EXPERIMENTAL STUDIES OF THE PROCESS OF DIRECTIONAL SPLITTING

OF NATURAL STONE BY A PRESS WITH A SELF-ADJUSTING WORKING HEAD

O. D. Alimov, M. T. Mamasaidov, and A. Ya. Khokhlov

Processing of natural stone by splitting is an advanced method requiring low energy and providing highly decorative architectural and structural blocks [1-4]. The starting material may be rejects from stone mining and processing enterprises which makes it possible to achieve low waste technology for processing stone and to make the finished product, i.e. split stone articles, considerably cheaper.

Processing of stone by splitting has been traditionally carried out manually using simple equipment. Recently abroad (in Italy, FRG, USA, France, etc.) special stone splitting machines and production lines have been created and used extensively for the production of various split blocks of natural stone.

Now in our country there is regeneration at a high quality level of work for creating and introducing into practice stone splitting presses with a self-adjusting working head [4]. Improvement in construction and high efficiency of these stone splitting machines leads to a need for studying the process of directed splitting of natural stone.

For these studies there are the following tasks: to study the features of the stone splitting process when two self-adjusting splitting tools are forced into a rock from op- posite sides; and to determine the effect of the mechanical properties of natural stone and its geometrical parameters on the force and energy indices of the splitting process.

Study Procedure. In order to study the splitting process an experimental test unit (Fig. i) was based on a prototype of a PKA-800 press [4] equipped with strain gauges gluded directly to the splitting tools of the upper working head and the stem of the hydraulic cy- linder, a hydraulic system pressure sensor 2, and a strain gauage set-up 3 consisting of a self-recording instrument (N338-8p), an amplifier (Topaz-l), and a power supply (B5-21).

Splitting tests on stone specimens were carried out using a splitting tool (Fig. 2) intended for work with press PKA-800 under production conditions. This tool consisted of a holder 1 made of steel 40Kh and a hard alloy plate 2 of grade VK-20.

Specimens of facing stones of different deposits (see Table i) were selected for the experiments.

As indices characterizing the stone splitting process the following were adopted: split- ting force (Fp); nominal stress* mp; enerby content of the splitting process (Wp); duration of the splittlng process (tp).

The splitting force was recorded by the strain gauge set-up and it was determined from the Fp(tp) recorded diagrams by the equation

Fp=~* m, kN, (i)

where ~* is maximum deviation of the pen of the self-recording instrument, mm; m is force scale, kN/mm.

Nominal stress was calculated as

T,, =Fp/S,, kN/cm 2 (2)

where Sp is s p l i t t i n g area , cm2; Sp = b 'h (see Fig. 1).

The energy content of the splitting process was determined by the relationship

*By nominal stress we understand the ratio of splitting force to splitting area.

Research Center "Impul's," Academy of Sciences of the KirgizSSR, Frunze. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 52-57, May- June, 1990. Original article submitted June 28, 1989.

0038-5581/90/2603-0229512.50 �9 1991 Plenum Publishing Corporation 229

TABLE 1

Facing stone

Granite

Granodiorite

Pink granite Granite

Granite

Marble

Coquina

Deposit

'~k-Ulen' (KirgizSSR) 'Kaindy' (Kirigiz SSR) Ditto 'Kurdai' (Kazakh SSSR) 'Kapustinskoe' (L~rSSR) 'Arym'

I KirgizSSR) Sary-Tash' (KirgizSSR)

Zc, MPa

t50--170

t40--204

140--20& 100--190

180--2i0

90--i30

50--75

Density, kg/m 3

2,61.10 a

2,7.t03

2.7.t03 No da ta

2,75. i0 a

2,3. t0 B

2,3.103

Grain size, I1~1.

No da ta

2--4

No da ta up to

5--50

0,5--5

1 . Fig.

i h i-3 it"

[ IL

._/

E ~'l ' ! ' l l I l q l "'~-~ i I.

Diagram of the experimental test unit.

Fig. 2. Splitting tool with strain gauges.

Wp = Ap/Sp kW'h/m 2 , (3)

where Ap is energy expended in splitting a stone specimen

t O . P c . Q . t p Ap---~ 102.60.3600 kW-h (4)

Pc is average value of liquid pressure in the hydraulic system during a complete stone split- ting cycle (Pc -= P*/2), MPa; Q is liquid consumption, liter/min; tp is duration of the split- ting process

tp = ~c/Ur sec (5)

Z r is length of the recorded diagram for the splitting process, nun; v r is chart movement velocity, ram/sec.

