GB 5959.4-1992 Safety of Electric Heating Equipment Part 4 General Requirements for Resistance Furnaces
Some standard content:
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National Standards of the People's Republic of China
Safety of electric heating equipment
Part 4: General requirements for resistance furnaces
Safety in electroheat installationsPart4: General requirements for resistance furnaces||tt ||GB5959.4-92
This standard is equivalent to the international standard IEC519-2 (1975) "Safety of Electric Heating Equipment Part 2 General Requirements for Resistance Furnaces 1 Subject Content and Scope of Application
This standard specifies general safety requirements for resistance furnaces. This standard applies to various indirect heating resistance furnaces except for paint drying and explosive atmosphere resistance furnaces and glass melting furnaces, graphitization furnaces, silicon carbide furnaces using direct resistance heating, etc. This standard does not apply to infrared heating elements, surface electric heating systems and devices for direct resistance heating as described in GB5959.2, GB5959.3 and GB5959.8. It also does not apply to rapid water heaters and electrodes for electrode steam boilers. pressure vessel. This standard should be used in conjunction with GB5959.1. 2 Reference standards 1
GB2900.23 Electrical terms Industrial electric heating equipment GB5959.1 Safety of electric heating equipment Part 1 General part Safety of electric heating equipment Part 2 Special requirements for electric arc furnaces GB5959.2
GB5959.3
Safety of Electric Heating Equipment Part 3 Special Requirements for Induction and Conductive Heating Equipment and Induction Melting Equipment GB5959.8
GB10066.1
Safety of Electric Heating Equipment Part 8 Part of the special requirements for electroslag remelting furnaces General parts of test methods for electric heating equipment
GB10066.4
Test methods for electric heating equipment Indirect resistance furnace GB4208
Classification of shell protection levels|| tt||GB3805
Adoption instructions:
Safety voltage
1) The standards listed here are the corresponding IEC publications in the original text of IEC519-2 (1975), among which GB2900.23 refers to IEC50 "International Electrotechnical Vocabulary (IEV)" (1983) Chapter 841 "Industrial Electric Heating". GB5959.1, GB5959.2, GB5959.3, GB5959.8 and GB4208 respectively adopt the IEC publications of the same name. , respectively IEC519-1 (1984), IEC519-4 (1977), IEC519-3 (1988), IEC519-8 (1983) and IEC529 (1976) GB10066.1 and GB10066.4 respectively refer to IEC398 (1972) " General test conditions for industrial electric heating equipment" and IEC397 (1972) "Test methods for Matata resistance furnaces with metal heating elements", GB3805 refers to IEC364-4-411982) "Building Electrical Installations" Chapter 4 "Safety Protection" "Part of Chapter 41 "Electric Shock Protection". Guohao Technical Supervision Bureau approved on 1992-07-01 for implementation on 1993-03-01
3 terminology
GB5959.4—92||tt| |Except for the following terms, the rest are in accordance with the provisions of Chapter 2 of GB2900.23 and GB5959.1. 3.1 Electrode
refers to the component that is in contact with the heated charge or heat transfer fluid and transmits current to them. 3.2 Glass. Melting furnace
refers to a furnace equipped with inserted electrodes in the bath for melting glass. The glass is melted by the heat generated by the current flowing directly in the bath
3.3 melting device (applicable. Bath furnace)
Auxiliary heating device that melts the solidified bath agent. 3.4 Heat transfer fluid
refers to the liquid, gas or fluidized solid particles used to transfer heat to the charge. 3.5. Immersion heater
An electric heating element immersed in the bath agent that transfers heat energy to the bath agent through its protective sheath. Immersion heaters can be fixed or mobile. 3.6 Thermal circuit breaker and fuse
refers to the device that disconnects the power supply of the electric heating device when the temperature exceeds a predetermined value. The thermal circuit breaker is resettable, but the fuse is not resettable and should be replaced after each operation. 3.7 Over-temperature controller
When the operating temperature of the electric heating device exceeds a predetermined value, it is a device that disconnects the heating power of the device and keeps it in a power-off state. Note: The over-temperature controller can only be set by qualified personnel. 3.8 High and low temperature controller
refers to the device used to control the furnace temperature when the furnace temperature exceeds or falls below a predetermined value. Note: The high and low temperature controller can only be set by qualified personnel. 3.9 Leakage current
refers to the current flowing through or climbing over the insulating parts by the live parts of the electric heating device during normal operation. 3.10 Electric shock protection Class I device
refers to a device that adopts additional safety measures in addition to basic insulation. This additional safety measure consists in connecting accessible conductive parts to the protective (earth) conductor in the fixed wiring of the equipment. In this way, in the event of failure of basic insulation, accessible conductive parts will not become live.
