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Some relative sliding machine tool zero, parts, such as skateboards and rails, shaft and sliding bearings, worm and worm gear and so on for some time in operation, the surface often scratches or grooves, we call this phenomenon of wounds . Grinding injury destroyed the accuracy of the machine tool, affecting the service life of the machine tool, if the repair is not timely, grind the particles produced, but also exacerbated the wounds, and research wounds to produce grooves easy to dirt, but also aggravate trauma, In serious cases, the sliding of each other can stop sliding, resulting in seizure. The traumatic injury is actually the non-normal wear and tear, and the common injury on the machine tool can be divided into two types according to the causes: one is the adhesive-type wound injury and the other is the abrasive-wear type wound injury . Now on the two types of injuries caused by the reasons, preventive measures and repair methods, to do some brief introduction. First, the adhesive wear type of injury This type of injury refers to the friction pair in the relative movement, due to mutual friction, the contact surface material from one surface to another surface transfer, resulting in scratches and grooves on the friction surface. 1. Adhesive and wear-type research on the mechanism of injury Research shows that: the solid surface conditions, from the microscopic point of view there is the bumpy defects, even after polishing can not completely eliminate the convex peaks and valleys. When the two friction surfaces are in contact, the peaks of the two friction surfaces actually touch each other. As the contact stress is large, resulting in elastic, plastic deformation, the contact area increased until it can withstand the full load up. In this case, a solid sticking point will appear on the metal contact surface, a phenomenon that is commonly referred to as cold bonding. These sticking points are produced without a surface film, and when there is a surface film on the surface of the rubbing pair, it is only exerted by the normal force and the cold welding adhesion does not occur. If at the same time the role of tangential force, and the normal force and tangential force are large, and do relative sliding, the friction surface temperature will rise under high temperature and pressure, resulting in the destruction of the oil film, the contact surface of the metal It softens or melts, and the contact points create a stick-to-tear-to-stick-to-tear cycle in which the material contacting the surface is transferred from one surface to the other such that one of the surfaces (or both surfaces) The formation of scratches and grooves, that is, the formation of adhesive wear type of injury. 2. Adhesive and wear type of injury According to the friction on the surface of the damage degree of injury, we can be common on the machine tool wear and tear injuries are divided into four categories: (1) smear injury occurred only in the shallow metal layer Surface, a thin layer of soft metal to be scratched is transferred to a hard metal surface by painting, for example, after the worm gear has been operated for a while, copper on the worm surface is smeared on the surface of the worm. (2) Scratch Researcher injury occurs in the shallower part of the surface of the soft metal surface. The way of destruction is to make small scratches along the movement direction, and sometimes the hard metal surface may be scratched. The most common is the initial operation of the machine, shaft and sliding bearings in the wear and tear of the period. (3) gluing (or avulsion) injury occurred in the mutual friction of two parts of one or both of the substrate deep, due to the local surface temperature is high, the pressure is large, so that the adhesive bond strength of any base metal shear Intensity, when the friction pair to do relative sliding when the surface to do a day monk hit a day of avulsion destruction, there adhesion injury. Such as the cam, worm, gear pairs, more common; machine skateboards and rails in the absence of lubricating oil caused by dry friction, often produce such injuries. (4) When the temperature of the surface of instantaneous flashing is relatively high, the adhesive area is large and the strength of the adhesive point is also quite high. The adhesive can not be cut off from the base so as to cause the relative movement to stop. Kill dead is the most serious kind of injury. Such as shaft and plain bearings when poor lubrication and the emergence of the "axle", the majority of this research injury; large machine rails lack of oil caused by a large area of ​​injury will also produce biting. 