Glass processing

Glass processing

The formed glass products, in addition to very few (such as bottles and cans) that can directly meet the requirements, most also need to be processed to obtain products that meet the requirements; Before processing certain flat glass, the original glass sheet needs to be processed. Processing can improve the appearance and surface properties of glass, and can also be used for decoration.

Cold working of glass

Cold working of glass, also known as mechanical processing, refers to the process of changing the appearance and surface state of glass and glass products through mechanical methods at room temperature. The basic methods of cold (mechanical) machining include grinding and polishing, cutting, sanding, sandblasting, engraving, sand carving, drilling, and cutting.

Grinding and polishing

Grinding and polishing of glass involves processing an uneven glass surface to create a flat and smooth surface; Alternatively, it is a cold working method of grinding and polishing the shape and size of glass blanks to meet the specified shape and size requirements, with a smooth surface. At present, optical glass and lens processing are the most widely used in glass grinding and polishing; The rolling method used in special circumstances requires grinding and polishing of wire clamped flat glass; Microcrystalline glass substrates and ultra-thin glass substrates produced by certain methods also require grinding and polishing. The grinding of glass can be divided into coarse grinding and fine grinding. Coarse grinding is the use of coarse abrasive to remove the rough and uneven surface of glass or the remaining part of the product during forming, which has a grinding effect to make the product have the desired shape and size, or a flat surface. Starting with coarse abrasive grinding is highly efficient, but the glass surface leaves pits and crack layers. Fine abrasive grinding is necessary until the rough surface of the glass becomes finer. Then, polishing materials are used to make the rough glass surface transparent, smooth, and shiny. Grinding and polishing are two different processes, which together are called polishing. Glass that has been ground and polished is called polished glass.

The Mechanism of Glass Grinding and Polishing

Over the years, there have been many studies on the mechanisms of mechanical grinding and polishing by scholars from various countries. The coexisting opinions can be summarized into three different theories: the theory of grinding action; Flow layer theory; Chemical action theory. Grinding theory: For grinding, many scholars believe that starting with grinding. In 1665, Hooke proposed that grinding is the use of abrasives to grind glass to a certain shape, and polishing is an extension of grinding; This makes the glass surface smooth, purely mechanical. This understanding continued until the end of the 19th century. Flowing layer theory: Represented by British scholars Rayleigh and Pepe, it is believed that when glass is polished, the surface has a certain fluidity, also known as a plastic layer. The flow of the plastic layer fills the surface of the ground glass with a rough surface. Chemical action theory: Preston in the UK and Grebinchikov in the Soviet Union proposed that in the polishing process of glass, there are not only mechanical effects, but also physical and chemical effects, which is a combination of the three or two theories mentioned above.

(1) Grinding mechanism of glass

The grinding process of glass first involves relative motion between the grinding disc and the glass. The mechanical action of free abrasive under the load of the grinding disc is to scratch and peel off the surface of the glass, while also generating microcracks on the glass. The water used for abrasives not only plays a cooling role, but also generates hydrolysis with the new surface of glass to generate silica gel, which is conducive to stripping and has a certain chemical effect. By repeating this process, a concave rough surface is formed on the glass surface with a certain depth of crack layer

According to the research of Soviet scholar Kachalov, it is believed that the average depth h of the concave layer is determined by the properties of the abrasive and the particle diameter, and its relationship is: h=K1D (16-1) 

In the formula, K1- represents the grinding constant of different abrasives, as shown in Table 16-1 

D - is the average diameter of the abrasive. The relationship between the average depth of the crack layer f and the average depth of the depression layer h is f=2.3h (16-2)  

And the maximum crack layer depth: F=3.7-4.0h (16-3)

The physical, mechanical, and chemical properties of glass with different chemical compositions vary greatly, which has a significant impact on the depth of the concave layer and crack layer generated on the ground surface. Table 16-2 shows the comparison of the depth of the concave layer and the crack layer obtained under the same grinding conditions using 105-150 micrometer silicon carbide abrasives for various types of glass. From the table, it can be seen that glass with high mechanical strength has a relatively small depth of depression and crack layers.

