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Malinda

Optimum particle size distribution of clay roofing tile industry

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Hi Milanda, welcome to the forums.

the question is simple enough, but the parameters are not. You used two terms: " industrial and production." From which I am going to assume you are producing and or firing tons per day. In asking about specific particle distribution, I will also assume you have the resources to either air float, slurry, or access to powered screens/ sieves. Finally I will have to assume you mean production of classic terra cotta ( colored) roofing tile; also commonly called Spanish tiles. The combination of these ales mean cone 04-06 firing; perhaps even unglazed? I will also assume you are using a power extruder much like a brick extruder with specific dies?

The methods you use to form, the cone you fire to, and the raw materials you have access to will all play roles in PSD. ( particle size distribution)  Sub micron  materials yield the highest green strength, in addition to decreasing absorption rates. Intermediate particles ( typically 200 mesh  gives the required body the ability to hold its extruded shape. Large particles ( 60-80 mesh) will be required in this case to allow oxygen to move easier within the body to prevent carbon coring and bloating.

Terra Cotta (color) starts with 50-60% of high iron clay (5-7% iron), that generally is red in color. Most red clay in the USA is air- floated, with a fairly even particle size of 200 mesh. Assuming you will be processing your own local material: a sieve test will be required to determine exact PSD. 

General distribution should be 15% of 50-80 mesh, 60-80% of intermediate particles 200 mesh, and 15-20% of sub micron (325+ mesh).Total clay content of the recipe should not exceed 80% of the total recipe additions; with the red clay not exceeding 60%. Once you determine the PSD of your local clay; fire clay, grog, ball clay(s) can be used to fill any deficiencies. Talc is often used in low fire recipes to help control expansion, although not mandatory.

additional thoughts:

1 sub micron ball clay adds green strength and lowers absorption. However, they also increase plasticity and shrinkage rates because they hold more water than larger particles. Extruded bodies tend to be low plasticity in commercial production. Cone 04-06 bodies typically run 10% shrinkage! and given the shapes you plan to make: this should not be an issue.

2. High iron clay bodies are more prone to carbon coring and bloating. Your firing method and rate of climb will be critical in preventing these issues. However, large particle mesh, grog, or sand can be used to open the body to aid in escaping gases and supplying oxygen to the body core.

Tom

 

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On 4/28/2018 at 5:31 PM, glazenerd said:

Hi Milanda, welcome to the forums.

the question is simple enough, but the parameters are not. You used two terms: " industrial and production." From which I am going to assume you are producing and or firing tons per day. In asking about specific particle distribution, I will also assume you have the resources to either air float, slurry, or access to powered screens/ sieves. Finally I will have to assume you mean production of classic terra cotta ( colored) roofing tile; also commonly called Spanish tiles. The combination of these ales mean cone 04-06 firing; perhaps even unglazed? I will also assume you are using a power extruder much like a brick extruder with specific dies?

The methods you use to form, the cone you fire to, and the raw materials you have access to will all play roles in PSD. ( particle size distribution)  Sub micron  materials yield the highest green strength, in addition to decreasing absorption rates. Intermediate particles ( typically 200 mesh  gives the required body the ability to hold its extruded shape. Large particles ( 60-80 mesh) will be required in this case to allow oxygen to move easier within the body to prevent carbon coring and bloating.

Terra Cotta (color) starts with 50-60% of high iron clay (5-7% iron), that generally is red in color. Most red clay in the USA is air- floated, with a fairly even particle size of 200 mesh. Assuming you will be processing your own local material: a sieve test will be required to determine exact PSD. 

General distribution should be 15% of 50-80 mesh, 60-80% of intermediate particles 200 mesh, and 15-20% of sub micron (325+ mesh).Total clay content of the recipe should not exceed 80% of the total recipe additions; with the red clay not exceeding 60%. Once you determine the PSD of your local clay; fire clay, grog, ball clay(s) can be used to fill any deficiencies. Talc is often used in low fire recipes to help control expansion, although not mandatory.

additional thoughts:

1 sub micron ball clay adds green strength and lowers absorption. However, they also increase plasticity and shrinkage rates because they hold more water than larger particles. Extruded bodies tend to be low plasticity in commercial production. Cone 04-06 bodies typically run 10% shrinkage! and given the shapes you plan to make: this should not be an issue.

2. High iron clay bodies are more prone to carbon coring and bloating. Your firing method and rate of climb will be critical in preventing these issues. However, large particle mesh, grog, or sand can be used to open the body to aid in escaping gases and supplying oxygen to the body core.

Tom

 

thank you.How I identify optimum particle size distribution of local clay??

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