RU2157304C1 - Method for separating elongated rope blank - Google Patents

Abstract

FIELD: cutting of steel ropes by preset-length pieces, namely at making special flexible member of modern locking devices. SUBSTANCE: method comprises steps of performing local recrystallization annealing of zone for cutting by means of electric-resistance heating before thermally separating rope due to melting it at passing welding electric current; subjecting annealed portion to axially symmetrical plastic deformation by value consisting no less than 0.7 of initial diameter of blank in order to form necking portion with symmetrical or non-symmetrical profile. Method allows to shape non-twisting end portions in the form of pointed head and flat tail maximally corresponding to final design of flexible member. EFFECT: enhanced efficiency of method. 3 dwg, 1 ex

Description

 The invention relates to the field of machining associated with the operation of cutting steel ropes (cables) into separate segments of a given length.

 In many industrial enterprises, steel wire ropes are widely used as a supporting element. Usually they are delivered to consumers in the form of bays, wound on special coils (spools), in which the total length of the rope is hundreds and thousands of meters. In this case, it often becomes necessary to cut the ropes into separate pieces (segments) of a certain size. Such a technological operation, as a rule, is one-time in nature. On the other hand, there may be cases when such cutting of a wire rope blank is required on a mass scale. In particular, a similar situation is encountered in the manufacture of a special product - a flexible element (called a "whip"), used as the main unit of special locking devices.

A flexible element is usually made of a steel rope (galvanized or uncoated) with a diameter of up to 6 - 7 mm. Usually two types of whip are used - 350 and 450 mm long. Its design provides for the presence of a front pointed end (in the form of a cone or a multifaceted pyramid with an angle at the apex of 80-90 ^o ). The rear end is usually in the form of a flat heel.

 Since a long rope billet is used for the manufacture of a flexible element, the procedure of dividing it into measured segments becomes an important technological operation. In this case, it is fundamentally important to use such a technology that eliminates the violation of contact mating of strands of twisted rope and their fan-shaped separation (the formation of a "fluffy" end). Otherwise, there is a serious technical difficulty in the subsequent technological operation associated with obtaining a pointed warhead and processing the rear end.

 There are known examples [1] of mechanical cutting of a rope billet with special scissors when, in order to prevent unwinding of strands and individual wires, two dressings are made previously on the rope with a soft annealed wire at a distance of 1-4 rope diameters. This method has obvious laboriousness and low productivity.

Methods based on the use of electric contact heating proved to be more effective. So, in [1] a technology was described that provides for uniform heating of a portion of a rope sandwiched between the electrodes of a butt machine to temperatures of 1450-1500 ^o C by passing a pulsed welding current, after which a smooth dilution of the electrodes is carried out until the rope breaks completely. The final procedure is the rapprochement of the broken ends, due to which the arising spark process ensures uniform melting of the ends. In [2], a method of electric cutting of stranded wires was used, based on heating by the method of electrical resistance and simultaneous application of a tensile load, while at the time of local thinning of the material, the mechanical load is removed and a more powerful pulsed current is supplied, leading to the final separation of the workpiece and the formation of fused ends.

 A very similar method [3] involves cutting the rope by electric heating with simultaneous twisting and stretching, while at the beginning of the process the wires and strands are heated and then stretched to form a cone, which is finally burned by further heating.

Closest to the claimed method is a method of separating a steel rope [4], based on electrical contact heating of the cut to a state of melting while twisting this section in the direction of winding strands, while the torsion axis of the ends clamped by the electrodes are at an angle of 0-20 ^o .

