IMPROVED OF

DESIGN

INTEGRAL

BASKETS

WELDED

FOR

M,

M.

AND

FABRICATION CYLINDRICAL

CENTRIFUGE

TECHNOLOGY SCREEN

BOWLS UDC 621.928. 0 2 8 . 0 0 4 . 6 8

Abelev

The shape and s i z e of s c r e e n s l o t s in c e n t r i f u g e bowls, as well as the bowl design, a r e d e c i s i v e f a c t o r s in c e n t r i f u g e c a p a c i t y and p e r f o r m a n c e . S c r e e n s f a b r i c a t e d to f a i r l y c l o s e t o l e r a n c e s , with s l o t widths l e s s than 0.2 m m , a r e n e e d e d if the m o d e r n h i g h - c a p a c i t y l o w - c o s t continuous c e n t r i f u g e s a r e to gain a c c e p t a n c e . N H K h i m m a s h has c a r r i e d out a s t u d y of the d e s i g n and f a b r i c a t i o n t e c h n o l o g y of i n t e g r a l welded c y l i n d r i c a l c e n t r i f u g e bowl s c r e e n s ( F i g . 1) f o r the N G P - 2 K - 2 0 0 and NOGSh-85/120 model machines. As we see, the s c r e e n b a s k e t c o n s t i t u t e s a s h e l l c o n s i s t i n g of p e r f o r a t e d s c r e e n e l e m e n t s , s e m i r i n g s , and r i n g s , j o i n e d by a r g o n - a r c welding. The s c r e e n b a s k e t m u s t c o n f o r m to the following r e q u i r e m e n t s : s l o t width d e v i a t i o n s (0.1, 0.15, 0.2 r a m ) m u s t not be g r e a t e r than • mm; I . D . o u t - o f - r o u n d n e s s m e a s u r e d at the hub m u s t not e x c e e d • 0.5 ram, and o u t - o f - r o u n d n e s s of the e x t e r n a l s u r f a c e s c o n f o r m i n g to X 3 o r C 3 and m e a s u r e d on the s c r e e n mount m u s t not e x c e e d the d i a m e t e r t o l e r a n c e ; the edges of the s c r e e n b a s k e t m u s t not wobble m o r e than 0.1 m m off p o s i t i o n at the c e n t e r s when c h e c k e d on the s c r e e n mount, and the s c r e e n s m u s t not p r o t r u d e m o r e than 0,5 m m on the i n n e r s u r f a c e of the c y l i n d e r . But the f a b r i c a t i o n t e c h n o l o g y of welded s c r e e n s f o r NVV-1000 c e n t r i f u g e bowls p r a c t i c e d at the P e n z k h i m m a s h F a c t o r y , which had been d e v e l o p e d at N I I k h i m m a s h R e s e a r c h Institute, m a k e s no p r o v i s i o n s f o r m a n u f a c t u r i n g c y l i n d r i c a l s c r e e n s m e e t i n g t h e s e r e q u i r e m e n t s . This t e c h n o l o g y * c a l l s f o r r e i n f o r c i n g the s c r e e n s with s t i f f e n e r s j o i n e d by r o l l welding with the aid of s p a c i n g r a c k s with t e e t h m a t c h i n g the p r o f i l e of the s c r e e n m e s h . Some s c r e e n s d e f o r m o r b e c o m e d i s e n g a g e d f r o m the s p a c e r r a c k s during contact welding b e c a u s e of the f o r c e s t r a n s m i t t e d to the p a r t by the r o l l e r s , and b e c a u s e of t e m p e r a t u r e effects; this i n c r e a s e s or d e c r e a s e s s l o t width f r o m z e r o to 0.3-0.5 ram. The useful c r o s s s e c t i o n of the s c r e e n b e c o m e s s m a l l e r as a r e s u l t of butt welding, we might add.

z[-

~

S m a l l - s i z e bowl s c r e e n s , for e x a m p l e s c r e e n b a s k e t s as s m a l l as 200 m m in d i a m e t e r , cannot be f a b r i c a t e d by this technology.

