A casting process for superconducting solenoid coils of a medical ion beam accelerator

Abstract

The application discloses a casting process for a superconducting inclined solenoid tube type coil of a medical ion beam accelerator. The superconducting inclined solenoid tube comprises, from outside to inside, an arc tube shaped coil outer framework, a coil inner framework and a stainless steel support tube which are sequentially sleeved. The casting system comprises a casting tool. The casting process comprises the following steps: coil framework structure optimization design; preparation of the casting tool; installation of the superconducting inclined solenoid tube; preheating; epoxy resin preparation; vacuum casting; solidification; demolding and the like. The application adopts a vacuum casting method of the epoxy resin from bottom to top, greatly improves the casting permeability of the superconducting inclined solenoid tube during casting, and guarantees the insulation performance and electromagnetic performance of the superconducting inclined solenoid tube.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting magnets, and in particular relates to a casting process for a superconducting inclined solenoid coil of a medical ion beam accelerator. Background Art

[0002] In the field of cancer treatment, ion beams are widely used as the ideal radiation source for radiotherapy. The rotating gantry (Gantry) in treatment devices is the ideal treatment terminal because it can rotate the radioactive beam 360°, providing a full 4π solid angle of delivery. Compared to conventional horizontal and vertical treatment terminals, the Gantry provides a better and more reliable treatment plan, minimizing radiation dose to sensitive organs.

[0003] Existing Gantry treatment devices, whether using conventional or superconducting magnet structures, are bulky, expensive, and require high operation and maintenance costs, hindering the widespread adoption of ion beam cancer treatment. In recent years, with the rapid advancement of superconducting magnet technology, superconducting inclined solenoid coils, as a new structure, have begun to be used in ion beam accelerating magnets and medical treatment devices. In these applications, energy conservation and miniaturization are crucial factors for future development.

[0004] Compared to traditional racetrack coils, the skewed solenoid coil offers a novel and lightweight structure, superior magnetic field quality, outstanding mechanical properties, and a simple winding process with minimal bending, making it suitable for a wide range of currently available superconducting wires. The skewed solenoid coil's bobbin is made of G10 fiberglass. Each bobbin layer has 110 turns of wire slots, each containing two superconducting wires. For a total of 2 x 110 turns, the radial clearance between the outer and inner bobbins is 1.45 mm per side.

[0005] Traditional racetrack coils typically are placed within a casting cavity and cast using an immersion casting process in a vacuum chamber. However, the gap between the inner and outer layers of the inclined solenoid coil is only 1.45mm per side. Conventional casting processes make it difficult to achieve a solid and thorough casting, resulting in poor quality and a low yield rate for the cast product, and the coil's insulation and electromagnetic properties cannot be guaranteed. Summary of the Invention

[0006] The present invention provides a casting process for superconducting inclined solenoid coils for medical ion beam accelerators, aiming to solve the problem of poor casting quality and low yield rate when producing inclined solenoid coils using conventional processes.

[0007] To this end, the present invention adopts the following technical solutions:

[0008] A casting process for a superconducting inclined solenoid coil for a medical ion beam accelerator. The superconducting inclined solenoid comprises, from the outside to the inside, an arc-tube-shaped coil outer frame, a coil inner frame, and a stainless steel support tube, which are sequentially arranged. The coil outer frame and the coil inner frame are of equal length, while the stainless steel support tube is longer than the coil inner frame. Both ends of the stainless steel support tube extend outside the coil inner frame. An inner casting cavity is formed between the inner wall of the coil outer frame and the outer wall of the coil inner frame, and an outer casting cavity is formed between the inner wall of the coil inner frame and the outer wall of the stainless steel support tube.

[0009] A support plate is fixedly connected between the end faces of the coil outer frame and the inner frame of the coil. The inner diameter of the support plate is not less than the outer diameter of the coil inner frame, and the outer diameter is not less than the inner diameter of the coil outer frame. The support plate is provided with a plurality of annular guide grooves along the circumference. The guide grooves pass through the support plate and connect to the inner casting cavity. The left end fixed plate is intermittently welded to the stainless steel support tube, and the weld gap connects to the outer casting cavity.

