RU2423194C2 - Water-cooled mandrel and piercing mill stand rod - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: mandrel is mounted on hollow rod with feed tube arranged there inside. Better internal cooling of mandrel via circulation of coolant and coolant flows separation to impart them different rates results from arrangement of tapered plug in feed tube. Note here that said plug is arranged asymmetrically with specified eccentricity of ε=0.1*0.3 relative to feed tube and mandrel.

EFFECT: wear-resistant mandrel for piercing mill stand.

2 dwg

Description

Usage: mainly when flashing the workpiece on the transverse helical rolling mills with water-cooled mandrels without holes for the removal of water and steam in the bow. An increase in the wear resistance of the mandrel is achieved by installing a conical plug in the inlet tube and streamlining the geometry of the cooling cavity. Moreover, the tube is installed asymmetrically relative to the axis of the tube and the mandrel. Separation and imparting of different speeds to the fluid flows contributes to a better washing of the inner surface of the mandrel and increased heat dissipation.

The invention relates to pipe rolling production and can be used for flashing blanks on helical rolling mills with water-cooled mandrels without holes for water and steam in the bow.

Cooling of the “non-replaceable” mandrels is carried out constantly from the inside by the water coming through the tube inside the holding rod, and from the outside by a spray device, in the pauses between the firmwares. Water leaving the inlet tube washes the inner surface and is removed through an annular gap between the inlet tube and the mandrel, also partially in the form of steam and liquid through openings in the bow. The efficiency of internal cooling is greater, the higher the speed of movement of water near the wall of the hollow mandrel, the larger the surface of this wall, its thickness is lower and the thermal conductivity of the mandrel material is higher.

During rolling of the workpiece into the sleeve, the mandrel receives a significant amount of heat. The most vulnerable part of the mandrel, the sock, can warm up to 900 ° C and is plastically deformed, incapacitating the mandrel, therefore, this part requires maximum cooling. To achieve a high flushing speed of the inner wall of the mandrel requires a significant flow of water through its cavity. The large hydraulic resistance of the cooling system, which takes place in practice, requires a significant increase in pressure, which is far from always rational. The efficiency of internal cooling also depends on the ratio of the areas of the flow sections of the tube and the annular gap between the inlet tube and the mandrel.

When flashing stainless steel blanks, water entering the inner surface of the sleeve is undesirable. Therefore, in the nose of the mandrel, there should not be openings for water and steam to the outer surface. If there are no holes in the bow without changing the geometry of the inner surface of the mandrel, the required cooling will not be carried out, since in the bow (the most prone to heat), intense evaporation of water and the formation of a vapor plug that impedes the circulation of water. Cooling the bow will almost cease. For better flushing of the mandrel wall, the cooling water speed is increased; for this, a conical plug is mounted in the inlet tube. Moreover, the plug is installed asymmetrically relative to the axis of the pipe and the mandrel, the maximum clearance is 8 mm, and the minimum is 4 mm, the diameter of the plug is 9 mm. For better flow around the wall with water, it is also desirable to rationalize the geometry of the cavity. The splitting of the water flow and the difference in their velocities increases the intensity of the heat sink. Water under the action of centrifugal force, when the mandrel rotates with the speed of rotation of the stitched sleeve, rushes along the inner wall in a spiral to the mandrel nose, seamlessly washes the inner wall and is discharged through the annular gap.

A close technical solution is a reference rod with a lead-in tube (Calibration of tools for pipe mills. Yu.M. Matveev, Ya.L. VATkin. M. Metallurgy, 1970, p. 480). In this design, the coolant after contact with the surface of the mandrel cavity is partially diverted through the holes in the working part of the mandrel and through the annular gap between the supply tube and the rod.

The disadvantage of this design is that when flashing some alloy steels, the ingress of water on the inner surface of the sleeve is not only undesirable, but also unacceptable. The use of piercing mandrels without holes at the junction of the working part and the sock with the same rod design leads to a sharp decrease in its resistance due to insufficient cooling caused by the formation of a vapor plug in the bow. The main reason for the failure of the mandrels and their frequent replacement is the deformation of the sock, accompanied by sunset mandrel, and the development of the working surface of the spherical section. The firmware on such a mandrel is associated with the appearance on the inner surface of the liner of defects in the form of captives and sunsets.

