Experimental investigation on the forming and evolution process of cell structure in gas counter pressure assisted chemical foaming injection molded parts

Abstract

By using a standard stretch spline as the research object, the influence of gas counter pressure (GCP) technology on melt foaming behavior in chemical foaming injection molding (CFIM) process was investigated. Related experimental line for GCP assisted CFIM foam was designed, and the effect of GCP technology on melt flow front, spline surface quality and internal cell was studied. According to the results obtained from the experiment, two critical GCP pressures and one critical GCP holding time were innovation proposed. Two critical GCP pressures are the critical GCP pressure of melt flow front cell not cracking and the critical GCP pressure of melt not foaming, respectively. The critical GCP holding time is the secondary foaming behavior time. Based on the proposed critical GCP pressures and critical GCP holding time, the influence mechanism of GCP technology on melt foaming action during CFIM process was revealed.

Effect of Gas Counter Pressure on the Surface Roughness, Morphology, and Tensile Strength between Microcellular and Conventional Injection-Molded PP Parts

“…This is caused by gas penetration into the melt during the melt filling process [ 23 ]. However, Li et al [ 29 ] observed several pits caused by cell rupture and many gas marks on the melt front when not using GCP, although they used CBA foaming. There is a series of cells along the transition area between the skin and core layers of the part with a holding time of 10 s as shown in Figure 4 C1.…”

“…The surface roughness at the gate, mid, and flow end are 49.4, 47.37, and 45.69 μm, respectively, for microcellular injection-molding. The microcellular injection-molding has silver streaks, swirl marks, and blisters on the surface, which are caused by microcells on the melt front of the core section trapped by the mold wall (this is the fountain flow effect in the filling process), thus leading to the rough surface [ 29 , 35 ]. The gate has the highest surface roughness of the three positions.…”

“…A laser 3D profile microscope is expensive and needs careful operation, so a surface gloss instrument is used to depict the surface roughness value. Li et al [ 29 ] used chemical foaming, gas counter pressure, and surface gloss methods to study the surface roughness of foamed parts. Their results show that surface gloss values are 6.2 and 11.8 for counter pressure of 0 and 0.6 MPa, respectively.…”

Lightweight and High Mechanical Properties of In Situ Poly(ethylene terephthalate) Reinforced Polypropylene Composite Foams by Chemical Foam Injection Molding

“…Sometimes, the decomposition residues will cause frosting on the surface of the plastic part. 6 It is reported that "gas-counter" 7 and "core-back" 8 technologies were applied on the basis of the traditional CFIM process, which increases the equipment cost and makes the process control more complicated. Therefore, it is almost impossible to optimize the cellular structure by simply adding a new process or regulating the molding process parameters.…”

A simple melt blending method for preparing PP/HMSPP foaming composites with superior surface appearance and mechanical performance

“…There are two mainstream ways to improve the surface quality of foaming products: using gas counter pressure (GCP) technology [8][9][10][11][12] or reducing the cooling rate by increasing the mold temperature. 7,[13][14][15][16][17] Many researchers focused on using GCP technology to improve surface quality.…”