230

F - a ~Jf f f l l tTL~r.Tf ' , 'sr~" , . , '~ '~f f l ; .~[ r~'"~ _ - r " : :T ' : " : 'Z""TT.~. ' :'7 ;:'r'L~Z

F i g . 3. N a t u r e o f t h e change i n l o a d on a t o o l d u r i n g stone splitting: a) with a sawn surface; b) with an unprocessed surface.

1: I.i;i~,jd; : !iJli!!!l!!i!! 'iiil',li!i~ i~.' . . . . ~, i l , , , ~ , ' , ' ~ i l l !

I :.1 ~ ii~;q , I t l , . ~ h , , ~ [ i i d

' ~ , , : �9 i ' ' ','~ ~ , 7 , ' ~ ] ~:

[ ... 1,..,,,.1:.,,,,,,! ....... ~ : , , ~ , ~ fll, rflJ[~ff, | ~ I' i ,,:f I?:'.i'/;.i.y,t'ffltt!//ii/IL~/.~/fil/Itffff/if/l~tlllllfffft [ = , ii l iltlti;Ittftt!!tilttt;ii!~'tllttlIil~lllilll#l! ItlllllH!!ii

: ; ' , 1 i , ~ : ; l [ ~ l i I i I

E : d ' : ' ttl, t!V~'i i: i ::, !'! !t.:L t: ! ! t l ; i ! i ~ ~ [ :i I:';.!tlili:':~l : (~?,l~':!t:.;iiili~t~f~,illlliillh - ~ ~ ... . ""t,, ,til~1!IlliliI~l!tllltt!it!

~~?..~.,',;,.t~,',\~,tllllllt~l\\\l\tl'~,

L,c ~/:~`~!///`~i~/~/~#~ ~L!I~.fk~ ~ / ~ / , !~ /~ / / i~L~!~L '~ fL~.~ ]i,~i/!,l!fl!l!tilll/ltill!Sll]ll!/ll~f!llfl/!llJ<!l~i!!1i/s'sJ;/l/l!Hl/./!l!/llll/IH]/i

lI;i:~l~l ....... JI,, ,,,I/J!,,,!L~!It,,I,I!I//~,:I:,,~ , I,!,,,~,l~,, ,,, l l l , , I , ~ I~liifilhi!!i!i~ll~i!i![ljliliifitl!liiiiiiiliii!lliH,il;~!!i~liil(i '~ililu !iiL~ltllJ<

l~!i!i!!l!l!!~!!: l!':ti:'!t~!,,!i!!~!~l!{t:s . I ! ' : ' . ~ ,'~l~%!!!li!!!i~!il!~i

F i g . 4. N a t u r e o f change in l o a d on a t o o l d u r i n g s p l i t t i n g : Kurda i g r a n i t e ; b) g r a y Ka indy g r a n i t e ; c ) Ar~m m a r b l e .

a)

By substituting (4) and (5) in (3) we obtain

10 , P c , Q . t p = (6) ~Vp 102.60- 3600. Sp 0,0~<~ kW" h/m 2.

In o r d e r t o d e t e r m i n e t h e s e l e c t e d i n d i c e s o f t h e p r o c e s s d u r i n g e x p e r i m e n t s t h e f o l l o w - ing p a r a m e t e r s were r e c o r d e d : p r e s s u r e P* in t h e h y d r a u l i c s y s t e m d u r i n g s p l i t t i n g , MPa; w i d t h h and h e i g h t b, cm, o f t h e r o c k spec imen in t h e s p l i t t i n g p l a n e ; l e n g t h ~r o f t h e r e - c o r d e d d i a g r a m , mm. L i q u i d consumpt ion Q and c h a r t movement v e l o c i t y v r were t a k e n in a c - c o r d a n c e w i t h t h e s p e c i f i c a t i o n s o f t h e h y d r a u l i c p r e s s and s e l f - r e c o r d i n g mach ine .

The r e s u l t s o f e x p e r i m e n t s were p r o c e s s e d u s i n g m a t h e m a t i c a l s t a t i s t i c s a c c o r d i n g t o which t h e c o e f f i c i e n t o f v a r i a t i o n f o r t h e r e c o r d e d p a r a m e t e r s d id n o t exceed 215%.

