The application of thin-wall three-piece cans in the beverage industry

Abstract: The lightweight of metal packaging containers is the development trend of the industry. It can directly and effectively reduce the cost of packaging and form environmental protection and economic effects. The lightweight thin-walled three-piece cans were used in the beverage industry, and an appropriate amount of liquid nitrogen was injected into the containers. After liquid nitrogen gasification, not only the packaging strength but also the flavor of the preserved beverages could be extended.

1 Introduction

Metal beverage cans have undergone a long period of development since their invention, with many inherent characteristics. First, metal beverage cans provide strong light and antioxidant properties that help extend shelf life, maintain freshness and flavor of beverages; metal cans can accommodate high filling speeds, facilitate product stacking, and are easy to distribute, with additional The packaging method can not be compared with the level of production efficiency; the durability of metal beverage cans also reduces the loss caused by product crushing in the production process. The metal beverage cans are easily recycled and recycled as raw materials after consumption, and can be recycled for many times, without losing or changing their properties. It is the world's most recyclable beverage package.

2 New products for reduced packaging - thin-wall three-piece cans

In today's world, advanced packaging companies in developed countries continue to reduce weight and reduce the development of environmental resources. Current engineering techniques allow tank manufacturers to reduce the thickness of the tank wall while still providing high performance containers. Compared with 20 years ago, aluminum beverage cans were reduced by 28% and steel food cans were reduced by 33%. For example, the European 350ml metal cans have been reduced from 45g to about 30g, and the weight has been reduced by 33%. The three-piece cans of French food have used 0.14mm thick DR materials; while the metal three-piece cans in China are still in large-scale use 0.24 to 0.19. The mm thickness of tinplate consumes 2.4 million tons of tinplate in 2008 alone. The resource utilization rate per unit of production is 11.5 times that of Japan, 4.3 times that of the United States, and 2 times the world average.

The three-piece cans currently used in beverages in China generally use SR materials (thick cold rolled tinplate) with a thickness of 0.19 mm or more and secondary cold-rolled tin-plated thin steel plates of 0.18 mm. According to the annual consumption of about 9 billion beverage cans in the Chinese market, the use of 691#250ml beverage cans with a thickness of 0.20mm consumes about 280,112 tons of steel, if it is changed to a thin-walled three-piece can using 0.15mm steel, consumption of steel is about 209,863 tons. Saving 70,249 tons of steel. If it is fully promoted in the food and beverage industry, the use of 0.12mm thin-walled three-piece steel can saves more than 600,000 tons of steel annually.

Table I. Tank internal pressure and strength data of 310ml beverage cans

Note: The force of radial compression deformation 4mm, KN, refers to the force required to compress the recess 4mm in the tank wall. After the tank wall is pressed, the deformation area of ​​15mm*15mm will form a significant depression, and the height of the depression at this time is about 4mm. Therefore, the radial deformation of 4mm is used to evaluate the stress of the sidewall.

* Because the three-piece cans are under negative pressure in vacuum, the radial pressure capacity is weak.

From the data results, it can be seen that the thin-walled three-piece can is a product with a comprehensive performance between the ordinary three-piece cans and the two-piece cans. And subvert the traditional three-piece cans in the form of vacuum pressure, is a positive nitrogen injection tank. With better pressure strength, it is not easy to damage and deform during storage and logistics.

3 Use liquid nitrogen injection technology to increase the packaging strength

Internationally, there have been studies on liquid nitrogen filling technology for non-carbonated beverage cans. In Japan, tin cans were used for the first time in hot cans in 1975. Later in 1981, Japan's Daiwa Can made use of self-flowing liquid nitrogen filling systems. Filling; At the same time, the United States Reynolds company uses liquid nitrogen spray filling. So far, liquid nitrogen filling has been developed for three generations. Among them: the first-generation injection controller uses uninterrupted liquid nitrogen flow into the tank; the second-generation syringe uses a solenoid valve to control the liquid nitrogen entering each target tank. The accurate capacity of the third generation; the third generation of microcomputer control is further connected with the pressure detector after capping, and the amount of nitrogen injection is adjusted according to the data of the pressure in the tank after sealing.

