Research on Machine Tool Injury and Repair Technology

Injury is a common wear and tear on the machine under normal circumstances, the consequences of a direct result of reduced precision machine tools, shortened service life. If not repaired in time, the particles produced by the injury, but also exacerbated the wounds, the final slide is to stop each other sliding parts, resulting in "bite" phenomenon.

We generally classify the causes of injury on the machine into two types:

First, adhesive wear-type wounds

The relative movement of the friction pair, due to mutual friction, the contact surface of the material from one surface to another surface, the friction surface scratches and grooves of the injury. We call it adhesive-type wounds.

(A) adhesive wear injury mechanism of injury

Production practices and research indicate

Solid surface conditions, from the microscopic point of view is the existence of bumpy defects, even after polishing and other finishing can not completely avoid this phenomenon. When the two friction surfaces are in contact, the peaks of the two friction surfaces are in fact in contact with each other. Due to the large contact stress, as well as elastic, plastic deformation, physical contact area increased until it can withstand the full load so far. At this point, the metal contact surface will appear a firm point of adhesion, we usually call this phenomenon called cold welding adhesion. These sticking points are very easy to produce without a surface film. If the friction surface of the surface film, or only by the normal force. This phenomenon will not happen.

If at the same time the role of tangential force, and the normal force and tangential force are large, then the relative sliding, the friction surface temperature will rise under the dual role of high temperature and pressure, resulting in the destruction of the oil film, the contact The metal surface softens, or melts, the contact points are created. Adhesive rips and sticks are peeled off to allow the material touching the surface to be transferred from one surface to the other so that one of the surfaces (or both surfaces) Marks and grooves, that is, adhesive wear type injury (two) the classification of adhesive wear injury

According to the degree of friction on the surface of the surface injury, the general adhesion of wear and tear on the machine-type injuries are divided into four categories:

1. smear This happens only to the shallow surface of soft metal, was scratched soft metal layer by way of painting, transferred to the hard metal surface. Example: Copper on the surface of the running worm is applied to the surface of the worm.

2. Scratch damage is generated along the direction of movement of small scratches occurred in the soft metal surface below the shallow part. Sometimes hard metal surface will be scratched, common in the equipment run-in period.

3. Glue (avulsion) when the friction pair to do relative sliding. Adhesive points cut off from the base metal, so that the surface of the avulsion damage, adhesive damage occurs. Much of the friction between the two parts of the substrate deeper. Such as machine rails and skateboards in the absence of oil caused by friction and more belong to such research injury.

4 biting the relative sliding parts of the surface flash instantaneous temperature is very high, the adhesion area is large, the adhesion point is also very high strength, adhesion can not be cut off from the substrate, resulting in the phenomenon of relative motion termination. This is one of the most serious types of research wounds we study, and the idiom is also called "Axis of Obligation."

(C) Adhesive and wear injury-related factors

Many factors will affect the occurrence of research injury. We can take measures to study the true nature of these factors and prevent the occurrence and development of the research injury.

Lubricant factors Lubrication of sticky wear-type injury has a great impact, can maintain the friction surface is always strong enough to maintain the lubrication of the film to avoid friction between the surface of the metal surface to form a direct contact between the friction or semi-dry friction, Is to prevent the occurrence of adhesive wear-type wounds the key. It is important to ensure good lubrication of the friction surface.

2. The pressure factor Under normal circumstances, as the pressure increases, adhesive wear type injury will be increased. When the pressure load exceeds the hardness of the friction pair material, the oxide film on the surface of the friction pair is crushed, and the protruding spots of the new surface between the two surfaces are embedded with each other, while the movement of each other aggravates such study. In severe cases, the surface of the friction pair is glued , Or even killed. Heavy machine belongs to such research injury.

3. Temperature factors in the friction heat generated during the friction surface temperature to a certain extent, the light damage the lubricating film, so that the surface is in direct contact with the formation of dry friction or semi-dry friction: severe dry the material can be dry Tempering the state and reduce the hardness of the material; more serious phenomenon is the local high temperature friction material on the surface of the melting state. Therefore, the temperature has a great impact on the adhesion-induced wear injury.

4. Sliding speed factors When the pressure is fixed, the sliding speed is small, the role of the formation of lubricating film is reduced, then the film across the smaller, often due to oil film can not afford the pressure of the moving part of the damage, resulting in two metals see direct contact , Easily lead to research injury. However, when the sliding speed reaches a certain level. Also easily lead to the temperature of the friction pair, easy to damage the lubricant film, which in turn lead to injury.

5. The more smooth the surface roughness factor, the greater the ability of anti-adhesive wear type injury. Appropriate to reduce the value of surface roughness can prevent such injuries. Therefore, the maintenance of machine tools, often scratched the surface of the guide rail pattern, the purpose is to facilitate the storage of oil, to prevent wounding.

