Thin-walled extracorporeal circulation cannula forming process and adopted covering head die core rod assembly and equipment

Abstract

The present application belongs to the technical field of plastic processing, and particularly relates to a thin-walled extracorporeal circulation cannula forming process and a coating head die core rod assembly and equipment used in the same. The wall thickness of the cannula can be between 0.5-1.0 mm, and the cannula can be formed through secondary coating by the principle of gravity negative pressure coating, so that stable and continuous production can be achieved. The inner wall of the cannula is embedded with densely wound reinforcing steel wires. This method is suitable for forming thin-walled cannulas made of polyurethane, nylon, Pebax, PP and the like. The cannula of the product is thin-walled, has good support and is not prone to deformation, has better flexibility, has greater flow under the premise of the same outer diameter, and has good coating integrity.

Description

Technical Field

[0001] This invention belongs to the field of plastic processing technology, and specifically relates to a thin-walled extracorporeal circulation cannula forming process and the coating die core rod assembly and equipment used therein. Background Technology

[0002] Thin-walled reinforced tubing has wide applications in the medical device and aerospace fields. In cardiopulmonary bypass surgery, the blood pump needs to deliver high-flow-rate blood with minimal pre-fill volume. Traditional tubing, due to its large wall thickness (typically ≥1.2mm), has a limited inner diameter for the same outer diameter, leading to insufficient flow or requiring an increased outer diameter, thus increasing the risk of surgical trauma. Negative pressure suction during surgery easily causes tubing collapse, and existing ordinary thin-walled tubing (wall thickness <0.8mm) cannot meet the requirements for resisting negative pressure.

[0003] Currently, there are two processes for forming thin-walled extracorporeal circulation cannulas: dip molding and conventional coating molding. Dip molding is inefficient and inconsistent; the steel wire skeleton is impregnated with polymer slurry and then cured, resulting in a single production cycle of over 30 minutes and a capacity of less than 150 pieces per hour, making it difficult to scale up. Furthermore, the thickness fluctuates by ±0.3mm, indicating significant and uneven wall thickness. In addition, the adhesion between the dip-coated layer and the steel wire is weak, making it prone to delamination under high pressure; the cannula wall has a high micropore defect rate, easily leading to blood residue and infection risks.

[0004] In conventional overmolding, the extrusion process requires a wall thickness of ≥1.0mm to cover the steel wire due to melt strength limitations; otherwise, it is prone to breakage. Thicker walls lead to increased outer diameter, increasing surgical trauma and directly reducing flow efficiency. Simultaneously, wire misalignment occurs, causing the wire to float in the melt during extrusion with an eccentricity >10%, resulting in tube deformation and uneven flow.

[0005] like Figure 1 , 2 As shown, the die head of the existing coating extruder is equipped with a die 5 and a mandrel 6, with a certain gap 7 between the die 5 and the mandrel 6, which serves as a material flow channel. The mandrel has a through hole in its center, through which the processed preform enters the extruder head from top to bottom for secondary coating molding.

[0006] The existing secondary coating molding technology uses a top-down coating process. During the coating process, the molten material flows downward under the action of gravity. By drawing a vacuum, the molten material is coated on the outer surface of the tube blank and fills the spring gap. However, the wall thickness of the products processed by this process is relatively thick, generally around 1 mm, which cannot meet the thin-wall requirements under certain conditions. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a simple manufacturing process and precise dimensional control for forming thin-walled extracorporeal circulation cannulas, as well as the coating head mold core rod assembly and equipment used therein.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a coating machine head die core rod assembly, comprising a die and a core rod, with a gap formed between the die and the core rod for feeding molten material, a core rod center hole, a straight groove at the top outlet end of the die, a funnel-shaped inclined groove below the straight groove, the highest point of the straight section of the core rod being flush with the bottom surface of the inclined groove of the die, and a heat insulation cover with a top opening provided along the inner wall of the straight groove.

[0009] Furthermore, the inclination of the inclined groove is 5°-45°, and the straight section of the gap between it and the mandrel is 5-20mm.

[0010] Furthermore, the heat insulation cover extends from the top surface of the mold and is made of high-temperature resistant glass; the heat insulation cover and the mold are connected and fixed by threaded parts.

[0011] Furthermore, the upper inner diameter of the hole in the mandrel is small, while the lower inner diameter is large, with a smooth transition section at the junction of the diameter changes.

[0012] A coating machine for secondary forming of thin-walled reinforced tubes adopts the above-mentioned coating machine head die mandrel assembly. The central hole of the mandrel is connected to the central hole of the machine head, and their center lines are on the same straight line. A vacuum chamber is connected below the machine head, and the central hole of the vacuum chamber is connected to the central hole of the machine head and the central hole of the mandrel. A sealing gasket is connected to the lower end of the vacuum chamber, and a through hole is opened on the sealing gasket to allow the tube blank to pass through. An adjustable pressure vacuum air source is connected to the outside of the vacuum chamber.

