RU2631738C2 - Gear of the drilling bit - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: gear of a drill bit consists of a shank with a convex generatrix and a convex rock-breaking part. The convex shank generatrix is designed so that the center of the shank has a diameter D exceeding the diameters at its ends by an amount δ=(0.3-0.4)Δ, where Δ - the calculated diametrical tightness of the shank of the tooth in the slot of the cutter. The convex shank generatrix can be made along a certain arc of a circle, a broken line or a logarithmic curve.

EFFECT: uniform distribution of contact pressures along the entire shank of the gear, reducing the crushing-shearing surface of the socket when pressing the gear.

2 dwg, 1 tbl

Description

The invention relates to cone drill bits, in particular teeth of carbide carbide weapons cones. A tooth consists of a shank in the form of a body of revolution with a convex generatrix and a protruding rock-cutting spherical or conical-spherical part, coaxial with the shank.

Carbide teeth are known for cone drill bits containing a cylindrical shank and a spherical or conical-spherical rock cutting part [1]. A disadvantage of the known clove is that when it is pressed into the cylindrical nest of the cone body, crushing-cutting of the landing surface of the nest occurs, which reduces the calculated interference in the connection by 10-15% and, therefore, reduces the force of fixing the clove.

Another disadvantage is the occurrence of a contact pressure concentration at the ends of the cylindrical shank, reaching a value of 140-150% of their average calculated value [4, 6]. When drilling in a shock-vibration field, these stresses can reach the plasticity limit of the material of the cone nests and lead to the loss of teeth in the face or chip of the hard alloy of the tooth.

Also known are teeth with a shank in the form of a convex body of revolution representing a sphere [2] - a prototype. And as is known from analytical geometry, such a surface is characterized by a center of curvature located on the axis of rotation of the generatrix. The disadvantage of the prototype is that to eliminate the concentration of contact pressures at the ends of the shank, reducing their diameters in relation to the diameter of the tightness in the middle of the shank for pressing the clove into the cone nest significantly (at times!) Exceeds the value of this tightness Δ. In the practice of bit construction, the relative diametric interference is Δ / D = 0.005-0.010. And the shanks of the teeth according to the technical specifications TU 48-4205 - 88 - 2009 [1] have a ratio of the height h of the shank to its diameter D equal to h / D = 0.5-1.0. From geometric constructions it follows that even with the most favorable ratio h / D = 0.5, the underestimation of the diameters of the ends of the shank, made in the form of a sphere, will be 0.134D, i.e. will exceed the calculated relative interference by 27-13 times. And from this it follows that after pressing in with a technologically justified fit Δ, the contact of the shank with the socket will be provided only on a small part of its length and, accordingly, its retention in operation will not be provided. Even in this very favorable ratio h / D = 0.5, no more than 15 ... 20% of the length of the shank will be in contact with the socket, and the contact pressures at the ends of the shank will be 0.

The technical problem to which this invention is directed is to determine the magnitude of the understatement γ _{o of the} convex generatrix at the ends of the shank, at which the contact pressures along the entire shank are evenly distributed and a reduction in the shear-shear of the surface of the socket when pressing the clove will be reduced. The problem is solved in that the generatrix of the shank of the clove is made so that the diameters at the ends of the shank are less than the diameter at its middle by δ = (0.30-0.40) Δ, where Δ is the diametrical interference in the middle of the shank of the clove in the cone;

The design of the tooth is shown in FIG. 1. It consists of a shank 1 with a convex generatrix 2 and a rock-cutting spherical or conical-spherical part 3.

Here H is the total height of the clove; h is the height of the shank, mating with the cone nest; D is the outer diameter in the middle of the shank; γ _o - understatement of the generatrix of the shank at its ends relative to the middle; r is the radius of the sphere of the rock-cutting part; C is the value of the chamfer at the end of the shank.

The study of contact pressures on the interface surface of the shank with the socket was performed according to the Lame formulas [4] for thick-walled pipes. In our case, the clove is considered as a covered part, and the body of the cone as covering. To draw up a design diagram of the outer diameter of the female part (cone) for each tooth, a scan of the outer surface of the cone body with the whole set of nests is constructed on a scale, from which it was established that the wall thickness between adjacent nests is on average 0.5D, therefore, the estimated external diameter of the cone the details is d _o = D + 2 (0.5D) = 2D.

