Discussion on vacuum packaging of the hottest heav

2022-07-24
  • Detail

Discussion on vacuum packaging of heavy export machineries

heavy export machineries often experience impact, vibration, drop and severe environmental changes in the process of shipping, among which the changes of temperature and humidity in environmental factors are particularly severe, and the performance requirements of packaging materials are very high. Therefore, it is necessary to study the performance of packaging materials, find out the factors that affect their performance, and carry out targeted protection. Whether the sealing performance of the main packaging materials meets the requirements, whether the fixation of the product in the packaging box affects the sealing performance, and the impact of the environment on the sealing performance of the materials. This paper focuses on the sealing of packaging materials, and discusses the effects of heat sealing of materials, heat sealing strength and environmental temperature and humidity on packaging materials

the principle of vacuum packaging is to extract the air in the packaging, and then use the impermeable packaging film for sealing packaging. The purpose is to keep the sealed space in a low oxygen and low humidity state, so as to prevent corrosion on the surface of metal products. Vacuum packaging requires the use of high barrier, high strength composite materials and desiccants. As the vacuum packaging does not affect the shape, size and material of the packaged products, this paper puts forward some other requirements and restrictions on PP as the interior material, and the operation method is simple: it is convenient to open and close, so it is widely used in practical operation. At present, most of the vacuum packaging materials used are aluminum-plastic composites, which have the greatest advantages of high barrier and high strength

vacuum packaging process

(1) cleaning and drying of packages: cleaning and drying of packages is the preparation process of vacuum packaging. Cleaning is to clean the condensate, dust, sweat and other foreign matters on the surface of metal products. The choice of cleaning fluid depends on the characteristics and protection grade of metal products. Drying is a necessary process for cleaning metal products. Common drying methods include compressed air drying, heating drying, infrared drying, bath dehydration and wiping

(2) bottom layer protection: lay two layers of PVC bubble plastic film on the basis of waterproof material at the bottom of the wooden box to prevent the composite material from damaging its sealing performance due to contact and friction with the bottom of the wooden box, and then lay the composite material on the bubble plastic film

(3) fixation of machinery: move the machinery to the wooden box base and fix it on the wooden box sleeper

(4) fixing of accessories: after the installation accessories or parts of the machine are properly packaged, they are fixed at the appropriate position on the base of the wooden box

(5) calculation and selection of drying utilization: because the mechanical products to be protected are usually small in volume and different in shape, the composite materials cannot be completely attached to the surface of the machine after vacuum pumping, so there is a lot of space in the vacuum packaging, leaving a lot of air, Therefore, the placement of desiccant is particularly important. It is necessary to keep the air in the sealed space dry during the whole transportation and storage of mechanical products. Scraping: the type of drying agent can select fine pore silica gel or coarse pore silica gel according to the value of the packaged mechanical products or the material of the machinery. The amount of desiccant can be calculated according to the empirical formula recommended by Ch 4879:

empirical formula:

(w=k1arm + K2D)

where:

w - the amount of desiccant required, kg

a - the surface area of the packaging surface that can be permeable to moisture m2

r - the moisture permeability of the packaging material, G/m224h

m - the storage time of the packaging, month

d - the mass of the buffer structure material, kg

k1 - the temperature humidity relationship coefficient, 0.12 - 0.0007

k2 - type coefficient of buffer material, 0.84 I ().04 (check standard)

desiccant shall be packed in breathable paper bags, cloth bags or fine porous metal containers and put into envelopes for sealing

(6) making envelopes: cover the products to be packaged with composite materials, seal the long edges, make envelopes, and then vacuum

(7) air extraction and sealing: use air extraction equipment to extract the air in the envelope, and finally seal the air extraction port

existing problems and solutions

(1) bottom layer protection: PVC bubble plastic film is a kind of shockproof cushioning material, which can be used for a long time under the condition of 20g per square centimeter. It can directly package products, and is suitable for packaging small mechanical products or drugs. For sharp products with high quality and concentrated load, it can not play the role of shockproof and cushioning. Therefore, it has the characteristics of being a packaging material for bottom layer protection, and the price of PVC bubble film is relatively high, which increases the packaging cost. Therefore, you can choose materials that are relatively cheap and can play a role in isolation and protection, such as ordinary fiber materials

(2) mechanical fixation: mechanical fixation is to fix the base of the machine to the sleeper of the wooden packing box. In the current operation method, the screw of the fixed machine needs to penetrate the composite material, so the sealing property of the composite material will be damaged. In order not to damage the sealing property on the basis of mechanical fixation, we can add a layer of rubber gasket between the 1 and 2 layers to prevent the metal gasket on the surface from scratching the composite material, and the rubber gasket should be made of rubber with high elasticity and no aging, so as to more effectively prevent the air leakage of the threaded rod perforation. If necessary, apply a layer of sealant around the screw, or select new packaging materials such as heat shrinkable materials to reduce the air permeability of the perforation

