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Main Advantages of the Microwave Heating

  • Speeding up: minutes instead of hours!!
  • Volume Energy transmission - cold vessel
  • ENERGY Savings, Room Savings
  • Efficiency 70%
  • Automatization
  • Safety *
  • Environment *

Comparing to the processes using the combustion


REFERENCES

ECONOMY
  • just hours instead of whole shifts
  • continuous operation
  • minimal space
  • elimination of scrap
  • minimum heat loss  
DOZENS OF MICROWAVE DRYERS ROmiLL
are successfully deployed long-term in the ceramics industry

Drying of complex sanitary ceramics


From mould to firing
  • MICROWAVES HAVE REVOLUTIONIZED sanitary ceramics manufacturing process due to the fact that a similarly fast, effective and balanced removal of water cannot be achieved by any drying method other than dielectric
  • MODULAR CONCEPT combines characteristics of a standing chamber and conventional tunnel-throughput dryers  


1. SHAPE STABILIZATION BY PRE-DRYING AND PORE
OPENING FOR DUFFUSION OF WATER FROM WITHIN PRIOR TO THE MAIN DRYING PROCESS

Semi-finished products of fresh-cast ceramics are prone to shape spoilage. Due to the need for immediate handling it is therefore desirable, immediately after removal from the mould, to reduce excessive plasticity by removing some of the moisture. At the same time due to the warming of the entire mass, its pores open, through which the fluid is attracted by capillary forces to the surface during the further drying process. Unlike ceramic materials water absorbs microwave energy and is heated simultaneously in all depths of the product wall. With the increase in temperature the pressure increases too, and hence the water molecules are forced onto the surface, where the pressure is lower. The microwave output can be very precisely controlled so that evaporation in this phase, sensitive to formation of micro-cracks, is sufficiently gradual.

By a prompt pre-drying process (taking just minutes) microwaves stabilize the semi-finished product in the first module for handling. In the attached modules where reduction of moisture content proceeds to the critical limit, the semi-finished product progresses through the microwave dryer. The technological arrangement is effective, energy-saving and preventive of products forming defects.


 MOISTNESS START FINISH DRYING TIME  RESULT
Stabilizing 20 % 18 % 0,25 h swift overcoming of the delicate consistency of a fresh casting, which limits manipulation and retouching, with no downtime and need for any interim storage
Critical 10 % 2,25 h gentle but rapid evaporation of free and physically / mechanically bound water enables further, more intensive drying without occurrence of (cracked) scrap 
Firing 1 % 7 h removal of free water is complete, mainly water with physical/chemical bond is evaporated, for firing remains only crystalline water

2. DRYING TO CRITICAL MOISTURE CONTENT
Firstly, intermolecular water which is separating the solid particles from one another evaporates. As this water leaves, solid particles become closer, increasing the density. When moisture content reaches the critical point the particles are touching and the shrinkage stops. Hot air drying first heats the surface which shrinks before the colder deeper layer, causing tensile stress create cracks on the surface. Microwave dryers ROmiLL achieve an even temperature throughout the product wall. Deformation is prevented because there is zero tension between the surface and the deeper layers. Power is adequately regulated according to type of the raw material, its size, shape and thickness of walls. The course of removal of moisture is optimal at each stage of the microwave drying process.

When the moisture content is below the critical level there are no more volume changes of the product and drying can continue faster. Inclusion of additional microwave modules lead to significant shortening of the remaining drying phase to the values required for firing.

3. DRYING TO THE FIRING-MOISTURE CONTENT
Capillary water bound by physical attraction is released inside the pores in a form of vapour with a much larger volume, slowing down its diffusion and creating capillary rise of moisture to the surface. Due to the lower temperature within the material during a hot-air drying process, the moisture transfer is of low intensity until the core of the wall is heated from the surface. Overheating on the other hand causes over-pressure, resulting in ware destruction, if the steam cannot escape through the pores in time. Microwaves do not heat surrounding air and thus impermeable crust preventing evaporation is not created unlike during the convective processes. Setting the parameters of hot air dryers is crucial for each type of product. Each product requires a different combination of temperature, humidity, airflow and speed of passage through the drying tunnel. However, optimal set up of conventional throughput lines in operation is practically impossible. Microwaves are governed by the radiated output power alone and the modes can be sensitively set at levels that can cope with various stages of drying. 

PRACTICE
Modular dryers of sanitary ceramics are predestined to be used for complicated shapes. Freshly cast toilets, bidets, and similar ware dry inside them within hours, to values which allow firing. The transfer cycle from one module to another corresponds with the time required for casting. This may vary depending on the type of material, moulding method, its shape and size. Typical pressure casting of a toilet bowl and its transport by a robotic arm to the first module takes 15 minutes. During this period the shape stabilization takes place by microwave pre-drying. At the same time the entire thickness of the wall perfectly warms throughout allowing water to rise through the capillaries to the surface. This promotes drying acceleration from the very beginning, first to the critical, then to the firing value, in different modules. Microwaves shorten the drying process by an order of magnitude if we take in consideration that the process from the de-moulding to firing can take even 2 days.

OPERATION
The control system allows programming the drying modes according to the technologistīs requirements, it monitors faultless functionality, reports deviations and stores records. Operation can be managed by staff without qualifications. Control can be subjected to a system of robot that is manipulating the semi-finished products. The device does not require special interventions. Consumable items are easily replaceable by an electrician. Even with the given information the manufacturer of course guarantees the post-warranty service.

INVESTMENT
Compared to lengthy inefficient hot air technologies, that apart from water unnecessarily heat the mass itself where also the heat from the surface enters the core slowly, the cost of microwaves have no competition.
The design and components used allow for longevity in continuous trouble-free operation.