FR2630964A1 - METHOD AND DEVICE FOR BLOW MOLDING A HOLLOW BODY OF THERMOPLASTIC MATERIAL - Google Patents

Abstract

The present invention relates to the shaping of hollow bodies by blow molding in a mold. After placing a blank in a blow mold, a rod 15 is introduced through the blow mandrel. The draw rod is then moved mechanically by means of a roller guide 20 on a curved path and the blank is thus axially pre-stretched by a defined partial length. A wall portion of the blank, which preferably will be shaped during blow molding as a narrowing neck portion, is stretched into a thinner walled portion. After pre-stretching, the drawing of the blank is continued with compressed air, the draw rod being driven in such a way that it constantly guides the bottom of the blank centrally while the blank is widened to form the finished hollow body. A hollow body is thus obtained in a material with biaxial orientation, of optimized thickness.

Description

The invention relates to a method and a device for the molding by

  blowing a thermoplastic hollow body, in which a closed-bottom blank carried by a blowing mandrel is placed in a blow mold, a draw bar is introduced into the blank through the blowing mandrel , the blank is axially stretched by the draw bar and is expanded by the supply of blow air to form the

hollow body finished.

  In order to increase the resistance of plastic hollow bodies, the biaxial orientation of the blank in the blow mold is known.

  in place in the blow mold at the target temperature

  tation being stretched axially by a draw bar, until it comes to apply to the bottom portion of the mold, while occurs the radial flare by the blowing air. The plastic is in this way oriented biaxially and it receives

  desirable improved properties.

  As we know, the training of the rod

  drawing can be achieved by a pneumatically actuated piston.

  mechanically by a cam drive.

  US-A-4,409,161 discloses a pneumatic drive of drawing mandrels. EP-A-008481 discloses the displacement, respectively each on a curved path, of both a blowing chuck carrying the blank and a drawing mandrel penetrating the throat mandrel in such a way that that the blow mandrel is first fed into the blow mold and placed therein while the drawing mandrel is in a height-reminder, after which the drawing mandrel advances and axially stretches the mandrel. draft. Also known (DE-A-24 54 066) the axial stretching of the blank before closing the blow mold, an extension mandrel guided by a cam path being moved upwards, until the bottom of the blank comes to apply on the bottom of the blow mold. In

  another known blow molding device (DE-

  A-32 47 194), a blank pressed on a chuck

  ge is placed in a blow mold and a drawing mandrel is introduced into the blank, until it is applied to the bottom of the blank. a curved path drives the drawing rod. At the end of the curved path the drawing rod is coupled with a drawing cylinder and the axial drawing of the blank

  is achieved by the drawing cylinder.

  The fundamental object of the invention is to control the drawing process of the blank so that the distribution of the wall thicknesses of the hollow body to blow is optimized, that the resistance increases.

  and that matter is saved.

  The stated purpose is achieved by providing that the blank is stretched by the drawing bar over a predetermined partial length of the blow mold, that the blowing air is fed after this pre-stretching, that the blowing air continues this stretching. roughing and flattens it, and during this time, the drawbar

  is maintained on the bottom of the blank.

  Preferably: - the blank is sufficiently stretched by the drawing bar so that a predefined longitudinal fraction of the blank

  is stretched with a wall of smaller thickness.

  Advantageously, the stretched longitudinal fraction of the blank constitutes, during enlargement, a portion of the hollow body in which the radial expansion is relatively small. It is interesting to envisage, in this case, that the stretched longitudinal part constitutes a region of

hollow body neck.

  in the longitudinal part of the predefined preform for stretching, the wall thickness is kept lower. Advantageously, at the connection to the outlet part of the blank, the latter is stretched into a

thinner wall thickness.

  - For stretching the blank, the drawing bar is driven by a mechanical guiding device. - For maintaining the bottom, the drawing rod is driven pneumatically. The invention also provides a device for implementing the above method, comprising

  blow molds placed on a wheel driven

  a blowing mandrel, a drawing rod which can be introduced into the blank through an axial bore of the blowing mandrel and a drawing rod drive which consists of a jack, and wherein the cylinder of the jack can be moved axially by a curved path

  for the pre-stretching of the blank, and it is actuated tire-

  the subsequent movement of the stretch rod

  ge after leaving the curved path.

  Preferably, in this device: - the jack is a telescopic jack, in which a piston rod constituting the drawing rod can move in an inner cylinder, which is disposed of

  moving way in a fixed outer cylinder. advantageously

  the inner cylinder is driven by the

  curved and pneumatically operated.

  the inner cylinder is fixed on a mobile carriage on guide rods. Advantageously, this inner cylinder is fixed on the carriage on its end facing the blowing mandrel, and the carriage carries at its lower end a roller which enters the curved path. the device comprises two guide rods on each

on both sides of the cylinder.