R e s u l t s o f E x p e r i m e n t a l S t u d i e s . O b s e r v a t i o n s o f t h e s p l i t t i n g p r o c e s s f o r n a t u r a l s t o n e showed t h a t i n t r o d u c t i o n o f a t o o l i n t o a p r e v i o u s l y p r o c e s s e d (sawed) s t o n e s u r f a c e ( F i g . 3a) o c c u r s w i t h a s m a l l i n c r e a s e in l o a d i n i t i a l l y ( s e c t i o n s 1 - 2 ) . There i s p l a s t i c d e f o r m a t i o n , i . e . , c o m p a c t i o n o f p a r t o f t h e r o c k under t h e c u t t i n g edge of t h e t o o l and in i n d i v i d u a l c a s e s s e p a r a t i o n o f i t f rom t h e main mass which i s i n d i c a t e d by a s h o r t = t e r m drop in l o a d ( p o i n t 3 ) . S u b s e q u e n t l y c o m p a c t i o n o f t h e c o r e p r e v e n t s p e n e t r a t i o n o f t h e t o o l i n t o t h e s t o n e as a r e s u l t o f which t h e r e i s a s h a r p i n c r e a s e in l o a d ( s e c t i o n s 4 - 5 ) accompan ied by e l a s t o p l a s t i c d e f o r m a t i o n o f t h e s t o n e spec imen w i t h s e p a r a t e jumpwise f a l l s as a r e s u l t o f b r i t t l e c h i p p i n g o f s t o n e p a r t i c l e s and v a p i d r emova l ( r e b o u n d i n g ) o f them from b e n e a t h t h e c u t t i n g edge o f t h e t o o l . An i n c r e a s e in l o a d c o n t i n u e s u n t i l s t o n e s p l i t - t i n g .

The n a t u r e o f t o o l i n t r o d u c t i o n i n t o an u n p r o c e s s e d (uneven ) s t o n e s u r f a c e i s somewhat d i f f e r e n t : i n t r o d u c t i o n o f t h e t o o l o v e r t h e whole e x t e n t t o s t o n e s p l i t t i n g has a c l e a r l y d e f i n e d jumpwise n a t u r e ( F i g . 3b) . Th i s i s e x p l a i n e d by t h e f a c t t h a t due t o s u r f a c e uneven - n e s s t h e t o o l comes t o b e a r o n l y a t i n d i v i d u a l p o i n t s and t h e r e f o r e s p e c i f i c l o a d s in con- t a c t a r e a s a r e h i g h . S i n c e p r o t u b e r a n c e s have f r e e s u r f a c e s t h e y m a i n l y b r e a k and t h e l o a d v a r i e s jumpwise . For t h e r e s t , t h e n a t u r e o f i n t r o d u c i n g a t o o l and s t o n e s p l i t t i n g w i t h an u n p r o c e s s e d s u r f a c e i s s i m i l a r to t h a t d e s c r i b e d above .

I t has been e s t a b l i s h e d by e x p e r i m e n t t h a t t h e n a t u r e o f t h e l o a d on a t o o l d u r i n g i n - t r o d u c t i o n depends n o t o n l y on t h e s t a t e o f t h e s t o n e s u r f a c e , bu t a l s o on i t s s t r u c t u r e . With s p l i t t i n g o f g r a n i t e spec imens from t h e ' K u r d a i ' d e p o s i t t h e change in l o a d on t h e t o o l

231

Fp . kN

a

~20

YSO

BO

IfO0 200 .~DO .S,, cm 2 ~, kN/cm 2

\ a , \ igranites ,0 oo

;{ o - ~7

I t00 200 300 %. (

Fp. kN

,,D|

$0 90 f2O fSO ~ , MPa WD, kW'g/m 2

- r~ I \! I i d i

�9 I \ i i \:granitesl

,ol : ~ r -L . i 7.o i \ -I o / ~ .....: i V } I~

J r 2~ 300 %,. cm

Fig. 5. Dependence of force and energy indices for the split- ting process on the mechanical properties and geometrical di- mentions of stone specimens; i) Kaindy granodiorite; 2) Ak-Ulen granite; 3) pink Kaindy granite; 4) Kurdai granite; 5) Kapustinsk granite; 6) Arym marble; 7) Sary-Tash coquina- limestone.

(Fig. 4a) increases almost uniformly over the whole process. This may be explained by the fact that Kurdai granite, which has a coarse grain size due to the marked content of quartz (25-35%), splits well in a prescribed direction. Conversely, gray Kaindy granodiorite, which has a comparatively low quartz content, is not amenable to directional splitting, and dur- ing splitting the load on the tool (Fig. 4b) had an uneven clearly defined jumpwise nature. It is interesting to note that marble from the Arym deposit (Fig. 4c) also splits direc- tionally, although it exhibits considerable toughness and splitting is immediately preceded by formation of numerous cracks which give rise to the comparatively long duration of the process and significant unevenness of the split surface.

Force and duration of the splitting process depend both on mechanical properties of the stone and on its geometrical parameters. It is natural that with an increase in split- ting surface (Sp = b'h) and greater stone strength the duration of the splitting process increases.

