CN213704479U

CN213704479U - Bidirectional stretching die head device for producing thin-wall plastic microtubes

Info

Publication number: CN213704479U
Application number: CN202022565563.9U
Authority: CN
Inventors: 顾兴中; 李书翔; 全祎
Original assignee: Taizhou Institute Of Biomedicine And Medical Devices Southeast University
Current assignee: Taizhou Institute Of Biomedicine And Medical Devices Southeast University
Priority date: 2020-11-09
Filing date: 2020-11-09
Publication date: 2021-07-16
Anticipated expiration: 2030-11-09

Abstract

The invention relates to a bidirectional stretching die head device for producing a thin-wall plastic micro-tube, which is arranged at the head of an extruder, the device is hollow inside, a core rod is sleeved at the center of the device, one side of the device is an inlet of an extrusion material, the other side of the device is an outlet of the extrusion material, and the outlet is provided with a neck mold. The frustum can realize axial stretching under the traction action and simultaneously realize radial stretching accurately, and is particularly suitable for the production and preparation of the biaxial stretching self-reinforced micro-tube.

Description

Bidirectional stretching die head device for producing thin-wall plastic microtubes

Technical Field

The invention relates to a die head of an extruder, in particular to a bidirectional stretching die head device for producing a thin-wall plastic micro-tube.

Background

After the permanent stent is placed in a stenotic blood vessel, the permanent stent can be used as a foreign body to generate long-term biocompatibility with the blood vessel over time, a patient needs to take corresponding antiplatelet drugs for a long time to prevent thrombus formation, other potential risks such as late stent thrombus, anaphylactic reaction, in-stent restenosis and the like still exist, and therefore the biodegradable stent is produced at the same time.

The biodegradable stent can be completely prepared from polylactic acid PLLA, but the premise is that a pipe extruded by the PLLA must simultaneously meet two requirements of high radial strength and high fracture toughness, and then the biodegradable stent can be prepared by laser cutting to achieve the purpose of treating angiostenosis. Therefore, the extruded PLLA pipe must be biaxially stretched (axially and radially) to orient the polymer inside to achieve the desired mechanical properties.

The traditional pipe production is always the problem of weak hoop strength in unidirectional stretching, the thickness of the pipe needs to be increased to improve the mechanical strength, the cost and the consumption of raw materials are greatly increased, and the heat transfer of the pipe is not uniform. The bidirectional stretching is an effective means of polymer self-reinforcement, and the high polymers of the pipe in the axial direction and the annular direction are oriented by stretching the pipe in the axial direction and the annular direction, so that the mechanical property of the pipe is greatly improved.

At present, a plurality of methods for the biaxial stretching of large-caliber plastic pipes emerge from the market. Such as a die-drawing experimental device designed by Phi Coates in UK, a biaxial tension polyolefin pipe compressed air continuous extrusion molding method designed by Yanming at southern Aritman university, an internal pressure expansion device developed by Wangke at Shanghai university of transportation, roll forming, a high-pressure water molding device, and the like. However, the inner diameter and the wall thickness of the tube for preparing the degradable vascular stent are extremely small, so that few and few biaxial stretching devices are used for the thin-wall micro tube, the existing methods are two-step methods, namely, the extruded micro tube blank is heated and pressurized to expand to a specified size in a die to realize orientation, the method has the problems of repeated heating, complex process flow, low material utilization rate and the like, particularly for medical PLLA materials for preparing the degradable vascular stent, the cost of the materials is extremely high, and the two-step method can cause waste of a plurality of raw materials, so that the cost is increased. The invention provides a one-step continuous biaxial tension die head device for producing degradable vascular stent thin-wall plastic micro-pipes and a corresponding preparation method, and the device has the advantages of high production efficiency, high material utilization rate and the like.

There are already in the prior art radially stretched moulds by suction with air pressure, which in use are only suitable for products with a large diameter, the uniformity of the tube wall being difficult to control when producing microtubes.

Disclosure of Invention

The invention provides a bidirectional stretching die head device for producing a thin-wall plastic micro-tube, and provides a novel bidirectional stretching die.

