referring to fig2 a thrust force ( propulsion ) is applied in an axial direction to a rod - like si material 1 by a driving system 2 . the driving system 2 includes , e . g ., an air cylinder and a guide roller group 3 . the si material is fed in a predetermined direction by the guide roller group 3 which functions as a feeder mechanism . a heater 4 is arranged in the vicinity of the guide roller group 3 at an upstream ( front ) side of a traveling direction of the si material 1 . the heater 4 includes a heating coil 4 a and a high frequency generator 4 b . when the si material 1 passes through the heating coil 4 a , a high frequency current flows into the heating coil 4 a from a high frequency generator 4 b . an induced current flows in the si material 1 , so that the si material 1 is heated locally . the rotatable arm 5 includes a clamping or holding portion 5 b supported on a rail 6 so as to be rotatable around a rotary shaft 5 a . the holding portion 5 b is made of the same material as the si material 1 or a material having a hardness higher than the si material . the rotary shaft 5 a has its axis in a direction perpendicular to the axial direction of the rod - like si material 1 being fed by the guide roller group 3 . then , the heated si material 1 is fed so that the axial direction thereof follows a circular - arc orbit guided by the holding portion 5 b . while the si material 1 is held by the holding portion 5 b , the rotatable arm 5 is pushed by the si material 1 , and then , is rotated , and thereby , continuously applies a bending moment to the heated portion of the si material 1 . as described above , the heated portion of the si material 1 is in a state in which a slip is easy to generate between lattices or between crystal grains , so that a slip is generated by the applied bending moment . as a result , a bend is formed in the si material 1 . according to the bending method as described above , it is possible to carry out so - called continuous dieless bending without the use of molding dies , and to bend the rod - like si material 1 into a gentle circular - arc shape . moreover , since no molding dies are used , the heated portion of the si material 1 has no contact with the surface of a molding die . therefore , the bending is performed in a manner which reduces or eliminates contamination such as metal pollution , oxidation or the like from contact with molding dies . referring to fig2 the above bending method produces a constant bending accuracy . first , in the above machining system , a bending moment is uniquely applied only to the front side from a bending fulcrum with respect to the traveling direction of the si material 1 . in general , according to bending for a steel pipe , a workpiece has a temperature distribution with respect to the traveling direction thereof controlled by water cooling ( quenching ). even if a bending moment is uniquely applied only to the front side from a bending fulcrum with respect to the traveling direction of the workpiece , a deformation is generated only in portions having no cooling , and thereby , bending accuracy is kept constant . on the other hand , in bending a brittle material such as si material 1 , the cause relied on for deformation is mainly a slip between crystals . when slip deformation is generated , a generated bending moment is absorbed by a feed of the guide roller group 3 and by a rotation of the rotatable arm 5 . according to the above bending method , by continuously feeding the si material 1 , a bending moment is continuously applied to the si material 1 . as a consequence , a process is performed in which the generation of a slip deformation is continuously repeated . thus , bending is performed without dispersion by a self - adjustment operation . in order to feed the si material 1 , a thrust force ( propulsion ) is applied to the si material 1 from the pressure cylinder of a driving system 2 , and a traction force may be applied to the si material 1 by rotating and driving the rotatable arm 5 . the si material 1 is locally heated directly after the si material 1 is fed from the guide roller group 3 . thereby a heated region in the si material 1 is successively moved with the feed of the si material 1 and a gentle temperature distribution is given to the si material 1 . therefore , by carrying out the aforesaid continuous dieless bending , the si material 1 is deformed while absorbing heat impact . then , the deformed portion is gradually enlarged , and thus , a predetermined bending portion is realized , so that preferable bending is performed . in the heated region of the si material 1 , the highest temperature region is situated to the rear , or upstream side , of a bending fulcrum with respect to the traveling direction of the si material 1 , and thereby , preferable bending is performed . the holding