Wood-Mizer Vacu-Kiln FAQ

Q. How does it work?

A. A vacuum is pulled on the loaded kiln chamber reducing the boiling point to 105-110 degrees F. The drying is achieved by adding heat through layers of thin heating blankets between which layers of wood are stacked, bringing the temperature of the wood to a point higher than boiling, and then allowing the boiling vapors to escape from the wood. These vapors then condense back into liquid form on the interior of the kiln walls. Both the rate at which heat is added to the wood and the rate at which vapor is boiled out of the wood is controlled by microprocessor circuitry. The microprocessor is completely field programmable and allows the operator to rapidly schedule the drying rate required for the specific species and thickness of wood being dried.

Q. What are the blankets made of?

A. Blankets are an .011" thick sandwich of aluminum foil with a polyester film laminated to both sides to make them durable.

Q. How long do the heating blankets last?

A. Blankets will usually last two years or more, depending on use.

Q. What about tears in the heating blankets?

A. Tears do not ruin the heating blankets unless they are over half the width of the blanket. Simple holes and small tears can be repaired with clear, 2" wide shipping tape. The repairs will last the lifetime of the heating blanket.

Q. Where does the water go?

The vacuum pump operates periodically to maintain the vacuum. The vacuum pump also pumps the water out which has condensed into liquid and formed on the interior kiln walls. The water can be either collected to aid in determining drying rates or safely dumped into a sewer.

Q. How much power does it use?

A. To dry green red oak to 6-8% MC requires less than a kilowatt hour per board foot. If you are paying 7 cents per kilowatt hour, ,this translates to less than 7 cents per board foot.

Q. What kind of electrical service do you need?

A. Service required is 230 volt, 100 amp single-phase service. Three-phase (230 volt) service can be adapted to,work also.

Q . How fast does it dry?

A: It takes about 5 days to dry 1" green red oak from 80% to 6% MC. Woods such as birch, cherry, and pine dry faster. With ,a Wood-Mizer bandsaw mill you could go from a standing tree to a dried piece of finish lumber in less than one week. Wide, thick red oak should be air-dried before kiln drying to minimize checking.

Q. Is there a lot of maintenance?

A. No, because so few moving parts are used in manufacturing the kiln, no maintenance is required besides cleaning an easily accessible vacuum line filter and lubricating of the vacuum pump and chamber cooling fans every 6 months.

Q. Does the kiln require a lot of operator attention while it is operating?

A. No, the wood is loaded, the chamber closed and sealed, and the drying schedule is put in. The kiln automatically starts, dries the wood, and then turns itself off at the desired final moisture content. Daily inspection of the kiln for proper operation is all that is required.

Q. What lengths of boards will fit into the kiln?

A. Any combination of lengths that will total 25 feet, 20 feet, 15 feet, or 12 feet. (For example, two 12' boards = 25', or two 10' boards = 20'.)

Q. Do boards need to be end coated?

A. No, if the wood is green and can be loaded into the kiln right away, it is not necessary to end coat. Wood to be air-dried first or to be stacked for several days first should be end coated.

Q. How long does it take to load the kiln?

A. Depending on sizes and thickness, loading or unloading takes anywhere from 3 man hours to 4 man hours.

Q. Can you use it outside?

A. The preferred location is an enclosed building with concrete floors and room temperatures not less than 60 degrees Fahrenheit.

Q. Is there schooling?

A: Schooling is included in the purchase price of a kiln. Normally a 2-day training period is sufficient, but you may stay longer.

Q. How do I know when the load is dry?

A. The kiln is automatically turned off by computer monitoring of the heating blankets. When the wood in the heating blankets has reached the final maximum temperature limit set into the control panel, (See heading "Final Max Temp" in Section 2-3 of the manual), then the heating blankets will be turned off. After the wood cools by one degree, the heating blankets will be turned on again. The amount of time that each blanket remains on depends upon the dryness of the wood near the controlling temperature sensor for that heating blanket. As the wood near that controlling temperature sensor dries out, the percent of time that the heating blanket remains on decreases. (See heading "$ Heat ON" in Section 2-3), until the average percent of on-time of all the heating blankets in use at the time decreases to the final dry point set into the control panel. (See heading "Final Dry Point" in Section 2-3). When that happens, the kiln will turn itself off, and the "load dry" light will come on.

Q. At what temperatures is the wood dried?

A. Green lumber is dried in the range of 100-115 degrees F. "Bound water" drying will occur between 125-160 degrees F., depending upon species.

Q. Is it necessary to drill holes in the lumber to be dried to install the temperature sensors?

A. No, the temperature sensors are built into strips of aluminum which lay on top of the wood to be dried.

Q. Is it necessary to know the initial moisture content of the wood before starting the kiln?

A. No, the kiln will sense the presence of "free water" by using its temperature sensors and will automatically adjust the drying schedule for either low temperature "free water" drying, or higher temperature "bound water" drying.

Q. What about shrinkage?

A. The shrinkage rates of wood dried in the Model 2000 are about the same as those published in the U.S. Department of Agriculture (Handbook #188), Dry Kiln Operators Manual.

Q. Is it necessary to set the pitch of softwoods?

A. Yes, some softwoods need to have their pitch hardened by raising the wood temperature to 160 degrees F. for a few hours after drying.