Research on Machine Tool Injury Phenomenon and Repair Technology

Grinding is a common cause of wear on the machine tool in an abnormal situation. The consequence of this is a direct decrease in the accuracy of use of the machine tool and a reduction in its service life. If it is not repaired in time, the granules produced by the research and injury will also aggravate the research and injury. Eventually, the sliding parts will end up sliding, resulting in a phenomenon of “killing”.

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

First, adhesive wear type grinding

Relatively moving friction pairs, due to friction with each other, contact the surface of the material from one surface to another surface, so that the friction surface scratches and grooves of scratch. We call it adhesive wear.

(I) Mechanism of Adhesive Abrasion Injury

Production practice and research show

Solid surface conditions, from the microscopic point of view, there are uneven defects, even after polishing and other finishing can not completely avoid this phenomenon. When two friction surfaces are in contact, it is actually the peaks of the two friction surfaces that are in contact with each other. Due to the large contact stress, elasticity and plastic deformation are generated and the contact area is physically increased until it can withstand the full load. At this point, the metal contact surface will have a strong adhesion point, we usually call this phenomenon cold welding adhesion. These stickies are easily produced without a surface film. If there is a surface film on the surface of the friction pair, it is only affected by the normal force. This phenomenon will not happen.

If at the same time there is a tangential force and the normal force and tangential force are both large, then the temperature of the friction surface will increase when it slides relative to one another. Under the double action of high temperature and high pressure, the oil film will be destroyed and contacted. The metal surface softens or melts, and the contact point produces a viscous, avulsive, avulsed, and avulsed cycle, causing the material of the contact surface to transfer from one surface to the other so that one of the surfaces (or both surfaces) is defined. Marks and grooves, that is, adhesion wear type grinding injury (two) classification of adhesion wear type grinding injury

According to the degree of grinding on the surface of the friction pair, the common adhesive wear on the machine is generally divided into four categories:

1. smear It occurs only on the surface of the soft metal surface. The thin layer of soft metal that has been scratched is transferred to the surface of the hard metal by smearing. For example, the copper of the worm gear surface after operation is applied on the worm surface.

2. Scuffing Damage is caused by small scratches along the direction of movement and occurs in the shallower part of the surface of the soft metal surface. Sometimes hard metal surfaces can also be scratched, which is common during the equipment run-in period.

3. Gluing (avulsion) When the friction pair does relative sliding. The sticking point is cut off from the base metal to cause avulsive damage on the surface and galvanic damage. It occurs more deeply in the base of the two parts that rub against each other. Such as machine tool guides and skateboards in the lack of lubricating oil and resulting in friction are mostly such injuries.

4. Scratching The temperature of the instantaneous flash of the relatively sliding parts is quite high, the adhesive area is large, and the adhesion point strength is also very high. The adhesion cannot be cut off from the substrate, causing the relative movement to stop. This is the most serious type of injury in our study, and the colloquial language is also called the "axis of suspension."

(C) Adhesive wear-related injury factors

Many factors have affected the occurrence of the research and injury phenomenon. We can take measures to really prevent sexual abuse by studying these factors, so as to prevent the occurrence and development of the research and injury phenomenon.

1. Lubricating Oil Factors Lubricating conditions have a great influence on adhesive wear. It is possible to maintain a lubricating film that always maintains sufficient strength on the friction surface to avoid direct contact with the metal surface between the friction surfaces to form a thousand friction or semi-dry friction. It is the key to prevent adhesive wear. It is important to ensure good lubrication of the friction surface.

2. Stress factors Under normal circumstances, with the increase of pressure, adhesive wear will increase. 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 points on the new surface between the two surfaces are embedded in each other, and mutual movement makes this kind of grinding damage worse. In severe cases, the surface of the friction pair is glued. Even killed. Heavy-duty machine tools are mostly such injuries.

3. Temperature factors In the heat generated by the friction process, when the temperature of the friction surface rises to a certain extent, the light damages the lubricating film, making direct contact with the surface to form dry friction or semi-dry friction: when severe, the material can be dried. The tempered state reduces the hardness of the material; the more serious phenomenon is that the local high temperature causes the friable material of the friction surface to be in a molten state. Therefore, the temperature has a great influence on the adhesive wear type grinding.

4. Sliding speed factor When the pressure is constant, the sliding speed is small, and the function of forming the lubricating film is reduced. At this time, the oil film traverse is small. The oil film is often partially damaged due to the pressure of the moving parts, causing the two metals to have direct contact. , easily lead to injury. But when the sliding speed reaches a certain level. It is also easy to cause the temperature of the friction pair to rise, and it is easy to damage the lubricating film, which in turn leads to scratching.

5. Surface Roughness Factors The smoother the surface, the greater the resistance to adhesive wear. Properly reducing the surface roughness value can prevent such grinding. Therefore, in the maintenance of the machine tool, the pattern is often scratched on the surface of the machine tool guide, the purpose is to facilitate the storage of oil, prevent research and injury.

6. Material factors Brittle materials have higher anti-adhesion and wear ability than plastic materials: friction pairs composed of mutually-soluble materials are more prone to adhesive wear than non-miscible materials. Friction pairs made of metal and non-metal have a small tendency to produce such scratches.