portion 5 b is made of the same material as the si material 1 or a material having a hardness greater than the si material 1 . therefore , bending is performed while reducing contamination such as metal pollution , oxidation or the like . the type of heater is not limited to the above heater 4 using high - frequency heating . instead , radiant heating , using a gas burner or high frequency , may be used . if the heating temperature is set about 900 ° c . or more , preferable bending is performed , and more preferably , the heating temperature is set about 1300 ° c . or less in view of limiting the aforesaid contamination . referring now to fig3 and 3 a , a thrust force ( propulsion ) is applied to a rod - like si material 1 in an axial direction of the material 1 by a hydraulic cylinder 2 used as a diving device ( actuator ). the rod - like si material is fed in a specific direction . more specifically , a rod 2 a of the hydraulic cylinder 2 includes a holding ( retaining ) portion 2 b . the rod - like si material is held by the holding portion 2 b . a rotatable arm 5 , including a holding portion 5 b , is supported on a rail 6 so as to be freely rotatable around a rotary shaft 5 a . the holding portion 5 b is made of the same material as the si material 1 or a material having a hardness higher than the si material . an axis of the rotary shaft 5 a is perpendicular to the axial direction of the rod - like si material fed by the hydraulic cylinder 2 . a heater 4 is disposed at a position where the rod - like si material 1 thus fed runs on a circular - arc orbit of the holding portion 5 b , or on the neighborhood position . the heater 4 may be a hydrogen - oxygen mixed gas burner , for example . the si material 1 is heated by the heater 4 . the heated si material 1 is fed with its axial direction running along the circular - arc orbit of the holding portion 5 b . with the si material 1 held by the holding portion 5 b , the rotatable arm 5 is pressed by the si material 1 , and thereby is rotated . in this manner , a bending moment is continuously applied to a heated portion of the si material 1 . the heated portion of the si material 1 is in a state in which a slip is easy to generate between its lattices or between its crystal grains . for this reason , a slip is generated in the si material by the applied bending moment ; as a result , a bend is generated therein . the above bending machine is controlled so that a flow rate of hydraulic oil supplied to the hydraulic cylinder 2 remains approximately constant . the highest ( maximum ) pressure is previously set so that an internal pressure of the hydraulic cylinder 2 does not exceed a reference value . more specifically , as shown in fig3 and 3 a , a pressure compensating type flow regulating valve 11 and a relief valve 12 are located ahead of the hydraulic cylinder 2 . the pressure compensating type flow regulating valve 11 is composed of a variable orifice 13 and a fixed differential pressure type pressure reducing valve 14 . the front - position fluid pressure of the variable orifice 13 is introduced into a pilot chamber of the pressure reducing valve 14 . the rear - position fluid pressure of the variable orifice 13 is introduced into a spring chamber of the pressure reducing valve 14 . a differential pressure between front and rear positions of the variable orifice 13 is maintained at a pressure controlled by a spring force . thus , even if the fluid pressure varies , the flow rate of fluid flowing through the variable orifice 13 remains constant . also , the relief valve 12 is actuated ( operated ) so that a fluid pressure of the hydraulic cylinder 2 does not exceed a reference pressure . in the bending method , the rotatable arm 5 is supported so as to be freely rotatable . referring now to fig4 and 5 , the following is a description of a bending operation of the si material in the case of using the aforesaid bending machine . that is , the bending machine is controlled so that a flow rate of the fluid supplied to the hydraulic cylinder 2 remains constant . the drawings show the elapsed changes of a temperature t of the heated portion in a bending operation , a feed speed v of the rod - like si material 1 , and an internal fluid pressure p of the hydraulic cylinder 2 . first , as shown in fig4 when the temperature t of the heated portion of the si material 1 is lowered due to any factors ( disturbance ) ( time 1 ), a deformation resistance of the si material 1 increases . also , a feed rate of the hydraulic cylinder 2 is reduced while the feed speed v of the si material 1 decreases ( time 2 ). as a result , the internal fluid pressure p in the hydraulic cylinder 2 increases ( time 3 ). the highest ( maximum ) internal pressure of the hydraulic cylinder 2 is regulated by the aforesaid relief valve 12 . this prevents bending and breaking