  - The curved path is mounted adjustably on a pivot axis. Advantageously, this curved path

  is arranged to grip the roll on both sides.

  In the process according to the invention, the blank introduced into the blow mold is first stretched mechanically with a predefined and adjustable stroke, then the blowing air is introduced and the continuation of the axial stretching is carried out. simultaneously by blowing air

  and the low water chuck. The drawing mandrel is preferably

  The end of the drawing rod is held on the blank so that the end of the drawing rod is held on the bottom of the blank. The axial stretching as well as the radial expansion of the blank into a finished hollow body are therefore carried out by the blowing air, while the drawing rod, after the mechanical stretching, has the function of guiding so on the bottom of the blank until its application on the bottom part of the blow mold, so that the bottom can not shift laterally. The pre-stretching of the blank which is carried out with forced guiding is intended to stretch a predefined wall part of the blank and in particular at the location o, during the subsequent blow-molding of the blank, the radial enlargement is lower than predefined by larger diameter

outside the hollow body.

  A typical example of use is a bottle with a conical neck region. In a certain area, between the outlet portion of the bottle and the bottle body, the material of the blank is extended by the pre-stretching due to the drawing rod. This stretched area is then shaped into a conical neck portion when

of the blowing process.

  In order to define the portion of the blank to be stretched, it is possible to impart to the blank in the heater a temperature profile which causes the wall portion to be stretched at a higher temperature. Preferably, however, the blank is produced with a smaller wall thickness in the predefined wall portion, so that even without a temperature profile, the draft of the blank occurs in the

  area of the thickness of. weaker wall.

  - * A smaller wall thickness can be achieved during the injection molding of the blanks by a suitable conformation. Preferably section variation when forming the party? Outlet can be done on the draft. For this purpose, the end

  opening of a tubular blank is heated to the temperature

  deformation and, in an outlet mold, is formed a thread for the introduction of a screw closure and a bead for the establishment of a crown closure. Axial drawing of the wall portion of the blank adjacent to the outlet portion is known in this regard. In this way, a wall thickness distribution is obtained which, starting from a thinnest location in the vicinity of the outlet part, increases

  gradually to the original thickness of the wall of the blank.

  This is for example described in DE-A-31 01 284. 1-09.

  If, therefore, the mechanical drawing of the heated blank is carried out at the orientation temperature,

  the sectional area below the closing flange

  ture is stretched to a thin wall thickness.

  In a 1.5 liter bottle, for example, the conical section wall portion below the closure flange is stretched about 2 cm in length.

  at a length of about 8 cm. This stretched part corre-

  to the subsequent conical bottle neck.

  According to the invention, the blank is stretched first

  by a drawing mandrel actuated to drive it mechanically

  nically and then by blowing air. he's from

  this possible way to set the mechanical stretch to one.

  perfectly defined course, which leads to an optimization of the wall thickness, then, at precisely defined instant o the blank has reached a defined length, to trigger the supply of blowing air to execute

  end-of-stretch processes as well as expansion

  ment. This is an important element of the invention.

  During the continuation of the air stretching process

  the drawing rod must be kept

  it is not released, while, on the other hand, the drawing rod must not form a blow on this bottom. Preferably

  this is achieved thanks to a corresponding adjustment of the training

  pneumatic operation of the drawing rod.

  We will now describe in more detail an embodiment of the invention in view of the drawing. The latter represents:

  FIGS. 1 to 4 are a diagrammatic representation

  FIG. 5 shows a section of the blank, FIG. 6 a side view through an actuating device of the drawing rod for a blow mold fixed on a blowing wheel, and FIG. Figure 7 a section of the blow mold

  and the drawing device, the drawing rod being

  felt in two successive positions.

  In Figure 1 a blank V pressed on a blowing mandrel 10 is placed between two halves of blow mold 11, 12. A drawing rod 15 is below the blowing mandrel 10. The drive

  of the drawing rod 15 is made by a telescopic jack

  16, whose outer cylinder 16 is fixed. In the outer cylinder can move an inner cylinder 18, in which again is movable a piston 19 connected

to the drawing rod 15.

  In Figure 2, the drawing rod 15 is in the forward position, and is therefore introduced into the blank

  V through the blowing mandrel 10 and is

  below the bottom of the blank V. For this purpose, compressed air was introduced into the inner cylinder 18, which moved the piston 19 of the drawing rod to the position

  high. Race I has been covered.

  In this position of the drawing rod 15, a roller 20 fixed on the inner cylinder 18 moves on a curved path 21, which in Figure 3 is obliquely ascending. When the blow mold arrives from the drawing position of Fig. 2 into the position of Fig. 3, the drawing rod 15 is mechanically displaced upwardly by the roller 20 which moves on the curved path. The mechanical pre-drawing of the blank

  V then reaches the stroke length II.