[0010] The pouring system includes a vacuum box and a pouring tooling arranged in the vacuum box;

[0011] The pouring tooling includes a cubic frame, a horizontal support member is provided at the bottom of the cubic frame, an epoxy barrel for storing epoxy resin is provided on the support member, a glue inlet pipe is connected to the bottom of the epoxy barrel, and the glue inlet pipe is connected to a peristaltic pump, a booster pump, a first flow meter and a first stop valve according to the flow direction of the epoxy resin;

[0012] The coil and the casting cavity are placed vertically in a cubic frame. The lower end of the stainless steel support tube passes through the support member, and the lower end surface of the casting cavity is placed on the support member. The middle and upper parts of the superconducting inclined solenoid are connected with support rings for fixing. The support rings are fixedly connected to the cubic frame.

[0013] The end of the glue inlet pipe is connected to the lower end of the pouring cavity. The top of the pouring cavity is connected to an overflow pipe. The connection between the glue inlet pipe and the overflow pipe and the pouring cavity is sealed with vacuum sealant to ensure the vacuum performance of the pouring cavity. The tail end of the overflow pipe is connected to the overflow bucket. The overflow pipe is connected to a second stop valve, a vacuum gauge, and a second flow meter according to the flow direction of the epoxy resin.

[0014] The pouring process comprises the following steps:

[0015] 1) Prepare epoxy resin according to requirements and test the viscosity of epoxy resin at different temperatures to determine the temperature at which the viscosity of epoxy resin is lowest. The lower the viscosity, the higher the fluidity of epoxy resin. The temperature at which the viscosity is lowest is the holding temperature of epoxy resin.

[0016] 2) Fix the superconducting inclined solenoid to the casting fixture and place it in an oven; adjust the oven temperature to the holding temperature determined in step 1) for a holding time of not less than 6 hours;

[0017] 3) The epoxy resin prepared according to the preparation method of step 1) is degassed in a vacuum device, preheated to the holding temperature of step 1), and finally transferred into the epoxy barrel;

[0018] 4) The first stop valve is closed, the second stop valve is opened, the vacuum unit connected to the overflow cylinder sidewall is opened, the glue feeding pipe, the pouring cavity and the overflow pipe are vacuumized, the vacuum gauge on the overflow pipe is less than 5 Pa, the vacuum unit is closed, the first stop valve, the peristaltic pump and the booster pump connected to the epoxy cylinder sidewall are opened, and the pouring operation is started;

[0019] The epoxy resin enters the pouring cavity through the glue feeding pipe, then enters the inner pouring cavity through the flow guide groove on the support disc, enters the outer pouring cavity through the gap between the coil inner framework and the stainless steel support pipe, and immerses in the gap between the formwork and the outer framework through the gap between the formwork joints; the epoxy resin liquid level rises until the inner pouring cavity and the outer pouring cavity are filled and overflowed from the overflow pipe;

[0020] The readings of the second flow meter on the overflow pipe and the first flow meter on the glue feeding pipe are observed, and when the readings of the two flow meters are consistent and epoxy resin overflows in the overflow barrel, the second stop valve is closed first, then the first stop valve on the glue feeding pipe is closed, the booster pump and the peristaltic pump are closed, and the pouring is completed;

[0021] 5) Curing, removing the epoxy barrel, booster pump, peristaltic pump, first flow meter, vacuum pump, overflow barrel, vacuum gauge and second flow meter on the pouring system, and retaining the first stop valve and the second stop valve;

[0022] The coil, pouring cavity and cubic frame are transferred into the oven as a whole, the oven temperature is adjusted according to the curing temperature curve of the epoxy resin, and the epoxy resin is cured;

[0023] 6) Demoulding, the superconducting solenoid is demoulded after the furnace is cooled to room temperature.

[0024] Further, a circle of screw holes is formed on the end face of the coil outer framework and the coil inner framework, two circles of through holes are formed on the support disc in the circumferential direction, and the through holes on the support disc correspond to the screw holes on the coil outer framework and the coil inner framework one by one; the support disc is fixedly connected with the coil outer framework and the coil inner framework through screws.

[0025] Further, the flow guide groove on the support disc is located between the two circles of through holes, and the flow guide groove is arc-shaped.

[0026] Further, the covers of the epoxy barrel and the overflow barrel are organic glass plates, which facilitate observation of the amount of epoxy resin in the barrels.

