The main cause of high pressure hose failure

High pressure hose is an important part of hydraulic system of construction machinery such as concrete transporter, roller, excavator and loader. In use, leakage, cracking, cracking, loosening and other faults often occur. But people often simply replace the hose without analyzing the cause of the failure, and the same failure will be repeated soon after use. Loose or broken high-pressure hoses not only waste hydraulic oil, pollute the environment, but also affect work efficiency, and even cause accidents, endangering man-machine safety.Construction machinery pipes are divided into high pressure hose and low pressure hose. The high pressure hose is made of steel wire braided winding hose, which is generally composed of four parts: outer rubber layer, steel wire strengthening layer, middle rubber layer and inner rubber layer. The inner rubber layer is in direct contact with the hydraulic oil and is generally made of synthetic rubber. The load carrying capacity of the hose depends on the steel wire stiffener, which is the skeleton of the hose and is usually made of steel wire braided and wound. Multi-layer steel wire is mostly used for high pressure and ultra-high pressure braid, winding skeleton; Low pressure hose with braided cotton and twine instead of braided steel wire, generally used for low pressure oil return pipeline. The main reasons for the failure of the hose are improper installation and use, unreasonable system design and unqualified hose manufacturing.First, the failure of the external rubber layer1. Cracks on the surface of the hose: in a cold environment, cracks on the surface of the hose will make the hose bend. If there are cracks on the outside of the hose, pay attention to whether the rubber inside the hose is cracked, and decide whether to replace the hose immediately. Therefore, do not move the hose or repair the hydraulic system at will in a cold environment, if necessary, it should be carried out indoors. If you need to work in a cold environment for a long time, it is necessary to replace the cold hose.2. Foam on the surface of the hose: Foam on the surface of the hose is due to unqualified hose quality or improper use. If bubbles appear in the middle of the hose, it is mostly a hose production quality problem, and the qualified hose should be replaced in time; If air bubbles appear at the hose joint, it is likely due to improper fitting of the joint. The connecting end of the braided winding hose joint and the hose can be disassembled and buttoned. The removable joint sleeve and joint core are hexagonal, and the outer wall of the joint core is conical, which is easy to disassemble and assemble the hose. After the connector is connected to the nut, thread the steel wire to prevent loosening. The push-button hose connector consists of a connector jacket and a connector core. When assembling, it is necessary to strip the outer rubber layer, insert the joint core, tighten the joint sheath, and then fasten the hose with a mold on the special device to make the hose get a certain amount of compression and achieve tight connection.3. The hose is not broken but a large amount of oil leakage: if the hose is not broken but a large amount of oil leakage, the reason is that when the hose passes through the high-pressure liquid flow, the inner rubber is corroded and scratched until a large area leaks out of the wire layer, resulting in a large amount of oil leakage. This failure usually occurs at the bend of the pipe. Check and replace the hose to ensure that the bending radius of the hose meets the technical requirements in use.4. The outer rubber layer of the hose is seriously deteriorated, and the surface is slightly cracked: this is the performance of natural aging of the hose for too long. Due to aging metamorphism, the outer layer is constantly oxidized to make its surface embrittlement. With the extension of time, the embrittlement layer is deepened, as long as the hose is slightly bent in use, there will be a small crack. In this case, the rubber hose should be replaced.Second, the failure of the strengthening layer1. A rubber hose is broken. Braided wire rust near the fracture: If the hose is broken, strip the outer rubber layer and check the braided wound wire near the fracture for rust. This is mainly due to the wet or corrosive substance of the outer rubber layer, which weakens the strength of the hose and causes the hose to break under high pressure. This condition is usually accompanied by damage, scratches or severe deterioration of the outer layer, so that the outer layer loses its protective effect on the reinforced layer. At this time, we must first check and exclude the mechanical damage, chemical corrosion, high temperature baking and other adverse factors of the outer rubber layer, and then replace the hose. However, there are also cases where the outer rubber layer is maintained well, but the reinforcement layer is cracked, and the cracks are generally within 200mm of the hose joint. Most of the reasons are unqualified joints. As moisture enters the inner edge of the sheath, the reinforcement absorbs moisture and causes rust, resulting in reduced pressure strength and rupture of the hose.2. The rubber hose strengthening layer does not rust. However, irregular wire breakage occurs: if the hose is broken, peel the outer rubber layer and check that the strengthening layer is not rusty, but irregular wire breakage occurs in the direction of the length of the strengthening layer, mainly due to the high-frequency impact force of the hose. There are many crossing points between the steel wires in the reinforcement. When the pressure in the tube changes greatly, these