Usually could be divided into three states of machine oil leakage and dripping and flow of oil. In general, the static combining face, every half an hour to drop a drop of oil and dynamic combination of facial every 6 min drip a drop of oil are leaking. Both dynamic joint surface and the static joint surface, every 2 to 3 min drip a drop of oil, as the drops of oil; More than 5 drops per minute for the flow of oil. Make the equipment meet the general requirements for leakage, external static equipment in combination with surface can not have leakage phenomenon, the dynamic binding surface to allow a slight leakage, but are not allowed to flow to the ground. Allow some leakage inside the equipment, but are not allowed to penetrate into the electrical box and transmission belt, can be returned to the lubrication in the box.

Design is not reasonable

(1) poor oil or no oil return channel
For example: bearing oil return not free, easy product oil, formation pressure and oil. Some oil return hole position design is not reasonable, easy to contamination jams. Some back to the tank capacity is too small, resulting in oil spilled from the back to the tank. Some not recycling device design. Such as: a heavy machine tool plant production TX6216C landing key bed, the front pillar and spindle box installed on the slide, slide by sealing hydraulic unloading equipment. Its design idea is the pressure oil flux into the slide under 6 unloading oil cavity of uniform distribution, the oil pressure not to raise the size of the slide, pillar mobile flexible and fast moving current less than 6 a is preferred. Slide at the bottom of the polyurethane (pu) seal, seal oil will not leak. Use after a period of time, found that slide oil leakage is more serious, machine tools guide on both sides of the ground is oil. Analysis was thought that the oil use after a period of time, the oil dirty and machine tool in machining parts will have some iron powder fell to guide surface, it is not easy to be cut, scrape. Slide movement at the end of the iron into the sealing ring, sealing ring wear oil is produced. These parts of the sealing ring change rise very inconvenience, must be weighed before 10 tons of pillar and the replacement of the slide up to at the same time. This is where the machine design is not reasonable, the designer should consider this, and should design a set of oil filter recovery unit, can decrease the number of replacement for sealing ring, but also reduce the waste of the hydraulic oil, and can also keep the environment clean.
(2) the sealing ring and doesn't fit the conditions of use
The most commonly used O shaped rubber sealing ring, must according to the using condition of the equipment selection and working condition. Under the condition of oil lubrication, oil resistant rubber O ring hardness, when the oil pressure < 2.9 MPa, can choose low hardness; When the oil pressure in the 2.9 4.9 MPa, should choose the hardness. When the oil pressure is 4.9 to 7.8 MPa, should choose high hardness. If choose the sealing ring, its allowable stress under working pressure will leak.
(3) there is no design seal or sealing structure is not reasonable
For example: design of the screw hole on the box into the hole, and no sealing measures; No box cover gasket design; Shaft and housing holes fit clearance is too large; Sealing ring and shaft with the interference amount of undesirable; Seal groove design is not reasonable, etc., can make the lubricating oil leakage.

Caused by casting defects and damage of parts of oil spill

(1) the casting defects such as voids, porosity, crack, loose organization, and did not take measures, equipment in use process, these defects is often the root causes of oil leakage.
(2) pipe, pipe joint choose plastic or oil resistant rubber products, the use of time, material aging will harden brittle, tubing and pipe rupture caused by oil spill.
(3) the sealing ring after using for a long time, especially those parts of the sealing ring, due to the friction and wear loss of sealing performance. Other such as shaft and the shaft hole (collar) between clearance increases, also caused the spill.
(4) precision parts processing error and other reasons. For example: the box body and box cover joint surface flatness error and surface roughness is too big, workpiece deformation caused by the residual stress of workpiece, the joint surface laminating imprecise. Loose or fasteners, etc., can cause oil leakage.

Improper maintenance
(1) related to choose or assembled not appropriate to the situation of the oil spill are common. For example: O ring caused by improper oil leakage often occurs in maintenance. General maintenance personnel, when they found the O ring on the deformation or damage to the machine tool needs to be replaced, tend to grab a shape similar to the size of the sealing ring to install, rarely consider the size of the pressure. Normally, general machine tool lubrication pressure < 3 mpa, creating a kind of wrong idea, O ring as long as the same size, it can be used to replace. That in the case of low pressure is ok, but when you have more than 5 mpa pressure high, problems arise, such as application of machine tool hydraulic system, its working pressure are more than 5 mpa. As a result, the replacement of the machine tool hydraulic valve and outlet O ring should be paid attention to when the hardness of sealing ring.
Often find some equipment still leak after replace the sealing ring, still further compression screw oil leak, don't realize is improper replacement of sealing ring of the spill. Between the box body and box cover joint surface with paint, burr, the impurities or damaged, the joint surface joint is lax, and forget the seal or gasket is disassembled have damaged. Screw nut screw too loose, when installation will leak.
(2) oil change undesirable, and often cause machine oil. The problem of oil change mainly for three aspects. First, for the parts and components, high viscosity lubricating oil when the oil change at random to switch to low viscosity lubricating oil, can make the corresponding box, axle hole and other sealing performance is affected by a certain, sometimes will greatly reduce the sealing parts. Second, the oil change without cleaning tank, fuel tank in the dirt is likely in the lubrication system, congestion causes oil spill oil, wear the seals. Third, when the oil change amount to much, especially in the part of the rotating parts, due to the effect of agitation of the rotating parts, oil spill occurs more easily.
(3) on the lubrication system components caused by improper selection and adjustment of the oil. For example: the pressure is too high at the beginning of maintenance or out of the oil pump of the large amount of oil, or adjust the system pressure, overflow valve, safety valve, relief valve pressure regulation is too high, the machine tool lubrication system such as heavy traffic and oil return system and sealing system does not match, can cause oil leakage.

Some numerical control machine tool of the lead screw and guide rail lubrication, now with the design of add lubricating oil regularly, this design is generally not oil recovery system design, thus once regularly add lubricating oil system of a problem, or lead screw and guide rail lubrication, either flow rate is too large around is oil. Therefore, machine oil should cause the attention of the machine tool manufacturers.