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Analysis on the Content of JB / T4088 - 2012 Standard for Tubular Electric Heating Elements
Dec 30, 2017

Analysis on the Content of JB / T4088 - 2012 Standard for Tubular Electric Heating Elements

The standard for new tubular components for daily use has been in effect since November 2012. I was a member of the revised edition of the Standard 98 and the revised version of 2012. I am familiar with the standard. The new version of the standard compared with the old version of a lot of content has been modified, in addition to the gate and increase. In order to facilitate the domestic enterprises to accurately understand and facilitate the operation, and further to the new standard as a benchmark to improve the technical level of daily tubular electric components to adapt to the needs of domestic and international application market. I am here to this article on the new standards related to the provisions of a number of changes in the analysis, treatment, in this and everyone to communicate. Since I am not within the scope of official duties, all views can only be of an academic nature and do not have any interpretive authority. All content is for reference only!


1 range


Compared with the old version, the voltage was changed from 440V to 480V, and the power was changed

 from 4000W to 6000W. This is to adapt to market development needs.



Terms and Definitions


2.1 The new standard on the definition of damage to a little change, the old standard on the 

withstand voltage value is less than the specified value is damaged, and the new standard to

 withstand the voltage value is lower than 75% of the normal value of damage. Pressure 1500V

 product is intact, after a period of use can only withstand 1200V pressure, this product can not

 use the old standard, and the new standard that is not damaged.


2.2 An explanation of the equivalent resistance has been added


The equivalent resistance is primarily used as an alternative to the quick inspection of the power

 delivered to the factory. We all know that most of the varieties of electric components can not be

 carried out by the power of one by one, (because the surface of the tube after the oxide layer and

 time-consuming) Therefore, most manufacturers are measuring DC resistance to determine the power 

of qualified or not. However, due to resistance wire material at different temperatures its

 resistance has a certain change, we are accustomed to this change is called resistance temperature

 coefficient. Here refers to the equivalent resistance is different according to the operating 

temperature, measured resistance multiplied by a factor multiplied by the element than the normal

 temperature of the temperature value.


The relationship in the standard: R (T) = R0 [1 + a (T-T1)]


Equivalent resistance = normal temperature resistance x [1 + resistance fixed temperature

 coefficient (operating temperature - normal temperature) for this formula I have two ideas;


A temperature coefficient of resistance is directly related to the temperature of course, but it is

 not a linear relationship.


B The resistance wire has a correction factor for the relevant temperature coefficient in the 

professional standard of the resistance wire. This correction value refers to the temperature of 

the resistance wire itself, not to the surface temperature of the element.


In view of the above two points, I think this formula can not be accurately calculated. So I 

suggest that resistance wire should be at different temperatures when the correction value into

 the formula for calculation.


R (T) = Ro x Ct


The text describes: equivalent resistance = temperature resistance x temperature coefficient


For example: a component 220V 1000W work when the component surface temperature of 300 ℃, the 

resistance wire itself temperature 450 ℃,


Look-up table at this time resistance wire corresponding to the correction value, and then into 

the calculation. Here suggest: resistance wire material with different correction factor is 

different. It is important that the equivalent resistance is accurate (consistent with the accuracy

 of the power). It is recommended that the manufacturer verify the thermal resistance of the 

component at the simulated operating temperature (this is the true equivalent resistance). The 

verification steps are as follows:


A first measured cold resistance;


B Connect the component to the power supply to allow the component to reach its normal operating 

temperature;


C When the temperature is stable, note down the power (display voltmeter /, power meter must be

 accurate);


D the measured power value into Ohm's law to calculate: the equivalent resistance = the square of 

the voltage / measured power value


E calculate the number of resistance temperature ct = equivalent resistance / cold resistance


Ohm's Law for the calculation is very accurate, no doubt, if the conditions can be equipped with

 electronic bridge that is power measurement. In the actual work of enterprises on the equivalent

 power of alternative resistance to the scope of control should be left a certain margin.



