A magnesium alloy injection screw barrel structure

Abstract

The application discloses a magnesium alloy injection screw cylinder structure, which comprises a cylinder and a screw, the screw is arranged in the inner cavity of the cylinder, the screw and the cylinder are wear-resistant structures made of die steel numbered 1.2888, the end of the screw is provided with a screw head capable of increasing the mixing effect of the magnesium alloy semi-solid, and the screw head is detachably connected to the end of the screw. The application has the advantages that the screw and the cylinder are wear-resistant structures made of die steel numbered 1.2888, the problems such as wear, surface oxidation, sticking to the mold and local overheating are reduced under the long-term high-temperature and high-shear working condition, the good plasticizing capacity is maintained for a longer time, and the service life of the cylinder and the screw is prolonged; the mixing head is arranged at the end of the screw, the mixing effect on the magnesium alloy semi-solid is increased, and the discharging effect is more ideal.

Description

Technical Field

[0001] This invention relates to the field of injection molding machine barrel and screw technology, and more particularly to a barrel structure for magnesium alloy injection molding screws. Background Technology

[0002] A Chinese invention patent application (CN200910066566.3) entitled "Method for Semi-Solid Injection Molding of Magnesium Alloys" discloses a method for semi-solid injection molding of magnesium alloys. The method is characterized by: mixing magnesium alloy chips and spherical magnesium (aluminum) alloy metal powder in a metal powder mixing device under argon gas protection; feeding the uniformly mixed metal powder into the hopper of an injection molding machine; quantitatively feeding the powder into a metal sleeve via a screw metering device; applying shearing force to the metal powder using a screw conveyor within the metal sleeve device, completely melting the magnesium alloy chips and achieving a slightly molten surface on the spherical magnesium (aluminum) alloy metal powder, forming a solid-liquid mixture; and injecting the semi-solid slurry into a mold using a reciprocating screw injection molding machine to form the product. The resulting high-solid-volume-fraction semi-solid magnesium alloy exhibits well-formed, nearly spherical solid particles; it can be used to manufacture complex-shaped parts; the product quality is high; it can undergo heat treatment; and the processing equipment is compact, easy to manufacture, and convenient to use and maintain. However, the barrel and screw used in this magnesium alloy production process are prone to accelerated wear, surface oxidation, mold sticking, and localized overheating under prolonged high-temperature and high-shear conditions. Severe wear can cause the gap between the screw and barrel to exceed 0.3 mm, resulting in a decrease in plasticizing capacity. Excessive gap will directly lead to fluctuations in injection volume, unstable pressure, product dimensional deviations, and even failure to form properly. Therefore, the barrel and screw structures used in this method require further improvement. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a magnesium alloy injection molding screw barrel structure that can be slowly worn under long-term high temperature and high shear conditions, has a long service life, and has a good material mixing effect, in view of the above-mentioned existing technology.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: The present invention is used for a screw and barrel structure for magnesium alloy injection molding, including a barrel and a screw, wherein the screw is inserted into the inner cavity of the barrel. The screw and the barrel are wear-resistant structures made of mold steel with the number 1.2888. The end of the screw is provided with a screw head that can increase the semi-solid mixing effect of magnesium alloy. The screw head is detachably connected to the end of the screw.

[0005] As an improvement, the screw head preferably includes a screw head body, a check ring, and a limiting protrusion. A barrier section is provided at the front of the screw head body, and a discharge through-hole is axially provided on the barrier section. The limiting protrusion is connected to the middle and rear part of the screw head body. The check ring is fitted onto the screw head body between the barrier section and the limiting protrusion. A gap is left between the inner wall of the check ring and the outer wall of the screw head body for material passage, and this gap communicates with the discharge through-hole. Magnesium alloys have fast thermal conductivity and low specific heat capacity, resulting in rapid molten cooling. They are prone to stagnation and localized overheating and decomposition at the screw head. Therefore, by providing a discharge through-hole in the barrier section, the flow of the magnesium alloy semi-solid is accelerated, reducing the probability of stagnation. Simultaneously, it reduces shear heating and prevents material degradation.

[0006] Further improvements include the option ring preferably having a connecting gap and a through hole on the outside of the check ring distributed along its circumference. This enhances the connectivity between the gap and the outside of the check ring, facilitating venting and heat dissipation, reducing the probability of oxidation of the magnesium alloy melt within the gap, resulting in more uniform plasticization of the magnesium alloy melt and better mixing performance.

