" " wisno wood furniture finishing: Oven in the finishing room

Wednesday, March 31, 2010

Oven in the finishing room

Drying room 
Drying room is a room in the finishing room to put the wet coated product by the finishing material to stay until it is dry and ready to go to the next process. The drying room should be made and designed based on the drying time of the finishing materials used. There are 2 factors that influence the drying time: the finishing material itself and the environment condition.
Drying time of each finishing material varies depending on the type of finishing materials used. Nitrocellulose is a finishing material that dry quickly and considered as the easiest material to be handled. The polyurethane especially the exterior polyurethane is a material that requires long time to dry. As a comparison only, for a similar condition the nitrocellulose sealer can be dried for sanding in about 30 minutes, while an polyurethane exterior sealer need  about 6 hours to get dry enough for sanding. 

We can adjust the drying time with the adjustment of the solvent of thinner used. A fast drying solvent such as M.E.K. can be added to the paint mix to shorten the drying time. While the slow dry thinner such as B.A. or Buthyl cellusolve will make the material dry slower. But the adjustment with solvent is limited because the thinner has to be compatible with the finishing material. We also cannot play too much the thinner too much, since it could be lead to the application problem. To fast dry finishing material will result difficulty in application such as uneven coat or rough surface. 

Another factor that influence the drying time is environmental conditions. Temperature and humidity are the main external factors that determine the drying time of a finishing layer. The higher air temperatures will make the solvent evaporate more quickly and easily, and at last will make the drying time becomes shorter. The other environmental factors affect the speed of drying is the humidity. The drying process is the release of solvent into the air, because it is the air condition like the humidity is really correlated with the drying process. The humid air will not accept the solvent evaporation from the finishing surface. The humidity is really affecting the drying process for the water based coating, since the water based is use water as his thinner, the humid air environment will block the evaporation of the water from the coating. That way for the water based coating is take very long time to dry in the humid condition. When the day is hot the water based coating ca easily dry for just half or 1 hour, but in the rainy day it may take a day to get the water based coating finish to dry.


Oven 

In a finishing,  the drying time is factor that determine the speed finishing process. The drying time affect production speed more than the working process time. The processing time can be shortened by add more peoples to do the process. But the drying time is just time for waiting. To increase the speed of finishing process the drying time has to be shortened. The drying time can be set by adjust the finishing material. But it is relatively limited, because the finishing materials is chemical that has their typical physical and chemical properties depending on the type of the material. The other way to shorten the drying time is by adjust the environment condition with an oven. Oven is a facility to heat the room and circulate the air inside the room to make better control to the room humidity and temperature.
  • The air temperature
The higher air temperature is higher will make the solvent evaporation easier. High air temperatures will also accelerate the chemical reactions that occur during drying finishing layer. In a chemical solution the increasing temperature 10 Celsius would raise the reaction speed to 2X. The increased of the reaction rate in the wet film may not as big as in the solution but nevertheless the high temperature will speed the chemical reactions that also directly shorten the drying time in the finishing process. 
  • The air humidity 
The humidity is another environmental factor that determines the speed of evaporation. Dry air will accept the solvent evaporation faster and easier than the saturated air. For the water base finishing material, then the humidity is very affect the speed of drying. The humid air and saturated with water vapor air will not be able to receive more water vapor. Therefore one of the obstacles that must be considered in the application of water based coating is the humidity. In the conditions on environmental air which is very humid or in the rainy day, then the application of water base coating become very difficult and take long time to dry.
  • The principle of the oven 
 Oven is an equipment to heat the air and control the air temperature in the finishing room. With the use of the oven then a finishing process could be accelerated and controlled independently with the changes and weather conditions in the finishing room. The basic principle of the oven is to heat the air and do a good circulation to air in the drying room. Heating the air will make the drying process of finishing materials to be faster because it will accelerate the evaporation of solvent in the finishing layer and also the chemical reactions that occur in the finishing layer. The increase in air temperature will also be lower the humidity and it also will make more rapid drying.
In addition to the air heated the oven should also be equipped with good air circulation. The air was saturated with solvent vapor or moisture can not receive the evaporation of solvent anymore, since that an oven also need a fan and system to ensure good air circulation in the drying room. With good circulation, the air is already saturated with water vapor can be removed and replaced with new air that can accept thinner vapor.

Selection oven. 

The design of oven is depend on the type of material that is applied in the finishing process. The air temperature is highly dependent on the type of finishing material is applied. Usually the air temperature in the furniture finishing ranges from 35 to 45 degrees Celsius. Temperature that is too high will cause problems in the finishing layer such as: bubble, pinhole or even a crack at finishing layer. For the water based coating the humidity is other important factor instead of air temperature. The drying room for water base coating should be set with the air humidity is maintained between 50 % to 60%.
  • Oven with electric lamps 
It is the simple equipment and very easy to be made. This equipment is made by placing some lamp to heat the air and put a fan to flow the air in the drying room. The air temperature settings regulated by adjusting the number of lights which is on. If the temperature is too hot, we can turn off some lamp to low down the air temperature. This oven is relatively expensive in operating costs since heating with electric lights have very low energy efficiency. In order to maximize the heat generated the infrared lamp is better used. The infra red lamp will convert the electric energy into heat better than other types of lamps.
  • Oven with the heater equipment.
This oven is recommended for finishing room with a large scale. Heating air is done by the heater then the hot air is then channeled circulated into the room to keep the room temperature. Heater can be used various kinds, depending on air temperature and the desired capacity of the oven. The air heater that mostly use is water steam or gas that flowed in a coil. The hot air around the coil is bowed and flowing to the drying room.  This type of oven is suitable for a big finishing room with a large scale production, with a higher flexibility for setting of the room temperature as needed.



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