Failure Analysis of Hydraulic Hose at the Reinforcement Layer and Rupture

Fault Manifested in the Reinforcement Layer

(1) hose rupture, rusting woven steel wire near the rupture hose rupture, peel off the outer rubber layer to check, found rusting woven steel wire near the rupture. This is mainly due to the layer by the role of moisture or corrosive substances, weakening the strength of the hose, resulting in high-pressure rupture. This situation, generally accompanied by the outer rubber layer fracture, abrasion or serious deterioration of the phenomenon, so that the outer layer lost to strengthen the protective role of the layer. This must first check and exclude the outer layer of mechanical damage, chemical corrosion, high temperature baking and all other undesirable factors, and then replace the hose. But there is also a good outer rubber layer to maintain the strengthening layer rust and rupture, and the rupture is usually in the range of 200mm from the hose joint number, most of the reasons are unqualified joints, moisture into the inner edge of the jacket, so that the strengthening layer to absorb moisture, resulting in rust caused by hose pressure strength reduction and rupture.

(2) hose reinforcement layer is not rusted, but the reinforcement layer appears irregular broken wire phenomenon. Hose rupture, peel off the outer rubber layer was not found to strengthen the layer of rust, but the length of the reinforcement layer irregular broken wire, the main reason is that the hose is subjected to high-frequency impact force. Woven reinforcement layer of steel wire and steel wire between a lot of intersections, when the tube pressure changes significantly, these intersections also change with the diameter of the tube and the wrong movement, the steel wire friction between each other. If the hose is subject to high-frequency impact pressure, the intersection of frequent friction, resulting in wire breakage. For the hose often subject to high-frequency impact, the steel wire winding skeleton should be used as a reinforcement layer.

Failure Manifested at the Rupture

(1) one or more rupture of the hose, the cleft neatly, the other parts remain good. 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 see if it meets the design requirements.

(2) hose rupture at the twist, the reason for this phenomenon is the hose in the installation or use process by excessive twisting caused. After the hose is twisted, the reinforcement layer structure changes, the gap between the braided steel wire asks to increase, reducing the pressure strength of the hose, the hose is easy to rupture under high pressure. Therefore, in the use or custody of the hose process, do not make the hose to withstand the torsional moment, the installation of the hose as far as possible to make the axis of the two joint number in the plane of movement, so as to avoid the hose in motion by the twist.

(3) hose rupture at the mouth of the steel wire curl, near the rupture with obvious shrinkage neck phenomenon, strengthen the layer loose the reason for this phenomenon is that the hose is subject to excessive stretching deformation, the layers are separated, reducing the pressure strength. Hose under high pressure will occur in the direction of length contraction or elongation, general expansion and contraction of + 2% to 4% of the normal state. If the hose is selected too short when installed, the work is subject to a large stretching effect, serious breakage or loosening and other failures; in addition, the span of the hose is too large, the hose self-weight and the weight of the oil will also give the hose a large stretching force, serious failure will also occur as described above. Solution: If the installation is pulled too tight, should be replaced by a new tube with a longer length; if the span is too large, should be added to the middle support clip.

Summary

Through the above analysis, the following matters should be noted when using hydraulic parts in the future.

①The hose arrangement should avoid heat sources as far as possible and stay away from the performance of the engine exhaust pipe. If necessary, devices such as casing or protective screen can be used to avoid heat deterioration of the hose.

②Hose must cross or work with mechanical surfaces where friction may occur, the application of hose clamps or springs and other protective devices to avoid damage to the outer layer of the hose.

③When the hose must be bent, the bending radius should not be too small, it should be more than 9 times the outer diameter. The connection between the hose and the joint should be a straight section greater than 2 times the outside diameter of the hose.

④The hose should be installed to avoid being in a strained state, even if there is no relative movement between the two ends of the hose, the hose should be kept loose, the tensioned hose will expand under pressure and the strength will be reduced.

⑤ Do not twist the hose during installation. Hose subjected to slight twisting may make its strength reduced and loosen the joint, assembly should be tightened on the joint in the hose, rather than the hose tightened on the joint.

⑥Hose is recommended to be inspected or replaced periodically if it is configured on critical parts.