Extrusion device for extrusion type 3D printer

Abstract

The utility model provides an extrusion device for an extrusion type 3D printer, which comprises a needle head, a charging barrel and a temperature control device, the needle head and the charging barrel are in plug-in connection, the temperature control device comprises a cylindrical needle head heat conduction block, a charging barrel heat conduction block, a sleeve and a protective cover, and the sleeve and the protective cover are sleeved outside the charging barrel heat conduction block; a needle head insertion hole and a charging barrel insertion hole which are coaxially formed are respectively formed in the middle of the needle head heat conduction block and the middle of the charging barrel heat conduction block; heating rods and thermistor sensors are arranged in the charging barrel heat conduction block and the needle head heat conduction block; and the protective cover is connected with a three-dimensional moving device of the printer. Wherein the needle head insertion hole and the charging barrel insertion hole realize the insertion type installation of the needle head and the charging barrel, so that the disassembly of the heat conduction block during the installation of the needle head of the charging barrel is avoided, the installation error caused by frequent disassembly and assembly of the heat conduction block is also avoided, and the printing efficiency is improved. Partitioned heating is adopted for the needle head and the charging barrel, and a thermistor sensor is arranged to monitor and adjust the regional temperature in real time, so that the printing temperature is controlled more accurately.

Description

Technical Field

[0001] The utility model belongs to the technical field of biological 3D printing, and in particular relates to an extrusion device for an extrusion-type 3D printer. Background Art

[0002] 3D bioprinting technology, based on the principles of additive manufacturing, precisely controls the spatial placement of living cells, biomaterials, and biochemical factors based on computer-generated three-dimensional models. This technology can create complex, biomimetic tissue structures, with applications in regenerative medicine, pharmacokinetics, and cell biology. Generally speaking, 3D bioprinting uses living cells as one of its basic raw materials, and the cell-laden printing material is called bioink. 3D bioprinting is also often considered an enabling technology for tissue engineering, aiming to construct physiologically functional tissues and organs for transplantation and repair of damaged tissues. This technology is increasingly being used in the life sciences and has become one of the many technologies with significant development potential in the 21st century.

[0003] Unlike conventional 3D printing, tissues and organs created using bioprinting possess specific biological functions, providing conditions for further cell and tissue growth. During cell or tissue culture, different cells selectively express different genes, leading to changes in their microstructural composition and function over time. Furthermore, due to differences in genetics and the construction of 3D models, the tissues or organs created using this printing technology possess physical, chemical, and personalized properties. These characteristics present technical challenges for bioprinting, but also demonstrate its enormous potential and promising future. The emergence of bioprinting technology has brought new ideas and approaches to drug development and screening, medical mechanism research, and clinical treatment, while also promoting further advancements in medicine, pharmacy, materials science, and tissue engineering.

[0004] The microstructure of tissue engineering cell scaffolds must be suitable for cell growth, typically forming interconnected three-dimensional mesh structures. During the preparation process, printing temperature significantly affects the raw material. Conventional extrusion 3D printers use extrusion devices, which are cumbersome to install and require frequent disassembly during use, leading to significant installation errors. Furthermore, conventional extrusion devices have significant temperature measurement errors, resulting in inaccurate temperature control during the printing process. Furthermore, the threaded mounting method used for the needle and barrel can also cause material overflow during use. Utility Model Content

[0005] In order to solve the problems existing in the above-mentioned prior art, the present invention provides an extrusion device for an extrusion-type 3D printer, wherein the needle insertion hole and the barrel insertion hole provided in the needle heat conductive block and the barrel heat conductive block realize the insertion installation of the needle and the barrel, avoiding the step of disassembling the heat conductive block when installing the needle and the barrel, making the installation simpler and more convenient to use, and also avoiding the installation error caused by frequent disassembly of the heat conductive block, thereby improving the printing efficiency. At the same time, the coaxial arrangement of the cylindrical barrel heat conductive block and the needle heat conductive block and the barrel insertion hole and the needle insertion hole ensures the coaxiality and concentricity of the equipment, so that the centers of its various parts are on the same axis, ensuring the printing accuracy and preventing it from being offset. The needle and the barrel are heated by zone and a thermistor sensor is provided to monitor and adjust the regional temperature in real time to more accurately control the printing temperature. At the same time, the needle and the barrel are installed by insertion, solving the problem of overflow during use caused by traditional threaded loading and unloading.

