CN112326723A - Method for measuring heating history temperature of crosslinked polyethylene material - Google Patents
Method for measuring heating history temperature of crosslinked polyethylene material Download PDFInfo
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- CN112326723A CN112326723A CN202011042594.4A CN202011042594A CN112326723A CN 112326723 A CN112326723 A CN 112326723A CN 202011042594 A CN202011042594 A CN 202011042594A CN 112326723 A CN112326723 A CN 112326723A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/02—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering
- G01N25/12—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering of critical point; of other phase change
Abstract
The invention provides a method for measuring the heated historical temperature of a crosslinked polyethylene material, which comprises the following steps: carrying out first temperature rise on a crosslinked polyethylene sample to obtain temperature and heat flow data in the first temperature rise process; cooling the crosslinked polyethylene sample from the first preset temperature to a second preset temperature; carrying out secondary heating on the crosslinked polyethylene sample, and acquiring temperature and heat flow data in the heating process; and processing the temperature and heat flow data in the two temperature rising processes to obtain a derivative curve of heat flow to temperature in the two temperature rising processes, and determining the heated historical temperature of the crosslinked polyethylene sample according to the derivative curve. According to the invention, through carrying out temperature rise on a single crosslinked polyethylene sample twice, the heating history temperature of the crosslinked polyethylene sample can be determined according to the derivative curve of heat flow to temperature in the two temperature rise processes, so that the measurement times and the required sample number are reduced, the data processing process is simplified, and the heating history temperature of the crosslinked polyethylene material can be rapidly determined.
Description
Technical Field
The invention relates to the technical field of cable insulation material performance testing, in particular to a method for measuring the heating history temperature of a crosslinked polyethylene material.
Background
Crosslinked polyethylene materials are insulating materials that are widely used in current power cable equipment. The thermal history of the crosslinked polyethylene material has a significant impact on the thermal aging behavior and performance of the power cable insulation. Many factors in the cable production, storage, transportation, laying and operation process can cause the insulation material of the cable to be subjected to unexpected high temperature, and the insulation performance of the crosslinked polyethylene insulated cable deviates from the designed value. In some cases, overheating of the insulation material results in insulation breakdown of the crosslinked polyethylene. Therefore, the historical temperature of the cable is an important basis for evaluating the cable state and analyzing the fault cause.
At present, the relevant domestic standards only indicate that the sample is heated to a high enough temperature before the differential scanning calorimetry measurement is carried out so as to eliminate the previous thermal history of the test material, and no method for measuring the thermal history of the crosslinked polyethylene material is given. For crosslinked polyethylene cables, the history of cable heating during production, storage, transportation, installation and operation is eliminated when the heating temperature exceeds the main melting temperature (about 105 ℃) of the crosslinked polyethylene material. It is noted that if the heat history temperature T of the crosslinked polyethylene material is lower than the main melting temperature, the differential scanning calorimetry temperature rise curve of the material will show a small melting peak P1 (above the temperature T) and P2 (below the temperature T) on either side of the temperature T. Researchers put forward a method for calculating the heating history temperature and the corresponding heating time of the cross-linked polyethylene material by adopting a data fitting formula, but the method needs to carry out sampling measurement for many times to determine a fitting coefficient, and is easily influenced by the difference of the heating history temperature of the material in practical application. Researchers have proposed the temperature corresponding to where P1 begins to appear as the heat history temperature of the crosslinked polyethylene material, but no method for confirming the temperature is given, and the temperature results cannot exclude the influence of experimenters.
Disclosure of Invention
In view of this, the invention provides a method for measuring the heating history temperature of a crosslinked polyethylene material, and aims to solve the problems that in the prior art, the heating history temperature of the crosslinked polyethylene material needs to be calculated by carrying out sampling measurement for multiple times to determine a fitting coefficient, so that the test process is complicated, and the test efficiency is low.
