US3455134A

US3455134A - Hydrostatic extrusion processes

Info

Publication number: US3455134A
Application number: US666295A
Authority: US
Inventors: Peter John Thompson
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1966-09-15
Filing date: 1967-09-08
Publication date: 1969-07-15
Anticipated expiration: 1986-07-15
Also published as: CH463438A; DE1602378A1; GB1188116A

Description

y 6 P. J. THOMPSON 3,455,134

HYDROSTATIG EXTRUS ION PROCESSES Filed Sept. 8, 1967 3 Sheets-Sheet 1 July 15, 1969 P. J. THOMPSON 3,455,134

HYDROSTATIC EXTRUSION PROCESSES I Filed Sept. 8, 1967 5 Sheets-Sheet 2 406'M7l/7/A/6' 5/2 35 I l a 70/741 P145774 l l d/Px 5 l Aw/a Pa xm;

July 15, 1969 P. J. THOMPSON 3,455,134

HYDROSTATIC EXTRUSION PROCESSES Filed Sept. 8, 1967 5 Sheets-Sheet 5 FIG. 3.

US. Cl. 72-60 8 Claims ABSTRAQT OF THE DISCLOSURE A process in which a billet is extruded from a container through a die by pressurisation of hydraulic liquid in the container about the billet a direct mechanical loading being applied on the billet to supplement the stresses acting to extrude the billet. For example a tensile drawing load is applied on the extruded length of the billet outside the extrusion container. The billet has a tapered rear end and as the tapered rear end of the billet is extruded the pressure in the hydraulic liquid surrounding the billet is gradually reduced as the stresses required to extrude the tapered rear end reduce. Finally at termination of extrusion of the tapered rear end of the billet the pressure in the hydraulic liquid is reduced to substantially atmospheric pressure.

BACKGROUND OF THE INVENTION This invention related to extrusion processes and in particular to hydrostatic extrusion processes. In a conventional extrusion process a billet held within a container is subjected to a direct mechanical loading to extrude the billet from the container through a die. The billet is a close fit in the container and extrusion pressure is applied on the end face of the billet by a ram operating in the bore of the container. Hydrostatic extrusion has several advantages over conventional extrusion and differs from conventional extrusion in that a liquid is used to apply extrusion pressure on the billet. The liquid envelops the billet in the extrusion container and is pressurised to act directly on the billet. Because the liquid envelops the billet there is no frictional contact between the container and the billet. Die friction is also reduced because the pressurised fluid adjacent the throat of the die provides hydrodynamic lubrication between the extruding material and the die.

An inherent difiiculty arises in operation of a hydrostatic extrusion process when a billet is fully extruded by this method, in that as the rear end of the billet passes out through the die the pressurised liquid in the extrusion container is released with considerable force which may damage the extruded product or the extrusion apparatus.

In hydrostatic extrusion the material of the billet is subjected to a hydrostatic stress system which results in extrusion of the material of the billet through the die.

The stresses set up in the billet and hence the forces acting to extrude the material of the billet through the die are dependant on the pressure applied in the liquid surrounding the billet. The degree of pressure which must be applied in the liquid to cause extrusion depends on the yield stress of the material to be extruded and the degree of reduction to be achieved.

In the case of material having a very high yield stress the pressure required in the liquid to effect hydrostatic extrusion may be prohibitively high because of the difficulties arising from containment of liquid subjected to such high pressure.

This latter dilticulty can be avoided by use of a mechanically augmented hydrostatic extrusion process,

nited States Patent 3,455,134 Patented July 15, 1969 wherein a direct mechanical loading is applied on the billet so that the applied mechanical loading supplements the stresses acting to extrude the billet. The plastic work of deformation of the billet is shared between the pressure of the liquid surrounding the billet in the extrusion container and the force of the applied mechanical loading. By this means extrusion of the billet is effected using a much lower pressure in the liquid surrounding the billet than is required in the liquid for operation of a purely hydrostatic extrusion process. A compressive mechanical loading may be applied on the billet by a ram acting in the extrusion container on the back end of the billet. Alternatively a tensile drawing load may be applied on the extruded length of the billet outside the extrusion container.

