1、 Drying temperature

Definition: The temperature required to dry the polymer in advance to ensure molding quality

Function: 1. Remove water from raw materials 2. Ensure the quality of finished products

Setting principles: 1. The polymer is not prone to decomposition or agglomeration (polymerization) 2. The drying time should be as short as possible, and the drying temperature should be as low as possible without affecting its drying effect Drying temperature and time vary depending on different raw materials

Note: 1, A indicates using a hot air dryer

2, D indicates using a dehumidification dryer

3, * indicates that drying is not usually necessary

4. * * indicates that drying depends on the condition category, and it is best confirmed by the material supplier

2、 Material temperature

Definition: The temperature applied to the material pipe to ensure smooth molding

Function: Ensure good polymer plasticization (melt adhesive), smooth mold filling, and molding

Setting principle: (1) Do not cause decomposition and carbonization of plastics (2) From the feeding cutoff to the nozzle, it rises sequentially (3) The nozzle temperature should be slightly lower than the temperature at the front of the barrel (4) The required temperature varies depending on the type of material (5) Not to have a bad quality impact on the product

3、 Mold temperature

Definition: Temperature of the mold cavity surface contacted by the product

Function: Control the cooling speed of the product in the mold cavity and the apparent quality of the product

Setting principles: (1) Consider the properties of the polymer (2) Consider the size and shape of the product (3) Consider the mold structure and runner system

4、 Injection speed

Definition: The speed at which molten adhesive is injected into the mold from the nozzle under a certain pressure

Function: (1) Increasing the injection speed will increase the mold filling pressure (2) Increasing the injection speed can increase the flow length and uniform production quality (3) High viscosity and fast cooling speed during high speed injection, suitable for long process products (4) Smooth flow and stable product size at low speeds

Setting principle: (1) Prevent formwork support and avoid edge overflow (2) Prevent scorching due to excessive speed (3) Under the premise of ensuring product quality, try to choose high-speed filling to shorten the molding cycle

5、 Melting speed

Definition: The rotational speed of the screw during the melting process

Function: An important parameter that affects the plasticizing ability and quality. The higher the speed, the higher the melt temperature, and the stronger the plasticizing ability

Setting principle: (1) When adjusting the melt speed, it is generally adjusted gradually from low to high (2) The rotation speed of the machine with a screw diameter greater than 50MM should be controlled below 50RPM, and the machine with a screw diameter less than 50MM should be controlled below 100RPM

6、 Ejection pressure

Definition: The maximum pressure at the exit of the screw tip is closely related to the oil pressure generated in the injection cylinder

Function: It is used to overcome the pressure loss of the melt from the nozzle - runner - gate - cavity, ensuring that the cavity is filled and obtaining the required product

Setting principle: (1) Must be within the rated pressure range of the injection molding machine (2) Try to use low pressure when setting (3) Try to avoid using high voltage at high speeds to avoid abnormal conditions

7、 Back pressure

Definition: The pressure established by the plastic in the melting cavity during the plasticizing process

Function: (1) Increase the specific gravity of the melt (2) Plasticize the melt evenly (3) Reduce the gas content in the melt and improve the plasticizing quality

Setting principles: (1) The adjustment of back pressure should consider the properties of plastic raw materials (2) The adjustment of back pressure should refer to the apparent quality and foot size accuracy of the product

8、 Mold locking pressure

Definition: The clamping system applies a tightening force on the mold to overcome the expanding force that separates the mold during the injection and holding stages

Functions: (1) Ensure that the mold will not expand during injection and pressure maintaining processes, and (2) ensure the apparent quality of the product (3) Ensure the dimensional accuracy of the product

Setting principles: (1) The size of the clamping force depends on the size of the product and the size of the machine (2) Generally speaking, under the condition of ensuring that the product does not produce burrs, the smaller the mold closing force requirement, the better (3) The setting of the clamping force should not exceed the rated pressure of the machine

9、 Maintaining pressure

Definition: The injection pressure that continues to be applied to the mold cavity plastic from the time the mold cavity is filled with plastic until the gate is completely cooled and closed depends on a relatively high pressure, which is called pressure retaining