The technical scheme of the invention is as follows: a bidirectional stretching die head device for producing a thin-wall plastic micro-tube is arranged at the head of an extruder, the device is hollow inside, a core rod is sleeved at the center of the device, one side of the device is an inlet of an extruded material, the other side of the device is an outlet of the extruded material, a neck mold is arranged at the outlet, and an expansion frustum is arranged and connected after the core rod extends out of the neck mold.

Preferably, the diversion cone is provided with an air hole, the center of the core rod is provided with a cavity, one end of the cavity is in contact with the air hole, the other end of the cavity is communicated with the expansion frustum, and the air hole is connected with an air pipe.

Preferably, the inlet side of the core rod is connected with a diverging cone, the outlet side of the core rod is connected with a necking section, gaps are reserved between the outer shell of the device and the diverging cone, and between the core rod and the necking section, and extruded materials pass through the gaps.

Preferably, the die is stepped in profile, and a flange is pressed against the step to connect the apparatus to the extruder head.

Preferably, the device is provided with an offset nut in a penetrating way, and the concentricity between the core rod and the neck ring die is adjusted.

Preferably, the device is provided with a positioning pin hole in a penetrating manner, and the positioning pin fixes the position of the tap cone in the machine head body.

Preferably, the mandrel and the expansion frustum are connected through threads or interference fit.

Preferably, the front end of the mouth mold is provided with a detachable split assembly along the direction of the extending end of the core rod.

Preferably, the device has a flange on the other side, which is connected to the extruder head.

The device has the advantages that the device can form the biaxially oriented thin-wall plastic micro-pipe by a one-step method, does not need to be heated for many times like a two-step method, and can greatly reduce the production time and improve the material utilization rate. Simultaneously, compared with the vacuum adsorption stretching in the prior art, the radial stretching is realized by a pure physical structure, so that the stretching uniformity is easily ensured, and the production of the microtube with small diameter is more facilitated.

Drawings

FIG. 1 is a sectional view of the structure of the embodiment.

FIG. 2 is a cross-sectional view of the mandrel and expansion cone in an example embodiment.

FIG. 3 is a first schematic view of the combination of dies in the embodiment.

FIG. 4 is a schematic view of the die assembly of the second embodiment.

Detailed Description

The technical solution of the present invention will be further explained with reference to the accompanying drawings

According to the technical scheme provided by the invention, the continuous biaxial stretching die head device comprises a device 1, an offset nut 3, a flange pressing plate 4, a die 5, a core rod 6, an air pipe 7 and a spreader cone 8. The device 1 is provided with a positioning pin hole 2 and a flange 9, the positioning pin hole 2 is used for positioning the shunting cone 8 in the device 1, and the flange 9 is used for connecting the device and an extruder. The core rod 6 and the spreader cone 8 are provided with air holes, dried compressed air is input through the air pipe 7, and the compressed air passes through the air holes, then is discharged from the expansion frustum 10 along the central hole of the core rod 6 and is introduced into the tube blank extruded by melting, so that the roundness of the inner hole of the tube blank is ensured and certain internal pressure expansion is realized. The core rod 6 is connected with the spreader cone 8 through threads. The function of the offset nut 3 is to adjust the concentricity between the core rod 6 and the die 5 so as to adjust the uniformity of the wall thickness of the pipe. The front end of the core rod 6 is provided with an expansion frustum 10, after molten material flow is formed by a die head, the radial stretching of the pipe is realized by the characteristics of the expansion frustum 10, and the bidirectional stretching of the pipe can be realized by matching with the traction action. The angle of the expanding cone angle 10 is designed and determined according to the inner and outer diameter parameters of the pipe which is actually required to be produced.

Because the core rod 6 is additionally provided with the expanded taper angle 10 relative to the traditional core rod, the diameter of the foremost end (i.e. the end close to the expanded taper angle 10) of the core rod 6 is larger than the aperture of the front end of the neck ring mold 5, and then the problem of incapability of assembling is caused. To solve this problem, the present invention can use two methods, and other similar methods are within the scope of the present invention:

1. when the inner diameter and the outer diameter of the pipe to be produced are large (at the moment, the inner diameter and the outer diameter of the pipe are still millimeter-sized), the core rod 6 can be designed into the taper angle section 10 and the main body section 11, and the taper angle section 10 and the main body section can be connected through threads or interference fit. During assembly, the core rod main body section 11 is firstly installed, then the neck mold 5 is installed, and finally the expansion taper angle section 10 extends into the inner hole of the neck mold 5 and then is screwed into the core rod main body section 11.