Grind the original rough glass into a precise shape or a flat surface product, usually with a grinding amount of 0.2-1 millimeters or more. So we need to use coarser abrasives to improve efficiency. However, due to the large depth of the concave layer and crack layer left on the glass surface by coarse particles, it is not conducive to polishing. The depth of the concave layer and crack layer on the grinding surface must be minimized as much as possible, so the abrasive particle size should be gradually reduced to make the glass surface as fine as possible. Generally, the average depth h of the concave layer on the glass surface ground in the final stage is 3-4 microns, and the maximum crack depth F is 10-15 microns.

The main process factors affecting the glass grinding process 

During the glass grinding process, the grinding speed and quality are marked by the amount of glass removed (the number of glass removed per unit time) and the depth of the concave layer of the ground glass. A large amount of grinding results in high grinding efficiency, while a small depth of the concave layer results in good grinding quality. Some process factors only have an impact on one of them, while others have an impact on both. However, they often have a positive impact on one and have the opposite effect on the other. The effects of various process factors are described below.

(1) Abrasive properties and particle size

The hardness of abrasive is large, and the grinding efficiency is usually high. The grinding efficiency of emery and silicon carbide is much higher than that of quartz sand. However, abrasives with high hardness cause a greater depth of indentation on the ground surface, as can be clearly seen from the above formula (16-1) and Table 16-1. The relationship between the size of abrasive particles and the amount of glass removed is shown in Figure 16-2. The amount of glass removed increases with the increase of particle size. According to formula 16-1, the concave depth of ground glass increases with the increase of particle size, which means that the grinding quality deteriorates with the increase of particle size. Therefore, at the beginning of grinding, coarser particle sizes are used to improve grinding efficiency, in order to achieve a suitable appearance or surface flatness of the glass product in a short period of time. Afterwards, fine abrasives are used to gradually improve the grinding quality, ultimately achieving the required surface quality for polishing.

(2) Concentration and feed rate of abrasive suspension

Abrasive suspension is generally made by adding water to the abrasive and used as a suspension. Water not only disperses and evenly distributes abrasives on the working surface, but also takes away the ground glass debris, cools the heat generated by friction, and promotes the hydrolysis of the glass surface into a silicone film. So the amount of water added has a certain impact on the grinding efficiency. The concentration of the suspension is usually represented by measuring the specific gravity of the suspension or calculating the liquid-solid ratio of the suspension. Abrasives of various particle sizes have their most suitable concentration, and either too large or too small can affect the grinding efficiency, as shown in Figure 16-3. If the abrasive concentration is too low, it can also cause scratches on the grinding surface.

Glass grinding fluid is a water-soluble synthetic cutting fluid that is particularly suitable for cutting and grinding various glass lenses and crystal materials, mainly used for precision grinding. Odorless, free from harmful substances, with excellent cooling and powder settling properties, it can provide high surface smoothness and good antibacterial performance, greatly improving the service life of oil products.

1、 Excellent cooling, lubrication performance, and certain extreme pressure performance, suitable for grinding processing needs, can improve the surface accuracy and smoothness requirements of workpieces.

2、 Good washing performance, cleaning the waste residue adhered to the workpiece, which is beneficial for reducing power consumption, reducing tool and grinding wheel wear, effectively extending tool service life, reducing grinding and trimming frequency, and saving energy and consumption. Increase production capacity.

3、 Good rust resistance, providing good protection for machine tools, workpieces, and cutting tools.

4、 Good machining visibility, high visibility in the cutting area, convenient for operators to observe the cutting process status.

5、 Long storage and service life, shelf life: one year, with reasonable maintenance, only a small amount of additives are needed in daily life, saving costs.

6、 The pH value of the product is 8.2 ± 0.5, which is non irritating and beneficial for protecting the operator's health.

7、 Complies with national cutting fluid environmental protection requirements, with simple waste liquid treatment and environmentally friendly processing operation fluid.

Glass grinding fluid product usage:

1. Dilute the original solution with 20-30 times tap water or deionized water to obtain the working solution, or depending on the processing difficulty and actual situation.

2.During use, the consumed working fluid can be replenished at a concentration of 3-5%.

3. Do not mix this product with other oil products, as even a small amount of decayed residue in the system can affect the effectiveness of the new solution. When diluting, please add this product to water slowly while stirring, and do not add water in the opposite direction to the concentrated solution.