The process of separating the rope billet according to the above method is adopted as a prototype method. However, as the study showed, this method with respect to the technology for producing a flexible element is not sufficiently adapted. The fact is that the cutting operation should not only act as a way of dividing a long rope billet into segments of a predetermined length, but at the same time be used as a preparatory process for subsequent technological processing - the formation of the required geometry of the ends (pointed front and flat rear). The need for subsequent mechanical processing of the end sections (with a cutter or abrasive wheel) requires that the strands be stiff enough at the melted ends, and at a well-defined distance from the end, not less than 0.9 d _k (d _k is the rope diameter). In the case of separation of the workpiece by the prototype method, such conditions are difficult to withstand, which leads to difficulties in subsequent machining - when forming a pointed end, separation of the strands and individual wires is observed, making, therefore, the high-quality performance of this final technological operation is impossible.

The proposed method allows to avoid these disadvantages by conducting two technological treatments before the operation of the electrical contact separation of the rope billet:
- in a given local area of the long billet by contact heating, annealing is carried out at temperatures not exceeding 0.5 of the melting temperature of the material;
- the annealed section is then subjected to local plastic deformation by rolling the rope with profiled rollers along the lateral surface (axisymmetric deformation diagram) to a diameter of at least 0.7 of the rope diameter (Fig. 1).

 After these treatments are carried out, the final separation of the preform into segments of a given length is carried out by electrocontact heating of the annealed and deformed section to the state of melting.

 The need for such preliminary operations is dictated by the following considerations.

It is known [5] that, in accordance with the Joule-Lenz law, the amount of heat generated during the passage of electric current is Q = I ² Rτ, where I is the current strength, R is the electrical resistance and τ is the time. In turn, R = ρL / S, where ρ is the electrical resistivity, L is the length of the conductor, and S is its cross-sectional area. The rope cross section S _{K is} not continuous and is determined by the sum of the cross sections of the individual wires. In FIG. Figure 2 shows a graph that allows you to find the actual area S depending on the ratio d / d _K , where d is the diameter of the compressed section and S _K = πd $\genfrac{}{}{0ex}{}{\text{2}}{\text{K}}$ /4. It can be seen from the graph that the actual decrease in area S begins at d / d _K <0.7. Local thinning of the conductor (cable billet) should lead to a stronger heating of this section, which reduces the physical time required for self-separation. In addition, during deformation of the local section, conditions are created for the subsequent favorable formation of the desired profile of the obtained ends of the segment. In particular, the local ring compression of the rope billet can be carried out with a tool having a different cross-section in shape - asymmetric or symmetrical. These types of tools are intended for those cases when it is necessary: 1) to give a divided segment a pointed shape for the head section and flat for the tail section (Fig. 1, a); 2) to provide both ends with a pointed or flat shape (Fig. 1, b, c). The shape of the head portion can be conical, sigmoidal, bullet-shaped, etc.

The minimum values of L and 1 can be calculated in accordance with the initial geometric dimensions for each of the three schemes:
L _MIN = 0.5d _K (1 + md / d _K ) (1 / tg0.5α ₁ + 1 / tg0.5α ₂ );
I _MIN = 0.5d _K nd / d _K (1 / tg0.5α ₁ + 1 / tg0.5α ₂ ),
where m and n are constants equal to 0-0.5 and 1-1.5, respectively.

 Thus, the implementation of local plastic deformation of the rope billet in the future electric cutting section has two objectives: firstly, to form profiles of both ends closest to the geometry required in advance, and secondly, to provide more intensive heating of this section and reduce the physical time required for subsequent separation.

Local circular radial compression (axisymmetric deformation) of the strand of the rope by the specified value (not less than 0.7 (d _to ) provides not only continuous filling of the cross section with metal, but also creates the desired thinning with the formation of a “neck” of a given profile (asymmetric or symmetric).

