CONTENT
一、The principle of selecting fine grinding pellets
二、The precautions of diamond tubby grinding wheels
三、The principles of selection of cleaning agents
四、The selection of polishing powder
五、Photosensitive adhesive Precautions
六、The selection of optical glue
七、The calculating concentration method of diamond
一、The principle of selecting fine grinding pellets
The following points must be noticed when selecting diamond fine grinding pellets:
1、Selection of granularity
Since fine grinding process is between rough grinding and polishing processes, it has something to do with these two processes. Therefore, it is important to select fine grinding pellets with proper diamond granularity. The principle of selection is based on the fact that the fine grinding pellets selected can remove rough grinding trace left in the last process, and the fine trace left in this process can be removed completely by polishing. For optics used in normal binoculars, one process of fine grinding with metal based pellets W14 or W10 will be enough (the surface roughness Ra value of the optics reaches 0.16 – 0.32). Then it is ready for polishing. For optics used in the microscope and camera, two processes of fine grinding will be done. The first process is done with metal based pellets W20 or W14, then the second process is done with resin based pellets W10 or W7 (the surface roughness Ra value of the optics reaches less than 0.10 µm).
If the granularity of the pellets is too fine, the trace like chrysanthemum left by rough grinding can be seen on the surface of the optics after fine grinding, or some bright spots will be left on the surface of optics after polishing.
2、Selection of fine grinding pellet size
The size and applicable range of fine grinding pellets can be decided according to the curvature radius of the optics to be processed and the surface area of the cast iron mould on which the pellets are bond. The details is shown in the following table:
|
Curvature radius of optics ( mm) |
10 – 20 |
20 – 30 |
30 – 50 |
|
Surface area of fine grinding plate (mm2) |
6 – 25 |
25 – 50 |
50 – 150 |
|
Pellet size: Diameter x height (mm) |
Φ 4*3 |
Φ 6*3 or
Φ 8*3 |
Φ 8*3. Φ 10*3(4),
Φ 12*3 (4) |
Note: For optics with curvature radius less than 10 mm, it is suggested to use diamond grinding head .
3、Determination of coverage ratio
The coverage ratio of the pellets mainly depends on the curvature radius of the find grinding plate. It can be calculated in the following formula:
Coverage ratio P =ZAp/Aw = Z (D/2)2 π/2π Rh=ZD2/8Rh
Where Z – Total number of grinding pellets
Ap – area of each pellet
Aw – surface area of the mould on which the pellets are bonded
D – diameter of the pellet
h – vector height of the mould
In practical application, the bigger the coverage ratio is, the difficult the coolant flowing will be. It is possible that the grinding chips can not easily go out and the grinding efficiency goes down. It is suggested to use grinding plate with lower coverage ratio (about 20% – 30%) to grind flat surface and big spherical surface. In arranging the pellets, the density at edge should be higher than that in the center of the grinding plate. In this case, the pressure can be raised and cutting ability be increased. Whereas, the grinding plate with high coverage ratio (about 30% – 40%) should be used to grind optics with small spherical surface to ensure that the form of the grinder is stable.
二、The precautions of diamond tubby grinding wheels
Ø The grinding wheel diameter is normally 2/3 of the diameter of work-piece to be ground. If the grinding wheel diameter is increased, linear speed is big and grinding ability is increased accordingly. For hard optics with bigger diameter, it is better to use the grinding wheel with rough diamond granularity. For optics with smaller diameter and high requirement on the surface quality, it’s better to use grinding wheel with fine diamond granularity.
Ø The grinding wheel must fit the coupler of the equipment.
Ø The radial and transverse off axis of the grinding wheel should meet the requirement. Otherwise, the work-piece might be damaged or even exploded, which results in damage to the operator.
Ø When purchasing the grinding wheel, if the wall of the grinding wheel is increased, the grinding ability can go down due to the fact that the contact area between the wheel and the work-piece is increased. Normally for the grinding wheel with diameter less than Φ20, the wall thickness of the wheel should not be more than 2 mm. And for grinding wheel with diameter Φ20 –Φ50, the wall thickness of the wheel should not be more than 3 mm.