Function: (1) Replenish the amount of material close to the gate location, and prevent the flow back of hardened plastic in the mold cavity under residual pressure before the gate is cooled and closed, preventing shrinkage of the workpiece, avoiding shrinkage, and reducing vacuum bubbles (2) Reduce the possibility of mold sticking cracking or bending due to excessive injection pressure

Setting principles: (1) The pressure retaining pressure and speed are usually set to 50 to 60% of the maximum pressure and speed when the mold cavity is filled with plastic. (2) The length of the pressure retaining time is related to the material temperature. High temperature gates have a long closing time and a long pressure retaining time (3) Pressure retaining is related to the projected area and wall thickness of the product. Thick and large products require a longer time (4) Pressure retaining is related to the size and shape of the gate Setting of pressure maintaining switching position, metering length, and release stroke

10、 Metering stroke

Definition: After plasticizing starts, during the rotation of the screw, it starts to retreat under the force of the plastic melt from the injection termination position until it reaches the retreat limit switch. This process is called the metering stroke

Function: Ensure that there is enough plastic to fill the mold cavity to achieve the desired appearance and size of the product

Setting principles: (1) The metering stroke should be set according to the size of the product and the size of the machine (2) The metering stroke should not be too large to avoid carbonization caused by the injection of excess plastic remaining in the material tube for too long (3) The metering stroke should not be too small to ensure sufficient metering for filling and avoid mechanical damage to the screw and nozzle. There should be a buffer capacity of 3-5 mm

11、 Ejection stroke

Definition: Changes in the position of the screw during injection

Function: Combining speed and pressure to control the flow state of plastic

Setting principle: (1) The measuring position is determined by the filling amount of the finished product, and the final setting is usually determined by adding 3~5mm of impulse to this value (2) The transition point to the second speed is usually switched to the full hot runner, feed head position (3) Set the switching position to the third speed conversion point using 90% of the filling degree of the formed product (4) The pressure maintaining switching point is generally set at 90% of the filling level of the finished product (Note: The above takes the four paragraphs as an example)

12、 Loosening amount

Definition: After the screw is pre molded (metered) in place, it reverses linearly for a certain distance. This backward movement is called back loosening, and the loosening distance is called the loosening amount or anti extension amount

Function: The function of back loosening is to increase the specific volume of the melt in the metering chamber and decrease the internal pressure, preventing the melt from flowing out of the metering chamber

Setting principles: (1) Set based on the viscosity, relative density, and actual conditions of the plastic raw material. A large amount of looseness can cause the melt to mix with bubbles, affecting product quality (2) The setting of the loosening amount should adapt to the screw speed and back pressure (3) For materials with high viscosity, such as PC materials, there is no need to set a loosening amount

13、 Buffer

Definition: After the injection molding of the screw is completed, it is not desired to eject all the molten material from the head of the screw, but also to retain some. This amount of material is called the buffer amount

Function: (1) Prevent mechanical damage accidents caused by contact between screw head and nozzle (2) Control the repetitive accuracy of injection volume

Setting principles: (1) The buffer amount should not be too large or too small. If it is too large, it will cause excessive excess material, resulting in pressure loss and raw material degradation. If it is too small, it will not achieve the purpose of buffering (2) The buffer amount is generally determined as 3-5 mm

14、 Period

Definition: The time from the end of mold opening to the end of mold opening after the completion of cooling for the next injection

Function: Ensure the molding and complete cooling of the product

Setting principle: (1) The cycle should be as short as possible (2) Shortening the cycle must be carried out on the premise of ensuring product quality

15、 Cooling time

Definition: The time required for a product to cool and solidify without causing deformation after demolding

Function: (1) Allow the product to solidify; (2) Prevent the product from deforming

Setting principles: (1) Cooling time is an important component of cycle time, which should be kept as short as possible while ensuring product quality (2) The cooling time depends on the melt temperature, mold temperature, product size, and thickness

16、 Holding time

Definition: The pressure that continues to be applied after injection to prevent plastic backflow and cooling and shrinkage after injection

Function: (1) Prevent melt backflow after injection molding (2) The feeding effect of cooling shrinkage