  When the position of the blank V shown in FIG. 3 is reached, a predefined wall portion of the blank is elongated by the stroke length II, and is thus stretched with a thinner wall thickness, then the blowing air which enters through a slot not shown between the drawing rod 15 and

  the blow mandrel 10 inside the blank.

  The stretching of the blank is continued axially by the compressed air until it comes to apply to the upper bottom portion of the blow mold 11, 12. During the axial stretching due to the curve the upper part of the large piston is under vacuum, so that the follower roller passes, in the groove, from the lower face to the upper face. That is, the inner cylinder 18 is forced to move upward, so that the drawing rod, after it has left the curved path, follows the axially stretched blank, and he guides this rod to the center. Simultaneously, the radial expansion of the blank is achieved by blowing air to achieve

in the finished state.

  Figure 5 shows a cross section of a blank V made by the method described. The blank V consists of a tubular wall portion with a bottom

  closed. At the open end is a part of

  M, which is suitable for setting up the screw closure. The outlet portion terminates in a flange portion F. Between the flange F and the cylindrical rough portion is a zone B which has a variable cross section. The thinnest part of the cross section is below the flange F, and the cross-section increases steadily from there until it reaches the wall thickness in the cylindrical area. A section distribution of this type can be obtained by forming the outlet portion

  M and the flange F by stretching the blank.

  The zone B of the blank is stretched according to the process shown in FIGS. 1 to 4 by the mechanical pre-stretching of the blank and subsequently constitutes the conical neck of the hollow body, which is represented in FIG. the invention, it is therefore possible to stretch in a controlled manner a predefined part of the blank and to thin in this way the wall in the zone of col H. A device for implementing the method

  is shown in Figures 6 and 7. On the outer periphery

  30 of a blowing wheel 31 driven in rotation about a vertical axis not shown are fixed at equal peripheral distances, a series of blowing stations, among which a blowing station

  32 is shown in Figure 6. Each station of

  Flage 32 consists of two blow mold halves 33, 34, a bottom mold 35 as well as a not shown mechanism for opening and closing the blow mold halves. A drawing mandrel 36 carries a blank V visible in FIG. 7. The drawing mandrel is transferred from a heating wheel to a blowing mandrel holder 37 and is then closed, as shown in FIG. between the blow mold halves 33, 34 when closing these halves. The blow mandrel 36 has a central bore 38 through which a drawing rod 40 can be inserted. An annular slot between the bore 38 and the drawing rod serves for the introduction of the blowing air into the blank V. The annular slot is in connection with a supply of air

blowing not shown.

  The drawing rod 40 is driven by a telescopic jack 42. An outer cylinder 43 having a cylinder head 44 is fixed on the outer periphery of the blowing wheel 31. The drawing rod 40 carries a movable piston 46 in an inner cylinder 48, the lower part of the cylinder 48 being open and the upper part being closed by a cylinder head 49 which

is fixed on a stirrup 50.

  The stirrup 50 is a part of a carriage 52, which is movable on two guide rods 53, 54 fixed on both sides of the cylinder 43 placed at the outer periphery 30 of the blower wheel 31. At the lower end of the carriage 52 is also a stirrup, which carries in its middle a rotating roller 56. When the roller 56 moves on a guide path 60, the carriage 52 moves and the inner cylinder

48 which is fixed there.

  At the lower part of the inner cylinder 48 is fixed a piston 57, movable in the outer cylinder 43. In the lower head 58 of the outer cylinder 43 is provided an air supply 59. The pressure can be applied via this channel 59 on the piston 46 for the drawing rod 40 and the piston 57 for the inner cylinder 48. In the upper cylinder head 44 is provided a compressed air channel 45 through which the pressure can be applied.

be applied to the piston-57.

  The curved path 60 is made on a lever 62, pivoting about a pivot axis 63, which makes it possible to adjust the stiffness of the slope of the curved path 60. The adjustment is performed by a spindle drive 65 driven by motor electric. As shown in Fig. 6, the lever 62 is U-shaped so that the roller 56 moves between the curved path 60

and the upper wing 66.

  The operation of the drawing rod 40 will now be explained: initially, the drawing rod is in the retracted position, in which the head 68 of the drawing rod is under the mandrel After the closure of the blow mold halves 33, 34, the blowing wheel, which is rotated continuously, reaches the position shown in FIG. 7. The drawing rod 40 is then pushed towards the high through the drawing mandrel 36 in the blank V and the head 68 of the drawing rod is below the closed bottom B of the blank V. For this forward stroke of the rod 40 the cylinder 43 is connected to the compressed air by the channel 59, so that the piston 46 connected to the drawing rod 40 is moved from the lower position to the upper position.

  represented. To precisely define the upper position

  a stop (not shown) is provided. The inner cylinder 48 is not actuated here because the piston 57 is likewise subjected to air pressure through the channel 59, a higher counter-pressure being however applied to the piston 57 from above by the channel 45, so that

  the inner cylinder 48 executes no movement.

