Wire bending and swing test
About wire swing
Currently, before testing the swing, customers will be required to provide the following parameter descriptions. The definition of the test parameters directly affects the quality of the product test data. Including the following main parameters:
■Swing angle
■Swing speed
■Sample load
■Swing radius
■Distance between the rotation axis and the load position
The main parameters of the equipment are as follows:
Wire swing has standard tests, corresponding to specific safety regulations, such as UL BS GB GS.
When customers require swing, it is necessary to understand the customer's test conditions, including the swing angle, frequency, hoisting weight, fixture R angle, standard and other basic requirements. Generally speaking, under the same conditions, the larger the swing angle, or the heavier the hoisting weight, the smaller the fixture R angle, the faster the frequency, the worse the wire swing, and vice versa.
Wire with good bending performance
■ Filling structure design (general)
Filling is to ensure the roundness of the wire on the one hand, and to protect the wire from damage when it is bent on the other hand, and to play an anti-swaying role. Commonly used fillers are: nylon yarn (bulletproof yarn), Kevlar, cotton yarn, PP hem-p, hem-p rope, PVC strips, etc. In terms of material anti-swaying performance, Kevlar is better than nylon yarn (bulletproof yarn), and nylon yarn (bulletproof yarn) is better than cotton yarn, cotton yarn is better than PP hem-p, hem-p rope, PP hem-p, hem-p rope is better than PVC strips, etc. When filling, nylon yarn (bulletproof yarn) and Kevlar are usually used for conductor filling or twisted wire filling; cotton yarn, PP hem-p, hem-p rope, PVC strips, etc. are usually used for twisted wire filling.
■Sheath part (main)
Sheath material directly protects the entire wire. Generally, thicker is better than thinner, softer is better than harder, and tighter is better than tighter in extrusion. Sheath is usually made of PVC, but also TPU, TPE and other materials. Since TPE and TPU have better elongation and elasticity than PVC, their anti-swaying performance is also better.
■Insulation structure design (important)
Insulation materials provide insulation protection for conductors. Depending on the material, common ones include FEP, PTFE, nylon, Haicui, anti-shrinkage PP, PE series (low-density LDPE, medium-density MDPE, high-density HDPE), semi-rigid SR-PVC, PVC, FoamPE (not recommended for testing swaying wires), FoamPE+Skin (not recommended for testing swaying wires), etc.; from the perspective of insulation materials, under the same conditions, FEP and PTFE insulation are used for better prices, followed by Haicui, followed by nylon, and finally anti-shrinkage PP (Not ordinary PP), then the PE series, choose the PVC series when the price is the lowest. Because the insulation thickness is too thin, the conductor will not be protected enough, and the insulation thickness is too thick, the line will be too hard. Neither will have the best effect, so it is also important to design the appropriate thickness; when the product is DP, HDMI and other video signal cables, the internal foam signal cable will be easy to break due to the foam material's lack of swing resistance. Therefore, the swing of this type of cable is mainly improved from the conductor twisting distance, composition, and assembly filling. If it doesn't work, it is also possible to replace the foam insulation material with a high swing resistance material with the same dielectric parameters.
■Conductor structure design (very important)
Conductors are usually divided into single or multiple conductors. According to the material, the common ones are bare copper, tinned copper, silver-plated copper, copper foil, copper-clad steel, etc. From the material point of view, copper foil has the best swing, and the thinner and softer the conductor, the better the swing performance; to improve the swing, multiple conductors are usually used, and nylon, Kevlar (bulletproof yarn) and other filling materials are added when necessary. When the price is better, bulletproof wire is added. If the price is not too beautiful, nylon wire can be used; for conductors composed of multiple conductors, under the premise of meeting the UL twist requirements, the smaller the twist, the better the swing. When the customer requires swing, first choose a conductor with a smaller single conductor, such as a single 0.05, 0.06, 0.08 conductor. If necessary, the conductor can be added with Kevlar (bulletproof wire), nylon, or the conductor twist can be reduced. No copper foil is required. As long as the price is in place, the material is expensive.
