Injection Screw Barrel Overview
The injection screw barrel assembly is an important component of the machine, mainly used for the melting, mixing, and conveying functions of plastic raw materials. Through the rotation and forward and backward movements of the screw in the barrel, plastic will generate friction and mutual movement on the inner wall of the barrel, the bottom surface of the screw groove, the advancing surface of the screw edge, and between plastic and plastic. The forward advancement of plastic is the result of this combination of movements, The heat generated by friction is also absorbed and used to raise the temperature of plastic to melt it. The structure of the screw will directly affect the degree of these effects
Application Field
Auto Parts
Bottles
Construction
Packaging
Housewares
Aerospace
Electrical Parts
Furniture
Applicable Plastics
Common Plastics: PP, PE, PVC, ABS, PMMA
Enginner Plastics: PA, POM, PBT, PET, PC, PPO, PPS, LCP, PI, PTFE, PEEK, PSF, PEI, PC/ABS, PC/PBT
Thermoset Plastics: UF, PU, LSR
set Assembly Parts Include
(Complete Set)
01/
Screw: Main conveying parts for the unit, it's a spiral shape made by high strenght steel with various design geometry
02/
Barrel: Also called cylinder, the holding part for the unit with center hallow shape, outside with heating band
03/
Screw Tip Set: Also called torpedo set or ring plunger set, serves as material flow and prevent from flow back while processing
04/
Endcap: Also called injection head, joint adaptor for front nozzle tip, some machiens also directly with nozzle tip without endcap
05/
Nozzle: Shot components which contact with orifice, depends on function, also have open, shutoff, mixing or filter type
06/
Flange: For holding barrel to injection unit or else cooling system function, depends on structrure may not have
Injection Machine Nozzle Selection
The nozzle is the transitional part that connects the material barrel and the mold. During injection, the molten material inside the barrel is pushed by the screw and injected into the mold through the nozzle at high pressure and speed. Therefore, the structural form of the nozzle, the size of the nozzle hole, and the manufacturing accuracy will affect the pressure and temperature loss of the molten material, the range, the quality of the filling effect, and whether there is "salivation" phenomenon. Currently, there are many types of nozzles used, and they all have their applicable ranges. Here, we will only discuss the most commonly used three types.
1. Straight through open nozzle
This type of nozzle has a short tube shape, and when the molten material flows through this nozzle, the pressure and heat loss are very small, and it is not easy to produce stagnation and decomposition, so it is generally not equipped with a heating device on the outside. However, due to the short nozzle body, the length of the nozzle that extends into the fixed template hole is limited, so the main channel of the mold used is longer. To compensate for this deficiency, increasing the length of the nozzle has become an improved form of straight through nozzle, also known as extended nozzle (long nozzle). This type of nozzle must be equipped with a heating band. In order to filter out solid impurities in the molten material, a filter cartridge can also be added to the nozzle. The straight through nozzle is suitable for processing high viscosity plastics. When processing low viscosity plastics, there may be drooling.
2. Shutoff nozzle
During the injection process, in order to prevent drooling or retraction of the molten material, it is necessary to temporarily seal the nozzle channel and use a locking nozzle. Among which most popular is spring type self-locking nozzle, pneumatic or hydraulic drived shutoff nozzle. Spring loaded shut off nozzle is achieved by pressing the valve core inside the nozzle with a spring to achieve self-locking. During injection, the valve core is pushed open by the high pressure of the molten material, and the molten material is then ejected into the mold. When melting glue, the valve core resets and locks itself under the action of the spring. Its advantage is that it can effectively prevent the phenomenon of leaking when injecting low viscosity plastics, is convenient to use, and has a significant self-locking effect. However, due to it's relatively complex structure, there will some injection pressure loss, and the requirements for springs are high.
Needle type of nozzle (pneumatic or hydraulic drived) also serves the same function. It uses an external hydraulic or pneumatic system to control the linkage mechanism to open and close the valve core through a lever. When in use, the actuate system can be operated as needed to accurately and timely open the valve, which has the advantages of convenient use, reliable self-locking, small pressure loss, and accurate measurement. In addition, it does not use springs, so there is no need to replace them. The main disadvantage is that the structure is more complex and the cost is higher.
