CN114393766B - PTFE cylindrical blank and segmented molding process - Google Patents
PTFE cylindrical blank and segmented molding process Download PDFInfo
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- CN114393766B CN114393766B CN202111582061.XA CN202111582061A CN114393766B CN 114393766 B CN114393766 B CN 114393766B CN 202111582061 A CN202111582061 A CN 202111582061A CN 114393766 B CN114393766 B CN 114393766B
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- 229920001343 polytetrafluoroethylene Polymers 0.000 title claims abstract description 54
- 239000004810 polytetrafluoroethylene Substances 0.000 title claims abstract description 54
- 238000000034 method Methods 0.000 title claims abstract description 50
- 238000000465 moulding Methods 0.000 title claims description 16
- 238000003825 pressing Methods 0.000 claims abstract description 151
- 230000000754 repressing effect Effects 0.000 claims description 12
- 239000002994 raw material Substances 0.000 claims description 10
- 239000002184 metal Substances 0.000 claims description 9
- 238000011049 filling Methods 0.000 claims description 8
- 238000007906 compression Methods 0.000 claims description 4
- 238000007723 die pressing method Methods 0.000 claims description 4
- 230000006835 compression Effects 0.000 claims description 2
- 239000002245 particle Substances 0.000 claims description 2
- 230000005540 biological transmission Effects 0.000 abstract description 5
- 230000009286 beneficial effect Effects 0.000 abstract description 4
- 230000000052 comparative effect Effects 0.000 description 16
- 239000000047 product Substances 0.000 description 10
- -1 Polytetrafluoroethylene Polymers 0.000 description 3
- 238000000748 compression moulding Methods 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 238000000462 isostatic pressing Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000005245 sintering Methods 0.000 description 3
- 238000005056 compaction Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- BFKJFAAPBSQJPD-UHFFFAOYSA-N tetrafluoroethene Chemical group FC(F)=C(F)F BFKJFAAPBSQJPD-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/02—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B11/00—Making preforms
- B29B11/06—Making preforms by moulding the material
- B29B11/12—Compression moulding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/32—Component parts, details or accessories; Auxiliary operations
- B29C43/58—Measuring, controlling or regulating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/32—Component parts, details or accessories; Auxiliary operations
- B29C43/58—Measuring, controlling or regulating
- B29C2043/5808—Measuring, controlling or regulating pressure or compressing force
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Powder Metallurgy (AREA)
Abstract
The invention relates to the technical field of PTFE mould pressing, in particular to a PTFE cylindrical blank and a segmented mould pressing process. The invention adopts a multi-stage pressing process, and the pressure of each stage of pressing process is controlled to be increased section by section, which is beneficial to the uniform transmission of pressing force in the blank, so that the middle position of the blank is better densified.
Description
Technical Field
The invention relates to the technical field of PTFE molding, in particular to a PTFE cylindrical blank and a segmented molding process.
Background
Polytetrafluoroethylene (Teflon or PTFE), commonly known as "plastic king", is a polymer compound polymerized from tetrafluoroethylene, and has been widely used in various fields such as chemical industry, electronics, etc. because of its excellent chemical stability, corrosion resistance, sealing property, etc.
Because PTFE has a molecular weight of more than a million levels and an ultra-large melt viscosity, the PTFE cannot be processed by a melt extrusion mode, and the PTFE needs to be processed by a compression molding and sintering mode in a similar way to metal metallurgy. PTFE compression molding is an important step in determining the quality of the article. The applications of PTFE in the market at present mainly include polytetrafluoroethylene tubes, rods, tapes, plates, films, etc., wherein most of the products such as plates, films, etc. are obtained by rotary cutting cylindrical blanks.
For the cylindrical PTFE blank, because the cylindrical PTFE blank has a certain height, single-sided pressing is often adopted during die pressing, the density of a product is uneven, the density of a stressed end is high, after improvement, a gasket is used for supporting a male die during pre-pressing, the gasket is moved during main pressing, the male die is suspended, the male die is prevented from being directly stressed, the pressure error is reduced, the effect of balancing stress at two ends can be achieved, the powder can be initially pressed during the pre-pressing process, the density of a blank is improved, the exhaust of a blank is facilitated, and the occurrence of cracking of the blank is reduced. The density of the middle part of the final product is improved, but the problems of large density at two ends and small density in the middle part cannot be avoided, so that the physical property of the middle part of the manufactured turning film is poor, and the using effect of the turning film is affected.
