Tears which can be blamed on the open-hear th shop arise from small inclusions and seams, which on being

rolled form holes weakening the strip cross section, and Iaminations. A large number of tears of the strip i tself also

take place because of ragged edges usually at the working speed, and as a rule lead to rol l -changing on two or three stands.

Tinpla te and pickled steel are roiled on the 1200-mm mil l in approximate ly equal quantities. The absolute figures for the number of tears for t inplate is two to four times larger than for pickled steel: this is explained by the smaller thickness of t inplate and by the compara t ive ly larger effect of variations in the roll 's temperature profile, and also by the larger total reduction and by the longer t ime taken in rolling.

Tearing of the strip because of technical imperfections and poor quality starting mater ia l can be considerably curtai led if the interstand tension is reduced, especia l ly between the stands III and IV, and also between stands IV and V.

A forced reduction of the interstand tensions between the last stands (this is desirable at the present t ime from the point of view of raising productivity) can c lear ly be e l imina ted if methods are found of controlling the distribu- t ion of tension across the width. To a certain degree such a satisfactory roiling rggime is successfully accomplished when the temperature profile of the working rolls is held steady for a long period of t ime. At the present t ime, the intensity of roll cooling on the mil l is inadequate. Moreover, a uniform distribution of lubricant over the width of the strip must be achieved, and also the set t ing-up of the mi l l must be substantially improved.

The fitting of the mi l l with dynomometers and the instai la t ion of contactless micrometers will make it possible to improve the qual i ty of, and to acce le ra te , the set t ing-up of the mi l l , and to mainta in the reduction schedule more accura te ly at the working speed. All these measures, without large capi ta l expenditure, wil l reduce tears in the strip i tself and wil l raise the mi l l ' s productivity by 10-12%.

The reduction in the tearing of the strip itself, together with increased abi l i ty of the seam to pass through, wil l make it possible to considerably increase the mi l l ' s productivity by 20-25~

E L E C T R I C W E L D E D S T A I N L E S S T U B I N G

V. I . G a p i c h a n d G. D. D u p l i i

Nikopolsk South Tube Factory Translated from Metallurg, No. 5, pp. 19-21, May, 1968

R E P L A C E S S E A M L E S S

The wide use of welding in al l sectors of the national economy has made i t possible to go over to the produc- t ion of welded tubing instead of seamIess, while ensuring that their properties are equivalent .

The value of this is especia l ly important for the production of small d iameter tube from stainless and special steels that are difficult to work, since the possibili ty opens up of producing tube from sheet with a high surface quali ty and highly accurate geometr ica l dimensions.

To solve the problem put by the Party and government of replacing seamless stainless and acid-resis tant tubing by welded tubing, the production of welded tubing by argon-arc welding with a nonconsumable e lectrode was mastered at the Nikopolsk South Tube Factory.

Welded stainless tubing is usually dispatched in the welded condition without heat t reatment . In this form the tubes have a work-hardened surface on the meta l of the tubing, and an as-east , not normalized, structure in theweld - seam meta l . This considerably lowers the total corrosion resistance of the tubing and especial ly of the searn.

Welded tubes of stainless and acid-resis tant steels in the welded condition do not, therefore, always satisfy the requirements of the chemica l industry and of chemica l machine-construct ion as to geometr ica l dimensions in the seam zone, and also as to technical properties and corrosion resistance.

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Fig. 1. Defects on the externalsurface of the welded seam. Fig. 2. A lap on the internal burr of welded tubing.

Heat t rea tment considerably improves the technica l and mechanica l properties of the tubing, making them approach those of seamless tubing, and raises the corrosion resistance of the seam and tube metal : i t does not i m - prove its geometry, however.

To obtain tubing equivalent to seamless in geometry, surface quali ty, and technical properties, and in a number

of cases to ensure equal corrosion resistance and to widen the range of products considerably, the necessity arose of co ld- ro l l ing the welded tubing in cold-rol l ing mil ls .

The production of cold-deformed stainless tubes from a welded tube-b i l l e t has a nm-nber of advantages over their production from a hot - ro l led seamless tube-b i l l e t . One of the chief advantages is the fact that from a welded tube -b i l l e t it is always possible to obtain the finished tube in one pass on cold-rol l ing mil ls . The price of the welded tube-b i l l e t going for cold reduction is 10-15% less than the price of a hot- rol led intermediate product. Expenses on cold-reducing the tube -b i l l e t are also several t imes less, since the cycle of cold reduction is considerably shortened. Moreover, a high accuracy in geometr ica l dimensions, and the absence of hot-rolling defects on the inside surface are ensured.