3. Filter nozzle
With certain injection field, recycled material are widely used, which is with much impurities and in order to prevent block or demage manifold, filter nozzle are required, filter cartridge can have several types, simple mesh, split type are common used, also can customize according to the filter size requirement
4. Color Mixing Static Mixer Nozzle
Not always plastics are well blended, in lot cases, plastic with addtioinal masterbatch can be hard to mixing well and dispersive evenly on product. With such situation, static mixer nozzle can be a good selection due to it's easier process and economic cost.
5. Selection of nozzle
During injection, the plastic melt is pushed by the screw and flows through the nozzle at a very high shear speed before entering the mold cavity. Under this high-speed shear action, the melt temperature rapidly increases. Improper nozzle selection can directly affect the stability of injection molding and product quality.
(1) For high viscosity PVC, PP-R, PMMA, PC, high impact ABS, etc., a small nozzle hole diameter can cause high-temperature decomposition of the plastic.
(2) For thin-walled precision products that are difficult to mold, it is advisable to use a nozzle with a longer injection range.
(3) For thick walled products, a nozzle with good plastic filling effect is required.
(4) For certain plastics with low melt viscosity (such as PA), it is necessary to use self-locking nozzles with anti drooling function.
(5) On many machines, in addition to universal nozzles for general viscosity, there are also specialized nozzles such as self-locking nozzles, PVC nozzles, PMMA nozzles, etc.
Different Screw Geometry Designs
Injection screw design can be much difference, the factors that affect the screw designs include
- Running polymer details
- Product to be finish
- Additives
- Product finishment requirement
Common used screw design
- General purpose single flighted screw
- Barrier type screw
- Mixing type screw
- Dispersive type screw
Screw Barrel Manufacturing Process
Screw Process: Rough Turn - Machine Bimetallic Channel (if bimetallic) - Bimetallic Spray - Machining Flight - Key Machining - Drilling - Grinding - Heat Treatment - Polish - Inspection
Barrel Process: Rough Turn - Boring - Centrifugal Casting - Outside Machining - Grinding - Thread Machining - Inspection
With decades experience, we have massive database for various machines screw barrel, You can always find your need here
- Japanese Injection Machines: Fanuc, Sumitomo, Toyo, Toshiba, JSW, Sodick, Mitsubishi, Kawaguchi...
- Chinense Injection Machines: Haitian, Chenhsong, Powerjet, Yizumi, Beston, Borche, Cosmos (Welltec), Log, Dakumar, FCS, Haida, Haijing, Haitai, Haixing, CLF, Haixiong, Hengrun, Hwamda, Golden Eagle, Leadway, Lanson, Sound, Shuangma, Tederic, Tongjia, Multiplas...
- European Injection Machines: Engel, Arburg, Demag, Netstal, Battenfeld, Krauss-Maffei, Milacron, BOY...
- American Injection Machines: Cincinnati, Remu, Husky...
- Else Brands: LG, Woojin, Asian, Victor, Huarong, Kinki, Liansu...
Not only we can supply per machine or tailor to your customize drawing with measurement. We have engineer with decades experience of designing, which can offer optimize solutions.
Materials selection for Screw Barrels
Screw Barrel material is optional depends on actual running situation, the screw barrel wears can be 3 aspects, which are adhensive wear, abrasive wear and corrosive wear. We can offer material for different polymers with long lasting lifespan.
For adhensive wear, one proven effective way is to increase material hardness and toughness, both screw and barrels
For abrasive wear, normally it's caused by recycle matrerial itself or reinforce additives like calcium, glass fiber, use high strength and hardness screw barrel can offer effective protection from these wears, we have cooperation with materials from Hitachi, Boller, Stellite.. and proven to be durable under 65% glass filled plastic processing
For corrosive wear, some plastics can generate corrosive gas while high temperature processing and corrode screw barrel surface, use Ni-based or Chronium treatment material can be a good way to resolve these problems.
Factors that relate to injection screw barrel set pricing
Price are more or less relate to the material used, heat treatment, geometry design, processing time.. consult our sales representatives and ask for more details.
And some common design parameters
Compression Ratio: different plastic require different compression ratio, it's relate to plastic property itself, regular comparession ratio can be from 1.8:1 to 2.5:1
L/D ratio: Means Length to Diameter ratio, longer LD rato can offer longer time of polymer mixing and better plasticizing, but if it's too long, it can also over degrade some material