[0006] An extrusion device for an extrusion-type 3D printer, comprising:

[0007] Plug-in connection needles and barrels;

[0008] A temperature control device for inserting the needle and the barrel and heating and controlling the temperature of the two, the temperature control device comprising:

[0009] A cylindrical needle heat conducting block, wherein the middle of the needle heat conducting block is provided with a needle insertion hole penetrating along the thickness direction thereof;

[0010] A cylindrical barrel heat conducting block, wherein the middle of the barrel heat conducting block is provided with a barrel insertion hole running through the barrel heat conducting block along its length direction;

[0011] The barrel heat conducting block and the needle heat conducting block are both provided with a heating rod and a thermistor sensor;

[0012] The sleeve and the protective cover are sequentially sleeved on the outside of the barrel heat conduction block, and the three are detachably connected by screw holes and screws;

[0013] The needle heat conductive block is detachably mounted inside the lower end of the sleeve through a screw hole. The barrel heat conductive block and the needle heat conductive block are spaced apart in the upper and lower parts of the sleeve, and the barrel insertion hole and the needle insertion hole are coaxially arranged.

[0014] The protective cover is connected to the three-dimensional moving device of the printer.

[0015] In the above technical solution, the needle insertion hole and the barrel insertion hole match the dimensions of the needle and barrel, respectively. The sleeve is hollow and cylindrical, and the outer dimensions of the needle and barrel heat conductive blocks are identical and match the inner dimensions of the cylindrical sleeve. The heating rods of the needle and barrel heat conductive blocks can be ceramic heating rods. The needle and barrel heat conductive blocks are spaced apart within the sleeve, providing insulation and reducing the temperature interaction between the needle and barrel areas. Furthermore, the plug-in connection between the needle and barrel effectively prevents raw material overflow at the installation site.

[0016] Preferably, the heating rod and thermistor sensor within the barrel's thermal block are located on the sidewall at its lower end and radially inserted. This solution allows heat from the heating rod to be transferred throughout the barrel in a step-by-step, decreasing pattern from bottom to top. During the heating process, the thermistor sensor can quickly detect temperature changes within the barrel's thermal block, enabling more accurate temperature control.

[0017] Preferably, the heating rod and thermistor sensor within the needle tip thermal block are located on the sidewall of the central portion and radially inserted. This technical solution ensures that heat provided by the heating rod is relatively evenly distributed throughout the entire needle tip. During the heating process, the thermistor sensor can quickly detect temperature changes in the needle tip thermal block, enabling more accurate temperature control. Furthermore, the needle tip can quickly reach the desired printing temperature, meeting the temperature requirements of the printing process.

[0018] Preferably, the connection between the needle heat conductive block and the sleeve, and between the barrel heat conductive block, the sleeve and the protective cover are respectively achieved by multiple sets of screw holes.

[0019] There are multiple sets of corresponding screw holes on the needle heat conducting block and the sleeve respectively, and there are multiple sets of one-to-one corresponding screw holes on the barrel heat conducting block, sleeve and protective cover respectively, so as to realize quick installation and disassembly through the screw holes.

[0020] Preferably, the heater rods and thermistor sensors of the needle and barrel heat conductive blocks are located on the same side, and hollowed-out relief grooves are provided on the sleeves corresponding to the heater rods and thermistor sensors. The relief grooves, located on one side of the sleeve's lower end, are open at the bottom. The relief grooves not only prevent the sleeves from interfering with the installation of the heater rods and thermistor sensors but also provide heat dissipation.

[0021] Preferably, at least one heat dissipation hole is provided on the side wall of the sleeve at the interval between the needle heat conductive block and the barrel heat conductive block. Preferably, the at least one heat dissipation hole is evenly distributed along the circumference of the sleeve. More preferably, three heat dissipation holes are provided. Even more preferably, the heat dissipation holes are waist-shaped holes, and the waist-shaped holes are arranged horizontally.

