What are the effects of temperature on cable selection?

Whether our colleagues in electrical design or factory electrical maintenance can not open the topic of cable selection, we often see that the AAC Cable selection size of the same equipment under the same power will be different in the work, some may be less than one or two levels, and some friends may be confused by which right? Why do you choose different? Today we will learn how to choose the cable and how to consider it from? What is the effect of temperature on the selection of cables?


1、 Cable selection
(1) Select cable according to temperature rise
We all know that when the conductor passes through the load current, the temperature of the conductor will rise, the conductor has insulation layer, and the conductor temperature shall not exceed the maximum temperature allowed for a long time by the conductor insulation, and the conductor will be damaged after exceeding.
(2) According to mechanical strength
When laying, the conductor has a minimum section allowed according to the laying mode and the distance between the support point and the distance.
(3) Select according to economic conditions
That is, choose the most economical way.
(4) Select by line voltage drop
We all know that when the current passes through the conductor, the voltage drop will be generated in the line due to the existence of line impedance. If the voltage drop is too large, the voltage at the end of the line, that is, the load end is too low, which will cause the equipment to fail to work or affect the equipment life. Therefore, it is required that the voltage drop cannot be too large, so the cable section should be selected reasonably.

(5) Cable selection shall meet the requirements of load protection
When the circuit is in fault, the protective device should act according to the specified time, whether it can operate reliably or not has a great relationship with the cable section. Therefore, we should consider the requirements of reliable action when choosing the ACSR Cable.
(6) Select cable according to the requirements of thermal stability
In case of failure of cable or electrical equipment, the cable shall meet the requirements of thermal stability, and the size of cable section shall be considered in order to meet this requirement. The maximum cross section is the final result by combining the above conditions.

Difference between low voltage cable and medium voltage cable

There are many kinds of AAAC Cables. According to voltage, they can be divided into low-voltage cable, medium voltage cable and high-voltage cable. What we can often touch and use in our life are low-voltage cable and medium voltage cable. How can we distinguish them? Some people say it’s 1kV, others say it’s 10kV. How to distinguish between low voltage cable and medium voltage cable? Now let Dr. Bao popularize science for you.
1、 Voltage level
According to different voltage levels, cables are habitually divided into low voltage power cables (3KV and below), medium voltage power cables (6kV ~ 35kV), high voltage power cables (66kV ~ 220kV) and ultra-high voltage power cables (above 220kV).
2、 Application and laying
Low voltage cable
Low voltage cables are used to transmit and distribute electric energy, mainly used in urban underground power grid, outgoing lines of power stations, internal power consumption of industrial and mining enterprises, and power transmission under river and sea water; It has the characteristics of reliable operation, no pole, no occupation of the ground, no hindrance to the view, less external influence and so on. The common laying methods include direct buried laying, AAC Cable trench laying, tunnel laying and wall laying.


■ medium voltage cable
MV cables are mostly produced as part of power generation and distribution networks for many applications such as utilities, petrochemicals, transportation, wastewater treatment, food processing, commercial and industrial markets. The common laying methods are underground direct buried laying; Laying of protective pipe (steel pipe, plastic pipe, row pipe, etc.); Laying of cable structures (cable trench, tunnel or working shaft, etc.); Laying in other public facilities (public facilities such as roads, railway bridges, tunnels or underground shopping malls, wharves, trestle roads, etc.); Underwater laying, etc.
3、 Observe the appearance
■ insulating materials
Low voltage power cable insulation material can be: PVC, cross-linked polyethylene;
Medium voltage power cable insulation material: cross linked polyethylene.
■ number of cable cores
The number of low-voltage power cable core is divided into: 1, 2, 3, 4, 5 core, 3 + 1 core, 3 + 2 core, 4 + 1 core
The number of medium voltage power cable core is divided into: 1 core, 3 core (so this kind of cable is mainly used for trunk transmission, 3-phase balance).
Minimum specification
The minimum specification of low voltage power cable is 1.5mm ²;
Minimum specification of medium voltage power cable: 3.6/6kv: 10mm ², 6/6kV, 6/10kV:16mm ², 8.7/10kV, 8.7/15kV:25mm ², 12/20kV:35mm ², 18/30kV:50mm ², 21/35 kV、26/35 kV: 50mm ²。
Color discrimination
Low voltage power cable cores are distinguished by different insulation colors, color lines or digital marks;
The core of medium voltage power cable shall be distinguished by ribbon.


