A screw with no compression ratio

Abstract

A kind of screw rod without compression ratio, is arranged in barrel, screw rod includes feeding section, compression section, homogenizing section and pin head, the volume of compression section single groove is greater than the volume of feeding section single groove, the volume of homogenizing section single groove is equal to the volume of compression section single groove, the pitch of compression section is greater than the pitch of feeding section, the pitch of homogenizing section is greater than the pitch of compression section, the depth of homogenizing section single groove is less than the depth of compression section single groove, the groove of homogenizing section is double-sided groove and local groove depth in groove is "shallow-thin" change, and the groove of homogenizing section is wavy; The total compression ratio of screw rod changes in the range of 1.7~2.5. Screw rod of the present invention adopts isometric groove in compression section and homogenizing section, after fiber is added, it is possible to realize spiral propulsion in isochoric process, avoid the high shear brought by volume mutation, greatly reduce the loss to fiber length, and the compression ratio of screw rod is relatively small, avoids strong shearing effect, greatly reduces the loss of long glass fiber.

Description

Technical Field

[0001] The invention relates to the technical field of equipment in the molding and processing of fiber-reinforced polymer-based composite materials, in particular to a screw rod with no compression ratio. Background Art

[0002] Compared with traditional short glass fiber reinforced thermoplastics (SFT), the glass fibers in long glass fiber reinforced thermoplastics (LFT) products are longer and form a reinforcing skeleton network, which greatly improves the reinforcement effect and gives the products better mechanical properties, dimensional stability and temperature resistance, making LFT widely used in the automotive industry, home appliances, industrial equipment, communication facilities, outdoor products and other fields.

[0003] Currently, the injection molding methods for producing long glass fiber plastic (LFT) products can be divided into two types: online compounding and direct injection molding of LFT pellets. Online compounding has advantages such as flexible adjustment of glass fiber content and low material costs, but also has disadvantages such as large fixed investment and poor equipment versatility (it cannot accommodate the molding of other materials). Online compounding injection molding is the newest and most effective method for molding fiber-reinforced polymer-based composites at home and abroad. This molding process directly mixes continuous long fibers, plastics, and additives on the injection molding line, integrating the compounding and injection processes into a single process. The final product is then injected into the mold cavity to form the final product. Compared with the conventional two-step injection molding method, it reduces the granulation step, hence the name "one-step method." The one-step method eliminates the intermediate granulation step, saving energy and eliminating the need for storage during the granulation process. It also avoids fiber shearing during the granulation process, retaining the fiber length in the final product to the greatest extent possible, and maximizing the overall performance of the composite material.

[0004] In the online compounding injection molding process, the dispersion of melt and fiber is crucial. The uniform dispersion of melt and fiber is directly related to the service performance of the composite material. Composite materials are plasticized by screw mixing, and the most critical factor that determines the dispersion effect is the screw.

[0005] Since the early days of injection molding, materials and products have rapidly evolved and expanded, but fundamental research on screws has never ceased, and the basic screw design has remained unchanged since the 1950s. The diverse problems currently faced in production sites may stem from this peculiar situation: the plasticization of the screw. This simple question was the catalyst for the research and development of a compression-free screw. In screw visualization experiments, a special barrel, the Sapphire Barrel, is used to repeatedly observe and analyze the phenomena occurring within the barrel. By exploring a solution using direct injection molding, the following findings were observed in the feeding section: the LFT pellets were continuously compacted within the screw groove in the feeding section, with the pellets randomly oriented. Furthermore, within this region, the LFT existed as solid pellets, and the glass fiber length did not significantly decrease, indicating that the fibers were not significantly damaged within the feeding section. However, in the compression section, the situation was quite different: the glass fibers were significantly damaged, and fluffy glass fibers were observed. The glass fiber clusters tended to be oriented toward the screw groove and concentrated on one side of the groove. In the homogenization section at the very end, the shallow groove of the conventional screw homogenization section exerted high shear strength on the glass fibers. The glass fibers exhibited a laminar flow pattern in the homogenization groove, which was not conducive to fiber mixing and dispersion. Analysis of the burned glass fibers and observations of their morphology in the conventional screw pin mixing head revealed that the glass fibers were oriented along the flow path, exhibited a laminar distribution, and were subject to high shear. The pin mixing head could only achieve a simple two-dimensional "divergence-reunion" process, unable to separate the glass fiber clusters or flip the mixed glass fibers in the radial dimension.