Note: Basic insulation
Insulation used for live parts to provide basic protection against electric shock. 3.11 Electric shock protection Class 1 device
refers to a device that uses additional safety measures such as double insulation or reinforced insulation in addition to basic insulation. This device has no protective earthing and is not dependent on the condition of the equipment. —Insulation consisting of both basic insulation and supplementary insulation. Note: Double insulation
Supplementary insulation
is a separate insulation that can still provide electric shock protection after the failure of basic insulation. Reinforced insulation - A single insulation system used on live parts that provides a level of protection against electric shock equivalent to double insulation. 4 Classification of electric heating capacity according to voltage
4.1 Rated voltages belonging to the first and second voltage sections can be used (see GB5959.1 Articles 3.1.1 and 3.1.2). Note: The rated voltage of the electric heating installation and its protection measures should be selected so that workers are not subject to electrical injuries caused by leakage current under normal working conditions. 4.2 For salt bath furnaces and other baths, the maximum permitted rated voltage of immersion heaters should be 400V. 4.3 For vacuum furnaces, when selecting the voltage applied to the components in the furnace, consideration should be given to preventing flashover and breakdown. 5 Classification of electric heating devices according to frequency
According to the requirements of Article 3.2 of GB5959.1.
6 General requirements
6.1 Resistivity
GB5959.4—92
The resistivity of the heating conductor should be considered when calculating and selecting electric heating devices (applicable to indirect resistance Heating) or the change in the resistivity of the heated charge (applicable to direct resistance heating) during operation. 6.2 Auxiliary devices
Protective measures should be taken for the auxiliary devices such as the operation, transportation, loading and unloading of the resistance furnace so that they do not pose a hazard. 6.3 Exposed heating conductors
Generally, exposed heating conductors should be placed so that they do not come into contact with workers, the heated charge or the charge conveying device under normal operating conditions, but must comply with the "safety voltage" requirements in GB3805 Except for exposed heating conductors of the power supply. 16.4 Leakage current
Effective measures should be taken to ensure that leakage current through the furnace body containing the charge or through the charge will not cause any electrical damage. 6.5 Steam, sediment and slag generated by the charge. For furnace materials that generate steam, sediment, slag quenching, etc., the possible physical and chemical effects on workers and/or electric heating devices should be considered.
6.6 Requirements for salt bath furnaces and melting furnaces
6.6.1 The maximum allowable temperature of the furnace should be clearly marked on the temperature indicator or temperature controller (see Article 13.5.1). 6.6.2 Nitrite salt bath furnaces used for processing aluminum or wrought aluminum alloys shall not be used to process workpieces made of the following materials: a.
cast aluminum alloy;
b.| |tt||Aluminum alloys of unknown composition;
c.
Other light metals and their alloys;
d. Heavy metals and their alloys;
e. Steel.
If the furnace temperature may exceed 550℃ during operation, the warning "Not for use on light metal" should be clearly marked on the outer surface of the furnace shell. 6.6.3 For internally heated salt bath furnaces, the immersed heating element assembly (heater) should be positioned so that no deposits are produced on it. 6.6.4 For baths with a depth exceeding 1.5m, unless other precautions are taken, a melting device that can ensure preheating without any danger should be provided to form a vertical melting channel in the solidified bath agent. 6.6.5. For externally heated salt bath furnaces, the heating element assembly (heater) should usually only be installed on the furnace wall to avoid local overheating at the furnace bottom. 6.6.6 For large externally heated melting furnaces, if heating at the furnace bottom cannot be avoided, the following requirements should be met: the unit surface power of the furnace bottom heating should be lower than that of the furnace wall, and its value should be determined by the manufacturer according to the specific application conditions. Regulations; a.
b. The heating of the furnace bottom should be controlled individually: c.