The study was carried out on the teeth of the G 2613 × 12 ... G 2613 × 19 family according to TU 48-4205-88-2009 [1] in bit cone bits 250.8 OK - PGV and 244.5 OK - PGV.

If we denote the relative thin-walledness of the covered part, the tooth is a ₁ = d / D = 0 / D = 0 (for a solid part, the inner diameter is taken d = 0) and the covering part a ₂ = D / d _o = D / 2D = 0.5 then

Lame's formula [4] for calculating the contact pressure in conjugation is written as follows:

where C ₁ = (1 + a ₁ ² ) / (1-a ₁ ² ) = 1; C ₂ = (1 + a ₂ ² ) / (1-a ₂ ² ) = 1.25 / 0.75 = 1.67;

A is the calculated diametrical interference in conjugation of the tooth with the socket;

d, D and d _o - the inner diameter of the clove (male part), the outer diameter of the clove and the outer diameter of the female body part of the cone, respectively;

E ₁ and E ₂ are the elastic modulus of the tooth material and the cone body, respectively, E ₁ = 6 * 10 ⁵ MPa, E ₂ = 2 * 10 ⁵ MPa;

μ ₁ and μ ₂ - Poisson's ratio of the tooth and cone body, μ ₁ = μ ₂ = 0.3.

From dependence (1) it follows that the contact pressure is directly proportional to the value of the interference in the connection. From the theory of resistance of materials [3, 5] it is known that in such compounds the stress concentration at the ends of a cylindrical shank is 140-150% of the average calculated value. In rolling bearings at the ends of cylindrical rollers, the stress concentration is 140% of their magnitude in the middle of the rollers [6]. Therefore, to eliminate the concentration of contact pressures in these zones, the tightness at the ends of the mating surfaces must be reduced. The criterion for reducing the interference fit at the ends of the shank is taken from the following considerations: from the constructive and technological practice of chisel construction, the tooth landing in the cone is carried out according to the quality landings (socket / shaft) - U8 / u7. This means that the minimum interference Δ _min is approximately two times less than the maximum Δ _max = 2Δ _min , the average interference Δ = 1.5Δ _min or Δ _min = Δ / 1.5 = 0.666Δ. Obviously, in order to avoid insufficient tightness at the ends of the shank in the most “weakened” pairs of teeth - the socket of the interference on them should not be lower than half the minimum interference, i.e. the underestimation of the diameter at the ends should be δ = 2γ _about = 0.5Δ _min = 0.5 × 0.666Δ = 0.333Δ. Given the technological capabilities of this invention, an underestimation of the diameters at the ends of the shank δ = (0.3 ... 0.40) Δ or the range of convexity of the middle of the generatrix of the shank relative to the ends γ _o = 0.5δ = (0.15-0.20) Δ .

The convexity of the generatrix is performed by several methods. The simplest is to execute it along an arc of a circle, FIG. 1, where R is the radius of the arc of a circle, O-O are the centers of curvature of the arcs. From elementary geometry it is known that for circular arcs, if the arrow γ _about the chord arcs is less than 0.01 of the length of the chord h, then with an error of no more than 2% the arrow (in our case this is the convexity of the generatrix) is determined by the formula γ _о = h ² / 8R, whence we obtain the expression for the radius of convexity of the generator

Geometrical constructions show that an arc of a circle representing the shape of a change in the convexity of a generatrix along a shank can be replaced with an error of no more than 10% by a broken line consisting of a segment parallel to the axis of the shank on its middle part along the length (0.3-0.4) h , and segments inclined at an angle β to the axis at the ends of the shank, which is determined by the formula

In FIG. 2 shows a tooth made with a generatrix in the form of a broken line. Here H, h, r, C is similar to FIG. one; 2 _c - forming a cylindrical middle section; 2 _to - forming conical sections at the ends of the shank; l _C , l _k - the length of the cylindrical and conical sections, respectively; β is the angle of inclination of the generatric conical sections to the axis of the shank.