[0006] The following conclusions can be drawn from the incineration test:

[0007] 1. Melt pressure seriously affects the breakage of glass fiber. The higher the melt pressure, the greater the shear strength, and the more severe the breakage of glass fiber.

[0008] 2. From the feeding section to the homogenizing section, the volume of the traditional screw groove changes greatly, the high compression and the melt pressure change dramatically, causing serious damage to the glass fiber;

[0009] 3. The glass fiber is transported in the screw in the form of laminar flow. Even the pin mixing head cannot achieve the "groove top-groove bottom" flipping of the glass fiber, nor can it rub apart the glass fiber clusters, which is not conducive to the dispersion of the glass fiber.

[0010] Therefore, the traditional plasticizing system causes severe damage to the glass fiber, and the residual length is even less than 1mm, which does not meet the requirements of long glass fiber.

[0011] Relevant data shows that the mechanical properties (rigidity, strength, and toughness) of long glass fiber reinforced plastic (LFT) products are closely related to the length of the glass fibers within the product. When the glass fiber length increases from 1mm to 10mm, the mechanical properties of the product show a significant improvement. Therefore, suppressing glass fiber breakage and increasing the glass fiber length within the product are the primary goals of LFT injection molding.

[0012] Therefore, further improvements are necessary. Summary of the Invention

[0013] The purpose of the present invention is to provide a screw with no compression ratio that has simple structure, low shear, good processing performance, reduced probability of fiber breakage, good heat conduction and strong practicality, so as to overcome the shortcomings of the prior art.

[0014] A screw with no compression ratio designed for this purpose is installed in a barrel and is characterized in that: the screw includes a feeding section, a compression section, a homogenizing section and a pin head, the volume of a single screw groove in the compression section is greater than the volume of a single screw groove in the feeding section, the volume of a single screw groove in the homogenizing section is equal to the volume of a single screw groove in the compression section, the pitch of the compression section is greater than the pitch of the feeding section, the pitch of the homogenizing section is greater than the pitch of the compression section, the depth of a single screw groove in the homogenizing section is less than the depth of a single screw groove in the compression section, the screw groove of the homogenizing section is a double-sided groove, and the local groove depth in the screw groove varies from "shallow to thin", and the screw groove of the homogenizing section is wavy; the compression ratio of the screw varies within the range of 1.7 to 2.5.

[0015] The screw groove of the homogenizing section is provided with a first flow area and a second flow area, the first flow area and the second flow area are staggered with each other, and when the screw rotates, the melt in the first flow area flows into the second flow area.

[0016] The depth of a single screw groove in the compression section is greater than the depth of a single screw groove in the feeding section.

[0017] The volume of a single screw groove in the compression section is between 1.4 and 2 times the volume of a single screw groove in the feeding section.

[0018] The feeding section has a screw groove depth of 16.5 to 18 mm, a screw pitch of 70 to 75 mm, a diameter of 108 mm, and a length of 1258 mm.

[0019] The screw groove depth of the compression section is 18-23 mm, the screw pitch is 100-105 mm, and the length is 774 mm.

[0020] The depth of the screw groove of the homogenizing section is 8-11 mm on one side and 12-15 mm on the other side, the pitch is 108-112 mm, and the length is 565 mm.

[0021] A glass fiber feeding port is provided on the barrel at a position corresponding to the compression section.

