FR2524001A1 - COOLING PROCESS MINIMIZING DEFORMATION OF METALLURGICAL PRODUCTS - Google Patents

Abstract

1. Method of cooling basically long or flat metallurgical products (1) having a substantially constant thickness with a view to minimizing the geometric distortions without altering the use properties, characterised in that substantially half the lateral surface is covered by a layer (2) which is insulating or a poorer conductor of heat than the product to be cooled (1) before the covered surface (2) of the product is brought into contact with an aqueous cooling medium (4).

Description

COOLING METHOD MINIMIZING DEFORMATIONS

METALLURGICAL PRODUCTS

  This invention relates to an economical cooling process

  metallurgical products which minimizes the deformations of those

  ci, while preserving their employment properties.

  The cooling of metallurgical products is involved in a large number of operations such as casting and solidification, after

  hot processing on various tools (rolling mills, presses,

  ler, etc.) or-again in the case of metallurgical quenching.

  For reasons of productivity (especially for cooling

  products continuously at the parade), and / or metallurgical

  (solidification, quenching), it is often necessary that these coolers

  High velocities, for example high-pressure water spraying or two-phase spraying (air-melting). It is known that the heat density extracted from the products can reach 1 to 5 MW / m 2 for the order of 20 kg / m 2 sec,

that is 1200 l / m 2 minute.

  However, these methods have the following disadvantages

  (a) high-volume water spraying (> 2000 l / m 2 min) and under

  pressure (p> 1.5 M Pa or 15 bar) leads to high water consumption and requires expensive equipment (booster pump).

very strong capacity).

  Moreover, it is not suitable for cooling the min-

  these, in particular to thin sheets or strips of light alloys because the impact force of the jet causes significant deformation of these products; (b) in the pneumatic spraying of water and pressurized air, these

  two fluids are introduced simultaneously into the spray nozzles.

  low-flow pneumatic system, or separately by blowing compressed air at the outlet of the mechanical water spray nozzle,

high flow rate.

  Pneumatic spraying has the disadvantage of being expensive because of the cost of nozzles (ten times higher than

  mechanical nozzles) and the high cost of investment and

  In addition, this system is dangerous because of the risk of bursting compressed air

excessively noisy.

  In addition, with high cooling rates, the products are the seat of a high level of internal stresses if they are thick, or very large deformations if they are thin, these two effects being harmful:

  Deformations or distortions of cooled products often

  straightening or shaping them with powerful means such as presses, roller planing machines, traction benches,

  operations which, in turn, induce in them

  harmful internal stresses, for example, distortions in a factory

  subsequent chemical or mechanical

  The use of special devices limiting or eliminating

  torsions during cooling, for example during quenching,

  such as frames, flanges, press quenching etc. is of course

  not effective, but however limited because, in any case, and despite all the precautions taken, the level of internal stresses

remains high.

  The method according to the invention, which eliminates, or at least minimizes, these distortions, consists in cooling the metallurgical product with a

  different cooling between approximately two adjacent halves

  of its outer surface, each extending along the

  long direction or the main plane of the product, when it (s) exists (s).

  Thus, for a rectangular bar, a different cooling is applied between the two adjacent lateral faces of the product and the

  two opposite sides For a tube or a cylindrical bar,

  that a different cooling between the two semi-cylindrical surfaces

  opposing driques of the lateral surface For a sheet or a strip,

  a different cooling is applied between its two opposite faces.

  Of course, the method is generalizable to other metallurgical products.

  stamped, spun, forged or molded provided they are not

  self-restrained by their shape and / or their dimensions during cold weather

  is lying. Differentiated cooling can be provided by various means such as:

  in the case of immersion cooling in a cooling medium

  coating by coating about half of the external surface with a coating of an insulating product or with a significantly lower heat conductivity than the alloy to be cooled (eg: steel / Al alloy plating, insulating and refractory powders) ); in the case of cooling by spraying or spraying, by different watering of the two halves of the product, the latter being

  stationary or not (at the parade)? Parrosagc differentiated the two my-

  is caused by the difference in nature, composition, pressure, surface flow temperature and / or impact velocity of the coolant or by a difference in the surface condition of the two halves considered (eg raw and etched surface, surface coated or uncoated with little or no heat-conducting coating, etc.)