The isostatic pressing is also called hydraulic forming, and although the density of the prepared PTFE product is uniform by utilizing an elastic die and high-pressure fluid, the process is limited by the principle that the isostatic pressing uses the high-pressure fluid to pressurize, and the isostatic pressing can only provide the pressure of 20MPa at maximum and cannot meet the requirement of larger pressing pressure required by cylindrical products.
Therefore, there is still a need for a molding process that can effectively improve the density uniformity of PTFE cylindrical billets to meet the needs of actual production.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a PTFE cylindrical blank and a segmented molding process, wherein the density of a finished product of the PTFE cylindrical blank is uniformly distributed by further disassembling the molding process and controlling the pressure, so that the technical problems of high density at two ends and low middle density of the finished product prepared by the prior art are effectively solved.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
The PTFE cylindrical blank sectional molding process comprises the steps of filling, pre-pressing and main pressing, wherein re-pressing is further arranged between the pre-pressing and the main pressing, and the pressing pressure of the re-pressing is between the pressing pressures of the pre-pressing and the main pressing.
The invention adopts a multi-stage pressing process, controls the pressure of each stage of pressing process and increases the pressure section by section, thereby being beneficial to the uniform transmission of pressing force in the blank and leading the middle position of the blank to be better densified.
Preferably, in the above process, the step of filling specifically includes adding PTFE raw material into a molding die, and lifting a die male die with a metal gasket; further preferably, the particle size of the PTFE raw material is in the range of 100 to 300. Mu.m, and the addition volume of the PTFE raw material is 3 to 5 times the volume of the obtained billet.
Preferably, in the above process, the pre-pressing step specifically uses a pressing pressure of 2-3 MPa and the holding time is 0.6-1 min; further preferably, the pre-compression process uses a compression pressure of 2 MPa.
Preferably, in the above process, the re-pressing step is specifically to use a pressing pressure 3-6 times that of the pre-pressing pressure, and the holding time is 0.6-1 min, and the metal gasket under the die is removed; further preferably, the repressing process uses a pressing pressure in the range of 8 to 10MPa.
Preferably, in the above process, the main pressing step is specifically to use a pressing pressure 9-18 times that of the pre-pressing pressure, and the main pressing step is kept for 5-10 min; further preferably, the pressing pressure used in the vermilion pressing process is in the range of 24-30 MPa.
The ratio of repressing pressure between repressing and main pressing to pre-pressing in the mould pressing process is an important parameter affecting the density of the middle position of the blank, and the uniformity of the whole density of the blank can be obviously improved by controlling the proper ratio.
Preferably, in the above process, after the pressing pressure is maintained, the press pressure is returned to zero, and then the next operation is performed, so that when the mass of the blank is larger (more than 300 kg), the returning step can facilitate the exhaust of the blank, reduce the residual gas in the blank, and avoid cracking the blank after sintering.
Preferably, in the above process, the aspect ratio of the PTFE cylindrical blank is less than or equal to 3.0.
Preferably, in the above process, the pre-pressing, re-pressing and main pressing processes all use pressing rates of 10-50 mm/min.
The invention also provides a PTFE cylindrical blank which is manufactured by the die pressing process, the density of the PTFE cylindrical blank is 2.18-2.24 g/cm 3, and the density uniformity is 99.50% or more.