The closest technical solution is a mandrel with a mandrel shaft (US Patent 3049947. Water-cooled mandrel. Milnes J.A., 1962). The mandrel, having complex internal geometry, is mounted on a hollow tip deeply extended into the mandrel, which in turn is held by a threaded connection in the shaft. The inlet tube is mounted inside the rod. The coolant, leaving the supply tube, is directed into the cavity between the inner surface of the mandrel and tip. On the inner surface of the mandrel there are spiral flanges that, when the mandrel rotates, improve the flushing of the mandrel wall with water. Water, reaching the tip of the mandrel, is directed by a special rush in the tip to the inside of the nozzle cavity, thus removing the spent water. The elaborated cooling scheme leads to a very complex design of such a mandrel, which will become a stumbling block for use in mass production.

The objective of the invention is to increase the wear resistance of the mandrel due to improved internal cooling. To ensure proper circulation cooling of the mandrel, the water supply pipe should extend as close to the tip of the mandrel as the tube is too extended can make it difficult to put the mandrel on the tip. And to separate the coolant flows and give them different speeds, a conical plug is welded into the inlet tube. Moreover, the plug is installed asymmetrically with respect to the axis of the supply tube and the mandrel. If we consider the fluid motion in the pipe to be steady, then we can apply the Bernoulli equation to it.

Pressure equation:

If the inlet pipe at the outlet (with an inner diameter d _ext = 21 mm) and the plug (d _pr = 9 mm) installed with an eccentricity ε = 0.2, is divided into two sections (figure 2) - the area of the holes obtained will be:

S ₁ = 158.76 mm ² ;

S ₂ = 123.98 mm ² .

From the continuity equation:

.

.

Thus, the flow rates will be:

,

,

V ₂ -V ₁ = 6 m / s.

With an eccentricity of more than ε = 0.35, the cork will completely shift to the second section and the area ratio will be:

The difference in the speed of the pots will be equal to:

V ₂ -V ₁ = 8 m / s

With a shift with a relative value of ε = 0.05, the area ratios will be close:

.

.

And the speed difference will be:

V ₂ -V ₁ = 1.5 m / s.

Thus, the rational range of eccentricity is ε = 0.1 ÷ 0.3. Because setting the cork outside these values will not bring the desired effect. When mounting with a relative displacement of less than 0.1, the difference in the flow rates will be insufficient, which will make it difficult to knock down the steam cushion in the cooling cavity at the tip of the mandrel. A further shift of more than 0.3 does not lead to an increase in the difference in flows, but may be the cause of uneven cooling inside the mandrel.

These features distinguishing the proposed technical solution from the known ones allow increasing the wear resistance of the mandrel by improving internal cooling and improving the quality of seamless pipes.

Figure 1 shows the mandrel with the proposed design; figure 2 is a diagram of the installation of a conical plug in the inlet tube with a circuit for calculating flow rates.

The mandrel consists of a working part 1, a sock 2, a cylindrical section 3, a reverse cone 4, having an inner Central cavity 5 for supplying coolant. The mandrel is installed on the self-braking cone of tip 6 and the holding rod, inside of which the supply tube 7 is located. It is proposed to weld an asymmetric conical plug 8 into the supply tube extended 50 mm from the tip.

When using mandrels when flashing alloy steels without holes in the bow and with the known design of the holding rod, the resistance is one firmware.

The proposed design of the piercing mandrel was tested under the conditions of rolling pipes from alloy steels at TPA SinTZ OJSC.

Experimental rolling was carried out on February 21, 2009. For flashing, we used one rolling rod с83 mm with a reconstructed head, consisting of a conical plug in the lead tube, and two mandrels made of 35KHN2F steel with a developed inner surface without holes in the bow. Laminated 60 pipes of 101.6 × 6.5 mm from steel 38G2SF. For firmware we used a blank ⌀ 120 mm 2000 mm long with a temperature of 1250-1260 ° C. Mill setting - in accordance with TI 161-T2-1542. The pressure on the coolant supply pipe to the holding rod is 4 atm.

30 blanks were stitched on each mandrel until the mandrel failed. When inspecting pipes, captures and undercuts were not found on the inner surface. The geometry of the pipes is within the scope of the technical documentation.

Therefore, there was an increase in the resistance of piercing mandrels with the proposed rod design from 1 cycle to 30.

Claims (1)

A water-cooled mandrel mounted on a hollow rod including a supply tube placed with an annular gap, characterized in that a conical tube with an eccentricity ε = 0.1 ÷ 0.3 is installed inside the feed tube with a gap to improve circulation cooling of the mandrel.

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