Weld Line Strength Improvement

Polycarbonate (PC) 15-40 Automotive exterior body applications (i.e.. fascia and side cladding parts) Improved weld-line strength Improved flex modulus Low CLTE Improved siuface appearance... 

An important application for polybntylene is plumbing pipe for both coimnercial and residential use. The exceUent creep resistance of polybntylene aUows for the manufacture of thiimer wall pipes compared to pipes made from polyethylene or polypropylene. Polybutylene pipe can also be used for the transport of abrasive fluids. Other applications for polybutylene include hot melt adhesives and additives for other plastics. The addition of polybutylene improves the environmental stress cracking resistance of polyethylene and the impact and weld line strength of polypropylene. Polybntylene is also used in pack aging applications. 

In these blends, ABS s role is to improve flowabihty and reduce cost, while that of PSF is to improve the shape retention at high temperatures. ABS/PSF blends are compatibilized either by phenoxy, EVAc-GMA, or SMA copolymers. They have good processability, high notched Izod impact strength, plateability, hydrolytic stability, and economy. However, they may show poor surface and weld-line strength. Arylon and Mindel A are examples of the commercial ABS/PSF alloys, while Ucardel is an example of PSF blends with SAN. Evolution of ABS/PSF blends technology is summarized in Table 1.19. 

These unique combinations of transparency, hydrolytic, and heat resistance of polysulfones would be lost if other polymers are blended. Hence, there has been very little commercial incentive for blends of polysulfone. Nevertheless, in the early days of polysulfone commercialization, some blends with ABS and PET were developed primarily to lower the cost but also to improve selected properties such as plateability or chemical resistance. A PSU/ABS blend (Mindel A) was commercially offered for some time but is now no longer available. Additives such as phenoxy resins, styrene-maleic anhydride copolymers have been claimed to improve the compatibility and weld-line strength of the PSU/ABS blends (Robeson 1985). The blend was evaluated for selected appliance, plumbing, and sterilizable equipment plated parts. This blend lacked the heat resistance needed for the vapor phase solderability in electronic applications. 

Internal lubricants typically reduce bulk viscosity by being partially compatible with the polymer, with the lubricant s soluble component helping to open the polymer chain, and the less soluble portion of the lubricant molecule providing intermolecular lubrication (e.g., fatty alcohols, esters, ethylene-vinyl acetate waxes). They promote flow with a reduction in die swell. In injection moulding, the provide improved weld line strength, clarity, die filling and rate of production. In extrusion it reduces head and back pressure while affecting paintability. However, an increase in internal lubricants lowers heat distortion. 

Other applications include hot-melt adhesives and additives for other plastics. The addition of polybutylene improves the environmental stress cracking resistance of polyethylene and the impact and weld line strength of polypropylene. Polybutylene is also used in packaging applications. 

Very fast injection speed (0.2 to 0.3 seconds fill time) needs to be maintained to improve weld line strength and flow. To achieve optimum mechanical performance the injection velocity is usually moderate. The portion, which is difficult to fill, the molder can increase the injection velocity to improve melt flow as Increased injection velocity can be more effective than raising the melt temperature and is less likely to degrade the resin. 

Carefully consider the orientation of fibres to improve weld line strength. 

To achieve desired injection speed, it is necessary to have enough injection pressure. Higher injection pressures will improve the weld line strength and at the same time may lead to flashing. 

When power ultrasound oscillation was introduced to polymer melts, the mobility of the polymer molecules was increased such that, many of the common problems encountered in polymer processing could be resolved. For example, in the case of injection molding, ultrasonic osdllations were applied to improve molecular diffusion across the weld line so as to enhance the weld line strength. 

In contrast, high-power or low-frequency ultrasound can be used to compatibi-lize immiscible polymer pairs by the high shear and degradation of the polymer chains. Moreover, in many cases there was no deterioration in mechanical properties, despite a lowering of both the molecular weight and viscosity. Dramatic improvements in the weld line strength of immiscible PS/HDPE blends were... 

Lu, C Yu, X., and Guo, S. (2005) Ultrasonic improvement of weld line strength of injection-molded polystyrene and polystyrene/polyethylene blend parts. Polym. Eng. Sci.. 45,1666-1672. 

The process has even demonstrated the ability to remove a 0.1mm EVOH barrier resin from 2.5mm thick multi-layer blow molded containers. In this case the additive was included in the EVOH resin. The trim and scrap was pulverized to liberate the EVOH particles. The separator provided clean polyethylene without the diminished weld line strength, gels and the moisture problems of regrind that contains this common barrier resin. This offers the molder substantial resin savings and improved product quality. 

Calculated results in this paper were compared with that of ref. [7], the minimum error of PC weld-line strength is 0.54% and maximum error is 3.05%. The improved formulas of this paper are valid and reliable. The maximum calculation error is 2.56% of PA6 and 1.78% of nano-compositePA6, respectively. 

Orientation of polymer chains has been shown to have a major effect on component properties. The chain orientation at the end of fill of a component is diflferent from most other areas. Overflows have been used in various areas of the plastics industry to improve weld line strength and provide a more consistent gas channel in gas-assist molding. This study will investigate if the use of overflows to change the orientation of the polymer chains provides a more capable molding condition. 

Overflow tabs have been used throughout the plastics industry for several applications. They are used in the injection molding industry for the improvement of weld line strength of filled materials, but showed very little success [1]. They have also been used to increase the gas/liquid channel in gas-assist [2], liquid-gas assist [3], and water-assist [4] to provide a more uniform wall thickness and reduce material usage. 

The SCORIM Process. It is possible to attach the SCORIM unit to the injection molder to manipulate the filling process of the mold so that in the area of the weld lines the resin is mixed [16]. This will improve the structural strength substantially and at the same time the unwanted orientation of metallic pigments is prevented. This process typically requires a 10-15°C higher temperature of the resin and the mold. The process is based on a prolonged flow ability of the polymer. 

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