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AD-A093 075 'FORESTPRODUCTS LAB MADISON VI F/G 11/12 ACCELERATING THE KILN DRYING OF OAK.(U) UN S 'SEP 00 A T SIMPSON UNC LASIIE SS FPL-37P FPL 3 NL

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Page 1: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

AD-A093 075 'FOREST PRODUCTS LAB MADISON VI F/G 11/12

ACCELERA TING THE KILN DRYING OF OAK.(U)

UN S 'SEP 00 A T SIMPSONUNC LASIIE SS FPL-37P FPL 3 NL

Page 2: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

United States

Department ofFriet Serte Accelerating theAgricultureForest Service

ForestLaorao Kiln DryingResearchPaper of OakSeptember 1980

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Page 3: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

AbstractReducing kiln-drying time for oak

lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this work, 1-inch north-ern red oak and white oak were kiln-dried from green by a combination ofindividual accelerating techni-ques-presurfacing, presteaming,accelerated and smooth schedule,and high-temperature drying below18 percent moisture content. Resultswere compared with those achievedby conventional kiln drying. Dryingtime in the combined techniques pro-cedure was reduced by more than50 percent. The results for quality ofthe lumber were mixed. In most of thematerial, the quality was acceptable,but enough honeycomb was presentto be of concern.

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Page 4: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

United StatesDepartment ofForecutusrve Accelerating the,Agriculture])Forest Service,--_ !

ForestProdctsKiln DryingProductsLaboratory'

of Oak&

By IW:. WILLIAM T. SIMPSON Project Leader -. .

u tears and fractures, and that by plan- oak and developed an acceleratedIntroduction ing as little as 1132 inch from the sur- schedule for white oak. The white oakface the tears could be efiminated. schedule reduced drying time by an

Research in kiln-drying 414 oak Furthermore, he showed that lumber estimated 22 percent without increas-lumber has shown individual acceler- dried with these surface tears and ing degrade.ating techniques such as presurfac- fractures was more susceptible to Rice (10) tested McMillen's ac-ing and the schedule acceleration it surface checking than lumber that celerated schedule for northern redallows, presteaming, schedule was planed to remove the torn sur- oak on a larger scale-6,000 boardsmoothing, and high-temperature dry- face layer. The implication is that the feet loads. He dried two presurfaceding below 18 percent moisture con- tears and fractures are concentration loads and found 9 percent and 23 per-

* tent, can reduce drying time of oak points for drying stresses and they cent reductions in kiln time comparedlumber without loss of quality to the open up much more easily than does to that of a rough load and no in-lumber. These techniques have been an undamaged surface. In 1964, crease in surface checking. Cuppettinvestigated mainly on an individual Leney (3) and in 1966, Rietz and and Craft (1) compared the kiln-dryingbasis, although Wengert and Baltes Jensen (9) confirmed this reduced time of rough and presurfaced red(19)2 studied some combinations of in- tendency of surfaced lumber to check and white oak in mixed loads, anddividual techniques. The combination during drying. found a 50 percent reduction in kilnof all of these techniques might offer The significance of this observation time of the presurfaced loads com-a dramatic reduction in drying time on surfacing lumber before drying is pared to that of the rough load, againyet maintain acceptable quality the potential to accelerate kiln-drying with no increase in defects.lumber. One of the most significant oak lumber. Reducing the tendency to Presteaming is another pretreat-benefits of reduced kiln-drying time is surface check should allow the use of ment that shows promise for ac-reduced energy requirements. Heat more severe (and faster) drying celerating drying. In, 1975, Simpsonlosses from a kiln are directly propor- schedules without causing surface (12) reported steaming wood at 212" Ftional to drying time; thus a reduction checking. McMillen (4) explored this in saturated conditions before dryingin drying time will cut heat losses, potential on northern red oak and Increased subsequent drying rate ofReduction in lumber inventory is developed an accelerated schedule several species. Increases wereanother substantial benefit of re- estimated about 30 percent shorter largest for oak. Beyond the timeduced drying time. than the previously recommended kiln necessary to heat the wood to the

The concept of surfacing oak schedule for 414 northern red oak. In steaming temperature, the increase inlumber before drying dates back to 1972, McMillen and Baltes (5) reportedthe work of Gaby reported in 1963 (2). on further work on northern red oak ,Maintained at Madison, Wis., in cooperationwith the University of Wisconsin.Gaby showed that lumber produced and on white oak. They confirmed the ,Numbers italicized in parentheses refer toby circular sawing has many surface 30 percent estimate for northern red Literature Cited at end of report.

