Quality test and analysis of tubular heating elements

- Apr 27, 2020-

Standards and quality testing;
Electric heat pipe test executable industry standard JB / 4088-2012 "HR tubular electric heating element (in F JB/T 4088-2012) and the national standard GB 4706.1-2005" (household and similar electrical appliances safety part 1: I use requirements (f. GB 4706.1 2005), and according to the China quality certification center CQC product the factory quality assurance ability requirement of voluntary certification implementation rules.
High standards will promote the improvement of production technology, equipment, personnel, testing, standards, management and other aspects.

Power test of tubular heating element:

The power test of the electric heat pipe shall be conducted according to the deviation of +5% and -10% of rated power stipulated by the industry standard JB/T 4088-2012, which is equivalent to the power deviation of gb4701.1-2005, and the power variation is within the range of +5% and -10% of technical indexes. Because when electric heat pipe components are assembled on household appliances, most of them are tested in accordance with relevant national standards and GB 4706.1-2005 requirements, which are equivalent to the industrial standards and customer requirements of electric heat pipe.
Commonly used testing instruments are resistance tester, power meter, tape measure. In the test, in order to improve the accuracy, resistance meter tester is often used to test the resistance, the test value conversion success rate and should meet the JB/ 40882012 standard on the power deviation requirements.
leakage current test of tubular heating element:

Leakage current test is mainly aimed at the situation of the oxidized magnesia in the electric heat pipe containing impurities, grease, residues, iron, excessive trace elements, various impurities mixture, B/ 4088-2012 test method requirements higher than GB 4706.1-2005 requirements. The leakage current limit is set to 0.5 mA, and the digital stability is the limit data. The leakage current test is conducted until the digital display is stable, when the leakage current is greater than
Unqualified at 0.5 mA. Generally, when testing the electric heat pipe below 3,000 w, the heating medium is tested at 100-200 ℃, and the data is usually less than 0.1-0.2 mA. When the data is unstable and the leakage current is greater than 0.5 mA, it can be judged that the oxidized magnesia contains more iron impurities, or there are cracks in the pipe wall with water seepage, so the leakage current tester can be used as a kind of reliable instrument to determine the oxidized magnesia material.
Electrical strength test
At present, electrical strength test is usually the most important technical index of enterprise delivery. Electric strength test JB/T 4088-2012 in the working temperature of 1000 V / 60 min not breakdown for qualified, and at present enterprise order delivery are stated in the contract with supplier under 2 000-2 500 V voltage electric strength test for mutual acceptance standard technical requirements, 100% of routine testing was carried out on the intensity of electric factory, enterprise to use the electric strength of the standard is twice higher than industry standards and national standards, and 2 0002500 V at room temperature. The instrument commonly used is the pressure tester.
Test the evenness of the heating wire of the electric heat pipe
The test method is to connect the voltage regulator with power supply to the load, apply voltage to the finished product of the electric heat pipe, slowly increase the voltage, observe whether the color of the tube body is uniform when the electric heat pipe is red-hot. The color of qualified electric heat pipe heating wire is red and evenly distributed when it is heated, without local heating, and the power generated by voltage drop is evenly distributed. Uneven performance is prone to red and dark color inconsistency, which will directly affect the service life of the electric heat tube.
Technical analysis of production process:
1- Filling of magnesia oxide powder:

(1) in the quality control of magnesia oxide, it is mainly to control the magnesia oxide before production as early as possible. The disqualified MgO powder directly affects the service life of the electric heat pipe and the electrical strength of the filling process was broken down in the test.
(2) in order to ensure the quality, the general inspection of purchased magnesia oxide is mainly to visually measure its uniformity, i.e. particle size. Manufacturer to purchase the oxidation of magnesia subject to ball mill grinding again and again through the electromagnet iron removal equipment to remove the iron impurities, and then into the already warming in the oven to 125 ℃ for 4 h moisture removal, moisture to dry heat treatment, for temperature zone of the reentry after into the powder filling high voltage electrical strength test, to determine whether the insulation performance meet the requirements.
2 -Production of electric heating wire:
(1) in the production process, The Times of tube shrinkage and the density of magnesium oxide are different, the heating area of the electric heat pipe is also different. In the electric heat pipe power design, the resistance value and heating area of the electric heat pipe must be considered first. When making the selection of line diameter, it can be obtained by looking up the table or by calculating the heating area.
(2) if the heating wire is not uniform in the production control, the local surface heating will be uneven in the future use. The resistance of the part of the internal electric heating wire which is more dense will be larger, and the voltage drop will also be larger, which will make the local power on the high side, the temperature is too high, thus affecting the life of the electric heat pipe. During the test, the voltage can be reduced by a voltage regulator. At the same time, a temperature tester can be used to test the surface at multiple points and the red-dark ratio to determine whether the heating wire is uniform. If the temperature difference of the electric heating wire is large and the color difference of daily measurement is large, it cannot meet the use requirements. If it is installed in the electric heating appliance, the electric heating wire will burn off in the use process, affecting the use of the electric heating appliance

(3) iron winding is used for electric heat pipe with operating temperature less than 500℃, and nickel winding is used for heating pipe with operating temperature more than 500℃. The electric heating wire interacts with magnesium oxide to produce different chemical reactions, which will produce heat and affect the insulation performance of magnesia oxide. The winding wire diameter is usually 0.15-1.0mm.
3-Electrical strength test of metal pipes:
When filling magnesia, if the center heating wire is away from the center of the metal tube, the electrical clearance or creasing distance is less than 2 mm, and the filled magnesia material is poor, it can be measured by the electrical strength test. It can also be tested by the industry standard 1000 V/60 min electrical strength test method.
Raise the voltage to more than 30% of the test voltage, 3s can be measured one, called equivalent method test; The voltage can also be adjusted to 2,000-2,500 v, and 1s failure is considered qualified. Currently, manufacturers often use this method of applying high voltage for testing
4-Hydrostatic test:
The purpose of the hydrostatic test is to examine whether the electric heat pipe has destructive damage after all the production processes and whether it conforms to the safety performance stipulated by the national standard.