[0022] The provision of at least one heat dissipation hole and an avoidance groove on the sleeve can increase the heat dissipation at the interval between the needle heat conductive block and the barrel heat conductive block, and further reduce the mutual influence of the temperature between the needle and barrel areas.

[0023] Preferably, a wire harness storage slot is provided on the side of the protective cover connected to the three-dimensional movement device. The wire harness storage slot can store the printing wire assembly, fix the printing wire assembly to one side of the protective cover, reduce the impact of the printing wire assembly on printing work, and keep the printer neat and beautiful.

[0024] Preferably, a hollow structure is provided on the side of the protective cover that is not connected to the three-dimensional mobile device to increase heat dissipation.

[0025] Preferably, the protective cover is made of aluminum 6061 material.

[0026] Preferably, the needle heat conducting block and the barrel heat conducting block are both made of brass material. Using brass material to make heat conducting blocks can greatly improve heat conduction performance.

[0027] Preferably, the sleeve is made of polyetheretherketone (PEEK). The sleeve is made of PEEK, a special engineering plastic with excellent performance. It has the advantages of high temperature resistance, corrosion resistance, anti-aging, easy processing, high mechanical strength, etc. It not only protects the heat conducting block inside but also plays a certain role in heat insulation.

[0028] Preferably, the heating rods and thermistor sensors of the needle heat conductive block and the barrel heat conductive block are respectively connected to the control components of the printer for real-time monitoring and adjustment of the temperature of the corresponding areas.

[0029] It is worth noting that in the entire extrusion device of the present application, all screw holes and screw connections are coated with thermal oil to facilitate disassembly and heat conduction.

[0030] Preferably, the insertion point between the needle and the barrel corresponds to the gap between the barrel heat conducting block and the needle heat conducting block.

[0031] Preferably, the needle is provided with a plug-in portion at one end close to the barrel, and a plug-in groove is provided at the other end of the barrel close to the needle, which is interference-fit with the plug-in portion, so that the barrel and the needle are plug-in-connected via the plug-in portion and the plug-in groove. Furthermore, the plug-in portion is a hollow cylindrical structure.

[0032] The needle is preferably made of SUS303 (austenitic free-cutting stainless steel that is wear-resistant and burn-resistant). This material has good burn resistance and corrosion resistance and can be used in high temperature environments for a long time.

[0033] As a further preference, the barrel is made of soft material (such as medical silicone material, which not only has good chemical and thermal stability to meet the needs of long-term high-temperature use, but also has the characteristics of corrosion resistance, aging resistance and high resilience) to achieve plug-in installation under the condition of interference fit between the plug-in part and the plug-in slot, and make the plug-in tighter.

[0034] Preferably, a cylindrical barrel channel is provided inside the barrel, a cylindrical needle channel is provided inside the needle, and the lower ends of the barrel channel and the needle channel are funnel-shaped respectively;

[0035] The diameter of the upper end of the needle channel (the end close to the barrel) is smaller than the diameter of the lower end of the barrel channel (the end close to the needle), and the two are transitionally connected.

[0036] As a further preference, an inverted angle structure is provided at the top end of the needle channel to achieve a transition connection between the upper end of the needle channel and the lower end of the barrel channel, and to allow the raw material to better enter the interior of the needle.

[0037] Preferably, clamping parts are provided on both sides of the middle portion of the outer surface of the needle to facilitate installation and removal of the needle.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] The extrusion device for the extrusion-type 3D printer of the present invention is provided with a cylindrical barrel heat-conducting block and a needle heat-conducting block, and the barrel insertion hole and the needle insertion hole are coaxially provided, which can realize the insertion installation and disassembly of the needle and the barrel, reducing the tedious steps of disassembling the heat-conducting block when installing the needle barrel before printing, and also avoiding the installation error caused by frequent disassembly of the heat-conducting block, greatly improving the printing efficiency and saving time and effort. In addition, the needle and the barrel are heated by zone and a thermistor sensor is installed on one side of the heating rod, so that the real-time temperature of the heat-conducting block can be transmitted to the device (the control component of the printer) as accurately and quickly as possible, so as to better control the printing temperature. In addition, the barrel heat-conducting block and the needle heat-conducting block of the temperature control device of the present invention are made of brass, which greatly improves the thermal conductivity and heat transfer efficiency compared with the previous materials such as stainless steel and aluminum. At the same time, the needle and the barrel are installed by insertion, avoiding the occurrence of the previous overflow problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a three-dimensional structural diagram of an embodiment of the utility model;