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Page 5: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

Table 1.-Drying schedules for 11 experimental dry kiln runs kiln.drying time of 4/4 oak lumber. Inthe approach a number of individualKiln ryi hnue Spces accelerating techniques are combinedrun' curve shdl

........... 1!! .............. ................. into one drying process. The in.PRELIMINARY EXPERIMENTS dividual techniques are the following:

1. Presurfacingla Figure 3 Conventional Red Oak

2a Figure 3 Accelerated Red Oak 2. Presteaming3b Figure 4 Conventional Red Oak 3. Accelerating kiln schedule4b Figure 4 Accelerated Red Oak 4. Schedule smoothing

ADDITIONAL EXPERIMENTS 5. High-temperature drying below5c Figure 5 Conventional Red Oak 18 percent moisture content6c Figure 5 Accelerated (steaming at 190" F) Red Oak The specific objectives were:7c Figure 5 Accelerated (steaming at 212* F) Red Oak 1. To determine the reduction in

8d Figure 6 Conventional White Oak kiln-drying time for 44 red oak9d Figure 6 Accelerated (steaming at 1900 F) White Oak and white oak lumber by apply-

10 Figure 6 Accelerated (steaming at 212" F) White Oak ing the combination of the five11 Accelerated (steaming at 190* F) Mixed Red/ accelerating techniques and to

White Oak determine the effect of the

presteaming temperature on the'Superscripts ot same letter denote end-matched material. reduction in drying time.

drying rate was found independent of have compared kiln-drying time of 4/4 2. To compare the amount of sur-steaming time. In 1976 Simpson (13) northern red oak lumber dried with a face and internal checks thatreported results of tests on 4/4 oak conventional, stepwise, manually develops in lumber dried underlumber dried by a conventional operated schedule to that dried by a these accelerated techniquesschedule. The lumber was steamea at schedule smoothed to continuous with the amount that develops185* F for 2 hours, then kiln-dried. A changes, and found an 18 percent when lumber is dried by conven-17 percent reduction in drying time time savings. tional means.was observed. The effect of steaming High-temperature (2300 F to 240* F)temperature on the reduction in dry- kiln drying is being used successfullying time has not been determined, in some softwood drying processes, Experimental

Wengert and Evans (19) explored and results in significant time andthe idea of automating dry kiln con- energy savings. The suitability of The research included a total of 11trol. An advantage of their automation high-temperature kiln drying for hard- kiln runs. After four preliminary runsscheme is any desired wet- or dry- woods has not been fully tested. The the results were promising enough tobulb temperature changes can be literature does not contain much in- continue with further tests, an addi-made automatically at any moisture formation on whether or not high- tional seven kiln runs. The dryingcontent desired. This suggests the temperature drying can be used schedules of the 11 experimental kilnpossibility for schedule without causing excessive degrade in runs are given in table 1."smoothing"- many small changes hardwood lumber. The technicalin kiln conditions instead of the large feasibility will very likely depend on Drying Timestep changes in a conventional, species and initial moisture contentmanually controlled schedule. The of lumber when high temperature is Preliminary experiments-Four kilnchanges can be made small enough applied. Success (lack of drying runs (1-4) were conducted from twoto approach a smooth, continuous defects) has been noted for several groups of experimental material. Eachchange over the entire drying species that have been partially air- two paired runs was a comparison ofschedule. The hypothesis is that dried before high-temperature drying. the response of lumber dried by therelatively large, abrupt changes in Wengert (16) has reviewed the combination of techniques with thatequilibrium moisture content condi- literature on high-temperature kiln of end-matched lumber dried conven-tions in a conventional kiln schedule drying of hardwoods and has dis- tionally. Northern red oak logssubject a wood surface to abrupt and cussed what little is known about the 8-1/2 feet long were obtained fromsteep moisture gradients that tend to factors causing success or failure. In southern Wisconsin and sawed intoaggravate or cause surface checking. addition, Wengert (17) conducted lumber 1-1/8 inches thick. EachIf these changes were smaller and some exploratory research on high- 8-1/2-foot board was cut into twomore numerous, lumber should be temperature drying of hardwoods, and equal lengths. One length was to beless susceptible to surface checking. observed that drying defects were kiln-dried by the combination ofFurthermore, if the tendency toward negligible in red oak predried to techniques; the other, conventionally.surface checking were reduced, it below 20 percent moisture content Of the two paired kiln loads, one setshould be possible to make these before application of high contained 25 boards; the other, 51smaller changes in kiln conditions a temperature. boards.little earlier in the drying schedule The objective of this investigation The conventional method of dryingand thus effectively accelerate the was to determine the technical was by the kiln schedule recom-schedule. Wengert and Baltes (18) feasibility of one approach to reduce mended for 4/4 red oak by Rasmussen

2

Page 6: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

(7), and is shown in table 2. The com- Table 2.-Kiln schedules recommended by Rasmussen for 4/4 northern red oak and whitebination of techniques was as oakfollows: Moisture Dry-bulb Wet-bulb

1.Prsufae ube t 11/2content temperature __..._temperature1. Presurface lumber to 1-1/32 ..... ... ........ . .... .......... ........ .. ...........t m.l .r..tr..e .. . ..... . ..te ...,tr.......

