Common faults and causes of rubber hydraulic hoses for construction machinery Rubber hydraulic hoses are important components of hydraulic systems for construction machinery such as concrete transporters, road rollers, excavators, and loaders. Leakage, cracks, cracks, and looseness often occur during use. Such as failure, but people often do not analyze the cause of the malfunction but simply replace the hose, and will repeat the same failure soon after use. Loose or broken hydraulic hoses not only waste hydraulic oil, pollute the environment, but also affect work efficiency, even accidents, and endanger human-machine safety.
Hydraulic rubber hose is divided into two kinds: high pressure rubber hose and low pressure rubber hose. The high pressure rubber hose is steel wire braiding and winding rubber hose. It is generally composed of outer rubber layer, steel wire reinforced layer, middle rubber layer and inner rubber layer. The inner rubber layer is directly connected with hydraulic pressure. Oil contact, generally made of synthetic rubber. The bearing capacity of the hose depends on the steel reinforcing layer, which is the skeleton of the hose and is usually woven from steel wire and entwined. High-pressure, high-pressure multi-layer steel wire braided, winding frame; low-pressure hose to woven cotton, twine instead of braided steel wire, generally used for low pressure return pipeline. The main causes of failure of hydraulic hoses are: improper installation and use, improper system design, and unqualified hose manufacturing.
1, the outer layer of the fault
1.1 Cracks appear on the outside of the hose In the cold environment, cracks appearing on the outside of the hose will bend the hose. If any cracks are found on the outside of the hose, it is necessary to observe the presence of cracks in the hose and decide whether to replace the hose immediately. Therefore, do not arbitrarily move the hose or remove the hydraulic system in a cold environment. If necessary, do it indoors. If you need to work in a cold environment for a long time, replace the cold-resistant hose.
1.2 Blisters appear on the outer surface of the hose. Blisters appear on the outer surface of the hose because the hose is unqualified or improperly used. If bubbling occurs in the middle section of the hose, the production quality of the hose is mostly a problem. The qualified hose should be replaced in time. If the bubbling occurs at the joint of the hose, it may be due to improper installation of the joint. Steel wire braiding, winding hose joints and rubber hose joints are detachable, buckle type two forms, detachable joint jacket and joint core has a hexagonal shape, the outer core of the joint core is conical, easy to disassemble the hose. After the connector core is connected with the nut, the steel wire is inserted to prevent loosening. The buckled hose joint consists of the joint jacket and the joint core. When assembling, the outer rubber layer needs to be peeled off, the joint is connected to the core, the joint jacket is tightened, and then the special equipment is used to withhold the mold, so that the hose is compressed to a certain degree to achieve tightness. connection.
1.3 The hose is not broken but a lot of oil seepage If the hose is not cracked but a lot of oil is leaking, the reason is that when the hose passes through the high-pressure liquid flow, the inner rubber is eroded and scraped until a large area leaks out of the steel wire layer and causes large amount of seepage. oil. This fault usually occurs at the bend of the pipe. Check the replacement hose and make sure that the bend radius of the hose meets the technical requirements in use.
1.4 The outer rubber layer of the hose is seriously deteriorating, and the surface appears micro-cracking. This is the performance of natural aging when the hose is used for a long time. Due to ageing and deterioration, the outer layer is continuously oxidized to embrittle the surface layer, and the embrittlement layer is deepened with time. As long as the hose is slightly bent during use, micro cracks will be generated. In this case, the hose should be replaced.
2, the failure of the inner layer
2.1 The inner rubber layer of the hose is hard and cracked. Due to the plasticizer added to the rubber product, the hose is flexible and plastic. The hose operates at high temperatures and pressures. Overheating of the hose will allow the plasticizer to overflow. In addition, when the overheated oil passes through the cylinders, valves or other components in the system, if a large pressure drop occurs, the oil will be decomposed, resulting in the oxidation of the inner hose layer and hardening. In this case, check whether the working temperature of the hydraulic system is normal, whether the valve throttling point or the suction path of the pump is unblocked. Replace the hose after removing all the factors that may cause the oil temperature to be too high and the oil to be decomposed. If only the internal rubber under the broken opening of the hose is hard and the top is well maintained, this indicates that the phenomenon of the hose bursting excessively squeezing, bending too fast or twisting causes the oil to heat up and accelerate oxidation, which can cause the internal rubber to harden. .
2.2 The rubber layer in the hose is seriously deteriorating and is obviously swollen. The reason that the rubber layer in the hose is seriously deteriorating and obviously swelled is due to the fact that the hydraulic oil has expired or the oxidized deteriorated dirt is present in the hydraulic system, and the hose is chemically affected. On the other hand, crumb rubber tablets will be found at the return port. If this happens, check the physical and chemical indicators of the hydraulic oil and check the compatibility of the system oil and the rubber material in the hose and whether the working temperature meets the standard.
