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I. Structure and function of plastic injection machine screw
I.1 Function of plastic injection machine screw
🔹 Plastic injection machine screw is an important component in plastic injection machines. It has a spiral shape that helps transfer material in granular form from the hole down the plastic to the nozzle in liquid form
Refer to the following video to clearly understand its uses
https://asg.vn/wp-content/uploads/2023/11/Injection-Molding-Animation-1.mp4
I.2 Structure of plastic injection machine screw
The basic screw is composed of 3 parts:
🔹 Screw part
The screw part is a screw-shaped section consisting of 3 regions: feeding region, compression region, and dosing region
– Feeding area: The task is to push the plastic particles from the hole down into the plastic around the cylinder barrel.
– Compression area: The task is to compress the plastic volume from a large volume to a smaller volume (because the plastic changes from a stacked particle structure to molten plastic).
– Quantitative area: The task is to stabilize the structure of the liquid mass to prepare for injection into the mold.
Depending on the type of plastic, the ratio of the length of these segments to the diameter will be different, and the compression ratio of the compression zone will also be similar.
🔹 Threaded part and centering hole
– The threaded part is used to assemble the rocket head onto the screw
– Centering hole to center the rocket head and screw, limiting the phenomenon of rotation when the rocket head rotates.
🔹 Shank & key part
This part is to connect and drive the machine capacitor
To handle rotational motion, a key is needed (there are many different types of keys according to the manufacturer's design, the most common are flat key, rectangular key, stem key...)
To handle the pullback motion, the two halves of the flange will be used to attach to the shaft shank.
II. Method of manufacturing plastic injection machine screws
There are many different screw production methods (screw manufacturing technological processes), each type has certain advantages and disadvantages, so it will be suitable for each specific use case. There is no comprehensively good solution and no comprehensively bad solution.
Basically, to produce screws, you will have to process several steps
– Shape the shank
– Shape the twisted part
– Shape the thread and centering hole
– Create surface hardness
– Cool, polish
Depending on each production method and technology, the order and way of performing these operations will be different
II.1 Screw nitrided, chrome plated
The shaft is completely machined and shaped with all parts made of steel before heat treatment. Then hardened by nitriding method; chromium plating or a combination of nitriding and then chromium plating
Advantage: Production is very fast, with low tool and machinery loss due to being done completely before heat. The produced shaft has high surface hardness for abrasion resistance. This type is usually suitable for non-corrosive plastics and has a glass ratio < 15%.
II.2 PTA alloy top welding screw
All parts of the shaft are machined, the twisted part is made to have an outer diameter smaller than the drawing requirements, then welded over a layer of alloy, then the twisted profile will be reprocessed and the outer diameter will be ground.
Advantage: Cheap price due to pre-heat processing. The top of the tooth is very hard due to being welded with a layer of highly wear-resistant alloy. The shaft can be plated with an additional layer of chromium to increase the mechanical properties of the spiral groove surface. This type is usually suitable for non-corrosive plastics, glass ratio < 15%
https://asg.vn/wp-content/uploads/2023/11/PTA-PLASMA-TRANSFERRED-ARC-SC.mp4
II.3 HVOF coating screw
All parts of the shaft are machined, twisted to reduce the profile in the diameter direction by 0.5~1.5mm in thickness, then use HVOF alloy powder spraying technology to cover the screw surface. alloy powder layer. Then grind and cool the screw.
Advantage of this method is the ability of the screw to adapt to different types of plastic customized based on the alloy coating. This coating creates a highly technologically capable screw at a good cost since the inner core only needs to be made of base material.
Refer to the video:
https://asg.vn/wp-content/uploads/2023/11/HVOF-SCREW-INJECTION-MOLDING.mp4
II.4 Completely rigid screw
There are two technologies in this type of shaft
Technology 1: The entire shape is then vacuum annealed to achieve the required hardness. At that time, the shaft will be bent, de-warping using heat, and grinding to finish the product. The advantage is that it is cheap because it is still pre-heat processing, but the de-curving straightening process has many uncheckable risk points (cracks, residual stress, local hardness...)
Technology 2: Heat treatment to achieve hardness and then machine the parts. The advantage is that the shaft has uniform hardness, without risk points, but technology 1. Depending on the manufacturing material, it can meet 5VA 5VB corrosive plastic with a glass ratio of up to 50%.
ASG Vietnam Engineering Company Limited is a unit specializing in handling plastic injection problems with more than 10 years of experience. We are always ready to listen to your questions 24/7 via hotline 0917.54.88.11
