**9. Control and faults**

Quality control for foundry coatings and coating application process control as far as sand moulds and cores and expendable or meltable patterns are concerned is important for production of high quality castings. Establishing the quality of foundry coatings is defined by different standards for this type of refractory products. Standards are used to establish both, foundry classification and quality requirements, as well as technical conditions of application, coating sampling methods, coating test methods and marking of coatings and the way of delivery. Most often, the following coating properties are tested:


Assessment of a coating is done according to the following criteria either:


Ceramic Coating for Cast House Application 283

Table 7. Visual control: typical casting surface faults caused by inadequate refractory coating

**a. Uneven and rough casting surfaces** caused by both grain-like pattern surface and thicker layers of

ceramic coating

layers

**b. Surface porosity, uneven and** 

**c. Metal penetrating the mould,** 

**d. Insufficient replenish fault,** 

penetration of thinner coating layers, inadequate inflow system design, thick-walled casting shrinkage insufficiently

**e. Sintered sand on casting surface**  caused by application of thinner layers of diluted coatings

**f. Pattern surface fault,** fully

application.

reproduced on casting surface

casting walls

compensated

**wrinkled casting surface** caused by application of thicker coating

thinner coating layers, with thicker

**Uneven surface of coating layers,** with quickly dried thicker coating layers on polymer pattern **Bubbles on the coated surface of polymer pattern,**  caused by rapidly stirring the coating suspension during application Dried ceramic coating layers cracking on the polymer pattern, when the drying is rapid and with thicker coating layers

Table 6 shows typical faults detected on the surface of the coated polystyrene patterns. (Aćimović-Pavlović 2010, Clegg 1978)

Table 6. Typical faults on the polystyrene pattern-coating contact surface

The role of ceramic coatings is to attain a high quality moulding surface. Furthermore, moulding quality is significantly influenced by critical process parameters (casting technology); at first, the choice of material for production of castings, moulds, cores, patterns, ceramic coatings, design faults, i.e. faults concerning pattern construction, inflow system choice and calculation, as well as faults due to disturbance of technological process (human factor). It requires both control and optimization of all process parameters aimed at attainment of the desired structure and utilization properties of castings. Detection, examination and estimate of castings faults should be carried out systematically, at the stage of casting process development and concrete castings production mastering, with an aim to avoid these through preventive measures and to minimize the production costs. Presence of castings faults does not always mean the loss of their utilization value, for it depends on the type, size and position of the fault, as well as on the type of the construction where the castings are installed and on the load character during their exploitation. Therefore, it is necessary to classify the faults with regard to their nature and origin, as well as to the fault outer appearance. This enables the faults to be easily visually detected, estimated and eliminated. Table 7 shows typical moulding surface faults caused by an inadequate ceramic coating application (Acimovic Pavlovic et al., 2007, Cibrik 1977, Svarika 1977, Tsai & Chem, 1988).

Table 6 shows typical faults detected on the surface of the coated polystyrene patterns.

(Aćimović-Pavlović 2010, Clegg 1978)

**Uneven surface of coating layers,** with quickly dried thicker coating layers on polymer pattern

**Bubbles on the coated surface of polymer pattern,**  caused by rapidly stirring the coating suspension during application

Dried ceramic coating layers cracking on the polymer pattern, when the drying is rapid and with thicker coating layers

Table 6. Typical faults on the polystyrene pattern-coating contact surface

Pavlovic et al., 2007, Cibrik 1977, Svarika 1977, Tsai & Chem, 1988).

The role of ceramic coatings is to attain a high quality moulding surface. Furthermore, moulding quality is significantly influenced by critical process parameters (casting technology); at first, the choice of material for production of castings, moulds, cores, patterns, ceramic coatings, design faults, i.e. faults concerning pattern construction, inflow system choice and calculation, as well as faults due to disturbance of technological process (human factor). It requires both control and optimization of all process parameters aimed at attainment of the desired structure and utilization properties of castings. Detection, examination and estimate of castings faults should be carried out systematically, at the stage of casting process development and concrete castings production mastering, with an aim to avoid these through preventive measures and to minimize the production costs. Presence of castings faults does not always mean the loss of their utilization value, for it depends on the type, size and position of the fault, as well as on the type of the construction where the castings are installed and on the load character during their exploitation. Therefore, it is necessary to classify the faults with regard to their nature and origin, as well as to the fault outer appearance. This enables the faults to be easily visually detected, estimated and eliminated. Table 7 shows typical moulding surface faults caused by an inadequate ceramic coating application (Acimovic

Table 7. Visual control: typical casting surface faults caused by inadequate refractory coating application.