Ø The increase of useful grinding layer height of the wheel might cause structure loose of the wheel in the middle section, hence the processing coherence can be affected. It is suggested to use grinding wheel with diameter less than Φ6 and useful grinding layer height less than 5 mm. For the grinding wheel with diameter bigger than Φ6, the useful grinding layer height should be less than 10 mm.
Ø For the grinding wheel with diameter less than Φ5, the cost will be rather high since it is difficult to make.
Ø If the grinding wheel with big diameter is used, the working linear speed can be increased, which results in high grinding efficiency. However, the included angle between the tool shaft and lens shaft can not be very big in order to prevent the grinding wheel from being cracked by accident due to too big side pressure.
三、The principle of selection of cleaning agents
|
1 |
Medium MXB – 01 or MBX04 – 5F
Concentration 3﹪– 5﹪
Temperature 75℃-80℃
Ultrasonic cleaning time 3 – 5 minutes |
|
2 |
Spray 1 – 2 minutes with tap water having temperature of 60℃ |
|
3 |
Medium MXB – 01 or MBX04 – 5F
Concentration 1﹪– 3﹪
Temperature 40℃-50℃
Ultrasonic cleaning time 1– 2 minutes |
|
4 |
Medium DQ – 01 or 05 – 06 #
Concentration 1﹪– 3﹪
Temperature 20℃-35℃
Ultrasonic cleaning time 1– 2 minutes |
|
5 |
Rinsing with flowing tap water for 1– 2 minutes |
|
6 |
Rinsing with deioned water for 1– 2 minutes |
|
7 |
Rinsing with deioned water for 1– 2 minutes |
|
8 |
Rinsing with deioned water for 1– 2 minutes |
|
9 |
Dewater and blow dry |
Note: Steps 6 – 8 can be combined into two steps according to real situation.
Precaution:
Ø Solution concentration, cleaning temperature, ultrasonic power and ultrasonic cleaning time can be adjusted properly according to real condition.
Ø As for the optical parts with poor chemical stability, it is necessary to make a cleaning test in small amount. If test result is OK, cleaning can be carried out in batches.
The series of cleaning agents can be used in ultrasonic cleaning system, they can also be used to clean the optical parts in a simple way as follows:
1. Dip the parts in the cleaning agent with concentration of 5﹪and temperature of 75℃-85℃, and shake for 2 minutes.
2. Dip the parts in the cleaning agent with concentration of 2 – 3﹪and temperature of 40℃-50℃, and shake for 2 minutes.
1. Dip the parts in the cleaning agent with concentration of 1 – 2﹪and temperature of 20℃-35℃, and shake for 2 minutes.
2. Rinsing with flowing tap water and blow dry finally.
Suggestion for waste liquid drainage
The product can be biodegradated.
Before waste water drainage, the solution must be neutralized or become neutral. It can be neutralized with thin hydrochloric acid or vitriol.
Consider local regulations.
四、The selection of polishing powder
At present, there are many kinds of polishing powders. However, the most applicable polishing powder with mature technology and good effect are cerium – rare earths oxide polishing powders. They can be classified into three kinds according to cerium content.
1. Polishing powder with high cerium content:
Its cerium oxide content is more than 95%. It is yellowish with specific gravity of 7.3. It is mainly used for classical polishing and high precision processing. Many manufactories also use it for high speed polishing.
2. Polishing powder with rich cerium content:
Its cerium oxide content is between 70% and 85%. It is yellow or brown with specific gravity of 6.5 and suitable for high speed polishing.
3. Mixed rare earth polishing powder:
Its cerium oxide content is between 40% and 60%. Normally it is red or maroon and used for the polishing of kinescope glass, spectacle lens and flat glass. Some high quality polishing powders are also used for optic polishing.
The selection of polishing powder depends on polishing method. For classical polishing, it is better to use polishing powder with high cerium oxide content. Normally polishing powder with rich cerium oxide content contains certain additive. If it is used for classical polishing, it will have a counter function. Meanwhile, part of polishing powders is made with high fluoride oxide content. The use of this kind of polishing powder might hurt the skin and bone of the operator.
