RU2200077C1 - Method for abrasive working of screws by embracing tool - Google Patents

Abstract

FIELD: machine engineering, possibly finish abrasive working of screw surfaces of high-accuracy screws, for example screws of screw pump made of hard-to-polish materials by embracing polishing method. SUBSTANCE: method comprises steps of imparting rotation to part and imparting reciprocation lengthwise feed to tool; using as tool embracing member - toroidal elastic envelope with abrasive layer on inner surface of tore; performing cross in-feed of tool due to supplying compressed air into elastic envelope; setting revolution number of part depending upon cutting properties of abrasive material. Method provides intensified working of screw surfaces at uniform distribution of taken off allowance value. EFFECT: enhanced quality and efficiency of polishing due to increased surface area of contact between tool and work. 2 cl, 3 dwg

Description

 The invention relates to mechanical engineering - to the field of machine tool engineering and can be used in the final abrasive treatment of screw surfaces of precision screws, for example, screw pumps, from hard-to-grind materials using the method of covering grinding. A known method of belt grinding of bodies of revolution with a complex contoured surface with an endless abrasive tape pressed by a rigid or elastic counterbody [1].

 The disadvantages of the above grinding method are: the relatively low resistance of the tape; sophisticated kinematics control system for belt grinding; complex aggregation and automation of the belt grinding process; low productivity, low accuracy and processing quality.

 The objective of the invention is to improve the quality, performance and accuracy of processing screws by using the method of encompassing grinding, which increases the contact area of the tool and the workpiece and allows you to intensify the processing of screw surfaces.

 The problem is solved by the proposed method of abrasive processing of screws with a covering tool, including a message of a rotation part, and a tool with a reciprocating longitudinal feed, moreover, a toroid-like elastic shell with an abrasive layer on the inner surface of the torus is used as a tool, and the speed of rotation of the part is set in depending on the cutting properties of the abrasive, and the transverse flow - cutting due to the supply of compressed air into the elastic shell.

 In addition, the method is intended for processing screws of screw pumps.

 The essence of the method is illustrated by drawings.

 In FIG. 1 shows a processing scheme for the proposed method; in FIG. 2 is a section AA in FIG. 1; in FIG. 3 - toroidal elastic shell with an abrasive layer on the inner surface of the torus.

When finishing abrasive treatment of screws 1 (for example, screw pumps having a profile and dimensions D, D ₁ , t, e, e ₁ shown in Fig. 1) according to the proposed method into a covering toroidal elastic shell 2 with an abrasive layer 3 on the inner surface of the torus introduce the workpiece - screw 1. The diameter of the inner surface of the torus of the shell 2, on which the abrasive layer 3 is applied, is equal to the maximum diameter of the protrusions of the workpiece 1. With this ratio of diameters, the part 1 freely enters the hole of the shell 2.

 To increase the durability period, elbor, artificial and natural diamonds with rubber bonding are used as abrasive material, the thickness of the abrasive layer is 1 mm or more.

The screw 1 is informed of rotation around its axis with a speed of v _d = v _and equal to the speed of the tool during abrasive machining. The speed is assigned according to the characteristics of the covering abrasive shell 2 and the cutting properties of the abrasive layer 3, as in conventional conventional abrasive processing.

 A female toroidal elastic envelope 2 with an abrasive layer 3 on the inner surface of the torus is installed in the housing 4, which is mounted on a support, for example, a lathe (not shown).

 The workpiece - screw 1 is fixed in the cartridge 5 of the spindle 6 of the front headstock 7, for example, a lathe and is pressed by the center 8 of the tailstock 9.

 After the part 1 is fixed in the cartridge 5 and is tightened by the center 8, the main movement is turned on - the part 1 is rotated, and air is supplied under pressure P, bringing the tool 2 to working condition, into the elastic shell 2.

Simultaneously with the main cutting movement, which is the rotation of part 1, the tool 2 is informed of the reciprocating longitudinal feed _Sp .

The elastic abrasive shell 2 under pressure P of air covers the work screw 1 with a force proportional to the pressure P of compressed air, providing a radial infeed of cutting S _p . The inner surface of the shell 2 increases and decreases in diameter and takes the form of depressions and protrusions of the helical surface of the machined screw 1, conducting intensive abrasive processing along the entire length of the screw captured by the tool.

