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With analysis of damage phenomena

Author: ComeFrom: Date:2013/11/18 10:08:15 Hits:3739
Normal wear and failure of the belt
 
        In the belt running 2-3 years later, when it reached the fatigue life of the core wire , belt failure is a normal situation . After a long run , because the wire belt and failure to reach the fatigue life , which belongs to the ideal belt failure modes. Figure 1 is a 45- degree angle to the uneven broken jagged belt , which wire belt is typically achieve a normal result of the fatigue life .
        Likewise the teeth belt will fail, but this is not the ideal belt failure modes. In the long run , while the belt to maintain the original size and shape , but the belt teeth are worn . Canvas belt causes the exposed fiber frizzy looks rough belt teeth , shown in Figure 2 .
        Belt running 2-3 years do not need to take any improvement measures. Belt life due to different applications , as well as various objective factors which have a greater change . The factors affecting the life of the belt includes a matching level of quality pulley transmission power level , the environment , the belt installation tension , with the wheels , even how the cutting , packing, transport and install the belt .
 
Flex belt failure
 
        Belt bend fracture surface usually presents failure modes are aligned wire . As shown in Figure 3 .
        When bending the belt to a very small wire diameter , this failure mode occurs . Sharp bend belt will bend and damage the fiber core wire under enormous pressure , so that the tensile strength of the belt drops . Folding belt failure is the most common failure mode , the belt is usually improper operation , low installation tension pulley and the pulley diameter is too small , there are foreign substances and so on.
        Since the operating belt bending caused by improper reasons are: improper storage , improper operation , and improper belt installation before packaging and installation. In the low belt tension situation might have been running jump teeth until it reaches an acceptable tension , this phenomenon is called automatic tensioning .
        Automatic tensioning the belt or belt teeth loose side into the slot where the driven wheels wheels can most clearly observed . When the automatic belt tensioning when the belt teeth will pop groove pulley wheel until the tension of the belt tight side to strengthen the teeth and then forcing the belt pulley wheel into the slot . Wheel belt pulley groove when forced back , often leading to the belt and pulley dramatic point of contact , the instantaneous bending , this bending can cause damage to the belt wire . This part of the core wire damage is called folding . If you can not make the tight side tension pulley wheel belt teeth into the slot , then the belt will have to jump teeth , will also produce flex belt failure or damage to the teeth .
        Belt pulley into the diameter is too small will cause belt damage or bend the wire failure . Between the idler pulley and back below the predetermined minimum value , the belt and the idler pulley with the hand or with a small acute angle bend the belt , the belt will cause bending failure.
        Transmission of a foreign body into the belt will also generate bending , they will form between the belt and pulley two corners , making it appear belt wire bending . Pry tool to force the belt pulley belt will also be damaged. Improper use of tools ( such as a screwdriver ) belt after injury , belt will not fail immediately, but will decline in overall life belt by the entry of foreign matter or installation.
 
Impact load
 
        When intermittent or cyclical torque load driven equipment requirements than the normal level , the impact load to more than belt can withstand the force of the impact load transmission appeared . Failure of the belt tends to increase . Ordinary moments slipping belt can be used to mitigate the impact load , but the timing belt must transmit all loads.
        Can lead to severe impact loads to the belt wires form the uneven rough fracture , shown in Figure 4 . Belt teeth after tooth roots can develop into cracks and / or the teeth immediately after impact load shedding in the pulley . If an impact load occurs only once or repeated a fixed position of the belt loop , and the remaining portion of the belt teeth may still look normal. Figure 5 illustrates how the diffusion root cracks in the teeth . Root cracks may spread to form prongs . When the accumulation of excessive shear cracks in the teeth will be , will be only part of the tooth .
        Impact load generated by the slave devices may be part of an operation inherent in the transmission system , or may come from accidental demanding situations , such blockage. If the drive system inevitably impact load , the core need to improve the strength of the belt , instead of the belt drive or bring about intermittently slip triangle.
 