[0007] Further improvements include the option of providing an annular groove on the outer wall of the check ring corresponding to the through hole, with a piston ring embedded in the groove, the top surface of which protrudes above the outer wall of the check ring. This enhances the sealing between the outer wall of the check ring and the inner wall of the barrel, preventing check ring failure.

[0008] In a further improvement, the check ring through holes can preferably be in two sets, with the through hole spacing of the set of check ring through holes closer to the limiting protrusion being smaller than that of the other set of check ring through holes farther from the limiting protrusion. Since the backflow melt and the forward melt are more intensely compressed on the side closer to the limiting protrusion, increasing the number of through holes helps to expel air and dissipate heat more quickly, reducing the probability of melt sticking to the mold and burning.

[0009] As an improvement, an annular groove can preferably be provided at the root of the barrier section, with the bottom surface of the annular groove flush with the inner wall of the corresponding discharge through-hole. This facilitates the discharge of molten magnesium alloy, further accelerates the flow of semi-solid magnesium alloy, and reduces the probability of retention.

[0010] As an improvement, the middle and rear part of the screw head body can preferably be provided with a protrusion, and the limiting protrusion abuts against the protrusion. This facilitates the positioning and installation of the limiting protrusion.

[0011] As an improvement, the screw can preferably include a rod body and screw ribs, the screw ribs including a feeding section, a compression section, and a homogenizing section, the screw groove depth gradually decreasing, the screw compression ratio being 1.4–1.6, and the screw length-to-diameter ratio being 16–20. This compression ratio and length-to-diameter ratio balance plasticizing efficiency and thermal stability; the segmented design of the screw allows the feeding section to preheat and convey solid particles, the compression section to shear and plasticize, densifying the material, and the homogenizing section to homogenize the melt and facilitate metering. The screw groove depth gradually decreases, promoting melt uniformity and optimizing shearing and conveying efficiency.

[0012] As an improvement, the surface of the screw and the inner wall of the barrel are preferably covered with an aluminum nitride layer. This further extends the service life of the screw and barrel.

[0013] As an improvement, the end of the barrel can preferably be connected to a long nozzle via a flange, and the end of the screw head extends into the injection chamber of the long nozzle. This achieves precise material discharge, and the long nozzle is easy to install and replace.

[0014] Compared with the prior art, the advantages of the present invention are as follows: the screw and barrel are made of wear-resistant structure of mold steel with part number 1.2888. Under long-term high temperature and high shear conditions, it can reduce the occurrence of problems such as wear, surface oxidation, sticking to the mold and local overheating, maintain good plasticizing ability for a longer time, and extend the service life of the barrel and screw; a mixing head is set at the end of the screw to increase the mixing effect of magnesium alloy semi-solids and the output effect is more ideal. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention; Figure 2 for Figure 1 The structural diagram of the screw is shown separately in the image; Figure 3 yes Figure 2 A separate cross-sectional view of the screw head is shown in the image. Figure 4 yes Figure 3 Side projection view of the screw head; Figure 5 yes Figure 1 A structural diagram showing the connection structure between the barrel and the long nozzle is displayed separately. Figure 6 yes Figure 3 Enlarged view of section I; Figure 7 yes Figure 3 Enlarged view of Part II. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0017] like Figures 1 to 7 As shown, the screw and barrel structure for magnesium alloy injection molding in this embodiment includes a barrel 2 and a screw 1. The screw 1 is inserted into the inner cavity of the barrel 2. The screw 1 and the barrel 2 are wear-resistant structures made of mold steel with the part number 1.2888. The end of the screw 1 is provided with a screw head 3, which can increase the semi-solid mixing effect of magnesium alloy. The screw head 3 is detachably connected to the end of the screw 1.