The invention provides a method for measuring the heated historical temperature of a crosslinked polyethylene material, which comprises the following steps: carrying out first temperature rise on a crosslinked polyethylene sample at a first preset temperature rise rate, keeping the temperature rise rate at a first preset temperature for a first preset time length, and obtaining temperature and heat flow data in the first temperature rise process; cooling the crosslinked polyethylene sample from the first preset temperature to a second preset temperature at a preset cooling rate, and keeping the temperature for a second preset time; carrying out second heating on the crosslinked polyethylene sample at a second preset heating rate, keeping for a third preset time after heating to a second preset temperature, and obtaining temperature and heat flow data in the second heating process; and processing the temperature and heat flow data in the first heating process and the second heating process to obtain a derivative curve of heat flow to temperature in the two heating processes, and determining the heating historical temperature of the crosslinked polyethylene sample according to the derivative curve.
Further, in the method for measuring the historical temperature of the cross-linked polyethylene material after being heated, the processing the temperature and heat flow data in the first heating process and the second heating process includes: and respectively calculating the derivative data of the heat flow to the temperature in the first heating process and the second heating process.
Further, in the method for measuring the history temperature of the cross-linked polyethylene material, the determining the history temperature of the cross-linked polyethylene sample further includes: drawing a heat flow-to-temperature derivative curve in the two temperature rising processes by using the same temperature coordinate axis, and taking a peak value curve only existing in the first temperature rising process as a thermal history peak of the crosslinked polyethylene sample; and determining the heated historical temperature of the crosslinked polyethylene sample according to the intersection point of the heat flow-temperature derivative curve in the second heating process and the heat history peak in the first heating process.
Further, in the method for measuring the historical heating temperature of the cross-linked polyethylene material, two cross points are provided, and the smaller value of the two temperature data corresponding to the two cross points is used as the historical heating temperature of the cross-linked polyethylene sample.
Further, in the method for measuring the historical heating temperature of the crosslinked polyethylene material, the heating intervals in the first heating process and the second heating process cover the historical heating temperature of the crosslinked polyethylene sample.
Further, in the method for measuring the history temperature of the cross-linked polyethylene material, the first preset temperature and the second preset temperature are 120-160 ℃.
Further, in the method for measuring the historical temperature of the cross-linked polyethylene material after being heated, the first preset heating rate is the same as the second preset heating rate.
Further, in the method for measuring the historical temperature of the cross-linked polyethylene material after being heated, the first preset heating rate and the second preset heating rate are both 10-20 ℃/min.
Further, in the method for measuring the historical temperature of the cross-linked polyethylene material after being heated, the preset cooling rate is 10-20 ℃/min, and the second preset temperature is 15-25 ℃.
Further, in the method for measuring the historical heating temperature of the crosslinked polyethylene material, differential scanning calorimetry is adopted to obtain temperature and heat flow data in the first heating and the second heating.
According to the method for measuring the historical heating temperature of the crosslinked polyethylene material, provided by the invention, through carrying out twice heating and once cooling treatment on a single crosslinked polyethylene sample, the historical heating temperature of the crosslinked polyethylene sample can be determined according to the derivative curve of heat flow to temperature in the twice heating processes, the measurement times and the required sample number are reduced, the data processing process is simplified, and the historical heating temperature of the crosslinked polyethylene material can be rapidly determined.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a schematic structural diagram of a method for measuring a history temperature of a cross-linked polyethylene material subjected to heat according to an embodiment of the present invention;
FIG. 2 is a graph of heat flow versus temperature derivative during two temperature increases of a cross-linked polyethylene material according to an embodiment of the present invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Referring to fig. 1, the method for measuring the heating history temperature of the cross-linked polyethylene material according to the embodiment of the present invention includes the following steps:
and step S1, carrying out first temperature rise on the crosslinked polyethylene sample at a first preset temperature rise rate, keeping the temperature rise rate for a first preset time after the temperature rise rate reaches a first preset temperature, and acquiring temperature and heat flow data in the first temperature rise process.