The need for recrystallization annealing before the operation of local deformation is explained by the following. As is known [3], carbon steel with a content of 0.6-0.7% C is usually used for the manufacture of steel ropes. In this case, the wires forming the strands of the rope are subjected to special hardening treatment — patenting and subsequent cold drawing with large total reductions, in As a result, the wire billet, from which the rope is then twisted, has high strength indices (σ _in reaches 2300-2500 MPa and even more). Therefore, the deformation of such a high-strength material requires a lot of effort, and is also fraught with the danger of destruction of individual wires in strands. Thus, the feasibility of annealing to remove hardening in the area of the alleged local deformation seems quite logical. In this case, heating for the implementation of heat treatment is carried out in the same way as the separation operation itself, on an electric contact machine. The lower temperature limit for such heating is not less than 0.3 of the melting temperature of the material, and it is then that the recrystallization process becomes possible. The position of the upper boundary — 0.5 of the melting point — is due to the following consideration. When performing recrystallization annealing of steel, it is important to select a temperature that would not exceed the polymorphic transformation temperature (727 ^o C) associated with the formation of austenite. The undesirability of such a phase transition is explained by the fact that subsequent cooling in individual microvolumes due to accelerated cooling can lead to the formation of martensite (i.e., local hardening) and, as a result, an unacceptable sharp increase in hardness.

 It should be noted that during the operation of thermal separation of the rope billet at the melted ends, individual strands may diverge somewhat, while maintaining, however, a rigid connection to each other. This leads to a slight increase in the diameter of the end sections (by 10-15%). In order to avoid this effect, as well as to create more favorable conditions for the formation of pointed ends simultaneously with the passage of the welding current, the sections clamped by the electrodes rotate around the longitudinal axis in the direction of the strand stranding.

Concrete example
As a starting material for the manufacture of a flexible element, a standard galvanized rope of construction 6x19x1 o.s. diameter of 6.2 mm made of carbon steel 60. The total length of the cable was 50 m. The specified workpiece was subjected to the following operations:
1. In order to conduct recrystallization annealing on an ASA-30 contact welding machine, the rope was periodically (with a step of 350 mm) heated locally to a temperature of about 600-650 ^o C for 2 seconds (voltage 220 V, current strength 70 kA, distance between electrodes 35 mm).

2. After that, the treated rope was supplied to a device that provides periodic annular radial and longitudinal plastic deformation of the annealed sections by rolling rollers around the rope (Fig. 3), the profile of which was defined by the following initial dimensions: α ₁ = 90 ^° , α ₂ = 135 ^° and d / d _k = 0.6. The force on the rollers was transmitted from a 5 kW drive. The time to carry out such a local deformation was no more than 2 seconds.

 3. The final operation — thermal separation of the workpiece by electric contact heating — was carried out again on an ASA-30 machine (voltage 220 V, current strength 35 kA, distance between electrodes 35 mm, duration of current transmission 2 seconds). At the same time, one of the sections clamped by the electrodes undergoes torsion in the direction of the strand stranding.

 4. The separated segment is then subjected to abrasive grinding on an emery wheel to finalize the head and tail ends of the segment.

Sources of information
1. Cherednichok V.T., Chmyrev I.A. The use of contact machines for cutting and securing the ends of steel wire ropes // Automatic Welding, 1961, N 10, p. 78-79.

 2. The method of electrical cutting of stranded wires // Auth. N 365944. BI, 1973, N 8, p.31.

 3. Buckstein M.A. Production and use of steel ropes. M .: Metallurgy, 1973.360 s.

 4. The method of cutting a steel rope // Auth. N 929365. BI, 1982, N 19, p. 57.

 5. Kabardin O. F. Physics. Reference materials. M .: Education, 1985.335 s.

Claims (1)

 A method of separating a long rope billet, comprising contact heating of a local section of the workpiece to a state of melting and simultaneously rotating its end around a longitudinal axis in the direction of twisting of the strands of rope, characterized in that said section of the workpiece is previously subjected to recrystallization annealing by means of contact heating to a temperature of not higher than 0.5 from the melting temperature of the workpiece material, and then on the annealed section carry out axisymmetric deformation at y, component of at least 0.7 of the initial diameter, with obtaining the neck of a symmetric or asymmetric profile.

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