Brief Introduction to Plastic Forming: Raw Materials (Part 2)

1. PC+ABS material
Since PC+ABS resin has special fluidity, its molding conditions and changes are also quite excellent. It is an ideal material for thin-walled and complex finished products
The melting temperature of PC+ABS resin has excellent thermal stability under the recommended resin melting temperature range; The general rule is that when molding at the highest temperature, the resin retention time should be minimized
Mold temperature:
The middle value of the recommended range is that the appearance and molding cycle time of each finished product are different in order to achieve good results. High bonding strength and low molding internal stress, while when using a lower recommended mold temperature, there will be high molding internal stress, and when using a lower recommended mold temperature, there will be a combination of high molding internal stress and compromise finished products
Injection Pressure
The actual injection pressure depends on a variety of variables, such as resin melting temperature, mold temperature, finished product shape, finished product wall thickness, flow length and mold and machine equipment. Generally speaking, the lowest injection pressure is more beneficial to the required finished product characteristics, appearance and molding cycle time
Back pressure
The recommended back pressure is 3kg/cm2~7 to ensure uniform melting and consistent injection. High back pressure is used to improve the mixing effect of resin at high melting temperature
injection speed
The fast filling speed can provide a longer flow. Fill the thin wall and a better appearance surface. The slow filling is recommended to be used for the finished products of the direct material mouth and the edge material mouth to avoid nozzle marks and z phenomenon (serpentine). At the same time, on the thicker finished products, the slow filling can help solve the phenomenon of bubbles and depressions. On the material mouth of the small point feeding, such as the needle point material mouth and the submerged material mouth, it is recommended to use the segmented injection, At the beginning of injection, with a slow injection rate, it can eliminate the bad appearance such as material halo, Z phenomenon and material burning. Therefore, when different materials of PC+ABS are used, the forming conditions should also change. The changing rules are relative to the material grade setting conditions
2. HIPS material
HIPS material is a polymer of styrene (abbreviated as PS). In industry, it is made of styrene or other biopolymers or co-polymers of styrene and other unsaturated compounds. Polystyrene can be processed by extrusion, injection molding, and other aspects. Attention should be paid during processing. If there is little water absorbed, it does not need to be dried. Due to small specific heat capacity, heating and cooling curing, melt viscosity is good for shearing, and can be injected by needle points. The molding shrinkage is small, about 0.4%~0.6%. It is fragile
3. ABS material
ABS resin is a terpolymer of acrylonitrile, butadiene and styrene. It is named after the first letter of their English name. It is a resin with high strength, good toughness, excellent comprehensive performance and wide use
ABS resin is generally opaque, with a light ivory appearance, and can match any color. It has good comprehensive performance, high impact strength, medium impact, high impact and ultra-high impact. It has good dimensional stability and creep resistance; In terms of thermal properties, the thermal deformation temperature varies from 65 ℃ to 124 ℃ depending on the ABS resin and the measurement conditions. The upper limit temperature is the number of hot wire resistance and low load measurement time
In addition, ABS resin still has certain chemical stability and good electrical properties, but poor weather resistance
ABS resin can be processed by extrusion, injection molding and thermal molding
However, the following points should be noted during processing
(1) Resin is easy to absorb moisture. Pay attention to drying;
(2) ABS resin begins to melt at 175 ℃. The melt viscosity decreases steadily with the increase of temperature. When the temperature is higher than 28.8 ℃, the resin will drop, decompose and release harmful gases
(3) The molding shrinkage is about 0.3%~0.6%
4. ABSV0 material
(ABS is the same as above) The ABS material itself is not flame retardant, and because of its benzene ring structure, it is very easy to produce black smoke when burning. In order to meet the requirements of V2 or V0 produced by UL-94, in order to achieve smoldering flame retardant, all other grades are only 1/16 "HB specification with better fluidity and stability, which is easier to form and process than flame retardant ABS
5. Acrylic material
This material is strong and tough, with poor material flow, and is only formed at low temperature, so the screw design should strengthen the compression rate, so the storage pressure is large, and the rod diameter should be reduced as far as possible, which can reduce the rotating force and strong pressure injection force, and the quality is smooth and flat. The slow rotation method should be used to make the pipe temperature stable, the temperature difference is not large, the mold increases the runner, and the nozzle hole is enlarged. When designing the mold, it is a technical processing and forming high-quality product. During operation, a clean room should be opened to isolate dust, and the funnel should be clean, Take out the mold easily and keep it clean with white gloves
6. PC material
This material has high melting viscosity, high injection pressure, high temperature in the pipe or stagnation, which is easy to cause thermal decomposition, discoloration and reduce physical properties. It should be noted that the mold temperature is 85OC~120 OC. However, when the mold temperature is low, the thick product is not only difficult to form, but also increases the residual stress, which is the cause of easy cracking in the future, in order to avoid cracking.