DE2923044A1 - Split composite sand block casting mould prodn. - by vacuum coating pattern with thermosetting shell and covering with sand contg. binder clay - Google Patents

Abstract

In the prodn. of split composite sand block casting moulds preheated patterns of a lower and upper mould are vacuum coated on the pattern side with a thin shell of thermochemically hardening masking material. Then moulding sand contg. binder clay is applied to each shell and consolidated to a composite sand block. By using the vacuum forming principle, odour and smoke from the decompsn. prods. of phenolic sand binders are eliminated, without losing the dimensional accuracy and surface quality of the castings.

Description

June 6, 1979

Dipl.-Ing. Eugen B lh 1 e r, Scülexfweg 3

8871 Burtenbach.

(~), Method and device for manufacturing

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of split composite sand block molds. %

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Description of the invention

The invention "relates to a method and an apparatus for the production of eomposite sand block casting molds

From the German Auslegeschrift 26 53 788 are a process and a device for the production of boxless casting molds from molding sand containing molds, so-called O sand block molds, known in which the use of a vacuum for sand compaction creates dust and noise pollution the atmosphere in the molding shop is largely avoided · By using the clay-bound molding sand used for this However, there are limits to the application of this molding process, because this molding material naturally has a certain amount Quenching effect on the melt.

With many series castings, especially with automobile castings, however, very strict requirements are placed on the surface quality and dimensional accuracy of the castings, which cannot be met with the usual tGngebüixdejieü molding sands. ,, Such Castings are therefore manufactured using special processes, taking into account technological and economic aspects, of which the mask molding process named after its inventor "croning" should be mentioned. Included becomes a flowable or free-flowing one encased with phenolic resin clay-free sand in bulk or by means of compressed air applied to a preheated model plate and for so long heated until a solid mask has formed as a result of the thermo-chemical reaction of the resin, which is half of a Casting mold is used. In order for this mask to be able to withstand the casting pressure, it must have a sufficient thickness of at least 6 mm

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to have. The individual masks are, if necessary, after the insertion of cores glued together to form complete casting molds, Clamped together in clamping devices for shaped stacks and after backfilling with loose support material poured off like dry sand or steel grit.

When the phenol-n-resole resin cures during mask production and also afterwards, considerable smoke and odor nuisance occurs in the relevant operating departments, which cannot be managed satisfactorily with the suction devices normally installed. Since the penetrating phenol odor - apart from possible health hazards - can still be felt strongly on the skin and in the hair despite intensive washing after the end of the shift, the workforce increasingly refuses to work in departments with such phenol odor.

In the course of the humanization of the Airbsitsplatzss arose hence the task of looking for ways to reduce the odor and

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"'Sand binders in the molding shop and foundry to a large extent eliminate without losing out on the clear advantages of these molding sands in terms of dimensional accuracy and surface quality of the castings produced therein.

This task became surprising through the application of the per se well-known vacuum IOrm principle and the production of composite sand block casting forines solved according to this or the vacuum shooting principle.

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When manufacturing such a sand mold, the Resin-coated mask molding sand now contrary to the "previous Operating mode applied to the preheated model plate under negative pressure. This can be done in that the sand reservoir is connected to an induced draft fan, which constantly creates a slight negative pressure in the storage container. The preheated pattern plate is then connected to the sand storage container and carried out in a manner known per se Turn coated with molding material, whereby after setting

a sufficiently thick shell, the remaining molding material falls back into the tilted container.

A particularly good utilization of the machine is achieved, however, if a model device provided with air nozzles is used will. Then, according to the "matchplate" system, they will be on both sides "Model plates arranged on a hollow model plate carrier"; one after the other with the opening of a shell molding material container connected airtight and by means of an in the hollow, with a partition wall provided model plate carrier jerky / generated vacuum, which is through the air nozzles in the model equipment continues into the molding material container, suddenly acted upon with mask molding material. The vacuum will be so long Maintain until there is a molded shell of the desired thickness Tauf has formed on the model After the vacuum is released, the mold material that has not set falls back into the storage container,, the model plate carrier is turned by 180 ° around its horizontal axis, and now the wide model half is the device placed on the firing opening and coated in the same way with mask molding material.