[0022] Compared with the existing traditional screw, the screw without compression ratio of the present invention has the following advantages:

[0023] 1. The screw compression is relatively small, which avoids strong shearing and greatly reduces the breakage of long glass fibers;

[0024] 2. The up and down kneading action of the wave screw disperses the fibers, which is beneficial to the dispersion of fibers and polymers. At the same time, it also forms a stretching and extrusion effect to a certain extent, causing the viscosity of the composite melt to decrease and the fluidity to increase. Therefore, a high proportion of fibers in the composite material can also have good fluidity and processing performance.

[0025] 3. Protect the length of the fiber in the product; after the melt produces a melt film, it enters the non-compression zone (wave section). Since the volume of the melt does not change, the pressure of each unit of the melt does not differ or change, which minimizes the probability of fiber breakage;

[0026] 4. Enhanced the uniformity of temperature and pressure; because of the presence of waves, heat conduction is increased, and the uniformity of plasticization, temperature, pressure, etc. is enhanced;

[0027] 5. Improve the interfacial compatibility between fiber and polymer, strengthen the plasticizing effect of compounding; reduce the internal stress in the product and make it homogenized. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the overall structure of the screw in one embodiment of the present invention.

[0029] Figure 2 Schematic diagram of the plasticizing and melting mechanism of the screw in one embodiment of the present invention.

[0030] Figure 3 Schematic diagram of the structure of the screw homogenizing section in one embodiment of the present invention.

[0031] Figure 4 Schematic diagram of the structure of the plasticizing system in one embodiment of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] See also Figures 1-4, a screw with no compression ratio is installed in a barrel 5, and the screw includes a feeding section 1, a compression section 2, a homogenizing section 3 and a pin head 4. The volume of a single screw groove in the compression section 2 is greater than the volume of a single screw groove in the feeding section 1, the volume of a single screw groove in the homogenizing section 3 is equal to the volume of a single screw groove in the compression section 2, the pitch of the compression section 2 is greater than the pitch of the feeding section 1, the pitch of the homogenizing section 3 is greater than the pitch of the compression section 2, the depth of a single screw groove in the homogenizing section 3 is less than the depth of a single screw groove in the compression section 2, the screw groove of the homogenizing section 3 is a double-sided groove, and the local groove depth in the screw groove changes from "shallow to thin", and the screw groove of the homogenizing section 3 is wavy; the compression ratio of the screw is 1.7 to 2.5. This zero-compression screw addresses the breakage mechanism of glass fiber during conventional screw conveying, while also taking into account conventional plastic molding. Its design combines zero-compression "isovolumetric flow" with low shear and "isobaric flow" to maximize fiber length. The zero-compression "isovolumetric flow" maintains the volume of adjacent channels in compression section 2 and homogenization section 3, ensuring consistent melt pressure within each channel and preventing sudden changes in melt pressure that could lead to significant fiber breakage. The low-shear "isobaric flow" achieves lateral flow and tumbling mixing within the melt channel by varying the local depth from shallow to thin, breaking up laminar flow and avoiding high shear. This creates an extensional rheological effect, promoting the unbundling of glass fiber clusters while enhancing heat conduction and melting to suppress high shear. Plasticizing systems using this screw are compatible with the plastic molding of other plastics.

[0034] The screw groove of the homogenizing section 3 is provided with a first flow area a and a second flow area b, which are staggered with each other. When the screw rotates, the melt in the first flow area a flows into the second flow area b.

[0035] The depth of a single screw groove in the compression section 2 is greater than the depth of a single screw groove in the feeding section 1.

[0036] A glass fiber feeding port is provided on barrel 5 at a position corresponding to compression section 2. Glass fiber has the following characteristics during processing: it is insensitive to screw speed, has certain temperature requirements, and is sensitive to back pressure. The greater the back pressure, the more fragile the glass fiber. Glass fiber is required to maintain its original length as much as possible during processing, so adding glass fiber in compression section 2 can reduce glass fiber breakage.

