Chapter IV Other Shaped Containers
Section 1 Thermoformed Containers <br> 1. Overview
1, concept (definition)
The thermoplastic sheet is clamped on the frame and heated to the softening temperature (to the thermal-elastic state), under the action of external force (such as using plunger, core-mechanical method; or using vacuum to generate air pressure, compressed air and other pneumatic methods) A method of heating the softened sheet against the contour of the mold and cooling it to obtain a container.
2. Features
1 advantages:
a. Obtain the thinnest (0.05mm) plastic container;
b. Can be made from small to super large (1.2 × 3.6m2) plastic containers;
c. Suitable for small to large-scale production;
d. The thickness of the sheet (more liberal) is not strictly limited;
f. Equipment investment is low, mold cost is low, and modification is easier.
2 disadvantages:
a. Low dimensional accuracy of the product;
b. The ratio of depth to depth is limited; (mostly half-shell containers have a certain depth and shallow depth)
c. It must be trimmed and processed with high labor intensity.
3 Scope of application:
Cups, plates, bowls, boxes, etc. used for the packaging of daily-use foods and frozen foods.
It is used for packaging and manufacturing of large-scale products such as industrial products, vehicles, cruise ships, bags, and refrigerators.
Second, thermoforming method
1. Vacuum forming method
2. The pressure forming method is a method of molding a plastic plate heated and softened into a cavity by the pressure of compressed air.
Third, thermoforming container structure design
1. Geometry and dimensional accuracy 1. Geometrical and dimensional accuracy requirements must not be too high;
2 It is recommended to form semi-shell thin-walled products with wide bore and shallow depth.
3 Avoid side holes and undercuts.
2, appearance 1 no gate and mold line;
2 surface roughness affected by the mold;
3 When color decoration is required, the colored sheet is selected, and when the pattern is required, the sheet with pattern is selected.
3, mold wall gradient concave mold is greater than 1/120, 1/60 good convex extension ratio: product depth and width or diameter ratio.
Diameter ratio: the reciprocal of the extension ratio.
The extension ratio is related to the design of the product:
1 The extension ratio reflects the degree of ease of molding. The larger the value, the more difficult the molding.
2 The extension ratio is related to the minimum wall thickness. The larger the value, the smaller the minimum wall thickness.
3 The extension ratio is related to the shape of the die. The larger the value, the greater the inclination of the die.
4 The extension ratio is related to the plastic type. The larger the value, the greater the stretchability of the plastic.
Excessive ratio of plastic parts will appear wrinkled or even broken. Therefore, when designing a thermoforming product with a relatively large extension, it is necessary to comprehensively consider the size, material, expansion ratio and forming method of the sheet in order to obtain good results.
5, corner and large plane design 1 corner (corner)
a. No acute angles are allowed;
b. The arc radius is as large as possible, and the minimum arc radius = sheet thickness. Generally four to five times the thickness of the sheet is used. However, if the arc radius is too large, the rigidity of the product will decrease.
2 Large-format flat-faced thermoformed products should be designed to have a frame-like arched portion throughout its entire surface to form a good rigid body and effectively cover up wrinkles caused by residual air, or a difference in thickness. Scars.
Section 2 Rotary Molding Containers <br> I. Overview
1, concept (definition)
After the powder or paste (liquid) resin is measured (measured by the weight of the product), it is placed in a rotomolding mold, and the mold is melted and fluidized by heating the mold and rolling and rotating (longitudinally and laterally). Depending on their own weight, the various parts of the mold cavity can be evenly distributed. After cooling, the mold can be demoulded.
2, and injection molding, blow molding the difference between the use of powder or paste resin;
2 resin in the mold melt plasticization;
3 Use biaxial rotary molds;
4 The mold is not under pressure and there is no need to install complex water cooling pipes.
3, Features 1 advantages:
a. Fully hollow products with complex shapes without seams;
b. The wall thickness is relatively uniform, the interior should be extremely small, the dimensions are stable, and it is not easy to deform and sink.
c. Low investment in equipment;
d. Products that can be molded into a double-layer structure;
e. Less waste;
f. Economics of production of large volume products 2 Disadvantages:
a. The appearance of the product is not very good;
b. Low dimensional accuracy;
c. Long molding cycle and high energy consumption.
3 Scope of application for large hollow products with low precision requirements
4, commonly used materials
PVC, PE, PP, modified PS, ABS, PA, PC, etc.
Second, the design of rotary molding products
1. General requirements 1 Opening of hollow products with insulation board can also be P172 Figure 10-9
Minimum clearance d ≥ 4t
2t inward convex
3 To increase the rigidity and widen the low ribs and large planes with decorative ribs or pattern text bump 4 thread trapezoid or arc
2, product wall thickness 1 range
1.6～6mm PVC Minimum wall thickness ≥ 0.4mm Maximum wall thickness ≤ 12mm Design deviation is ±5%
2 Wall thickness adjustment by the amount of control wall thickness uniformity L/D ≤ ​​4
3, corner and corner radius 1 outside the corner by the mold surface control for easy molding r ≥ 2t naturally formed by the corner, rounded slightly larger than r
2 Avoid sharp or sharp edges
4, stripping draft angle 1 generally can not design stripping slope; because the product cooling and shrinking in the female mold, there is a gap formed, naturally detached.
2 If the material is hard or low shrinkage, it can be designed as a draft angle of 1 ° ~ 5 °.
5, inserts:
Inserts (metals or high melting temperature plastics) may be designed, but the inserts should be able to be enclosed and fixed in the female mold. Hmin ≥ 4t
6, the size of the dimensional accuracy of tolerance is low, the deviation is ± 5%
Select low shrinkage plastic when high dimensional accuracy is required
7, the shape of hollow products large and complex
8, the appearance of a better appearance, gloss, mold grinding better
9, mold line depends on the accuracy of the mold
10, small production volume
11, hole set insulation plug