[0013] A thin-walled extracorporeal circulation cannula forming process includes the following steps:

[0014] S1. A soft mandrel is manufactured using an extruder;

[0015] S2. A layer of inner blank is wrapped around the outside of the soft mandrel by coaxial wrapping;

[0016] S3. Inner blank sleeve reinforcing liner, wherein the reinforcing liner is stainless steel wire;

[0017] S4. The tube blank with a soft mandrel, inner blank and already fitted with a reinforcing liner is fed into the above-mentioned coating machine for secondary forming of thin-walled reinforced tube. The tube blank moves from bottom to top, and the molten material enters the die mandrel assembly at the head of the coating machine. A molten material pool is formed between the inclined groove and the straight groove of the die. When the tube blank passes through the molten material pool, the vacuum chamber is evacuated, so that the molten material adheres to the outer surface of the tube blank under the action of gravity and negative pressure, and fills the gaps between the stainless steel wires.

[0018] S5. After the tube blank is coated and formed, it is cooled and then removed from the soft mandrel.

[0019] Furthermore, the soft mandrel has an internal hollow structure or a solid structure, and the material of the soft mandrel is PTFE, POM, PP or HDPE; the wall thickness of the inner blank is 0.2-0.5mm, and the material of the inner blank is polyurethane, nylon, Pebax or PP.

[0020] Furthermore, the stainless steel wire is tightly wound around the outside of the inner blank using a spring winding machine, or the pre-formed stainless steel wire spring is rewound around the outside of the inner blank using a rewinding machine.

[0021] Furthermore, in step S4, a thin-walled reinforced tube of the corresponding size is obtained by adjusting the extruder speed and stretching speed, and the vacuum degree of the vacuum pump is 10~20kPa during the coating process.

[0022] Furthermore, the steel wire is either round or flat. The round wire has a diameter of 0.1-0.3 mm and a pitch of 0.3-0.5 mm; the flat wire has a thickness of 0.1-0.3 mm, a width of 0.5-0.7 mm, and a pitch of 0.6-0.8 mm, resulting in a thin-walled reinforced tube with a wall thickness of <1.0 mm.

[0023] The advantages and positive effects of this invention are as follows: the operation steps are simple, the wall thickness can be precisely controlled, and thin-walled reinforced tubes with a wall thickness of less than 1.0 mm and internally embedded steel wire can be processed, thereby increasing the liquid flow rate while ensuring the outer diameter of the product. The resulting thin-walled reinforced tubes have stable dimensions, thin walls, good resistance to negative pressure, and can be produced continuously with high production efficiency. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the head die core rod assembly of an existing coating machine.

[0025] Figure 2 This is a schematic diagram of the structure of the inner preform after coating in the coating die head using existing technology.

[0026] Figure 3 This is a schematic diagram of the coating machine head die core rod assembly structure of the present invention.

[0027] Figure 4 This is an enlarged view of the principle of the gravity negative pressure coating process of the present invention.

[0028] Figure 5 This is a schematic diagram illustrating the principle of the gravity negative pressure coating process of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] In the description of this invention, it should be noted that the terms "upper", "middle", "lower", "inner", "outer", "both sides", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the purpose of simplifying the description of this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] like Figure 3 , 4 As shown, the coating machine head die-piston assembly of the present invention includes a die 13 and a mandrel 11. A gap 16 for feeding molten material 25 is formed between the die 13 and the mandrel 11. The mandrel has a central hole 12 at its center. A straight groove 15 is opened at the top outlet end of the die 13. A funnel-shaped inclined groove 14 is opened below the straight groove 15. The highest point of the straight section of the mandrel 11 is flush with the bottom surface of the inclined groove 14 of the die. A heat insulation cover 29 with a top opening is provided along the inner wall of the straight groove 15.

[0033] Furthermore, the inclination of the inclined groove 14 is 5°-45°, and the straight section of the gap 16 between it and the mandrel has a dimension of 5-20mm.

[0034] Furthermore, the heat insulation cover 29 extends out of the top surface of the die 13 and is made of high-temperature resistant glass; the heat insulation cover 29 and the die 13 are connected and fixed by a threaded part 31.

[0035] Furthermore, the upper inner diameter of the hole 12 in the mandrel is small, and the lower inner diameter is large, with a smooth transition section at the junction of the diameter changes.

