Color is normal on the surface of products, though black spots or lines occasionally occur.
The dark spots or black lines are fundamentally caused by the thermal degradation of material or carbonization of impurities due to various factors.The raw material is mixed with impurities (such as impurities falling off when the operator is unripping the package of plastic raw materials or foreign matters accidentally mixed during color mixing etc) and remnant from decomposition of materials exists in the barrel; insufficient plastication results in overhot or partially overhot melt in the barrel (melt temperature is too high and duration at high-temperature section is too long); overfast injection rate and oversmall section of gate result in excessive shearing of plastics; the surface of molding parts is not smooth and the melt is sprained when flowing through; the inadequate exhausting leads to the storing up of gas in the mold, the rising of temperature thereof under compression and the carbonization of plastics around the air mass; the rough surface of molding parts and the oversmall draft result in the plastic powder (which has been scraped from the previous plastic part during ejection) remnant on the surface of molding parts.
Solutions:
1 Reduce the addition amount of recycled plastic materials, reinforce clearing of remnant in the barrel and cavity and avoid interfusion of impurities in the raw materials.
2 Sufficiently dry the materials, reduce content of volatile component in raw materials and improve thermal stability of resins and additives.
3 Optimize screw structure, reduce plastication pressure and shearing rate of screw, shorten the storing time of melt in the plastication room of barrel and properly reduce melt plastication temperature.
4 Reduce screw injection rate, increase section dimension of nozzle and gate to avoid degradation caused by shearing and overfast flow of melt.
5 Improve mold exhausting condition and optimize exhausting scheme. 6 Reduce roughness on the surface of molding parts and increase draft.
Dark spots on injection molded products can be caused by a variety of factors. It is important to first identify what the root cause of these spots are in order to correctly address them.
The most common causes of dark spots on injection molded parts are: inadequate mold temperature, incorrect gate size, imbalanced venting pressure, contaminants or foreign material in the raw materials (such as metal) and incorrect filling time. Inadequate mold temperatures can lead to incompletely cured thermoplastic materials that give off an oily residue when exposed to heat and pressure during the manufacturing process; this oily residue accumulates at the surface creating dark discolorations. Incorrect gate size will cause incomplete packing out of the part due to low pressures or excessive flow resulting in poor part cooling with thicker sections showing discoloration more than thinner ones; this will also be exacerbated if there is insufficient venting pressure which prevents air from being displaced properly as plastic flows into the cavity. Contaminants and foreign material from outside sources such as water, dust particles or metal shavings/fragments can become mixed with polymer pellets prior to entering into heated barrel causing dark spots upon hardening; these must be identified and removed prior to production for optimal results. Lastly, incorrect filling times during injection molding will affect part quality thus leading to uneven distributions across different sections due to high plastic shrinkage rates causing some areas having less density than others resulting in unwanted appearances like darkened colorations on certain regions of a given product surface need additional consideration for additives such as lubricants and waxes accordingo improve process reliability , reduce cycle times & cost while meeting performance demands expected by modern customers .
Depending on your specific needs you may choose one approach over another but whatever solution you decide it is important that all steps along production processes takes place under strict monitoring & control systems ensure reproducible outcomes every single time . With proper maintenance tools & diagnostic techniques any problems related irregularities should easily diagnosed before they lead bigger issues later down road !