Setting principle: (1) Holding time varies depending on the thickness of the product (2) The holding time varies depending on the temperature of the melt, with higher temperatures requiring longer time and lower temperatures requiring shorter time (3) In order to improve production efficiency, the pressure holding time should be kept as short as possible while ensuring the production quality and quantity

17、 Ejection time

Definition: The time taken for the melt to fill the entire mold cavity

Function: The injection time is determined by factors such as injection pressure, injection speed, and the size of the product

Setting principle: (1) Keep the injection time as short as possible under the condition of ensuring the molding of the product (2) The injection time is influenced by factors such as material temperature and mold temperature

18、 Melting time

Definition: The time required for the screw to reach the metering end position after injection termination

Function: Ensure sufficient melt adhesive

Setting principle: (1) The screw speed and back pressure are controlled mutually (2) Do not allow the molten plastic body to stay in the screw for too long, as this may cause the plastic to decompose and carbonize under long-term high-temperature conditions

19、 Drying time

Definition: The time required to dry raw materials in advance using drying equipment

Function: (1) Improve surface gloss, improve bending resistance and tensile strength, and avoid internal cracks and bubbles (2) Improve plasticizing ability and shorten molding cycle (3) Reduce moisture and moisture in raw materials

Setting principles: (1) The drying time varies depending on the raw material (2) The setting of the drying time should be appropriate. If it is too long, it will reduce the drying efficiency and even cause the raw material to agglomerate. If it is too short, the drying effect will be poor

Common injection molding calculation formulas

Locking force F (TON) F=Am * Pv/1000

F: Locking force TON

Am: projected area of mold cavity CM2

Pv: filling pressure KG/CM2

(Generally, the filling pressure of plastic material is 150-350KG/CM2)

(Take a lower value for good liquidity and a higher value for bad liquidity)

Filling pressure/0.4-0.6=injection pressure

Example: projected area of mold cavity 270CM2, filling pressure 220KG/CM2

Locking force=270 * 220/1000=59.4TON

2. Injection pressure Pi KG/CM2 Pi=P * A/Ao

Pi: Ejection pressure

P: Pump pressure

A: Effective area of injection cylinder

Ao: cross-sectional area of screw

A=π * D2/4 D: diameter π: pi 3.14159

Example 1: Calculating the injection pressure from a known pump pressure?

Pump pressure=75 KG/CM2, effective area of injection cylinder=150CM2

Screw cross-sectional area=15.9CM2 (∮ 45)

Pi=75*150/15.9=707 KG/CM2

Example 2: Calculating pump pressure from known injection pressure?

Required injection pressure=900 KG/CM2 Effective area of injection cylinder=150CM2

Screw cross-sectional area=15.9CM2 (∮ 45)

Pump pressure P=Pi * Ao/A=900 * 15.9/150=95.4 KG/CM2

3. Injection volume V CM3 V=π * Do2/4 * ST

5: Injection volume CM3

π: Pi

Do: screw diameter CM

ST: Ejection stroke CM

Example: Screw diameter 42mm, injection stroke 165mm

V= π*4.2*4.2/4*16.5=228.6CM3  

4. Ejection weight G Vw=V* η*δ

Vw: Ejection weight G

5: Ejection volume

η： proportion

δ： Mechanical efficiency

Example: Ejection volume=228.6 CM3 mechanical efficiency=0.85 specific gravity=0.92

Ejection weight Vw=228.6 * 0.85 * 0.92=178.7G

5. Injection velocity S CM/SEC S=Q/A

S: Injection rate CM/SEC Qr: pump output (per revolution/CC) CC/REV

A: Effective area of injection cylinder CM2 Q=Qr * RPM/60 (per minute/L)

Q: Pump output RPM: motor rotation per minute

Example: Motor speed 1000 RPM Pump output 85 CC/REV

Effective area of injection cylinder 140 CM2

S=85*1000/60/140=10.1 CM/SEC

6. Ejection rate Sv G/SEC Sv=S * Ao

Sv: Ejection rate G/SEC

S: Ejection velocity CM/SEC

Ao: cross-sectional area of screw

Example: Ejection speed=10CM/SEC screw diameter Φ 42

Area=3.14159 * 4.2 * 4.2/4=13.85CM2

Sv=13.85*10=138.5G/SEC