Reduce Energy Consumption & Improve Product Quality In The Ceramic Industry’s Drying Process
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Reduce Energy Consumption & Improve Product Quality In The Ceramic Industry’s Drying Process

By 11/08/2022August 29th, 2022No Comments

Measurement and Control in Ceramic Drying

Drying is a ubiquitous operation found in technological processes used in the pharmaceutical, paper, mineral, polymer, ceramic, textile, food and agricultural industries. Depending on the particular sector and quality criteria of products, drying will be managed in different ways by controlling its kinetics.

Drying is a critical stage in ceramics manufacture procedure. The drying process sometimes places more stress on ceramic pieces than during firing process, therefore the drying needs to be done slowly, to prevent warping and cracking of the green body pieces. This step is complicated due to simultaneous and coupled heat and mass transfers, often accompanied by dimensional variations. It presents a permanent challenge for manufacturers mainly due to two aspects. First, it requires a significant consumption of energy, the ceramic manufacturing companies need to minimize the time for this process for the efficient production. The second important point is that mechanical stresses that occur within the material during drying may create damage in the final product if the drying conditions are not carefully chosen and controlled.

The need for precise clay moisture levels has become a critical component during production. Being such a porous material, clay can easily become either too wet or too dry wasting manufacturers time and money. With countless installations and applications along with over 30 years of knowledge, Dpstar has proudly provides a range of instruments for environmental monitoring and control which is ideally suited to measure the moisture levels in the clay production process while improving manufactures product quality and lowering their energy costs.

High quality requirements are set for ceramic products. During the drying process it’s extremely important that no damage occurs to the product. Proper air humidity control and air circulation are required to achieve this. You can rely on Dpstar to work in accordance with the strictest regulations of high standards

The Importance of Humidity & Temperature Control in the Drying Process

Why need to measure humidity & temperature?

Investigating the physical drying phenomena in ceramic materials is then a necessity to optimize this step and obtain high quality samples for industrial applications while minimizing drying costs. In other words, one of the keys in development of ceramic processing is to improve the drying step. Humidity and temperature are the variables that need to be controlled for successful drying. In this respect, real-time control systems offer potential since by monitoring drying parameters, they can detect abnormalities during the process and provide corrective action. Indeed, by controlling the wet product state in real time during drying, the drying air conditions (temperature, relative humidity and airflow rate) can be adjusted. Therefore, an appropriate selection of drying conditions should improve the quality of products and reduce operation time, thus saving energy. Whether drying takes place as a separate process or is a preliminary stage in a firing cycle, air movement can be key to uniform drying.

Investigating the physical drying phenomena in ceramic materials is then a necessity to optimize this step and obtain high quality samples for industrial applications while minimizing drying costs. In other words, one of the keys in development of ceramic processing is to improve the drying step. Humidity and temperature are the variables that need to be controlled for successful drying. In this respect, real-time control systems offer potential since by monitoring drying parameters, they can detect abnormalities during the process and provide corrective action. Indeed, by controlling the wet product state in real time during drying, the drying air conditions (temperature, relative humidity and airflow rate) can be adjusted. Therefore, an appropriate selection of drying conditions should improve the quality of products and reduce operation time, thus saving energy. Whether drying takes place as a separate process or is a preliminary stage in a firing cycle, air movement can be key to uniform drying.

During the early stages of drying, it is best for the air to be hot, humid and under a slight amount of pressure in order to flow through the load uniformly. Once the chamber is heated to temperature, forced convection fans inside the chamber move air through the load, and draft-inducing blowers pull ambient air through the chamber. As the temperature rises, the air loses some of its humidity, allowing the water content from the load to be taken up by the air. As the cycle progresses, more water content is absorbed and removed by the air flow until drying is complete and the product is ready for firing.

In the building industry, for fabrication of clay bricks for example, water (ranging between 15 and 30%) is added to aid forming the basic shape. Therefore, drying becomes a necessary step in order to obtain products containing 1 to 2% of residual moisture before final firing. In such a case, when drying conditions are not well controlled, several defects can be created. They are summarized in the table below with their likely causes:

Defect Cause
Warping Condensation of moist air on cold bodies during initial drying
Cracks High drying rate resulting large moisture gradients and heterogeneous shrinkage
micro-cracks Unsuitable drying rate, too dry body before firing
Moisture spots on body surface Lack of air stream to sweep away vapour in certain locations

Table 1: Defects related to the drying step for clay bricks

During the early stages of drying, it is best for the air to be hot, humid and under a slight amount of pressure in order to flow through the load uniformly. Once the chamber is heated to temperature, forced convection fans inside the chamber move air through the load, and draft-inducing blowers pull ambient air through the chamber. As the temperature rises, the air loses some of its humidity, allowing the water content from the load to be taken up by the air. As the cycle progresses, more water content is absorbed and removed by the air flow until drying is complete and the product is ready for firing.

