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How does a foundry work? In collaboration with Zanardi Fonderie

In the metallurgical branch, foundries are those factories where many metallic parts and components that will be used in different industrial sectors such as transportation or petroleum plants are produced.
The foundry, through melting and casting process, produces countless parts of various shapes and dimensions: the melting and casting process is one of the most ancient working techniques: the first casted pieces were found in 4000 b.C.

In this video, we will visit Zanardi Fonderie, a company specialized in the production of cast-iron items since 1931; we will show you their plant, how cast-iron parts are realized, and how this company has been able to continuously improve and innovate during the years such an ancient process.

Jaes, leader in the industrial spare parts supply, works with companies like Zanardi Fonderie for facilities maintenance and to support the technicians to make the most accurate choice for spare parts. Zanardi Fonderie is located in Minerbe, in the province of Verona, north-center of Italy; they boast a production capacity of 18.500 tons per year, with pieces that can weigh from 1 to 120 kilos (2 lbs to 265 lbs).

Our visit starts inside the design and co-design offices. Generally, the customer realizes his own drawing of the component he needs (typically regarding machined component). According to this approach, the foundry designer starts the study of the moulding scheme of the raw part considering also that the material allowance has to be applied. To put it in other words, the designer has to study the shape of the mould where the cast-iron will be poured in order to obtain the raw cast part. There is no single solution, but the choice of a certain shape is determined by the technical and economical advantages during production and casting stages. Firstly, it depends on the moulding process (green sand moulding or resin sand moulding), the dimensions of the casting, the number of pieces that need to be casted, and the functional and dimensional requirements (in order to avoid shape and dimensional defects).

Secondly, it is utterly important to produce good castings, without any cavities or porosities, at least where they’ve already been machined (wire drawing) or where they are exposed to relevant strains (for example, in order to avoid crack initiation because part may break). For this reason, engineers create virtual simulations of the pouring process phases to find out any possible modification that can be made to refine the filling and solidification stages of the mould in order to improve the costs and quality of the cast part. In this scenario we’re analyzing a horizontal green sand moulding process with closed brackets and foundry pattern. Specifically, there are several aspects to keep in mind when defining the shape:
1) Pattern division line
2) Undercuts identification (definition of foundry cores and core heads)
3) Type and position of the feeding system
4) Feeders removal and deburring type

The pattern division line (1) identifies the dividing plans of the 2 brackets so that the pattern can be extracted from the sand mould easily. The line is defined in accordance with the dimensions and the casting shape: in this last case, if the model has some “undercut” areas or very deep bowls so that the risk of extracting sand residues when removing the pattern is high, the cores are used. The pattern division line or junction (shape-shape or core-shape) determines in the casting a parting line (which depending on the processing type will be or won’t be removed). Most of the time, the cast orientation, or at least the parts that must have better characteristics, are facing the lower moulding bracket since waste and gases tend to rise upwards: even the feeding system can contribute to this.
When we talk about cores (2), core prints have to be added to the pattern plate in order to obtain proper core head seats for assembly into the mould. Core heads must ensure the stability of the core during the pouring process, resisting to both thermal shock and metallostatic pressure.

Let’s now move onto the sand and molding line. The sand, mostly composed of siliceous sand, sea coal, bentonite (a particular quality of clay that makes the molding stronger), and water, is used to create the mould cavity in which the liquid cast iron will be introduced. The plant constantly fuels the molding line and the quality of the green sand is monitored through the control of many physical features, which basically are humidity, cohesiveness, permeability and several other factors that determine an optimal product.

The pattern plates, consisting of slabs with the pattern, the pouring and the feeding system shown above, are the result of the design study. They are used to create inside the two half of the mould into the sand, through the moulding process, a negative print of the whole cluster which will be filled by cast iron. The pattern plates components, depending on the number of pieces to realize, can be made in cast iron or aluminium for large productions, in resin for medium-sized productions, or in wood for samples and prototypes. Basically, the model is the machined component requested by the client with the addition of the necessary adjustments to produce the raw component: material allowance, drafts, shrinkage, core heads, supports for cores, coolers, protections, etc.

The cores are products that are mainly produced with siliceous sand and a binding agent (resin) that gives a certain thermal and dimensional stability during the casting process. They are used to obtain the internal parts of the raw casts, the holes, and the undercuts parts, that is, those areas which stay in the shadows compared to the direction of the pattern plate extraction after the moulding phase. There are many technologies for cores manufacturing, in Zanardi Fonderie, they are obtained through the Ashland process (“cold-box urethane”. In the cold box process, cold hardening of the cores is obtained through to a gaseous catalyst (amine).

In order to regulate the flow of the cast iron during the mould filling and to detect impurities such as slags or sand particles that could give birth to some defectiveness on the casts, usually some extruded ceramic filters with regular holes are used, or alternatively some silicon carbide “spongy “ filters. These filters are located in special housings that are directly obtained through the forming process.

Following the moulding steps necessary to obtain 2 green sand half moulds, the operators place the cores, the coolers and the filters on the lower moulding bracket while on the upper one some holes whose function is to facilitate the exit of the exhaust gases generated during the filling and subsequent combustion of the cores will be created. Once these operations are finished, the 2 semi-moulds are coupled and closed through a clip closure system. From now on the whole mould is ready to be filled with the liquid cast iron on the next pouring station

In the next video we will discover how melting ovens work and how the cast iron is cast inside the mouldings.