Extrusion molding foam mesh
DATE：2022/11/9 8:35:41 / READ： / SOURCE：This station
Extrusion molding foam mesh
Polyethylene foam mesh is a kind of plastic product with light and elastic material. This kind of foam mesh is used for packaging apples, pears, peaches and melons, as well as for packaging ceramics, glass products and precision instruments, which can play a role in shockproof or shock absorption. Therefore, it is widely used in the packaging of these fragile items.(1) Raw material selection
Low density polyethylene resin with a melt flow rate (MFR) of 0.3~1.0g/10min shall be selected as the main raw material for forming foam mesh. The reference formula of raw material combination for foam mesh extrusion molding is as follows (weight parts): 100 parts of low-density polyethylene, 8 parts of sodium bicarbonate foaming agent, and 10 parts of polybutadiene crosslinking agent.
(2) Equipment conditions
The equipment used for extrusion molding of foam mesh shall be a general-purpose single screw extruder for extruding PE materials. The screw diameter is+45mm or 65mm in the middle, and the length diameter ratio L/D ≥ 20:1. It is better to use a barrier type mixing head structure at the front of the screw, which can improve the extrusion quality of raw materials at lower process temperatures.
The structure of the forming die is identical to that of the die for extruding wire mesh, and the rotary die is used. The diameter of the stretching cylinder is 60~300mm.
The traction speed of the traction foam mesh shall match the speed of the foam mesh extruded from the molding die mouth. Within the operating speed range required by the production process, the working speed of the traction device shall be able to continuously change to meet the needs of production.
(3) Process temperature
① The temperature of each section of the extruder barrel (from the feeding section to the homogenizing section) is 90~110 ℃, 120~140 ℃ and 140~160 ℃.
② The temperature of forming die is 150~160 ℃.
(4) Key points of process operation
① The control of raw material plasticizing process temperature has a great impact on the molding quality of products: when the temperature is low, the raw material plasticizing is not sufficient, and various auxiliary materials are mixed unevenly, resulting in uneven foaming of products; When the temperature is too high, the viscoelasticity of the plasticizing molten material will drop, and large bubbles or bubbles will break easily, affecting the product quality.
② With the increase of the extrusion melt pressure, the gas solubility of the melt increases, the nucleation number increases, and the proportion and average pore diameter of the foam are smaller.
③ The amount of foaming agent in Italian raw materials and the amount of foaming agent will change the density of products. The application amount of different kinds of foaming agents can be calculated and selected according to the following formula.
Plastic density/foam plastic capacity-1
Gas generation=plastic density x mass percentage of foaming agent 100
④ See Table 10-3 for physical performance indexes of polyethylene foam mesh.
Table 10-3 Physical Properties of Polyethylene Foam Mesh
Physical performance index Physical performance index
Density/(g/cm ³) 0.128 resilience (single knot)/0.15/50, 0.35/100,
Large hole a=0.5,6=0.47 (mm/g) 0.88/200.1.54/400
Foaming pore size/mm large pore a=0.35, 6=0.31 Compressibility 0.015
Cell distribution/(piece/49, uniform size and distribution, tensile force/N: 25 per piece, 902 10mm in total ²) Diaphragm is honeycomb node bonding force/N
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