Conductor structure
The conductor of low voltage power cable can be round non compact, round compact and irregular compact;
The conductor of medium voltage power cable must be round and tightly pressed( At present, the medium and low voltage power cables produced by our company all adopt circular compact structure
Basic structure of cable
The basic structure of low voltage power cable is conductor + insulation + filling + wrapping + outer sheath;
The basic structure of medium voltage power cable is conductor + three-layer coextrusion (conductor shielding, insulation, insulation shielding) + copper tape shielding + filling + wrapping + outer sheath.
Low voltage cable and medium voltage cable have different uses due to different voltage levels, composition, structure, etc. when choosing, you can choose according to your own actual situation.

Operation and maintenance of protective layer protector

In order to reduce the induced overvoltage of the metal sheath of single core AAAC Cable lines of 110kV and above, a protective layer protector should be installed between the ungrounded end of the metal sheath and the earth.

In case of system trip or line lightning stroke, special patrol shall be conducted for cable sheath protector.
The valve plate of protective layer protector may be damaged during power frequency overvoltage. The damage degree of the valve plate is related to the overvoltage of the protective layer. If the valve plate is damaged, it should be replaced.

At present, zinc oxide sheath protector is widely used in high voltage ABC Cable lines, and its residual work ratio is 2.5 ~ 4.0. Insulation resistance monitoring should be carried out for sheath protector, which can usually be tested at 500V / min.
The cross transposition box should be cleaned once a year, and the underground transposition box should also be checked for ponding.

How to solve these problems in PVC

1、 Troubleshooting of common faults in injection molding of ACSR Cables
Under note
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Forming cycle is too short. It should be extended appropriately.
(3) Insufficient injection pressure. It should be improved appropriately.
(4) The injection rate is too slow. It should be accelerated appropriately.
(5) Insufficient supply. The supply shall be increased.
(6) The temperature of the die is too low, so it should be properly raised. In particular, the cooling circuit of the mold should be set reasonably to keep the temperature of the mold uniform.


(7) The shape and structure of plastic parts are not designed reasonably or the wall is too thin. Adjustments should be made in the event of possible changes.
(8) The structure size of the pouring system is small. Gate and runner sections shall be enlarged appropriately.
(9) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the AAAC Cables.
(10) The strength of the die is not enough. The rigidity should be improved as much as possible.
· shrinkage marks
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The holding time is too short. It should be extended appropriately.
(4) The cooling time is too short. The cooling efficiency shall be improved or the cooling time shall be prolonged.
(5) Insufficient supply. The supply shall be increased.
(6) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(7) The shape structure design of plastic parts is unreasonable or the wall of plastic parts is too thick. Adjustments should be made where possible.
(8) Gate cross section is too small. It should be increased appropriately.
· weld marks
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The injection rate is too slow. It should be accelerated appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The gate section is too small. It should be increased appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) The structure size of cold material hole is too small or the position is not correct. It should be adjusted reasonably.
(8) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
(9) The dosage of release agent is too much. The amount of the product should be minimized.
(10) The insert is not set up reasonably. It should be adjusted appropriately.
(11) The raw material is not uniformly colored. The colorant with good dispersibility and the mixing time should be prolonged to make the raw material coloring even.
Flow marks
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The holding time is too short. It should be extended appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(6) Gate cross section is too small. It should be increased appropriately.
(7) The structure size of cold material hole is too small or the position is not correct. It should be adjusted reasonably.
(8) The raw material is not uniformly colored. The color additive with good dispersibility should be selected, and the mixing time should be prolonged.


Poor gloss
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) Screw back pressure is too low. It should be improved appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The structure size of the pouring system is small. Gate and runner sections shall be enlarged appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
(8) The dosage of release agent is too much. The amount of the product should be minimized.
(9) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
· bubbles
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) Insufficient injection pressure. It should be improved appropriately.
(4) The injection speed is too fast. It should be slowed down appropriately.
(5) The holding time is too short. It should be extended appropriately.
(6) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(7) The shape structure design of plastic parts is unreasonable or the wall of plastic parts is too thick. Adjustments should be made where possible.
(8) Gate cross section is too small. It should be increased appropriately.
(9) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the die.
(10) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
? uneven color
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The raw material is not uniformly colored. The color additive with good dispersibility should be selected, and the mixing time should be prolonged.
Burnt and black
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The injection pressure is too high. It should be reduced appropriately.
(4) The injection rate is too fast. It should be slowed down appropriately.
(5) Screw back pressure is too high. It should be reduced appropriately.
(6) Gate cross section is too small. It should be increased appropriately.
(7) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the die.
(8) The dosage of release agent is too much. The amount of the product should be minimized.
(9) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
· overfill edge


