Lightweight bottles have thin walls, and high-speed molding requires high melting quality of glass liquid. Slight fluctuations in the uniformity and temperature of the glass liquid will affect molding. Therefore, under the premise that the batch material is fully melted, the stability of the kiln operation process indicators is crucial. The charging and discharging of the melting furnace maintain a dynamic balance, and the charging layer should be thin to ensure that the fluctuation of the glass liquid level is controlled within a very small range.
In order to ensure high-precision production process indicators, promote oil-fired kilns, improve kiln types, and use high-temperature, wide-section kilns. A series of measures are implemented for the kiln, including full insulation, pool bottom bubbling, electric melting, kiln sill, and microcomputer control of thermal parameters.
In order to ensure that the melted and clarified glass liquid is evenly cooled to the drop forming temperature, foreign countries have adopted a long feed channel with a length of 6~9m, a width of 0.4~0.9m, and a depth of 0.15~0.25m since the 1960s, and strictly divided it into a cooling section and a homogenization section, and a proportional mixing burner (natural gas or washing gas) or an auxiliary electric heating system is used for temperature control alone, without being affected by the temperature fluctuation of the melting furnace. Due to the high calorific value of heavy oil, multiple groups of burners cannot be configured to evenly heat the glass liquid. Therefore, it is inappropriate to use heavy oil as a heating fuel for the feed trough, and it is only used as a substitute when necessary. Due to the short life of the silicon carbon rod heating element, for this reason, a large number of molybdenum rods (plates) have been used as electrodes abroad, which are directly immersed in the glass liquid of the feed channel, relying on the "Joule effect" of ionic conductivity of glass at high temperature for heating. In order to prevent oxidation of the exposed end of the molybdenum electrode, a water-cooled chuck or an air-cooled chuck is used. Using the direct heating method of the molybdenum electrode, the temperature fluctuation of the feed trough can be controlled within the allowable range. If molybdenum electrodes are used properly, their service life can reach more than 8 years. With the continuous improvement of electronic control level, the drip temperature control of modern feed troughs can reach + (0.5~1) ℃. In addition, the zoning control and longitudinal cooling technology are used to cool and homogenize the glass liquid, so that the temperature fluctuation of the glass liquid at the outlet of the feed channel is within the range of + 0.5 ℃, which creates conditions for providing high-quality glass drops to high-speed bottle making machines, reducing process defects in the molding process, and manufacturing high-quality lightweight bottles.
In order to reduce the fluctuation range of drip weight, the glass liquid level in the feed trough is precisely controlled, and its error range is 0.2-0.5mm
The process of making glass products from glass liquid can be divided into two stages: molding and finalization. The molding operation is usually controlled by three characteristic temperature values: softening temperature, annealing temperature and strain point. For different products, reasonable process parameters should be determined through experiments. In addition, advanced bottle making, feeding and heating systems and the use of advanced molding processes are the fundamental guarantee for obtaining uniform wall thickness and achieving lightweight.
The latest design of air-conditioned constant temperature annealing furnace is one of the keys to solve the problem of annealing lightweight bottles. Since the average thickness of the wall of lightweight bottles is 2mm smaller than that of standard bottles, the heating rate of glass bottles and the heat dissipation rate of hot glass bottles are both faster, which requires the use of accelerated heat conduction rate to meet this requirement, that is, the use of closed air conditioning temperature to make the air flow move quickly from the glass surface of the bottle. The annealing furnace is divided into 10 areas. The 1st to 4th areas are heating zones (air conditioning). Usually, heating is not necessarily required in the 4th area, and the heating amount in the 3rd area is also very small. Each area is 1.8m long. One fan air conditioner is used in the 1st to 2nd areas respectively, while in the 3rd to 5th areas, especially in the 6th area, double fan air conditioners must be used, and the 7th to 10th areas still use single fan air conditioners. Thermocouples are used to measure temperature and control temperature in each area of the annealing furnace. In the rapid cooling zone, a blower is also used to blow cold air for adjustment. Practice has proved that when the temperature of lightweight bottles is below 400o℃, the cooling rate of the bottles is 20C/min, and no damage is caused to lightweight bottles. The annealing furnace is a full metal structure, without refractory masonry, heated by electricity or natural gas, and the latest insulating materials are used to ensure good thermal insulation performance. Therefore, the weight of the annealing furnace is much lighter than that of a general annealing furnace.
Lightweight bottle molding process
The main feature of lightweight bottles is thin and uniform walls. The key to its molding is to obtain a large-sized and reasonably shaped preform and ensure that it is fully and reasonably reheated. To solve this problem, it is related to which basic molding method is used.
