(a) the shape of the beads
According to morphological characteristics, beads can be divided into spherical beads, drum-shaped beads, cylindrical beads and other shapes (see Figure 5- 1-45).
Figure 5- 1-45 Different bead patterns
(2) Selection of bead materials
There are many raw materials for bead gemstones, most of which belong to middle and low grade gemstones, such as turquoise, malachite, chalcedony and wood stone. Some are man-made products, such as glass, plastics, ceramics, etc. Of course, there are high-end products such as jade.
Beaded gems are mostly used for polishing into necklaces, bracelets and so on. This determines that the size of beads and gems should be the same and the number is large. Therefore, processing this kind of cut requires batch mechanized production to improve processing efficiency, but at the same time, this batch production brings great losses and is not suitable for processing precious stones. Therefore, pearl gemstones are mostly made of low-grade gemstone materials with low prices.
(3) technological process of bead type
Like other cut gems, processing a piece of raw material into a beaded gem with regular shape and beautiful appearance goes through the following procedures: drilling → discharging → prefabrication → rough grinding → fine grinding → polishing → waxing → punching.
The technological process of gem stone is basically the same as that of globoidal gem, but the processing equipment is different.
1. Rock cutting
Because many pearl gems (such as tiger's eye stone, hibiscus stone and Dongling stone) are made of large pieces with a diameter greater than 30cm, they need to be cut into small pieces with a chipper, and the cut small pieces should generally not be larger than 15cm. In the process of slicing, attention should be paid to fixing raw materials, fully cooling and evenly feeding. The structure of the stone crusher is shown in Figure 5- 1-46.
Figure 5- 1-46 Structure Diagram of Stone Crusher
Step 2 make disappear
In the selection of materials, we mentioned that the diameter of the finished jewelry stone is roughly the same, so we should treat its raw materials to make it regular in shape and consistent in size.
Blanking generally goes through three processes: slicing, longitudinal cutting and crushing. See figure 5- 1-47 for the program.
Figure 5- 1-47 blanking process
Cutting raw materials requires a slicer. Pay attention to the following points when slicing.
1) plate parallelism is good, otherwise the cut blank is not cubic.
2) The flatness of the plate is better, otherwise the diameter of some finished beads will be reduced.
3) Before cutting, the raw materials should be clamped to avoid tumbling and dislocation during cutting.
4) Generally, the scale thickness should be 0.7 ~ 1.0 mm larger than the finished bead diameter.
After the raw materials are cut into pieces, they can be cut into strips and broken particles with a multi-knife cutting machine. Multi-cutter cutting of cubic bead blank not only has regular shape, but also has high cutting efficiency. After crushing, the blank should be selected, and the blank that does not meet the size and is damaged should be picked out. Cracked blanks should be properly treated. Generally, it is required that the edge collapse depth of the blank should not exceed one-fifth of the edge, that is; And the depth of the corner collapse is not more than one third, that is. If the crack is too large, it is impossible to polish the round beads that meet the size requirements.
preforming
Preforming, also known as chamfering, is to put a batch of neatly arranged blanks into a container, and grind off the edges and corners with fixed abrasive or free abrasive to achieve a high roundness. After preforming, the working procedure allowance is between 0.3 and 0.7 mm.
There are two chamfering methods: single chamfering and multi-chamfering. Single chamfer is mainly suitable for precious gemstone raw materials with few beads and large differences in shape and size. Single chamfering is completed with hand-held square beads on a grinder, and the method is basically the same as that of globoidal gems. Multi-particle chamfering is suitable for mass production. Chamfering equipment includes sand table chamfering and roller chamfering.
(1) sand table chamfering machine
The cubic bead blank is poured into the retaining ring, and the grinding wheel is driven by the motor to rotate, and the bead blank rolls on the surface of the grinding wheel at this time. Because the probability that the edges and corners touch the disk surface is much greater than that of the plane, the plane of the cube bead embryo will hardly be worn off, but the edges and corners will soon be worn off. The sand table chamfering machine can put 3 ~ 5 kilograms of blanks at a time, and the chamfering time is about tens of minutes to two hours, depending on the hardness of the gemstone raw materials. The structure of the sand table chamfering machine is shown in Figure 5- 1-48.
