Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives

Definitions

• the invention relates to compositions containing foundry sand and additive, the additive comprising cryolite.
• the additive is used in the manufacture of foundry cores and molds, especially those bonded with synthetic resins, to prevent casting defects.
• leaf ribs A e.g. Casting defects that are frequently encountered are known under the term "leaf ribs", the susceptibility to this defect being quite different in the individual core production processes.
• the appearance of leaf ribs means increased costs due to extra work, since they sometimes have to be ground away with great effort. But it can also lead to the casting being unusable if the leaf ribs are in inaccessible places.
• the thickness of the oxidic binder shells that surround the grains of sand have fundamental sand properties that are essential for their formation of casting defects are decisive; taking into account the stress conditions, the composition of sand mixtures can be controlled via the amount of iron oxide added.
• iron oxide also has disadvantages: due to its basicity, it shortens the processing time of cold box binders, and on the other hand it contributes greatly to the contamination of core manufacturing tools. The latter applies above all to finely ground, synthetic iron oxide.
• iron oxide is often a component of commercially available additives.
• Other active substances are e.g. Wood flour, minerals, carbohydrates, carbon, natural oils, mineral oils, waxes, natural and synthetic resins etc.
• cryolite or cryolite-containing additives to the foundry sand fulfills the stated task.
• cryolite enables a reduction in the amount of additive. This leads to an improvement in the casting surface, since conventional additives, especially wood meal-like additives, can cause increased surface roughness due to gas formation during pyrolytic decomposition.
• the additive according to the invention is added in an amount of 0.1 to 10% by weight, based on the sand.
• 0.1 to 7.5 wt .-% are used; the range from 0.1 to 5% by weight is particularly preferred.
• cryolite can be used alone as an additive or mixed with at least one component composed of minerals, wood flour, organic fiber material, carbohydrates, carbon, natural oils, mineral oils, waxes, natural resins and synthetic resins.
• Suitable minerals are, for example, colemanite, mica and iron oxide.
• a suitable wood flour is beech wood flour, for example.
• Polyethylene fibers are an example of suitable organic fiber material and as a carbohydrate
• starch can be used.
• Suitable natural oils are castor oil and linseed oil, while petroleum is an example of suitable mineral oils.
• polyethylene wax and petroleum jelly can be used as waxes.
• Balsam resin for example, can be used as the natural resin component in the additive, while phenolic resin solutions, for example, can be used as synthetic resins. If carbon is used as an additive component in addition to cryolite, it can be used, for example, in the form of coke and / or graphite and / or hard coal dust.
• Recycled foundry sand can also be used as sand.
• the additives according to the invention can be used both in the gas-curing process (eg cold box process) and in the warm box process, the hot box process, the croning process or the cold curing process (eg polyurethane cold resin) . Because the cold box process is particularly susceptible to leaf vein formation, the following experiments have been concentrated on this process.
• step cones were produced using the cold box method from quartz sand and a commercially available cold box binder (Isocure 300 OS4 / Isocure 600 OS4) from Ashland-Südchemie-Kernfest GmbH.
• the additive added was 0.5% by weight or 2.4% by weight based on sand, depending on the composition of the additive.
• the step cones were also placed in molds bonded with a synthetic resin (Pep Set 1505 / Pep Set 602 from Ashland-Südchemie Kernfest GmbH) and cast with spheroidal graphite cast iron (GGG 50) at 1398 to 1430 ° C.
• the step cone is a well-known test specimen which can be used to examine the thermal load during casting on a core (see also DM Gilson et al., Modern Casting, May 1995, pages 38-40).
• the thermal load is lowest at level 1, at level 6 against it the strongest. The number of leaf veins therefore increases from level 1 to level 6.
• the cavity between the core and the outer form is filled with the liquid metal.
• the casting is cleaned of adhering sand and, to assess the effectiveness of the additive, the leaf ribs which have formed on the individual stages of the casting are counted. The result is shown in Table I.
• cryolite and colemanite are successively filled with stirring in a laboratory wing mixer and mixed for about 10 minutes to homogenize the two components.
• the additive is prepared analogously to Example 3, but in this example it has the following composition: Beech wood flour (45% by weight), cryolite (19.5% by weight), mica (19.5% by weight; Suzorite Mica, Suzorite Mica Products, Canada) castor oil (6% by weight) and one commercially Resin solution available from Ashland-Südchemie-Kernfest GmbH (13% by weight).
• the additive is prepared analogously to Example 3, but in this example it has the following composition: Beech wood flour (55% by weight), cryolite (13% by weight), mica (13% by weight), castor oil (6% by weight) and a commercially available synthetic resin solution from Ashland-Südchemie-Kernfest GmbH (13% by weight) .-%).
• the step cone is produced as described in Example 1. However, 72 g (2.4% by weight) of additive BR 028/1, a commercially available iron oxide-free additive from Ashland-Südchemie-Kernfest GmbH, are used as the additive. The result of the assessment of the casting is shown in Table I.
• the step cone is produced analogously to Example 1, but 72 g (2.4% by weight) of BR 85 additive are used as additives R, a commercially available additive containing iron oxide from Ashland-Südchemie-Kernfest GmbH. The number of leaf veins that have occurred is shown in Table I.
• the step cone is produced analogously to Example 1, but 15 g (0.5% by weight) of colemanite are used as an additive.
• the number of leaf veins that have occurred is shown in Table I.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Mold Materials And Core Materials (AREA)

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Citations (7)

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• 1996
  • 1996-03-11 DE DE19609539A patent/DE19609539A1/de not_active Withdrawn
• 1997
  • 1997-03-11 EP EP97104054A patent/EP0795366A1/fr not_active Withdrawn
  • 1997-04-07 WO PCT/EP1997/001725 patent/WO1998045068A1/fr unknown

Patent Citations (8)

Non-Patent Citations (5)

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