The present invention provides for operation of such a mechanically augmented hydrostatic extrusion process (hereinafter referred to as of the kind described,) in a manner such that a billet can be fully extruded without the release of a blast of high pressure liquid as the rear end of the billet passes through the extrusion die.

SUMMARY OF THE INVENTION According to the present invention a hydrostatic extrusion process of the kind described is carried out on a billet having a tapered rear end decreasing in cross section from the cross section of the main length of the billet to a smaller final cross section, the pressure in the liquid surrounding the billet in the extrusion container being gradually reduced during passage of the tapered rear end of the billet through the die in a manner such that at all times, the sole action of the pressure in the liquid is insufficient to cause the tapered rear end of the billet to extrude through the die, the pressure in the hydraulic liquid being finally reduced to substantially atmospheric pressure at termination of extrusion of the tapered end of the billet.

In a particular form of the process of the invention, a billet is employed having a tapered rear end decreasing a cross section to a cylindrical end section of smaller diameter than the diameter of the main length of the billet, the diameter of the cylindrical end section of the billet being such that the sole action of the direct mechanical loading applied on the billet is sufficient to cause the cylindrical end section of the billet to pass through the die, the pressure in the liquid surrounding the billet in the extrusion container being gradually reduced during passage of the tapered rear end of the billet through the die in a manner such that at all times the sole action of pressure in the liquid is insufiicient to cause the tapered rear end of the billet to extrude through the die, the pressure in the liquid finally being reduced to substantially atmospheric pressure when the tapered rear end of the billet has passed through the die, so that the cylindrical end section of the billet is finally passed through the die by the sole action of the direct mechanical loading applied on the billet.

The method of the invention is particularly applicable in a process wherein the direct mechanical loading is applied on the billet by application of a tensile drawing load on the extruded length of the billet outside the extrusion container.

In one application of the method, during extrusion of the tapered rear end of the billet, pressure in the hydraulic liquid surrounding the billet is continuously reduced from the maximum operating pressure to substantially atmospheric pressure at the termination of extrusion of the tapered rear end of the billet, the pressure in the hydraulic liquid being reduced in such a manner that the direct mechanical loading necessary to maintain extrusion of the tapered rear end of the billet remains constant.

In another application of the method as the conically tapered intermediate section enters the extrusion die towards the end of extrusion of the billet the total plastic work necessary to maintain extrusion begins to fall and if, initially, the pressure in the hydraulic liquid surrounding the billet is maintained at its maximum this results in a reduction of the direct mechanical loading required to maintain extrusion. This application of the method is preferably carried out in the following manner,

Initially as the tapered rear end of the billet begins to extrude the pressure in the hydraulic liquid surrounding the billet is maintained at a maximum and the direct mechanical loading necessary to maintain extrusion is continuously measured, until, when the direct mechanical loading has fallen to a predetermined lower value, pressure in the hydraulic liquid surrounding the billet is gradually reduced, so that the direct mechanical loading necessary to maintain extrusion of the tapered rear end of the billet increases to compensate for fall in pressure in the liquid, reduction of pressure in the liquid being terminated when the direct mechanical loading has risen to a predetermined maximum value, extrusion of the tapered rear end of the billet continuing at a steady rate whilst the direct mechanical loading necessary to maintain extrusion again falls and when the direct mechanical loading reachesthe predetermined lower value for a second time pressure in the hydraulic liquid being again gradually reduced until the direct mechanical loading once again rises to the predetermined maximum value, this sequence of operations being repeated by the number of times necessary to extrude the tapered rear end of the billet, it being arranged that the pressure in the liquid is finally reduced to substantially atmospheric pressure when the tapered rear end of the billet has been passed through the die.

DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a semischematic cross sectional elevation of apparatus for carrying out a hydrostatic extrusion process in accordance with the invention,

FIGURE 2 is a graph.

FIGURE 3 is a semischematic cross sectional elevation of a second form of apparatus for carrying out a hydrostatic extrusion process in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGURE 1 of the drawings there is shown an extrusion container 1 fitted with an extrusion die 2. The extrusion die 2 is sealed in the bore of the container 1 by a copper mitre ring 3 and a rubber O-ring 4. A ram 5 is slidably sealed in the bore of the container 1 by a copper mitre ring 6 and a rubber O-ring 7. The container 1 has a cross bore 8 which is connected with an expansion device 9 by a high pressure pipeline 10.