[0027] The beneficial effects of the present application are as follows:

[0028] 1. The support plates at both ends of the superconducting inclined solenoid of the present invention are provided with 12 guide grooves along the circumferential direction. The guide grooves are in the shape of long arc-shaped slots, which increase the passage for epoxy resin to enter the inner casting cavity. The center of the guide groove coincides with the center of the inner casting cavity, reducing the flow resistance of the epoxy resin during casting and improving casting efficiency.

[0029] 2. The present invention places the superconducting inclined solenoid vertically by using a casting tool. During casting, the epoxy resin enters the inner casting cavity and the outer casting cavity from the lowest end of the superconducting inclined solenoid and overflows from the top, ensuring that the epoxy resin fills the gaps between the coil bobbins from bottom to top, ensuring that the coil can be cast solidly and thoroughly.

[0030] 3. The present invention tests the fluidity of the epoxy resin before formal pouring. By testing the viscosity of the epoxy resin at different temperatures, the temperature value at which the epoxy resin has the lowest viscosity and the highest fluidity is obtained. During formal pouring, the epoxy resin and the superconducting inclined solenoid are preheated according to the tested temperature to ensure that the epoxy resin maintains optimal fluidity during the pouring process, so that the epoxy resin fills the gaps between the coil skeletons, thereby improving the pouring quality.

[0031] 4. The present invention degasses the epoxy resin before pouring to reduce the risk of bubbles in the epoxy resin after pouring;

[0032] 5. The vacuum pouring system of the present invention is connected to a vacuum pump at the end for vacuuming. When the vacuum degree of the entire pouring system is lower than 5 Pa, pouring begins. During the pouring process, the booster pump and peristaltic pump are used to apply pressure to ensure that the epoxy resin fully fills the gaps between the ring frames, further improving the pouring quality.

[0033] 6. The vacuum pouring system of the present invention is equipped with a vacuum gauge, which can accurately measure the vacuum degree of the pouring system, making it convenient for the staff to accurately control the vacuum degree of the pouring system and ensure the pouring quality;

[0034] 7. The present invention is provided with flow meters on the inlet pipe and the overflow pipe, respectively, which can accurately measure the flow rate of epoxy resin flowing into and out of the coil skeleton gap, providing an accurate basis for determining whether the epoxy resin has completely filled the coil skeleton gap;

[0035] 8. In the vacuum pouring system of the present invention, the covers of the epoxy barrel and the overflow barrel are made of organic glass plates, so that the situation inside the barrel can be observed at any time, preventing the epoxy barrel from being sucked empty or excessive epoxy overflowing and causing waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the superconducting oblique solenoid coil structure of the present invention;

[0037] Figure 2 Schematic diagram of the fixed end plate structure of the superconducting oblique solenoid coil of the present invention;

[0038] Figure 3 is a cross-sectional view of a superconducting oblique solenoid coil of the present invention;

[0039] Figure 4 Schematic diagram of a superconducting inclined solenoid coil casting tool of the present invention;

[0040] Figure: 1. Coil; 2. Casting cavity; 3. Cube frame; 4. Overflow pipe; 5. Second shut-off valve; 6. Vacuum gauge; 7. Overflow cylinder; 8. Second flowmeter; 9. Booster pump; 10. Vacuum unit; 11. Epoxy cylinder; 12. Peristaltic pump; 13. First flowmeter; 14. First shut-off valve; 15. Rubber inlet hose.

[0041] 16. Coil (excluding junction box); 17- template;

[0042] 18. Junction box; 19. Right end plate; 20. Coil inner frame; 21. Coil outer frame; 22. Left end plate; 23. Stainless steel support tube. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the accompanying drawings:

[0044] like Figures 1 to 4 The figure shows a casting process for a superconducting inclined solenoid coil for a medical ion beam accelerator. The superconducting inclined solenoid comprises, from the outside inward, an arc-shaped coil outer frame, an inner coil frame, and a stainless steel support tube, which are sequentially nested. The outer coil frame and inner coil frame are of equal length, while the stainless steel support tube is longer than the inner coil frame. Both ends of the stainless steel support tube extend out of the inner coil frame, extending to equal lengths. An inner casting cavity 2 is formed between the inner and outer walls of the outer coil frame, while an outer casting cavity 2 is formed between the inner and outer walls of the inner coil frame and the outer wall of the stainless steel support tube.

