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Analysis of common failures and causes of rubber hoses for construction machinery

Nov. 02, 2018

Rubber hydraulic hoses are important components of hydraulic systems for construction machinery such as concrete trucks, road rollers, excavators, loaders, etc., and leaks, cracks, cracks, looseness, etc. are often encountered during use.




1 failure of the outer layer

(1) In a cold environment, cracks appear on the outside of the hose, which may cause the hose to be bent. If there is a crack on the outside of the hose, pay attention to the crack in the hose and decide whether to replace the hose immediately.

(2) Bubbling appears on the outside of the hose. Bubbling on the outside of the hose is due to unqualified hose quality or improper use. If bubbling occurs in the middle of the hose, most of which is a problem with the quality of the hose production, the qualified hose should be replaced in time; if the bubble appears at the joint of the hose, it is likely due to improper installation of the joint.

(3) The hose is not broken, but a large amount of oil is leaking. If the hose is not found to be broken, but a large amount of oil seepage, the reason is that when the hose passes through the high-pressure liquid flow, the inner rubber is eroded and scratched until a large area leaks out of the steel wire layer, resulting in a large amount of oil leakage.

(4) The outer rubber layer of the hose is seriously deteriorated, and the surface is slightly cracked. This is a manifestation of the natural aging of the hose over time.


2 Internal rubber layer failure

(1) The inner rubber layer of the hose is hard and cracked. The plastic is added to the rubber product to make the hose flexible and plastic. The hose works under high temperature and high pressure, and the hose overheats, which will cause the plasticizer to overflow. In addition, when the superheated oil passes through the cylinder, valve or other components in the system, if a large pressure drop occurs, the oil will be decomposed, resulting in oxidation and hardening of the rubber layer inside the hose. In this case, first check whether the hydraulic system operating temperature is normal, the throttle of the valve, the suction passage of the pump is smooth, etc., and replace the hose after removing all the factors that may cause excessive oil temperature and oil decomposition.

(2) The inner rubber layer of the hose is seriously deteriorated and obviously swells. The reason why the inner rubber layer of the hose is seriously deteriorated and the swelling is obvious is that the hydraulic oil is used in the hydraulic system due to the overdue use of the oil or the oxidized and degraded dirt. The hose is chemically deteriorated, and the rubber is found at the oil return port. sheet. If this happens, check the physical and chemical indicators of the hydraulic oil, check the compatibility of the system oil and the rubber material inside the hose and check whether the working temperature meets the standard.


3 reinforcement layer failure

(1) The hose is broken and the braided wire near the break is rusted. If the hose breaks, the outer rubber layer is peeled off and found to be woven near the crack, and the wound wire is rusted. This is mainly due to the wet or corrosive substance of the outer rubber layer, which weakens the strength of the hose and causes cracking at high pressure. This occurs, usually accompanied by external fractures, abrasions or severe deterioration, which causes the outer layer to lose its protective effect on the reinforcement layer. At this time, it is necessary to check and eliminate the mechanical damage, chemical corrosion and high temperature baking of the outer rubber layer, and then replace the hose. However, there is also a case where the outer rubber layer is kept good but the reinforcing layer is artificially broken and broken, and the rupture opening is usually within a range of 200 mm from the hose joint, and the reason is mostly that the joint is unacceptable, since moisture enters the inner edge of the outer casing, so that The reinforcing layer absorbs moisture, causing rust to cause the pressure resistance of the hose to decrease and rupture.

(2) The hose reinforcement layer is not rusted. However, if the hose breaks, if the hose is broken, the outer layer is peeled off and no rust is found. However, the irregular layer is broken in the length direction of the reinforcing layer. The main reason is that the hose is subjected to high-frequency impact. . There are many intersections between the steel wire and the steel wire of the braided reinforcing layer. When the pressure inside the pipe changes greatly, these intersections also shift with the change of the pipe diameter, so that the wires rub against each other.


4 failure at the rupture

(1) One or more hoses are broken and the cracks occur neatly. 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, the actual pressure resistance of the hose used should be checked to meet the design requirements.

(2) The hose is twisted at the rupture. This phenomenon occurs because the hose is excessively twisted during installation or use. After the hose is twisted, the structure of the reinforcing layer changes, the gap between the braided and wound steel wires increases, and the compressive strength of the hose is lowered, and the hose is easily broken under the action of high pressure. Therefore, during the use or storage of the hose, the hose should not be subjected to the torsional moment. When installing the hose, the axis of the two joints should be placed on the same plane to avoid the hose being twisted during use.

(3) The wire is curled at the rupture port of the hose. The obvious necking phenomenon causes this phenomenon because the hose is subjected to excessive tensile deformation, and the layers are separated to reduce the compressive strength. The hose will shrink or elongate in the longitudinal direction under the action of high pressure, and the general expansion and contraction amount is +2% to 4% in the normal state. If the hose is selected too short during installation, it will be greatly stretched during operation, and if it is severe, it will be broken or loose. If the span of the hose is too large, the weight of the hose and the weight of the hose will also be This will give the hose a large tensile force, which can also occur in severe cases. Therefore, appropriate solutions should be adopted depending on the specific situation. If the tension is too tight during installation, replace the lengthened new tube; if the span is too large, the intermediate support clip should be added.


5 Precautions when using hydraulic hoses

(1) The life of the hose is extremely short when it is operated at high temperatures. Therefore, the hose should be placed as far as possible from the heat source. If necessary, install a casing or a heat shield to prevent the hose from being deteriorated.

(2) Do not touch the hose or piping when installing the hose to avoid wear and tear. Where hoses must cross or work may be rubbed against mechanical surfaces, protective devices such as 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 bends should be avoided, and the bending radius R ≥ (g ~ 10) D (D is the outer diameter of the hose). The straight section of the hose joint to the beginning of the bend should be greater than 6 times the outer diameter of the pipe.

(4) The hose should be installed in a tight state when it is installed, and should have a certain length allowance. Keep the hose slack even if there is no relative movement at both ends of the hose. When the hose is pressed, a change in length and diameter occurs, so that the tensioned hose expands under pressure, resulting in a decrease in strength.

(5) The hose should be prevented from being twisted during installation.

(6) The bending of the hose and the hose joint should be mounted on the same plane to prevent twisting. In special cases, if the joints at both ends of the hose are to be placed on two different planes, the clamp should be installed in the appropriate position to divide the hose into two parts so that each part is on the same plane.

(7) If the hose is placed on a critical component, it is recommended to periodically check or replace it.

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