of the rod - like si material 1 by an abnormal increase in pressure ( time 4 ). as described above , when the feed speed v of the si material 1 decreases , the residence time of the si material at the heated portion increases . as a result , the amount of heat applied to the si material also increases . the temperature t of the si material in the heated portion increases ( time 5 ). whereupon a deformation resistance of the si material 1 is reduced while the internal fluid pressure p of the hydraulic cylinder 2 increases . the increased temperature increases the slip deformation generated in the si material 1 . as a result , the si material 1 is bent and deformed , and the feed speed v of the si material 1 is increased ( time 6 ). thereafter , the internal fluid pressure p of the hydraulic cylinder 2 is reduced ( time 4 ). then , the feed speed v of the si material 1 is increased . as a result , the residence time of the si material 1 in the heated portion is reduced . the amount of heat absorbed by the si material consequently is reduced . for this reason , the temperature t lowers ( time 7 ), and thereafter , the same operation as described above is repeated . according to the above bending method , as seen from the above description , the following sequence occurs : the above procedure is repeated in a feedback manner to provide smooth automatic bending . referring to fig5 conversely , when the temperature t of the heated portion of the si material 1 rises due to any factor ( disturbance ) ( time 1 ), the deformation resistance of the si material 1 is reduced while the feed rate of the hydraulic cylinder 2 is increased . as a result , the feed speed v of the si material 1 is increased ( time 2 ). then , the internal fluid pressure p of the hydraulic cylinder 2 is reduced by the increase in feed rate ( time 3 ). as described above , when the feed speed v of the si material 1 increases , the residence time of the si material in the heated portion is shortened . this reduces the quantity of heat absorbed by the si material . this lowers the temperature t of the si material ( time 5 ). whereupon the deformation resistance of the si material 1 increases while the feed speed v of the si material 1 decreases ( time 6 ). thereafter , the internal fluid pressure p of the hydraulic cylinder 2 increases ( time 7 ). then , the feed speed v of the si material 1 decreases . as a result , the residence time of the si material in the heated portion increases , and the amount of heat absorbed increases . for this reason , the temperature t increases ( time 8 ), and thereafter , the same operation as described above is repeated . according to the above bending method , as seen from the above description , the following operations occur in sequence : on the contrary , in fig6 if the feed speed v is held constant , the negative feedback in the above preferred embodiment is not accomplished . first , as shown in fig6 when the temperature t of the heated portion is reduced due to any factor ( disturbance ) ( time 1 ), the deformation resistance of the si material 1 increases due to the decrease in temperature of the si material . since the feed speed v of the si material 1 is constant , the internal fluid pressure p of the hydraulic cylinder 2 increases ( time 2 ). then , bending deformation becomes more difficult due to an increase in the deformation resistance of the si material 1 . as a result , the internal fluid pressure p of the hydraulic cylinder 2 gradually increases . finally bending and breakage of the si material 1 occurs ( time 3 ). as described above , by maintaining the flow rate of the fluid supplied to the hydraulic cylinder 2 constant , a bending deformation is generated when the temperature change of the heated portion of the si material 1 and the feed speed v of the si material 1 are well - matched . that is , bending proceeds under an operating condition of self - regulation operation as described in the following : an air cylinder may be substituted for the hydraulic cylinder 2 without departing from the spirit and scope of the invention . when using an air cylinder flow rate control is also carried out as described above . when the above - mentioned bending is carried out , the temperature of the heated portion is an important regulation factor . at the same time , the strain velocity applied to the si material 1 in the bending operation is also an important factor for determining the success or failure of the bending operation . referring to fig7 the relationship is shown between a temperature dependency of a yield stress ( upper yield stress ) of the si material 1 [ see j . r . patel and a . r . chaudhuri ; j appl . phys . 34 , 2788 ( 1966 )]. as shown in fig7 when the heating temperature increases , the yield stress is reduced , and at the same time , the yield stress is also reduced when the strain velocity decreases . now directing notice to a case of the strain velocity of 1 . 