3. Classification


   Compared with the old standard more refined, the shape, whether the vibration, whether embedded,

 heating characteristics of classification.



4. Technical requirements


   Compared with the old standard to the C grid content; around no explosive, flammable, corrosive

 gases and conductive dust. The grid goes to the ring temperature.


4.2 Power deviation requirements are not changed


4.3 Leakage current The original standard of not more than 0.5mA revised wood for more than 0.75mA. Here to explain, is not required to reduce, in essence, is due to the scope of the new standard is 6KW, we all know that the size of the leakage current and the size of the power has a certain relationship, so revised to 0.75mA power expansion is normal


4.4 electrical strength compared with the old standard to increase the requirements under the cold 

condition, in fact, this requires the production enterprises have been operating as a normal 

project. Because it is cold, so than the working temperature and the tide condition under the 

requirements of increased, so as 1500V. For the working voltage greater than 250V product voltage

 is 1.2 times the working voltage plus 1250V, the working temperature of the voltage value is 1.2 

times the working voltage plus 800V, the tide of the voltage value of 1.2 times the operating 

voltage plus 1000V.


4.5 to increase the requirements of harmful substances limits, in this regard the production

 enterprises to control.


4.6 General structural aspects


4.6.1 Adjust the tube body temperature limit in the old standard to Appendix C. Normative 

information


4.6.2 Adjust the wall thickness limit of the metal pipe to Appendix D. Information material


4.6.3 Adjust the insulation thickness and creepage distance between the electrodes of the component

 and the housing to see Appendix D.


4.6.4 In the new standard, the length limit of the rod in the pipe is greatly changed from the old

 standard.


   A Change the value of the pipe diameter to the interval value. So that in the actual work on the easy operation.


   B rationalize the lead rod specifications and diameter specifications with the rationality. For

 example, the original standard diameter diameter of 6.5mm supporting rod diameter 3mm-4mm, which 

is not realistic, and the new standard in the diameter 6.5mm matching leads between 2mm-2.5mm, this

 is In line with the use of. Here suggest that: If the customer is required to produce diameter 6,5

 mm and supporting rods for the diameter of 3mm, then it is not to meet the standard requirements. 

The standard form content is mainly to length can not be too short, if the length is less than the

 table requirements should be unqualified.


4.6.5 Tolerance of the geometric dimensions of the new standard GB / 1804 in the assessment by the

 V-class, so that the old standard with the


 More practical.

4.7 On the heating uniformity in the standard has no specific requirements, but referred to the 

temperature limit of the pipe body requirements. (Appendix C)


I have a few ideas for the heat uniformity:


A first of all affirmed in the future of our products used in the metal material temperature 

requirements must comply with the requirements of Appendix C;


B Appendix C can not replace the heating uniformity requirements, as the tubular electric heating 

element is concerned, it is a power after the heating body, the tube surface temperature should be

 uniform, the work can be uniform to the heating of various substances, the reality In which no 

heating device does not require uniform heating. Secondly, we all know that the electric components

 with the temperature of its insulation safety performance will change. In the same conditions, the

 higher the temperature the greater the leakage current; then the resistance wire is also the

 higher the temperature the shorter the life.


C I think the uniformity of the fever or should be assessed, but the old way of the components of

 the X-ray film inspection is not easy to operate and can not guarantee accuracy. Can not guarantee

 the exact reason is: to achieve uniform heating tube surface In addition to the resistance from 

the density of uniform density of wire packing must also be uniform, or the tube surface 

temperature is not necessarily uniform.


