The invention is directed to a vibrating compactor for the production of formed bodies by vibrating compaction of grainy raw materials, in particular for the production of anodes and/or cathodes for the electrolytic smelting process for the production of aluminium with the aid of a vibrating table carried on springs to allow oscillation on which a mould with cover weight can be clamped the top side of which being joined to a preloading device with spring.

Metallic aluminium is won from alumina by way of molten phase electrolysis in electrolytic cells in which anodes in the form of carbon blocks are suspended. These blocks are produced in anode plants normally from calcined petroleum coke and normally using pitch as binder. During that operation the hot mixture of petroleum coke and pitch is formed in a mould fastened to the table of a vibrating compactor by means of vibrating compaction to an anode block, i.e. to the so-called green anode which is afterwards baked in a furnace. Density and height of the block anode to be formed have to meet narrow tolerances.

Known vibrating compactors are those where after filling the mould with raw materials a cover weight can be introduced. The cover weight rod of said cover weight projects to the top and is carried in an open frame. It is, moreover, known from DE-A-2 041 520 and DE-A-37 24 199 to have the cover weight at its top supported by at least one spring for increasing its impact frequency and impact intensity. The spring, however, is exposed to the hot exhaust gases and vapors, e.g. pitch vapors, that escape from the hot raw materials and which will be of disadvantage especially if the cover weight pressure spring is a pneumatic spring made of resilient material. This is true above all if as known from DE-A-19 23 767 a firm hood has been placed on the mould of the vibrating compactor

and if the pneumatic springs for pressing the cover weight onto the paste have been provided inside the cover hood. Apart from the problem of a reduced service life of the cover weight springs, the cover hood impairs the accessibility to these springs.

The problem to be solved by the invention is to create a vibrating compactor of the type mentioned earlier with mould, preloaded cover weight and firm cover hood with at least one cover weight pressure spring featuring good accessibility and being characterized by a long service life.

That problem is solved according to the invention by a vibrating compactor comprising the features of claim 1. Advantageous embodiments of the invention are evident from the dependent claims.

For the vibrating compactor according to the invention the cover weight preloading device with its at least one spring has been provided outside the mould cover hood. This means that the cover weight spring which basically may be a mechanical spring but with special advantage is a pneumatic spring of resilient material of variable retractive force will no longer be exposed, e.g., to the chemically aggressive atmosphere within the vibrational^ supported system of mould/cover hood which will contribute to an extension of the service life of the cover weight preloading device. In addition, this arrangement of the cover weight-preloading device improves the accessibility during installation and maintenance.

According to a specific feature of the invention the cover weight preloading device including spring has been arranged within a rod supporting device which has been fixed to the upper side of the cover hood and, consequently, outside of same. This means that the at least one spring has been arranged between the top cover of the rod supporting device and the top end of the cover weight rod

which projects through the mould cover hood into the rod supporting device from below. In addition, a lifting yoke acts at the top end of the cover weight rod through the openings of the rod supporting device which during upward movement separates the connection between mould/cover hood and carries the com- ponents cover weight, cover hood and preloading device as connecting unit.

The invention and its further features and benefits are explained in more detail by the embodiment shown schematically in the figures. The figures show the following:

Fig. 1 the vertical section of the vibrating compactor according to the invention where the vibrational support of the vibrating table and the vibrating drive have been omitted and

Fig. 2 the vibrating compactor of Fig. 1 after partial upward movement of the lifting yoke.

Based on the typical embodiment of Figures 1 and 2 the vibrating compactor serves, e.g. for shaping anode blocks. The vibrating compactor shows in the forming station a vibrating table 10 which is carried on a base frame in a vibrational manner by means of spring elements not shown, in particular by pneumatic springs, and which can be made to perform vibrating motions by means of rotary out-of-balance exciters that have not been shown. In the forming station the mould 11 of mostly rectangular cross section to be filled with the hot grainy raw materials is clamped on vibrating table 10 which operates jointly with a cover weight 12. Its central cover weight rod 13 is guided axially in a sealing guide bush 15 within an opening in the upper side of a firm cover hood 14 which closes mould 11 at the top.

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During operation of the vibrating compactor, the paste filled in mould 11 is subjected to vibrating compaction in the space between the top of vibrating table 10 and the underside of cover weight 12 to form anode block 16 as shown in Figs. 1 and 2. Following a defined vibrating period, anode block 16 has reached its defined density and height. The vibrating process is then switched off.

As can be seen in Fig. 2, cover hood 14 with cover weight 12 and perhaps jointly with mould 11 are lifted off to the top by upward movement of a lifting yoke 17 prompted by a rope hoist or hydraulic means and the finish formed green anode block 16 is pushed off the upper side of vibrating table 10 to the side and the forming station of the vibrating compactor is cleared to accept a new anode block for being compacted by vibration.

To enhance uniform vibrating compaction, to generate an additional compaction pressure and to shorten the vibrating period, cover weight 12 has been fitted with a preloading device with at least one spring 18, especially in the form of bellows made of resilient material to which compressed air can be admitted which fact allows to change the normal mode of cover weight 12, in particular its impact frequency and impact intensity during vibrating compaction even during operation of the vibrating compactor. Fig. 2) shows pneumatic bellows 18 of Fig.

1 in compressed condition with cover weight 12 moved upward.

A characteristic feature of the vibrating compactor according to the invention is that the cover weight preloading device with at least one spring 18 has been mounted outside mould cover hood 14, i.e. arranged within a rod supporting device 19 fastened to the top of cover hood 14. Spring 18 has been arranged and/or clamped between top cover 20 of rod supporting device 19 and the upper end of cover weight rod 13 which projects through guide bush 15 in rod supporting device 19 from below. The compressed-air inlet as center opening in top cover 20 for compressed-air admission to spring 18 has been identified by 21.

At any rate, spring 18 will not come into contact with the chemically aggressive atmosphere within the system of mould 11 /cover hood 14, especially not if guide bush 15 features an additional sealing function.

The radial arms of a lower support disk 22 of lifting yoke 17 have been routed through the spaces between the rods distributed over the periphery of rod supporting device 19. A support ring 23 has been fastened to the upper end of cover weight rod 13 which supports the underside of spring 18. In addition, support disk 22, which encompasses cover weight rod 13 with a central opening, can be attached to support ring 23 from below upon upward movement of lifting yoke 17. Following upward movement of lifting yoke 17, cover hood 14 with or without mould 11 but at any rate with cover weight 12 and cover weight preloading device as connecting unit can be lifted off vibrating table 10 to the top. This operation will be facilitated provided stop cams 24 interacting with the upper side of cover 12 have been provided at the inside of cover hood 14.

The vibrating compactor according to the present invention is suitable to compact all possible grainy raw materials, e.g. granules of synthetic resin as well as grainy primary or secondary fuels, etc.