Section 4 Design Principles of Packaging Functions and Packaging Structures
First, the packaging function
a Protection function: that is to protect the value of the use of goods, which is the primary function of packaging.
b Convenient functions: mainly embodied in convenient storage and transportation, convenient use and convenient sales.
c Promotional function: mainly manifested in the appearance of the package, whether the modeling and decorating will meet the new trend will play a major role.
Second, the packaging structure design principles
a The principle of scientific and scientific nature is to apply advanced and correct design methods, apply appropriate and appropriate structural materials and processing techniques, make the design standardized, serialized and generalized, in line with relevant laws and regulations, and the product is adapted to batch mechanized automatic production.
b The principle of reliability and reliability is that the packaging structure design should have sufficient strength, rigidity and stability, and it can withstand the effects and influence of various external factors in the circulation process.
c The aesthetic appearance is to achieve the aesthetic requirements in the design of packaging and design, including the six elements of structure and six rules of structure.
d Economical It is an important principle of packaging structure design. It requires rational selection of materials, reduction of raw material costs, and reduction of raw material consumption. It requires design procedures to be rational, improve work efficiency, and reduce costs.
Section V Basic Factors of Packaging Structure Design
First, the contents
a Physical properties of the contents Solid, liquid, powdery, and gaseous.
b The chemical properties of the contents include vulnerability, deformability, water resistance, moisture resistance, rust resistance, and mildew resistance.
c Content Applications Food, medicine, electronics, chemicals, etc.
Second, the packaging container design materials
Important packaging materials in the modern packaging industry include paper, cardboard, plastic, metal, glass, ceramics and various composite materials.
a Physical properties of the material: transparency, thickness, barrier properties, etc.
b Chemical properties of the material: chemical stability, safety, corrosion protection, rust resistance, etc.
c Mechanical properties of the material: strength, elastic modulus, etc.
d Material forming process: rheology, plasticity, etc.
e The decorability of the material: printability, smoothness, etc.
Third, the circulation environment conditions
a Physical factors: impact vibration and stacking static pressure
b Biochemical factors: temperature, humidity, rain, radiation, harmful gases, microorganisms, etc.
c Man-made factors: rough handling, counterfeiting, etc. shall be considered in the design of the package in the above-mentioned circulation environment and the measures taken. Section VI: Packaging Structure Design Mechanics Principle Packaging structure design contains many basic principles of mechanics, such as Calculation of the compressive strength, stiffness, and stability of the container; stress concentration problems; calculation of the strength of the pressure vessel; bending of metal structures, mechanical problems in stamping, and the like. This section gives a brief introduction to these basic theories and applications of mechanics. In the future, it should further study with specific learning content.
1. The mechanical properties of the material tensile The example of the low carbon steel with the most extensive engineering application and the most representative mechanical properties is as follows:
It is divided into four main phases:
1) The elastic phase: oa segment, when the external force is removed, the deformation is completely restored.
2) In the yield phase: ac, there is a phenomenon of crystal slip, temporarily losing the ability to resist deformation, and causing plastic deformation.
3) Reinforcement stage: cd section, which produces irrecoverable plastic deformation.
4), local deformation: de segment, neck down until fracture.
When the structure is designed, it is generally required that the stressed material be within the elastic range. However, the plastic deformation characteristics of the material should be used in the production process such as stamping.
First, the mechanical properties of the material
The mechanical properties of the container are not only related to the structure, but also have a close difference with the mechanical properties of the material, so the mechanical properties of the material must be studied. The mechanical properties are determined by test methods. Tests are generally performed through tensile and compression tests.
2, material other mechanical properties
Creep properties of materials: At certain temperatures and stresses (below the yield point), the material slowly deforms plastically over time. Metal materials only have creep at high temperatures, and polymers can also occur at room temperature. Stress relaxation: The phenomenon that the stress of a material gradually decreases with time under the condition of a specified temperature and initial deformation is called stress relaxation. The fatigue limit of the material under the action of alternating stress: under the repeated action of vibration and impact of the package during transportation, if the stress received is far below the yield limit, it will be destroyed after a period of time. Therefore, we must consider the fatigue limit, reduce the stress concentration, and improve the surface finish of the product. Material Hardness: There are several methods of hardness measurement. Generally, the indentation method is used to indicate the ability of the material to resist plastic deformation within a small volume range. Fracture Toughness of Material: Reflects the ability of a material to resist crack propagation and is derived from experimental testing.
3, material design indicators and applications
Strength Index: The ability to reflect the ability of the material to resist plastic deformation, such as yield limit, strength limit, fatigue limit, creep limit, etc., is the main basis for strength calculation. Stiffness index: An index that reflects the ability of a material to resist elastic deformation, such as elastic modulus, shear modulus, etc. These parameters must be used in the calculation of stiffness, static indetermination, and stability issues involving the elastic deformation of components. Plasticity index: indicates the degree of plastic deformation of the material, such as the reduction of area, which is the basis of the material stamping and forming design. Toughness indicator: It reflects the comprehensive performance of material strength and plasticity and is an energy index. Reflects the ability of a material to absorb energy during deformation or fracture. It is an important indicator of the choice of materials.
Second, the material strength calculation
When the material is subjected to basic deformations such as tension, compression, torsion, and bending, the maximum stress may exceed the material's strength limit. Therefore, the strength must be verified when designing:
The commonly used strength theory is:
The maximum tensile stress theory: As long as the maximum tensile stress the component withstands reaches the ultimate stress value of the material, it will cause material damage.
Maximum elongation line strain theory: As long as the material's maximum line strain reaches a certain limit strain value, it will cause brittle fracture of the material.
Maximum shear stress theory: As long as the maximum shear stress in a component reaches an ultimate shear stress value, plastic yield of the material will result.
Shape change specific energy theory: As long as the shape change ratio of the component reaches a certain limit, plastic yield occurs.
The calculation of the strength of thin-walled pressure vessels In the structural design of metal vessels, when there is a large internal pressure (such as spray cans, etc.), the strength must be calculated to select the appropriate materials and thickness parameters, calculated as follows:
Third, the structural rigidity problem
A very important issue to consider in the design of packaging structures is the rigidity of the structure. Packaging containers such as cartons, paperboards, metal cans, plastic containers, etc. must have a certain degree of rigidity, ie the ability of the structure to resist deformation, so that Good protection of the product and the packaging structure itself.
Different structures have different stiffness calculation methods, and they should be selected according to specific conditions during design. In general, the methods for improving the stiffness of components include:
Select a material with a large elastic modulus.
Increasing the material thickness and bending section modulus to increase the strength of the structure (such as steel drums, cans, plastic containers, etc.)
Fourth, the structural stability calculation
When an elongate bar or a thin-walled structure (such as a post in a wooden box structure, a corrugated cardboard box, etc.) is subjected to pressure, even if the stress received is far below the material's strength limit, it will abruptly and rapidly deform due to loss of balance. Even damage, this phenomenon is called instability. For slender rods, the critical pressure can be determined by the Euler formula:
For medium and small flexibility rods, empirical formulas should be used. Reference can be made to the general materials mechanics textbooks.
The main measures to improve structural stability include:
Reduce the length of the pressure bar.
Choose a reasonable section shape and try to increase the moment of inertia of the section.
Increase the rod or plate end constraint.
Choose a material with a large elastic modulus