intersection points also move with the change of pipe diameter, so that the steel wire friction with each other. If the rubber hose is subjected to high-frequency impact pressure, frequent friction will occur at the intersection, resulting in wire breakage. For the hose that is frequently affected by high frequency impact, the wire winding skeleton should be selected as the strengthening layer.Three, the inner rubber layer failure1. The rubber layer inside the hose is hard and cracked: rubber products are flexible and plastic by adding plasticizers. When the hose is working under high temperature and pressure, the hose will overheat and make the plasticizer overflow. In addition, when the overheated oil passes through the cylinder, valve or other components in the system, if there is a large pressure drop, the oil will break down, causing the rubber layer inside the hose to be oxidized and hardened. In this case, you must first check whether the working temperature of the hydraulic system is normal, and whether the throttle of the valve and the suction channel of the pump are smooth. Replace the hose after removing all factors that may cause the oil temperature to be too high and the oil to break down. If only the inner glue below the hose break is hard, and the upper part remains good, it means that the phenomenon of excessive extrusion, excessive bending or twisting at the hose break causes the oil to heat up and accelerate oxidation, which will cause the inner glue to be hard.2. The rubber layer inside the hose is seriously deteriorated and obviously expanded: the reason for the serious deterioration and obvious expansion of the rubber layer inside the hose is that the use time of the hydraulic oil has passed or there is oxidation dirt in the hydraulic system, the hose is deteriorated by chemical action, and broken rubber pieces will be found at the oil return port. In the event of this phenomenon, the physical and chemical indexes of the hydraulic oil should be checked, the compatibility of the system oil and the rubber material in the hose should be checked, and the working temperature should meet the standard.Four, the fault at the break1. One or more cracks in the hose, the cracks are neat: the main reason for this phenomenon is that the system pressure is too high, exceeding the pressure resistance of the hose. If the system pressure meets the requirements, check whether the actual pressure resistance of the hose used meets the design requirements.2. Distortion at the hose break: This phenomenon is caused by excessive distortion of the hose during installation or use. After the hose is twisted, the structure of the reinforcement layer changes, the gap between the braided steel wire and the wound steel wire increases, reduces the compressive strength of the hose, and the hose is easy to break under high pressure. Therefore, the hose should not be subjected to torque during use or storage. When installing the hose, try to make the axis of the two joints on the same plane, so as to avoid distortion of the hose in use. 3 Wire crimp at hose break. There is an obvious necking phenomenon: the reason for this phenomenon is that the hose is over-stretched and deformed, stratified, and reduces the compressive strength. Under the action of high pressure, the hose will shrink or extend longitudinally, and the expansion and contraction amount is generally +2% to 4% of the normal state. If the hose is selected too short during installation, it will be greatly stretched during work, and it will break or loosen seriously. If the hose span is too large, the weight of the hose and the weight of the oil will also give the hose a larger pull, and the above faults will occur in serious cases. So we should take appropriate solutions according to the specific situation. If the installation is too tight, the extension pipe should be replaced.Five, the use of rubber hose should pay attention to matters1. The service life of rubber hose is very short when working at high temperature. Therefore, the hoses should be arranged as far away from heat sources as possible. If necessary, it is necessary to install a sleeve or insulation plate to prevent the hose from deteriorating due to heat.2. When installing the hose, do not contact with other hoses or pipes to avoid wear. Where the rubber hose must pass through or may rub against mechanical surfaces, protective devices such as rubber hose clamps or springs should be used to prevent damage to the outer layer of the rubber hose.3. When the hose must be bent, sharp bending should be avoided, and the bending radius R≥(9~10)d(d is the outer diameter of the hose). The straight line from the joint to the bending start should be 6 times larger than the outside diameter of the pipe.4. When installing the rubber hose, avoid being in a tight state, and there should be a certain length margin. Keep the hose loose even if there is no relative movement between the two ends. When the rubber tube is under pressure, the length and diameter will change, so the tensioned rubber tube will expand under pressure, resulting in a decrease in strength.5. Avoid twisting the rubber hose during installation. When the rubber hose is slightly twisted, its strength may be reduced or the joint may become loose.6. The bend of the hose and the hose connector should be installed on the same plane to prevent distortion. In special cases, if the joints at both ends of the hose need to be on two different planes, the clamp should be installed in the appropriate position to divide the hose into two parts so that the parts are on the same plane.7. If the rubber hose is installed on key components, it is recommended to check or replace it regularly.