Injection Processing of PVC
PVC material, because of low price, is inborn with anti-inflammatory properties, strong and strong, good anti chemical ability, the shrinkage rate is 0.2-0.6%, products in electrical appliances, machinery, construction, daily necessities, toys, packaging, the characteristics of PVC material, analysis product injection molding process as follows:
First, PVC properties PVC thermal stability, molding temperature and The decomposition temperature is close, the fluidity is not good, t
he appearance is easy to form the bad defect. The heat resistance of PVC material is not good, it is the most easy to burn, the acid gas is produced and the mold is corroded, and the plasticizer can be added to its fluidity when processing. Its strength, electrical insulation, drug resistance is good.
Second, the mold and gate are designed to shorten the injection molding cycle. The shorter the injection port, the better. The cross section should be circular, the diameter of the nozzle should be minimum 6 mm, the diameter of the nozzle is 6 mm, and the inner angle is 5 degrees. It is best to add cooling material well. The cold well prevents poorly melted semi-solid materials from entering the cavity, which can affect the surface modification and the strength of the product. The die-drawing angle should be between 0. 50 and 10 to ensure that there are enough exhaust equipment in the cavity. The commonly used exhaust hole size is 0. 03-0.05mm depth 6mm wide, or 0. 0 per thimble peripheral clearance. 03-0.05mm. The die is made of stainless steel or hard chromium plated. PVC is a thermosensitive plastic. Overheating or excessive shearing can lead to decomposition and spread rapidly because one of the fractions (such as acids or HCIs) can catalyze further decomposition of the process. Acidic substances can erode metals, making them sunken, and the protective layer of metals peeling off, causing rust, which is more harmful to the human body. The common screw length to diameter ratio is 18: 24: 1, the three-stage ratio is 3: 5: 2, and the compression ratio is 1.8 / 2. The depth of the screw groove in the feed section is recommended as follows: Mm) 35 50 60 75 100 screw groove depth (mm) the tip of the screw shall have an inner angle of 2530 degrees, and the distance between the tip and the nozzle shall be 0.7 to 1.8 mm when the screw is ejected. The screw must be made of non-embroidered steel or chrome plated.
1).Screw cushion: screw cushion between 2~3mm, larger opportunities.
2).Injection volume: the actual cylinder stay time can not exceed 3 minutes.
3) Setting the temperature of the cylinder: the temperature provided can only be used as a reference, according to the actual situation of the machine and raw materials to make appropriate adjustments, It is also possible to go beyond the recommended range. The injection volume used in the middle feed section of the front section of the position die nozzle is 20 / 85 of the theoretical injection volume of this machine. The smaller the injection volume is, the longer the retention time of the material is, and the greater the risk of degradation after heating is, as a result, the temperature of the middle feed section of the front part of the die nozzle is 0 CX-60-60-190-190-160-180-180-170-170-140-160.
4) Cylinder retention time: under the temperature control of 2000C, the maximum retention time of the cylinder can exceed 5 minutes
5)The injection speed is slow: the injection speed is slow. Otherwise, excessive shearing will degrade the material. When UPVC is used to produce extremely smooth thick wall products, multistage injection speed should be adopted. If there are light brown stripes radiating from the gate, it means that the injection speed is too fast.
6)Back pressure: the commonly used surface value is 5 bar. increasing back pressure is good for color mixing and exhaust, but the lower the back pressure, the better.
7)Downtime: due to the low thermal stability of PVC, it is very important for the stop part to be cleaned and clean without leaving any PVCs. It can be used in other thermoplastic materials with high overheating stability and no resistance to PVC (e.g., PMMA-PPP-LDPE, or GPP). Do not mix POMT POMT in the same cylinder, otherwise it will lead to excessive chemical reaction, causing serious damage to the machine.
8)Blending ratio: the maximum mixing ratio of water mouth material is 20%, otherwise the product quality will be affected.
9)The main purpose of the typical product: UPVC is to make drain pipes, or the housing of computers and television sets, water pressure filters, photocopiers, electric meters and gas, transparent covers of printing machines, style and various electronic parts, etc.