The expansion device 9 comprises a cylinder 11 having a main bore 12 and a smaller counter bore 13. The main bore 12 is closed by an end plate 14 clamped by a threaded ring 15. A- piston 16 is slidably sealed in the main bore 12 by a copper mitre ring 17 and a rubber O-ring 18. The piston 16 has an integral plunger 19 which extends into the counterbore 13 of the cylinder 11. The plunger 19 is of smaller diameter than the counterbore 13 and is sealed on entry into the counterbore 13 by a copper mitre ring 20 and a rubber O-ring 21. The lower end of the counterbore 13 is closed by a threaded plug 22 which is sealed in the counterbore 13 by a copper mitre ring 23 and a rubber O-ring 24. The pipeline 10 connects with the counterbore 13 through a drilling 25 in the plug 22.

Cross bars

26 and 27 in the cylinder 11 connect with the main bore 12 above the piston 16. A gas inlet line 28 connects with the cross bore 26 through a valve 29. A gas outlet line 30 leads from the cross bore 27 through a relief valve 31 and a gas flow regulating valve 32.

In operation of the arrangement shown in FIGURE 1 a billet 33 is extruded from the container 1 through the die 2. The plastic work of deforamtion of the billet 33 is shared between the pressure of hydraulic liquid 34 surrounding the billet 33 in the container 1 and a drawing force applied by a drawing device 35 on the extruded length of the billet outside the extrusion chamber 1. During extrusion of the main length of the billet 33 the liquid 34 in the container 1 is pressurised by loading of the ram 5.

The billet 33 has a tapered read end 37 decreasing in cross section to a cylindrical end section 36. The end section 36 of the billet 29 is of such a diameter that when the rest of the billet 33 has been extruded the drawing force alone is suflicient to cause the end section 36 of the billet to pass through the die 2.

During extrusion of the main length of the billet the stresses required for extrusion remain constant, as shown by the horizontal portion A-B of the curve I in FIGURE 2. Also if the pressure in the liquid 34 surrounding the billet 33 is maintained constant, (as shown by the horizontal portion A'B of the curve II in FIGURE 2) the augmenting stress (i.e. the drawing load) required to maintain extrusion will also remain constant. After extrusion of the main length of the billet 33 the conically tapered rear end of the billet 37 enters the die. As the end 37 of the billet extrudes the total plastic work necessary to maintain deformation begins to fall. If the pressure in the liquid 34 were maintained at its maximum this would result in a reduction of the drawing load required and the drawing load would eventually fall to zero. At the point when the intermediate section of the billet 37 begins to extrude through the die 2 the process can then be operated by one of two methods.

Firstly in operation of both the methods and prior to commencement of extrusion the main bore 12 of the expansion device 9 is charged with low pressure gas through the gas inlet line 28 and the valve 29, the relief valve 31 in the gas outlet line 30 being closed.

In carrying out the first of the two methods power is taken oif the ram 5 acting in the extrusion chamber 1 at the moment when the conically tapered intermediate section 37 of the billet 33 begins to extrude through the die 2.

Pressure in the hydraulic liquid 34 surrounding the billet 33 in the container 1 is then gradually reduced by opening of the relief valve 31 of the expansion device 9 so that the piston 16 of the expansion device 9' withdraws the plunger 19 from the counterbore 13 and the pressure of the hydraulic liquid in the counterbore 13 and hence the pressure of the liquid 34 in the container 1 begins to fall. The rate of decrease of pressure is fixed by the setting of the gas flow regulating valve 32. The valve 32 is adjusted so that the pressure of the liquid 34 in the container 1 falls at a rate such that the drawing load necessary to maintain extrusion remains at the maximum. To achieve this the pressure in the liquid 34 has to fall in the manner shown by the dotted line B'E in FIGURE 2. At the completion of extrusion of the tapered rear end 37 of the billet 29 the pressure in the liquid 34 has fallen to zero and the remaining cylindrical end section 36 of the billet 33 passes through the die 2 under the sole action of the drawing load.

