Model-side mold’s compaction
- Dosing of sand by weighing hopper of the molding machine and Formimpress® frame in upper position;
- Lifting of table with pattern plate carrier and flask;
- Filling of sand into the flask by opening of shutter unit;
- Shuttle of multiple squeeze head over the flask and levelling of the sand;
- Lifting of table with pattern plate carrier and flask to upper position and pre-squeeze of sand;
- Formimpress®: lifting of pattern plate and first compaction of the mold from below;
- Active squeezing from top up to 15 kg/cm2 and final compaction of the mold;
- Lowering of table with pattern plate carrier and flask and separating of mold and pattern by lifting of the Formimpress® frame;
- Complete lowering of the table (the flask with the mold is set onto the rollers of the mold conveyor and the pattern plate carrier is centred in the internal pattern change device) and transport of the molded flask out and simulations the empty flask in the molding station.
Extreme molds are guaranteed by Formimpress!
The concept of the FORMIMPRESS® molding system originated from the constant and careful observation of the difficulties usually met in attempting to obtain sufficiently accurate molding to achieve the highly precise castings able to meet increasing market requirements.
By talking about foundry jobs in the foundries, comparing the opinions and analysing advantages and disadvantages of the various processes employed in molding, it emerged that the ideal molds should have a high impression hardness, able to guarantee the production of dimensionally correct castings, also maintaining a good gas permeability (as for the jolting and compression molding). This was not easily achieved by any means. In fact, everybody knows that the dimensional reproducibility of the casting is strictly related to the mold hardness and that the mold hardness is attained with high pressure, to the detriment of the permeability and so on.
Among the noteworthy remarks emerging from the observations made, it turned out that, if it were physically possible to carry out the molding with high pressure and obtain, on the two faces of the flask, inverted hardness values compared to the normal situation, (that is to say, the hardness of the flask back side on the impression side and vice versa), the problem would be solved quite easily.
In fact, this way, one could obtain impressions with a constant hardness on the whole surface of the flask, maintaining at the same time a good gas permeability due to the natural shade originating near the walls of the flask itself. At this point, the idea of putting into practice the intuition of the old foundry men, who wanted to place the pattern on the contrasting plate of the machine, takes shape. Particularly by working on this intuition, we have come to the realization of the FORMIMPRESS® molding system. The idea of the “old foundry men” of using the pattern in order to compress the sand, has come to fruition!
The molding System proposed by the Savelli Company under the registered trademark FORMIMPRESS ® is extremely simple: It does not require any special and expensive equipment and, consequently, any technicians with special training. The molding system comprises a simple impression of the pattern into the molding sand contained in the flask. The forces originating during the squeezing phase are opposed by a counter force.
The principle of molding by impression differs from the normal high-pressure squeeze system only because of the different movements of the pattern and of the molding sand in comparison with the flask to be molded. With traditional molding systems the flask is on the pattern plate and the frame placed on the flask collects the soft sand required, which will consequently be compressed.
The pattern plate, the flask and the filling frame create a single group, in which the molding sand is pressed by the squeeze head (contrasting force) against the pattern plate, until the desired hardness is reached. With the FORMIMPRESS ® system, on the contrary, the filling frame is placed between the flask and the pattern plate. In this case the flask and the filling frame create a single group while the pattern plate, free to move, pushes the molding sand contained in the flask and in the filling frame against the squeeze-head placed on the upper side of the machine. The counter force produced by the squeeze-head makes it possible to pre-set the mold hardness.
With the FORMIMPRESS ® molding system we have, (in comparison with the traditional methods), an inversion of the flow conditions of the sand grains, as the sand layer in contact with the pattern receives the necessary energy for the compaction directly from the source. The sand grains which compose the contact sand layer are the first to be affected by the pattern movement, when they still have a good degree of mobility, which enables them to easily fill the microcavities. The sliding resistance offered by the flask walls and the damping realized by the upper sand layers, brings about a negative gradient of the degree of compaction.
The working cycle of our molding machine foresees that the quantity of molding sand (in accordance with the pattern plate) has to be weighed inside a weighing hopper, to make sure that the flasks are always correctly filled. (The quantity of molding sand is automatically corrected according to the compaction degree measured during the previous molding cycle). The weighing hopper is placed at a considerable height, which is calculated according to the type of flask employed. Such a height favours the pre-compaction of the molding sand during the fall phase, thereby avoiding the formation of damaging “air pockets”. The energy employed for this operation is cost-free and it does not produce any abrasive effect on the surface of the pattern plate. The FORMIMPRESS® System does not require any valves, nozzles, venting etc. Consequently, it does not imply any maintenance or spare parts cost. With this compaction we can make molds with excellent qualities which are reflected in the following advantages:
- an ideal resistance of the mold, with higher hardness values on the pattern side, while the molding sand thickness near the back of the mold decreases in relation to the employed counter force;
- excellent gas permeability;
- perfect reproduction of the pattern details;
- fettling is nearly non-existent;
- low-noise mold production;
- energy saving of 20-30 %, depending on the process employed for the comparison
The FORMIMPRESS® molding system is suitable for the production of all types of molds for iron castings, steel castings, non-ferrous metal castings and aluminium castings. Thanks to its special characteristics, it is particularly suitable for demanding castings that until now were thought to be obtained by pre-compression using compressed air and vacuum. With the FORMIMPRESS® this task is performed quietly and with low energy expenditure.
The modernisation plan of a foundry involving the complete automation of the production process inevitably requires the investment of large amounts of capital that are not always available, especially in the case of small facilities.
This is why Savelli has decided to direct its efforts towards the realisation of open, modular solutions that allow subsequent levels of automation to be achieved by completing the installation. In fact, the FORMIMPRESS® forming system is available on stand-alone single machines, which, depending on the need, can be expanded with additional auxiliary equipment to become mechanised and semi-automated forming centres.