Fault analysis and Troubleshooting:
(1) The temperature of the melt is too high. The temperature of the barrel and the nozzle shall be properly reduced.
(2) The injection pressure is too high. It should be reduced appropriately.
(3) The injection rate is too fast. It should be slowed down appropriately.
(4) The holding time is too long. It should be shortened appropriately.
(5) There is too much supply. It should be reduced appropriately.
(6) The closing force is insufficient. It should be improved appropriately.
(7) The mold temperature is too high. It should be reduced appropriately.
(8) The shape structure design of plastic parts is unreasonable, and should be adjusted appropriately in case of possible changes.
(9) The strength of the die is not enough. We should try to increase its rigidity.
(10) The insert is not set up reasonably. According to the shape of plastic parts and the structure of the mold, proper adjustment shall be made.
Warping and deformation
Fault analysis and Troubleshooting:
(1) The barrel temperature is too low. It should be improved appropriately.
(2) Forming cycle is too short. It should be extended appropriately.
(3) The injection pressure is too high. It should be reduced appropriately.
(4) The injection speed is too fast. It should be slowed down appropriately.
(5) The holding time is too long. It should be shortened appropriately.
(6) The mold temperature is too high. It should be reduced appropriately.
(7) The cooling system of the mould is not reasonable, and the cooling circuit should be set reasonably according to the cooling requirements of the plastic structure.
(8) Gate cross section is too small. It should be increased appropriately.
(9) The setting of ejector is unreasonable. The area of jacking out and the point of jacking shall be increased as much as possible.
(10) The strength of the die is not enough. We should try to increase its rigidity.
· delamination
Fault analysis and Troubleshooting:
(1) If the melt temperature is too low, the temperature of the barrel and nozzle should be increased properly.
(2) The injection rate is too fast. It should be slowed down appropriately.
(3) The mold temperature is too low. It should be improved appropriately.
(4) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
? discoloration of the surface
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. It should be reduced appropriately.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The injection rate is too fast. It should be slowed down appropriately.
(4) Screw back pressure is too high. It should be reduced appropriately.
(5) The gate section is too small. It should be increased appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
2、 Troubleshooting of common faults in injection molding of soft PVC
Poor gloss on the surface of the product
Fault analysis and Troubleshooting:
(1) The processing temperature is too low, and the material is not plasticized. The processing temperature should be improved properly to improve the plasticizing effect.
(2) The mold temperature is too low. The mold temperature should be increased appropriately.
(3) The material fluidity is too bad, the raw material should be replaced or the raw material formula should be adjusted.
(4) The surface finish of mold cavity is too poor. The surface finish of mold cavity should be improved properly.
(5) During the forming process, the auxiliary agent precipitates, and forms scaling on the surface of the mold. The mold surface scale should be removed in time. If it is serious, the formula should be adjusted.
(6) Too much recycled material. The amount of recycled material shall be reduced appropriately.
(7) The material temperature is too high, and the resin is decomposed. The injection temperature should be reduced and the thermal stability system should be improved.
? shrinkage deformation
Fault analysis and Troubleshooting:
(1) The holding time is too short. The time of pressure preservation should be prolonged, especially when shrinkage occurs near the gate, the method of prolonging the pressure holding time can be used to solve.
(2) The pressure holding pressure is too low. The pressure holding time should be improved properly.
(3) Injection pressure is too low. Injection time should be improved appropriately.
(4) The molding temperature is too high. The forming temperature shall be reduced appropriately.
(5) The amount of feed is insufficient. The amount of feed shall be increased appropriately.
(6) The mold temperature is too high or the heating is uneven. The cooling efficiency of the mould should be improved.
(7) The mold is opened too early and the product cooling is insufficient. The cooling time of the product in the mold shall be extended.
(8) The thickness difference of the products is too big, and the parts of the thickness of the products in process are prone to sag shrinkage due to the insufficient pressure. The design of the product shall be modified.
(9) Gate cross section is too small. It should be increased appropriately.
Under injection, lack of material
Fault analysis and Troubleshooting:
(1) Injection pressure or pressure retaining pressure is too low. Injection pressure or pressure retaining pressure should be increased appropriately.
(2) The holding time is too short. The holding time shall be extended appropriately.
(3) The processing temperature is too low. The processing temperature should be raised appropriately.
(4) The injection rate is too slow. The injection speed should be increased appropriately.
(5) The temperature of the mold or nozzle is too low. The temperature of the mold or nozzle shall be increased appropriately.
(6) Impurities or decomposition are blocked at the nozzle. The injection molding machine nozzles shall be cleaned.
(7) The gate section is too small. It should be increased appropriately.
(8) The exhaust hole of the mold is blocked. The plug in the die vent should be removed.
(9) Injection rate of injection molding machine is too small. The injection volume should be increased appropriately.
Coking decomposition
Fault analysis and Troubleshooting:
(1) The injection temperature is too high, the material is coking and decomposed, and the focus of the product is formed with the injection mold of the molten material. The injection temperature should be properly reduced to remove foreign matters from the dead angle of the barrel and the runner.
(2) Injection speed is too high. The injection rate should be reduced properly.
(3) Impurities or decomposition are blocked at the nozzle. The injection nozzle shall be cleaned.
(4) The thermal stability of raw materials is too poor. The material should be replaced or the formula adjusted to improve the thermal stability system.
(5) The lubricant is not used enough. The lubricant dosage should be increased appropriately.
(6) Poor exhaust of mould. The die exhaust system should be improved.
(7) The gate section of the mold is too small. The gate section of the mold shall be expanded appropriately.

