1, low pressure foam injection molding

PP structural foam injection molding generally adopts the following molding methods: the low-pressure foaming injection molding; the high pressure foaming injection molding; the counter pressure foaming injection molding; the two-component foaming injection molding.

The difference between structure foaming injection molding and ordinary injection molding. The nozzle adopts the blocking nozzle, generally adopts the injection method. This method can produce large thick wall products, the surface of its products is dense, can be printed or coated, but the surface roughness is poor.

Min Gan Cao with Sumitomo Corporation of Japan SSF100/150/200 of low foamed injection mechanism prepared structure of foamed PP board, and analyzed the influence of the process parameters on the properties of the product obtained optimal process parameters for injection time 5S, injection pressure of 80MPa, barrel temperature 240 DEG C, mold temperature of 70 DEG C, Paul pressure time 10s, cooling time 8s.

Peter zipper with low pressure injection molding method under different melting temperature injection molding the PP cylindrical samples, using small angle X-ray diffraction method of sample research, results show that the junction formation skin cycle and sample cylinder diameter and melting temperature, melting temperature is higher, the larger the size of the product, forming crusts cycle is long.

Sporrer, etc., developed a mold specially used for low-pressure foaming machine, known as the „exhaust mold“. The inner cavity surface of the carbon steel is covered with a number of grooves, and the mold filling is easier to control.. The experimental results show that the structure of the injection molding of this mould is good and the surface is smooth when the injection parameters are suitable..

2, high pressure foam injection molding

Compared to high pressure foaming injection molding cavity pressure for 7 ~ 15MPa, with ordinary injection machine, increasing the second clamping holding pressure device, the surface of the product is smooth, clear, to reflect the mold cavity in the shape of a small, but opening and closing will creases, stripes, so the mold of making precision requirement is high, and the mould cost is high, secondary mode-locked packing requirements.

Iris Chang with the second mold method successfully prepared structures of PP foam products, the product has more uniform cell distribution, bubble diameter are in 20 ~ 30 m density of about 15 percent decline and not of foamed PP mechanical properties compared, although tensile strength fell by 24.8%, but notched impact strength increased 125%, bending strength increased by 19.6%.

Norbert Muller, the second mold method, to PP / glass fiber blends as raw materials of high pressure foaming injection molding, the product of the density decreases by 10% to 15%, reduce the quality of the 30% ~ 40%. The expansion rate can reach 100% if the cut is replaced by the cut in the mould, the density can be reduced by 50% (the density is about 0.2 ~ 0.4 g/cm3).. The mold cavity thickness of 2 ~ PP when the molded 4mm structure of the foam products, foaming effect is best, bending strength is higher.

3, anti pressure foam injection molding

Counter pressure foam injection molding is prior to injection with high pressure gas (such as air or inert gas) will be full of the cavity of the mold, injection stop the plastic foaming expansion to obtain dense surface, using under injection and after injection of the weld material to gas emission in the plastic expansion and filled the cavity. Injection molding product surface roughness is better, the surface more uniform microstructure compact, but need to increase a gas storage pressure device and can be sealed cavity mold, high gas pressure (20MPa), investment is larger, and the mold seal is more difficult.

Peter zipper with wide-angle X-ray diffraction method were used to measure the low pressure foaming injection molding and anti pressure foam injection molding of PP samples. The results showed that the back pressure foam injection molded samples of surface quality is better.

4, two-component foam injection molding

Two foam injection molding is a kind of special high pressure foaming injection molding method, which uses special injection molding machine, the injection machine with two sets of injection devices: a set of injection molding product surface, another set of plastic core. Different formulations of raw materials, respectively, through the two injection molding device in a certain order successively injected into the same set of mold cavity, thus resulting in a dense surface and foam core of the light products. For large products, the core can be doped with filler, waste, paper, etc., thereby greatly reducing the production costs of the product.