So far, the basic molding methods for daily bottles and cans are nothing more than suction-blowing, blow-blowing and pressure-blowing. Their principles and effects are different. However, the same molding method adopts different working systems and the effects are not consistent. The molding situation is closely related to the molding method, which is particularly prominent in the molding of lightweight bottles.
Suction-blow method
Except for the core cavity, the preform is basically a solid block of material. Its size is quite small compared with the finished product. This molding method requires that the preform has a very high temperature when entering the molding mold, the glass has good fluidity, and it creeps greatly and redistributes to obtain the finished product. However, if the bottle wall is thin, the temperature of the glass in the molding mold is also low, and it is impossible to creep greatly, and the distribution will not be uniform, and a qualified lightweight bottle cannot be blown out.
Blow-blow method
The main measure to reduce the weight of the bottle in the blow-blow method is the internal shape design of the preform, which means that the size of the preform is enlarged and the shape is reasonable, and the increase in size must be the increase in the volume of the back-blowing air bubble to reduce the weight of the material. Production practice has proved that when the volume of the back-blowing air bubble reaches 20%~30% of the volume of the glass material, the production speed can be increased. This is because the heat removal of the preform mold is increased and the heat load of the molding mold is reduced. However, since the increase in the volume of the back-blowing air bubble in the blow-blowing method is based on the premise of increasing the heat dissipation of the primary mold, the temperature of the primary bottle blank becomes lower, the reheating capacity decreases, and the working time of the primary mold is prolonged, the reheating time of the primary bottle is also shortened, so the wall thickness of the finished product is thin but uneven. In addition, when the back-blowing air bubble reaches a certain volume in the blow-blowing method, a ring of wall thickness distortion will generally appear on the waist of the finished bottle, that is, a "gas hoop" (or "two-section waist") appears on the bottle body. Although vacuuming can be used instead of gas-blowing bottle heads to reduce the "gas hoop", the effect is very limited, which limits the blow-blowing method to obtain uniform wall thickness.
Press-Blow Method
The main feature of the press-blow method is that the bottle mouth and the preform are pressed out at one time by the punch. If this method is used to press the small-mouth preform, the size can be larger, the creep range is small when the glass is redistributed after entering the forming mold, and no "air puffing hoop" will be produced, and the uniformity of the wall thickness of the finished product can be guaranteed. In the common row machine press-blow method, the punch supports the material from bottom to top and stamps the preform step by step. This method is very effective in producing large-mouth bottles. With the rapid development of cooling technology and mechanical processing technology, the row machine can press the small-mouth preform. The temperature of the pressed small-mouth preform is higher than that of the blow-blow method, and the wall temperature is more uniform, the size is larger, and the shape is more reasonable. When entering the forming mold for blowing, the glass has good fluidity and a small creep range. The wall thickness uniformity of the obtained finished product is better, and the bottle can be made lighter. Therefore, compared with the blow-blow method, the press-blow method has unquestionable superiority in producing lightweight bottles.
However, when the line-type bottle making machine produces small-mouth bottles by the pressure-blow method, due to the structural principle of the line-type machine itself, some serious defects appear, which hinder the further development of lightweight bottles. The main manifestations are as follows.
1 The reproducibility of the operating cycle is poor.
The acceleration process of the mechanism lacks precise control.
The end point buffer (or air cushion) is inappropriate, the piston stroke length and time are inappropriate, and the adjustment range is very narrow. 4 The coordination and design between the various mechanism components are too complicated, and experienced personnel are required to make precise adjustments.
Small-mouth pressure-blow technology (NNPB)
Hermann Haye is one of the pioneers of European glass bottle manufacturing. In the mid-1960s, he first used the blow-blow (BB) method to test the weight reduction of bottles and jars. The test results showed that when using the blow-blow method to form, the bottle weight can only be reduced within a limited range, but the product cannot reach the level of lightweight bottles. The main reason is that the difference in the contact time between metal and glass at the location of the bubble in the forming stage leads to uneven distribution of glass in the bubble and the wall of the final product.
The solution to the above problem is to use the NNPB method. The process of NNPB molding is: feeding the drop into the initial mold → pressing the bubble → flipping the bubble to the molding mold → reheating → vacuuming the molding mold → auxiliary molding → final blowing → clamping the bottle to the cooling table.
From the process, it can be seen that there is no problem of different bubble contact time in the NNPB method, the process is simplified, and the pressed bubble has a more uniform wall thickness. Moreover, the NNPB method has a more sufficient reheating time than the BB method, which helps to equalize the glass temperature in the bottle wall after final blowing.
As can be seen from Table 2-39, the essence of the NNPB method is to make the glass evenly distributed and have sufficient reheating time, so as to fully exert the potential of material strength, so as to achieve the purpose of reducing the weight of the bottle and maintaining the strength.