Each polishing powder has a proper polishing concentration. Improper concentration would affect polishing quality. The normal polishing concentration is 3% = 5%. If the concentration is too high, it is possible to cause scratches on the polishing surface.
Requirement for polishing powder:
Ø Uniform appearance
Ø Uniform granularity
Ø Having certain crystal lattice state and crystal lattice defect and high
chemical activation.
Ø Having good decentralization and adsorption. The polishing powder grains can distribute evenly and adsorb on the polishing mould, they do not concentrate and flow away.
Ø Having proper hardness and specific gravity.
Ø The polishing powder to be used in cycling polishing system should have good suspension ability.
Ø Containing no substance that is harmful to human body.
五、Photosensitive adhesive Precautions
1、Match the cleaned optics. To ensure the reliability of cementing, try to inosculate the
Newton rings of both optics to be cemented. The good the inosculation of the rings is,
the better the reliability of cementing will be. If the inosculation of the rings is not good,
the reliable cementing can not be obtained.
2、Put the optics in the oven or infrared lamp box (under infrared lamp), heat them to
40℃-50℃for about 15 minutes for dewatering.
3、Drop the photosensitive glue on the negative lens under normal lamp, then move the
corresponding positive lens left and right to get rid of the bubble in the glue. Watch
carefully, if there is dust and dirt in the glue, remove it with blade.
4、Put the cemented lens in a well-leveled glass plate or other plate, move the lens with
hand or 3 round cylinders to let the edge of both lens coincide for centering..
5、Switch on the ultraviolet lamp or place it under sunlight, let the photosensitive glue
harden. Hardening takes about 2 – 3 seconds under the ultraviolet lamp with central
wavelength of 365mm and intensity of 1kw/80cm. If the glue is hardened under sunlight,
it takes about 2 – 10 minutes depending on the ultraviolet intensity of the sunlight.
Under normal condition, it is basically hardened if you can not move the lens with hand.
6、If cementing is done under spot light source, make the optical centers of both lenses
coincide with centering meter, switch on light source, let the optics positioned and
hardened initially, then place them under sunlight or ultraviolet lamp with low power for
final hardening.
7、In the area with low intensity of sunlight, centering can be done under sunlight, but the
time should be controlled within 3 minutes to prevent the glue from being hardened.
8、If the cemented optics need to be separated for repair, separation can be done by
heating them on the electric hot plate padded with soft metal plate. With the time goes
on, hardening is strengthened and heat resistance is increased. It is difficult to separate
the cemented optics.
9、The remaining glue at the edge of the cemented optics is not easy to harden since it
contacts air. It can be cleaned off with acetone or absolute ethanol.
10、The glue should be kept in a cool place without sunlight. The period of validity is 6
months.
Normal phenomenon, main cause and solution
|
S.N. |
phenomenon |
Main cause |
Solution |
|
1 |
Glue loose off |
Bad ring inosculation of optics to be cemented |
Try to get ring inosculation as good as possible when matching optics. |
|
There is water between the surfaces to be cemented. |
Increase the baking temperature and extend the baking time. |
|
Move the optics before completely hardening |
Extend the hardening time |
|
The glue is not useful due to improper storage |
Replace the glue with good one. |
|
Hardening is too fast |
Prevent it from sunlight or lower down the power of ultraviolet lamp |
|
2 |
Optics to be cemented is not clean |
The surface to be cemented is not clean |
Clean the surface carefully |
|
The glue is polluted due to improper storage |
Take out the dust and dirt in the glue with blade timely. |
|
The glue is greatly polluted due to improper storage |
Replace the glue with good one. |
|
3 |
Hardening is too slow |
The ultraviolet intensity is not enough |
Using ultraviolet lamp for baking or increase lamp power |
|
4 |
Hardening is too fast |
The ultraviolet intensity is too high |
Keep away from light or decrease lamp power |
|
5 |
Glue hardens during cementing |
The ultraviolet intensity is too high |
Keep away from light, use normal lamp with low power for illumination. Not to use fluorescent lamp or eye protection lamp. |
|
6 |
The edge is not clean |
Too much glue is used. |
Decrease the glue |
|
|
Clean the edge with acetone |