Is the thicker the cable insulation, the better?

Many friends may think that the thicker the AAC Cable, the better the insulation performance, the more durable the cable, and the better the quality. In fact, this idea is taken for granted, and there are some misunderstandings.
This is because the insulation performance of cables depends on the technical indicators. The state has strict technical standards for cables. Compared with the cable thickness specified in the national standards, it is unnecessary to say that if the cable thickness is thinner, even if it is thicker, it is also unqualified as long as it exceeds the specified value.

When the thickness exceeds the standard, the performance of the cable will be affected, such as the service life will be greatly shortened. Because when the cable is laid and put into use, it will be in the state of continuous power supply, and the heat will be generated in the process of power supply. If the thickness exceeds the standard, although the insulation looks better, the result is that the heat is difficult to dissipate( Learn more cable technology, please click here, a large number of dry goods waiting for you) with the accumulation of time, more and more heat accumulation, of course, will affect the normal service life of the cable.


When the situation is serious, it will even lead to short circuit, power failure, causing greater damage.
The so-called “too much is not as good as it can be”. Those who meet the national standards are the best.

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The 15 most common problems of cable materials!

The power cable industry is a large pillar industry in China. The production process needs high production standards, and maintains the safe operation of the whole industrial system. Therefore, the majority of power cable manufacturers need to conduct a very strict audit and purchase of cable production materials.
The following will introduce the problems of AAAC Cable materials, and provide some help for selecting materials.

1. heat shrinkable cap: the specification and size are not allowed, the material memory is poor, the long-term burning shrinkage, the strength is poor, etc.
2. copper tape: uneven thickness, oxidation discoloration, insufficient tension, lotus edge, insufficient softening, hard, short head, poor connection, falling off paint film or zinc layer, etc.
3. steel wire: the outer diameter is too large, the zinc layer falls off, the zinc coating is insufficient, the short head is too much, the tension is not enough, etc.
4. copper rod: made of recycled copper, surface oxidation and discoloration, insufficient tension, non-circular and so on.
5. XLPE insulation: short anti scorching time, easy to cross-linking in the early stage, etc.
6. silane crosslinking material: poor extrusion temperature control, poor thermal extension, rough surface, etc.
7. halogen free adhesive coated flame retardant tape: easy to break, wrinkle of belt plate, drawing of wire, poor flame retardant, smoke, etc.
8. PP filling rope: poor material, uneven diameter, poor connection and pimples.
9. PVC Plastics: many impurities, unqualified thermal weight loss, porosity in extrusion layer, difficult to plasticize, color incorrect, etc.


10. glass ribbon: thick, drawing, low density, mixed with organic fiber, easy to tear, etc.
11. PVC wrapping: thick, tensile force is not enough, short head is too much, thickness is uneven, etc.
12. refractory mica belt: lamination, insufficient tension, sticky, wrinkle of belt plate, etc.
13. alkali free rock wool rope: uneven thickness, insufficient tensile force, many joints, easy to fall powder, etc.
14. PE filler strip: hard, easy to break, and unequal radian.
15. non woven fabric: the actual thickness is wrong, the tension is not enough, and the width is uneven.