[0018] The screw head 3 includes a screw head body 30, a check ring 32, and a limiting protrusion ring 33. A barrier section 31 is provided at the front of the screw head body 30, and a discharge through hole 311 is axially provided on the barrier section 31. The limiting protrusion ring 33 is connected to the middle and rear part of the screw head body 30. The check ring 32 is fitted onto the screw head body 30 between the barrier section 31 and the limiting protrusion ring 33. A gap for material passage is left between the inner wall of the check ring 32 and the outer wall of the screw head body 30, and this gap communicates with the discharge through hole 311. The check ring 32 has a circumferentially distributed connecting gap and a check ring through hole 321 on the outside of the check ring. An annular groove is provided on the outer wall of the check ring corresponding to the check ring through hole 321, and a piston ring 34 is embedded in the annular groove. The top surface of the piston ring 34 is higher than the outer wall of the check ring 32. There are two sets of check ring through holes 321. The through hole spacing of the set of check ring through holes 321 closer to the limiting protrusion ring 33 is smaller than that of the other set of check ring through holes 321 farther from the limiting protrusion ring 33. An annular groove 312 is provided at the root of the barrier section 31, and the bottom surface of the annular groove 312 is flush with the inner wall of the corresponding discharge through hole 311. A protrusion 301 is provided in the middle and rear part of the screw head body 30, and the limiting protrusion ring 33 abuts against the protrusion 301.

[0019] The screw 1 includes a rod body and screw ribs. The screw ribs include a feeding section A, a compression section B, and a homogenization section C. The screw groove depth gradually decreases. The compression ratio of the screw 1 is 1.4 to 1.6, and the length-to-diameter ratio of the screw 1 is 16 to 20. The end of the barrel 2 is connected to the long nozzle 4 via a flange, and the end of the screw head 3 extends into the injection chamber 41 of the long nozzle 4.

[0020] The second embodiment of the screw and barrel structure for magnesium alloy injection molding includes a barrel 2 and a screw 1. The screw 1 is inserted into the inner cavity of the barrel 2. The screw 1 and the barrel 2 are wear-resistant structures made of mold steel with the part number 1.2888. The end of the screw 1 is provided with a screw head 3 that can increase the semi-solid mixing effect of magnesium alloy. The screw head 3 is detachably connected to the end of the screw 1.

[0021] The screw head 3 includes a screw head body 30, a check ring 32, and a limiting protrusion ring 33. A barrier section 31 is provided at the front of the screw head body 30, and a discharge through hole 311 is axially provided on the barrier section 31. The limiting protrusion ring 33 is connected to the middle and rear part of the screw head body 30. The check ring 32 is fitted onto the screw head body 30 between the barrier section 31 and the limiting protrusion ring 33. A gap for material passage is left between the inner wall of the check ring 32 and the outer wall of the screw head body 30, and this gap communicates with the discharge through hole 311. The check ring 32 has a circumferentially distributed connecting gap and a check ring through hole 321 on the outside of the check ring. An annular groove is provided on the outer wall of the check ring corresponding to the check ring through hole 321, and a piston ring 34 is embedded in the annular groove. The top surface of the piston ring 34 is higher than the outer wall of the check ring 32. There are two sets of check ring through holes 321. The through hole spacing of the set of check ring through holes 321 closer to the limiting protrusion ring 33 is smaller than that of the other set of check ring through holes 321 farther from the limiting protrusion ring 33. An annular groove 312 is provided at the root of the barrier section 31, and the bottom surface of the annular groove 312 is flush with the inner wall of the corresponding discharge through hole 311. A protrusion 301 is provided in the middle and rear part of the screw head body 30, and the limiting protrusion ring 33 abuts against the protrusion 301.

[0022] The screw 1 includes a rod body and screw ribs. The screw ribs include a feeding section A, a compression section B, and a homogenization section C. The screw groove depth gradually decreases. The compression ratio of the screw 1 is 1.4 to 1.6, and the length-to-diameter ratio of the screw 1 is 16 to 20. The end of the barrel 2 is connected to the long nozzle 4 via a flange, and the end of the screw head 3 extends into the injection chamber 41 of the long nozzle 4.

[0023] Both the surface of screw 1 and the inner wall of barrel 2 are covered with an aluminum nitride layer. Under low vacuum conditions, a high-voltage electric field is used to bombard the workpiece surface with nitrogen ions at high speed to form a dense aluminum nitride layer. The specific operation method is existing technology and will not be described in detail here.