The main features of the small-mouth pressure-blowing method are: the temperature uniformity of the glass droplets is good, the automatic control of the droplet weight device is introduced, the degree of pressing is improved, the process time is allocated according to the process requirements of the lightweight bottle, the mold lubrication is improved, the micro-damage on the inner and outer surfaces of the bottle is reduced, and the mold axial cooling system is adopted to form a uniform thin-walled product. The small-mouth bottle pressure-blowing molding process is shown in Figure 2-38.
Molding process: First, the droplets fall into the molding die and fall to the top of the metal punch that rises to the material receiving position. The blanking head moves to the specified position of the initial mold and seals the upper mouth of the initial mold. Then the punch moves upward to punch out the shape of the initial blank. Then the blanking head moves away and flips the initial blank into the molding die.
The molding die is closed, the jaws are opened, and the initial blank is placed in the molding die for reheating and stretching. Then the blowing head moves to the correct position above the forming mold, vacuum forming the blank in the forming mold, and positive blowing is performed at the same time, using compressed air for internal cooling to form the bottle. Finally, the formed bottle is clamped out with the forming mold. In order to successfully achieve the small-mouth pressure-blowing operation, first of all, the relevant hardware must be available, and in addition, the following basic operating conditions must be met.
(1) Bottle mouth When using a small mouth pressure-blow operation, the inner diameter of the bottle mouth of the produced bottle can be as small as 18mm. Depending on the height below the bottle mouth and the diameter of the bottle body, a smaller bottle mouth inner hole size can be produced.
(2) The height below the bottle mouth depends on the design of the blank. The maximum blank height of the punch mechanism's stroke limit is between 160 and 170mm. The maximum bottle height below the bottle mouth is related to the extension of the blank, which in turn is related to the design, quality and volume of the bottle. Bottles with a height below the bottle mouth of up to 280mm have been produced, but this limit can be exceeded depending on the design and weight of the bottle. Table 2-40 lists the relationship between bottle mass and volume.
The above diameter limit dimensions are for molds that use vacuum forming. If vacuum forming is not used or the width of the vacuum tank is reduced, bottles exceeding the above dimensions can be produced.
(2) The following factors should be considered in the process:
1. High standards of chemical and thermal uniformity of the glass liquid must be maintained.
2. The lowest possible softening temperature of the glass, that is, the lowest working temperature.
3. The glass must have good chemical and physical stability over the entire temperature range in which the bottle is used.
The following viscosity and temperature relationship can be referred to.
The production of lightweight bottles by small-mouth bottle pressure-blowing has high requirements for technology and equipment. In addition to the strict requirements for the preparation, transportation and storage of raw materials and batch materials and the melting of kilns mentioned above, the bottle making machine is required to have the necessary mechanisms and devices to reduce mechanical wear and maintain a good operating state; there are high requirements for the material and processing of key components, such as punches and cooling pipes. Due to their small diameters, the punches must be made of high-quality steel for the design of the mechanism and to meet the requirements of the mold device; the overall processing is to eliminate metal wear as much as possible; the punches must be precisely polished along their longitudinal axis; the connection dimensions of the punches and punch joints must be kept within the tolerance range. In addition, the design of the initial mold and the bottle shape must meet the process requirements of small-mouth bottle pressure-blowing.
Based on the small-mouth pressure-blowing process, in recent years, Haiye Company has successively developed the HAP method and several types of bottle making machines, including H1-2, H6-12, and H1-9. The wall thickness of the bottles and cans it produces can be reduced to 1mm, making it an ideal machine for producing lightweight bottles. The Haiye pressure-blowing method is used to produce lightweight small-mouth bottles. Due to the uniform thickness distribution, the maximum weight reduction rate can reach 33%. The strength standard of lightweight bottles is significantly improved compared to the standard of heavy bottles. Figure 2-39 shows the structure of the H1-2 Haiye bottle making machine.
The technical features of the Haiye bottle making machine are as follows.
1 The rotary table is used to make the droplets fall directly into the primary mold.
2 Both small-mouth bottles and large-mouth bottles are formed by the pressure-blow method.
3 It has strong adaptability and can produce heavyweight, lightweight and ultra-lightweight bottles and cans.
4 Using one primary mold and two forming molds, the single-cavity output is high, which is unmatched by any other bottle making machine.
5 The primary mold has sufficient reheating time during the transfer process and can be adjusted.
6 The primary mold does not need to be turned over when transferred from the primary mold to the forming mold.
7 The contact time between the glass and the forming mold and the contact time with the primary mold are in a suitable ratio.
8 The bottle is clamped by the mouth mold throughout the molding process.
9 Cool all molds evenly