Analyze how machine oil leakage occurs from various aspects?

The oil leakage of machine tools is usually divided into three states: leakage, dripping and oil leakage. Under normal circumstances, a drop of oil every half an hour on the static joint surface and a drop of oil every 6 minutes on the dynamic joint surface will be leakage. Regardless of whether it is a dynamic joint surface or a static joint surface, when one drop of oil is dripped every 2-3 minutes, it is dripping oil; more than 5 drops per minute is flowing oil. The general requirement for the equipment to achieve leakage control is that there should be no leakage at the static joint surface of the equipment, and slight leakage is allowed at the dynamic joint surface, but it is not allowed to flow to the ground. Some leakage is allowed inside the equipment, but it is not allowed to seep into the electrical box and transmission belt, and can be led back into the lubrication box.

unreasonable design

　　 (1) Poor oil return or no oil return channel

　　 For example: the oil return at the bearing is not smooth, it is easy to accumulate oil, build a certain pressure, and oil leakage occurs. The location of some oil return holes is unreasonable, and it is easy to be blocked by dirt. The capacity of some oil return tanks is too small, causing oil to overflow from the oil return tank. Some do not have a recovery device. For example, the TX6216C floor key bed produced by a heavy machine tool factory has its front column and headstock mounted on a sliding seat, and the sliding seat adopts a sealed hydraulic unloading device. The design idea is that the pressure oil flows into 6 evenly distributed unloading oil chambers under the sliding seat, and the hydraulic pressure should be such that the sliding seat is not lifted, the column moves flexibly and the fast moving current does not exceed 6A. The seal at the bottom of the sliding seat adopts a polyurethane sealing ring, so the oil will not leak. After using for a period of time, it was found that the sliding seat had serious oil leakage, and there was oil on the ground on both sides of the machine tool rail. After analysis, it is believed that after the oil is used for a period of time, the oil becomes dirty and some iron powder will fall on the guide rail surface when the machine tool is processing parts, which is not easy to be scraped off by the stripper. When the sliding seat moves, the iron powder enters the sealing ring, causing the sealing ring to wear and cause oil leakage. The sealing ring of these parts is very inconvenient to replace, and the front pillar and the sliding seat weighing more than ten tons must be lifted at the same time to be replaced. This is where the design of the machine tool is unreasonable. The designer should take this into consideration and design a set of oil filter recovery device, which can not only reduce the number of replacements of the sealing ring, but also reduce the waste of hydraulic oil, while maintaining the surrounding environment Clean. To

　　 (2) The sealing ring is not suitable for the use conditions

　　 The most commonly used O-shaped rubber sealing ring must be selected according to the operating conditions and working conditions of the equipment. Under oil lubrication conditions, the hardness of the oil-resistant rubber O-ring seal can be low hardness when the oil pressure is less than 2.9MPa; when the oil pressure is 2.9-4.9MPa, medium hardness should be selected; when the oil pressure is 4.9-7.8 When MPa, high hardness should be selected. If the seal ring is selected, its allowable pressure is lower than the working oil pressure and oil will leak.

　　 (3) No sealing design or unreasonable sealing structure

For example: the screw hole on the box body is designed as a through hole without sealing measures; there is no sealing gasket on the box body cover; the clearance between the rotating shaft and the box hole is too large; the interference between the sealing ring and the shaft does not meet the requirements; Unreasonable seal groove design and other conditions may cause lubricating oil to leak.

Oil leakage caused by casting defects and damaged parts

　　 (1) Castings have defects such as blisters, pores, cracks, and loose tissues, and no measures have been taken. These defects are often the source of oil leakage during the use of the equipment.

　　 (2) When oil pipes and pipe joints are made of plastic or oil-resistant rubber products, the materials will age and become hard and brittle after long-term use, causing oil pipes and pipe joints to rupture and cause oil leakage.

　　 (3) After long-term use of the sealing ring, especially those of the moving parts, the sealing performance will be lost due to friction and wear. In addition, if the gap between the shaft and the shaft hole (shaft sleeve) increases, it will also cause oil leakage.

　　 (4) Part machining accuracy error and other reasons. For example: the flatness of the bonding surface of the box body and the cover is too poor, the surface roughness is too large, and the residual stress of the workpiece is too large to cause deformation of the workpiece, and the bonding surface is not tightly attached. Or loose fasteners, etc., will cause oil leakage.

　　Improper maintenance

　　 (1) Oil leakage caused by improper selection or assembly of related parts is more common. For example: oil leakage caused by improper use of O-ring seals often occurs during maintenance. General maintenance personnel, when they find that the O-ring seal on the machine tool is deformed or damaged and needs to be replaced, they will often find a seal ring of similar size and shape to install it, and rarely consider its pressure resistance. Under normal circumstances, the lubrication pressure of general machine tools is less than 3MPa, which creates a wrong concept that O-rings can be replaced as long as they have the same size specifications. This is possible in the case of low pressure, but when encountering higher pressures above 5MPa, problems will arise. For example, the hydraulic system of medium and heavy machine tools has working pressures above 5MPa. Therefore, pay attention to the hardness of the sealing ring when replacing the hydraulic valve and O-ring at the interface on these machine tools.

　　 It is often found that some equipment still leaks oil after replacing the sealing ring, and the oil is still leaking after further tightening the screw. I did not realize that the oil leakage was caused by improper replacement of the sealing ring. There are paint, burrs, impurities or bruises on the joint surface between the box body and the lid, which makes the joint surface not fit tightly, and the gasket is damaged when the gasket is forgotten to be installed or removed. If the screws and nuts are too loose during installation, oil will leak.

　　 (2) Unsatisfactory oil change will often cause oil leakage from the machine tool. The problems in oil change are mainly manifested in three aspects. First, for parts that use high-viscosity lubricating oil, if you change the oil to low-viscosity lubricating oil at will, it will affect the sealing performance of the corresponding box and shaft hole to a certain extent, and sometimes greatly reduce the sealing performance of these parts. . Second, if the oil tank is not cleaned when changing the oil, the dirt in the oil tank may enter the lubrication system, block the oil circuit, wear the seals, and cause oil leakage. Third, the oil is added too much when changing the oil, especially in the parts with rotating parts, due to the stirring effect of the rotating parts, oil spills are more likely to occur.

　　 (3) Inappropriate selection and adjustment of lubrication system parts cause oil leakage. For example: the oil pump with too high pressure or excessive oil output is selected during maintenance, or when the system pressure is adjusted, the pressure adjustment of the overflow valve, safety valve, pressure reducing valve, etc. is too high, and the flow rate of the machine tool lubrication system is too large. The oil system and the sealing system are not matched, which will cause oil leakage.

For some CNC machine tools, the lubrication of the lead screw and guide rail is now mostly adopted the design of regular dripping lubricating oil. This design generally does not design an oil recovery system. Therefore, once the timing dripping lubricating system fails, either the screw or the guide rail Insufficient lubrication, or excessive flow is oil everywhere.