In operation of the second of the two methods, when the tapered rear end 37 of the billet 29 begins to extrude through the die 2 the pressure in the hydraulic liquid 34 in the container 1 initially maintained at the pressure employed in extruding the main length of the billet 29. This is as shown by the portion B-C' in the curve 11 of FIG- URE 2. As the tapered end 37 of the billet 29 extrudes the total plastic work necessary to .maintain extrusion :falls and as pressure is maintained in the liquid 34 the drawing load necessary to maintain extrusion falls. This is as shown by the portion B-C of the curve I in FIGURE 2. The drawing load is measured continuously, for example by an electrical load transducer. When the drawing load falls to a predetermined lower value, such as at the point C on curve I of FIGURE 2, power is then taken off the ram 5 acting in the extrusion container 1 and pressure in the hydraulic liquid 34 in the container 1 is gradually reduced for example to the point X in the curve II in FIGURE 2 by opening of the relief valve 31 of the expansion device 9. As the pressure in the liquid 34 falls the drawing load increases to compensate for the loss in pressure of the liquid. When the drawing force has risen to a predetermined maximum value, reduction in pressure of the liquid 34 is terminated by closure of the relief valve 31 of the expansion device 9. Whilst this action is taking place the tapered end 37 of the billet 29 continues to extrude through the die 2 at a steady rate and the drawing load again falls. When the drawing load again reaches the predetermine lower value pressure in the hydraulic liquid 34 surrounding the billet 33 is again reduced by means of the expansion device 9. Pressure in the hydraulic liquid is reduced, for example, from point D to point Y on curve II in FIGURE 2. This sequence of operations continues until the tapered end 37 of the billet 33 has been completely extruded and the pressure in the hydraulic liquid 34 has been reduced to zero. Finally the cylindrical end section 36 of the billet 33 is passed through the die 2 under the sole action of the drawing load.

Although the invention is described above as applied in a hydrostatic extrusion process wherein a tensile drawing load is applied on the extruded length of the billet outside the extrusion container the method of the invention is equally applicable in a hydrostatic extrusion process wherein an axial compressive loading is applied on the billet in the extrusion container for example by a ram acting in the bore of the extrusion container against the back end of the billet.

The apparatus shown in FIGURE 3 of the drawings comprises a massive base 41 supported on a welded construction 42. A cylinder 43 is supported on the base 41 by pillar bolts 43. The cylinder 43 has a double acting piston 45 having a head 45. A liquid pressurising plunger and cylinder assembly 47 is mounted on the base 41. The assembly 47 has a plunger 48 extending from the lower end of the piston 45. The plunger 48 operates in a cylinder 49 and is sealed in the cylinder 49 by a gland assembly 50. An extrusion container 51 is disposed with its longitudinal axis horizontal and is fitted with an extrusion die 52. The container 51 engages with the lower end of the cylinder 49 and has a duct 53 connecting the cylinder 49 with the interior of the container 51. The cylinder 43 is closed at its upper end by a plug 54 having a low pressure gas connection 55 whereby gas pressure can be applied to the head 46 of the piston 45. An annular space 56 defined in the cylinder 41 is connected to liquid pressurising means 57 via a metering valve 58. The annular space 56 is also connected, through a metering valve 59, with a pressure accumulator 60. The pressure accumulator comprises a cylinder 61 containing a free piston 62. Hydraulic liquid 63 is contained in the cylinder 61 below the piston 62 and a gas bottle 64 is connected to the cylinder 61 above the free piston 62.