[0041] Figure 2 This is a three-dimensional structural diagram of the temperature control device according to an embodiment of the present utility model;

[0042] Figure 3 This is a three-dimensional structural diagram of the temperature control device according to another embodiment of the present invention;

[0043] Figure 4 This is a three-dimensional structural diagram of the protective cover in the embodiment of the utility model;

[0044] Figure 5 This is a three-dimensional structural diagram of the sleeve in the embodiment of the utility model;

[0045] Figure 6 This is a three-dimensional structural diagram of the barrel heat-conducting block in the embodiment of the utility model;

[0046] Figure 7 This is a three-dimensional structural diagram of the needle heat conducting block in the embodiment of the present utility model;

[0047] Figure 8 This is a structural diagram of the needle-barrel combination in an embodiment of the present utility model;

[0048] Figure 9 This is a cross-sectional structural diagram of a needle in an embodiment of the present utility model;

[0049] Figure 10 It is a cross-sectional structural diagram of the barrel in the embodiment of the present utility model.

[0050] In the figure: 1-protective cover, 2-sleeve, 3-barrel heat-conducting block, 4-wiring harness storage groove, 5-needle heat-conducting block, 6-barrel insertion hole, 7-heat dissipation hole, 8-heating rod insertion hole, 9-sensor internal thread mounting hole, 10-screw hole, 11-heating rod internal thread fixing hole, 12-needle insertion hole, 13-avoidance groove, 14-needle, 141-clamping part, 142-needle channel, 143-plug-in part, 144-inverted angle structure, 15-barrel, 151-barrel channel, 152-plug-in groove. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] In the following description, more details are elaborated to facilitate a full understanding of the technical solution of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the scope of protection of the present invention should not be limited by the content of this specific embodiment.

[0053] like Figure 1 As shown, an extrusion device for an extrusion-type 3D printer includes a needle 14 and a barrel 15 that are plug-connected, and a temperature control device for inserting the needle 14 and the barrel 15 and heating and controlling the temperature of the two.

[0054] As shown in Figures 2 to 7 , the temperature control device includes: a cylindrical needle heat conducting block 5 , a cylindrical barrel heat conducting block 3 , a hollow cylindrical sleeve 2 , and a protective cover 1 .

[0055] The needle heat conductive block 5 has a needle insertion hole 12 running through its thickness and sized to fit the needle 14. The barrel heat conductive block 3 has a barrel insertion hole 6 running through its length and sized to fit the barrel 15. Both the needle heat conductive block 5 and the barrel heat conductive block 3 are made of brass, significantly enhancing their thermal conductivity and ensuring optimal heating of the raw materials in the needle 14 and barrel 15.

[0056] A heating rod (not shown) and a thermistor sensor (not shown) are mounted on the lower sidewall of the barrel heat-conducting block 3. The corresponding barrel heat-conducting block 5 is provided with a heating rod insertion hole 8 and a sensor internal thread mounting hole 9. A heating rod and a thermistor sensor are mounted on the middle sidewall of the needle heat-conducting block 5. The corresponding needle heat-conducting block 5 is provided with a heating rod insertion hole 8 and a sensor internal thread mounting hole 9. The heating rod can be a ceramic heating rod.

[0057] The heater rod insertion holes 8 and the internally threaded sensor mounting holes 9 of both the barrel heat conductive block 3 and the needle heat conductive block 5 are radially oriented. Furthermore, corresponding to the heater rod insertion holes 8, internally threaded heater rod fixing holes 11 are provided on both the needle heat conductive block 5 and the barrel heat conductive block 3, perpendicular to the heater rod insertion holes 8, for mounting the heater rod fixing screws.