The beneficial effects of the invention are as follows:
1. According to the invention, the repressing step is added between the pre-pressing step and the main pressing step, and the pressure of each section of pressing process is controlled to be increased section by section, so that the uniform transmission of pressing force in the blank is facilitated, the middle position of the blank is better densified, and the overall density uniformity of the blank is effectively improved;
2. Experiments prove that when the length-diameter ratio is larger than 3, the pressing force cannot be effectively and uniformly transmitted due to the fact that the pressure transmission distance is longer and the pressure loss is larger, so that the PTFE cylindrical blank with the length-diameter ratio smaller than or equal to 3 is prepared by the process provided by the invention, and the blank can obtain better density uniformity;
3. By arranging the interval between each step of pressing process, the blank body is convenient to exhaust, and particularly for large-scale finished products, the residual gas in the blank body can be reduced, and the blank body is prevented from cracking due to the existence of the residual gas after sintering.
Detailed Description
The invention is further illustrated below with reference to examples.
Example 1
The PTFE cylindrical blank has an slenderness ratio of 2 and is prepared by the following steps:
s1, filling: adding PTFE raw material into a mould pressing mould, and supporting a male mould by using a metal gasket;
S2, prepressing: pre-pressing at a pressing rate of 30mm/min and a pressing pressure of 2MPa for 0.6min, returning the press to the pressure return to 0, and continuing the next operation;
s3, repressing: re-pressing at a pressing rate of 30mm/min and a pressing pressure (6 MPa) 3 times that of the pre-pressing for 0.6min, stopping pressing after the pressing is finished, and taking out the gasket under the die;
s4, main pressure: and (3) carrying out main pressing by adopting a pressing rate of 30mm/min and pressing pressure (18 MPa) which is 9 times of the pressing pressure, wherein the holding time is 5min, and taking out the blank after the pressing is finished.
Example 2
The PTFE cylindrical blank has an slenderness ratio of 2 and is prepared by the following steps:
s1, filling: adding PTFE raw material into a mould pressing mould, and supporting a male mould by using a metal gasket;
S2, prepressing: pre-pressing at a pressing rate of 30mm/min and a pressing pressure of 2MPa for 0.6min, returning the press to the pressure return to 0, and continuing the next operation;
s3, repressing: re-pressing at a pressing rate of 30mm/min and a pressing pressure (8 MPa) which is 4 times of the pre-pressing, wherein the holding time is 0.6min, stopping pressing after the pressing is finished, and taking out the gasket under the die;
S4, main pressure: and (3) carrying out main pressing by adopting a pressing rate of 30mm/min and pressing pressure (24 MPa) which is 12 times of the pressing pressure, wherein the holding time is 5min, and taking out the blank after the pressing is finished.
Example 3
The PTFE cylindrical blank has an slenderness ratio of 2 and is prepared by the following steps:
s1, filling: adding PTFE raw material into a mould pressing mould, and supporting a male mould by using a metal gasket;
S2, prepressing: pre-pressing at a pressing rate of 30mm/min and a pressing pressure of 2MPa for 0.6min, returning the press to the pressure return to 0, and continuing the next operation;
S3, repressing: re-pressing at a pressing rate of 30mm/min and a pressing pressure (10 MPa) which is 5 times of the pre-pressing, wherein the holding time is 0.6min, stopping pressing after the pressing is finished, and taking out the gasket under the die;
S4, main pressure: and (3) carrying out main pressing by adopting a pressing rate of 30mm/min and pressing pressure (30 MPa) which is 15 times of the pre-pressing, wherein the holding time is 5min, and taking out the blank after the pressing is finished.
Example 4
The PTFE cylindrical blank has an slenderness ratio of 2 and is prepared by the following steps:
s1, filling: adding PTFE raw material into a mould pressing mould, and supporting a male mould by using a metal gasket;
S2, prepressing: pre-pressing at a pressing rate of 30mm/min and a pressing pressure of 2MPa for 0.6min, returning the press to the pressure return to 0, and continuing the next operation;
S3, repressing: re-pressing at a pressing rate of 30mm/min and a pressing pressure (12 MPa) which is 6 times of the pre-pressing, wherein the holding time is 0.6min, stopping pressing after the pressing is finished, and taking out the gasket under the die;
s4, main pressure: and (3) carrying out main pressing by adopting a pressing rate of 30mm/min and pressing pressure (36 MPa) which is 18 times of the pressing pressure, wherein the holding time is 5min, and taking out the blank after the pressing is finished.