i

Ai--

A-A

-

jr~

z/

Fig. I. Integral welded cylindrical screen baskets for centrifuge bowls: i) lip ring; 2) screen mesh elements; 3) semiring. Translated from Khimicheskoe

This a r t i c l e c i t e s r e s u l t s of e x p e r i m e n t a l s t u d i e s on the m a n u f a c t u r e of c y l i n d r i c a l b a s k e t s 85, 120, 198, and 2 6 4 m m in d i a m e t e r ; the t e s t s w e r e conducted at N I I k h i m m a s h . The m a t e r i a l used in the f a b r i c a t i o n of the b a s k e t s was s h a p e d w i r e c o n s i s t i n g of OKhl8N9T o r Khl8N10T and OKh23N28M3D3T c o r r o s i o n - r e s i s t a n t s t e e l s , f a b r i c a t e d and m a d e a v a i l a b l e to i n d u s t r y by the M e t a l w a r e R e s e a r c h I n s t i t u t e to c o n f o r m to p r o v i s i o n a l t e c h n i c a l conditions. The w i r e is d e l i v e r e d as e t c h e d a f t e r a box anneal; the r a d i i of c u r v a t u r e of the a c t i v e faces of this w i r e a r e not g r e a t e r than 0.05 ram. The w i r e is s t r a i g h t e n e d on a s p e c i a l s t r a i g h t e n e r whose r o l l e r s run in the h o r i z o n t a l and v e r t i c a l p l a n e s and f e a t u r e g r o o v e s m a t c h i n g the w i r e p r o f i l e , with one r o w of h o r i z o n t a l r o l l e r s f e a t u r i n g g r o o v e s matching the * M. M. Abelev, B. A. G a l i t s k i i , a n d I . M. Samochatov, K h i m i c h e s k o e M a s h i n o s t r o e n i e , No. 2 (1961).

i Neftyanoe Mashinostroenie,

No. 9, pp.ll-13,

September,

1966.

571

1

2

3

q

kl '%''

9 j

Fig. 2. F i x t u r e of welding a s s e m b l y of w i r e m e s h s c r e e n into c y l i n d r i c a l s c r e e n b a s k e t : 1) pivot r i n g s ; 2) s p a c e r bushings; 3) g e a r r a c k ; 4) p r o t r u d i n g r o d s ; and 5) j a w m a n d r e l .

Fig. 3. Assembly of mesh elements in welding fixture.