 Thus, the elastic shell 2 allows the radial movement of the abrasive layer 3 during abrasive processing, contributing to a uniform distribution of the removed allowance.

 The elastic shell 2, being a damper, smoothes out impacts and reduces vibrations, acts as a lunette, orients screw 1 along the line of machine centers and allows covering the processing of long non-rigid screws 1 without support from the rear center 8.

Example. The left screw N41.1016.01.001 of the screw pump EVN5-25-1500 was processed, which had the following dimensions: total length - 1282 mm, length of the screw part - 1208 mm, screw cross-section diameter - ⌀27 ^-0.05 mm, D = 30 mm, eccentricity e ₁ = 1.65 mm, e = 3.3 mm, pitch t = 28 ^{± 0.01} mm, roughness R _a = 0.4 μm; single-helical screw surface, left direction; material steel 18HGT GOST 4543-74, hardness HB 207-228, weight 5.8 kg. Side allowance - 0.25 mm. The processing was carried out on a mod screw-cutting machine. 16K20 using a female head consisting of a body and an elastic shell with a diamond layer on the inner surface of the hole отверстия 30 mm and a torus height of 200 mm, the thickness of the diamond layer is 1.0 mm, the diamond content at a 100% concentration of 56 carats. The elastic shell was fabricated on a fabric-rubber basis and a rubber-containing binder (analogue of the diamond endless seamless tape ALSHB used at the base enterprise). Cutting fluid - sulfofresol.

The peripheral speed of the workpiece - v _d = 169.56 m / min (2.82 m / s), n _d = 2000 rpm, the longitudinal feed S _ol = 2.8 mm / rev, the required roughness and accuracy of the screw surface was achieved after T _m = 5.5 min (against T $\genfrac{}{}{0ex}{}{\text{bases}}{\text{m}}$ = 16.5 min according to the basic version with traditional grinding using a grinding head, followed by polishing with a diamond strip on a 1K62 lathe at Livhydromash JSC). The control was carried out by an indicator bracket with an indicator ICh 10 B cells. 1 GOST 577-68. The cumulative error between any non-adjacent steps was not more than 0.1 mm, the clearance during control by the straightedge of the protrusions forming in diameter was not more than 0.07 mm, which is permissible according to the technical specifications.

 The advantages of the proposed method of abrasive machining with a female tool are the possibility of abrasive machining of shafts with a variable cross-section, in particular screws, the desired cutting speed, high productivity are easily achieved.

 The advantages of the proposed method of abrasive machining with a covering tool: lack of joints; smoother processing; high rigidity of the technological system; there is no need to support a machined non-rigid screw having a long length with a small diameter from the bend of the rest (with traditional round grinding, the presence of a rest is necessary); the quality and accuracy of processing are improved due to the tool covering the treated surface while removing large uneven allowances; processing productivity is increased by a factor of 2–3 due to the large contact area of the tool with the workpiece and a reduction in the number of passes.

 Thanks to the application of the proposed method for abrasive processing of screw surfaces of screws with a female tool, the quality is improved and productivity is increased due to the increased contact area of the tool and the workpiece, which makes it possible to intensify the processing of screw surfaces and the uniform distribution of the removed allowance.

 The female tool in the form of an elastic shell, being a damper, smooths out impacts and allows vibration-free processing, performs the function of a backrest, automatically orientates the part — the screw along the line of the machine’s centers, and allows covering the processing of long non-rigid screws without back center support. The method is easy to automate.

Sourse of information
1. Abrasive and diamond processing of materials. Directory. Ed. A.N. Reznikova. - M .: Engineering, 1977, p.246-252, Fig. 3.15e - prototype.

Claims (2)

 1. The method of abrasive processing of screws with a covering tool, including the message of the rotation part, and the tool - reciprocating longitudinal feed, characterized in that as the tool using the covering part is a toroidal elastic shell with an abrasive layer on the inner surface of the torus, while transverse cutting the tool by supplying compressed air to the elastic shell, and the speed of rotation of the part is set depending on the cutting properties of the abrasive.  2. The method according to p. 1, characterized in that it is intended for processing screws of screw pumps.

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