There is especial importance in the production of th in-wal led tubing from a welded tube-b i l l e t of steels and alloys that are diff icult to pierce, since the technical cycle of their cold reduction is thus made several t imes shorter,

and difficult operations, such as the boring and dressing of the tube-bi l le t , are done away with. Production expenses and the yard required for equipment are correspondingly reduced.

In mastering the production of intermediate tubes and in developing the production technique for cold-deformed stainless tubing from a welded tube-b i l l e t , the following difficulties were met at the Nikopolsk South Tube Factory.

1. The tube-b i l l e t , welded by the organ-arc method in the middle of the seam had, on the inside surface, a network of holes and porosity.

2. A loose layer of meta l was formed on the external surface of the seam: this lead to the format ionofdefects on the seam in cold-rol l ing the tubing (Fig. 1), and reduced the corrosion resistance of the seam meta l in aggressive media .

3. The internal burr turned out, as a rule, to be high, and this led to the formation of a lap in the form of a seam at the edges of the weld-seam during the cold-roi l ing of the tubing (Fig. 2).

The reason for the formation of holes and porosity on the internal surface of the seam and for the loose l aye ro f seam meta l on the outside was the absence of an effect ive method of cleaning the edges of the strip before welding.

In shaping the strip into the tube-b i l l e t , an ernulsion was fed onto the bottom rolls of the shaping mil l to prevent the meta l sticking to the rolls and harming the surface of the tube-b i l l e t . In addit ion this contaminated the edges, which had a harmful effect on the quali ty of the welded seam and its corrosion resistance.

To obtain an in termedia te tube-b i l l e t , welded by the argon-arc method with a sound seam and without an in- ternal burr, the following measures were put into effect .

1. Degreasing of the strip was introduced into the welding mi l l l ine, with the appl ica t ion of ultrasound in a UZV-4 bath (composit ion of the solution: 3 g of trisodium phosphate per l i ter of water and 3 g of an OP-10 addit ion per l i ter of water; temperature 55-60~ with subsequent washing with hot water and drying. Ultrasonic waves are imparted to the strip from a UZG-10 ultrasonic generator . Degreasing of the strip is made necessary because the strip is contaminated during transport.

2. Shaping of the strip with bui l t -up roils of textol i te and steel was introduced (Fig. 3).

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3. A new nozzle design was developed and introduced for the gas supply to shield the weld pool inside the

the tube with a supply of argon (Fig. 4).

4. Dressing of the outside surface (removal of the layer of loose meta l ) of the seam in the welding mi l l l ine with a wire brush was introduced. It can thus be guaranteed that an in termediate tube -b i l l e t is obtained without an internal burr and with a high qual i ty surface. However, in rolling such a tube -b i l l e t on cold-rol l ing mills in roils with grooves ca lcula ted according to the groove-design adopted in the factory, cracks of varying depth were formed on the inside surface of the tube at the boundary of the seam with the base meta l . As a result of experiments it was

established that the reason for the formation of these cracks

l t /

V/

Fig. 3. Textol i te roll with steel core (a).

was the large d iameter - reduct ion given to the tube-b i l l e t without a reduction in wall thickness; this is bas ica l ly the foundation of the factory's existing groove design. By an exper imenta l method it was established that tubes, welded by the argon-arc method allow a d iameter - reduct ion , with- out a decrease in wall- thickness, of not more than 8 % of the external d iameter .

To observe this given condition, the gap in d iameter between the cyl indrical part of the mandrel and wall of the tube-b i l l e t should in pract ice be not more than 2 mm

for KhPT-32 mil ls , and not more than 3 mm for KhPT-S5 mil ls . With this condition it is in pract ice impossible to

obtain a considerable reduction in tube -b i l l e t d iameter with a possible large detbrmat ion in the wail. Thus, on

KhPT-32 mil ls with a mandrel taper of 0.02, the max imum possible reduction in tube -b i l l e t d iameter is 11 m m schedule 38x2 .5 m m --," 27x 1 .0 ram,mandre l 31x 25 ram).

The planning of cold-roi l ing schedules for welded tube on mandrels with a small taper with a small reduction in tube -b i l l e t d iameter is uneconomical , since, to obtain tube of small d iameter (less than 15 ram) numecbus co ld- drawing drafts are required after cold rol l ing.