.For more information on cables, click Joy ’cable Blog

Seemingly the same national standard cable, the difference is not just the price!

Often hear AAC Cable practitioners complain: it is too difficult to sell national standard. You say you are national standard, and those who sell non-standard also say that he is national standard. As a result, the price is more than 10% cheaper than yours, so it is helpless. Here, we will review and summarize the four rounds of the national standard and non-standard confrontation.

The first round of confrontation is calculated by the weight of copper. At first, it worked, but the national standard ignored a problem. Your copper is oxygen free rod, but not standard one. When the weight of waste copper and oxygen free rod is the same, the price of waste copper and oxygen free rod is 10%. So the national standard cable spent great efforts in propaganda, and finally failed, the difference between national standard and non-standard guarantee bottom was 10%.
The second round of confrontation, auxiliary materials on the work and materials. The state has increased resistance inspection, and also increased the inspection of conventional products. Non-standard cables began to work on auxiliary materials. If copper accounts for 70% of the cost of cables, the cost of auxiliary materials takes up about 20%, which is 20% of the cost. If the materials are used a little bit, the price is 5% different from that of national standard. We also see that many of the cables exposed recently have problems with accessories.

The third round of confrontation, the wire is short to the cable short meter. In fact, the short meter has always existed, this is the most difficult to check. It used to be common on BV, such as 95 meters, 98 meters, or 90 meters. Now, because of the increase of inspection items, all the products inspected have been included, so non-standard ones have begun to work in this direction again. I hope you can draw attention, 100 meters reduced by 1 meter, 1% of the profit came out.
The fourth round of confrontation, both sides thick and thin. That is to say, both ends of the cable are national standard, the middle part is non-standard, so it saves a lot of costs, the corresponding cable price will be much lower. You can’t cut the cable from the middle, so the leak is just drilled.
Huaxing Cable Factory has always adhered to the business philosophy of “innovation technology +, continuous improvement +”. Strictly control the product quality, select the high-quality raw material supplier as the cooperation unit, and 99.99% and above oxygen free copper is used for copper core. The products are superior to our standards, have better conductivity, lower consumption, safer and environmental protection. Is many consumers more assured choice!

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Requirements for fire protection certification of cables

In order to solve the long-standing problem of the lack of flame retardant classification standards in the AAC Cable industry and the imperfection of the evaluation index dimension in the original flame retardant standard system, the former Sichuan Fire Protection Research Institute of the Ministry of public security organized relevant units to take the lead in formulating the national mandatory standard GB 31247-2014 “classification of burning performance of cables and optical cables”, which was issued on December 5, 2014 and officially implemented from September 1, 2015. On the basis of full investigation and verification test, combined with the relevant requirements of EN 13501-6:2014 and the actual grading assessment needs of domestic cables and optical cables, GB 31247-2014 finally forms four grades A, B1, B2 and B3. The assessment dimensions include the main grading indexes such as combustion calorific value, flame spread, heat release, smoke production characteristics and smoke density, and the main grading indexes such as combustion droplet / particle, smoke emission and so on The toxicity and corrosivity of flue gas are three additional classification indexes. Generally speaking, these assessment indexes can more truly reflect the combustion characteristics of cables under actual fire conditions, and the evaluation of cable combustion performance grade will be more scientific, reasonable and practical.


In order to promote the flame retardant cable classification standard and link up the related testing and certification work, China Quality Certification Center and National Center for quality supervision and inspection of fire resistant building materials (nftc) have cooperated closely since the standard drafting stage to develop cqc17-463416-2015 “implementation rules for classification certification of burning performance of cables for construction Engineering”, Since 2015, we have held publicity and implementation meetings on standards and certification in Nanjing, Yixing, Guangzhou, Jinan, Chengdu and other places, actively promoting the application and acceptance of standards to relevant architectural design units and architectural design specifications, and achieved good promotion results. This work also lays a foundation for the domestic flame retardant cable export to meet the relevant technical requirements of the European Union CPR building product regulations.
Considering the identification and type selection requirements of cables with different flame retardant grades, the new version of the implementation rules (cqc17-463416-2020) in 2020 adds the model naming provisions of cables with flame retardant grades, and adds some products with flame retardant grades B1 and B2, such as wdzb1-yjy, zb2-bv, etc., and provides the new products to Jiangsu Shangshang, Wuxi Jiangnan, Wuxi Jiangnan, etc Some excellent cable enterprises such as Jiangsu Zhongmei and Sichuan Xinshiji have issued the first batch of new CQC fire prevention certificates.


