GB2097711A - Piston extruder - Google Patents

Abstract

A piston extruder for the extrusion of plastic material, especially plastic explosive, comprises a plastic material container (5) guided to be axially movable along carrier posts (3) for axial separation from a die (14) provided with a conical projection (20) capable of being fitted into a seating bore (12) of the container (5). A die holder (22) which concentrically surrounds the die (14), is separable from the container (5) in mountings (24, 24') and is disposed coaxially to a through passage (13) in a stationary pressing table (1). In order to facilitate access to the die (14) independently of the arrangement of the posts (3) and their method of installation, the die holder (22) is pivotally connected to the mountings (24, 24') by trunnion bearings which have a common rotational axis and which are disposed at the external periphery of the die holder in a plane oriented perpendicularly to its longitudinal axis. <IMAGE>

Description

SPECIFICATION Piston extruder The present invention relates to a piston extruder die for extruding plastic material, especially plastic explosive.

A piston extrusion press die for this purpose is disclosed in DE-PS 2 704 832. its form of construction, characterised by an axially slidable and divided die holder, serves essentially for the purpose of facilitating access to the die for its installation and removal. By the construction of the die holder in half-components, of which one ha If-component is guided on tension bars of the extruder, easier handling of the die introduced into a pressing table of the extruder is achieved, especially as only one half-component of the holder has to be removed for dismantling of the die.

The thereby achieved saving in weight of components which need to be removed for cleaning purposes effects a reduction in the work required.

In order to ensure exact alignment of the die and thus of its sealing surface to that of a container for the material to be extruder, the die holder components must be fitted to each other during assembly and secured by bolted connections. The manual operations to be carried out in assembly and also in disassembly are time-consuming and a nuisance to the maintenance personnel. The maintenance of the die is rendered particularly difficult when the piston extruder is mounted not in a vertical position but in a horizontal position. The columns then restrict the clearance required for the dismantling of the die, especially when the columns have to pass through a viewing slit which permits observation of the die from a room separated off for safety reasons.

There is accordingly a need for an extruder in which good access to the die is provided independently of the arrangement of support or guide means of the extruder and the method of erection thereof, in particular so that the die can be installed and removed conveniently for maintenance purposes without undue effort or expense.

According to the present invention there is provided a piston extruder for plastic material, the extruder comprising plastic material charging means mounted to be movable along guide means, a die sealingly engageable with the charging means and arranged to receive plastic material therefrom, a die holder concentrically surrounding the die and so pivotably mounted at its periphery to displaceable mounting means as to be pivotable about an axis perpendicular to the axis of concentricity of the die and holder, and a backing element having a through passage co-axial with the die and holder.

With such an arrangement, the die may be able to be readily removed from the die holder for the purpose of cleaning, without an excessive amount of time being required for this task. The pivotal arrangement of die holder and die allows the latter to be removed in a desired pivoted position, without special dismantling operations, by using a lifting device.

This is particularly so in the case where the extruder is mounted in the horizontal position and where the guide means comprise elongate guide members arranged one above the other for safety reasons and for the purpose of allowing adequate observation of the die and the column of material extruded therefrom.

Preferably, the pivot axis intersects the axis of concentricity. This achieves the result that the pivotal movement of the die can take place with minimal pivoting radius and the space required for handling the die is thus kept to an absolute minimum.

Preferably, the mounting means comprises a respective slide element slidably mounted on each guide member, the slide elements being rigidly interconnected by a bridge member extending around a portion of the periphery of the die holder.

This ensures accurate and tilt-free guidance of the die without adversely affecting its accessibility and ease of handling.

For preference the die holder is provided with a bore extending along said axis of concentricity and receiving the die with a clearance between the wall of the bore and the periphery of the die. A gap-free sealing between the charging means and the die can be ensured in that, by centering of frustro-conical sealing surfaces thereof, there is obtained a fit which automatically adapts to thermal expansion.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic elevation of a piston extruder of horizontal form in accordance with the said embodiment, part of a die of the extruder being shown in section; Figure 2 is a view similar to Figure 1 but showing the parts of the extruder moved apart and the die placed in readiness for removal; and Figure 3 is a cross-section, along the line Ill-Ill of Figure 2, of the extruder.

Referring now to the drawings, there is shown a piston extruder comprising a pressing table 1 and crosshead 2, which are firmly connected together by tension arms 3 and nuts 4 threaded thereon.

Arranged between the pressing table 1 and the crosshead 2 is a material container 5 which is guided to be axially movable along the arms 3. The axial movement of the container 5 is effected by hydraulic piston-cylinder units 6, the cylinders 7 of which are connected with the table 1, and the pistol rods 8 with the container 5, by bolted connections 9 and 9'.

A pressing cylinder 10 and associated pressing ram 11 are mounted in the crosshead 2. The container 5 is formed with a bore 12 which is axially aligned with the ram 11 and serves for reception of batches of material, for example plastic explosive, to be extruded. The table 1 has a through passage 13 with a conical outlet 15 and a die 14 is insertable in the passage.