To extrude a billet 65 from the extrusion container 51 a constant gas pressure is applied above the piston head 46 and the piston 45 is held in a raised position by pressurisation of hydraulic liquid in the annular space 56 below the piston head 46. The hydraulic liquid is pressurised by the means 57 through the metering valve 58. The pressure accumulator 60 is shut oil from the cylinder 43 by closure of the metering valve 59. Release of pressure in the hydraulic liquid via the metering valve 58, causes the piston 45 to be moved downwardly under the action of gas pressure above the piston head 46. The speed of the piston 45 is controlled by the metering valve 58 which controls the rate of flow of hydraulic liquid from the annular space 56. In moving downwardly the piston 45 forces the plunger 48 into the cylinder 49 to pressurise hydraulic liquid contained therein, the pressure being transmitted, via the duct 53, to hydraulic liquid surrounding the billet 65 in the extrusion container 51. Simultaneously a tensile drawing load is applied, by a drawing device 66, on the extruded length of the billet outside the extrusion container. The main length of the billet 65 is extruded through the die 52 under the combined effect of pressure of hydraulic liquid in the container 51 and the drawing load exerted on the extruded length of the billet outside the container 51. As can be seen from FIG- URE 3 the billet 65 has a conically tapered rear end 67 decreasing in cross section to a cylindrical end section 68 of smaller diameter. After extrusion of the main length of the billet 65 the tapered rear end 67 of the billet is extruded through the die 52. Whilst the tapered rear end 67 of the billet extrudes through the die 52, the pressure in the hydraulic liquid surrounding the billet in the container 51 is gradually reduced in accordance with the method of the invention. The metering valve 58 is closed and the metering valve 59 is opened to admit pressurised hydraulic liquid 63 from the pressure accumulator 60 into the annular space 56 below the head 46 of the piston 45. Thus a proportion of the downwards loading is taken oil the piston 45 and hence off the plunger 48 so that pressure in the hydraulic liquid in the cylinder 49 and in the container 51 is reduced.

Either of the two methods of pressure reduction in the hydraulic liquid previously described in relation to the apparatus of FIGURE 1 may be used in operation of the apparatus of FIGURE 3. For example the pressure of the hydraulic liquid in the container '51 may be continuously reduced whilst the tapered rear end 67 of the billet 65 extrudes through the die. This is achieved by continuous bleed of hydraulic liquid into the cylinder 43 from the pressure accumulator 60 under control of the metering valve 59. The valve 59 is set to give a rate of bleed such that the hydraulic liquid in the extrusion container falls from its maximum operating pressure to substantially atmospheric pressure during extrusion of the tapered rear end 67 of the billet. The cylindrical end section 68 of the billet is finally drawn through the die 52 under the action of the drawing force alone.

Alternatively, as also previously described in relation to FIGURE 1, when the tapered rear end 67 of the billet begins to extrude the pressure in the hydraulic liquid surrounding the billet 65 in the container 51 is initially maintained at the maximum employed for extruding the main length of the bittle. As the tapered end 67 of the billet extrudes, the drawing load necessary to maintain extrusion falls and when the drawing load has fallen to a predetermined lower value the metering valve 58 is closed and pressure reduced in the hydraulic liquid in the container 51 by feed of hydraulic liquid from the pressure accumulator 60 into the cylinder 43 under control of the metering valve '59. The drawing load necessary to maintain extrusion of the tapered end 67 of the billet will rise to compensate for reduction of pressure of the hydraulic liquid in the extrusion container 51. When the drawing load reaches a predetermined maximum valve reduction of pressure of the hydraulic liquid in the container 51 is terminated by closure of the metering valve 59. The drawing load necessary to maintain extrusion of the tapered end 67 of the billet will again fall and the above sequence of operations is repeated by the number of times necessary to extrude the tapered and 67 of the billet. It is arranged that the pressure of the hydraulic liquid in the container '51 is finally reduced to substantially atmospheric pressure at the termination of extrusion of the tapered end 67 of the billet and the cylindrical end section '68 of the billet is finally drawn through the die 52 under the action of the drawing force alone.

Finally continuous reduction of pressure in the hydraulic liquid during extrusion of the tapered rear end of the billet can also be simply achieved without recourse to pressure relieving devices as shown in the appaartus of FIGURES 1 and 3. Taking for example the apparatus of FIGURE 3, if the volume of the tapered rear end 67 of the billet is made equal to the volume which the hydraulic liquid in the container 51 and the cylinder 49 must expand on falling from the maximum operating pressure to substantially atmospheric pressure then closure of the metering valve 58, as the tapered end of the billet commences to extrude, will then result in a continuous fall in pressure in the hydraulic liquid during the period whilst the tapered end of the billet extrudes through the die. The fall in pressure in the liquid is due to the expansion permitted in the liquid by extrusion of the tapered end of the billet through the die.

