an angle of 43 with the grinding disc, select the position of three holes of the octagonal hand, and grind eight waist facets on the left side of the pavilion through eight-sided rotation.
(3) Hold the platform still, select four holes of the octagonal hand and grind eight waist facets on the right side of the pavilion (as shown in figure 1 1-4- 10).
Figure 1 1-4- 10 grinding steps of circular diamond pavilion
A- The first step is to polish eight sides of the exhibition hall; B— The second step is to polish 16 lower waist surface.
Step 8 polish the pavilion
Pavilion polishing is the same as crown polishing. Polishing the main surfaces of the eight pavilions first, and then polishing the 16 waist facet.
9. Post-processing
After the pavilion is polished, if you are afraid that the bottom tip of the gem pavilion will be damaged, you can grind a facet at the bottom tip and polish the facet and waist. Then, the gem and the wooden stick are heated under an alcohol lamp, and after the glue melts, the glue is removed, and the gem and the wooden stick with glue are put into alcohol respectively, and then the gem is washed, and finally the gem is washed with clear water.