Regmas Vibratory Sand Reclamation Unit

Dańko, R. – AGH University of Science and Technology Kraków

World production of castings, which in 2015 reached 104.1 million ton is accompanied by large quantities of production wastes, mainly used moulding and core sands.  Production of 1 metric ton of casting from ferrous alloys generates circa 1 metric ton of waste, which due to containing certain amounts of harmful and dangerous compounds should undergo a reclamation – at least of the main component, which means a moulding sand.

The paper, especially dealt with problems of scientific and development research concerning the results of reclamation of used foundry sands with organic resins, carried out in new, vibratory sand reclamation unit REGMAS developed by researches from AGH-University of Science and Technology, Faculty of Foundry Engineering in Cracow (Poland).   Functional characteristics of reclamation unit, mechanism of liberating sand grains from envelopes of used binding materials, and the influence of the intensity of the reclamation treatment on the quality of reclaimed sand grains are given.

Additionally paper presents actually used industrial tests of the quality of the reclaim and the new more advanced methods of its evaluation

Device characteristics

Within the project [1] the prototype of the unit of a yield of 1.5 Mg/h was developed [2]. It is used for the reclamation process investigations in the Laboratory of Machines of the Faculty of Foundry Engineering and enables transferring of the obtained results to foundry plants interested in reclaiming small amounts of various kinds of used sands. For financial reasons these foundries are unable to apply professional systems of the sand grains reclamation.  The universal vibratory reclaimer REGMAS, functionally integrated with the pneumatic cascade classifier is intended to the dry mechanical reclamation of practically each used sand.

It can be installed in reclamation seats of small and middle size foundry plants. The view of the unit with the cascade classifier, without the external screen is presented in Fig. 1.

Fig.1 View of the experimental REGMAS reclaimer

Used sands, after separation of metallic contaminations, are supplied to the device charge. The primary reclamation is realised on the crushing grid and on the set of 3 sieves.  The lowest sieve is of a conical shape of clearances between vertical elements of palisade (slits) being 1.25 mm. At the reclaimer bottom, in its buffer part, loose metallic abrasive elements (spheres) are placed. Together with the vibratory influence they realise the secondary reclamation. The sand screened via the conical sieve is transferred by the vibratory trough and proportioning system into the cascade classifier, supplied from the bottom by the fan of a controlled air speed. The reclaimer is set in motion by means of two rotodynamic motors of a controlled rotational speed and a set vibration excitation force.

Program of investigations

The used sand was subjected to the reclamation treatment according to the schedule presented in Figure 2. Used sand agglomerates on the crushing sieve can be seen in Figure 3.

Fig 2: Assumed parameters of the reclamation tests of used moulding sands with organic binder – in the REGMAS device [10]

 

Fig 3: Agglomerates of used moulding sand with furan resin (on the crushing sieve)

For each set of parameters of the reclamation treatment the following values were determined:

– ignition loss,

– dust content in the reclaim on the trough and after the classification,

– pH reaction value of the reclaim and dusts obtained in the classification process.

The technological suitability of the reclaimed material was determined in the foundry, from which used sands originated. It was applied as a partial substitute of moulding sand grains for making moulds and test castings.

Reclamation results

The obtained results of ignition losses, pH values and dusts content of the investigated reclaimed materials are listed in Table 1. Reclaim samples were tested before the classification in the cascade classifier (marked: not dedusted) and after this process (marked: dedusted).

The obtained results confirm that simultaneous increase of the vibration excitation force, electrovibratory motors frequency as well as an application of additional crushing elements causes more accurate cleaning of sand grains from a spent binder, which – after dedusting of the reclaim – is demonstrated in lower ignition losses.

Load of the REGMAS Reclaim dedusting Vibration frequency [Hz]
40  50 60 40  50 60 40  50 60
 Ignition loss, %  pH reaction

reclaim/dust

Dusts content, %
Vibration excitation force: 50%
Used sand app.

 390 kg

 

Not dedusted 3.09 3.04 3.09 3.09 3.09 3.07  0.402 0.457 0.503
Dedusted 2.93 2.89 2.74 3.15/

  4.80

3.22/

4.47

3.58/

4.47

 0.115 0.142 0.153
 Used sand and crushing elements

 app. 480 kg

Not dedusted 3.05 3.07 3.10 3.06 3.08 3.11  0.579 1.120 0.804
Dedusted 2.86 2.73 2.41 3.43/

4.27

3.52/

3.94

3.74/

4.38

 0.194 0.250 0.293
Average efficiency of the grain fraction removal: da<0.1 mm (%) 68.5 75.1 65.9
Used sand app.

 390 kg

Vibration excitation force: 65-70%
Not dedusted 3.08 3.06 3.08 3.02 3.05 3.05  1.002 1.080 1.09
Dedusted 2.73 2.65 2.62 3.42/

4.23

3.48/

4.10

3.71/

4.38

 0.161 0.256 0.363
Used sand and crushing elements

app. 480 kg

Not dedusted 3.07 3.08 3.05 3.06 3.07 3.08  1.090 1.107 1.491
Dedusted 2.62 2.29 2.12 3.59/

4.19

3.71/

4.25

3.91/

4.28

 0.363 0.226 0.300
Average efficiency of the classification, % 74.9 78.0 74.3

Danko_Table1: Ignition losses, pH reactions and dusts content of the obtained reclaimed materials

The results of pH reaction measurements presented in Table 1 obtained for various reclamation conditions of used sands with furan resin and of the after reclamation dusts (under the same conditions) provide important information concerning the proper application of the reclaimed materials for the moulding sands preparation. Sand grains with acidic hardener are of a higher pH reaction when they are cleaned better. Under the same conditions of the reclamation treatment the pH reaction values of the after reclamation dusts are, on average, by 25 % higher than pH values for the reclaimed sand grains. This can mean the zone acidity distribution in the binding material layer on sand grains. Dusts originated from external layers of the binder coatings are less acidic, while the coatings still remaining on grain surfaces have a stronger acidic reaction. The noticed effect is justified by the sand preparation technique, since the acidic hardener – introduced to the mixture as the first substance – covers sand grains by thin coatings, which is followed by 2-3 times larger amount of resin forming the proper binder layer.

Conclusions

The performed investigations of the functional qualities of the developed vibratory reclaimer REGMAS fully confirm the structural and exploitation assumptions. The possibility of obtaining satisfactory effects of the reclamation process and pneumatic classification at the yield of 1.5 t/h can be stated. Investigations allowed to perform immediate improvements of the existing device structure as well as to develop assumptions for building the series of types enabling to raise the reclaimed material quality in relation with the one presented in the hereby paper. The industrial tests of the reclaimed material from used sands with furfuryl resin for making steel castings were carried out. It indicate the potential possibility of using this device in foundry plants applying these sands.

 

References

[1] The presented device is the realisation effect of the Research Project, financed by the European Union funds. Project title: Design and development of a novel type of vibratory reclamation system using modern techniques for reclaiming spent moulding sands

[2] United States Patent US9061288B2

Prof. Rafal Danko