To ensure a large reduction in the tube-b i l l e t d iameter with considerable wall deformation, the possibili ty was investigated of rolling on mandrels with a large taper.

From tube-b i l l e t (steel 1Khl8N9T), welded by the argon-arc method, a large batch of tubes was rolled accord- ing to the schedule 38x 2.5 -> 25x 0.96 mm with subsequent cold-drawing without a mandrel according to the schedule 25 x 0.95 -~ 19 x 0.98 ~ 16 x 1.0 ram. This made sure of a high surface quali ty, and the absence of cracks on the ex - ternal surface of the tube at the boundary between the weld seam and the base meta l . Moreover, a number of batches

of tube were prepared with different amounts of deformation in the tube-b i l l e t 5 -6 diameter and wall . The productivity of cold-rolling mil ls in rol l ing the welded

~ A ~ I tube-b i l l e t was proved to be the same as the productivity in roll ing tube from a ~ t < A _ _ J r ~ seamless tube-b i l le t .

/!S~l The marked increase in the mandrel taper, necessary for the large reduc- - 7 5 - - - tion of the tube-b i l l e t d iameter with the large deformation of the wall , led to a

considerable lowering of the coid-rol l ing mi l l ' s productivity. In roll ing tube a c - Fig. 4. Nozzle for gas supply to

the internal burr. cording to the schedule 38x 2.5 ~ 2 0 x 0.9fi m m the mi l l ' s productivity was iow- ered by a factor of about two, and tube surface quality was impaired. This is explained by the fact that, with a considerable increase in mandrel taper, and

consequently in the steepness of the groove flange as well , it becomes necessary to increase groove width: this leads to an impai rment of the meta l deformation conditions, since the tube becomes oval in the compression part of the grooves.

To ensure a high interior surface quali ty on the tubes in the welded seam zone, rolling has to be carried out with a m i n i m u m gap between the cyl indr ical part of the mandrel and the interior surface of the tube-b i l l e t , that is, with a m i n i m u m diameter reduction.

To obtain cold-deformed tube with a high exterior surface quali ty in the seam zone, one must ensure that a good quali ty surface is obtained with final cleaning off of the upper toose layer either in or outside the welding mi l l l ine .

216

Progress must be made in the direct ion of replacing the steel rolls of the forming and sizing mills with rolls made of plastics or other mater ia ls , which will accomplish the forming and sizing of the tube without the roils ' being

supplied with cooling or lubricat ing fluids, and which have adequate hardness and strength. This will ensure a high seam quali ty and will make it possible to hea t - t r ea t the welded tube-b i l l e t without its pre l iminary degreasing.

G R O O V E D E S I G N W I T H L I N K E D C O M B I N E D D I A M O N D G R O O V E S

Y a . I . M o i o d a n o v

Groove designer, Lugansk October Revolution Locomotive Factory Translated from Metallurg, No. 5, pp. 22-23, May, 1963

For a number of years, a cogging stand on a 500-ram section rolling mil l with combined diamond grooves has been in use at the Lugansk Locomotive Factory.

The 500-ram mil l in our factory is designed for the production of small batches, 5-10 tons in weight, of various sections and bi l le ts . The cogging stand rolls blooms and ingots of 200-ram square section from carbon steels of ordi- nary quali ty according to GOST 380-60, and converter steel according to GOST 9543-60. The stand is equipped at the front with a working rol ler-conveyor and ti l t ing fingers and at the rear, with a lifting and tilting table.

The groove design of the cogging stand gives the possibility of producing a large number of square billets of various dimensions: 130, 125, 100, 90, 85, 75, 63, 50 ram, and starting squares for rolling rounds, strip, and other

sections on the 500-mm rail1.

2/

Fig. 1. Init ial design of the linked com- bined diamond groove.

1600

Fig. 2. Groove design for the rolls of [he cogging stand.

The output from the cogging stand (set out ina single train with the mill) of billets of al l the necessary d imen- sions should be ensured, without roll changing, ona single set of rolls.

The smallest section bi l le t (50-mm square) is ob- tained in 12 passes. The even number of passes was fixed by the positioning on one side of the mil l of the preheat- ing furnace and the cutting equipment. This also gave rise to the necessit / of developing a new groove design for the three-high cogging stand with unusual linked com- bined diamond grooves, formed from various triangular grooves. The use of such grooves was also occasioned by

Fig. 3. Design of upper combined linked diamond groove.

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