[0037] See also Figure 1The screw without compression ratio is divided into feeding section 1, compression section 2, and homogenization section 3. There is a pin head 4 at the rear end of the homogenization section. The compression ratio of the entire screw varies in the range of 1.7 to 2.5. The screw groove of the feeding section 1 is relatively deep, ranging from 16.5 to 18 mm, with a pitch of 70 to 75 mm, a diameter of 108 to 112 mm, and a length of 1258 mm. In the feeding section 1, the thermoplastic material is added to the spiral channel composed of the screw and the barrel 5 to form a solid plug 6, which is softened under the dual heating system of screw shear heat and external heating to form a melt pool 7 and is pushed forward by friction. During the processing, the glass fiber is required to maintain its original length as much as possible to reduce the damage caused by the screw shear process. Therefore, the glass fiber is added in the compression section 2 to avoid the long thermomechanical process to reduce the breakage of the glass fiber. In order to continuously add the glass fiber into the screw, it is required to unload the pressure in the glass fiber addition section. The volume increases, unloading the pressure, and reaching an area consistent with the external pressure. At this time, the pitch increases to 100-105mm, the screw groove depth increases to 18-23mm, and the length is 774mm. The volume of a single screw groove in compression section 2 is 1.4-2 times that of a single screw groove in feeding section 1, releasing the pressure transmitted from feeding section 1. Due to the increase in screw groove volume, there is no pressure-building effect, but the melt can be continuously transported. The glass fiber is mixed with the molten polymer. The increased volume meets the needs of glass fiber addition and mixing, and prepares for the subsequent upper and lower kneading of the mixture. In homogenization section 3, the pitch continues to increase to 108-112mm, the screw groove is 8-11mm deep on one side and 12-15mm on the other side. The length of the homogenization section is 565mm. Compared with compression section 2, the pitch of homogenization section 3 is increased, but the screw groove depth is reduced. The volume of a single screw groove does not change much, achieving a smooth transition of the melt from compression section 2 to homogenization section 3. Figure 3 , the first flow zone a and the second flow zone b are staggered with each other, and the melt in the first flow zone a flows to the second flow zone b. The lateral flow and flip mixing of the melt in the groove are achieved through the "shallow-thin" change of the local groove depth in the groove, breaking up the laminar flow, avoiding high shear, triggering the stretching rheological effect, and prompting the fiber clusters to be rubbed apart. The pin head 4 at the tail of the screw, this mixing head can only achieve a simple two-dimensional "divergence-convergence", and has no mixing effect on the fiber and the melt. The addition of glass fiber requires a small range of volume change fluctuations, and the volume compression ratio of the screw in the compression section 2 and the homogenization section 3 is close to one, ensuring that the melt flows in a state of approximately constant volume. By keeping the volume of adjacent screw grooves in the compression section 2 and the homogenization section 3 consistent, the melt pressure of each screw groove can also be kept consistent, avoiding sudden changes in melt pressure that lead to severe breakage of the glass fiber.

[0038] See also Figure 2As can be seen from the figure, in compression section 2, most of the pellets have melted, making it suitable for glass fiber addition. Simultaneously, the screw channel deepens, the pitch increases, and the volume of a single screw channel increases. Pressure is released, and glass fiber is added to the screw channel in this section. Meanwhile, when the melt transitions to homogenization section 3, the volume of a single screw channel remains essentially unchanged, with no sudden change, and the strong shearing effect is not obvious.

[0039] See also Figure 4 This is a compression-free, low-shear plasticizing system designed for in-line compounding of long glass fibers. The first dropout station, c, features a special design to ensure smooth, blockage-free pellet transportation. The pellets are plasticized and melted by the compression-free "isovolumetric" and low-shear "isobaric" plasticizing systems, d, where they are evenly mixed with the external long glass fibers. They then flow through the three low-flow resistance components, e, and into the low-flow resistance nozzle channel, f. Under screw injection pressure, they are injected into the mold cavity to form the finished product. The three low-flow resistance components, e, balance response time and flow pressure loss, while the low-flow resistance nozzle channel, f, promotes melt flow.