Common Problem Solving Cases
What are the common reasons for failing the bending swing test? And how can we improve it?
l Broken at the bend
(may break at the same place, or slightly scattered), or the wire break rate exceeds the regulations; this is a common phenomenon. The breakpoints are basically at the most vulnerable part of the structure. If one hand holds the plug and the other hand pulls the wire, the place with the smallest bending radius is the most likely place to break the wire. The slightly scattered break position is often because there is a grid at the end of the net, or the grid is crossed and misaligned, so the breakpoint is not necessarily one point, but multiple points, but generally very close.
l Broken at the riveted place
Currently, there are three workstations involved. The traditional practice is to manually make a small jig to manually hit the copper buckle, hot peeling, hit the copper buckle, remove the aluminum foil, and finally complete the production process. You may not have noticed that if the riveting is excessive, the conductor is very damaged, and when bending, the conductor will actually stretch in the insulation. As a result, the bend may not be broken, but the riveted part is completely broken or partially broken. It can be clearly seen through dissection. Pay attention to the dissection, heat the plug, and handle it carefully. This situation is also very common for manufacturers whose riveting quality is not controlled.
l The core wire comes out and the sheath shrinks inside
This is mainly because the temperature and pressure when the plug is formed are not enough to fuse the PVC and the wire sheath, especially when the sheath is large or the rubber sheath (this cannot be fused at all), so the bonding force between the sheath and the plug is insufficient, so that the displacement slides out during repeated bending. It is also possible that the adhesion of the wire itself is not well controlled. There are many tricks to control the adhesion.
l Large voltage drop
If the wire breaks during riveting contact, it will naturally cause the conductor cross-sectional area to decrease, which directly causes the temperature rise at that location to increase. If the wire breaks at the end of the mesh, although there will be a local temperature rise, it may not be transmitted to the part where the temperature rise is tested. However, no matter where it breaks, if the overall voltage drop is tested, it will definitely increase; if the standard method is followed, only the wire break at the riveting location will affect the voltage drop.
l The conductor can be seen when the insulation breaks
There are three reasons for this situation. One is that the insulation breaks under repeated bending; the second is that the PVC at the end of the plug mesh breaks, and the tear extends all the way, tearing the insulation; the third is that the copper wire breaks and pierces the insulation.
l The conductor pierces the insulation and is exposed
The bent part of the conductor breaks, the insulation becomes thinner after being stressed, the copper wire at the break will extend out of the insulation, and even conductors of different polarities will contact, causing arcing.
l Temperature rise
It is recommended to change the expensive material and use one with a low dielectric coefficient.
l The plug mesh tail is broken
The plug glue is not good, or the mesh design at the SR is not good, resulting in excessive deformation or stress concentration, causing the mesh tail to break. It is better to use a double-layer curved pattern.
Wire bending and swing test
About wire swing
Currently, before testing the swing, customers will be required to provide the following parameter descriptions. The definition of the test parameters directly affects the quality of the product test data. Including the following main parameters:
■Swing angle
■Swing speed
■Sample load
■Swing radius
■Distance between the rotation axis and the load position
The main parameters of the equipment are as follows:
Wire swing has standard tests, corresponding to specific safety regulations, such as UL BS GB GS.
When customers require swing, it is necessary to understand the customer's test conditions, including the swing angle, frequency, hoisting weight, fixture R angle, standard and other basic requirements. Generally speaking, under the same conditions, the larger the swing angle, or the heavier the hoisting weight, the smaller the fixture R angle, the faster the frequency, the worse the wire swing, and vice versa.
Wire with good bending performance
■ Filling structure design (general)
Filling is to ensure the roundness of the wire on the one hand, and to protect the wire from damage when it is bent on the other hand, and to play an anti-swaying role. Commonly used fillers are: nylon yarn (bulletproof yarn), Kevlar, cotton yarn, PP hem-p, hem-p rope, PVC strips, etc. In terms of material anti-swaying performance, Kevlar is better than nylon yarn (bulletproof yarn), and nylon yarn (bulletproof yarn) is better than cotton yarn, cotton yarn is better than PP hem-p, hem-p rope, PP hem-p, hem-p rope is better than PVC strips, etc. When filling, nylon yarn (bulletproof yarn) and Kevlar are usually used for conductor filling or twisted wire filling; cotton yarn, PP hem-p, hem-p rope, PVC strips, etc. are usually used for twisted wire filling.
■Sheath part (main)
Sheath material directly protects the entire wire. Generally, thicker is better than thinner, softer is better than harder, and tighter is better than tighter in extrusion. Sheath is usually made of PVC, but also TPU, TPE and other materials. Since TPE and TPU have better elongation and elasticity than PVC, their anti-swaying performance is also better.