side profile of the wire, and the bottom vertical row of rollers matching the total profile, while the remaining rollers match the smooth cylindrical face of the wire. The wire is considered to be straightened when deviations from rectilinearity do not exceed 0.5 mm over a I000 mm length of wire. After the wire has been cut to length according to specifications, one of the ends is sharpened to form a slight chamfered surface to facilitate passage of the screen through the racks when the screen basket is welded together. Figure 2 shows a fixture used as an aid in assembling and welding the screen mesh into a fully assembled cylindrical screen basket. The fixture consists of ring pivots and a jaw mandrel. The pivot rings are connected by spacer bushings which set the position of each ring to match the positions of the parts (rings and semirings) on the outer screen surface, and to match the protracting rods. Each ring pivot consists of three components hinged together. Two racks are mounted on the inner surface of the ring pivot element. The rack troughs are shaped to conform to the mesh. Each ring thus consists of three parts, and the number of parts in the racks must be double that. The reason is so that the fixture can be dismantled after the screen basket has been welded together, and the welded cylindrical screen basket can then be removed from the fixture. The jaw mandrel designed to position and release the screen mesh elements later to be assembled into a cylindrical screen basket with the aid of the gear racks, consists of three jaws, distance taper sleeves, retainer rings, tension rods, and retainer plates. Compression and release of the jaws (active cycle) is brought about by mutually displacing the d i s t a n c e t a p e r s l e e v e s and t e n s i o n r o d a x i a l l y . When the r e t a i n i n g r i n g s r e a c h t h e i r l i m i t p o s i t i o n , i . e . , when the i n n e r f a c e s of the r e t a i n i n g r i n g s c o m e up a g a i n s t the s h o u l d e r s of the end g r o o v e s on the m a n d r e l jaws, the o u t e r d i a m e t e r of the jaws w i l l equal the n o m i n a l i n n e r d i a m e t e r of the c y l i n d r i c a l b a s k e t . The r e t a i n e r p l a t e s a r e to keep the r e t a i n i n g r i n g s in the end g r o o v e s of the m a n d r e l jaws (these p l a t e s c o v e r the end g r o o v e s o v e r half t h e i r width), and a r e s c r e w e d in. The jaw m a n d r e l is f o r m e d by s l a n t e d r e c e s s e s which, in c o n t r a s t to r e c e s s e s cut a x i a l l y , do not allow the w i r e m e s h e l e m e n t s to lodge in the s l o t during a s s e m b l y of the s c r e e n b a s k e t . F i x t u r e p a r t s a r e m a d e of c a r b o n s t e e l , and the r a c k s a r e m a d e of LS-59 b r a s s . The choice of b r a s s as the r a c k m a t e r i a l is d i c t a t e d by a p r e f e r e n c e f o r r a c k t e e t h with m i n i m u m d e v i a t i o n s . Welding a s s e m b l y of the s c r e e n m e s h e l e m e n t s p r o c e e d s as follows. The m e s h e l e m e n t s which have had t h e i r ends c h a m f e r e d and have been d e g r e a s e d in B-70 g a s o l i n e o r in a c e t o n e a r e s o r t e d out

572

Fig, 4. Basket with jaw m a n d r e l , p r e p a r e d for machining,

Fig. 5. Integral welded cylindrical baskets : a) hole width 2 ram; b) hole width 0.1 ram.

according to the width of the active part, with deviations not exceeding mandrel and the pivot rings are then set vertically on a base flange.

•

to 0.03ram.

The jaw

Next the mandrel, with jaws squeezed together, is released slightly and the mesh elements (eight in number) with chamfered ends are inserted into the gear racks at equal spacings along the periphery (Fig. 3). The ends of the mesh elements are brought out to the surface of the base flange. The fixture is then set up horizontally and the racks are filled with the mesh elements (with deviations no greater then +0.02 to +0.03 ram). The ends of the mesh elements are brought out as far as they will go. After all the troughs in the racks have been filled with mesh elements, the mandrel jaws are squeezed shut by means of the rod and a handle. The jaws are squeezed up to the point where the mesh elements lie tight against the rack teeth profiles, with no clearance in between, and the active surface of the mesh elements acquires a cylindrical shape pushed tight up against the outer surface of the mandrel jaws. If the measured inner diameter of the assembled screen basket is equal to the dimension specified on the drawing, then assembly of the mesh screen can be considered complete. Next the rods are screwed loose, the distance bushings are removed, and the thrust ring is removed. Mesh screens so assembled are now ready for welding. Semirings and rings are welded to the mesh screens in two technological steps: tack welding and finish welding. The semiring whose inner diameter equals the outer diameter of the cylindrical basket assembly is placed on the lateral surface of the ring pivot and is tack-welded to the mesh elements by nonconsumable-electrode wire-filler argon arc welding. Filler metals can be welding wire of grades Sv-04KhI9N9, Sv-06KhI9NgT, Sv-08KhI8NIOB, and Okh23N28M3D3T, as required, and the nonconsumable electrodes can be VTI5 tungsten rods or tungsten lanthanated rods. A second semiring is butted against the tack-welded semiring, and is also tack-welded by argon arc welding. The length of the tack welds is 10-15 ram, and they are spaced 50-75 mm apart. Tack welding of the second semiring and next semiring proceed in the same sequence of steps as the first. Next the rings are tack-welded to the ends of the mesh elements. The size and the number of tack welds is the same in the case of the semirings. Semirings and rings are tack-welded by rotating the fixture through 180 ~. Once the screen basket has been completely welded, the pivot rings are disassembled (pins are extracted from the pivots and the rack sector is removed). The outer surface and the end surface of the jaw mandrel is then machined, along with the welded cylindrical screen (Fig. 4). The outer surfaces are center-turned, while riding on the jaw mandrel, screw-cutting lathe. Ends of the screen basket are cut on the same mandrel, with + 0.5 mm tolerance, and grooves are machined. The welds are machined to match the inner cylindrical face. The surfaces are machined