D of the component heating uniformity of the assessment methods:


D1 components connected to the power to be stable after the temperature test;


D2 if the surface load is too large should be reduced voltage for testing;


D3 must be measured using a surface temperature thermometer:


D4 temperature requirements should be controlled at 10% is moderate (refer to the relevant foreign

 standards), this requirement does not reduce the comparison with the old standard;


D5 on the surface of the component evenly distributed 5-point test and calculation, for the 

intuitive uniformity of the fever must be used as a point test;


D6 is calculated as follows:


, Tc = max [| 1- (Tn / T flat) |] × 1%


    In the formula:


Tc ---- temperature difference


         Tn ---- any point temperature


         T Average of all test points


4.8 The requirements of the new standard for tensile testing of lead-out bars are the same as those

 of the old standard, but the requirements for tensile tests and inserts for welded lugs on lead

 bars are increased.


     In view of this content I view is as follows:


   A electrode sheet is a small part, but it is very important with the lead out of the stick, if 

the contact will be in the process of using the ignition or out of touch, the general electrical 

lugs are charged, the emergence of this The situation is very dangerous.


   B Electrode inserts, like lugs, are also important in their size requirements in addition to 

their secure contact with the lead-out bar. If the size of the thickness of thin, then the use of

 poor contact, this is a security risk. Based on this point, it is recommended that attention 

should be paid to manufacturing enterprises. Familiar with the relevant requirements in GB / 17196

 (insert standard), the size requirements and insertion force should be strengthened and controlled

.


4,9 new standards to increase the anti-dry requirements


Anti-dry test is mainly for liquid heating elements in the junction scale, dehydration, the 

components from the liquid into a gas plus


Heat and the contents of the assessment. For dry-burning conditions, there is no clear requirement

 in the standard, written only in consultation with the user. Correct


In the anti-dry test I have the following view:


A standard has been expressly provided for must be implemented, but because of this test, 

components, if the use of copper pipe is clearly not suitable;


B. It is not possible to use a dry-burning test to ensure that the water element can be completely 

safe (no thermal breakdown, no bursting, no burn-out) after the scale has been applied, since the

 packing inside the element sometimes takes a long time Will change.


C In order to adapt to the dry burning test, we need to adjust the design of water components, tube

 surface load to reduce, if the load is still relatively large can not use modified magnesium oxide

, and to select high-temperature magnesium oxide.


D standard of the pipe surface load is greater than 10W of the article does not apply, so I think 

it is wrong, because the tube surface load the greater the scale of the device components, the 

faster the scale, the electrical properties of the possibility of the decline of the more Big.

 Based on this we must have this understanding of production enterprises, can not have a lucky 

heart, (not assessment of dry), whereas 10W negative charge of the product should consider the use

 of filler selection of high temperature magnesium oxide.


In order to improve the technical performance of water heating elements to ensure that no burst,

 no heat breakdown burned, I also wrote a reference for information.


4.10 The new standard adds to the flammability requirements of the sealing material


   This article basically according to the requirement in GB / 4706.1.



5 on the test method


5.1 on the measuring instruments to increase the humidity of the instrumentation and precision 

requirements.


5.2 Measuring power I suggest to be equipped with a regulated power supply, the test voltage should

 be measured first, to ensure accurate measurement of electrical power after the voltage can be 

accurate. As mentioned earlier, the equivalent resistor center value must be verified by a power 

test at a simulated operating temperature.


5.3 Leakage current measurement at operating temperature


Specific methods of testing and attention to items:


A component must be insulated from the earth;


B at a simulated operating temperature;


C adjust the voltage to 1.15 times the rated power voltage;


D Both ends of the component are measured, whichever is greater.


 


Here suggest that in the course of the test if the peak and then down, then this component should

 be the peak to determine the results. Because as an electrical product in the course of the moment

 if there is a security risk, product manufacturers can not avoid responsibility.


5.4 Sealing test and leakage current test after water pressure


These two states of the leakage current are in fact the scope of cold leakage current on the cold

 leakage current test most companies do not seriously done, in fact, it is a substitute insulation

 resistance test method, because the standard from the 98 version to cancel Insulation Resistance 

Item Requirement. Test method is the use of AC voltage, (1.06 times the rated voltage), components

 are not energized, AC voltage is applied between the electrode and the shell.



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