Specifically, in this example, a single crosslinked polyethylene sample was taken and tested, and the temperature of the crosslinked polyethylene sample before the test was regarded as normal temperature, for example, 20 ℃. And acquiring temperature and heat flow data in the first temperature rise by adopting a differential scanning calorimetry measurement method. Wherein: the first preset heating rate can be 10-20 ℃/min, preferably 20 ℃/min, and the test time can be shortened by increasing the heating rate, and meanwhile, the excellent sensitivity and the characteristic resolution capability can be achieved. And covering the heating history temperature of the crosslinked polyethylene sample in the heating interval of the first heating process. In this embodiment, the first predetermined temperature is 120-. The first preset time period is 1-8min, preferably 5 min.
And step S2, cooling the crosslinked polyethylene sample from the first preset temperature to a second preset temperature at a preset cooling rate, and keeping the temperature for a second preset time.
Specifically, the preset cooling rate is 10-20 ℃/min, and preferably 20 ℃/min; the second preset temperature is 15-25 ℃, and preferably 20 ℃; the second preset time is 1-8min, preferably 5 min.
And step S3, carrying out secondary heating on the crosslinked polyethylene sample at a second preset heating rate, keeping for a third preset time after heating to a second preset temperature, and acquiring temperature and heat flow data in the secondary heating process.
Specifically, differential scanning calorimetry is used to obtain temperature and heat flow data during a second temperature rise, wherein: the first preset heating rate and the second preset heating rate are the same, and preferably, the second preset heating rate can be both 10-20 ℃/min, and more preferably 20 ℃/min.
And covering the heating history temperature of the crosslinked polyethylene sample in the heating interval in the second heating process. In this embodiment, the second predetermined temperature is 120-160 ℃, preferably 150 ℃. The third preset time is 1-8min, preferably 5 min.
And step S4, processing the temperature and heat flow data in the first heating process and the second heating process to obtain a derivative curve of heat flow to temperature in the two heating processes, and determining the heating history temperature of the crosslinked polyethylene sample according to the derivative curve.
Specifically, the processing the temperature and heat flow data in the first heating process and the second heating process includes: and respectively calculating the derivative data of the heat flow to the temperature in the first heating process and the second heating process.
The derivative data of the heat flow to the temperature in the two temperature raising processes can be calculated by any method in the prior art, for example, the derivative data can be calculated according to the following method:
the first step is as follows: setting positive integers m and n, wherein m is less than n. The temperature data array T [ m + n ] and the heat flow data array HF [ m + n ] are extracted from the raw measurement data.
The second step is that: t [ m + n ] and HF [ m + n ] are smoothed. More specifically, starting from the first element of T [ m + n ] and HF [ m + n ], the following m elements are selected, and the average value of the m elements is taken as the value of the first element. The smoothing process starts from the first element of T [ m + n ] and HF [ m + n ], and the elements are processed one by one to obtain a smoothed temperature data array T '[ n +1] and a smoothed heat flow data array HF' [ n +1 ].
The third step: heat flow versus temperature derivative data is calculated. The specific mode is that two adjacent elements T 'k, T' k +1, HF 'k and HF' k +1 are respectively selected from the smoothed temperature data array T 'n +1 and the smoothed heat flow data array HF' n +1, the heat flow temperature derivative D [ k ] is calculated according to the following formula, and the D [ k ] is used as the kth element of the heat flow temperature derivative array D [ n ].
Wherein the content of the first and second substances,
d [ k ]: the kth element of the heat flow derivative to temperature array D [ n ] has the unit of W/(g ℃);
HF' [ k +1 ]: the (k +1) th element of the smoothed heat flow data array HF' [ n +1], the unit of which is W/g;
HF' [ k ]: the kth element of the smoothed heat flow data array HF' n +1 is in W/g;
t' [ k +1 ]: the (k +1) th element of the smoothed temperature data array T' [ n +1], the unit is;
t' [ k ]: the kth element of the smoothed temperature data array T' [ n +1], with the unit being;
k: a positive integer less than or equal to n.