Second, abrasive wear grinding injury

Contamination of the particles entering between the two friction surfaces produces significant cutting action as the surface moves, resulting in scratches and grooves on the friction surface.

(A) The Mechanism of Abrasive Wear Grinding

After the hard particles enter between the two friction surfaces, they are subjected to two forces, one being the force perpendicular to the surface and the other being the force parallel to the surface. Hard particles penetrate into the surface under the former and tangential movement under the latter results in scratches or grooves on the surface.

(B) Classification of Abrasive Wear Grinding Injuries

We classify the common abrasive wear on machine tools into three categories:

1.Impact caused by bumping In the course of our production and processing, the guide rails of the machine tool are inevitably bumped by high-stressed articles such as workpieces or tools. Therefore, the surface of the guide rail is pitted, and at the same time, protrusions or burrs occur around it. If it is not repaired in time, when the skateboard is on the rails in East China, it will inevitably hurt the skateboard.

2. The external chips and sand caused by the entrance of the hard particles into the friction surface between the machine and the sliding plate will form a typical abrasive wear type grinding injury: the chip or sand presses the guide rail under the vertical pressure. Or the surface of the skateboard, when the skateboard moves, the guide rail and the skateboard are scratched.

3. Dirt caused by the dirt entering the friction surface through the lubricating oil into the friction surface between, although not crush the friction surface, but can change the contact surface of the friction surface, due to the dirt support, the pressure contact with the dirt place to withstand increased pressure Large, long-term operation will also produce scratches or minor scratches. No matter what kind of measures we take, the problem of machine tool injury is inevitable. Therefore, the purpose of our research on the mechanism and types of research injuries is to find out ways to repair injuries.

Once a machine tool is damaged, it must immediately stop running, find out the reason, apply the right medicine, and repair it in time. In general, a slight scratch on a smear may not be repaired, but lubrication must be strengthened to prevent the development of the wound. However, it is necessary to repair the wounds such as glue and bite. Now we discuss the repair and repair of several common friction pairs:

(c) Repair of Sliding Bearings and Shafts

1. After the sliding bearing surface is scratched, the preferred method is scraping. Sliding bearings generally have a margin for adjustment and repair, which can completely meet a machine repair cycle. If the research injury is very serious and the repair allowance cannot be met, it is necessary to replace the bearing in time.

2. When the journal has a scratch, you can use a small grinding journal, replace the sliding bearing method. However, the amount of shaft dressing should not be too large, such as the machine tool spindle, the amount of grinding can not exceed the surface of the bearing quenching, carburizing, oxidation, and carbonitriding thickness, after repair grinding surface hardness is not less than the original design of the hardness Lower limit: For drive shafts, the journal should not be smaller than the dimensions of the front journal or boss in the assembly direction when assembled.

Of course, it is also possible to repair the journal using a welding repair method, but the influence of the heating process on the geometric accuracy, the mechanical strength, and the surface hardness of the shaft should be considered.

It is also important to note that after the journal has been repaired, it is generally necessary to reconfigure the journal bearing or bearing sleeve.

(d) Repair of Worm Pairs

When the worm is bonded or scratched, the tooth surfaces of the worm are hardened and scratched, the surface hardness of the worm is reduced, and cracks may occur on the surface of the carburized worm. When repairing the worm gear, it is to repair the worm gear scrapped worm gear, or to repair the worm gear scrapped worm gear, or to repair them. In addition to their damage degree, the worm gear vice drive structure should also be considered. When the drive is a worm gear with a fixed center distance transmission, only one piece can be repaired. Replace one piece. The tooth thickness reduction of the repaired piece is compensated by the tooth thickness of the new thickened piece, so as not to increase the meshing backlash. From the standpoint of considering the tooth strength, it is not appropriate to reduce the tooth thickness of the worm gear, but the method of repairing the worm should be preferred. If the worm is carburized and quenched, the amount of tooth surface grinding should not be too large. If the value of the worm gear is considered more expensive, a method of repairing the worm gear and replacing the worm gear may also be used.

(five) repair of machine tool rails

For minor scratches and scratches on the machine's guide rails, it can be continued as long as it is repaired with a spatula or a grindstone.

For gluing, it needs to be repaired by welding or filling and gluing.

The welding repair and adhesion of machine tool guide rails is relatively complex, especially for large-area repairs. Before repairing, more consideration should be given to comprehensiveness: First, consider the accuracy of the guide rails used in the repair process and the mechanical properties. influences. If it is affected by temperature, will it cause deformation of the guide rail, whether it will change the mechanical strength of the guide rail, surface hardness, etc. Secondly, consider the adaptability of the repair technology used to guide rail materials. For example, cast iron rails generally do not use cast iron welding. Because of the poor weldability of cast iron, it is easy to produce cracks, air holes and other defects, and should not be processed. Third, consider the mechanical strength of the repair layer itself and the actual working environment of the guide rail. Different machine tools with different specifications, different performances, and different practical environments shall be selected for repair and adhesion repair materials, as well as advanced repair methods and new techniques.