6 material factors brittle material than the plastic material anti-adhesive wear ability: a large miscibility of the material composed of friction than the miscibility of the material composed of friction pair, prone to adhesive wear type injury. The friction pair of metal and nonmetal has the tendency to produce such a wound.

Second, abrasive wear-type wounds

Pollution The particles that enter between the two friction surfaces cause significant cutting action on the surface, resulting in scratches on the friction surface and the type of trench injury.

(A) abrasive wear injury-type mechanism of injury

Hard particles enter between two friction surfaces and are subjected to two forces, one perpendicular to the surface and one parallel to the surface. Hard particles pierce the surface under the former's action, while under the latter they produce a tangential movement, which results in scratches or grooves on the surface.

(B) abrasive wear type injury classification

We wear abrasive abrasive injury commonly found on the machine can be divided into three categories:

1. Bump Caused In our production and processing, the guide of the machine tool will inevitably be subject to the workpiece or tools and other high-stress objects bump, it is the surface of the guide pits, while the surrounding there will be raised or burr at the same time. If not repaired in time, when the skateboard on the rail east, it is bound to skate injury.

2. Hard particles into the friction surface between the eight caused by the outside of the chip and sand into the machine to return to between skateboard, will form a typical abrasive wear type injury: the chip or sand under vertical pressure, crushing the guide Or skateboard surface, when the skateboard moves, make the track and skateboarding injury.

3. dirt into the friction surface caused by the dirt into the friction surface through the lubricant, although not crush the friction surface, but can change the friction surface contact state, due to dirt support, contact with the dirt position to withstand the compressive stress Large, long run, will also have scratches or slight scratches. No matter what kind of measures we take, the problem of machine-wounding is also unavoidable. Therefore, the purpose of our study on the mechanism and type of wound development is to find ways to repair wounds.

In the event of a grinding machine injury, it must immediately stop running, find out the reason, the right medicine, timely repair. In general, smear a minor injury, you can not repair, but must be strengthened to prevent injury to expand. The glue, biting and other research wounds, you must repair. Now common to several pairs of friction wound repair study:

(C) the sliding bearing and shaft repair

1. Sliding bearing surface was ground injury, the preferred method is scraping method. Sliding bearings are generally available for adjustment and repair of the margin, fully meet the machine's a repair cycle. If the research is very serious injury, repair allowance can not be met, we must promptly replace the bearing.

2. When the journal has a research injury, you can use grinding small journals, replace the sliding bearing method. However, the journal grinding amount should not be too large, such as the spindle, grinding amount can not exceed the surface of the bearing quenching, carburizing, oxidation, and carbonitriding thickness, after grinding the surface hardness of the journal is not less than the original design hardness Lower limit: For driveshafts, the journal should not be smaller than the size of the journal or boss at the front of the assembly direction during assembly.

Of course, welding repair method can also be used to repair the journal, but to consider the welding process when the heating geometry of the shaft accuracy, mechanical strength and surface hardness.

Another point to note, the journal repair, generally need to be re-made by journal bearings or bearing sleeve.

(Four) worm repair

Worm adhesion or injury, the worm tooth surface are hardened and scratched, the worm surface hardness will decline, sometimes carburizing worm tooth surface cracks. When repairing a worm gear pair, repair the worm-worn worm or repair the worm-scrapped worm gear, or both, in addition to depending on their level of damage, the worm gear drive configuration should be considered. When the transmission is a fixed center away from the worm gear drive, generally only one repair, replace one, was repaired thickening of the tooth thickness thickening thickening by the new tooth thickness compensation, so as not to increase meshing backlash. From the viewpoint of considering the tooth strength, it is not advisable to reduce the tooth thickness of the worm gear, but the method of repairing the worm should be preferred. If the worm is carburized quenching parts, the amount of grinding teeth should not be too large. If you consider the value of the worm is more expensive, you can also choose to repair the worm, the worm replacement method.

(E) machine tool rail repair

For a slight grinding and scratching of the guide rails of the machine, the scraper or the grindstone can be used to repair the scratches and abrasions.

The adhesive injury, you need to use welding repair or filling sticky method to repair.

On the welding machine tool rail repair and adhesion, the relatively complex process, in particular, a large area of ​​repair, repair should be considered before more comprehensive: First, we must consider the use of the repair process on the rail accuracy, mechanical properties have influences. As affected by the temperature, will cause rail deformation, will change the mechanical strength of the rail Oh surface hardness. Second, to consider the repair process used on the adaptability of the rail material, such as cast iron rail generally do not use cast iron surfacing, due to poor weldability of cast iron, easy to produce cracks, porosity and other defects, it is not suitable for processing. Third, to consider the repair layer itself, the mechanical strength and the actual working environment guide. Different specifications, performance, different practical environment for machine tools, repair time to choose the appropriate welding repair and repair materials and advanced repair methods and new technology.