Example 5
A PTFE cylindrical blank having an aspect ratio of 3 was prepared in exactly the same manner as in example 1.
Comparative example 1
The PTFE cylindrical ingot has an aspect ratio of 2, and the production steps are different from those of example 1 in that the repressurization pressure and the main-pressure are respectively greater than those of example 1, specifically, in this comparative example, the repressurization pressure is 18MPa (9 times of the pre-compaction pressure) and the main-pressure is 42MPa (21 times of the pre-compaction pressure), and other technical details are the same as those of example 1.
Comparative example 2
The PTFE cylindrical ingot has an aspect ratio of 2, and the preparation steps are different from those of example 1 in that the prepressing repressurization pressure and the main-pressure are respectively smaller than those of example 1, specifically, in this comparative example, the repressurization pressure is 4MPa (2 times the prepressing pressure) and the main-pressure is 12MPa (6 times the prepressing pressure), and other technical details are the same as those of example 1.
Comparative example 3
The PTFE cylindrical ingot has an aspect ratio of 2, and the production process differs from that of example 1 in that the pre-pressing in this comparative example is followed by no further pressing step and direct main pressing, and other technical details are the same as those of example 1.
Comparative example 4
A PTFE cylindrical ingot having an aspect ratio of 4 was prepared in the same manner as in example 1.
The density of the PTFE cylindrical billets prepared in examples 1-5 and comparative examples 1-4 was measured according to GB/T4472-2011 as follows:
The upper end position is one end of a fixed pressure head of the contact press, the middle position is the middle position of the whole product in the vertical direction, the lower end position is one end of a movable pressure head of the contact press, three parallel tests are taken at each position, and the average value of the three tests is the density value.
The products obtained in examples 1-5 were uniform in upper, middle and lower densities without significant differences.
Example 1 compared with examples 2 and 3, the density values and density uniformity of each part of examples 2 and 3 are better than example 1, and the density values are better because the repressurization and main-pressure values of examples 2 and 3 are larger than example 1, and the optimization of the density uniformity proves that the pressure proportional relationship used in examples 2 and 3 is beneficial to improving the density uniformity.
In example 1, the density uniformity was similar to that in example 4, but since the pressures in the re-pressing and main-pressing steps of example 4 were respectively higher than those in the two steps of example 1, the density values of the respective portions of the blank obtained in example 4 were higher than those of the respective portions of the blank obtained in example 1.
Compared with the embodiment 5 and the comparative example 4, the embodiment 1 has better density value and uniformity, because the pressure loss in the pressing process is larger when the length-diameter ratio of the pressing is larger, the pressing process cannot optimize the pressure conduction, so that the density difference between the middle position and the two ends of the blank is larger, and the condition that the end value of the length-diameter ratio, namely the length-diameter ratio is 3 and 4, respectively, is proved that the blank with the length-diameter ratio of 3 can obtain better density uniformity when the process is used for die pressing.
Compared with the embodiment 1, the density values of all parts of the blank prepared in the embodiment 1 are larger than those of the blank prepared in the embodiment 1, because the repressing pressure value and the main pressure value of the embodiment 1 are larger than those of the embodiment 1, but also because the pressure value is larger, the middle part of the blank is preliminarily compacted in the repressing process, the middle part of the blank is tightly attached to the inner wall of a die in the main pressing process, the friction force is overlarge, so that larger compression molding pressure loss is caused, the transmission of force is not facilitated, the density of the middle part cannot be further increased, and therefore, the density uniformity of the prepared blank is poor, and the problems of high density at two ends and low middle density still exist.
Comparative example 2 compared with example 1, the density values of each part of the blank obtained in comparative example 2 were smaller than those of the blank obtained in example 1, because the repress and main pressure values of comparative example 2 were smaller than those of example 1, and when the repress and main pressure values were smaller, the main pressure process further compacted the intermediate part of the blank, but the density uniformity was superior to that of the other comparative examples, but the density of each part of the blank could not reach the proper density, and the quality of the finished product produced by the secondary process was not acceptable.
