Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C5/00—Machines or devices specially designed for dressing or handling the mould material so far as specially adapted for that purpose
  • B22C5/18—Plants for preparing mould materials
  • B22C5/185—Plants for preparing mould materials comprising a wet reclamation step

Definitions

• the invention relates to a method and a device for removing organic and inorganic binder residues from foundry rubble, in particular core and molding sand, the grains of which are bound with binder or surrounded by binder shells, the binder being separated from the sand and the Sand and the binder are obtained as individual fractions.
• Foundry rubble with inorganic binder residues can be partially freed of the binder residues by mechanical action and stringing together the sand grains and subsequently divided into ground binder and sand dust as well as finer and coarser sand fractions by means of known separating devices.
• a method for recovering foundry rubble sand is also known which is contaminated with organic binders.
• the foundry. Rubble is subjected to a chemical treatment, the material being initially subjected to an oxidation and then a neutralization process.
• the organic binder casings which surround the grains of sand are treated, for example, with an oxidizing acid and subsequently brought into contact with a base. This chemical cleaning process does not leave any pure sand.
• the binder residues are chemically degraded and cannot form any compounds when the sand is reused with the newly added binder.
• the grain of sand is at least partially exposed for contact with the new binder and thus allows a new setting.
• Foundry rubble sand which is regenerated by this method, cannot be reused for all applications and also cannot be brought into contact with any binders. Its re-usability is limited and the S-and becomes unusable after repeated use.
• the foundry rubble can mostly only be partially freed from the binder residues. These binder residues adhere to the depressions and cracks in the grain of sand and can only be partially exposed when the grains of sand are ground and broken. These mechanical procedures ⁇ occurs a considerable development of dust, and the grain size or the grain size of the sand mixture is significantly changed. The material loss is approx. 30 - 45%.
• the regenerated sands occurring here are therefore mostly only of limited use for reuse and cannot be regenerated as often as required. A maximum of 70% regenerated sand should be added, for example, 30% new sand.
• the process auxiliaries used should be able to be used in the process in a circuit and should not additionally burden the environment.
• this object is achieved in that the rubble sand contaminated by the binder is mixed with a heated liquid wetting agent, the binder casings are wetted and thereby removed from the sand grains, the binder casings are completely separated from the sand grains by moving the resulting mixture and the resulting mixture is then separated into a solid fraction consisting of sand and a sludge fraction consisting of binder and swelling agent.
• the sand fraction is then preferably subjected to a washing process with water, the water is again separated from the sand and the sand is subsequently completely dried by heating. It has proven to be expedient to heat the sand to approximately 450 ° C. and to use cleaned hot exhaust gases from the foundry process.
• the sand obtained after the application of these process steps only has a residual proportion of sludge of approximately 0 to 0.3%.
• the rubble sand contaminated with binder is advantageously mixed with sodium hydroxide solution heated to a maximum of 90 ° C. and in a concentration of at most 20%.
• a more heated wetting liquid would evaporate, and the aggressive exhaust gases could damage parts of the system or the environment. In practice, therefore, even when using sodium hydroxide, this is only heated to approx. 80 ° C. It can too other wetting agents, such as hydrofluoric acid, are used, although the latter is normally too aggressive. For some applications, hot water can also suffice.
• the choice of wetting agent depends in part on the later intended use of the regenerated rubble sand.
• the binder obtained after the separation treatment of the sludge fraction is in the form of a dry substrate and has a residual moisture content of 3 to 5%. If the rubble sand treated contains only one type of binder, the binder can be partially reused.
• the device according to the invention for carrying out the method is distinguished by the fact that it has a mixing and stirring unit for mixing the rubble sand with the wetting agent, a separating device for fractionating sand and sludge, a washing device for the sand with a water separation device and a subsequent drying oven.
• a mixing and stirring unit for mixing the rubble sand with the wetting agent