[0045] A support disk is fixedly connected between the end faces of the coil outer frame and the coil inner frame. The inner diameter of the support disk is equal to the outer diameter of the coil inner frame, and the outer diameter is equal to the inner diameter of the coil outer frame. A circle of screw holes is respectively provided on the end faces of the coil outer frame and the coil inner frame. The support disk is provided with two circles of through holes along the circumference. The through holes on the support disk correspond one-to-one to the screw holes on the coil outer frame and the coil inner frame. The support disk is fixedly connected to the coil outer frame and the coil inner frame by screws. The support disk is provided with a number of annular guide grooves along the circumference. The guide grooves are located between the two circles of through holes and are arc-shaped. The guide grooves pass through the support disk and are connected to the inner casting cavity 2. The left end support disk is fixed to the stainless steel support tube by intermittent welding, and the weld gap is connected to the outer casting cavity 2.

[0046] The coil (without terminal box) is wrapped with a mold plate. The mold plate is used to make the thickness of the epoxy layer on the outer surface of the coil uniform and smooth after pouring. The mold plate is made of FR-4 epoxy resin plate and is wrapped along the outer surface of the coil in sections. The joints are smooth and have no leaks. The epoxy resin is poured from the gaps between the joints of the mold plate and forms the outermost epoxy layer of the coil. The coil wrapped with the mold plate is placed in the vacuum pouring cavity 2 as a whole. Pads are placed between the two end surfaces of the coil and the pouring cavity 2 to ensure that there is enough space between the coil and the pouring cavity 2.

[0047] The pouring system includes a pouring tool. The pouring tool includes a cubic frame 3. Two horizontally spaced support beams are arranged at the lower part of the cubic frame 3. An epoxy barrel for storing epoxy resin is arranged on the support beams. The bottom of the epoxy barrel is connected with a glue inlet pipe 15. The glue inlet pipe 15 is connected with a peristaltic pump 12, a booster pump 9, a first flow meter 13 and a first stop valve 14 in the flowing direction of the epoxy resin.

[0048] The coil and the pouring cavity 2 are vertically placed in the cubic frame 3 as a whole. The lower end of the stainless steel support pipe penetrates through the support member. The lower end surface of the pouring cavity 2 is placed on the support member. The middle and upper parts of the superconducting inclined solenoid are connected with support rings for fixation. The support rings are fixedly connected with the cubic frame 3.

[0049] The end of the glue inlet pipe 15 is communicated to the lower end of the pouring cavity 2. An overflow pipe 4 is connected to the top of the pouring cavity 2. The connection between the glue inlet pipe 15 and the overflow pipe 4 and the pouring cavity 2 is sealed with vacuum sealing mud to ensure the vacuum performance of the pouring cavity 2. The tail end of the overflow pipe 4 is connected to an overflow barrel. The overflow pipe 4 is connected with a second stop valve 5, a vacuum gauge 6 and a second flow meter 8 in the flowing direction of the epoxy resin.

[0050] The pouring process includes the following steps:

[0051] 1) The epoxy resin is prepared according to the requirements. The viscosity of the epoxy resin at different temperatures is tested by experiments to determine the temperature value at which the viscosity of the epoxy resin is the lowest. The lower the viscosity, the higher the flowability of the epoxy resin. The temperature value at which the viscosity is the lowest is the heat preservation temperature of the epoxy resin.

[0052] The epoxy resin in this embodiment is a low-temperature impregnation resin with the brand IR3 series developed by the Institute of Physical and Chemical Technology of the Chinese Academy of Sciences. The resin has the characteristics of simple curing process, wide applicable temperature range of 323K to 4K, low viscosity, high low-temperature strength, good toughness, high insulation strength and good radiation resistance. Through experiments, it is found that the viscosity of the epoxy resin is the lowest and the flowability is the best at 60℃. Therefore, the coil and the epoxy resin are preheated to 60℃ in an oven before pouring to improve the flowability of the epoxy resin.

[0053] 2) Fix the superconducting inclined solenoid to the casting fixture and place it in an oven. Adjust the oven temperature to 60°C and keep it at this temperature for at least 6 hours. Heat the casting fixture, the superconducting inclined solenoid, and other components to 60°C to reduce heat loss during the epoxy resin casting process and maintain the epoxy resin at its optimal fluidity to improve casting quality.