[0058] The barrel heat conductive block 3 and the needle heat conductive block 5 have identical outer dimensions and match the inner dimensions of the sleeve 2. The barrel heat conductive block 3 and the needle heat conductive block 5 are installed inside the sleeve 2 with screws spaced apart from each other, and the barrel insertion hole 6 is coaxial with the needle insertion hole 12. The needle heat conductive block 5 is fixed to the interior of the sleeve 2 using four sets of screws. The protective cover 1 is mounted on the outside of the sleeve 2, and the barrel heat conductive block 3, sleeve 2, and protective cover 1 are detachably connected using four sets of screws. Screw holes 10 for screw installation are provided at corresponding positions on the needle heat conductive block 5 and sleeve 2, and at corresponding positions on the barrel heat conductive block 3, sleeve 2, and protective cover 1.

[0059] The heating rod insertion hole 8 and the sensor internal thread mounting hole 9 of the needle heat conductive block 5 and the barrel heat conductive block 3 are arranged on the same side, and the sleeve 2 is provided with a hollow avoidance groove 13 corresponding to the heating rod insertion hole 8 and the sensor internal thread mounting hole 9, and the bottom of the avoidance groove 13 is opened.

[0060] The sleeve 2 also features three horizontal, waist-shaped heat dissipation holes 7 along its circumference, located on the sidewall of the sleeve 2, corresponding to the gap between the needle heat conductive block 5 and the barrel heat conductive block 3. Made of polyetheretherketone (PEEK), the sleeve 2 not only protects the heat conductive block within but also provides a certain degree of insulation.

[0061] The protective cover is machined from aluminum 6061 and mounted to the printer's 3D motion mechanism (a platform equipped with dovetail screws) using four sets of screw holes. The side of the protective cover 1 that connects to the printer (3D motion mechanism) features a cable storage slot 4 for the printer cable set; the side not connected to the printer is hollowed out to enhance heat dissipation.

[0062] The heating rods and thermistor sensors of the needle heat conductive block 5 and the barrel heat conductive block 3 are respectively connected to the control components of the printer for real-time monitoring and adjustment of the temperature of the corresponding areas.

[0063] In the above temperature control device, all screw holes and screw connections are coated with thermal oil to facilitate disassembly and heat conduction.

[0064] As shown in Figures 8 to 10 , the connection between the needle 14 and the barrel 15 corresponds to the gap between the barrel heat conducting block 3 and the needle heat conducting block 4. The outer dimension of the needle 14 is smaller than the outer dimension of the barrel 15.

[0065] An inserting portion 143 is provided at one end of the needle 14 close to the barrel 15, and an inserting groove 152 that is interference fit with the inserting portion 143 is provided at one end of the barrel 15 close to the needle 14. The barrel 15 and the needle 14 are plug-in connected through the inserting portion 143 and the inserting groove 152, and the inserting portion 143 is a hollow cylindrical structure.

[0066] The needle 14 is made of SUS303 (austenitic free-cutting stainless steel that is wear-resistant and burn-resistant). This material has good burn resistance and corrosion resistance and can be used in high temperature environments for a long time.

[0067] The barrel 15 is made of soft material (such as medical silicone material) to achieve plug-in installation under the condition of interference fit between the plug-in portion 143 and the plug-in groove 152, and to make the plug-in more compact.

[0068] The barrel 15 is provided with a cylindrical barrel channel 151, and the needle 14 is provided with a cylindrical needle channel 142. The lower ends of the barrel channel 151 and the needle channel 142 are funnel-shaped, respectively. The upper end diameter of the needle channel 142 is smaller than the lower end diameter of the barrel channel 151. The top of the needle channel 142 is provided with an inverted angle structure 144 to achieve a transitional connection between the upper end of the needle channel 142 and the lower end of the barrel channel 151, and to facilitate the entry of the raw material into the needle 14.

[0069] Clamping portions 141 are provided on both sides of the middle portion of the outer surface of the needle 14 to facilitate installation and removal of the needle 14 .