3, strengthen the layer of failure
3.1 The hose is broken. Weaving steel wire near the break is rusted. If the hose is broken, the outer rubber layer is peeled off, and weaving is found near the break. The winding wire is rusted. This is mainly due to the damp or corrosive substances in the outer layer, weakening the strength of the hose. Causes breakdown at high pressure. When this happens, it is generally accompanied by outer fractures, scratches, or severe deterioration, which causes the outer layer to lose its protective effect on the reinforcement layer. At this time, it is necessary to first check and eliminate the mechanical damage, chemical corrosion, and high temperature baking of the outer rubber layer, and then replace the hose. However, there are cases where the outer layer is well maintained but the layer is embroidered and broken, and the breakage is usually within 200 mm from the hose fitting. The reason for this is that the joint is mostly unacceptable and moisture enters the inner edge of the outer sleeve. The reinforcing layer absorbs moisture, causing rust to cause the pressure resistance of the hose to decrease and break.
3.2 The hose reinforcement does not rust. However, if there is an irregular broken wire, if the hose breaks, the outer rubber layer is peeled off and no rust is found on the reinforcing layer. However, irregular broken wires appear in the length direction of the reinforcing layer. The main reason is that the hose is subjected to high frequency impact force. . There are many intersections between the steel wire and the steel wire of the weaving reinforcement layer. When the pressure in the pipe changes greatly, these intersection points also shift along with the change of the pipe diameter, causing the steel wires to rub against each other. If the hose is subjected to high-frequency impact pressure, frequent friction will occur at the intersection, causing the wire to break. For hoses that are frequently subjected to high frequency impact, the steel wire winding skeleton should be used as a reinforcement.
4, failure at the broken mouth
4.1 One or more breakages of the hose, the reason for the phenomenon of neat gaps is mainly the system pressure is too high, exceeding the pressure resistance of the hose. If the system pressure meets the requirements, check that the actual pressure resistance of the hose used meets the design requirements.
4.2 Torsion at hose breakage _ This phenomenon occurs due to excessive twisting of the hose during installation or use. After the hose is twisted, the structure of the reinforcing layer is changed, and the gap between the wound steel wires is increased, which reduces the pressure resistance of the hose, and the hose is easily broken under high pressure. Therefore, during the use or storage of the hose, the hose should not be subject to torsional moments. When installing the hose, the axes of the two joints should be placed on the same plane as much as possible to avoid twisting the hose during use.
4.3 The wire is curled at the broken end of the hose. The phenomenon of obvious necking caused this phenomenon is that the hose is excessively stretched and the layers are separated, which reduces the compressive strength. Under the effect of high pressure, the hose will shrink or stretch in the length direction. Generally, the expansion and contraction amount is +2% to 4% under normal conditions. If the hose is selected to be too short during installation, it will be subjected to a large tensile force during operation, and may be broken or loose in severe cases; if the span of the hose is too large, the hose's own weight and oil weight are also This will give the hose a large tensile force, which can also occur in severe cases. Therefore, appropriate solutions should be taken depending on the circumstances. If it is too tight during installation, it should be replaced with a new long tube; if the span is too large, an intermediate support clip should be added.
5, when using the hydraulic hose precautions
(1) The hose has a very short life at high temperatures. Therefore, the hose should be arranged as far away as possible from the heat source. When it is necessary to install the sleeve or insulation board, the hose can be damaged by heat.
(2) When installing the hose, do not touch it with other hoses or pipes to prevent wear and tear. Where hoses must cross or work where friction may occur on the mechanical surfaces, hose clamps or springs should be used to protect the outer layer of the hose from damage.
(3) When the hose must be bent, sharp bending should be avoided, and its bending radius R ≥ (9 ~ 10) D (D is the outer diameter of the hose). The straight section of the hose joint to the start of bending should be greater than 6 times the outer diameter of the pipe.
(4) The hose should be avoided from being in a tensioned state and should have a certain length margin. Even if there is no relative movement between the two ends of the hose, keep the hose loose. When the hose is pressurized, changes in length and diameter occur, and the tensioned hose will expand under pressure, resulting in reduced strength.
(5) Avoid twisting the hose during installation. When the hose is slightly twisted, it may reduce its strength or loosen the joint.
(6) The bending of the hose and the hose connector should be installed on the same plane to prevent twisting. In special circumstances, if the joints at both ends of the hose are to be on two different planes, the clamps should be installed in place to divide the hose into two parts so that each part is on the same plane.
(7) If the hose is configured on a critical part, it is recommended that it be regularly checked or replaced.