The model plate carrier with the coated model plates is then transferred to a vacuum molding machine,

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in which the mold cavity is created by jerkily generated negative pressure full bullets with moist molding sand containing binding clay a. will. As most of the air nozzles in the model interior are already covered with a shell made of mask molding material, the jerky build-up of the vacuum in the molding box takes place mainly through! rows of nozzles on the edge of the model plates, which are covered during the coating with mask molding material have been.

■ Since the backs of the bowls facing the sand block are made of Mask molding material is very rough according to the production process and the mask molding material is usually very rough at the speed of the molding process is also still warm and somewhat plastic, the molded sand containing binder clay binds to the shell

fine Koiaposit form block, which extends smoothly from the model plate can take off. As a rule, therefore, there are no additional release agents on the model equipment before it is coated necessary. However, they can be used if necessary will. If necessary, the mold can also be detached by briefly blowing compressed air into the hollow Model plate carriers are supported.

»The lifted composite halves of the mold can be used after the possible inserting of cores are immediately put together and transported to the casting line * It is with molds with z. B. laterally molded sprue but also possible to erect the collapsed forms and put together to form a strand with vertical Formteil.ung.

Such Eomposite sand block molds contain only one very low proportion of relatively expensive and unpleasant combustion gases forming mask fabric, because the actual

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Borrowed mold is only very thin. It has been shown that a shell thickness of 0.5 mm - 5 wa, mostly even only from O ^ - Λ wo. Completely is usually sufficient to achieve the desired casting surface. A further saving in mask molding material can be achieved in that the model plates are coated with mask molding material only at those points which actually come into contact with the melt in the finished form. To cut out the other - points, the model plate is covered with an 'unheated stencil or mask on which no ■ shell made of hardened molding material' forms.

It has been shown, however, that the coefficient of friction between the smooth surfaces made of hardened shell molding material is considerably smaller than between the surfaces made of sand containing clay. There. However, the divided sand block casting molds are usually moved on automatically driven transport lines to the casting line and support each other, special precautions must be taken to prevent misalignment between the upper and lower boxes until after casting. The molding of safety reliefs in the plane of division has proven to be a safe measure that does not require any additional effort. These safety reliefs can, for example, be hemispherical or frustoconical, as they are known as centering cones in divided models. . ·, ·. However, the entire pattern set can also be designed as relief plates, which provides additional protection against metal breakthroughs during casting

When pouring clay, most of the phenol-containing combustion gases condense in the clay-containing sand of the pormblock and the odorous substances are retained in it until

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the IOrmballen in a provided with a suction device Cooling drum with downstream air cleaning system to be emptied o This is in addition to a considerable Saving of resin-coated JOrmstoff, especially the odor nuisance of the workforce in the molding and foundry largely eliminated by smoke gases containing phenol.

: J "' S-In'.deni-'Abbinungeij. ^ Is; a ^ for ^ production ^J _; yonvKomp ^ dsit-'',,'" - ■ - .-, - -JSandblLo'ck ^ casting molds' suitable / Scheme shown in the system. Show in detail "thereby:

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1: a plan view of a vacuum molding machine which is connected to a model plate coating machine by a model plate carrier transport device, and FIG

Fig. 2: a sectional view through the coating station the model plate coating machine.

In Fig. 1 , the system consists of a vacuum mold shooting machine 1, a model plate coating machine 2 and a model plate carrier transport device 3. The vacuum mold shooting machine is equipped and has for the simultaneous shooting of upper and lower mold halves according to the "matchplate" system a turntable 4 ₄ which pivots the closed mold by 180 ° between a molding station and a core insertion station 7.