Belt installation tension is too high
 
        Timing belt installation tension is too high will lead to belt teeth cut or broken. Many high belt tension in the belt tooth surface are clear signs of wear left a tooth . Figure 6 is a surface region of the belt is pressed over and root cracking examples. Tooth root cracking is usually extended to its neighbor by cracking at the core , the individual belt teeth will slowly fall off. Figure 7 is a high belt tension pulley is grinding on the big scene. Surface high pressure will cause the belt belt wear large area , resulting in belt wire exposed. To prevent such wear problems , proper installation of the belt tension must be accurately set .
 
Belt installation tension is too low
 
        Moderate to high load transmission installed in the belt tension is too low will lead to premature failure . Usually low belt tension caused by the failure mode performance jump teeth . Toothed belt jumping teeth of the belt to climb out of means corresponding cam groove , and the roots are no longer withstand the load . Further the load acting on the drive side of the belt tooth portion of the curved belt , and beat. When scrolling the teeth can lead to tooth rubber from tearing along the core wire . With the proliferation of rubber tear , the belt teeth begin to strip off the belt , as shown in Figure 8 . Failure caused by excessive tooth jump may seem like enough viscosity of rubber and cord . However , due to lack of viscosity caused by the failure of the belt exposed wires are usually kept clean , and hobbing different failure modes .
        When the belt teeth climb out of the tank and automatic tensioning pulley wheels when the front and the teeth to tear off the rubber belt prone to jump teeth . Skip tooth belt wire damage caused by the belt strength often leads to early failure , injury and failure bending wire breakage similar ( neat fracture ) are also similar to the impact load break ( jagged and angular ) . If the belt does not jump teeth and also continue to operate in the self- tensioning , which often occurs in the case of belt teeth excessive wear. This is called the hook -shaped tooth wear of wear , due to the belt tooth portion and the pulley does not match , as shown in Figure 9 . Wear due to the hook -shaped belt installation tension and not firmly enough in the case of the transmission system of the low tension caused by the change of the center distance .
        Usually improve belt installation tension belt to prevent premature jump hook shaped teeth and wear . If you increase the tension after installation still does not prevent the belt failure could be transmission structure is not strong enough , can not prevent bias. In order to improve the performance of belt use , is necessary to improve the supporting force transmission structure. If installation tension unrealistic increase , increasing the diameter of the pulley , the belt can pass at high load low tension . Suitable mounting tension values ​​can be obtained from the Gates of design software, calculation or seek support from the Gates salespeople through the design manual.
 
Pulleys are not parallel
 
        In operation the belt , the pulley shaft is angled or tapered pulley tooth problems exist in the processing , the load on the belt is uneven, there will be crushed between a toothed uneven . Belt from the tooth root cracking failure often at or from hosting the biggest belt tension began to tear the side and extended to the entire belt width , belt teeth eventually cut . Because of the relatively large fiber tension , the belt may also be extruded serious side significant wear , it is possible to climb out of the belt roll or pulley ribs in place.
        When not running parallel to the belt with the pulley ribs , if the belt is squeezed between two opposing wall , the sides of the belt can cause severe wear . In this case , the belt will crack or tear from both sides from the tooth root . This will eventually extend to the entire tear belt causes the belt tooth portion of the shear .
        Belt pulley run when a wall on both sides and a pulley no ribs on both sides , if the two pulleys are not parallel , it will be part of the belt pulley to move no wall , no wall pulleys in this part of the belt will bear the entire load and may produce a concentrated area of wear after running for some time. Figure 11 is the most concentrated tooth wear , other places do not wear. There may be at the root of wear areas below the cracks . Belt tooth surface fatigue strength or will eventually lead to premature failure of the belt.
 