  In the position of the drawing rod 40 represents

  7 in the right half, in which this rod is introduced into the blank V, the roller 56 moves on the carriage 52 on the curved path 60. The continuation of the stroke of the rod 40 occurs mechanically under the effect of the guide path 60, the chario 52 being moved upwards, the inner cylinder 48 being pushed upwardly outwardly of the outer cylinder 43, until the position represented in the left half is reached of FIG. 7. In this position, the blank V has been stretched in the axial direction by a predefined length which is defined by the adjustment of

  height of the lever 62. During the mechanical stretching of the

  the annular space between the inner cylinder 48 and the outer cylinder 43 is evacuated by the channel so that, due to the pressure acting on the underside of the piston 57, the roller 56 remains in abutment with the upper flange 66 after leaving the

  curved path 60 and it is then released.

  As a result of the mechanical drawing process shown in FIG. 7 the subsequent drawing of the blank V as well as its expansion into a finished hollow body by feeding the blowing air into the blank takes place. by means of the blowing mandrel. In this way, the inner cylinder continues its stroke under the action of compressed air, the pressure being chosen so that the head 68 of the drawing rod follows the bottom B and remains applied to the bottom, to guide the latter in a centered manner, until the bottom B comes to rest on the mold base 35. The enlargement of the blank occurs simultaneously until it is applied to the halves of blow mold. The process of

blowing is then complete.

Claims (16)

  A method of blow molding a thermoplastic hollow body, wherein a closed bottom blank (V) carried by a blow mandrel (10) is placed in a blow mold, a drawing rod (15) is introduced into the blank through the blow mandrel, the blank is axially stretched by the drawing rod and is expanded by supplying blow air to form the finished hollow body, characterized in that the blank is stretched by the drawing rod on   a predetermined partial length (II) of the blow mold   flage, in that the blowing air is brought after this pre-stretching, in that the blowing air continues this stretching of the blank and widens it and that, during this time, the drawing bar is maintained applied on the bottom of the sketch.   2. Method according to claim 1, characterized in that the blank is sufficiently stretched by the drawing bar so that a predefined longitudinal fraction of the blank is stretched with a thick wall. weaker.   3. Method according to claim 2, characterized in that the stretched longitudinal fraction of the blank is, during enlargement, a portion of the hollow body in which the radial expansion is relatively low.   4. Method according to claim 3, characterized in that the stretched longitudinal portion constitutes a neck region of the hollow body.   5. Method according to one of claims 1   to 4, characterized in that, in the longitudinal part of the predefined blank for the drawing, the thickness wall is kept lower.   6. Method according to claim 5, characterized in that the connection to the outlet portion of the blank, the latter is stretched to a wall of thinner thickness.   7. Method according to one of claims 1   to 6, characterized in that, for drawing the blank, the drawing bar is driven by a mechanical device guidance.   8. Method according to one of claims 1   at 7, characterized in that, for maintaining the bottom,   the drawing rod is driven pneumatically.   9. Device for implementing the   Method according to one of Claims 1 to 8,   blow molds (33,34,35) on a rotatably driven wheel (31), a blow mandrel (36), a draw rod (40) which can be introduced into the blank through a bore axial axis of the blow mandrel and a draw rod drive which consists of a jack (42), characterized in that the cylinder (48) of the jack is axially displaceable by a curved path (60) for the pre-stretching of the blank, and that it is pneumatically actuated for further movement of the drawing rod (40) after leaving the curved path.   10. Device according to claim 9, characterized   characterized in that the jack is a telescopic jack (42), wherein a piston rod constituting the draw rod (40) is movable in an inner cylinder (48), which is movably disposed in an outer cylinder (43) fixed.   11. Device according to claim 10, characterized   characterized in that the inner cylinder (48) is driven   by the curved path (60) and pneumatically actuated.   Device according to one of the claims   9 to 11, characterized in that the inner cylinder (48)   is fixed on a carriage (52) movable on rods of age (53, 54).   13. Device according to claim 12, characterized   characterized in that the inner cylinder (48) is fixed on the carriage (52) on its end facing the blowing mandrel (36), and in that the carriage carries at its lower end a roller (56) which enters the curved path (60).   14. Device according to one of the claims   9 to 13, characterized in that it comprises two guide rods (53, 54) on each of the two sides of the cylinder (42).   15. Device according to one of the claims   9 to 14, characterized in that the curved path is mounted   adjustably on a pivot axis (63).   16. Device according to claim 15, characterized   terized in that the curved path is arranged to grasp the roller (56) on both sides.