JP2011235409A - Machining method for sliding surface and cast iron material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a sliding surface having high lubricity with simple machining instead of scraping.SOLUTION: A bed of a machine tool is cast using spheroidal graphite cast iron of FCD450, and its sliding surface is ground into a flat surface by machining. The sliding surface of a column to be put on the bed is also ground into a flat surface in the same manner. The spheroidal graphite appears on the sliding surface and, by ejecting water jet to the sliding surface, the spheroidal graphite on the sliding surface is removed. Since the size of the spheroidal graphite is within the range of 5-80 μm, the size of a minute recessed part after removing the spheroidal graphite is nearly the same as that of the spheroidal graphite. Since the minute recessed part serves as an oil reservoir of lubricating oil, an oil film is uniformly formed between the sliding faces and the sliding face has high lubricity.

Description

  The present invention relates to a method for processing a sliding surface of a machine tool or the like that omits scraping and a cast iron material.

  Spheroidal graphite cast iron is cast iron in which black iron crystallizes into a spherical shape, and is frequently used as a structural member of machine tools because of its high mechanical properties and vibration absorption performance. When used on sliding surfaces of machine tools such as tables and columns, the surface is subjected to scraping to improve mechanical accuracy, and the recess on the scraping surface becomes an oil reservoir to improve lubricity. This improves the positioning accuracy of the machine tool and enables high-speed movement of the table, column, and the like.

  However, in order to scrape the sliding surface, processing by a skilled technician is necessary, and there is a problem that processing takes time. On the other hand, if the scraping operation is omitted, there is a problem that the sliding resistance increases because the oil cannot be accumulated. Further, a sliding surface in which a large number of shallow dish-shaped concave portions are formed by machining instead of scraping is known (see Patent Document 1), but processing of such a complicated sliding surface takes time and effort. There is a problem that it takes.

JP 2003-213333 A

  Accordingly, an object of the present invention is to obtain a sliding surface that can obtain high lubricity by simple processing instead of scraping.

  The method for processing a sliding surface according to the present invention is characterized in that the spherical graphite is removed by a water jet from a cast surface made of cast iron and spherical graphite appears on the surface to form a large number of minute recesses. That is, the spherical graphite exposed on the sliding surface is removed by the impact of the water jet, and a large number of minute recesses are formed in the part where the spherical graphite is peeled off. Alternatively, the sliding surface may be mirror finished by buffing or the like. In that case, for example, the surface roughness by mirror finishing is set to a range where the maximum height is 0.1 μm or less.

  The cast iron material of the present invention is characterized in that it has a sliding surface made of spheroidal graphite cast iron having a large number of fine concave portions having the shape and size of spheroidal graphite on the surface. Further, the sliding surface is mirror-finished, and preferably has a surface roughness in the range of a maximum height of 0.1 μm or less.

  A bed of a machine tool is cast using spheroidal graphite cast iron, and its sliding surface is finished to a flat surface by cutting and grinding. Spherical graphite appears at a constant area ratio on the ground sliding surface. A water jet is sprayed onto the sliding surface on which the spherical graphite appears, and the spherical graphite is removed. Thereby, a large number of minute concave portions having the shape and size of spherical graphite are formed on the sliding surface. The size of the minute recesses depends on the size of the crystallized spherical graphite, and the length and depth are several μm to several tens of μm.

  The water jet is injected by using a high-pressure pump capable of obtaining a predetermined injection pressure, and water is injected from the tip of the water jet gun at a predetermined injection pressure. Also, the residual stress on the sliding surface can be relaxed by adjusting the jet pressure of the water jet. A sliding surface having the same micro concave portion or a smooth sliding surface having no micro concave portion or scraped depression is overlapped on the sliding surface having such a micro concave portion with a lubricating oil having a predetermined viscosity. Match. In this superposed state, the minute concave portion becomes an oil reservoir for lubricating oil, so that an oil film is uniformly formed between the sliding surfaces, and high lubricity can be given to the sliding surfaces.

  As described above, according to the method for forming a sliding surface of the present invention, a large number of minute recesses can be formed on the sliding surface by removing the spherical graphite that appears on the sliding surface with a water jet. These minute recesses are not formed by machining, but are formed by jetting a water jet having a predetermined pressure, so that it is not necessary to perform any machining on the sliding surface. Moreover, since it is not heated by machining, the mechanical properties of the sliding surface are not affected at all.

  Further, the sliding surface after removing the spherical graphite may be subjected to surface treatment such as quenching and polishing. The sliding surface is hardened by induction hardening or laser hardening. By this quenching, part or all of the base structure of the spheroidal graphite cast iron is changed from the ferrite structure to the pearlite structure, and the hardness of the sliding surface is increased.

For the polishing process, for example, buffing using an abrasive in which calcined alumina is mixed with fats and oils is used. When mirror finishing is performed by buffing, a lubricant having a high kinematic viscosity is used. For example, a kinematic viscosity at 40 ° C. having a midpoint viscosity of 60 or more is used. The surface roughness (Rmax) is selected in the range of 0.05S to 0.4S, but is preferably 0.1S or less. As a result, slip resistance can be reduced, positioning accuracy can be improved, and processing time can be shortened by high-speed driving.

  The sliding surface formed as described above can be used not only for the bed of a machine tool but also for each sliding surface such as a column. Further, it can be widely applied to machines other than machine tools (for example, bearings). In addition, if the spherical graphite on the sliding surface can be efficiently removed and minute irregularities having the shape and size of the spherical graphite can be formed on the sliding surface, the spherical graphite is removed by a method other than water jet. Also good.

A machine tool bed is cast with spheroidal graphite cast iron of FCD450, and the sliding surface made flat by grinding is ground. The sliding surface of the column placed on the bed is similarly ground. By this grinding process, the surface roughness (Rmax) becomes about 3.2S. Further, spherical graphite appears on the sliding surface, and a water jet is jetted onto the sliding surface. The injection pressure is about 50 MPa. Since the spherical graphite on the sliding surface is removed by the water jet and the size of the spherical graphite is in the range of 5 μm or more and 80 μm or less, the size of the minute recesses after the removal of the spherical graphite is substantially the same.

After removing the spherical graphite, induction sliding is performed on the sliding surface. The hardened layer is formed by heating the surface of the sliding surface to a predetermined temperature by high frequency induction with an induction hardening device. Subsequently, the sliding surface after the quenching treatment is buffed with 0.3 μm alumina so that the surface roughness (Rmax) is 0.1 μm or less. Then, a lubricating oil having a kinematic viscosity of 85 to 170 millisquare meters / second at 40 ° C. is interposed on the sliding surface. The relationship between the surface roughness and the kinematic viscosity of the lubricating oil and the effect thereof are disclosed in Japanese Patent No. 4228078.

Claims (6)

It is made of spheroidal graphite cast iron, and the spherical graphite is removed by spraying a water jet at a predetermined pressure on the sliding surface where the spherical graphite appears on the surface, thereby forming a large number of minute recesses on the sliding surface. A processing method of a sliding surface characterized. The sliding surface processing method according to claim 1, wherein after the spherical graphite on the sliding surface is removed, the sliding surface is mirror-finished. The method for processing a sliding surface according to claim 2, wherein the surface roughness by the mirror finish is a range having a maximum height of 0.1 μm or less. A cast iron material characterized by having a sliding surface made of spheroidal graphite cast iron having a large number of fine recesses on the surface of the shape and size of spheroidal graphite. The cast iron material according to claim 4, wherein the sliding surface is mirror-finished. The cast iron material according to claim 5, wherein the surface roughness by the mirror finish is in a range of a maximum height of 0.1 μm or less.