Pulley failure
 
        Whether it is due to the belt pulley production does not meet the standards or worn beyond standard caused premature failure is often difficult to identify. Partly because when the belt fails , few people go to carefully check the pulleys , and belts are usually considered to be their own problems . Belt running on a pulley size problem when it appears highly tooth flank wear , while the belt on the side of the canvas into a blur of villous or flake . As shown in Figure 12.
        Arc tooth belt runs over a small diameter pulley system , a large area of ​​the body will bring the belt tension and the fracture splitting , as shown in Figure 13 . Trapezoidal (XL, L, H) is usually a belt or toothed tooth shear fracture , but not quite common belt tensile fracture .
        Excessive tension may cause more wear of the pulley . Run time is very long or canvas belt tooth surface may wear away completely , this situation indicates that the wear on the pulley has been generated . After the belt wear will make contact with the wire pulley , causing the outer circumferential groove pulley wheel also wear. Tooth top pulley wheels are raised is a sign of wear and tear , as shown in Figure 14 . Note: The milled surface is very sharp with a screwdriver to feel better , to prevent hands were scratched. In this case , you should replace the pulley .
        In corrosive air , pulley most likely to be quickly worn. Severe wear of the pulley wheels usually presents pulley groove wear and reduce machining diameter. Failure causes the belt pulley and wear performance of a typical toothed belt tooth bottom portion regional polishing damage size and shape. After a hard chrome plating over a pulley can extend its life in corrosive air. Another case , if the new belt after replacement lower than the previous life of the belt pulley is also carefully check the excessive wear and tear.
 
Pulley beating
 
        Belt pulley runout run the system, when the belt tension pulley rotate periodically lift . The more severe beating , the maximum tension on the rise higher . Affected by this, the bottom looks like the teeth are ground as shown in Figure 15 . The band body may be crushed and high belt tension phenomena resulting in a moderate size of the pulley is similar to the operation . The tension changes often lead to extreme cyclical belt teeth tear or fracture belt tension .
        Cone pulley to put the installation, or the smallest pulley on the basis of re- light hole reaming after installation, are often prone to beat. How to follow the standard installation, and how to ensure with shaft hole .
 
Corrosive air
 
        Belt corrosive applications running in the air , such as foundry mixer , iron ore processing equipment, phosphate mining transportation equipment, toothed belt tooth flank and base height would wear, wear bright area often . Figure 16 is in a highly corrosive environment protection and strong GT2 belt is worn . In corrosive air pulley usually wear faster, so the pulley and the belt should be replaced together . In order to extend the life of the belt and pulley , there is clean air is best to install a pressurized enclosures to prevent corrosive and contaminated objects into dust .
 
High temperature degradation
 
        When the rubber belt to work after high temperature ( above 85 ℃) for an extended period of time , the rubber composition will harden due to bending during operation cause back cracking. The cracking of the direction parallel to the teeth , and often occurs in the middle toothed . Figure 17. Because the teeth shear belt tension will lead to fracture .
        High temperature rubber belt structure may be used for this application requires a high temperature environment , the belt structure of these special increases the life of the belt .
        If you want to understand the special high temperature structural belt is a belt can improve performance in specific applications , please contact Gates salespeople .
        Strong security gates GT2 belt material with a thermoplastic polyurethane materials are (with the melting point ) . When the temperature exceeds 85 ℃ , with teeth may become soft and deformed. In addition , the core wire will be completely lost their ability to support the body on the tape . Figure 18 is exposed to high temperature conditions under strong security GT2 belt.
 
Chemical degradation
 
        Failure in the rubber belt and the volatile organic solvents and ozone environment under high temperature conditions similar failure . Rubber components will harden , belt will show back cracking. However, the form of cracking is not consistent because the hardening of the rubber composition of the belt surface occurs almost , which may lead to cracking of the belt to the aspect , there may have various shapes .
 
Foreign matter into
 
        When foreign material from entering between the pulley and the belt , causing damage to the teeth and the core will bring . Inner core typically fracture ( Figure 19 ) , or failure due to excessive bending ( Figure 20 ) shortly. After the core part of the belt breaks, the entire root tensile strength of the belt will fall significantly. This also leads to a significant decrease in belt life . If you find that the belt is damaged , you should replace the belt and pulley checked , and if found damaged pulley , it should be replaced.
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