The design of the circuit should ensure that when preheating the crucible, the furnace wall is heated first; only when the crucible is filled The furnace bottom heating can only be performed when the material is heated by the furnace wall alone and has been partially melted. d.
6.7 Heating of the solidified body in the bath
When preheating the solidified body in the bath, care should be taken to avoid surface spraying. For electrode salt bath furnaces, the melting device should be able to generate a large enough current in the initial stage to avoid ejection of objects in the tank. Adoption instructions:
1) The original text of IFC519-2 (1975) is: ", except for exposed conductors powered by power supplies that comply with the \Safety Extra Low Voltage" (SELV) requirements in IEC364-4-41" . The "safety voltage" of GB3805 is equivalent to the "safety extra low voltage" (SELV) of IEC364-4-41. 7 The earth should be regarded as a part of the effective circuit and should comply with the requirements of Chapter 5 of GB5959.1. |8 Nameplate, marking and circuit diagram
GB5959.4-92
In addition to the requirements listed in Chapter 6 of GB5959.1, the following content should also be included. 8.1 The rated temperature should be given on the nameplate. .
8.2 When the input power of the electric heating device in the cold state is more than 30% greater than its input power at the rated temperature, the maximum power value should be given on its nameplate
8.3 pair. Spare parts of heating element assemblies (heaters) and individual heating element assemblies (heaters), such as sheathed heating conductors, shall be securely marked with the name of the manufacturer or element manufacturer, model number, rated voltage and rated power 8.4. If necessary, the moisture-proof level should be given on the nameplate (see GB4208). 8.5 For heating covers and similar heating devices, if their operating temperature exceeds 250°C and the inner surface facing the heated object cannot be subject to GB5959. If the protective measures in 1 are not met, permanent warning signs should be provided. 8.6 The instructions for use should include all main parameters, such as the maximum allowable operating temperature. At the same time, necessary instructions for the hazards mentioned in Article 8.5 should be given to arouse the attention of workers. Note. 9 Overcurrent protection
should comply with the requirements of Chapter 7 of GB5959.1
10 Isolation and opening and closing
Precautions should be taken for electric heating devices that are manually turned off to cut off the power supply. Measures should be taken to ensure that the operator is in a safe position when the switch is turned on. 11 The connection to the power grid and internal connections
11.1 shall comply with the requirements of Chapter 9 of GB5959.1. 11.2 Three-phase four-wire resistance furnaces shall not be used for power supply. 12 Protection against electric shock
12.1 Protection against direct contact
12.1.1 For electric heating equipment with a working voltage exceeding AC 25V or DC 60V, if the furnace door or similar After the closing device (such as the cover or bottom plate) is opened, the furnace materials or tools will come into contact with the exposed heating conductors, and a device that can reliably cut off the power supply of all non-grounded heating conductors when the furnace door is opened should be equipped. 12.1.2 If electric heating is used. Accessible parts of the device (such as ceramic parts) will become conductive under normal operating conditions, the device shall also meet the requirements of Article 12.1.1
12.1.3 Touch of safety switch. The head should be opened manually with the operating lever and should be reliable in action. 12.1.4 The design and arrangement of the safety device should be able to protect it when the return spring of the operating mechanism breaks. 12.1.5 When an instantaneous contact safety limit switch is used. When operating, a separate device (such as a contactor) should be provided to reliably disconnect all wires (except the ground wire). If there are multiple security systems, they can act on the same device. 12.1.6 When it is necessary to use other control devices to replace safety switches with manually operated normally closed contacts, they must have the same level of protection.
Adoption instructions:
1) The original text of IEC519-2 does not have this article.