[0024] Working Principle: The barrel and screw operate continuously at 580–610℃, therefore the materials must possess excellent thermal strength, fatigue resistance, and oxidation resistance. Because magnesium alloys, in their semi-solid state at approximately 550–620℃, still exhibit strong chemical reactivity and are prone to interfacial reactions with iron-based materials, leading to material adhesion, corrosion, and wear, ordinary nitrided steel used in injection molding machines cannot meet the requirements for long-term stable production. This technical solution selects 1.2888, a DIN standard number corresponding to the domestic grade 40CrMnMo7 material. 1.2888 is a high-strength, high-heat-resistant, and high-wear-resistant cold work die steel. After appropriate heat treatment (the specific steps of which are well-known technologies and will not be described in detail here), it possesses the following characteristics: excellent thermal stability, capable of long-term operation below 600℃ without significant softening, perfectly covering the typical temperature range for semi-solid injection molding of magnesium alloys; excellent fatigue resistance, able to withstand alternating stresses from repeated pressing and rotational shearing of the screw, extending its service life; good wear resistance and erosion resistance, maintaining surface integrity even under continuous friction from magnesium alloy particles, reducing the risk of material spalling; good machinability and heat treatment response, facilitating the manufacture of complex screw profiles, and achieving a uniform microstructure through quenching and tempering.

Claims

1. A screw barrel structure for magnesium alloy injection molding, comprising a barrel (2) and a screw (1), wherein the screw (1) is disposed within the inner cavity of the barrel (2), characterized in that: The screw (1) and barrel (2) are wear-resistant structures made of mold steel numbered 1.2888. The end of the screw (1) is provided with a screw head (3) that can increase the semi-solid mixing effect of magnesium alloy. The screw head (3) is detachably connected to the end of the screw (1).

2. The structure for a magnesium alloy injection molding screw barrel according to claim 1, characterized in that: The screw head (3) includes a screw head body (30), a check ring (32), and a limiting protrusion ring (33). A barrier section (31) is provided at the front of the screw head body (30), and a discharge through hole (311) is provided axially on the barrier section (31). The limiting protrusion ring (33) is connected to the middle and rear part of the screw head body (30). The check ring (32) is sleeved on the screw head body (30) between the barrier section (31) and the limiting protrusion ring (33). A gap for material to pass through is left between the inner wall of the check ring (32) and the outer wall of the screw head body (30). The gap is connected to the discharge through hole (311).

3. The structure for a magnesium alloy injection molding screw barrel according to claim 2, characterized in that: The check ring (32) has a connecting gap and a check ring through hole (321) distributed around its circumference.

4. The structure for a magnesium alloy injection molding screw barrel according to claim 3, characterized in that: An annular groove is provided on the outer wall of the check ring corresponding to the through hole (321), and a piston ring (34) is embedded in the annular groove. The top surface of the piston ring (34) is higher than the outer wall of the check ring (32).

5. The structure for a magnesium alloy injection molding screw barrel according to claim 4, characterized in that: There are two sets of check ring through holes (321). The through hole spacing of the set of check ring through holes (321) closer to the limiting protrusion (33) is smaller than the through hole spacing of the other set of check ring through holes (321) farther away from the limiting protrusion (33).

6. The structure for a magnesium alloy injection molding screw barrel according to any one of claims 2 to 5, characterized in that: An annular groove (312) is provided at the root of the barrier section (31), and the bottom surface of the annular groove (312) is flush with the inner wall of the corresponding discharge through hole (311).

7. The structure for a magnesium alloy injection molding screw barrel according to any one of claims 2 to 5, characterized in that: The screw head body (30) has a protrusion (301) in the middle and rear part, and the limiting protrusion (33) touches the protrusion (301).

8. The structure for a magnesium alloy injection molding screw barrel according to any one of claims 1 to 5, characterized in that: The screw (1) includes a rod body and a screw rib. The screw rib includes a feeding section (A), a compression section (B), and a homogenization section (C). The screw groove depth of the screw rib gradually decreases. The compression ratio of the screw (1) is 1.4 to 1.6, and the length-to-diameter ratio of the screw (1) is 16 to 20.

9. The structure for a magnesium alloy injection molding screw barrel according to any one of claims 1 to 5, characterized in that: The surface of the screw (1) and the inner wall of the barrel (2) are covered with an aluminum nitride layer.

10. The structure for a magnesium alloy injection molding screw barrel according to any one of claims 1 to 5, characterized in that: The end of the barrel (2) is connected to the long nozzle (4) via a flange, and the end of the screw head (3) extends into the injection chamber (41) of the long nozzle (4).

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