The determining the heated historical temperature of the crosslinked polyethylene sample further comprises: drawing a heat flow-to-temperature derivative curve in the two temperature rising processes by using the same temperature coordinate axis, and taking a peak value curve only existing in the first temperature rising process as a thermal history peak of the crosslinked polyethylene sample; and determining the heated historical temperature of the crosslinked polyethylene sample according to the intersection point of the heat flow-temperature derivative curve in the second heating process and the heat history peak in the first heating process.
Further, the number of the intersection points is two, and the smaller value of the two temperature data corresponding to the two intersection points is used as the heating history temperature of the crosslinked polyethylene sample.
In this embodiment, the thermal history peak of the material is related to the property of the material itself, and in this embodiment, based on the two temperature rise intervals of 120-.
Of course, after the second temperature rise is finished, the crosslinked polyethylene sample can be naturally cooled, and the temperature of the crosslinked polyethylene sample can also be reduced.
In this embodiment, in order to reduce the measurement error, multiple measurements may be performed on a single crosslinked polyethylene sample, and the average value of the heating history temperatures obtained through the multiple measurements may be used as the final heating history temperature.
It can be clearly seen from the above that, in the method for measuring the historical heating temperature of the crosslinked polyethylene material provided in this embodiment, by performing two-time temperature raising and one-time temperature lowering processing on a single crosslinked polyethylene sample, the historical heating temperature of the crosslinked polyethylene sample can be determined according to the derivative curve of heat flow versus temperature in the two-time temperature raising processes, the measurement times and the number of required samples are reduced, the data processing process is simplified, and the historical heating temperature of the crosslinked polyethylene material can be quickly determined.
The following further describes an embodiment of the present invention with reference to fig. 2.
Taking a single crosslinked polyethylene sample, carrying out differential scanning calorimetry measurement on the single crosslinked polyethylene sample, and recording temperature and heat flow data, wherein the specific steps are as follows:
heating the crosslinked polyethylene material for the first time at a heating rate of 20 ℃/min to raise the temperature from 20 ℃ to 150 ℃, and keeping the temperature for about 5 min;
reducing the temperature of the cross-linked polyethylene material from 150 ℃ to 20 ℃ at a cooling rate of 20 ℃/min, and keeping the temperature for about 5 min;
the crosslinked polyethylene material was subjected to a second temperature increase from 20 ℃ to 150 ℃ at a temperature increase rate of 20 ℃/min and held for about 5 min.
Respectively calculating derivative data of heat flow to temperature in the two temperature rise processes; in a rectangular coordinate system, a derivative curve of heat flow to temperature in two temperature rising processes is drawn by using the same temperature coordinate axis, and a peak value curve only existing in the first temperature rising process is used as a thermal history peak of the crosslinked polyethylene material. The range of the temperature coordinate axis is [40, 120] ° C, and heat flow-temperature derivative curves of the first heating process and the second heating process are respectively drawn in a rectangular coordinate system. The first temperature rise process curve has 3 peak values, the second temperature rise process curve has 2 peak values, the comparison shows that the peak value in the range of [70, 85] ° c only exists in the first temperature rise process, and the peak value in the range of [70, 85] ° c is marked as a thermal history peak.
And determining the intersection point of the heat flow derivative curve of the temperature in the second temperature rise process and the heat history peak in the first temperature rise process, recording the intersection point as a first intersection point and a second intersection point, and taking the smaller value of the temperatures corresponding to the two intersection points as the heated history temperature of the crosslinked polyethylene material. The corresponding temperature of the first intersection is lower than that of the second intersection, so that the corresponding temperature (75.0 ℃) of the first intersection is used as the heating history temperature.