The new version of CQC fire prevention Certification Implementation Rules includes power cable, wiring, control cable, computer cable, flexible cable, communication cable, optical cable and other construction cable products. The CQC fire prevention certification mark shown in Figure 1 can be applied to the certified products to prove that the products meet the relevant requirements of each flame retardant grade. After the implementation and promotion of flame retardant classification standards and certification, many laboratories including the National Center for quality supervision and inspection of fire resistant building materials, the National Center for quality supervision and inspection of wire and cable products (Yixing) and Shanghai ABC Cable wisdom Testing Technology Co., Ltd. (istcw) have obtained the relevant recognition of the flame retardant classification certification.
3、 Some misunderstandings and development prospects of flame retardant graded cables
In recent years, with the popularization and application of GB / T 19666 “general rules for flame retardant and fire resistant wires, cables or optical cables” and the flame retardant categories of ZA, ZB, ZC and ZD, due to the common sense tendency to code a-b-c-d level arrangement and the non-metallic content from high to low in the test, there are a large number of manufacturers, users and technical institutions in the industry that bundle flame retardant ZA, ZB, ZC and ZD are flame retardant levels, It is also understood that flame retardant class A is superior to (covering) class B, class C, and then to class D.
However, the standard analysis shows that the main difference of bunched flame retardant (ZA, ZB, ZC, ZD) categories lies in the different application and evaluation occasions, and the grade relationship or classification concept is not mentioned in the relevant standards. In particular, in the article “understanding and suggestions on the requirements of Flame Retardancy for wiring bundles” recently received in the Journal of quality and certification, verification tests were carried out on five groups of samples of typical wiring products from different manufacturers: za-bv 450 / 750V 2.5 and wdza-byj 450 / 750V 2.5, and the above ten groups of samples were tested in accordance with GB / T 18380 series standards Class C and class D combustion tests. By analyzing the carbonization height of the samples before and behind the steel ladder after the combustion test, the results show that the carbonization height of most of the bundles of this kind of wire products is higher than that of class A, and even some of the samples have passed the flame retardant class a test, and the flame retardant class D is unqualified. The bundle combustion verification test of this cloth and wire product also proves that the traditional bundle flame retardant ZA, ZB, ZC and ZD do not belong to the classification of flame retardant performance, and there is no relationship between high and low levels.


In contrast, GB 31247-2014 “classification of burning performance of cables and optical cables” scientifically and systematically classifies the burning performance of cables used in construction projects through multi-dimensional index assessment and evaluation, which is close to the requirements of actual building fire safety scenarios, and gives a clear description of the performance grade in the standard, for example, the burning performance B1 is flame retardant 1 cable (optical cable), The combustion performance of grade B2 is flame retardant grade 2 cable (optical cable), etc( This also lays a solid foundation for the reference and acceptance of GB 31247-2014 flame retardant classification in GB 51348 standard for electrical design of civil buildings.
It is believed that with the promulgation and heavy implementation of GB 51348 “standard for electrical design of civil buildings” and subsequent relevant design specifications, a more unified and clear understanding and application of the classification of combustion performance of cables and optical cables will be formed from user units, design units, supervision units, testing and certification Institutions to manufacturers and other relevant policies, The flame retardant cables and optical cables used in domestic construction projects will also usher in a brighter development prospect.

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Discussion on cable production process: extrusion process

Extrusion process is an indispensable part in cable manufactor, which includes insulation and sheath production process. Insulation production methods include coating, winding, extruding and their combination. Now the main insulation production is coating (winding wire, no longer in the scope of production license management) and extrusion (wire and cable).
1、 Plastic extrusion equipment and mould
1. Plastic extrusion equipment: extruder
1.1 working principle of the extruder: the screw of specific shape is used to rotate in the heated barrel, and the plastic sent from the hopper is pressed forward to make the plastic plasticize evenly. The plastic is extruded into products of various shapes through the head and molds of different shapes.
1.2 basic structure of extruder: the extruder is composed of extrusion system, transmission system and heating system (cooling).
1.2.1 extrusion system (including screw, barrel, hopper, head and die)
① Screw: screw is an important part of the extruder. It is made of high strength, heat-resistant and corrosion-resistant alloy steel. Its function is to push the plastic forward, produce pressure, stir, and produce friction heat with the plastic when rotating, so as to melt the plastic and continuously send the melt into the extruder. It is directly related to the application scope and productivity of the extruder.


