When your business wants to replace an old injection molding machine in its manufacturing operation, it is always confusing about what injection molding machine to buy. The reasons for this confusion are not far-fetched. This is because injection molding machine technology on the market today continues to advance. When choosing a high-performance injection molding machine, one of the most important decisions is whether you want a screw or plunger injection molding machine.
Here, we consider the pros and cons of screw and plunger injection molding machines.
What Is a Screw Injection Molding Machine
A screw injection molding machine uses a screw plasticizing device to plasticize the molding material, and then fills the mold with a specially designed injection screw.
When the screw rotates, the plastic will cause friction and mutual movement between the inner wall of the barrel, the bottom surface of the screw groove, the propelling surface of the screw, and between plastics. The forward motion of the plastic is the result of this combination of motion, and the heat generated by friction is absorbed to increase the temperature of the plastic and melt it. The design structure of the screw will directly affect the degree of these effects.
Features of Screw Injection Machine
1. Good plasticizing effect
2. Strong adaptability
3. Short production cycle and high efficiency
4. Easy to realize automated production
5. The equipment price is high and the mold cost is high. Suitable for mass production.
What Is a Plunger Injection Molding Machine
A plunger-type injection molding machine is an injection molding machine that uses a plunger-type plasticizing device to plasticize the molding material, and then uses a specially designed injection plunger to fill the mold.
An injection molding machine that uses a plunger-type plasticizing device to plasticize the molding material, and then uses a specially designed injection plunger to fill the mold. Compared with ordinary plunger injection molding machines, it has the characteristics of uniform plasticization, stable injection volume, and small pressure loss. However, compared with screw injection molding machines, they have the disadvantages of complex structure, easy retention of molding materials, and difficulty in changing colors and materials.
Characteristics of Plunger Injection Machine
1. Poor plasticization uniformity and uneven temperature. Improving the plasticizing capacity of the barrel is limited
2. Simple structure and large pressure loss, not suitable for heat-sensitive plastics
3. Simple structure and small injection volume
4 Difficulty cleaning the barrel
Screw Vs Plunger Injection Molding Machine
Change the nature of logistics
After the plastic is heated, it becomes a viscous flow state. Its viscosity is very high. It flows in the barrel of the plunger injection machine in a stagnant form. The flow speeds at different distances from the barrel wall are also different, thus causing various particles. The residence time in the barrel is inconsistent, so the quality of the finished product will be affected. After using the rotating screw, the viscous plastic flow is no longer stagnant.
Even heating
The material is heated in the barrel of the plunger injection machine mainly by the heating of the barrel. Since plastic is a poor conductor of heat, the melt temperature is also inconsistent at different positions from the barrel wall.
The rotating screw gradually passes the material through the heating zone, and pressure will appear, squeezing the material very tightly. The rotation of the screw will cause strong internal friction (i.e. shearing force) to generate heat. This heat interacts with the barrel. The external heating works together to achieve good heating effect of the plastic, and the uniformity of heating is also greatly guaranteed.
Refining effect
The material is mixed well in the screw injection machine, the plasticizing time is shortened, and the injection volume is large.
The Difference Between Screw And Plunger Injection Molding Machines
Here’s a comparison table for Screw Injection Machines vs. Plunger Injection Machines:
| Feature | Screw Injection Machines | Plunger Injection Machines |
|---|---|---|
| Working Mechanism | Rotating screw melts, mixes, and injects material. | Plunger directly pushes molten material into the mold. |
| Material Mixing | Excellent mixing ensures uniformity and high-quality products. | Limited mixing; suitable for simpler applications. |
| Precision | High precision and consistency; ideal for intricate designs. | Less precise; suited for basic shapes. |
| Energy Efficiency | More energy-efficient due to efficient heating and plasticizing. | Less energy-efficient. |
| Material Compatibility | Suitable for a wide variety of materials, including thermoplastics. | Limited to basic materials. |
| Cost | Higher initial cost. | Lower initial cost; more budget-friendly. |
| Maintenance | More complex due to additional moving parts. | Easier to maintain with fewer moving parts. |
| Applications | Used for high-precision industries like automotive and electronics. | Best for large-scale production of simple items or prototypes. |
| Product Quality | Superior due to thorough mixing and precise injection. | Lower quality with minimal material blending. |
| Popularity | Dominates modern manufacturing for versatility and efficiency. | Less common; limited to niche applications. |
Which of These Two Injection Molding Machines Is Better?
Compared with plunger injection molding machines, screw injection molding machines have the following advantages:
1. The quality of screw-type pre-plasticizing raw materials is better than that of plunger-type plasticizing raw materials.
2. The mixing performance of the screw type is better than that of the plunger type
The plunger injection molding machine uses a plunger to push the raw materials falling into the barrel into the plasticizing cavity at the front end of the barrel. The raw materials in the cavity rely on the heat provided by the peripheral heater of the barrel to plasticize into a molten state, and then pass through the column. The rapid forward movement of the plug injects the molten material into the mold cavity and cools it for molding.
The structure and working method of the screw injection molding machine are the same as those of the plunger injection molding machine. The only difference is that the plunger in the first barrel is changed to a screw. The raw material is first plasticized by the screw, and then the molten material is pushed into the forming mold through the plunger to cool and form.
The plunger screw is a technology of the past. Its mixing performance is very poor, and its plasticizing performance is also not good. It needs to be equipped with a diverter shuttle device. The reciprocating screw is the most advanced technology at present, and its mixing and plasticizing properties are better than that of the plunger screw.
Summarize
In short, screw injection molding machines are now the mainstream plastic parts molding equipment. Therefore, when purchasing an injection molding machine, you must choose a molding equipment with a screw working structure.
Sunbun is China's leading injection molding machine manufacturer and supplier. We have always provided customers with the most advanced injection molding machines. If you need to purchase a high-performance and affordable injection molding machine. Then we are your best choice.
You can contact us by sending an email and tell us what your needs are. Our engineering team will give you the most reasonable solutions and guidance suggestions for your project. You are welcome to come for consultation!
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