Ceramic Coating for Cast House Application 285

Utilization of ceramic coatings with different types of fillers (talc-based, cordierite-based, zircon-based, mulite-based, mica-based, chromite – based and alike) in casting decisively depends on rheology coating properties, i.e. on sedimentation suspension stability. It is necessary to carry out researches referring to optimized coating properties and to their production procedures aimed to obtain the coating properties required. Coating application in practice shows positive effects regarding high quality castings, satisfactory structure and properties, shiny and smooth castings surfaces, with no surface or volume faults

Aćimović Z., Tomović M., Đuričić M. & Tomović S. (1994) *Litejnoje proizvodstvo*, Vol. 12,

Aćimović Z., Pavlović Lj., Trumbulović Lj., Andrić Lj. & Stamatović M. (2003) Synthesis and

Aćimović-Pavlović Z., Prstić A. & Andrić Lj. (2007) The characterization of talc-based

Aćimović-Pavlović Z., Đuričić M., Drmanić S., Đuričić R, (2010) The influence of the

Aćimović-Pavlović Z., Andrić Lj., Milošević V., & Milićević S. (2011) Refractory coating

Ballman R. (1988) Assembly and coating of polystyrene foam patterns for the Evaporate

Brome A.J. (1988) Mould and core coatings and their application. *British Foundrymen*. Vol. 80

Burditt M. (1988) EPCs Promise Belies Complex Process, *Modern Casting*. Vol 8 , August

Cho N. D. (1989) Effect of coating materials on fluidity and temperature loss of molten

Cibrik A.N. (1977) *Fizičko-hemičeskije procesi v kontaktnoj zone metal-forma*, Nauka Dumka

Clegg A. (1978) The Full-Mould Process-A Review, Part II: Production of Castings, *Foundry Trade* 

Davies R.W. (1996) The replacement of solvent based coatings in modern foundries,

Gorny Z. & Marcinkowski J.(1977) New ideas in investigating and evaluating the sand and

*Chemical Industry*. Vol.64, No.2, ISSN 0367-598X, pp. (121-127).

*Ceramic International*. Vol.37, No.1, ISSN 0272-8842,pp. (99-104).

Caracterization of the Cordierite Ceramics from Non-Standard Raw Materials for Application in Foundry. *Materials Letters*. Vol. 57, No 18, ISSN 0167-577X, pp. (2651-

coating for application for Al-Si alloy casting. *CI&CEQ.* Vol.13, No 1, ISSN 1451-

parameters of Lost foam process on the quality of the aluminium alloys castings,

based on cordierite for application in new evaporate pattern casting process.

Pattern Casting Process, *Proceedings of 92nd Casting Congress*, Hartford, Connecticut,

metals in full mould, *Proceedings of 56th World Foundry Congress*, Düsseldorf,

**10. Conclusion** 

whatsoever.

**11. References** 

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ISSN 0024-449x , p.19

9372,pp. (40-48).

USA, 1988,pp. 250.

Germany, No 7.1.7.10.

Kiev.

No.4, pp.( 342-350), ISSN 0007-0718.

*Journal*, Vol. 3, No. 8, ISSN 0015-9042,pp.(383-398).

core materials, *Transaction*. pp.(893-910).

*Foundrymen,* Vol. 89, No. 9, ISSN 0953-6035, pp.(287-290).

1988, ISSN 0026-7562,pp.(20-24).

For a detailed analysis of structural and mechanical casting characteristics after a visual examination, it is necessary to apply some other test methods either. Casting test without destruction may reveal the presence of volume faults in the casting. Microstructural tests of castings point to the influence of individual process parameters on the casting cooling and solidification in a mould. Figure 14 shows some faults in the casting structure caused by application of an inadequate ceramic coating in the casting process.

a. casting with no porosity

b. casting with classified porosity

c. intensive porosity over the volume, higher pattern density and thicker coating layers, EPC process

Fig. 14. Casting faults detected by radiographic method