② The barrel is a metal barrel, which is generally made of alloy steel or composite steel lined with alloy steel with high strength of heat resistance and pressure resistance, strong wear resistance and corrosion resistance. It and screw constitute the basic structure of the extrusion system for plastic plasticization and conveying. The length of the barrel is generally 15 ~ 30 times of its straight diameter, so as to make the material fully heated and plasticized. The barrel should have enough thickness, rigidity and smooth inner wall. A resistance or induction heater measuring device and a cooling system are installed outside the barrel.
③ The hopper is usually a conical container with a capacity of at least 1 hour. The bottom of the hopper is equipped with a device for cutting off the material flow. The side of the hopper is equipped with a sight hole for calibration and measurement.
④ The head is the forming part of the extruder. The head is mainly composed of filter device (perforated plate and screen), connecting pipe, diverter, mold core seat, mold, etc.
1.2.2 transmission system
Its function is to ensure that the screw rotates at a constant speed with the required torque and speed. Generally, Weidong system includes three necessary links: the prime mover, the transmission and the reducer. It is required that the rotation speed of screw should be stable and not change with its load, so as to ensure the uniform quality of products. But in different occasions, the screw is required to be able to change speed to meet the requirements of extruding products of different specifications with one equipment. For this reason, drive motor generally uses rectifier motor, DC motor, etc.
1.2.3 heating and cooling system
Function: through the heating or cooling of the barrel, to ensure that the plastic is always extruded within its process temperature range.
① Heating method of the extruder: when the screw speed of the extruder is kept constant, the main factor affecting the stability of the rubber output is the body temperature of the extruder.
There are usually two heating methods for cross-linking extruder, which are carrier heating (such as adding hot water) and resistor heating. The carrier heating is characterized by uniform heating and not easy to produce local overheating, but the carrier heating temperature has high requirements on the sealing performance of the system and high cost. Therefore, it can be used in the extruder with higher temperature control requirements.
② Cooling of plastic machine: in the extrusion process, the temperature of the plastic in the barrel is often too high and the heat is too much. If too much heat is not discharged in time, it is easy to cause “pre crosslinking” of the material; The extruder is generally cooled in two parts: barrel cooling and head cooling.
a. Barrel cooling (there are two methods of barrel cooling, air cooling and water cooling)
From the cooling effect, the air cooling is relatively soft, the cooling speed is slow, and the water cooling speed is fast, but it is relatively fierce, and it is easy to cause strong “thermal vibration”. The design of the water cooling system is relatively complex. In addition to its good cooling effect, it should also have good sealing to prevent leakage, so that when cooling is not needed, the water cooling system can be used for cooling, It is better to make all the water in the cooling system escape, so as to avoid the blockage of the cooling system due to the scale generated by the water storage. The structure should also be conducive to maintenance. Most of the current water cooling systems turn out the spiral groove on the outer surface of the barrel, and then coil the cooling pipe.


b. Screw cooling
The main purpose of the cooling screw is to prevent the plastic from overheating. In addition, the feeding section of the cooling screw is also conducive to the conveying of materials to the machine head. The cooling medium into the screw is usually water, and the water temperature can maintain a certain value according to the requirements. Even the cooling length of the screw can be adjusted, sometimes the whole length of the screw can be cooled, sometimes only part of the screw can be cooled, and the screw temperature of the latest designed extruder can be adjusted by zones.
1.2.4 screw parameters of extruder
The main parameters of screw are diameter length diameter ratio, compression ratio, pitch, groove width, helix angle, clearance between screw and barrel, etc.
① Screw diameter D: the size of the extruder is usually expressed by the screw diameter. The larger the diameter is, the larger the amount of glue will be. The extrusion amount is approximately proportional to its square. Therefore, a small increase in the screw diameter will cause a significant increase in the extrusion amount.
② Length diameter ratio L / D: the ratio of length L and diameter D of screw working part. When the screw diameter is fixed, increasing the length to diameter ratio means increasing the length of the screw. The larger the length to diameter ratio is, it is conducive to the full plasticization of the material. At the same time, it can produce greater pressure to ensure that the product is more dense and improve the quality. However, too large ratio of length to diameter is not enough, resulting in over plasticization of cross-linked materials, leading to early cross-linking of materials. For extruders of cross-linking units, the ratio of length to diameter is generally between 20 and 25 times.
③ The compression ratio is the ratio of the volume of the first slot in the feeding section to the volume of the last screw slot in the homogenizing section. The selection of compression ratio should not be determined according to the raw materials. The properties of plastics are different, and the compression ratio is also different. The particles are large and the compression ratio is small; The compression ratio of LDPE is 2 ~ 3 times.
④ Groove depth h: the difference between the outer radius and the root radius of the thread. According to the compression requirements, the groove depth of the feeding section is greater than that of the melting section, and the melting section is greater than that of the homogenizing section. The large groove depth of the feeding section is conducive to improving its conveying capacity. The grooves of the melting section and homogenizing section are shallow, and the screw can produce a higher shear speed for the material, It is beneficial to the heat transfer from the cylinder wall to the material and the mixing and plasticizing of the material.
2. Die of extruder
2.1 the die of extruder is divided into extrusion type, semi extrusion type and extrusion type( (see figure below)

