RESIN PATTERNS OBTAINED IN VACUUM-SEALED SAND MOULDS
(unprofessional own translation)
Technical University of Sofia, Bulgaria
In Bulgarian In Russian
The resin patternmaking in vacuum-sealed sand moulds [1,2] derives from the well known V-process [3-6], at that in the mould the compound is poured instead of metal. The liquid compound makes wet the foil well, but after the hardening of the compound, the finished pattern separates easily from the foil, because the hardened resin does not stick to it.
The technology realized in the vacuum-sealed moulds saves the positive sides of the patterns obtained in plastic moulds by the conventional technology : low cost, good wear-resistance, reduced adherence of the moulding mixtures, chemical and water resistance, etc., but excels the patternmaking in the plastic moulds in the flexibility of the process. Fast production of the sand moulds permits the duplication of many patterns by one master-pattern for minimum time. That decides various normal or urgently arising production necessities. In addition, the used master-patterns can be made of various materials, because their lifting out of the vacuum moulds is not a problem.
But, for the patternmaking in the vacuum-sealed moulds an equipment is necessary and that technology is dependent on the energy source. By reason of that, the utilization of the technology is the easiest in the foundries with installation for V-process.
All that shows the both technological systems must not to be opposed and they have to be used together when it is possible.
2. Aim and purposes of the research
The present research is a part of a dissertation material. The aim of this work is to investigate the features of the resin patterns obtained in vacuum-sealed sand moulds, at that the found results to serve for the building up the information basis of a computer program for exploitation prognoses of the patterns.
That involves the realization of the following tasks:
3. Technology and equipment
For the relationship with the V-process, the basic technological scheme (Fig.1) is not patented. The versions shown here briefly are under the protection of Bulgarian Patents and Author's Certificates. They refer to the producing of the vacuum-sealed sand moulds, the vacuum treatment of the liquid compound, resin pattern / core-box making, and to the equipment adapted to the technology.
Two versions of combined mould for producing of thin-walled (open to the parting line) resin patterns are shown in Fig.2 . The inside of the future resin pattern shapes up by furan sand insert covered with a foil. The foil is supported by the vacuum of the mould through some channels. That foil makes easier the separation of finished pattern and insert.
The treatment of the compound is possible by using the vacuum from the mould. For that purpose (Fig.3) , the foil is punched,
a cover is superimposed, and a vacuum chamber is formed over the compound. The vacuum treatment is effective in the period of 60-90 minutes after pouring. After that the vacuum chamber is expelled. The vacuum treatment by the scheme in Fig.4 is possible only to the end of compound pouring. In both cases, the vacuum of 0,2.105 Pa is enough for the separation of the gas bubbles.
1-foil; 2-transparent cover; 3-compound; 4-vacuum chamber. 1-foil; 2-transparent plate; 3-compound.
A method for manufacturing of wholly closed thin-walled (shell) resin patterns through lamination is demonstrated in Fig.5 . This method is applicable for patternmaking in the plastic moulds too. The pattern cavity is formed by the simple emptying of the sand which served for the wall support in the lamination.
Fig.6  presents the sequence for production of core boxes or plastic moulds for patternmaking by the conventional technology. The foil covered the master-pattern makes easier its moving out from the finished equipment and ensures the extremely smoothness of the core boxes (plastic moulds).
Fig.5. Manufacturing of wholly closed shell pattern Fig.6. Manufacturing of core-box or plastic mould
a) lamination with sand support; b) shell formation; c) emptying of the sand. a) covering with a foil and putting of a frame; b) compound pouring;
1-layered working wall; 2-sand; 3-closing wall; 4-shell pattern. c) lifting out of the master-pattern. 1-master-pattern; 2-foil; 3-frame; 4-compound; 5-core-box / plastic mould.
The equipment adapted to the technology comprises some new constructions of vacuum chambers and flasks.
In Fig.7  are shown two variants of vacuum chamber and a general view of the vibrating table in which one of these chambers is built. The air-permeable pattern plate consists of sand and epoxy resin. The whole area of this plate ensures uniformly evacuation and the qualitative covering with a foil irrespective of the master-pattern(s) disposition. Some vents cover holes for adjustment of the supports between the pattern plate and the bottom of the chamber.
Fig.7. Vacuum chambers and a general view of a vibrating table
a) a basic scheme of vacuum chamber; b) vacuum chamber with a collecting zone; c) vibrating table with a collector to the vacuum-sealed moulds.
1-pattern plate; 2-vent; 3-support; 4-collecting zone; 5-vibrating table; 6-master-pattern; 7-vacuum-sealed moulds.
An independent vacuum system for building in various flasks is illustrated in Fig.8 . Other flasks are presented in Fig.9 The more of elements are made of plastics for lack of melted metal.
Fig.8. A vacuum system for flasks with different sizes used in resin patternmaking in vacuum-sealed moulds
Fig.9. Flasks for producing of vacuum-sealed moulds
a) a flask with tubes out of the case; b) vacuum-sealed mould; c) a flask with a tube built in the case.
By way of example, in Fig.10 is placed a project for installation for resin/metal patternmaking in vacuum-sealed sand moulds. The parts of real installation for patternmaking are presented in Fig.11. In Fig.12 are shown epoxy patterns and core boxes made in the Foundry Lab at the Technical University of Sofia, Bulgaria.
Fig.10. An installation for patternmaking in vacuum-sealed sand moulds
1-vibrating table with a vacuum chamber; 2-heater; 3-hopper; 4-flask; 5-hoist.
Fig.11. Some parts of real installation for patternmaking
Fig.12. Epoxy patterns and core boxes made in vacuum-sealed sand moulds
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