  In particular, it has surprisingly been found that the cooling

  unilateral spraying by conventional spraying or spraying of half of the surface of the product, the latter being previously coated with an insulating or bad heat-conducting coating,

  at high cooling rates of thin products without

  noticeable twist The cooling fluid generally used consists essentially of water, possibly with certain

  additives (anticorrosion, antifoam, etc.).

  The coating may be carried out at any stage of the range of

  manufacture, prior to cooling provided that it remains

  and remain effective in the range (for example, the

  product can be coated before the solution heat

give up the quenching).

  It is preferable, in all cases, that the watering is done by the

  the lower part of the products, the long meaning of these products being

horizontally.

  As indicated, the process applies primarily but not exclusively

  -4- to long metallurgical products (wires, bars, tubes, prof iléê) or flat (strips, sheets, flats) of relatively small dimensions

transverse or thicknesses.

  For Al and aluminum alloys, the thickness of flat products

  is preferably less than or equal to 15 mm (which corresponds to

  sibly to a diameter of 30 mm for a solid round bar).

  For copper and copper alloys, the thickness is preferably

  less than or equal to 35 mm (or a diameter of approximately 70 mm).

  For steels or ferrous alloys, the thickness is preferably

  less than or equal to 8 mm (or a diameter of about 15 mm).

  Two products shall be considered to have equal cross-sections

  slow if the ratio of external surface area to volume is the same.

  The method is particularly applicable to quenching alloys

  high-strength Al compounds for which the

  mechanical resistance and / or corrosion) are practically unchanged.

  compared to traditional quenching, with, however, distortion

very low levels.

  When cooling is provided by spraying or spraying at

  With the help of nozzles, it is important that the impact zones of the

  the entire cooled surface of the product, either directly,

  or indirectly through runoff, rebounds, etc. The above-mentioned

  Water facials remain below 200 microns and preferably 800 microns; the nozzles are placed at a distance of less than 15 cm from the product surface, and the injection pressure is in

  1.5 M Pa (15 bar), and preferably 1 M Pa (10 bar).

  The process according to the invention offers, compared to the methods of

  conventional cooling, the following advantages Thin products (see dimensions above):

  absence of significant distortions or better flatness (or

  de) and low residual stresses after cooling; -5 elimination or simplification of planing, dressing or

  subsequent fitness (eg traction or compression

  controlled alloys of Ai before recapture or maturation).

  For products of any size; preservation of optimum properties (mechanical resistance, corrosion resistance) in the state of use;

  decrease in consumption or volumes of cooling fluid

put into play;

  better reliability or repeatability of cooling operations

is lying;

  possibility of control and modulation of cooling speeds

products.

  The invention will be better understood with the aid of the following drawings and examples.

  Fig. 1 shows an end view of products (1) (a) rectangular bar (e) angle (inner side) (b) round bar (f> angle (outer side) (c) sheet (g) profiled in T (d) cylindrical tube (h) any profiled with or without an insulating coating (2), about half of

  their outer surface and cooled by means of spray nozzles.

  (3), either by immersion in a cooling medium (4)

in a bin (5).

  Figure 2 shows the deformation characteristics after

  cooling: arrow (f) and tile (t), of a rectangular nlat product

re, initially plan.

EXAMPLE 1

  Three plates of dimension 400 x 400 x 10 mm in aluminum alloys (7075), were dipped by vertical immersion in cold water (200 C) or hot (600 C) after dissolution of 4 hours at 4700 C in the oven

ventilated air.

  The sheets A and B, uncoated, were soaked in tanks of water at temperatures respectively equal to 200 C and 600 C.

  T 8 was immersed in water at 60 ° C after decantation.

  page surfaces and coating a single large area by means of

  of a continuous insulating layer of low thermal effusivity,

  essentially composed of a mixture of sodium silicate in solution

  in water, barium sulphate and titanium oxide. Table I below gives the quenching speeds measured between 400 and 250 ° C. at 1.5 mm under each surface by means of thermocouples.

  places in the center of the large faces of the t 8 as well as the distorted

  macroscopic measurements measured after quenching (maximum deflection along the horizontal axis of maximum stress along the vertical axis of t 8s)

  and the longitudinal mechanical tensile characteristics at half

  Thickness at the center of the tees, measured after recovery at the T 6 state (24 h at 120 ° C. It is found, in particular, that the t Si (C) quenched according to the invention by asymmetric cooling, is provided with both

  mechanical characteristics of traction equivalent to those

  the dipped most quickly symmetrically in cold water

  (current practice) and significantly lower quenching deformations

  than the others t 18 including the t 8 the (B) symmetric quenching

  with relatively slow cooling speeds.

