Optimised feeding systems increase quality and reduce finishing costs
Increasing cost pressure, the trend towards intricate, thin-walled castings, and the rapid development in moulding plant technology create new challenges for feeder manufacturers. Nowadays, optimised feeder technology makes many things possible that were previously considered impossible.
GUIDO BRIEGER, DELLIGSEN
When the first generation of moulding machines with short cycle times was introduced where the ram-up application of feeders was mostly impossible, the feeders were inserted after moulding in the form of insert sleeves. With this method, the requirements on the stability of the feeder were rather low as the feeders were not exposed to the compressive pressure of the moulding plant. The challenge for a feeder manufacturer using the methods of that time, e.g. waterglass binder systems, was to produce dimensionally accurate feeders which the foundryman could insert into the mould as easily and evenly as possible. Yet the feeders were to have sufficiently stability in the mould to remain in their exact position during turning and assembly of the mould and subsequent pouring. In most cases, insert sleeves with breaker cores with as small a feeder neck diameter as possible were used to reduce the cutting and fettling costs. However, adequate space on the patterns was always required.
Technological development towards faster moulding plants with increasingly higher compressive pressure went along with the possibility for the foundryman to place the feeders on the pattern plate prior to moulding, which in technological terms meant great variability in regard to feeder geometries. Now a parallel-conical feeder sleeve design was no longer mandatory because the feeders could be rammed up. To take immediate financial advantage of these new opportunities, compact feeders with breaker cores (Figure 1) were used increasingly which, due to their much lower volume, yielded savings in liquid metal and/or gave better performance of the moulding plants. It was now possible to pour a higher number of flasks with the same quantity of liquid iron, or to reduce moulding plant downtimes caused by lack of iron. Even with this system, reduced breaker core diameters of the compact feeder systems or the use of spring loaded pins resulted in enhanced possibilities of feeder positioning. Since the fluorine-bearing feeder masses commonly in use at the time frequently led to a degeneration of graphite in feeders, these areas were commonly designed with a machining allowance of approx. 3 to 4mm which later had to be ground off again at great expense.
Increased compressive pressure at the moulding plants resulted in a higher hardness of the moulding sand and enabled the foundryman to produce increasingly complex and sophisticated castings. This, however, resulted in frequent breakage of breaker cores and feeders. The telefeeder was developed to solve this problem.
During compaction of the sand in the moulding plant, the upper section of the telefeeder (Figures 2a and b) slides telescopically over the lower section (Figure 3). This means that the lower section is practically not exposed to pressure and, therefore, damage.
However, with its two-piece design and combined with the recently developed fluorine-free Coldbox feeder material the telefeeder provides several other benefits:
> When the upper section slides over the lower section, additional compaction of the moulding sand under the lower section takes place (transition area between feeder and casting), precisely where shadows of poorly compacted sand may occur.
> The fact that both the upper and lower section are made of an exothermic material guarantees that the telefeeder spends up to 50 per cent of its volume to the casting (Figure 4).
> The significantly reduced contact area of the telefeeder allows for manifold ways of positioning the feeder on the pattern, and thus for accurate spot-feeding of the casting.
> The fluorine-free, exothermic feeder material prevents graphite degeneration, so there is no need for grinding allowances below the feeders. In addition, the fluorine-free feeder material is ecologically sound for the foundry sand system.
> The formation of a defined break-off point significantly reduces separation and cleaning costs compared to spring loaded pin feeders.
> The centering pins have a very simple, maintenance-free design and are cheap to manufacture.
> An air outlet is not required as the centering pin automatically breaks through the top of the upper section during moulding (Figure 3).
The R-type telefeeder
The R-type telefeeder is a consistent further development of the telefeeder, and it has been introduced successfully in many foundries all over Europe. The special feature of the R-type telefeeder is a metallic tube positioned in the lower section of the telefeeder, thereby constituting a transition between the casting and the exothermic feeder (Figure 5).
With the design of the R-type, the already small feeder tube diameter of the telefeeder has been further reduced by another 37 per cent with almost unchanged feeder neck diameter. This reduction provides the foundryman with significantly improved possibilities of application on sophisticated casting contours, combined with a very clean break-off point at casting surface level.
Exothermic contour breaker cores and segments
The trend towards ever more light-weight cast components used in mechanical engineering and vehicles construction implies that castings are increasingly difficult to pour, sometimes with major differences in wall thicknesses which often appeared almost impossible to feed. Due to their dimensional accuracy and neutral behaviour as regards graphite formation, the development of fluorine-free Coldbox feeder materials made it possible to break new ground in feeding technology. These characteristics allowed it to place exothermic segments onto certain sections of the casting geometries and/or to shoot them into a core.
These segments make it possible to keep thin-walled areas liquid and open for a longer period of time and thus guarantee a dense feeding of the areas below. In addition, combined with an appropriate feeder (Figure 6) exothermic contour breaker cores often provide the opportunity to reduce the overall number of feeders on the casting considerably and thereby achieve a cost advantage for the foundry.
The company based in Delligsen, Lower Saxony/Germany, is a subsidiary of Hüttenes Albertus in Düsseldorf. Founded in 1974, it has since become a major supplier to the foundry industry. Worldwide distribution takes place through Hüttenes Albertus. In the field of feeding technology, Chemex specialises in Coldbox binder systems and the telefeeder technology, which is patented throughout Europe (Figure 7).
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