• a separating device for fractionating sand and sludge
• a washing device for the sand with a water separation device and a subsequent drying oven.
• the device or system shown for removing organic and inorganic binder residues from foundry rubble sands has a rubble sand feed device 4.
• the rubble sand introduced into the system via this rubble sand feed device 4 falls into a filling funnel. ter 3 and arrives from there into a washing drum 1.
• a wetting agent metering device 2 In front of the washing drum 1 there is further arranged a wetting agent metering device 2, from which the wetting agent likewise enters the washing drum 1 via the filling funnel 3.
• 10% sodium hydroxide solution is supplied as the wetting agent via the wetting agent metering device 2.
• the ratio of rubble sand to wetting agent is approximately 1: 1.
• the washing drum 1 rotates about its central axis, as a result of which the rubble sand and the sodium hydroxide solution are mixed intensively with one another. Due to the intensive mixing and stirring of the wetting agent / rubble sand mass in the washing drum 1, the binder residues are detached from the sand grains, and a thin, fluid, sludge-like mass is formed.
• This mass passes from the outlet opening 23 of the washing drum 1 into an intermediate container 5 and is introduced from here into a pusher centrifuge 6 via a metering device (not shown).
• the pusher centrifuge 6 shown has two stages 17, 18, but can also have several stages. In the first stage 17, the sodium hydroxide solution and the binder residues are separated from the rubble sand.
• the first stage 17 of the thrust centrifuge 6 is equipped with sieve openings of a maximum of 0.02 mm. After the sodium hydroxide solution and the binder residues have been separated off from the rubble sand, water is added and this is then separated off from the sand again in the second stage 18 of the push centrifuge 6. The water separated in the second stage 18 reaches a water container 11 via the connecting line 19 and can be introduced from there via the connecting line 20 back into the pusher centrifuge 6.
• the system also has a control and cleaning device (not shown) for the water circuit, which ensures that the overrun centrifuge 6 is not supplied with excessively contaminated water and the sand is obtained in a neutral manner.
• the pure sand passes through a Vibrators' ionsrinne 12 13 in a vertical conveyor tikalcleaner 13 is necessary because the system shown is extended over several floors and not disposed on the same work plane.
• the cleaned sand reaches a sand dryer 14.
• This sand dryer 14 is heated with cleaned hot exhaust gases from the foundry process, the temperature of which is approximately 450 ° C.
• a sand cooler 15 As soon as the desired degree of drying of the sand has been reached, it is introduced into a sand cooler 15 via a connecting line 24 and cooled there.
• the resulting warm waste gases are e.g. used for heating the contents of the washing drum or for other heating purposes.
• Sand cooler 15 the now dry sand falls into a sand container 16, which can also be designed as a bunker. From here, the cleaned sand, which has a residual sludge content of approx. 0 to 0.3%, is returned to the foundry process for use.
• the costs for cleaning the rubble sand supplied via the feed device 4 until it is present in cleaned form in the sand container 16 are approximately 30 to 40% of the costs which would have to be expended for the same amount of new sand.
• the sludge fraction from sodium hydroxide solution and binder residues obtained in the first stage 17 of the pusher centrifuge 6 passes through an intermediate container 7 into a peeling centrifuge 8. From here it can be returned to the process via the connecting line 20 and the wetting agent metering device 2.
• the separated binder residues pass from the peeling centrifuge 8 into a binder container 10.
• the dry substrate present here has a residual moisture content. from approx. 3 to 5%.
• the dry substrate can be regenerated by further treatment or fed directly to the processing of synthetic fertilizers.
• the exhaust air obtained in the washing drum 1 and the exhaust gases from the sand dryer 14 and the sand cooler 15 are discharged from the system via an exhaust air duct 25. Before the exhaust gases are expelled from the exhaust air duct 25 into the circulating air, they can, depending on the degree of contamination, be passed through a commercially available dust separator and a gas cleaner.

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• 1985
  • 1985-02-01 WO PCT/CH1985/000017 patent/WO1985003462A1/de not_active Application Discontinuation
  • 1985-02-01 IT IT67094/85A patent/IT1182399B/it active
  • 1985-02-01 EP EP85900617A patent/EP0171400A1/de not_active Withdrawn

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