1 × 10 − 3 / sec ., when the heating temperature reaches the vicinity of about 1200 ° c ., the si material 1 yields at a stress of about 10 mpa . assuming a state that an si rod having a diameter of 8 mm is bent into a circular - arc shape having a radius of 50 mm over an angle of only 90 °, a strain generated at the rod inner and outer diameter is simply calculated to be about = 0 . 08 . when such a strain quantity is fed at the strain velocity of 1 . 1 × 10 − 3 / sec ., about 72 seconds is required to complete the bend . therefore , the si rod is fed at a speed of about 1 mm / sec . applying this condition to a case of the strain velocity of 1 . 1 × 10 4 / sec ., controlling the feed speed of the si rod to be about 0 . 1 mm / sec ., and the heating temperature to be 1000 - 1100 ° c ., bending of the si rod is carried out . from the above result , it is obviously favorable to carry out the bending operation of the si material 1 with the heating temperature of 900 - 1300 ° c ., preferably 1000 - 1250 ° c . from a viewpoint of reducing contamination , and at the strain velocity of 1 . 1 × 10 − 3 / sec . to 1 . 1 × 10 − 4 / sec . ( about 10 − 3 ˜ 10 − 4 / sec .) from a viewpoint of the bending workability , in addition to considering the melting point of si ( 1410 ° c .). with the use of the machining system as shown in fig3 and 3 a , a single crystal si rod having a diameter of 8 mm was heated to about 1250 ° c . by a gas burner while being fed at a speed of 0 . 5 - 0 . 7 mm / sec and then , was bent into a circular - arc shape having a bending angle of 90 and a radius of 50 mm while a thrust force ( propulsion ) of 11 . 5 kg being applied thereto . ten ( 10 ) si rods were subjected to bending ; as a result , an error in the bending angle was 90 ± 1 . 5 and in the radius was 50 mm ± 1 . 5 mm , and no breakage ( fracture ) was generated therein . referring now to fig8 a , the sem micrograph shows the appearance of the bent rod - like si material and a sem microphotograph of the fractured surface and the periphery surface of the bent rod - like si material . referring now to fig8 b , the upper portion of the sem microphotograph shows the peripheral surface of the bent rod - like si material , and the lower portion shows the fractured surface . slip lines can be clearly seen . a single crystal si rod having a diameter of 8 mm was bent into a circular - arc shape over a bending angle of 90 and a radius of 100 mm under the same machining condition as the above example 1 . ten ( 10 ) si rods were subjected to bending ; as a result , an error in the bending angle was 90 ± 1 . 5 and that in the radius was 100 mm ± 2 mm , and no breakage ( fracture ) was generated therein . next , the preferred application example of a binding method for si material of the present invention will be described below . this is a trial to manufacture a core wire member made of s - based material for manufacturing a polycrystal si by the above method . that is , a joint 23 extending from the core wire portion 21 to the connective portion 22 is formed by bending . and at the same time , the core wire member made of si material is made by connecting the rod - like si material using electron beam welding , laser welding , or mechanical joining method and the like . this core wire member made of si material , as shown in fig9 and 9 a , consists of a pair of core wire portion 21 , 21 extending substantially parallel with each other , a connective portion 22 connecting one end side of core wire portion 21 , 21 , each joint 23 extending from the core wire portion 21 to the connective portion 22 being formed by bending . in the joint 23 , abnormal growth of the polycrystal si is unlikely to occur , so that bending and cracking the rod - like polycrystal si is readily carried out . as a result , it is possible to improve a manufacture yield of the rod - like polycrystal si . the core wire member made of si material for manufacturing the polycrystal si may be manufactured utilizing other bending methods in addition to the above - mentioned bending method , so long as the same effect is obtained . the present invention is not limited to rod - like si materials having circular cross sections . for example , si materials having an ovoid or rectangular cross section are equally subject to bending using the techniques of the present invention . in addition , besides bending in the shape of circular arcs , the present invention is capable of bending si materials in other shapes such as , for example , in s turns or in a plurality of turns separated by straight sections . the above , and other objects , features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings , in which like reference numerals designate the same elements .