Manufacturing of high-performance glass lenses for sunglasses
In the numerous and complex factors that affect the quality of sunglasses, the compounding of raw materials is a major one and requires strict control. The quality of Sunphey lenses starts from the production of glass substrate, which adopts the most advanced continuous melting and shaping technology of the world. The technology features less processes, a high degree of automation and a high rate of finished products. The main processes are as follows:
Mixing of materials
According to its optical characteristics, optical glass can be divided into about 230 types. In the production of optical glass, about 70 kinds of raw materials are used. Generally, the production of one type of optical glass necessitates the mixing of tens or hundreds of kilograms of 5~15 kinds of raw materials of high purity, including silica, boric acid, lanthana, cerium oxide, columbium oxide, zirconium oxide, barium and potassium. Any minimum error at the time of weighing will cause changes to the refractivity and nature. Therefore, a scale of 1/10000 precision is used in the weighing of a formula. After being weighed according to the formula, the raw materials are mixed evenly in a blender.
The process of smelting includes 4 processes: melting, clarification, adjustment & homogenization, distribution.
- A tank furnace is heated with electric power (or natural gas or coal gas) to melt natural materials at 1400℃ ~ 1500℃ for formation of glass mixture in viscous state;
- Clarification: Raw materials will general massive air bubbles after melting and must receive debubbling treatment.The rising speed of bubbles is inversely proportional to the viscosity of glass liquid, while the viscosity is inversely proportional to temperature. Therefore, temperature is raised to lower viscosity to speed up debubbling;
- Adjustment and homogenization: Adjustment means the lowering of temperature to increase the viscosity of glass liquid so that it can meet the viscosity requirement for shaping; homogenization means the adequate blending in the adjustment and homogenization pool of the glass liquid of high temperature, low viscosity and uneven material quality in the clarification pool so that the quality is even and can meet the requirement for optical quality. The lowering of temperature takes place concurrently with blending during adjustment and homogenization;
- Distribution of glass liquid: The platinum feed pipe accurately the temperature of glass liquid to adjust viscosity and flow, which then flows out and is cut onto the material drops of required weight by scissors of special steel;
- Automatic profiling: The drops of glass liquid having the right viscosity and required weight are infused into the cavity of dies to be pressed into lens blanks by the automatic moulding press;
- Annealing: After the pressing, a removal device is used to take the lens blank out of the mould and feed it into a mesh belt annealing furnace. The lens blank is heated again to the annealing temperature, which is kept for a period of time before being lowered at a controlled speed to eliminate the inner stress;
- Monitoring: After its inner stress is eliminated through annealing, the lens blank will receive inspection of logistic characteristics and appearance quality to weed out any rejects. The items to be monitored include: refractivity, Abbe number, inner stress, stripes, bubbles, diameter, curvity, central thickness, edge thickness.
Processing of blanks
In batch production, moulded blanks are used for processing to reduce grinding workload. Generally, the convex mirror degree of the blanks is close to the processing mirror degree, while the concave mirror degree of the blanks is smaller than the processing mirror degree.
Grinding and polishing
The transformation of the optical glass raw materials from “blanks” to lenses is the first step in the production of glass lenses. A milling machine tool is used first for single-piece grinding so that the surface of the lens being processed can reach a certain radius of curvature and surface roughness. There is an intersection angle of α between the axis of the diamond grinding wheel and the axis of the working shaft of the lens, which intersect at the point of 0 and rotate separately around the axises. The two movements combine to get the radius of the spheric curvature necessary for lenses through grinding. To change the spheric diopter, it is only necessary to adjust the intersection angle into that of the diamond mould to gradually obtain the sphere of a lens. Then, the lenses are polished to get the finish of high quality.
Centering and edging
The optical axis of a lens must be kept parallel to the sight line. To achieve the coaxality of optical axis and sight line through positioning, centering and edging must be implemented for a lens to reduce or remove its central eccentricity. After the centering, diamond mould and grinding liquid are typically used to grind it to the excircle dimensions and precision required by design. The parameters of the grinding wheel and lens, e.g. linear speed feed, are selected on the basis of factors like diameter and glass hardness. As a part of the same process, we reduce the difficulty of our customers in assembling spectacle frames and inserting lenses through and appropriately cut oblique angle and the edge chamfer of lenses to ensure stability and ensure a perfect match between lens edge and the frame.
The fragility of glass lenses is a problem that customers are concerned about. The glass lenses of Sunphey use special chemical and physical hardening processes and have passed the drop ball test. This means that fragility may not become a barrier that prevents glass lenses from finding favor with the public. In fact, we have so far received no reported medical case about the harm caused to the eye by a broken glass lens.
Coating poses extremely strict requirement for lens cleanness. Therefore, the cleaning process before film coating is very important. Sunphey clears away the handprint, dust and processing media attachment from earlier processing by using the cavitation effect of the huge cavity bubble of approximate vacuum created by the ultrasonic field, which causes a series of physical and chemical changes to the substances under the support of the washing media.
Coating can be said to be an important process in the production of sunglass lenses. The coating of lenses can filter or intercept blaze and reduce dazzling light, thus reducing the amount of visible light that can reach the eyes and achieving better optical performance and higher clarity. In all kinds of materials that are coated, glass alone can withstand high temperature (350°-400°C) and high vacuum. This is necessary for excellent adhesion. Glass is the only base material that can ensure perfect agglutination between oxide and glass without deformation or damage to provide the same long life for the coating attached to the glass within the service life of the product. We can apply all kinds of layers in a composite coating to obtain various color changes or functions, e.g. hydrophobic and oleophobic coating. The unique coating we have developed causes the lens surface to be smooth and prevent water drops from sticking onto the lens surface. It can provide reliable protection even in extremely wet environment or on rainy or snowy days. More importantly, in everyday use, it can prevent most dusts and impurities from sticking onto the lenses and make it possible to use a cloth to quickly clean the surface and restore the original state of cleanness of the lenses.
Matching of frames
To ensure the best matching effect for the frames of customers, we provide lenses that can accurately match the frames through cutting. For the frames of classical models that have been licensed to us or do not involve a patent, we have the processes for the large-scale production of lenses to make sure that our customers can insert the lenses into the frames correctly. For customized new products, we ask the customers to provide precise frames or samples. Then, our technicians will decide on the dimensions and shape of the most appropriate frames. The lenses we provide can match the frames excellently.
Logos and marks
On the customized lenses can be printed a logo or design that does not involve any patent.
–Fog display marking
We can print unique mark on your lenses. An anti-fake mark can use laser carving or fog display carving (a mark that is displayed only when the lens is blown upon). We can also create a unique mark of fashion for your lenses through marking. Such marks can be large or small and will not interfere with the normal vision of a user through our unique technology.