Figure 5- 1-48 Structure diagram of sand table chamfering machine
(2) Drum chamfering machine
Drum polishing is accomplished by friction between bead blank and drum abrasive (see Figure 5- 1-49). Pay attention to the following points when polishing the drum: ① Clean the bead embryo before putting it into the drum, and pick out the damaged bead embryo in the previous process, otherwise it will affect the good bead embryo. (2) should control the speed of the drum. When the drum rotates, the beads will rise with the drum, and when they reach a certain height (called a turning point), they will start to slide down to form a flowing layer, thus causing friction between beads and polishing agent, and between beads. If the rotating speed is too fast, the beads will fall off when they reach the top of the cylinder, which reduces the friction and increases the collision, resulting in broken beads. On the other hand, if the rotating speed is too slow, the rising height of the beads will be reduced, mainly concentrated at the bottom of the drum, so that the distance between the flowing layers will be reduced and the polishing effect will be poor, so it is very important to control the rotating speed of the drum. (3) Due to the long working time of the drum, the pressure in the drum will increase during the kneading process. Therefore, after working for a period of time, it is necessary to stop the machine and open the cover once to release the gas inside, which is beneficial to safety.
Fig. 5- 1-49 Structure diagram of drum chamfering machine
The drum chamfering machine can put dozens or even hundreds of kilograms of blanks at a time, and the chamfering time is tens to hundreds of hours.
4. Rough grinding
Before rough grinding, it is necessary to divide the diameter of beads, that is, to screen out beads with the same diameter for use.
The rough grinding process is to further process the preformed bead blank into a round bead shape with a rough grinding machine, and reduce the machining allowance to 0.2 ~ 0.4 mm. During rough grinding, an orifice plate is selected according to the diameter of the bead blank, fixed on the base, and the position of the orifice plate is adjusted to be parallel to the surface of the sand table with an appropriate distance, and the bead blank is filled into the hole of the orifice plate, and then the upper plate is covered and appropriate pressure is applied. At this time, if the pressure is too large, the bead embryo will be fragile or the sand table will not rotate, and if the pressure is too small, the bead embryo will jump out of the hole.
5. Fine grinding
Fine grinding process is also called dimple bead. After rough grinding, there is still a certain machining allowance, and the roundness is not high, and the surface often has obvious scratches. In order to make this kind of bead blank reach a certain roundness and smoothness, we use a bead sleeve machine. The method of fine grinding is the same as that of coarse grinding, but the particle size of the container and abrasive used is different.
polish
Like other types of gemstone processing, the polishing of round bead gemstones is also to obtain a smooth appearance, but the polishing method is different. It uses two kinds of equipment: roller polisher and vibration polisher. The drum used in chamfering process can be used as a drum polisher, but it is small in size and fast in rotation speed.
Vibration polishing makes the blank in the container interact with the polishing agent by vibrating the container to achieve the purpose of polishing. Generally, vibration polishing has a long cycle and is divided into three steps: rough polishing, fine polishing and polishing. Rough polishing mainly uses coarse abrasive to remove obvious wear marks on the surface of the round beads; Fine polishing is to remove small traces on the surface and obtain good polishing effect by glazing. After fine polishing, the beads should be thoroughly cleaned. Then pour it into a container, add a proper amount of water and polishing agent (chromium oxide, diatomite or corundum powder), and let the polishing machine work for 24 ~ 48 hours, which can generally obtain good polishing effect.
7. Waxing
The purpose of waxing is to prevent the surface of beads from being polluted and eroded, and to fill tiny pits, cracks and scratches on the surface of beads, thus increasing the smoothness of the surface of beads.
The waxing process is relatively simple, that is, the waxing bucket filled with beads is immersed in the molten paraffin liquid. Because the waxing barrel is shaped like a colander, the beads can be fully waxed. Then, it is recommended to wipe the beads with a dry cloth. In this process, the temperature of paraffin liquid and the immersion time of beads should be controlled to prevent beads from overheating and cracking.
Step 8 weaken
Perforation of beads is difficult because it is easy to produce deviation and hole collapse.
There are many methods of perforation, such as hand drilling perforation, drilling machine perforation, ultrasonic perforation and laser perforation. The most commonly used perforation method is ultrasonic perforation (see Figure 5- 1-50).
Fig. 5- 1-50 Structure Diagram of Ultrasonic Piercer
Ultrasonic perforation is the use of ultrasonic high-frequency vibration to drive abrasive particles to grind gems. The cutter head of ultrasonic drilling adopts cemented carbide, which not only has high efficiency, but also has low wear rate. The vibration amplitude of the tool head (drill pipe) is 25? When the m sum frequency is 500Hz, the perforation effect is the best. The abrasive particle size is 180 #.
In order to prevent the collapse of the mouth, it can be solved by the method of opposite puncture at both ends, and in addition, it can avoid the phenomenon that one end is big and the other end is small during puncture.