Conventional Kilns
Conventional kilns have pipes that radiate heat into the kiln chamber. This heat is forged from steam or by hot water coils. The water extracted from the wood is converted into vapor and then released from the kiln through the hot air.
This type of kiln can typically dry 1-inch-thick (25 mm) green wood in 10 hours down to a moisture content of 18(1). However, 1-inch-thick green red oak takes almost 28 days to dry down to moisture content of 8%(2). Generally, cool dry air is found at one end of the kiln while warm water is discharged at the other. Conventional kilns require a considerable amount of energy as constant heating of air is needed.
Dehumidification Kilns
Dehumidification kilns have been used extensively in the lumber industry due to their recycling based characteristics. In fact, these types of kilns have a heat pump system that removes moisture from wood as the majority of the evaporated water is condensed on the refrigeration coils of the dehumidifier then drained as cool liquid instead of being ventilated away from the kiln. Even though dehumidification kilns use electricity, which can be more expensive than gas, they are still economically practical because they constantly conserve energy by recycling heat and as a result the amount of electricity demanded by the system is minimal.
Vacuum Kilns
Vacuum kilns are known for their high-drying speed systems. However, they are more costly than either conventional or dehumidification kilns since the heat of vaporization is being provided by electricity instead of local fossil fuel. In addition they have limited drying capacity in the chamber.
These types of kilns are based on using microwave radiation to heat the kiln.
The temperature at which water boils is determined by atmospheric pressure. For example, the higher up a mountain you go, the less pressure the atmosphere exerts, so water boils at a lower temperature up the mountain than at its base. So unless you can haul your vacuum kiln to the top of the Himalayas, it’s going to take more energy down where us commoners live.
Solar Kilns
A solar kiln relies on solar collectors to provide the heat energy that is needed for the water evaporation. Drying times in a solar kiln depend on the weather and are therefore unpredictable. Solar kilns usually use electric-powered fans to enable the air to freely circulate through the wood. However, the cost of running these fans is high and because of the long drying times, you’ve got to run the fans for a long time making solar drying quite expensive and inefficient.
High Frequency Vacuum Wood Dryer Kiln
High frequency vacuum wood dryer kiln is advanced wood drying equipment, which only needs electricity without boiler, environment friendly and easy to handle with.
Comparing with conventional kiln dryer,high frequency vacuum wood dryer machine capacity is small and flexible, less factory space needed; efficiency is much higher (more than 10 times faster than kiln dryer). After seasoning, timber is kept straight and in high quality without cracking.
Out-turn percentage of timber increased. HF vacuum wood dryer machine is the best choice for small and medium furniture manufacturers.
High frequency is called radio frequency. It’s heating principle is same with microwave, but wavelength different. High frequency generator generates electromagnetic fields between two electrodes through three phase alternating current. In this field, water molecules are polarized – rotated – heated by friction.
High frequency heating is not like conductive heating, which heat material step by step, but make the wood heated themselves by friction.
More than 50cm thick wood can dried by our high frequency vacuum wood dryer machine with uniform moisture contenct.
The HF vacuum wood drying kiln biggest advantage
1,The 2″ thickness pine wood from 30-40% moisture content only take 3 days to reach 6-8%MC.Uniform Moisture content, no bending, no cracking.
2,Penetration heating on the plate is the biggest advantage of High frequency dry,to dry wood inside and outside at the same time.
HF Vacuum Wood Dryer Kiln Related Information
Kiln Dried Wood – Why Moisture Readings are Important
When first harvested, lumber is “green” – meaning it’s not been dried. Since green lumber is very moist, it can warp and always will shrink for every percent of moisture content (MC) below the fiber saturation point. This can occur regardless of the drying method.
kiln dried wood
When lumber companies kiln dry their wood, they do so in a controlled environment using carefully monitored temperature and humidity levels in order to avoid over-drying or under-drying. This is critical because it allows the wood to dry to the correct MC for its ultimate intended use, thereby enabling the wood to maintain stability and dimension. Wood that is over dried or under dried will warp or shrink and will not have the correct MC for its intended use.
Depending on its final use, kiln-dried woods are dried to a specific MC range. For example, wood that is intended for musical instruments or indoor furniture is dried to a range of 6-8% MC. Wood that is intended for outdoors, such as lumber used for framing a house, may be dried to a range of 17-19% MC.
Moisture Readings are Important
When first learning to dry lumber, especially lumber thicker than one inch, woodworkers should monitor MC daily to avoid drying too rapidly. The best way to do this is with a moisture meter.
Using a moisture meter, woodworkers can monitor the drying rate by measuring the MC of the sample boards and comparing the daily rate of moisture loss with the “safe rate” for that species. The safe rate refers to the loss of moisture in one day.
Safe rates for drying 1- or 2-inch thick lumber from different species are available in safe rate tables. These safe rates must be followed until lumber MC drops to 20%. Exceeding the safe drying rate for a given species can cause defects in the lumber.
What Is High-Frequency Wood Drying Machine:
High frequency is also called radio frequency, it is a kind of direct heating. The principle is using the wood as a medium, capacitor is a group between two pieces of metal plate.Then give them voltage, the electric field produced between the two plates. The water molecules between electrodes will be polarized by the alternating magnetic field and move in very high speed rapidly.
The impact and friction (billions of times per second) among water molecules creates heating in very short time.
The conventional steam kilns or common vacuum kilns are use the heating transfer to dry the wood from surface to core. high frequency power does not heat wood moisture but make wood moisture heated themselves.
It is kind of directly heating,This continuous effect let whole wood heated surface to core wholly and uniformly.
That is one of the reason why the high frequency vacuum machine is 10 times faster than conventional wood drying kiln.
we rf wood dry kiln manufacturer provide High frequency wood kiln dryer and High frequency wood drying machine is good quality.