[0054] 3) Prepare epoxy resin according to the preparation method in step 1), place it in a vacuum device for degassing, with the pressure not exceeding 5 Pa, preheat to 60°C, and transfer it to an epoxy barrel.

[0055] 4) Close the first stop valve 14, open the second stop valve 5, and turn on the vacuum unit 10 connected to the side wall of the overflow tube 7. Evacuate the rubber inlet pipe 15, the pouring cavity 2, and the overflow tube 4 until the vacuum gauge 6 on the overflow tube 4 reads less than 5 Pa. Then, turn off the vacuum unit 10, turn on the first stop valve 14, the peristaltic pump 12, and the booster pump 9 connected to the side wall of the epoxy tube 11, and start pouring.

[0056] The epoxy resin enters the casting cavity 2 through the glue inlet pipe 15, then enters the inner casting cavity 2 through the guide groove on the support plate, enters the outer casting cavity 2 through the pores between the coil inner frame and the stainless steel support tube, and penetrates into the gap between the template and the outer frame through the gap in the template joint. The epoxy resin liquid level rises until it fills the inner and outer casting cavities 2 and overflows from the overflow pipe 4.

[0057] Observe the readings of the second flow meter 8 on the overflow pipe 4 and the first flow meter 13 on the glue inlet pipe 15. When the readings of the two flow meters are consistent and epoxy resin overflows from the overflow barrel, first close the second stop valve 5, then close the first stop valve 14 on the glue inlet pipe 15, turn off the booster pump 9 and peristaltic pump 12, and complete the pouring.

[0058] 5) Curing: Remove the epoxy barrel, booster pump 9, peristaltic pump 12, first flow meter 13, vacuum pump, overflow barrel, vacuum gauge 6, and second flow meter 8 from the casting system, and retain the first stop valve 14 and second stop valve 5; transfer the vacuum box into the oven, and adjust the oven temperature according to the curing temperature curve of the epoxy resin to complete the curing of the epoxy resin.

[0059] The curing procedure is to raise the temperature to 110°C within 60 minutes, keep it at this temperature for 5 hours, then raise the temperature from 110°C to 125°C within 30 minutes, keep it at this temperature for 16 hours to fully cure the epoxy resin, and then cool it down with the furnace.

[0060] 6) Demolding: The superconducting inclined solenoid is demolded after being cooled to room temperature in the furnace.