Uefaen of the vacuum form shooting machine 1 is the turnstile trained model plate coating machine 2 arranged. It has three work stations, namely a plate carrier turning station 8, on which the hollow model plate carrier 5, which is covered with coated model plates, is turned and opposed a model plate carrier with uncoated code plates coming from the molding machine Ί is exchanged, a Model plate heating station 9, in which the model plates are brought to the required operating temperature, and a model plate coating station 10 in which the Model plates 14 are coated with shell molding material.

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Pie plate carrier turning station 8 of the model plate coating machine 2 and the IOrmstation 6 of the molding machine 1 are carried by a model plate carrier transport device 3 overlapped, which receives the model plate carrier at the individual stations 8 and 6 and exchanges. It can be designed as a linear or rotatable plate carrier transport device.

At the model plate coating station 10, the model plate coating machine 2 has a vertically movable container 11 for mask molding material, which is U-shaped and has two upwardly open legs. Sin leg serves for switching on and replenishment of fresh shell mold material. In the other leg, a shooting grate 12 with hollow Eost bars is arranged at a narrowing similar to a venturi tube. At the upper end of the leg has an inner flange 13 which rests against the model plate 14 attached to the hollow model plate carrier 5 and thereby covers a row of air nozzles arranged on the end of the model plate 14.

The hollow model plate carrier 5 is centered with a partition 16 provided, each with one of the attached on both sides Model plates 14 · creates a separate chamber which is in the shooting position via a tubular socket-shaped connection piece via a valve device 17 and a corresponding pipeline system can be connected to a large vacuum vessel, not shown. Part of this pipe system forms a double-walled central stand tube 18, with which the hollow model plate carrier 5 in the direction of the arrow is rotatably connected.

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The system works as follows:

A hollow model plate carrier 5, which is placed at the plate carrier turning station 8 of the model plate loading machine 2 and covered on both sides with model plates 14, reaches the heating station 9 by a horizontal rotation of 120 ° around the central stand tube 18 heated to the required operating temperature, which can be between 400 ° K and 600 ° K depending on the type of resin used as a binder and the desired shell thickness. After a further rotation of 120 °, the model plate carrier 5 with the preheated model plates 14-comes into the coating station 10. There, the container 11 is connected to the model plate carrier by a lifting movement so that the inner flange 13 rests airtight on the model plate pointing downwards with the model contour and thereby covering the rows of air nozzles 15 arranged on the edge of the model plate 14. For coating this pattern plate, the valve is now 17 geöffnetο The prevailing in the central support tube vacuum λ propagates jerky by the underlying chamber in the hollow pattern plate carrier 5 "and the air nozzles · continues and causes in the pattern plate 14 15, ₃ that the through the firing grate, by if necessary, air is added in a controlled manner, a resin-coated sand intensely swirled with air is sucked onto the model plate, where it cakes to form a shell. The thickness of the shell that forms in the process depends not only on the type of resin but also on the contact time with the model plate and its temperature It has been shown that contact times, that is to say a shot duration of one second, can be achieved in order to obtain a shell with the desired strength.

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After closing the valve 17, the air pressure in the two legs of the container 11 is equalized, the non-baked Maskenformstöff separates by gravity from the sand-air mixture and falls on or back through the shooting grate in the container 11. The container 11 is lowered and the model plate carrier 5 ¹¹ Yes 180 ° around his

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horizontal axis is used, so that the not yet coated model plate 14 is directed with its model contour downwards. Then the container 11 is raised again and the pattern plate is coated in the same way.

After the container 11 has been lowered again, the model plate carrier arrives with the model plates which are now coated by a further rotation by 120 ° in the plate carrier = turning station 8, in which the model plate carrier by further 180 is turned horizontally into its original starting position. After that he will be exchanged for one Already molded model plate carriers with detached shells by the plate carrier transport device 3 to the forming station 6 in the vacuum iOrm shooting machine 1

transported, in which the sand blocks of the lower and upper mold are shot simultaneously on the coated model. After lifting the composite sand blocks from the model, if necessary, by introducing a short burst of compressed air into the chambers of the hollow model plate carrier can be supported, the upper and lower forms are put together in a manner known per se and used for the Casting line transported.