3. Adhesive and wear-related injury factors and preventive measures of such injuries There are many factors that we can take these factors to take appropriate measures to prevent its occurrence and development. (1) Lubricating grease factors Lubrication conditions have a great influence on adhesion and wear type injury. As long as the friction surface always maintains sufficient strength to lubricate the membrane to prevent the frictional surface from directly contacting with the metal to form dry or semi-dry friction, Effectively prevent and control the occurrence and development of adhesive and wear type wounds. Among the various factors that affect such an abrasive injury, ensuring that the lubricated surfaces are well lubricated is the most important factor. Lubricants add oil or viscosity additives, oil film can improve the adsorption capacity and film strength, can be multiplied to improve the ability of anti-injury. (2) pressure factor Adhesive wear-type injury, usually with the pressure increases. When the pressure load exceeds a certain value of the hardness of the friction material, the oxide film on the surface of the friction pair is crushed, and the protruding spots of the nascent surface between the two surfaces are embedded with each other. When the pressure is relatively moved, the type of the injury will sharply increase, Lead to friction surface cohesion, or even killed. Therefore, the use of machine tools, table, slide rail to avoid overload operation, such as gantry planer, milling machine, boring machine and other workpieces on the table clamping workpiece, it is necessary to distribute the reasonable, but also not overweight. Machine tools in the major repairs, the guide rail quenching, to prevent such injuries have a great effect. (3) Factors of temperature The impact of temperature on the adhesion-induced wear injury is also significant. The heat generated in the friction process, the temperature of the friction surface increased to a certain extent, the light, the destruction of the lubricating film, the metal surface in direct contact with the formation of dry friction or semi-dry friction; severe, make the material in the back Fire conditions reduce the hardness of the material; in heavier cases, the material on the surface of the friction in a localized area can be melted. All of these will prompt the development of such wounds. Selection of materials with high thermal stability or cooling and other measures to prevent sticking due to temperature and wear an effective method of wounding. (4) factors of sliding speed under certain pressure, the sliding speed is small, the role of the formation of lubricating oil film decreases, the smaller the film thickness, often due to the oil film can not afford the pressure of moving parts of the partial destruction, resulting in two metals in direct contact , Easily lead to research injury. However, when the sliding speed is large enough, the temperature of the friction pair is increased, the lubricating oil film is easily damaged, and the wounding is easily caused. Therefore, selecting a suitable sliding speed can reduce the tendency of adhesive wear injury. (5) the factors of surface roughness In general, the smaller the surface roughness of the friction pair, the greater the anti-adhesive wear type of injury, the appropriate reduction of surface roughness to prevent such injuries, the new machine tools are often used Gradually loading run-in operation, the purpose is to reduce the surface roughness, to reduce the early generation of adhesive wear-type wounds. However, the friction surface roughness drops too low, the lubricant can not be stored between the friction surface, and easily lead to research injury, so when the pattern on the machine tool is worn, when maintenance of the machine, often scraping pattern again , The purpose is to facilitate oil storage, prevention of wounds. (6) Factors of material The brittle material is more resistant to anti-adhesion and abrasion than the plastic material; the friction pair composed of large mutual solubility material is more likely to have wear-type wound than the friction material made of small miscibility material; Friction pair composed of nonmetal is less likely to produce such flaws than friction pair composed of two kinds of metal. Maintenance of machine tools, non-metallic coating can be used to repair skateboard rails, shafts and sets of different materials, or the shaft surface treatment process, reducing the occurrence of adhesive wear injury. Second, the abrasive wear-type grinding This type of grinding injury refers to the pollution into the friction between the two hard particles between the surface movement in the significant cutting effect, resulting in scratches and grooves on the friction surface. 1. Abrasion-type abrasive injury mechanism Hard particles into the friction between the two surfaces by the role of two forces, perpendicular to the surface and parallel with the surface force. The hard particles pierce the surface under the former action and the latter act tangentially, which causes the surface to be plowed or cut, leaving scratches and grooves, ie, wounds of injury. 2. abrasive wear type injury classification (1) bump caused, such as machine tool rails, by the workpiece or tool and other items of high stress bump, the surface of the track will appear pits, while the pit will appear around the convex Rise or burr. If not repaired in time, when the skateboard is sliding on the guide rail, the convex or burr on the guide rail is bound to hurt the skateboard. (2) hard particles caused by the friction between the two surfaces, such as chips or sand into the machine between the guide rail and skateboard, will form a typical abrasive wear injury research: chip or sand under vertical pressure, crushing the guide rail or slide Surface, the rail or skateboard will be injured when moving. (3) When dirt enters the friction surface, such as dirt entering the friction surface through the lubricating oil, it will not change the friction surface, but it can change the contact condition of the friction surface. Due to the support of the dirt, Compressive stress increases, after a long run, the friction surface is bound to produce scratches or scratches. 