[0070] During installation, fix the needle heat conductive block 5 inside the lower end of the sleeve 2 through four sets of screws, and then insert the barrel heat conductive block 3 into the sleeve 2 to complete the installation of the sleeve 2; then insert the installed sleeve 2 into the protective cover 1, adjust and align the four screw holes 10 respectively set on the barrel heat conductive block 3, sleeve 2 and protective cover 1, and then tighten them with screws; finally, install the corresponding heating rods and thermistor sensors on the barrel heat conductive block 3 and the needle heat conductive block 5, and install the protective cover 1 to the three-dimensional moving device of the printer through the screws.

[0071] After the temperature control device is installed, the needle 14 is inserted into the lower end of the barrel 15, filled with filler, and then inserted into the temperature control device from the top of the barrel insertion hole 6. Then, according to the printing process, when the preset processing temperature is reached, the tissue engineering scaffold preparation can be started according to the preset program.

[0072] Each extrusion-type 3D printer can be equipped with multiple extrusion devices as required.

[0073] During the printing process, since the temperatures required for the barrel 15 and the needle 14 are different, the barrel heat conductive block 3 and the needle heat conductive block 5 adopt a separate design, and the needle 14 and the barrel 15 are heated at different temperatures at the same time, which not only meets the different temperature requirements for different parts during printing, but also provides heat dissipation holes 7 at the gap between the sleeve 2 corresponding to the needle heat conductive block 5 and the barrel heat conductive block 3 to dissipate heat, so as to minimize the mutual influence of the temperature between the needle 14 and the barrel 15.

Claims

1. An extrusion device for an extrusion-type 3D printer, characterized in that: include: Plug-in connection needles and barrels; A temperature control device for inserting the needle and the barrel and heating and controlling the temperature of the two, the temperature control device comprising: A cylindrical needle heat conducting block, wherein the middle of the needle heat conducting block is provided with a needle insertion hole penetrating along the thickness direction thereof; A cylindrical barrel heat conducting block, wherein the middle of the barrel heat conducting block is provided with a barrel insertion hole running through the barrel heat conducting block along its length direction; The barrel heat conducting block and the needle heat conducting block are both provided with a heating rod and a thermistor sensor; The sleeve and the protective cover are sequentially sleeved on the outside of the barrel heat conduction block, and the three are detachably connected by screw holes and screws; The needle heat conductive block is detachably mounted inside the lower end of the sleeve through a screw hole. The barrel heat conductive block and the needle heat conductive block are spaced apart in the upper and lower parts of the sleeve, and the barrel insertion hole and the needle insertion hole are coaxially arranged. The protective cover is connected to the three-dimensional moving device of the printer.

2. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: The heating rod and the thermistor sensor in the barrel heat-conducting block are arranged on the side wall of the lower end thereof and are both inserted along the radial direction thereof.

3. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: The heating rod and the thermistor sensor in the needle heat conducting block are arranged on the side wall in the middle thereof and are both inserted in the radial direction thereof.

4. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: The heating rods and thermistor sensors of the needle heat conductive block and the barrel heat conductive block are arranged on the same side, and hollow avoidance grooves are provided on the sleeve corresponding to the heating rods and thermistor sensors.

5. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: At least one heat dissipation hole is provided on the side wall of the sleeve corresponding to the interval between the needle heat conductive block and the barrel heat conductive block.

6. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: A wire harness storage groove is provided on one side of the protective cover connected to the three-dimensional moving device.

7. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: A hollow structure is provided on the side of the protective cover that is not connected to the three-dimensional mobile device to increase heat dissipation.

8. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: The heating rods and thermistor sensors of the needle heat conductive block and the barrel heat conductive block are respectively connected to the control components of the printer for real-time monitoring and adjustment of the temperature of the corresponding areas.

9. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: The needle is provided with a plug-in portion at one end close to the barrel, and a plug-in groove is provided at one end close to the needle that is interference-fitted with the plug-in portion. The barrel and the needle are plug-in connected via the plug-in portion and the plug-in groove.

10. The extrusion device for an extrusion-type 3D printer according to claim 1, wherein: A cylindrical barrel channel is provided inside the barrel, and a cylindrical needle channel is provided inside the needle, and the lower ends of the barrel channel and the needle channel are funnel-shaped respectively; The diameter of the upper end of the needle channel is smaller than the diameter of the lower end of the barrel channel, and the two are transitionally connected.

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