Glass processing: how to improve annealing
Due to weather a fierce temperature change, the basis of reasonable annealed glass in the molding process. So that the inner and outer layers to produce a temperature gradient, and due to the finished shape, thickness, by the degree of cooling, such as glass machinery differences cause irregular thermal stress article. This thermal stress can reduce the mechanical strength and thermal stability of the products, but also affect the optical homogeneity of the glass, if the stresses exceed the ultimate strength of the finished product, it will break itself. Therefore, the presence of glass products in a non-uniform thermal stress is a serious drawback annealing is a heat treatment process, the presence of thermal stresses in the glass can eliminate or reduce as far as possible to allow the value. In addition to glass fiber and small thin-walled hollow articles, but really all glass products are necessary to perform annealing. Glass products in the thermal stress, according to the presence of features, tentatively divided into two kinds of stress and permanent stress.
Because of its poor thermal conductivity, ① temporary stress. When glass is heated or cooled at a temperature below the strain point. Each site will form a temperature gradient, resulting in inevitable thermal stresses. This thermal stress, temperature differences exist with the greater the temperature difference, the greater the stress tentatively, and with the temperature difference vanishes. This thermal stress tentatively called stress.
But before the temperature imbalance, we should pay attention to, of course, let's dispel stress can perhaps themselves. When the temporary stress value exceeds the ultimate strength of the glass, the glass will break itself abnormal, so the glass in the brittle temperature range of heating or cooling speed not too fast.
Thermal stress generated by the temperature difference, ② permanent stress. From a temperature above the glass strain point start cooling. Glass is cooled to room temperature, the temperature of the inner and outer layers disorders, and can not completely dissipated, glass modeled still some remnants of stress, this stress is called stress water for a long time. The size of the finished product depends on the permanent stress at a temperature above the strain point of the cooling rate, the glass viscosity, thermal reduction factor and thickness of glass machinery products.
Glass products is to have a permanent stress reheating the glass particle can be moved inside temperature annealing glass. Gripping the stress dispersion particle displacement (called stress lax) to eliminate or weaken the permanent stress. Stress relaxation rate depends on the glass temperature, the higher the temperature, the faster the relaxation. Therefore, a suitable annealing temperature range, brilliant annealed glass to give the key to the quality of the actual production process, it is impossible to completely eliminate permanent stress residual stress wishes to add or homogenized within the constraints of the minimum by annealing to enhance the glass machinery production style pattern strength and thermal stability characteristics of thick thick glass annealed glass, there are two important reverse method and baffle method, where important negotiations thick glass baffles produced during annealing. Production of thick glass baffles The main principle is to liquid glass "thaw" baffle area. Its important feature is as follows annealing, a. Thick glass produced in this way since the cooler edge portions, the thickness of the glass edge portion is thin, and therefore the edge portion of the large compressive stress. 2. The thicker the glass, the longer the heat link in the body of the hour glass. 3. In order to meet the cut request, must reduce steel stress. 4. To prevent side sub-cooling after annealing zone too quickly, while the child tentatively generated at a higher tensile stress, resulting in longitudinal losses.
Thickness curve control edge thicker glass and annealed glass is closely related to the pros and cons, annealing improved improved thickness curve. Especially the edge of the glass thickness, the thickness of the individual requirements of the curve to ensure that the sub 25 mm thickness at the edges than the flat thin uniform thickness of about 1 mm. Conventional production, I often can not do this, the first edge portion is too thin to reduce the load, in order to reduce steel production due to the added stress of thick glass thickness, resulting in heat in the glass body through connections hour delay, if production under high load thick tempered glass can cause increased stress in the glass body, to cut back and cut the customer's change difficult, but also make annealing cause trouble, burst increase, decrease yield. Therefore, the load must be reduced in order to meet the appropriate steel stress increases gas gun in the A zone and in the washing machine to increase the chilled water as previously described, the pros and cons edge stress directly affects the slitting of interest, which requires the glass annealing kiln A and B areas as much as possible the temperature of the edge forward, because at the entrance of the annealing furnace has added space gun, plus a pair of gas gun is in the A zone is a good choice, in order to advance tensile stress of the glass edge. Similarly, an increase in the washing machine is also extremely chilled water can improve the time being tensile stress edge, to achieve the purpose of improving slitting
The longer the heat to keep the body in the hour glass, as previously described proper temperature drop zone A thicker glass. Echoing its annealing hour longer. Due to the length of the annealing furnace annealing is flowing so you can probably drop by proper temperature annealing A delay zone to zone, and ultimately to reduce the stress of glass and steel purpose increased RET area edge gas gun. Production losses thick glass of the largest glass longitudinal, longitudinal occur if at least half an hour once, and more time there may perhaps need a few hours, I would particularly like to prepare it is to generate a similar situation in the production of thick glass, you can Perhaps take improved thickness curve, edge thickness control; reduce load; A area increased gas gun and increase in chilled water after washing machine; A proper drop zone temperature; increase gas lance edge RET area and other measures to achieve optimum yield and optimal cutting quality.