GB5959.4-92
Note: When the control device or related circuit fails or the power supply of these control devices is interrupted, it must still be able to provide protection. 12.1.7 When "safety voltage" that meets the requirements of GB3805 is used as a protective measure, the conventional electric shock protective measures for electric heating devices can be exempted. || tt | For hearth furnaces, etc., special attention should be paid and appropriate protective measures should be taken to ensure safety. For example, insulation or grounding measures should be taken for the charging mechanism that extends into the furnace, operators should wear appropriate shoes and gloves, and the working area should be kept dry. In addition, hazard warning signs should be set up to draw the attention of workers.
12.2.2 For continuous furnaces, if electrical protection against contact with exposed heating conductors cannot be provided due to the mode of operation, the furnace mouth structure should be able to prevent the furnace charge from coming into contact with exposed heating conductors when entering and exiting. 12.2.3 For some furnaces, if the grounding of the separable parts of the furnace body is disconnected before the power supply to the furnace is cut off through the contactor, special protective measures should be taken (such as setting up danger signs). This is the case, for example, with a pit furnace with a furnace pot, which is usually removable and itself serves as a cover for the heating chamber without a dedicated furnace lid. 12.2.4 If the protective line is in danger of being disconnected, appropriate measures should be taken, such as: a.
The measures described in Articles 10.2 and 10.3 of GB5959.1, and a separate protective line shall be laid;| |tt||b.
c
Use transformers with discrete windings to isolate from the power system and use differential circuit breakers;
d.
e.|| tt||Monitor the insulation condition.
12.2.5 During normal operation or failure, if a contact voltage with a risk of electric shock may be generated on the temperature sensor and its related measurement circuit, appropriate protective measures should be taken. 12.2.6 Immersion heaters used to heat liquids or other conductive media in electric heating equipment are not allowed to be used as electric shock protection devices. | | tt | And cause any harm to the staff, surrounding environment and furnace materials. 13.2 For parts of the electric heating device that are within the arm reach but do not need to be touched during normal use, the surface temperature may be higher than the value given in the table in Article 11.1 of GB5959.1, and a warning should be given in the instruction manual. Place appropriate warning signs on electric heating devices.
13.3 For situations that may be dangerous when a malfunction occurs (such as a malfunction of the temperature controller), the following measures should be taken: a. Provide a temperature-limiting safety device (see Articles 3.6 and 3.7). These devices should be functionally and electrically independent of each other; b. When using an electronic power controller and a circuit breaker at the same time and when using an electromagnetic contactor that frequently switches on and off, a separate contactor should be used to cut off the electric heating device. In the case of multiple furnaces, all control systems should cut off the power supply to their respective furnaces through their respective contactors. 13.4 In order to ensure safety when the control circuit fails, Table 1 specifies the corresponding safety devices and safety measures that should be equipped or taken for electric heating devices with different thermal safety levels. These safety devices include:
a. Thermal circuit breaker (A);
b. Fuse (B);
c. Over-temperature controller (C); ||tt ||d, high and low temperature controller (D).
Under supervised operation, the working status of the electric heating device should be checked regularly, and reasonable intervals should be set for inspections.
GB5959.4-92
The safety level applicable to the electric heating device should be given in the instruction manual. For example, thermal safety level 2 (according to Table 1). 13.5 Nitrite and nitrate salt bath furnaces. 13.5.1 For heat treatment of light metals, in order to control the temperature and prevent overheating, the furnace should be equipped with the following devices: a.
b.
Automatic temperature control device:
as specified in Article 13.3 The above-mentioned independent over-temperature controller and contactor are used to cut off the power supply of the electric heating device and start the alarm system when the salt bath temperature exceeds 550°C: c.