■Insulation structure design (important)
Insulation materials provide insulation protection for conductors. Depending on the material, common ones include FEP, PTFE, nylon, Haicui, anti-shrinkage PP, PE series (low-density LDPE, medium-density MDPE, high-density HDPE), semi-rigid SR-PVC, PVC, FoamPE (not recommended for testing swaying wires), FoamPE+Skin (not recommended for testing swaying wires), etc.; from the perspective of insulation materials, under the same conditions, FEP and PTFE insulation are used for better prices, followed by Haicui, followed by nylon, and finally anti-shrinkage PP (Not ordinary PP), then the PE series, choose the PVC series when the price is the lowest. Because the insulation thickness is too thin, the conductor will not be protected enough, and the insulation thickness is too thick, the line will be too hard. Neither will have the best effect, so it is also important to design the appropriate thickness; when the product is DP, HDMI and other video signal cables, the internal foam signal cable will be easy to break due to the foam material's lack of swing resistance. Therefore, the swing of this type of cable is mainly improved from the conductor twisting distance, composition, and assembly filling. If it doesn't work, it is also possible to replace the foam insulation material with a high swing resistance material with the same dielectric parameters.
■Conductor structure design (very important)
Conductors are usually divided into single or multiple conductors. According to the material, the common ones are bare copper, tinned copper, silver-plated copper, copper foil, copper-clad steel, etc. From the material point of view, copper foil has the best swing, and the thinner and softer the conductor, the better the swing performance; to improve the swing, multiple conductors are usually used, and nylon, Kevlar (bulletproof yarn) and other filling materials are added when necessary. When the price is better, bulletproof wire is added. If the price is not too beautiful, nylon wire can be used; for conductors composed of multiple conductors, under the premise of meeting the UL twist requirements, the smaller the twist, the better the swing. When the customer requires swing, first choose a conductor with a smaller single conductor, such as a single 0.05, 0.06, 0.08 conductor. If necessary, the conductor can be added with Kevlar (bulletproof wire), nylon, or the conductor twist can be reduced. No copper foil is required. As long as the price is in place, the material is expensive.
Common Problem Solving Cases
What are the common reasons for failing the bending swing test? And how can we improve it?
l Broken at the bend
(may break at the same place, or slightly scattered), or the wire break rate exceeds the regulations; this is a common phenomenon. The breakpoints are basically at the most vulnerable part of the structure. If one hand holds the plug and the other hand pulls the wire, the place with the smallest bending radius is the most likely place to break the wire. The slightly scattered break position is often because there is a grid at the end of the net, or the grid is crossed and misaligned, so the breakpoint is not necessarily one point, but multiple points, but generally very close.
l Broken at the riveted place
Currently, there are three workstations involved. The traditional practice is to manually make a small jig to manually hit the copper buckle, hot peeling, hit the copper buckle, remove the aluminum foil, and finally complete the production process. You may not have noticed that if the riveting is excessive, the conductor is very damaged, and when bending, the conductor will actually stretch in the insulation. As a result, the bend may not be broken, but the riveted part is completely broken or partially broken. It can be clearly seen through dissection. Pay attention to the dissection, heat the plug, and handle it carefully. This situation is also very common for manufacturers whose riveting quality is not controlled.
l The core wire comes out and the sheath shrinks inside
This is mainly because the temperature and pressure when the plug is formed are not enough to fuse the PVC and the wire sheath, especially when the sheath is large or the rubber sheath (this cannot be fused at all), so the bonding force between the sheath and the plug is insufficient, so that the displacement slides out during repeated bending. It is also possible that the adhesion of the wire itself is not well controlled. There are many tricks to control the adhesion.
l Large voltage drop
If the wire breaks during riveting contact, it will naturally cause the conductor cross-sectional area to decrease, which directly causes the temperature rise at that location to increase. If the wire breaks at the end of the mesh, although there will be a local temperature rise, it may not be transmitted to the part where the temperature rise is tested. However, no matter where it breaks, if the overall voltage drop is tested, it will definitely increase; if the standard method is followed, only the wire break at the riveting location will affect the voltage drop.
l The conductor can be seen when the insulation breaks
There are three reasons for this situation. One is that the insulation breaks under repeated bending; the second is that the PVC at the end of the plug mesh breaks, and the tear extends all the way, tearing the insulation; the third is that the copper wire breaks and pierces the insulation.
l The conductor pierces the insulation and is exposed
The bent part of the conductor breaks, the insulation becomes thinner after being stressed, the copper wire at the break will extend out of the insulation, and even conductors of different polarities will contact, causing arcing.
l Temperature rise
It is recommended to change the expensive material and use one with a low dielectric coefficient.
l The plug mesh tail is broken
The plug glue is not good, or the mesh design at the SR is not good, resulting in excessive deformation or stress concentration, causing the mesh tail to break. It is better to use a double-layer curved pattern.