2.2 characteristics of various molds:
2.2.1. Advantages of extrusion type
1) The structure of extruded plastic layer is compact and firm.
2) The insulation is closely connected with the conductor without gap, and the insulation strength of the extruded layer is reliable.
3) The outer surface is flat and smooth.
2.2.2. Disadvantages of extrusion type
1) It is not easy to adjust the eccentric core.
2) The accuracy of die matching is high, and the product quality is highly dependent on the die.
3) The bending of extrusion line is not good.
2.2.3 advantages of tube extrusion
1) The extrusion speed is fast.
2) The operation is simple and the core adjustment is easy.
3) Large clearance, small wear and long service life.
4) It is convenient to match the mold.
5) The extrusion strength of plastics increases with the directional drawing of plastics.
6) The sheath thickness is easy to control.
2.2.4 disadvantages of tube extrusion type
1) The density is poor.
2) The combination of plastic and wire core is poor.
2.2.5 semi extruded pipe: it absorbs the advantages of extruded pipe and extruded pipe.
2、 Crosslinking methods of cross-linked polyethylene materials are divided into chemical and physical methods
1. Chemical crosslinking: peroxide crosslinking (1) steam crosslinking (SCP); 2. Infrared crosslinking (RCP) and dry crosslinking; 3. Mdcv crosslinking; 4. Pressurized lava salt crosslinking (PLCV) process; 5. Silicone oil crosslinking (fzcv) process.) And silane graft crosslinking (one-step, two-step, copolymerization).
2. Physical crosslinking: high energy radiation crosslinking.

Seemingly the same national standard cable, the difference is not only the price

Often heard ACSR Cable practitioners complain: it is too difficult to sell national standard. You say you are national standard, and those who sell non-standard also say that they are national standard. The price is more than 10% cheaper than yours, so it is helpless.
Here, we will review and summarize the four rounds of the national standard and non-standard confrontation.


The first round of confrontation is calculated by the weight of copper. At first, it worked, but the national standard ignored a problem. Your copper is oxygen free rod, but not standard one. When the weight of waste copper and oxygen free rod is the same, the price of waste copper and oxygen free rod is 10%. So the national standard cable spent great efforts in propaganda, and finally failed, the difference between national standard and non-standard guarantee bottom was 10%.
The second round of confrontation, auxiliary materials on the work and materials. The state has increased resistance inspection, and also increased the inspection of conventional products. Non-standard cables began to work on auxiliary materials. If copper accounts for 70% of the cost of cables, the cost of auxiliary materials takes up about 20%, which is 20% of the cost. If the materials are used a little bit, the price is 5% different from that of national standard. We also see that many of the cables exposed recently have problems with accessories.


The third round of confrontation, the wire is short to the cable short meter. In fact, the short meter has always existed, this is the most difficult to check. It used to be common on BV, such as 95 meters, 98 meters, or 90 meters. Now, because of the increase of inspection items, all the products inspected have been included, so non-standard ones have begun to work in this direction again. I hope you can draw attention, 100 meters reduced by 1 meter, 1% of the profit came out.
The fourth round of confrontation, both sides thick and thin. That is to say, both ends of the cable are national standard, the middle part is non-standard, so it saves a lot of costs, the corresponding cable price will be much lower. You can’t cut the cable from the middle, so the leak is just drilled.
At present, the fourth one is the most worried. As long as the user and cable manufacturer conceal together, it can not be checked at all. Do you want to dig the cable out of the ground and measure it? This is why the price is so different, which is also called “national standard”.