2. When the inner diameter and the outer diameter of the pipe to be produced are extremely small, the front end of the core rod 6 is thin and cannot be connected through threads or interference fit, the neck ring mold 5 can be designed to be split (comprising 12 parts and 13 parts), and the two parts can be connected through bolts or other modes.

When the device is used, the whole die head device is connected with an extruder through a flange 9, and meanwhile, a heating ring is sleeved outside the die head device and a thermocouple is inserted to heat the whole device, so that the material flow is ensured to be in a molten state. The die head device designed by the invention is connected with a main machine of an extruder, and the heating jacket and the thermocouple aviation plug are inserted into a designated jack of the main machine of the extruder. When the device is used specifically, a PLLA material is added into a charging barrel above a main machine of the extruder, the device is started, corresponding parameters such as the temperature of each large heating area, the rotating speed of a screw rod, the traction speed and the like are set on a display screen, after a die head extrudes a pipe blank, the pipe blank is drawn into a sizing sleeve in a water tank for primary sizing, parameters of a diameter gauge are observed, and the wall thickness uniformity of the pipe is ensured by finely adjusting a deviation adjusting nut on a die head device and the corresponding parameters of the extruder. After the pipe is stably and uniformly extruded, a medical air compressor is started, the air inlet pressure is adjusted, and the dried and filtered compressed air is introduced into the pipe so as to ensure the roundness of the inner hole of the pipe and realize certain internal pressure expansion. Radial stretching of the pipe is realized through the characteristics of the expansion frustum 10 on the core rod 6 and the internal pressure expansion effect of compressed air input by the medical air compressor, so that the biaxial stretching plastic micro-pipe which can be prepared into the biodegradable intravascular stent by laser cutting is obtained.

Claims

1. A bidirectional stretching die head device for producing a thin-wall plastic micro-tube is arranged at the head of an extruder, the device is hollow inside, a core rod is sleeved at the center of the device, one side of the device is an inlet of an extrusion material, the other side of the device is an outlet of the extrusion material, and an opening die is arranged at the outlet.

2. The biaxial stretching die device for producing the thin-walled plastic microtube as claimed in claim 1, wherein the inlet side of the core rod is connected with a diverging cone, the outlet side of the core rod is connected with a necking segment, and the device has gaps among the outer shell, the diverging cone, the core rod and the necking segment, through which the extrudate passes.

3. The biaxial stretching die head device for producing the thin-walled plastic microtubes as claimed in claim 2, wherein the spreader cone is provided with air holes, the core rod is provided with a cavity in the center, one end of the cavity is connected with the air holes, the other end of the cavity is communicated with the expansion frustum, and the air holes are connected with air pipes.

4. The biaxial stretching die device for producing the thin-walled plastic microtube as recited in claim 1, wherein the die is stepped in profile, and the flange pressing plate is pressed against the step, thereby fixing the die to the device.

5. The biaxial stretching die head device for producing the thin-walled plastic microtubes as claimed in claim 1, wherein an offset nut is arranged on the device in a penetrating way to adjust the concentricity between the core rod and the die.

6. The biaxial stretching die head device for producing the thin-walled plastic microtubes as claimed in claim 1, wherein the device is provided with positioning pin holes, and the positioning pins fix the positions of the spreader cones in the machine head body.

7. The biaxial stretching die head device for producing the thin-walled plastic microtube as claimed in claim 1, wherein the core rod is connected with the expanding frustum by a thread or an interference fit.

8. The biaxial stretching die head device for producing the thin-walled plastic microtubes as claimed in claim 1, wherein the front end of the die is provided with a detachable split assembly along the direction of the extending end of the core rod.

9. The biaxial stretching die device for producing the thin-walled plastic microtube as recited in claim 1, wherein the device has a flange on the other side thereof for connection to the head of the extruder.