Temperature recording device (for multiple salt baths The furnace can use a multi-point recorder). For heat treatment of steel parts, the temperature recording device and any safety device in Article 13.5.1 can be omitted. 13.5.2
Table 1 Thermal safety protection
Level
0
1
Protected objects
Electric heating devices and their environment||tt| |Electric heating device and its
environment and charge
14 Fire protection and explosion protection
14.1 Nitrite and nitrate salt bath furnace
Protection scope
In the event of a malfunction, the electric heating device
will not cause any danger
In the event of a malfunction, the electric heating device or furnace
material will not cause any danger
Safety device|| tt||A
or
B
c
or
D
security measures
is supervised when running , and the charge is not dangerous
. Structural measures to eliminate
overheating
Depending on the application and installation site
Nitrite and nitrate salt bath furnaces for heat treatment of light metals, when empty, The salt bath temperature should not exceed 550°C. When processing magnesium alloy light metal, the maximum allowable temperature of the salt bath should comply with the requirements in Table 2. Table 2
Magnesium content, %www.bzxz.net
<0.5
>0.5~2.0
>2.0~4.0
>4.0~5.5
>5.5~10.0
Maximum allowable temperature of nitrite and nitrate salt bath, ℃
550
540
490||tt| | 435 | | tt | | 380 | Precautions should be taken for this\.
15 Instructions for inspection, putting into operation, use and maintenance of electric heating equipment:
1) IEC519-2 original text does not have "Preventative measures should be taken for this. This sentence. 15.1 Inspection and putting into operation|| |tt | Safety tests should be carried out in accordance with GB10066.1 and GB10066.41. 15.1.1 Requirements for insulation withstand voltage test
15.1.1.1 For electric heating devices with rated voltage exceeding AC 25V or DC 60V, the insulation withstand voltage test shall When delivered for use or with the consent of the user before shipment, it shall be carried out at the manufacturer after it has been installed and fully dried. 15.1.1.2 For electric heating devices belonging to Class 1 electric shock protection devices, it shall first be carried out in a cold state. The test voltage is AC 1500V, and then the same test is repeated at the maximum operating temperature. The test voltage should be equal to the rated voltage of the electric heating device. 15.1.1.3 For electric heating devices belonging to Class 1 electric shock protection devices, the test voltage should be at its maximum operating temperature. Carry out the test, the test voltage is AC 3750V
15.1.2 Leakage current
The leakage current measurement (GB10066.4 Article 6.19) should be carried out immediately after the electric heating device is installed and has been fully heated and After drying, proceed at the highest operating temperature. The electric heating device must be equipped with a safety grounding system; if necessary, appropriate leakage current detection devices should be installed to reliably detect any faults in the electrical insulation system and activate the corresponding protective devices. 2). 15.2 Use
15.2.1 The electrode and the fuse starter can only be inserted, moved and replaced when the electric heating device is disconnected from the power supply. This also applies to rated voltages below 25V AC and/or 60V DC. Electric heating equipment. 15.2.2 The melting device should be installed so that no sparks are generated at its joints. 15.2.3 For nitrite and nitrate salt bath furnaces, any salt that can cause burning of steel parts or explosion of light metals should be prevented. Bath overheating. Deposits can easily cause overheating and should be removed regularly. Proposed by the Ministry of Industry. This standard is under the jurisdiction of the National Industrial Electric Heating Equipment Standardization Technical Committee. The main drafters of this standard are Ge Huashan and Kou Jun.
1) IEC519-2. This sentence in the original text: "Proceed in accordance with IEC397 (revised edition)". The words "when necessary" in the last sentence of this article are not in the original text of IEC519-2.1 item.
Additional notes:
This standard is proposed by the Ministry of Mechanical and Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of the National Industrial Electric Heating Equipment Standardization Technical Committee. This standard is drafted by Xi'an Electric Furnace Research Institute. The main drafters of this standard are Ge Huashan and Kou Jun. Adoption instructions:
1) This sentence in the original text of IEC519-2: "Proceed according to IEC397 (revised edition)". 27 The words "when necessary" in the last sentence of this article are not in the original text of IEC519-2.1 item.
Additional notes:
This standard is proposed by the Ministry of Mechanical and Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of the National Industrial Electric Heating Equipment Standardization Technical Committee. This standard is drafted by Xi'an Electric Furnace Research Institute. The main drafters of this standard are Ge Huashan and Kou Jun. Adoption instructions:
1) This sentence in the original text of IEC519-2: "Proceed according to IEC397 (revised edition)". 27 The words "when necessary" in the last sentence of this article are not in the original text of IEC519-2.
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