The length of the die 14 is so dimensioned that it extends, above and below, beyond the table 1. The die 14 has a calibrated bore 16, from the outlet end of which a visually monitored removal of a extruded mass 17 can be effected by means of a cutting device (not shown). The die 14 includes a head portion 18, which bears against a surface 19 of the pressing table 1 and is formed with a conical projection 20.

The projection 20 fits, for the purpose of obtaining a sealed connection with the bore 12 of the container 5, into a corresponding conical recess 21 of the bore.

As can be seen from Figure 2 and in greater detail from Figure 3, the head portion 18 of the die 14 is loosely surrounded by a die holder 22, so that with adequate lateral clearance in the region of the bore 12, an automatic centering of the mutually adapted sealing surfaces, formed by the conical projection 20 and conical recess 21, is achieved. The die holder 22 serves for the insertion of the die into and lifting out of the die from the pressing table 1. Connecting means, (not shown) ensures that the die 14 is entrained by the holder. The die holder 22 is connected, for this purpose, with a mounting 23, which is composed of elements 24 and 24' respectively slidable on the arms 3.A cross-beam 25 serves for rigidly connecting together the two elements 24 and 24', so that a tilt-free guidance ofthe die 14 is achieved along the arms 3.

The displacement of the mounting 23 along the arms 3 is effected by towing bolts 26 fixed to the elements 24 and 24', these bolts sliding in projections 27 mounted on the container 5. The entraining of the mounting 23 by the container 5 and the piston-cylinder units 6 acutating the latter is effected by a threaded nut 28 adjustably mounted on each towing bolt 26. The entraining of the mounting 23 does not commence until part of the stroke of the container 5 has taken place, i.e. a stroke length which corresponds to the distance between the projection 27 and the threaded nut 28 (Figure 1).

After the die 14 has been raised, the container 5 being fully displaced, the die can be removed from the die holder 22. For this purpose, the die holder 22 is pivotally mounted in the mounting 23 by means of trunnion bearings 29 and 29', the rotation axis 30 of the bearings intersecting the longitudinal axis of the die 14. The trunnion bearings 29 and 29' are formed as bearing pins 31 and are each journalled with appropriate clearance in a respective one of the elements 24 and 24'. The trunnion bearings 29 and 29' may also be provided by cylindrical projections formed out of the mounting 23. To ensure that the changing of the die 14 can readily be carried out by hand, the bearing 29 loaded by the weight of the die 14 is combined with a ball thrust bearing 33.

In the pivoted position of the die 14 illustrated in Figure 2, the die can be easily drawn out of the die holder 22.

In this way, in conjunction with the actuation of the container 5, a changing of the die 14 easily carried out by hand is achieved. The operations for the installation and also for the removal of the die 14 are defined in a clearly separated sequence, so that a functionally correct installed position is ensured. The extruding of the mass 17, its travel and the transition between the container 5 and the die 14 can be easily observed from a lateral observation position where the piston extruder is mounted horizontally with the arms 3 one above the other. The removal of the die 14 does not require any complicated disconnection of components or lifting out, as the die 14, after being pivoted, can be easily pushed out of the holder 22 by hand with the assistance of a lifting device.

Similarly, installation of the die is simplified, in that, after pushing it into the die holder 22, a simple pivoting of the holder is all that is required to bring the die 14 into its final position, aligned with the longitudinal axis of the extruder.

Since a relatively quick changing of the die is possible in this manner, the risk of ignition or detonation of explosive residual extruded material is considerably reduced, which enhance the safety conditions for operating personnel. This is particularly so if the die holder is to be heated for the processing of certain materials.

Claims (9)

1. A piston extruder for plastic material, the extruder comprising plastic material charging means mounted to be movable along guide means, a die sealingly engageable with the charging means and arranged to receive plastic material therefrom, a die holder concentrically surrounding the die and so pivotably mounted at its periphery to displaceable mounting means as to be pivotable about an axis perpendicular to the axis of concentricity of the die and holder, and a backing element having a through passage coaxial with the die and holder.

2. An extruder as claimed in claim 1, wherein the die is provided with a frusto-conical projection sealingly engageable with a complementary seat of the charging means.

3. An extruder as claimed in either claim 1 or claim 2, wherein the holder is pivotably mounted to the mounting means by coaxial trunnion bearings.

4. An extruder as claimed in claim 3, wherein the trunnion bearings comprise bearing pins firmly retained in the mounting means.

5. An extruder as claimed in any one of the preceding claims, wherein the pivot axis intersects the axis of concentricity.

6. An extruder as claimed in any one of the preceding claims, the guide means comprising a plurality of elongate guide members.

7. An extruder as claimed in claim 6, the mounting means comprising a respective slide element slidably mounted on each guide member, the slide elements being rigidly interconnected by a bridge member extending around a portion of the periphery of the die holder.

8. An extruder as claimed in any one of the preceding claims, wherein the die holder is provided with a bore extending along said axis of concentricity and receiving the die with a clearance between the wall of the bore and the periphery of the die.

9. A piston extruder substantially as herein be fore described with reference to the accompanying drawings.