3 abrasive wear-type injury prevention (1) First of all, to prevent the surface of the friction bump wound bumps, such as not on the machine rail stacking tools, measuring tools, artifacts and other debris, followed by bump surface friction bump should be promptly repaired , Such as the bumps and burrs generated to use oil stone or scraper timely repaired to prevent abrasion friction surface; pits appear as much as possible to repair, to prevent the pit dirt, leaving a hidden danger to the injury. (2) fortification and configuration of the guard to prevent such as chips, sand and other hard particles into the friction between the surface, once found hard particles or debris into the friction surface, should be immediately ruled out to prevent the injury or expansion. (3) maintenance of machine tools on time, timely removal of rails, skateboards, oil holes and dead ends of the dirt grease to prevent dirt from entering the friction surface between the formation of abrasive wear-type wounds. Third, the wound repair wound friction in the event of a research injury, it must immediately stop running to find out the reasons for the degree of injury, take different measures. In general, the smear of a type of research injury, you can not repair, but to strengthen the lubrication, to prevent expansion; on the abrasion (including dirt caused by scratches), to remove dirt and grease or scraper scraper After the site is flattened, it can continue to run: while the glue, bite and hard particles caused by wounds, you must repair. At present, there are several kinds of friction pair repair injury will be some simple introduction: 1. Sliding bearing and shaft repair (1) sliding bearing surface was ground injury, the preferred repair program should be masonry method to repair. In general, the sliding bearings are left for adjustment and repair allowance to meet the machine's a repair cycle. If the injury is very serious, repair allowance can not be met, you need to consider the replacement. After the two half-watt-type sliding bearing research, you can reduce the shim reassembly, scraping the bore bearing bore precision requirements, continue to use after repair. (2) when the journal has a research injury, you can use grinding small journals, replace the sliding bearing method. However, journal grinding should not be too large, such as machine tool spindle, grinding amount should not exceed the surface of the journal quenching, or carburizing, nitriding, cyanide thickness, grinding surface hardness of the journal shall not be less than the lower limit of the original design hardness ; For the drive shaft, the journal should not be smaller than the size of the journal or boss at the front of the assembly direction during assembly. If repairing the journal with the method of welding, then consider the influence of the welding heating process on the geometrical accuracy, mechanical strength and surface hardness of the shaft. After the journal is repaired, it usually needs to make the plain bearing (or sleeve) according to the journal again. 2. Machine Tool Guide rail repair For the light rail scratches and abrasions, as long as the use of knives or Whetstone repair, you can continue to run. For adhesive injury, you need to repair or repair with welding repair or filling, even if the larger area of ​​injury, as long as the retention of the larger part of the intact rail surface, you can also use such methods to repair. Until the machine make repeated orders, and then use fine sharpener, fine grinding or sticky board, paneling and other methods of repair. Relatively speaking, the workmanship is comparatively complicated, especially for the repair of large-area wounds. Before the construction, more consideration should be given to some details. First, the precision, Whether the mechanical properties, such as welding repair and sticky mostly need to heat, then the process temperature will cause rail deformation, rail will change the mechanical strength and 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 the poor weldability of castings, easy to produce cracks, porosity and other defects, and the processing is also difficult. High temperature process (referring to gas welding), easily lead to rail deformation and so on. The third to consider the repair layer itself mechanical strength and the actual working environment guide. For example, we also use tin bismuth alloy surfacing repair 4m planer guide and T68 boring rail, the former rail lubrication conditions have been good, has been in use for 20 years, the situation is still good; the latter due to poor lubrication conditions, poor working environment, only Three years off off. In short, as much as possible to make the repair layer to meet a certain period of use. In the machine overhaul, the guide rail is generally taken as the following two ways to repair: First of all, the bed rail fine planing, fine milling or fine grinding, grinding injury trim, according to the size of the bed rail repair and skate wear , Or replace the skateboard, or in the skateboard rail bonding other compensation materials, such as polytetrafluoroethylene soft tape, epoxy wear-resistant coating, nylon or metal plates with inserts to compensate for the size of the chain Another way is to fine After processing the bed rails inlaid with pre-heat treated steel rails or hardened steel.
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