By analogy with the contact of cylindrical rollers with track rings in rolling bearings, providing a uniform distribution of contact stresses along the generatrix of the roller, underestimation along the generatrix of the convex generatrix of the shank of the tooth can be performed by a logarithmic curve [6], expressed by the dependence

where the coefficient A = (0.15-0.20) Δ / Dln [1- (2X _max / h + 2C) ² ] ^-1 is determined from the condition that the generatrix at the ends of the shank is underestimated relative to its middle by γ _о = 0, 5δ = (0.15-0.20) Δ, i.e. substituting in (4) the necessary underestimation of γ _о at the end and transforming with respect to A, we obtain its value.

D is the diameter in the middle of the shank, X _i is the distance of a particular section of the shank from its middle (see Fig. 1), X _max = 0.5h; h + 2C - the height of the shank, taking into account the chamfers. Perhaps convex execution of the generatrix and another type of mathematical dependence.

The change in understatement γ _{i of the} generatrix along the tooth axis G 2613 × 12 with a shank height h = 7 mm with a chamfer C = 0.7 mm and contact pressures P _i for various forms of the generatrix are presented in the table. For all versions, the understatement at the ends of the shank adopted 0.17 average interference Δ = 0.09 mm, i.e., γ _o = 0.09 × 0.017 = 0.015 mm. For a generatrix made along an arc of a circle, its radius is adopted in accordance with (2) 408 mm. For a broken line, the length of the middle cylindrical part is taken to be 0.4h = 0.4 × 7 = 2.8 mm, the angle of inclination of the generatrix in the conical section is β = arctg0.015 / 2.1 = 0.409 ° = 25'_ For the logarithmic curve, A = 0.000973, X _max = 0.5h = 0.5 × 7 = 3.5, and the length of the shank to ensure that at the edge of the start of the chamfer of understatement at a given level of 0.015 mm is taken as h + 2C = 7 + 2 × 0, 7 = 8.4 mm, at which the coefficient A is calculated and the γ _i generatrix in the remaining sections is understated.

The results of calculating the contact pressures on the interface between the tooth and the nest along its axis for various versions of the convexity of the generatrix presented in the table show their good coincidence. In this case, the difference between the understatement of the generatrix and, consequently, the diametrical interference and pressure in similar sections of the shank is no more than 6% of the average value (the worst case in the section is ± 0.4 h). A 33% reduction in design pressure at the ends of the liner eliminates the stress concentration at the ends of the liner inherent in a purely cylindrical liner and reaches 140-150% of the average value in them.

A comparison of the underestimation of the generatrix along the axis of the shank shows that all of them, with practical satisfactory accuracy, provide equalization of contact pressures along the shank.

Information sources

1. Polished carbide teeth polished for cone drill bits. TU 48-4205-88-2009, JSC Kirovograd ZTS, 2009

2. USSR Copyright Certificate No. 391259, Bull. 1973, No. 31.

3. Ivanov M.N. Machine Parts, Textbook for High Schools, Moscow: Higher School, 1976

4. Orlov P.I. "Fundamentals of designing", Reference and methodological manual, vol. 2 M .: Mechanical Engineering, 1988

5. Fedoseev V.I. Resistance of materials, Moscow: Nauka, 1967

6. Spector A.A. Optimization of internal geometry and calculation of contact interaction characteristics of parts of cylindrical roller bearings. Computer-aided design of rolling bearings. NGO VNIPPP. Collection of scientific papers. 3, M. 1987.

Claims (8)

A drill bit tooth, consisting of a shank with a convex generatrix and a convex rock cutting part, characterized in that the convex generatrix of the shank of the tooth is made so that the middle of the shank has a diameter D exceeding the diameters at its ends by δ = (0.3-0.4 ) Δ, where Δ is the calculated diametrical tightness of the tooth shank in the cone nest, and the convex generatrix of the tooth shank can be made along an arc of a circle of radius R, determined from the dependence

, or along a broken line, so that the middle part of the shank represents a cylinder of diameter D, and both ends at a length (0.25-0.35) h are made of conical surfaces with an inclination forming at an angle to the tooth axis

, or along a logarithmic curve with a current understatement of γ _i forming along the axis of the shank at a distance X _i from the middle of the shank, expressed by the dependence

, where h is the height of the shank, C is the value of the chamfer of the shank, coefficient A is determined by the dependence

.

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