with cutters equipped with T5KI0

and TI5K6

on a IK62 model to length specification flush on the inner diameter

hard alloy plates, at the

573

f o l l o w i n g c u t t i n g c o n d i t i o n s : v = 2 1 9 - 1 6 2 m / r a i n , s = 0.1 to 0~3 m m / r e v ; the g e o m e t r i c p a r a m e t e r s of t h e c u t t e r e d g e s w e r e a = 15 ~ ~/= 15 ~ (p = 45 ~ k = 0 ~ ( t h e s e c u t t i n g c o n d i t i o n s r e f e r to m a c h i n i n g w i t h o u t the u s e of c o o l a n t fluid). F i g u r e 5 s h o w s i n t e g r a l w e l d e d c y l i n d r i c a l s c r e e n s w i t h s l o t w i d t h s of 0.1 m m and 2 m m width between the individual elements. T h e f a b r i c a t i o n t e c h n o l o g y of i n t e g r a l w e l d e d c y l i n d r i c a l s c r e e n s h a s b e e n p u t into p r a c t i c e a t t h e e x p e r i m e n t a l N I I k h i m m a s h P l a n t . S c r e e n b a s k e t s f a b r i c a t e d at t h a t p l a n t a n d i n s t a l l e d in b o w l s of N G P - 2 K - 2 0 0 and N O G S h - 8 5 / 1 2 0 c e n t r i f u g e s h a v e b e e n r u n t h r o u g h i n d u s t r i a l t e s t s and a r e c u r r e n t l y b e i n g s u c c e s s f u l l y e m p l o y e d in a n u m b e r of c h e m i c a l p l a n t s . M e a s u r e s t a k e n of the a c t u a l d i m e n s i o n s of c y l i n d r i c a l b a s k e t s 85 m m in d i a m e t e r s h o w e d t h a t d e v i a t i o n s f r o m n o m i n a l d i m e n s i o n s w e r e w i t h i n the r a n g e p r o v i d e d f o r i n t h e d r a w i n g s affd s p e c i f i c a t i o n s . We c a n c o n c l u d e then, on the b a s i s of t h e s e s t u d i e s , t h a t the u s e of i n t e g r a l w e l d e d c y l i n d r i c a l b a s k e t s w i l l m a k e i t p o s s i b l e to m a n u f a c t u r e s c r e e n s with a m i n i m u m d i a m e t e r (25 to 50 ram), to o b t a i n a s l i t w i d t h of 0.1 m m w i t h d e v i a t i o n s f r o m t h i s w i d t h k e p t to w i t h i n =~0.05 to + 0.08 m m o v e r the e n t i r e a c t i v e s u r f a c e , to s t r e t c h t h e u l t i m a t e s t r e n g t h of t h e w e l d m e n t s to t h a t of t h e p a r e n t m e t a l , and to e l i m i n a t e butt w e l d i n g of s e c t o r s by i n c r e a s i n g t h e u s e f u l c r o s s s e c t i o n of t h e s c r e e n . I n t r o d u c t i o n of t h e s e i n t e g r a l w e l d e d c y l i n d r i c a l b a s k e t s on a w i d e s c a l e w i l l a l s o m e a n a r e d u c t i o n in the a m o u n t of metal required, higher centrifuge capacity, and much lower electric power costs.

574