[0036] like Figure 5 As shown, the coating machine for secondary forming of thin-walled reinforced tubes of the present invention adopts the above-mentioned coating machine head die mandrel assembly. The mandrel central hole 12 communicates with the machine head central hole 17, and their center lines are on the same straight line. A vacuum chamber 20 is connected below the machine head 24. The vacuum chamber central hole 18 communicates with the machine head central hole 17 and the mandrel central hole 12. A sealing gasket 19 is connected to the lower end of the vacuum chamber. The sealing gasket 19 has a through hole that allows the tube blank to pass through. An adjustable pressure vacuum air source is connected to the vacuum chamber 20.

[0037] The thin-walled extracorporeal circulation cannula forming process of the present invention includes the following steps:

[0038] S1. A soft mandrel is manufactured using an extruder;

[0039] S2. A layer of inner blank is wrapped around the outside of the soft mandrel by coaxial wrapping;

[0040] S3. Inner blank sleeve reinforcing liner, wherein the reinforcing liner is stainless steel wire;

[0041] S4. The tube blank with a soft mandrel, inner blank and a reinforcing liner is placed in the coating machine for secondary forming of thin-walled reinforced tubes. The tube blank moves from bottom to top, and the molten material enters the die mandrel assembly at the head of the coating machine. A molten material pool is formed between the inclined groove and the straight groove of the die. When the tube blank passes through the molten material pool, the vacuum chamber is evacuated, so that the molten material adheres to the outer surface of the tube blank under the action of gravity and negative pressure, and fills the gaps between the stainless steel wires.

[0042] S5. After the tube blank is coated and formed, it is cooled and then removed from the soft mandrel.

[0043] Furthermore, the soft mandrel has an internal hollow structure or a solid structure, and the material of the soft mandrel is PTFE, POM, PP or HDPE; the wall thickness of the inner blank is 0.2-0.5mm, and the material of the inner blank is polyurethane, nylon, Pebax or PP.

[0044] Furthermore, the stainless steel wire is tightly wound around the outside of the inner blank using a spring winding machine, or the pre-formed stainless steel wire spring is rewound around the outside of the inner blank using a rewinding machine.

[0045] Furthermore, in step S4, a thin-walled reinforced tube of the corresponding size is obtained by adjusting the extruder speed and stretching speed, and the vacuum degree of the vacuum pump is 10~20kPa during the coating process.

[0046] Preferably, the steel wire is a round wire or a flat wire. The round wire has a diameter of 0.1-0.3 mm and a pitch of 0.3-0.5 mm. The flat wire has a thickness of 0.1-0.3 mm, a width of 0.5-0.7 mm, and a pitch of 0.6-0.8 mm. The resulting thin-walled reinforced tube has a wall thickness of <1.0 mm.

[0047] Specifically, the mandrel's central hole 12 communicates with the die head's central hole 17, and their center lines are on the same straight line. The vacuum chamber 20 is connected to the bottom of the die head 24 via a thread. The vacuum chamber's central hole 18 communicates with both the die head's central hole 17 and the mandrel's central hole 12. One end of the vacuum chamber is connected to a sealing gasket 19, which has a through hole to allow the tube blank to pass through, thus providing a seal. The vacuum chamber 20 is externally connected to an adjustable pressure vacuum air source.

[0048] During secondary forming, the tube blank with steel wire reinforcement is first passed from bottom to top through the sealing gasket 19, the vacuum chamber central hole 18, the die head central hole 17, and the mandrel central hole 12, and then through the traction guide roller 27 and the traction roller 28. The tube blank moves from bottom to top under the traction of the traction machine. The raw material enters the extruder from the extruder 23 through the barrel 22. The molten material 25 enters the gap 26 between the die head and the mandrel and the gap 16 between the die 13 and the mandrel 11 through the extruder head, forming a molten material pool 21 between the inclined groove 14 and the straight groove 15 of the die. When the tube blank passes through the molten material pool 21, a vacuum is drawn in the vacuum chamber, causing the molten material to adhere to the outer surface of the tube blank under the action of gravity and negative pressure, filling the gaps between the steel wires. 23 is the extruder.

[0049] The main parameters for secondary coating extrusion include:

[0050] a. Extruder: Screw diameter: 25-30mm, screw speed: 0-100rpm;

[0051] b. Extruder head: By changing the die and mandrel, the diameter of the coating can be 3-18mm;

[0052] c. Air pressure control system adjustment: Air pressure adjustment range is -20 to 20 kPa. Time: 0 to 10 seconds, adjustable;

[0053] d. Traction machine: Traction speed 0-10m / s.