In summary, according to the method for measuring the heating history temperature of the crosslinked polyethylene material provided by the invention, the heating history temperature of the crosslinked polyethylene sample can be determined according to the derivative curve of the heat flow to the temperature in the two heating processes by performing two heating processes and one cooling process on a single crosslinked polyethylene sample, so that the measurement times and the required sample number are reduced, the data processing process is simplified, and the heating history temperature of the crosslinked polyethylene material can be rapidly determined.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A method for measuring the heating history temperature of a cross-linked polyethylene material is characterized by comprising the following steps:
carrying out first temperature rise on a crosslinked polyethylene sample at a first preset temperature rise rate, keeping the temperature rise rate at a first preset temperature for a first preset time length, and obtaining temperature and heat flow data in the first temperature rise process;
cooling the crosslinked polyethylene sample from the first preset temperature to a second preset temperature at a preset cooling rate, and keeping the temperature for a second preset time;
carrying out second heating on the crosslinked polyethylene sample at a second preset heating rate, keeping for a third preset time after heating to a second preset temperature, and obtaining temperature and heat flow data in the second heating process;
and processing the temperature and heat flow data in the first heating process and the second heating process to obtain a derivative curve of heat flow to temperature in the two heating processes, and determining the heating historical temperature of the crosslinked polyethylene sample according to the derivative curve.
2. The method of claim 1, wherein the processing the temperature and heat flow data during the first temperature rise and the second temperature rise comprises:
and respectively calculating the derivative data of the heat flow to the temperature in the first heating process and the second heating process.
3. The method of claim 1, wherein the determining the historical temperature of the cross-linked polyethylene sample further comprises:
drawing a heat flow-to-temperature derivative curve in the two temperature rising processes by using the same temperature coordinate axis, and taking a peak value curve only existing in the first temperature rising process as a thermal history peak of the crosslinked polyethylene sample;
and determining the heated historical temperature of the crosslinked polyethylene sample according to the intersection point of the heat flow-temperature derivative curve in the second heating process and the heat history peak in the first heating process.
4. The method for measuring the heating history temperature of the cross-linked polyethylene material according to claim 3, wherein the number of the intersection points is two, and the smaller of the two temperature data corresponding to the two intersection points is used as the heating history temperature of the cross-linked polyethylene sample.
5. The method for measuring the heating history temperature of the cross-linked polyethylene material according to claim 1, wherein the temperature rise interval in the first temperature rise process and the second temperature rise process covers the heating history temperature of the cross-linked polyethylene sample.
6. The method as claimed in claim 5, wherein the first predetermined temperature and the second predetermined temperature are 120-160 ℃.
7. The method according to claim 1, wherein the first preset temperature rise rate and the second preset temperature rise rate are the same.
8. The method according to claim 7, wherein the first and second predetermined heating rates are both 10-20 ℃/min.
9. The method for measuring the heating history temperature of the cross-linked polyethylene material according to claim 1, wherein the preset cooling rate is 10-20 ℃/min, and the second preset temperature is 15-25 ℃.
10. The method for measuring the heating history temperature of the cross-linked polyethylene material according to claim 1, wherein the temperature and heat flow data of the first heating and the second heating are obtained by differential scanning calorimetry.
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Citations (4)
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| JPS61117441A (en) * | 1984-11-13 | 1986-06-04 | Showa Electric Wire & Cable Co Ltd | Method for estimating heat history of polyethylene |
| JPH0510900A (en) * | 1991-02-28 | 1993-01-19 | Showa Electric Wire & Cable Co Ltd | Estimation of heat history of polyethylene |
| JP2009128010A (en) * | 2007-11-19 | 2009-06-11 | House Foods Corp | Mixing period estimation method of plastic piece |
| JP2009236745A (en) * | 2008-03-27 | 2009-10-15 | Sumika Chemical Analysis Service Ltd | Resin thermal history estimation method |
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2020
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61117441A (en) * | 1984-11-13 | 1986-06-04 | Showa Electric Wire & Cable Co Ltd | Method for estimating heat history of polyethylene |
| JPH0510900A (en) * | 1991-02-28 | 1993-01-19 | Showa Electric Wire & Cable Co Ltd | Estimation of heat history of polyethylene |
| JP2009128010A (en) * | 2007-11-19 | 2009-06-11 | House Foods Corp | Mixing period estimation method of plastic piece |
| JP2009236745A (en) * | 2008-03-27 | 2009-10-15 | Sumika Chemical Analysis Service Ltd | Resin thermal history estimation method |
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