|
7 |
It is difficult to remove the glue bubble |
The cementing surface is not clean, so it’s not easy for glue to dip on the surface |
Clean the surface to be cemented carefully |
|
Glue adhesiveness is too big, so it’s not easy for glue to dip on the surface |
Increase the baking temperature and extend the baking time |
|
Glue adhesiveness is too small, so the glue goes away, causing lack of glue |
Decrease the baking temperature and shorten the baking time |
|
The surface form of optics is not good, so the glue goes away, causing lack of glue |
Select optics with good surface form and increase the adhesiveness of glue |
|
Glue applying is not enough, causing lack of glue |
Increase the amount of glue |
|
8 |
Difficult to split the cemented optics |
The cemented optics have been kept too long, the glue is hardened completely |
Increase the temperature for splitting and extend the time |
|
Send the cemented optics to the special manufactory for splitting |
|
9 |
The optics are broken during splitting |
The temperature is too high and time is too long |
Decrease temperature and shorten the time of splitting |
|
The temperature of the optics goes down quickly |
Place the optics on a hot place and let the temperature goes down slowly |
|
10 |
The remaining glue at edge is not hardened |
The glue has a anaerobic property, and will not harden when contacting the air. Remove the remaining glue. |
六、The selection of optical glue
Most optics are made of glass. They are brittle and can not be connected by thread, riveting and welding. They can only be connected with glue. The glues used in optical industry are divided into two classes according to the application. One is used for technological process and the other for products.
1. Selection of glue for technological process
The technological glue means the adhesive used in optical processing for temporary optic positioning and mould manufacturing. According to the procedures and applications in the optical processing, the glue is specified as follows:
a. Proper adhesion, hardness, flexibility and thermal stability.
b. Good chemical stability, no peeling off under certain usage condition, no corrosion to the surface of optics.
c. Uniform composition, no bad and hard grain and impurity.
d. Easy operation and less poison.
e. Easy removing and cleaning.
Positioning and bonding of flat surface optics Since the optics fit well with fixture, there is only a small gap in between. Adhesive with less adhesiveness is used so that it goes into the bonding surface, such as rigid blocking that is used for positioning and bonding of right angle prism. Letai 412 instant glue is used for bonding of roof prism.
Positioning and bonding of spherical optics Since the optics do not fit well with fixture, there is big gap in between. Adhesive with more adhesiveness is used so that it can fully fill the bonding surface, such as the optical pitch used for lens blocking.
Polishing pellets are made of flexible materials, they will be bonded with polyurethane glue.
Since optical processing is normally carried out in the water solution, so the adhesive must be water resistant and thermal resistant.
2. Selection of glue for product
The glue for product means the adhesive used for bonding between optics and other parts during the assembly of optical instrument. Since the adhesive has something to do with the normal operation of the optical instrument, it is specified as follows:
a.Proper adhesion and hardness, flexible and thermal stability, reliable adhesion.
b.Good chemical stability and uniform composition.
c. Easy operation and less poison.
Photosensitive glue with similar refractive index and high transmissivity is used for the bonding between the concave and convex lenses. Epoxy resin with strong adhesion is used for the bonding between glass and metal, plastic, frame and base. Single liquid Kr-2 glue with less but reliable adhesion is used for the bonding of thread.
七、The calculating concentration method of diamond
The concept of concentration of diamond grinding tools means the diamond content inserted in the grinding layer. If one cubic centimeter contains 4.4 carat (1 carat = 0.2g) diamond, the concentration is specified as 100﹪. The corresponding relation between diamond concentration and content of normal diamond grinding tools is as follows:
|
Diamond concentration (﹪) |
25 |
50 |
75 |
100 |
150 |
200 |
|
Diamond content (ct/cm3) |
1.10 |
2.20 |
3.30 |
4.40 |
6.60 |
8.80 |
|
Volume of diamond in the grinding layer (﹪) |
6.25 |
12.50 |
18.75 |
25.00 |
37.50 |
50.00 |
|
LOCATION： Home
After-sales service