The nitrogen injection technique is to accurately and timely fill liquid nitrogen into the headspace of the vessel. Cold liquid nitrogen (-196°C) turns to nitrogen at room temperature and rapidly expands in volume. 1 g of liquid nitrogen can become 850 ml of nitrogen. When the beverage is filled into the container, liquid nitrogen is immediately added and the lid is closed for a certain period of time. This process produces the desired internal pressure in the container. Applicable to all PET bottles and thin-walled cans and other forms of packaging, increase the packaging strength, solve deformation and logistics issues, widely used in non-carbonated beverages (juice, milk, coffee, vegetable protein drinks, etc.), can extend the product shelf life, Ensure flavor, color and freshness. As a result, beverage packaging can use lighter and thinner materials, saving manufacturing costs.

Figure I. Schematic drawing of nitrogen injection in beverage cans

4 Key technologies in beverage production applications

Accurate liquid nitrogen filling technology:

Although liquid nitrogen injection technology has matured, there are still many uncertain factors. There are many factors that affect the final tank internal pressure of the product on the path from liquid nitrogen to the lid. These factors include: headspace, time to fill the lid, temperature of the product, surface characteristics of the product, airflow from filling to capping, smoothness of movement from filling to capping The state of liquid nitrogen (in which liquid nitrogen may exist in many small droplets, so that the surface area is large and volatile; it may also exist in the form of large droplets, which will volatilize relatively slowly). Among the above factors, there are some factors that are consistent among the tanks, but some factors will have greater differences. It is easy to calculate the theoretical amount of liquid nitrogen, but it is very difficult to calculate the amount of liquid nitrogen needed to add liquid nitrogen to the lid to compensate for the above consumption.

The latest type of liquid nitrogen injectors are equipped with nitrogen injection nozzles for pre-cooling function: the line starts to start, and the nitrogen is pre-dripping before the nozzle reaches the nozzle, so that the nitrogen injection nozzles are pre-cooled and the liquid nitrogen is vaporized due to the thermal nozzles. , Affect the liquid nitrogen dosing dose; The use of positive pressure nitrogen protection, to prevent wet air in the CIP / SIP operation intrusion into the fuselage so that the internal frost, impede the normal operation of equipment; nitrogen injection mouth and nozzle nitrogen blowing inside and outside, accelerate the frost Work, no need to stop operation; filling time from the lower limit of 12ms to 10ms, improve the nitrogen injection accuracy of low internal pressure.

Table 2 Factors Affecting Accurate Nitrogen Injection and Solutions

High pressure sterilization technology:

For beverage products requiring secondary high temperature sterilization, under the current requirement of high temperature sterilization (105~128°C) constant temperature 8-60 minutes, the nitrogen filling will drastically expand, making the pressure in the tank reach 0.5MPa or even higher. Thin-walled three-piece cans have their own flat bottom cover. The flat bottom cover is not suitable for pressure-resistant containers. The cover surface is easy to change, especially after the liquid nitrogen is injected. The cover surface is easily burst. Therefore, the sterilization process must use back pressure technology with a pressure of 1.5-4.0 atmospheres. In this range of back pressure sterilization equipment must be used internal circulation water-type sterilization, using a multi-channel pressure control, making the pressure control more accurate.

The sterilization process is as follows:

Pressurization: The product is placed in a sterilizing device and pressurized air is added to the pot through multi-channel pressure control.

Warming: The inner circulation of water starts to work and is heated to the required sterilization temperature. At the same time, the pressure will maintain a certain proportion with the temperature;

Constant temperature: When the temperature and pressure reach the sterilization setting value, it reaches an equilibrium state and the product is sterilized;

Cooling: After the sterilization is completed, the product is first sprayed and cooled.