I claim:

1. A hydrostatic extrusion process comprising steps of providing a billet having a tapered rear and decreasing in cross section from the cross section of the main length of the billet to a smaller final cross section enveloping said billet by liquid in an extrusion container, pressurizing the liquid to act directly on the billet and providing a direct mechanical loading on the billet to supplement the stresses acting to extrude the billet from an extrusion container through a die, gradually reducing the pressure in the liquid surrounding the billet in the extrusion chamber during passage of the tapered rear end of the billet through the die in a manner such that, at all times the sole action of pressure in the liquid is insufficient to cause the tapered rear end of tht billet to extrude through the die, and finally reducing the pressure in the hydraulic liquid to substantially atmospheric pressure at termination of extrusion of the tapered end of the billet.

2. A hydrostatic extrusion process comprising the steps of providing a billet having a tapered rear end decreasing in cross section to a cylindrical end section of smaller diameter than the diameter of the main length of the billet, enveloping said billet by liquid in an ex trusion container, pressurizing the liquid to act directly on the billet and providing a direct mechanical loading on the billet to supplement the stresses acting to extrude the billet from the extrusion container through a die, the diameter of the cylindrical end section of the billet being such that the sole action of the said direct mechanical loading applied on the billet is sufficient to cause the cylindrical end section of the billet to pass through the die, gradually reducing the pressure in the liquid surrounding the billet in the extrusion container during passage of the tapered rear end of the billet through the die, in a manner such that at all times the sole action of pressure in the liquid is insuflicient to cause the tapered rear end of the billet to extrude through the die, and finally reducing the pressure in the liquid to substantially atmospheric pressure when the tapered rear end of the billet has passed through the die, so that the cylindrical end section of the billet finally passes through the die by the sole action of the said direct mechanical loading applied on the billet.

3. A hydrostatic extrusion process as claimed in claim 1 wherein the direct mechanical loading is applied on the billet by application of a tensile drawing load on the extruded length of the billet outside the extrusion container.

4. A hydrostatic extrusion process as claimed in claim 1 wherein, during extrusion of the tapered rear end of the billet, pressure in the hydraulic liquid surrounding the billet is continuously reduced from the maximum opcrating pressure to substantially atmospheric pressure at the termination of extrusion of the tapered rear end of the billet, the pressure in the hydraulic liquid being reduced in such a manner that the direct mechanical loading necessary to maintain extrusion of the tapered rear end of the billet remains constant.

5. A hydrostatic extrusion process as claimed in claim 1 wherein as the tapered rear end of the billet begins to pass through the die the pressure in the hydraulic liquid surrounding the billet is maintained at a maximum and the direct mechanical loading necessary to maintain extrusion of the *billet is continuously measured until, when the direct mechanical loading has fallen to a predetermined lower value, pressure in the hydraulic liquid surrounding the billet is gradually reduced so that the direct mechanical loading necessary to maintain extrusion of the tapered rear end of billet increases to compensate for fall in pressure in the liquid, reduction in pressure in the liquid being terminated when the direct mechanical loading has risen to a predetermined maximum value, extrusion of the tapered rear end of the billet continuing at a steady rate whilst the direct mechanical loading necessary to maintain extrusion again falls and when the direct mechanical loading reaches the predetermined lower value for a second time pressure in the hydraulic liquid surrounding the billet being again gradually reduced, until the direct mechanical loading once again rises to the predetermined maximum value, this sequence of operations being repeated by the number of times necessary to extrude the tapered rear end of the billet, it being arranged that the pressure in the liquid is finally reduced to substantially atmospheric pressure when the tapered rear end of the billet has been passed through the die.

6. A hydrostatic extrusion process as claimed in claim 4 wherein the direct mechanical loading is applied on the billet by application of a tensile drawing load on the extruded length of the billet outside the extrusion chamber.

7. A hydrostatic extrusion process as claimed in claim 1 wherein the billet has a tapered rear end equal in volume to the volume by which the liquid surrounding the billet in the extrusion chamber will expand in falling to atmospheric pressure from the maximum pressure which is applied in the liquid during extrusion of the main length of the billet, whereby as the tapered rear end of the billet passes through the die the pressure in the liquid in the extrusion container gradually falls to atmospheric pressure in correspondence with the passage of the tapered rear end of the billet through the die.

8. A hydrostatic extrusion process as claimed in claim 5 wherein the direct mechanical loading is applied on the billet by application of a tensile drawing load on the extruded length of the billet outside of the extrusion chamber.

References Cited UNITED STATES PATENTS RICHARD J. HERBST, Primary Examiner US. Cl. X.R. 72271