(3) tightness of vacuum packaging marijn Dekkers repeatedly stated to investors in Berlin, Germany: the transaction of the business department (production of transparent plastics and foam chemicals) is expected to be completed by the end of this year: the sealing performance of composite flexible packaging directly affects the quality of packaging and the shelf life of packaged products, so it is required that the sealing performance of composite materials should reach the best state. There are three parameters to evaluate the sealing performance: heat sealing strength, sealing interface tightness and heat adhesion strength

sealing performance evaluation

(1) heat sealing strength

heat sealing strength refers to the energy required for the heat sealing interface of the standard sample to be stripped under the condition of constant temperature and humidity. The value reflects the highest pressure resistance of the sealing part of the film. Formula of heat sealing strength:

b= peak value of material stress f (n)/width of sample B (CM)

the greater the value of heat sealing strength, the better the heat sealing effect, that is, the greater the peak value of material stress, the better the heat sealing effect. The best sealing is that the strength of the sealing part is equivalent to that of the sealed body film. Samples can be taken for tensile test at the heat seal to check the strength value and fracture position. If the fracture occurs in the body material and the main body is damaged, it is mainly near the sealing place, because the material here has become thinner, such sealing is qualified; If the fracture is in the sealing area, the sealing area is a weak point

(2) sealability of sealing interface

sealability of sealing interface refers to the ability to resist the corrosion, penetration and diffusion of packaging contents caused by the compactness of heat sealing interface. In essence, it is a durability index of heat sealing performance, and the heat sealing strength is its basis

(3) thermal adhesive strength

thermal adhesive strength is used to characterize the heat sealing strength of the film in the semi molten state before sealing and cooling. The thermal adhesive strength is one of the important factors that restrict the packaging speed of the vertical automatic packaging machine. When a small hand-held heat sealer is used for sealing, the thermal adhesive strength has little effect on the sealing effect

factors affecting the heat sealing strength

heat sealing temperature, heat sealing pressure and heat sealing time are important factors for adjusting the heat sealing process. The two parameters affect the heat sealing strength. A good heat sealing effect can be achieved by reasonably setting or adjusting the size between the three parameters

heat sealing temperature

the function of heat sealing temperature is to heat the adhesive film to an ideal viscous flow state. You Xun: the polymer has no definite melting point, which is a melting temperature range, that is, there is a temperature zone between the solid phase and the liquid phase. When it is heated to this temperature zone, the film is sent to the single-chip computer for processing into the melting state. The polymer molecules in the molten viscous flow state are deformed and close to each other under the sealing pressure, and sufficient gravity is generated between the molecules to seal the heat sealing surfaces

the heat sealing temperature is not determined according to the characteristics of the heat sealing material, the thickness of the film, and the processing tolerance of the heat sealing die is 1/3 of the plastic tolerance. The number of pressing and the heat sealing area are not determined. In the case of non automated bag making, the heat sealing temperature mainly depends on the characteristics of the heat sealing material and the thickness of the material

heat sealing temperature directly affects the heat sealing strength of composite packaging materials. In the process of packaging or bag making, if the heat sealing temperature is not set properly or adjusted improperly, the following two situations will occur

when the heat sealing temperature is too high, which exceeds the heat shrinkage temperature time of the composite film surface material, the composite film will shrink and deform, resulting in adhesion between the composite film and the heat sealing knife, melting and extrusion of the heat sealing edge material, and reducing the heat sealing strength of the material. When the heat sealing temperature is too low, the polymer will not reach the melting state and become unstable; It can make the two films bond well and cause poor heat sealing. It also affects the heat sealing strength and sealing performance. Therefore, different heat sealing temperatures should be selected or set for different heat sealing layer materials in actual production. The heat sealing temperature and the heat sealing pressure and time should be adjusted and coordinated to achieve the best heat sealing effect. For example, when the thickness and heat resistance of the composite film surface material limit the heat sealing temperature, so that it can no longer rise and poor heat sealing occurs, it can be compensated by increasing the heat sealing pressure and prolonging the heat sealing time

heat sealing pressure

the function of heat sealing pressure is to make the polymer in viscous flow state produce effective macromolecule mutual penetration and diffusion between sealing interfaces. Applying appropriate pressure during heat sealing can promote the bonding and mutual fusion of heat cover materials, and play a positive role in improving the heat sealing effect. If the heat sealing pressure is insufficient or uneven, bubbles will be generated at the heat sealing part, resulting in faulty welding and poor heat sealing. However, if the heat sealing pressure is too high, the molten material will be extruded, resulting in brittle heat sealing edges and easy cracking, which will affect the heat sealing effect and reduce the heat sealing strength. After heat sealing of general materials, the strength loss at the sealing part shall not be greater than 10% - 15%

the change of pressure can change the heat sealing characteristics. When the pressure decreases, the heat sealing temperature or time can be increased to achieve the same heat sealing effect. On the contrary, when the pressure increases, the heat sealing temperature can be appropriately reduced or the heat sealing time can be shortened. In this way, the output can be increased by shortening the heat sealing time. However, it requires a very high temperature and the operation is more difficult. Therefore, it can be adjusted according to the actual production situation

heat sealing time

heat sealing time refers to the time that the film stays under the hot knife. The heat sealing time is related to the heat sealing temperature and pressure. When the heat sealing temperature is low, it is necessary to increase the heat sealing time. When the heat sealing pressure is small, it is also necessary to increase the heat sealing time. However, for the automatic sealing bag making, the heat sealing time determines the production efficiency of the heat sealing equipment. At the same time, the heat sealing time is also related to the characteristics of heat sealing materials. For example, for heat sensitive polymer materials (PVC, PAV, PP) and various heat sealing shrink films, the heat sealing time should not be too long to avoid degradation. It should be heat sealed at high temperature for a short time

heat sealing material

material properties and material thickness are the key factors affecting the heat sealing effect

material properties: different types of high

Copyright © 2011 JIN SHI