TABLE I

  Benchmark Temperature Condition of trem-IDeformations Characteristics sheet ea (C) surfaces under tensile stress Isurfaces Arrow Tile condition T 6 (C / sec) f (mm) t (mm) Rpo, 2 Rm A l (I) Pa) (M Pa)% A 20: 2 faces 165 IA 20 2 faces 165 + 17.1 -5.3 551 613 8.1 naked 185 l B 60 2 faces 86 -3.5 515 580 8.9 nude 93 C 60 1 face of 8 llcapee l 89 1 face re + 1.2 -1, 2 547 612 8.3 clothed | 17 l I i I

_ __ __

-.7-

EXAMPLE 2

  Thin sheets of dimension 630 x 350 x 2 mm (total thickness) in alloy 7475 plated with 70 m alloy 7072 on each face, were

  soaked after being dissolved for 30 minutes at 475 C, either by immersing

  vertical discharge in a water tank at 18 C according to the usual practice, either by spraying water at 180 ° C on the only static horizontal bottom surface of an uncoated sheet, and a sheet coated on its sole lower surface a layer made of the same coating

  sodium silicate base as in example n 1.

  Spraying was ensured over the entire lower horizon.

  plates by adjacent cone jet nozzles

  viron 60, delivering a surface flow of 145 l / min / m 2 under a pres-

3 bar (0.3 M Pa).

  Table II below gives the deformations of the plates after quenching, the surface electrical conductivity of the plates five days after quenching (which is all the lower in the tempered-mri state that the quenching is faster), the speed of average cooling of the sheets in the critical quenching range (400 250 C) and the mechanical characteristics on traction specimens treated by state-of-the-art

  -T 76 (6 h to 1070 C + 16 h at 160 C) after stripping the coating and trac-

  Controlled control of the sheets before income:

TABLE II

  Fashion of Coat Lifetime The Fora Ccnductivi Features

  quenching of cooling systems Electrical devices (Condition) T 7 d) (m) (% IACS) Rp O, 2 2 Rm A (M Pa) (M Pa) (%) Immersion no 350 C / s 31 4 29, 6,428,492 15.4 (bare sheets)

Pulveri Face inf.

  saration 54 C / s 2, 2 30,2 402 478 16,3 one-sided clad face-to-face inf 2300 C / s 3, 2 29,6 432 495 15,7 Fevêtue -8- It can be seen that Tempered sheets according to the invention have substantially lower residual deformations than those obtained by symmetrical quenching, while retaining substantially equal mechanical properties and although the surface flow rates used here are relatively low.

EXAMPLE 3

  We sprayed horizontally at the parade or

  that, sheets of dimension 650 x 350 x 4 mm alloy 2024 after setting

  in 30 minutes solution at 4950 C in a ventilated air oven.

  The quenching plant had a quenching window long of

  700 mm, consisting of spray bars located on both sides of

  trolley for supporting and translating the sheets with a flexible flow rate, so as to simulate the symmetrical or asymmetrical horizontal quenching at the exit at the outlet of the passage furnace The spray nozzles consisted of jet sprayers with

  solid cone, angle 601 C, fed by a flow of water at 151 C pressurized

  at a pressure of 6.5 bar A sheet was spray-quenched symmetrically on both uncoated sides, in accordance with the usual practice.

  other sheets were soaked by one-sided horizontal spraying

  the on the underside with the same surface flow with or without poteyage of the surface to be watered by an insulating coating based on

sodium silicate.

  Table III below gives the test conditions, the speeds

  average cooling temperatures measured between 400 and 2500 C per thermal O

  ples in the center of the sheets, the deformations of the sheets after quenching (longitudinal arrow transverse tile) as well as the sensitivity to

  intergranular corrosion of hardened and stripped sheets

  clothing as assessed by immersion test in chloride solution

  of sodium and distilled water according to the AIR 9048 standard.

See Table III below -9-

TABLE III

Tempering 1 Symmetry without

revite-

o 10

Unila-

lateral s / lower side. Takes. No

debit life sur-

  ) Facial assault of (caisec) ea / mn / m 2) Face Face

sup inf.

