Floware

FLOWARE – Research and Development of Flameware Stoneware Product Line

Through the FLOWARE project, the proposing consortium, composed of Grestel and Mota II, aims to develop two clay bodies (plastic and slip) and three glazes (transparent, opaque, and matte) in order to manufacture a product capable of withstanding the thermomechanical stresses resulting from direct exposure to the flames of domestic and industrial stove burners.

The project aimed to obtain:

• Two stoneware bodies (plastic clay for slip casting and pressing, and slip for casting) with water absorption ≤1%, three-point MOR greater than 35 MPa, fracture toughness K_C ≥1 MPa·m^1/2, and CTE between 20×10⁻⁷ K⁻¹ and 30×10⁻⁷ K⁻¹ over the temperature range of 20–800°C.
• Three glazes (transparent, opaque, and matte) with CTE between 15×10⁻⁷ K⁻¹ and 25×10⁻⁷ K⁻¹ over the same temperature range, softening temperature above 800°C, and fracture toughness K_IC ≥0.75 MPa·m^1/2.
• Nine finished stoneware products produced in a single firing, corresponding to the three forming methods used (pressing, slip casting, and casting) and the three glazes (opaque, transparent, and matte), with the form, microstructure, and mechanical and thermal properties optimized to withstand thermal shocks from direct exposure to flames from domestic and industrial gas burners.
• Three final products, selected from the nine previous ones (1 clay body + 1 forming method and 3 glazes), suitable for production and commercialization by Grestel after the project, in accordance with the requirements established for Flameproof tableware.

During the project, the consortium developed two clay bodies (plastic clay and slip) and three glazes (transparent, opaque, and matte) to manufacture products capable of withstanding thermomechanical stresses, particularly when exposed directly to flames from domestic and industrial burners.

Some constraints were identified initially, including difficulties in optimizing the design level of the pottery pieces and unforeseen challenges in sourcing raw materials from the market.

The transition of prototypes from pilot scale to industrial scale presented several challenges that had to be overcome:

• Slip Casting (Barbotine) – Difficulty in converting the plastic clay composition into a casting slip with the same characteristics as FLOWARE. Rheological issues and wall formation times caused pieces to have many pores.
• Dipping Glazing – While achieving the correct rheology was relatively easy, obtaining homogeneous glaze layers was challenging, leading to variations in the pieces’ performance under flame.
• Kiln – Difficulty in controlling temperature gradients in a large intermittent kiln when the product required very tight gradients. Issues arose during the cooling plateau, which required special intervention from the kiln supplier to allow proper programming of this cooling stage. Large-scale industrial tests were carried out, involving all production sectors for FLOWARE ceramic pieces.

Based on information from the University of Aveiro regarding the performance of FLOWARE pieces in the tests they were subjected to, corrections were made at the design level, particularly concerning the rim design, as well as the thickness of the base and walls of the pieces. With the production of larger series, some pieces were put into use in both domestic and industrial environments to assess their real performance and long-term behavior.

In terms of results promotion, an article was published in cfi – Ceramic Forum International [cfi/Ber. DKG 95 (2018) No. 9–10], titled “MOTA Ceramic Solutions (MCS) Low Expansion Ceramic Bodies and Glazes for Ceramic Flameware Manufacture”, and the results were also disseminated at specialized events.

Specific Results:

Through the execution of this project, it was possible to develop a flameware clay body that can be sintered at a firing temperature below 1250°C, with water absorption below 0.5% and a low CTE, allowing the manufacture of flameware pieces comparable to those already available on the market.

Additionally, an innovative firing curve was designed, introducing a plateau during the cooling phase to promote the formation of crystalline phases, thereby reducing the CTE.

The FLOWARE pieces demonstrated resilience when exposed to direct flame. However, weaknesses related to design were detected, including the presence of rims, variations in thickness, sharp angles between the base and walls, and the proportion of flame size to piece size. After adjusting the design, the pieces achieved performance comparable to competing products fired at higher temperatures.

The use of the pieces carries limitations similar to those of existing market products – they cannot withstand extreme thermal shocks, which imposes certain restrictions on their use.