I N C R E A S I N G T H E L I F E OF G R O O V E S ON A 2 8 0 - r a m M I L L

E . M. B o d r o v UDC 621.771.2.073.8

The 280-ram m i l l at the Saldinsk Meta l lu rg ica l factory is la id out in three trains, namely, a cogging stand with 620-mm diameter roils, a 375-mm roughing train consisting of one 3-high stand and two al ternat ing 2-high stands, and a finishing 280-ram train which has five al ternat ing 2-high stands. The rol l ma te r i a l is s teel 70, and on the three last stands ha l f -hard or white cast iron is used, depending on the sect ion being rol led.

In their service life, on an average 3,000 tons of me ta l are rol led on one set of rolE, and then they are writ ten off for remel t ing . To increase the service l ife of the rolls on the 375-mm train, hard- fac ing began to be carried

out on them with powder wire 3Kh2V8 under a layer of flux AN-20. After this, the groove life was increased (see table) .

When this method was introduced, great diff icult ies were exper ienced in machining the hard- fac ing on the rol l lathe with throw-away tips VK-6 and VK-8, s~ that now the machining of the rolts is carr ied out in the hot con- dit ion and this gives satisfactory results.

The increase in the groove l ife has made i t possible to reduce the t ime in rol l changing, since the grooves ensure the comple te fu l f i l lment of the requirements ent irely without regrinding the rolE. Roll changing is carried out on changing over to another gauge.

Metal Throughput of Rolls, Tons ,n

I n one Stanc~ WithoUt no. hard- i with hard-

facing I facing I

I 1 0 0 0 250~ I 1, I I I 800 2000

In entire camRflign

without !wi thhard- hard- facing I lacing

3000 15000 9400 12000

Kr

Fig. 1. Groove design for the roils of Stand I for ro l l -

ing s teel strip.

- - - - /22,5 �9 ~ 2 o --/~--20---- '- ' . ~- - -2o -~/-~- 2o ~ 2 ~

]

JF t I

55O - c . . . . . . . . .

Fig. 2. Groove design for the rolls of Stand i for rol l ing

s teel channel .

Saldinsk Meta l lurg ica l Factory. Translated from Metallurg, No. 8, pp. 30-31, August, 1966.

467

-- %

,~r Fig. 3. Groove design for the rolls of Stand I for rol l ing

periodic sections.

650

~1 [t~ I

Fig. 4. Combined groove design for the rolls of Stand I.

The use of water -cool ing equipment, especia l ly in roi l ing shaped sections, made it possible to replace rolts made from steel 70 on stands I and II on the 280-mm train by rolls made of white or ha l f -hard cast iron, to reduce the roi l ing cycle, and to carry out roll ing from a higher temperature . Whereas previously a hundred tons of steel angle were rolled on one groove of the finishing stand, now 200-250 tons can be rol led. As a result of corrections to the groove designs, an increase in the rolIing speed, and the introduction of the encircl ing equipment, the l ife of grooves has been increased by a factor of 1.5-2.0. The increase in their l ife has made it possible, for example , to replace three stands in the 280-mm train (Figs. 1-3) by a single (Fig. 4) train, thus giving the possibility of rolIing

a par t icular sect ion without rol l changes.

In this way, the increase in groove l ife and in the service l ife of the rolls as a whole has been carried out in the following directions:

1) A change in groove design and in the rol l ing schedules with a more uniform distribution of the reductions in each e l emen t of the grooves;

2) the mechaniza t ion of the rolling process;

3) the hard facing of the grooves with the aim of increasing their l ife and increasing the stable ro l ld iamete r ;

4) an increase in the number of grooves on the rol l f lank by a reduction in the cut and width of the shoulders;

5) an increase in the groove draft;

6) combined sets of rolls;

7) r ep lacemen t of s teel roils by cast iron;

8) regrinding of worn-out upper rolls for use as lower rolls;

9) a reduction in the roil ing cyc le due to the establishment of water -cool ing equipment, and consequently,

the possibil i ty of roi l ing from a higher temperature .

As a combinat ion, these measures have boosted the growth of production, shortened lost t ime, reduced the

output of second grade materials , and have reduced rol l consumption.

468