Claims

1. A casting process for a superconducting inclined solenoid coil for a medical ion beam accelerator, characterized in that: The superconducting oblique solenoid comprises, from the outside to the inside, an arc-shaped coil outer frame, a coil inner frame and a stainless steel support tube which are sequentially sleeved, the coil outer frame and the coil inner frame being equal in length, the stainless steel support tube being longer than the coil inner frame, and both ends of the stainless steel support tube extending out of the coil inner frame; an inner casting cavity (2) is formed between the inner wall of the coil outer frame and the outer wall of the coil inner frame, and an outer casting cavity (2) is formed between the inner wall of the coil inner frame and the outer wall of the stainless steel support tube; A support disk is fixedly connected between the end faces of the coil outer frame and the coil inner frame, wherein the inner diameter of the support disk is not less than the outer diameter of the coil inner frame, and the outer diameter of the support disk is not less than the inner diameter of the coil outer frame; the support disk is provided with a plurality of annularly arranged guide grooves along the circumference, the guide grooves pass through the support disk and are connected to the inner casting cavity (2); the left end fixed disk is intermittently welded to the stainless steel support tube, and the weld gap is connected to the outer casting cavity (2); The pouring system includes a vacuum box and a pouring tooling arranged in the vacuum box; The casting tool comprises a cubic frame (3), a horizontal support member is provided at the lower portion of the cubic frame (3), an epoxy barrel for storing epoxy resin is provided on the support member, a glue inlet pipe (15) is connected to the bottom of the epoxy barrel, and the glue inlet pipe (15) is connected to a peristaltic pump (12), a booster pump (9), a first flow meter (13) and a first stop valve (14) according to the flow direction of the epoxy resin; The coil and the casting cavity (2) are vertically placed as a whole in the cubic frame (3), the lower end of the stainless steel support tube passes through the support member, and the lower end surface of the casting cavity (2) is placed on the support member; the middle and upper parts of the superconducting inclined solenoid are connected with support rings for fixing, and the support rings are fixedly connected to the cubic frame (3); The end of the glue inlet pipe (15) is connected to the lower end of the pouring cavity (2), and the top of the pouring cavity (2) is connected to the overflow pipe (4). The connection between the glue inlet pipe (15) and the overflow pipe (4) and the pouring cavity (2) is sealed with vacuum mud to ensure the vacuum performance of the pouring cavity (2). The tail end of the overflow pipe (4) is connected to the overflow bucket; the overflow pipe (4) is connected to a second stop valve (5), a vacuum gauge (6) and a second flow meter (8) according to the flow direction of the epoxy resin; The pouring process comprises the following steps: 1) Prepare epoxy resin according to requirements and test the viscosity of epoxy resin at different temperatures to determine the temperature at which the viscosity of epoxy resin is lowest. The lower the viscosity, the higher the fluidity of epoxy resin. The temperature at which the viscosity is lowest is the holding temperature of epoxy resin. 2) Fix the superconducting inclined solenoid to the casting fixture and place it in an oven; adjust the oven temperature to the holding temperature determined in step 1) for a holding time of no less than 6 hours; 3) Prepare epoxy resin according to the preparation method of step 1), place it in a vacuum device for degassing, preheat it to the holding temperature of step 1), and finally transfer it to an epoxy barrel; 4) Close the first stop valve (14), open the second stop valve (5), turn on the vacuum unit (10) connected to the side wall of the overflow tube (7), evacuate the rubber inlet pipe (15), the pouring cavity (2), and the overflow tube (4) until the vacuum gauge (6) on the overflow tube (4) reads less than 5 Pa, close the vacuum unit (10), turn on the first stop valve (14), the peristaltic pump (12), and the booster pump (9) connected to the side wall of the epoxy tube (11), and start pouring; The epoxy resin enters the casting cavity (2) through the glue inlet pipe (15), then enters the inner casting cavity (2) through the guide groove on the support plate, enters the outer casting cavity (2) through the pores between the inner frame of the coil and the stainless steel support tube, and penetrates into the gap between the template and the outer frame through the gap of the template joint; the epoxy resin liquid level rises until it fills the inner casting cavity (2) and the outer casting cavity (2) and overflows from the overflow pipe (4); Observe the readings of the second flow meter (8) on the overflow pipe (4) and the first flow meter (13) on the glue inlet pipe (15). When the readings of the two flow meters are consistent and epoxy resin overflows from the overflow barrel, first close the second stop valve (5), then close the first stop valve (14) on the glue inlet pipe (15), turn off the booster pump (9) and the peristaltic pump (12), and complete the pouring; 5) After curing, remove the epoxy barrel, booster pump (9), peristaltic pump (12), first flow meter (13), vacuum pump, overflow barrel, vacuum gauge (6), and second flow meter (8) from the pouring system, and retain the first stop valve (14) and the second stop valve (5); The coil, the casting cavity (2) and the cubic frame (3) are placed in an oven as a whole, and the oven temperature is adjusted according to the curing temperature curve of the epoxy resin to allow the epoxy resin to be cured; 6) Demolding: The superconducting inclined solenoid is demolded after being cooled to room temperature in the furnace.

2. The casting process for superconducting inclined solenoid coil for medical ion beam accelerator according to claim 1, characterized in that: A circle of screw holes is respectively provided on the end faces of the coil outer frame and the coil inner frame, and two circles of through holes are provided along the circumferential direction of the support plate. The through holes on the support plate correspond one-to-one to the screw holes on the coil outer frame and the coil inner frame; the support plate is fixedly connected to the coil outer frame and the coil inner frame by screws.

3. The casting process for superconducting inclined solenoid coil for medical ion beam accelerator according to claim 2, characterized in that: The guide groove on the supporting plate is located between the two circles of through holes and is arc-shaped.

4. The casting process for superconducting inclined solenoid coil for medical ion beam accelerator according to claim 1, characterized in that: The barrel covers of the epoxy barrel and the overflow barrel are organic glass plates, which makes it easy to observe the amount of epoxy resin in the barrel.

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