A quite stable relationship is revealed between the splitting force and stone strength (Fig. 5b). With an increase in stone ultimate Strength in compression (ac) its splitting force increases. In addition, it was noted that Arym marble, which has a lower strength (o c) than Kurdai granite, splits with greater forces. At the same time, Kapustinsk granite with greater compressive strength than Kaindy granite splits with lower forces. It can be seen that in these cases stone structure plays a consierable role: Arym marble relates to tough rock with a low quartz content, but Kapustinsk granite is coarse grained (up to 50 mm) with inclusion of coarse crystals of feldspar.

Nominal stress (~D) and energy content (Wp) for splitting decrease (Fig. 5c, d) with an increase in split agea. This may be explained by the effect of a scale factor: the greater the dimensions of the specimen being split, the greater the probability of the pres- ence of factors (microcracks,inclusions, etc.) reducing its strength. For hard stones (granites) the reduction in Tp and Wp is most sensitive in the range of change of Sp from 100 to 300 cm 2 , and then the intensity of ~p, WD(SD) falls. For stone of medium and low strength (marble, coquina) there is a uniform-reduction in ~p and Wp with an increase in Sp.

232

Thus, the process of splitting has a pulsed (dynamic) character and the dynamic nature of the process depends markedly on the physicomechanical properties (structure, grain size, quartz content) and it increases markedly with an increase in surface roughness (unevenness) and the splitting area of stone specimens. In the main these factors specify the duration of the process and the force and energy content of splitting.

Quantitative data obtained in experiments for the splitting process and the dependence established for its indices on the parameters in question may be suggested as a basis for the improvement, planning, and operation of stone splitting presses with self-adjusting working heads.

i~

2.

3 .

4 .

LITERATURE CITED

Machines for Splitting Stone. Review. Modern Machines for Processing Facing Stone and Production Schemes [in Russian], TsNIIT~STROM, Moscow (1968). K. S. Vardanyan, Modern Stone Processing Machines and Flow Lines [in Russian], Aistan, Erevan (1975).

A. M. Orlov, Mining and Processing of Natural Stone [in Russian], Stroiizdat, Moscow (1977). O. D. Alimov, M. T. Mamasaidov, A. Ya. Khokhlov, and O. Yu. Sirmbard, "Structural features and results of industrial tests for a stone splitting press PKA-800 with a hydraulic drive," in: Hydraulic Drilling and Breaking Machines [in Russian], Ilim, Frunze (1988).

BREAKING MECHANISM FOR CORE SAMPLES FROM OIL FIELD RESERVOIRS

Yu. F. Kovalenko

It is well known that during recovery of core samples from oil field reservoirs, par- ticularly those characterized by high initial formution pressure, it is often not possible to obtain them without breakage. To a significant degree this depends on the rate of raising the core sample, i.e., with low rates the core remains whole, but with high rates it breaks.

In order to explain the reasons for core sample breakdage it is normal to use the reason- ing that breakage occurs as a result of the release of elastic deformation energy for the rock when the core sample is cut. Similar reasoning is also proposed in order to explain the reasons for disk formation in core samples from burst-prone sandstone overlapping coal seams.

In the present work another mechanism is suggested for the breakage of core samples from oil field reservoirs. In essence it consists of the following. In oil field reser- voirs there are numerous cracks and crack formations filled with oil and the initial oil pressure often markedly exceeds the saturation pressure for gas dissolved in it. As the core sample is raised there is gradual unloading from the vertical rock pressure component. Correspondingly there is expansion of oil and a reduction in its pressure~ In view of the low compressibility of oil, expansion of the oil itself does not lead to rock breakage. With a reduction in oil pressure below the value of the saturation pressure of dissolved gas, this gas starts to be released with a further reduction in pressure; this may rupture the rock and break the core sample.

From this point of view the dependence of core sample integrity on the rate of lift- ing them to the surface becomes understandable. This is connected with the fact that with a reduction in rock pressure, gas released from the oil may decrease pressure in two ways. First, as indicated above it may by expanding rupture the rock, and second, its pressure may decrease as a result of gas filtration from cracks and pores along filtration channels existing in the stratum. Therefore, if the rate of lifting a core sample is high, gas does not escape from cracks and there is core sample breakage by expanding gas. With a low lift- ing rate the amount of gas in cracks as a result of filtration decreases so much that its

Institute of Mechanics Problems (IPM), Academy of Sciences of the USSR, Moscow. lated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. May-June, 1990. Original article submitted October 20, 1989.

Trans- 57-62,

0038-5581/90/2603-0233512.50 �9 1991 Plenum Publishing Corporation 233