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The design is irrational (1) Poor oil return or no oil return passage. For example, poor oil return at the bearing, easy oil accumulation, formation of certain pressure, and oil leakage. Some oil return hole locations are not designed properly and are easily blocked by dirt. Some oil return tank capacity is too small, causing oil to overflow from the oil return tank. Some do not design recycling devices. Such as: a heavy machine tool factory TX6216C floor key bed, the front column and spindle box installed on the slide, sliding seat with a sealed hydraulic unloading device. The design idea is that the pressure oil is passed into the six evenly distributed unloading oil chambers under the sliding seat. The size of the oil pressure is not to lift the sliding seat, and the column moves flexibly and the rapid moving current does not exceed 6A. The bottom of the slide is sealed with a polyurethane seal and the oil will not leak. After a period of use, it was found that the oil leakage of the slider was serious and that the machine rails were oiled on the ground on both sides. According to the analysis, after the oil is used for a period of time, the oil becomes dirty and the machine tool will also have some iron powder on the rail surface when processing the parts, and it is not easy to be scraped off by the stripper. When the slide moves, iron enters the seal ring, causing the seal ring to wear and cause oil leakage. The seals in these areas are very inconvenient to replace, and the front columns and slides weighing more than ten tons must be lifted at the same time to be replaced. This is a place where the design of the machine tool is irrational. Designers should take this into consideration and design a set of oil filter and recovery device, which can reduce the number of seal ring replacements, reduce the waste of hydraulic oil, and maintain the surrounding environment. The cleanliness.
(2) O-Ring rubber seals that are not compatible with the use of the seal ring must be selected according to the operating conditions and operating conditions of the equipment. Under oil lubrication conditions, the hardness of the oil-resistant rubber O-ring seal can be selected to be low when the oil pressure is <2.9 MPa; medium hardness should be selected when the oil pressure is 2.9-4.9 MPa; when the oil pressure is 4.9-7.8 For MPa, high hardness should be used. If the seal is selected, its permissible pressure will be less than the working oil pressure.
(3) Unreasonable design of seal or unreasonable seal structure. Example: The screw holes in the box are designed as through holes and there are no sealing measures; there is no seal gasket at the box cover; the fit clearance between the shaft and box hole is too large; The amount of interference between the ring and the shaft is unsatisfactory; if the design of the seal groove is unreasonable, the lubricant may leak out.
Oil leakage caused by casting defects and parts damage (1) Castings have defects such as blisters, pores, cracks, and loose structures, but no measures are taken. During the use of equipment, these defects are often the root cause of oil leakage.
(2) When oil pipes or pipe joints are made of plastic or oil-resistant rubber products, the materials will age, harden, and become brittle, causing oil pipes and pipe joints to rupture and cause oil leakage.
(3) After long-term use of the sealing ring, especially those in the moving part, the sealing performance will be lost due to friction and wear. In addition, if the gap between the shaft and shaft hole (sleeve) increases, it also causes oil leakage.
(4) Part machining accuracy error and other reasons. For example, the flatness of the joint surface of the box and the box cover is too bad, the surface roughness is too large, and the residual stress of the workpiece is too large to cause the deformation of the workpiece, so that the joint surface is not closely attached. Or loose fasteners can cause oil leakage.
Inappropriate maintenance (1) It is common to cause oil spills when the relevant parts are not properly selected or assembled. For example, improper use of O-rings causes oil leakage to occur frequently during maintenance. General maintenance personnel, when they found that the O-ring on the machine tool was deformed or damaged and needed to be replaced, they would often find a similar size and shape of the seal ring to install, seldom consider the size of its pressure. Under normal circumstances, the general machine tool lubrication pressure is <3MPa, resulting in a wrong concept, O-ring seal as long as the same size, you can replace the use. This can be done under low pressure conditions, but when higher pressures above 5 MPa are encountered, problems will arise. For example, hydraulic systems in heavy-duty machine tools have working pressures of over 5 MPa. Therefore, the hardness of the seal ring should be taken into consideration when replacing the hydraulic valve on the machine and the O-ring on the interface.
It is often found that some equipment still leaks oil after replacing the seal ring, further tightening the screw still leaks oil, and it is not realized that the oil leakage caused by the improper replacement of the seal ring. There is paint, burrs, impurities, or bumps on the joint surface between the box and the lid, so that the joint surface is lax, and the seal is damaged when the gasket is forgotten or removed. If the screws and nuts are loose during installation, they will leak oil.
(2) Oil change is not required and often leads to leakage of the machine tool. The problems that arise in oil change are mainly manifested in three aspects. First, for components with high viscosity oils, changing the oil to a low-viscosity lubricating oil at will will make the sealing performance of the corresponding housing, shaft hole, etc., be affected to a certain extent, and sometimes the sealability of these parts will be greatly reduced. . Secondly, when the oil is changed, the fuel tank is not cleaned. The dirt in the fuel tank may enter the lubrication system, blocking the oil passage and wearing the seal and causing oil leakage. Thirdly, when the oil is changed, the amount of fuel is too much, especially in the parts with rotating parts. Due to the agitating action of the rotating parts, oil spilling is more likely to occur.
(3) Oil leakage caused by inappropriate selection and adjustment of lubrication system components. For example, if an oil pump with a high pressure or a large oil output is selected for 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 lubrication system of the machine tool is excessive. Oil systems and sealing systems do not match and can cause oil leaks.
Some NC machine tools lubricate the screw and guide rails, and they are often designed with time-dropping lubricants. This type of design is generally not designed for oil recovery systems. Therefore, once the oil system is regularly dropped, there are problems with the screw or guide rail. Insufficient lubrication or excessive flow is oil. Therefore, machine tool leakage should cause the importance of machine tool manufacturers.
How to analyze the leakage of machine tool from various aspects?
The leakage of the machine tool is usually divided into three states: leakage, dripping, and flowing oil. Under normal circumstances, static joint surface, a drop of oil and dynamic joints every half hour drops every drop of oil every 6 minutes are leakage. Regardless of whether it is a moving surface or a static surface, when a drop of oil is dropped every 2-3 minutes, it is oil; more than 5 drops per minute are flowing oil. The general requirement for the equipment to achieve leakage control is that there should be no leakage at the external static joint surface, and slight leakage at the dynamic joint surface is allowed, but it is not allowed to flow to the ground. Some leakage inside the equipment is allowed, but it is not allowed to penetrate into the electrical box and the belt and can be led back into the lubrication box.