1250 250

Unila-

  lateral i s / face | infer. Cool lives (t C / sec)

deform

matter (mm) Sensitivity to

internal corrosion

  It can be seen that the asymmetrical quenching of the coated sheet metal according to the invention improves both the quenching rates (× 2 ×) and the resistance to intergranular corrosion of the alloy, as well as

  the flatness of the sheets while increasing the productivity of the installation.

  (x 3) and by reducing the required water consumptions (: 2

  viron) compared to the symmetrical quenching of the bare sheets.

EXAMPLE 4

  We soaked by dissolving 1 and length 600 mm mechanical spraying with parade at 25 cm / s, after h at 500 C, angles of section 50 x 50 x 5 mm

made of 6061 aluminum alloy.

  Two angles were soaked in water at 18 C, either by spraying

  symmetrical (on both sides) or unilateral (on their underside

  by means of longitudinal spray nozzles with nozzles

  100 mm from the top of the angles, so as to cool directly

  the entire angle on both sides or on the underside.

  only, pre-coated with a uniform layer of sodium silicate (Na 2 O: 3.3 Si O 2) in solution in 1.08 density water

(see figure the).

  The nozzles gave full-cone jets of 601 ° C angle with a flow rate of 580 l / min / m 2 at a water pressure of 6 bar (0.6 M Pa). Table IV below gives the test conditions as well as cooling rates and mean longitudinal deformations (arrows) after quenching. The results show that the one-sided spray quenched angle on the coated surface according to the invention has a better compromised cooling-straightness speed as the angles symmetric cooling cooled angles

  by spraying or immersion.

TABLE IV next page

TABLE IV

  unilateral on the face in Nonfree water C, 1.5

0 290

  0.0 Unilateral spraying on the face in 0,680,27 0,66 lower water C Immersion water Not without 232 2,5 C q-CD CD Ir. CMJ Lni g-12-

  It should be noted that the critical quenching speed of 6061 is -

  Approximately C / sec. Unilateral uncoated spraying leads to perfect straightness without altering the properties of use. The coating can significantly increase productivity <x 3) with still acceptable quenching deformations. -13-

Claims (13)

  1 / Method for cooling metallurgical products (1) essen-   long or flat, in order to minimize geometric distortions   without alteration of their employment properties, characterized   between the two halves of their surface.   this lateral, a cooling mode significantly different.   2 / A method according to claim 1, characterized in that   one of the two halves of the lateral surface is covered by an insulating adherent coating (2) or the worst conductor of the   heat than the product to be cooled (1) before contacting the product   coating (1,2) with a suitable cooling medium (4).   3 / Method according to claim 2, characterized in that the cooling   drainage is by immersion in a fluid (or mixture of fluids) or an appropriate suspension.   4 / Method according to claim 2, characterized in that the re-   cooling of the coated product is by spraying or spraying   with a fluid or a mixture of fluids using nozzles.   Method according to claim 4, characterized in that the spraying or spraying is limited to the coated lateral surface (2) of the product.   6 / Method according to one of claims 1 to 5, characterized in that   that the long direction of the product (1) is substantially horizontal.   7 / M 4thode according to one of claims 1 to 6, characterized in that   that the cooling of the product is done by its (or its) face (s) férieure "s).   8 / Method according to one of claims 1 to 7, characterized in that   that the cooling medium (4) is essentially aqueous.   9 / Method according to one of claims 1 to 8, characterized in that -14-   that the product (1) is a heat treated Al alloy product.   that the cross-section is equivalent to that of a product   flat of thickness less than or equal to 15 mm.   10 / Method according to one of claims 1 to 8, characterized in that   the product (1) is a copper or copper alloy product whose cross-section is equivalent to that of a flat product of which   the thickness is less than or equal to 35 mm.   11 / Method according to one of claims 1 to 8, characterized in that   that the product (1) is a ferrous alloy whose cross section is equivalent to that of the flat product whose thickness is less than or equal to 8 mm.   12 / Method according to one of claims 4 to 11, characterized in that   that the surface flow rate of the nozzles is less than 2000 lmn min and preferably 800 lin min 1   13 / Method according to one of claims 7 to 12, characterized in that   the nozzle supply pressure is less than 1.5 M Pa (15   bars) and preferably less than 1 M Pa (10 bar) -   14 / Method according to one of claims 4 to 13, characterized in that   the distance from the nozzles to the product is less than or equal to 15 cm.