Heat treatment furnace before or after the acceptance of a period of time, according to temperature requirements of the system to test the accuracy of the system to verify its temperature control system and temperature recording system compliance with the standard requirements of the allowable error. This paper introduces the method and requirement of the precision test of the heat treatment furnace system, and gives the corresponding measures to solve the problem of precision tolerance in the process of system precision test.
1, the system accuracy test requirements and methods
1.1, the system accuracy test related requirements
Heat Treatment Furnace The system accuracy test is to calibrate the temperature of the sensor temperature indication or recorded at an operating temperature compared to the temperature corrected by the test sensor on the test instrument to determine whether the measured temperature deviation is within the permissible range. The calibration method is called system accuracy test.
Heat Treatment Furnace The system accuracy test should be calibrated and meet the requirements of the test instrument, test sensors and compensation of the three components of the standard system for comparison testing, so the requirements of the temperature meter and thermocouple accuracy should be equal to or higher than the measured instrument The accuracy.
The diameter of the thermocouple wire has a more stringent requirements: the use of the following 540 ℃, wire diameter requirements of not more than 0.5 mm, above 540 ℃ use, wire diameter requirements of not more than 0.8 mm.
Check the temperature of the choice also has a clear request. Selection of initial calibration temperature points: For equipment used at temperatures above 100 ° C, the maximum and minimum values for each specific process temperature range shall be used and the interval between the temperature measurement points in the system calibration shall not be greater than 150 ° C.
Heat Treatment Furnace The choice of periodic calibration temperature point should be made at a common process temperature point. If you often use a lot of work temperature, each time only select a temperature point test, in a year on each temperature point alternately verified. When the system accuracy test is carried out, it is necessary to check and read the calibrated meter and test instrument when the temperature of the heating furnace is stable.
1.2, the system accuracy test method
Place the test thermocouple in the same temperature field as the thermocouple of the calibrated temperature system, whichever is less than 75 mm. First, select the process temperature to be verified, the school equipment will be in the no-load (except vacuum furnace) temperature, heat treatment furnace temperature stability, can only be verified, read the instrument calibration, test equipment readings. And the calibration readings are recorded. Vacuum furnace instrumentation system accuracy test can be used with the production of heating at the same time.
Any system that will affect the accuracy of the system after the maintenance of the system should be re-tested, including the replacement of thermocouple and instrument adjustment and calibration, compensation wire replacement.
2, Heat Treatment Furnace the system accuracy test process often appear problems and solutions
In the process of system accuracy test practice often due to various factors caused by the system accuracy of the situation, if the lack of appropriate solutions, problems can not be handled, the equipment can not be used because of tolerance, delay production. In recent years, through continuous practice and exploration, we have accumulated some practical experience, the basic can solve the problems in production, the following accumulated experience for everyone to share. There are many reasons for the system accuracy tolerance, such as thermocouple error value is too large, the temperature meter by the external interference and deviation, heating furnace insulation performance is not good, even with the type of dual process.
In addition, there are temperature and compensation wire itself, there are errors and other factors. In general, can be summarized as a process instrument, compensation wire and thermocouple and temperature field stability of these reasons, the following were introduced.
2.1, the reasons for the instrument
Heat Treatment Furnace Now the digital instrument accuracy level is higher, the error value is generally below 0. 2, so the instrument error value is relatively small. But also consider the instrument failure or part of the non-digital instrument tolerance factors. In the heat treatment workshop of a three-zone temperature control furnace furnace system for the accuracy of the test found that there is a way of temperature control system accuracy of the system, after repeated troubleshooting, found that the temperature control instrument for the existence of ultra-poor. The solution to this problem is to replace or repair the instrument. As long as the accuracy of temperature control instruments meet the requirements, the problem is easy to solve.
2.2, compensation for the reasons for the wire
Heat Treatment Furnace It may be because the choice of compensation wire type and thermocouple does not match or compensate for wire error is too large and the overall system error caused by too large. The correct way is to choose the correct type and accuracy of the compensation wire. Due to compensation for the cause of the error caused by the wire is generally installed in the new equipment or replace the compensation wire, pay attention to the good quality, to prevent such problems occur.
2.3, the cause of thermocouple
Heat Treatment Furnace This is the easiest part of the problem. If the equipment some time ago its system accuracy to meet the requirements, and the temperature uniformity is better, but the last time the system accuracy test found that the accuracy of tolerance, the most likely reason is that the thermocouple in high temperature environment for some time after the use of even silk Organization and performance changes, and cause the accuracy of the thermocouple down, making the accuracy of the entire system tolerance.
2.4, the impact of test methods
Different test methods to produce the accuracy of the deviation is not the same as a vacuum furnace, for example, one is extrapolation, the other is the internal type. When the thermocouple is at room temperature, the temperature has little effect on the cold junction of the thermocouple, so the test result is more accurate; the other way is the internal connection, the thermocouple is in the vacuum furnace insulation screen and the furnace shell Between the part of the temperature is high, sometimes up to 200 ℃ or so, this will affect the thermocouple cold junction temperature, thus affecting the system's test accuracy.
2.5, the stability of the temperature field
The reason of the furnace itself: such as the door seal is not tight, heat quickly, causing the furnace to continue heating, making the temperature control instrument temperature fluctuations, and thus affect the system accuracy test. The solution is to enhance the door and other parts of the seal, improve the overall insulation performance of the furnace.
2.6, the impact of the external environment
Heat Treatment Furnace We have appeared in the production of temperature recorder temperature and instrumentation temperature curve from time to time the sudden emergence of the temperature of the situation, sometimes zero degrees, sometimes two or three degrees, sometimes there will be four or five degrees of beating, the system accuracy Has been difficult to test qualified. After the cause of the search, found mainly due to external interference factors: power lines and complementary wires placed in the same trunking, making strong and weak mutual interference, due to fluctuations in voltage caused by constant thermocouple voltage beating, and thus affect The temperature instantly produces a big change. The reason to find out, the problem is easy to be resolved. We will separate the power cord and compensation wire away, the distance between the two as large as possible to reduce the impact of strong electricity on the weak. Equipment protection can be used to consider the use of shielded compensation lines and recording instruments.
2.7, the impact of different temperature systems
Heat Treatment Furnace According to the requirements of AMS2750D, record the instrument need to record the temperature of temperature control, in order to meet the requirements, we use from the cold junction of the thermocouple lead two sets of compensation wire and access to temperature control instruments and recording instruments, which will cause two The system will produce interference between, and thus affect the temperature accuracy. After the upgraded version of the AMS2750E high temperature measurement standards: to allow temperature control instruments and record the temperature control point of the recorder each connected to a thermocouple, but the two require the same type of thermocouple, and the distance between the thermocouple Not more than 10 mm.