In the building industry, for fabrication of clay bricks for example, water (ranging between 15 and 30%) is added to aid forming the basic shape. Therefore, drying becomes a necessary step in order to obtain products containing 1 to 2% of residual moisture before final firing. In such a case, when drying conditions are not well controlled, several defects can be created. They are summarized in the table below with their likely causes:

Defect Cause
Warping Condensation of moist air on cold bodies during initial drying
Cracks High drying rate resulting large moisture gradients and heterogeneous shrinkage
micro-cracks Unsuitable drying rate, too dry body before firing
Moisture spots on body surface Lack of air stream to sweep away vapour in certain locations

Table 1: Defects related to the drying step for clay bricks

Challenges in Ceramic Drying

Clay requires a carefully controlled drying process

The drying speed depends on the temperature and humidity

Heat recovery of periodic ovens makes dryer control challenging

High energy consumption

Improper drying can cause defects in ceramic products

Challenges in Ceramic Drying

Clay requires a carefully controlled drying process

The drying speed depends on the temperature and humidity

Heat recovery of periodic ovens makes dryer control challenging

High energy consumption

Improper drying can cause defects in ceramic products

How we can help?

The ceramic manufacturing companies need to minimize the time for this process for efficient production. It is known that the quality of the structural ceramics and the final properties of ceramics are mostly influenced by the process of ceramics drying, as an inappropriate drying regime can be the main reason for causing first defects in ceramic objects. Reducing the drying time of ceramic production is something that many manufacturers aim for. However, it is not easy as it requires optimizing the drying parameters such as temperature, relative humidity, and air movement. It involves many variables; we provide effective instrumentation to achieve your objectives.

Dpstar is very experienced with the requirements in the production of clay. We provide a range of instruments for environmental monitoring and control. We offer Vaisala Humidity and Temperature Transmitters with warmed-probe technology, which were instantly able to provide accurate measurement even in condensing conditions and allow optimal control of the drying process. With our flexible transmitter, the outputs can be set to the customers’ requirements. With both digital and a range of analogue outputs available as well as several probe mountings options, products can be selected for all applications. The recorded data can be viewed on the local display or transferred to a PC with Microsoft Windows software. Ease of calibration and sensor replacement ensures down time is kept to an absolute minimum.

Our Success Story

The process begins in the clay preparation area, where raw materials and additives are mixed to achieve the correct grain size and moisture level. The clay is then sent for forming, where the tiles are pressed into metal molds and transferred to large drying chambers. After drying, the tiles are coated before finally being fired in kilns. Drying is the most critical stage in this process. What makes energy recovery challenging is the cyclical nature of the periodic dryers. The energy-recovery solution involves a temperature-controlled system for mixing the hot air – at temperatures of up to 750 °C – from the periodic kilns with cool air and then supplying this 130 °C air to the drying stage, which operates at 45–85 °C. Relative humidity transmitters, located in the drying chambers, control the drying process. The humidity must remain at a high level at the beginning of the process. Too fast drying will lead to cracked tiles and lost production. The humidity in the chamber is controlled by letting moist air out, according to a control signal from the humidity instrument.

After implementing the heat recovery system, the humidity measurement system used previously did not respond at the beginning of the drying cycle.  This causes the humidity control in the dryer to function improperly. The condensing environment may saturate the humidity sensor, making the measurement instruments unresponsive. The Vaisala warmed-probe technology enables reliable measurements in near condensing conditions. The previous humidity instrument has been replaced with Vaisala HMT337 transmitters with warmed-probe technology, which can immediately provide accurate measurements and allow optimal control of the drying process. Energy makes up 20–25% of total production costs. The new heat recovery system has enabled our customers to cut the energy consumed in the drying process by 75%.

A 48-hour drying cycle with the old system (left) and the Vaisala Humidity Transmitter with warmed probe (right). The warmed-probe technology provides accurate relative-humidity readings at the beginning of the process, where the non-heated probe is saturated by condensed water.

Benefits of Reliable Humidity & Temperature Measurements

Reduced Energy Consumption

Improved Dryer Control

Improved End-product Quality

Increased Plant Efficiency

Reduced Start-up Times

Less Waste & Downtime

100% Product Inspection

Instant ROI

Our Products Solutions

Vaisala DMT345 and DMT346 Dew Point Transmitters 

Vaisala Handheld Humidity and Temperature Meter HM70

Vaisala DM70 Handheld Dewpoint Meter 

Talk to an Expert

Whether you are producing raw material or processing that raw material into ceramic products, moisture is key to achieving the best quality end product. Without accurate moisture testing instruments, quality is depleted and waste occurs. But choosing the right instruments from Vaisala HUMICAP and DRYCAP technology, you will achieve your production objectives with success! Our measurement technology experts will help you find the right measuring device to measure and monitor your system’s dream point. Contact us now, we look forward to advising you!

Get In Touch With Our Experts Today!

Dpstar Group
No 35, Jalan OP ½, Pusat Perdagangan One Puchong,
Off Jalan Puchong, 47160 Puchong,
Selangor Darul Ehsan, Malaysia.
Email: [email protected]

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