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The invention is not restricted to the example shown and described. Rather, this example is was chosen to show that existing Vakttum HOrm shooting machines own design can also be subsequently combined with a model plate coating machine and then, as required, homogeneous or composite sand block casting molds alternatively can be produced. The heating, coating, turning and lOrm stations can also ^ can be combined and integrated into a single machine. Also, without departing from the scope of the invention, (j) let a different than the described vacuum shooting principle

be used for molding sand compaction, for example; Principle of simultaneous application of Luftünterdruck behind the pattern plate and of air pressure upstream of the: firing grate, or the principle of Lüftunterdruck behind -the pattern plate and mechanical compression of the bindeton- ■ '-containing molding sand. Finally, one can also use liquid

Synthetic resins mixed moist sand, so-called hot box sand, '-': can be used as a shell molding material for shell manufacture.

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List of reference symbols

1 vacuum IOrm shooting machine

2 model plate coating machine

3 Model plate carrier transport device 4- turntable

5 model plate carriers,. ^r >, ■; ^,; -] '"* £>.

O, 7 core loading station

8 model plate carrier turning station _

. 9 .Model plate heating station '',; _ .. ■. .% _

10 model plate coating station. '.'_.

, 11 containers

12 shooting grate. . / · '

•% - * 13 inner flange -ί

14- Model plate - -. ■ '- - ■

^ '15 -Air nozzles

16 partition

17 valve setup

18 stand tube

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Claims (1)

Claims 1.) A method for the production of split composite sand block casting molds, characterized in that preheated model plates of a lower and upper mold on the model side with a thin shell of thermo-chemical ./. hardening mask molding material are coated under vacuum, and that subsequently molding sand containing binding clay is applied under vacuum to the respective shell made of mask molding material - and is connected to this under compression to form a composite sand block - ' ^f * L · 2.) Method according to .Anspruch 1, characterized in that the model plates each with the model contour directed downwards according to the vacuum shooting process with an f ~. thin shell made of mask molding material, and that subsequently binding clay-containing molding sand is shot onto the respective shell made of mask molding material by the vacuum shooting process and is connected to this su a composite sand block. 3e) Method according to claims 1 and 2, characterized in that that the Mödell plates only on. the one with melt areas of the mold that come into contact with mask molding material coated and that the remaining areas in the coating be covered with unheated stencils or masks » 030050/0388 > f f t 4) method according to claims 1 to 5, characterized in that ia. the shells made of molded plastic Centering and / or safety reliefs; will. 5.) Process according to claims 1 "to 4-, characterized in that the shell thickness is kept between 0.5 mm and 3 mm 6 _# ) Process according to claims 1 to 5, characterized in that a free-flowing dry quartz, chromite or zircon sand coated with a mixture of phenolic resin of the novolak-iCyps with vinyl acetate is used as the molding material and a moist natural or synthetic! Molding sand is used. 70 method according to one or more of the preceding? Claims, characterized in that in order to excavate the model device from the composite sand block, compressed air is blown through the model device against the composite sand block. 8.) Device for the production of split composite sand block casting molds, characterized by a model plate loading machine and a vacuum jamming machine connected to this by a model plate transport device 9 ·) Device according to claim 8, characterized in that the model plate coating machine is designed as a turnstile and a model plate heating station, one after 030050/0398 ^{β /} · lt> 3 - the Vatoixua shooting principle working model plate Besciiiclituiigsstationioii and a plate pick-up and transfer station, the rotary movement is synchronized with the work cycle of the vacuum Pormaiascnine, and that the vacuum forming machine a ^! "Vacuum shooting machine is , '■, 030050 / 039S