Comparative example 3 compared with example 1, comparative example 3 is a conventional molding process, and since the re-pressing process is not used, the billet is not further compacted before the main pressing process, so that the molding pressure loss is large and the pressure cannot be uniformly transferred to each part of the billet in the main pressing process, and the problems of high density at both ends and low intermediate density still exist.
While the present invention has been described with reference to the embodiments and the comparative examples, it should be understood that the present invention is not limited to the scope of the present invention, and various modifications or variations may be made by those skilled in the art without the inventive effort on the basis of the technical solutions of the present invention.
Claims (6)
1. The PTFE cylindrical blank sectional die pressing process comprises the steps of filling, pre-pressing and main pressing, and is characterized in that re-pressing is further arranged between the pre-pressing and the main pressing, and the pressing pressure of the re-pressing is between the pressing pressures of the pre-pressing and the main pressing;
The filling step comprises the steps of adding PTFE raw materials into a mould pressing mould, and supporting a male mould of the mould by a metal gasket;
The pre-pressing step is specifically to use pressing pressure of 2-3 MPa and keep the pressing time for 0.6-1 min;
The re-pressing step is specifically to use pressing pressure which is 3-6 times of the pre-pressing pressure, keep the pressing pressure for 0.6-1 min and take down the metal gasket under the die;
the main pressing step is specifically to use pressing pressure which is 9-18 times of the pre-pressing pressure and keep for 5-10 min;
The length-diameter ratio of the PTFE cylindrical blank is less than or equal to 3.0;
the pre-pressing, re-pressing and main pressing processes all adopt pressing rates of 10-50 mm/min;
the particle size of the PTFE raw material ranges from 100 to 300 mu m, and the adding volume of the PTFE raw material is 3 to 5 times of the volume of the prepared blank.
2. The PTFE cylindrical billet segment molding process of claim 1, wherein the pre-compression process uses a compression pressure of 2 MPa.
3. The PTFE cylindrical billet segment molding process of claim 1, wherein the repressing pressure used in the repressing process is in the range of 8 to 10MPa.
4. The PTFE cylindrical billet segment molding process according to claim 1, wherein the main pressing process uses a pressing pressure ranging from 24 to 30MPa.
5. The PTFE cylindrical billet segment molding process of claim 1, wherein the pre-pressing and re-pressing processes are performed in the next step after the press pressure is returned to zero after the pressing pressure is maintained.
6. A PTFE cylindrical billet produced by the PTFE cylindrical billet segment molding process of any one of claims 1 to 5, wherein the PTFE cylindrical billet has a density of 2.18 to 2.24g/cm 3 and a density uniformity of 99.50% or more.
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| CN202111582061.XA CN114393766B (en) | 2021-12-22 | 2021-12-22 | PTFE cylindrical blank and segmented molding process |
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| CN202111582061.XA CN114393766B (en) | 2021-12-22 | 2021-12-22 | PTFE cylindrical blank and segmented molding process |
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| CN114393766B true CN114393766B (en) | 2024-07-12 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111844824A (en) * | 2020-06-24 | 2020-10-30 | 腾辉电子（苏州）有限公司 | Preparation method of PTFE composite material sheet, PTFE composite material sheet and copper-clad plate using PTFE composite material sheet |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3981852A (en) * | 1974-06-17 | 1976-09-21 | E. I. Du Pont De Nemours And Company | Polytetrafluoroethylene molding powder |
| WO2003013821A1 (en) * | 2001-08-03 | 2003-02-20 | Coltec Industrial Products Llc | Method of manufacturing a pfte preform compression moulding |
| JP2004291462A (en) * | 2003-03-27 | 2004-10-21 | Ntn Corp | Method for manufacturing billet consisting of residual material of tetrafluoroethylene resin and recycling system |
| CN111976164A (en) * | 2020-06-24 | 2020-11-24 | 腾辉电子（苏州）有限公司 | Preparation method of polytetrafluoroethylene-based metal substrate and metal substrate |
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| CN111844824A (en) * | 2020-06-24 | 2020-10-30 | 腾辉电子（苏州）有限公司 | Preparation method of PTFE composite material sheet, PTFE composite material sheet and copper-clad plate using PTFE composite material sheet |
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