[0040] The screw with no compression ratio is required to be able to add glass fiber in the compression section 2. The design adopts a large screw groove depth. Therefore, the pressure in this section is unloaded, the volume increases, and an area consistent with the external pressure is reached, which is conducive to the addition of long glass fiber. The homogenization section 3 and the compression section 2 adopt isovolumetric screw grooves, and the volume change fluctuation range is small. The volume compression ratio of the screw in the compression section 2 and the homogenization section 3 is close to one, ensuring that the melt flows in a state of approximately constant volume, so that the melt volume does not change. After the fiber is added, the spiral propulsion in the isochoric process can be achieved, avoiding the high shear caused by the volume mutation, greatly reducing the loss of fiber length, and the melt is coated on the glass fiber, realizing lubrication of the glass fiber transportation. At the same time, the pressure of each unit of the melt at this stage is unchanged, reducing the probability of the glass fiber being broken by back pressure; the screw groove depth in the homogenization section 3 becomes shallower, but the pitch increases. The polymer after the fiber and the melt are mixed smoothly transitions between the compression section 2 and the homogenization section 3, without compression and pressure mutation, thereby maximizing the fiber length. This screw with no compression ratio is suitable for the processing of long fiber online compounding polymer composite materials, and can maintain good fiber dispersion and mixing effects.

[0041] The above is a preferred embodiment of the present invention, which illustrates and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A screw without compression ratio, installed in a barrel (5), characterized in that: The screw comprises a feeding section (1), a compression section (2), a homogenizing section (3) and a pin head (4); the volume of a single screw groove of the compression section (2) is greater than the volume of a single screw groove of the feeding section (1); the volume of a single screw groove of the homogenizing section (3) is equal to the volume of a single screw groove of the compression section (2); the pitch of the compression section (2) is greater than the pitch of the feeding section (1); the pitch of the homogenizing section (3) is greater than the pitch of the compression section (2); the depth of a single screw groove of the homogenizing section (3) is less than the depth of a single screw groove of the compression section (2); the screw groove of the homogenizing section (3) is a double-sided groove, and the local groove depth in the screw groove changes from shallow to thin; the screw groove of the homogenizing section (3) is wavy; the compression ratio of the screw is 1.7 to 2.5; The pin head (4) is arranged at the rear end of the homogenizing section.

2. The screw with no compression ratio according to claim 1, characterized in that: The screw groove of the homogenizing section (3) is provided with a first flow area (a) and a second flow area (b), the first flow area (a) and the second flow area (b) are staggered with each other, and when the screw rotates, the melt in the first flow area (a) flows into the second flow area (b).

3. The screw with no compression ratio according to claim 2, characterized in that: The depth of a single screw groove of the compression section (2) is greater than the depth of a single screw groove of the feeding section (1).

4. The screw with no compression ratio according to claim 3, characterized in that: The volume of a single screw groove of the compression section (2) is between 1.4 and 2 times the volume of a single screw groove of the feeding section (1).

5. The screw rod with no compression ratio according to claim 4, characterized in that: The feeding section (1) has a screw groove depth of 16.5-18 mm, a screw pitch of 70-75 mm, a diameter of 108 mm, and a length of 1258 mm.

6. The screw rod with no compression ratio according to claim 5, characterized in that: The screw groove depth of the compression section (2) is 18-23 mm, the screw pitch is 100-105 mm, and the length is 774 mm.

7. The screw rod with no compression ratio according to claim 6, characterized in that: The depth of the screw groove of the homogenizing section (3) is 8 to 11 mm on one side and 12 to 15 mm on the other side, the pitch is 108 to 112 mm, and the length is 565 mm.

8. The screw rod with no compression ratio according to claim 4, characterized in that: A glass fiber feeding port is provided on the barrel (5) at a position corresponding to the compression section (2).

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