Depressurization: After the temperature decreases, the pressure begins to depressurize;

End: The temperature and pressure are reduced to the set point.

Since 2010, some sterilizing equipment manufacturers in China have begun to develop high-pressure spray sterilizing equipment. The design pressure of sterilizing equipment can meet the pressure of 0.35Mpa, and it has begun to be applied in beverage and food factories.

Online pressure detection technology:

Poorly sealed foods and beverages cause damages such as air leakage, liquid leakage, and microbial proliferation. Therefore, beverage and food manufacturers must control the risk of poorly sealed products inside the factory to prevent food safety complaints or accidents from flowing into consumers. The sound and wave detection, proximity detection, and squeeze detection methods commonly used in the food and beverage industry are used for sealing performance testing. Each detection method has its own advantages and disadvantages: the sound wave type detection has poor identification of positive pressure tanks; the proximity type is susceptible to container height or The influence of the height of the cover; extrusion type can easily cause crush damage to the tank wall.

There will be some internal pressure in the food and beverage containers. When the container leaks, the internal pressure will change, which will cause deformation of the cover. By detecting the amount of deformation of the cover, it is possible to detect leakage and internal pressure. However, the precise micro-injection of nitrogen in the thin-walled three-piece cans has a small deformation of the cover surface and is susceptible to the temperature of the product itself. Therefore, there is a need for a detection technology that can correct container height deviations and correct temperature deviations. The use of high-precision temperature sensors and high-precision eddy current sensors can solve this problem.

The online pressure testing equipment works as follows:

On the door or beam support, proximity switches, high-precision temperature sensors and high-precision eddy current sensors are installed;

A proximity switch is used to sense the position of the container to indicate that the temperature sensor and the eddy current sensor begin to operate;

Temperature sensor for detecting the temperature of the container;

Eddy current sensors are used to detect the deformation of the cover. Scan in the direction of movement of the container to identify the shape of the cover. Calculate the deformation of the cover shape;

The calculated deformation of the cap face and the detected temperature were compared with the standard temperature-deformation curve, and the deformation amount was calculated when corrected to room temperature at 20°C.

Above all have cpu and programming software automatic control. The temperature-deformation curve is manually entered before use. After the deformation results are obtained, the system automatically identifies whether the container is leaking (including no cover, lid) and whether the internal pressure is within the required range. Connected to the reject device, it can remove products that do not meet the set requirements from the production line.

5 Conclusion

China has a huge consumer group with a population of 1.3 billion. With the improvement of people’s living standards, China’s beverage industry is developing rapidly. In 2008, China’s beverage output exceeded 60 million tons, which is 210 times that of 1980, with an average annual increase of 21%. Become the world's second largest beverage producer.

Compared with the existing three-piece cans of SR beverages, the three-piece cans of the DR material can be controlled in cost, and the performance of the can body after nitrogen filling is similar to that of the two-piece cans, and is also applicable to the two-piece can filling production line. Customers have more room to choose. Not only does the effective reduction of material thickness, but also the new design will have its own bright spots. It is of great significance to promoting emission reduction and energy saving, reducing resource consumption, creating a conservation-oriented enterprise, developing a recycling economy, and achieving sustainable development. The metal packaging industry is developing in an inevitable trend and has a broad development prospect.

references:

[1] China Canned Industry Association Science and Technology Work Committee, edited. Tinplate food three-piece can process technology. China Light Industry Press. 2008.7

[2] Liu Xiaoxia. Metal packaging containers. Chemical Industry Press. 2004.10

[3] Xie cheerful translation. The application of liquid nitrogen in the beverage industry. Cryogenic technology. 1994 1

[4] Chen Shiwen. Liquid nitrogen injection technology for non-carbonated beverages. PACKAGING WORD 1996.4