[0054] This invention resolves the inherent contradictions between dip coating and conventional overcoating extrusion processes in controlling thin-walled (<1.0 mm) structures and steel wire reinforcement. Utilizing the fluidity and viscoelasticity of the polymer melt, under gravity and negative pressure, the extrusion rate and traction rate work in synergy to allow the melt to embed into the gaps of the steel wire reinforcement liner and adhere to the outer surface of the tube. Thus, through a novel overcoating extrusion process, zero-eccentric embedding of the steel wire reinforcement structure is achieved, resulting in a high degree of adhesion between the inner and outer layers and the production of a thin-walled reinforced tube with excellent resistance to negative pressure. This thin-walled reinforced tube can meet the triple requirements of high flow rate, low trauma, and safety in extracorporeal circulation surgery, while also satisfying the aerospace field's requirements for low weight and high throughput.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A coating machine head die-piston assembly, comprising a die (13) and a mandrel (11), wherein a gap (16) for feeding molten material (25) is formed between the die (13) and the mandrel (11), and the mandrel has a central hole (12) at its center, characterized in that, The top outlet end of the die (13) has a flat groove (15), and a funnel-shaped inclined groove (14) is opened below the flat groove (15). The highest point of the straight section of the core rod (11) is flush with the bottom surface of the inclined groove (14) of the die. A heat insulation cover (29) with a top opening is provided along the inner wall of the flat groove (15). The inclined groove (14) has an inclination of 5°-45° and the straight section of the gap (16) between it and the mandrel has a dimension of 5-20mm; The upper inner diameter of the hole (12) in the core rod is small, and the lower inner diameter is large. The junction of the diameter change is a smooth transition section. The tube blank moves from bottom to top, and the molten material enters the die mandrel assembly at the head of the coating machine. A molten material pool is formed between the inclined groove and the straight groove of the die. When the tube blank passes through the molten material pool, the vacuum chamber is evacuated, so that the molten material adheres to the outer surface of the tube blank under the action of gravity and negative pressure, and fills the gaps between the stainless steel wires.

2. The coating machine head die core rod assembly according to claim 1, characterized in that, The heat insulation cover (29) extends out of the top surface of the die (13) and is made of high-temperature resistant glass; the heat insulation cover (29) and the die (13) are connected and fixed by a threaded part (31).

3. A coating machine for secondary forming of thin-walled reinforced tubes, characterized in that, The core rod assembly of the coating head die as described in claim 1 or 2 is used. The core rod hole (12) is connected to the head hole (17) and the center line is on the same straight line. A vacuum chamber (20) is connected below the head (24). The vacuum chamber hole (18) is connected to the head hole (17) and the core rod hole (12). A sealing gasket (19) is connected to the lower end of the vacuum chamber. A through hole is opened on the sealing gasket (19) to allow the tube blank to pass through. An adjustable pressure vacuum source is connected to the vacuum chamber (20).

4. A thin-walled extracorporeal circulation cannula forming process, characterized in that, Includes the following steps: S1. A soft mandrel is manufactured using an extruder; S2. A layer of inner blank is wrapped around the outside of the soft mandrel by coaxial wrapping; S3. Inner blank sleeve reinforcing liner, wherein the reinforcing liner is stainless steel wire; S4. The tube blank with a soft mandrel, inner blank and already fitted with a reinforcing liner is fed into the coating machine for secondary forming of thin-walled reinforced tube as described in claim 3. The tube blank moves from bottom to top, and the molten material enters the die mandrel assembly at the head of the coating machine. A molten material pool is formed between the inclined groove and the straight groove of the die. When the tube blank passes through the molten material pool, the vacuum chamber is evacuated, so that the molten material adheres to the outer surface of the tube blank under the action of gravity and negative pressure, and fills the gaps between the stainless steel wires. S5. After the tube blank is coated and formed, it is cooled and then removed from the soft mandrel; Thin-walled reinforced tubes of appropriate size are obtained by adjusting the extruder speed and stretching speed. During the coating process, the vacuum pump vacuum degree is 10~20kPa. The steel wire is either round or flat. The round wire has a diameter of 0.1-0.3 mm and a pitch of 0.3-0.5 mm. The flat wire has a thickness of 0.1-0.3 mm, a width of 0.5-0.7 mm, and a pitch of 0.6-0.8 mm. The resulting thin-walled reinforced tube has a wall thickness of <1.0 mm.

5. The thin-walled extracorporeal circulation cannula forming process according to claim 4, characterized in that, The soft mandrel has an internal hollow structure or a solid structure, and the material of the soft mandrel is PTFE, POM, PP or HDPE; the wall thickness of the inner blank is 0.2-0.5mm, and the material of the inner blank is polyurethane, nylon, Pebax or PP.

6. The thin-walled extracorporeal circulation cannula forming process according to claim 4, characterized in that, The stainless steel wire is tightly wound around the outside of the inner blank by a spring winding machine, or the pre-formed stainless steel wire spring is rewound around the outside of the inner blank by a rewinding machine.

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