inches thick. Pct OF OF

2. Presteam lumber at 1900 F-3 to NORTHERN RED OAK (T4-D2)4 hours to attain 190* F and2 hours at constant 190 ° F. This 50+ 110 106was accomplished in a 50 110 1051000-board-foot experimental kiln 40 110 102

35 110 96with only the spray line on and 30 120 90an air speed as low as could be 25 130 80obtained, about 100 feet per 20 140 90minute (ft/min). 15 180 130

3. Use of an accelerated and WHITE OAK (T4C2)smoothed schedule. The 40+ 110 106allowable schedule accelerations 40 110 105that McMillen (4)and McMillen 35 110 102and Baltes (5) found acceptable 30 120 106for northern red oak and white 25 130 100

20 140 90oak after presurfacing are given 15 180 130in table 3. Without kiln automa-tion, in which very small changes Agric. Handb. 188 (7).in conditions can be made veryoften, the real potential of Table 3.-Accelerted schedules for northern red oak and white oak

schedule smoothing cannot be Moisture Dry-bulb Wet-bulbrealized. However, the same content temperature temperature EMCIphilosophy can be applied ....... ..... ........................... ............. ...manually to make some smaller Pct OF *F Pctschedule changes earlier and ac-complish some of the benefits of NORTHERN RED OAKsmoothing. Figure 1 shows the 55+ 115 ill 17.5accelerated schedule for north- 55 115 110 16.2ern red oak listed in table 3. The 45 120 112 13.4change points in the schedule 38 130 116 10.0are connected by straight lines in 30 130 94 4.6a manner that results in more 24 140 90 2.6

severe drying conditions (higher 18 180 130 3.3

temperature-lower EMC) at any WHITE OAKgiven moisture content point in 42+ 115 ill 17.5the schedule. Condition changes 42 115 110 16.2at every 5 percent moisture con- 37 120 112 13.4tent were taken from these 30 130 116 10.0straight lines to construct the 26 130 94 4.6kiln schedules for this work 21 140 90 2.6

(table 4). Air speed was 16_180_130 _ 3.3600 ft/min. EMC, equilibrium moisture content.

4. Drying at 230 ° F, no wet-bulbcontrol, below 18 percent Resultsmoisture content. 2. Steaming at 212 ° F was in a Drying Time

Additional experiments-Additional separate steam chamber because thekiln runs (5-10) were almost the same kiln could not attain steaming Preliminary experiments-Dryingas the preliminary runs except they , temperatures above 190 ° F. time curves for the two sets of com-included white oak as well as red Enough excess material from the parisons are shown In figures 3 and 4.oak, and each 8-1/2-foot board was logs provided about 300 board feet of in one comparison (runs 1, 2), the redcut into three 3C-inch sections to red oak and an equal amount of white oak dried conventionally fromallow three matched comparisons: oak to dry as full-length lumber by the 87.5 percent molsturp content toThe combined techniques with steam- accelerated techniques. It was dried 7 percent In 24.5 days, whereas theing at 2120 F, the combined tech- as mixed red and white oak by the matched material dried by acceler-niques with steaming at 190" F, and smoothed, accelerated red oak ated techniques required only 11 days

, conventionally dried material. The schedule (kiln run 11) (table 4). No to dry from 96 to 7 percent moisturerelevant kiln schedules are shown in conventionally dried control group content-a 55.1 percent reduction intables 2 through 4'and figures 1 and was included, time (fig. 3). In the other comparison

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230- Quality of Dried Material

The reductions in drying time are220 obviously highly significant and will

lead to reduced drying costs if quality210- of dried lumber is maintained.

* Preliminary experiments-in one200 SCHEDULES" comparison (kiln runs 1, 2), amount of

SEMI-smogTHED honeycomb was evaluated. Each-0McMILLEN'S ACCELERATED I board was crosscut into three pieces,

Z /90 - Mand honeycomb observed at each halfI of each fresh cut. Of 51 boards in the

18 0 - conventionally dried control, only one.R /board contained honeycomb, and

/70- there were only two individualhoneycomb checks. Of the 51 boards

,/ dried by accelerated techniques,-60 - seven contained honeycomb, and

there were 37 individual honeycomb150- checks.

IIn the other preliminary comparison

i40 - (kiln runs 3, 4), the number and totallength of both surface andhoneycomb checks were compared.

-Is'. /30 . No honeycomb was found in eitherSthe control or the accelerated group.

)/20 - Of the 25 boards in the control group,13 had surface checks after drying,

//o and the total length of the surfacechecks was 98.5 inches. Of the 25

I I I I I I I I boards in the accelerated group, 7had surface checks, and the total

70 60 1 50 I40 I30 120 1 /0 length of the surface checks was20- MOISTURE CONTENT (PCT) 70 inches.

Additional experimental-Thehoneycomb and the surface checkingcomparisons of the 25 boards in eachgroup of the red (kiln runs 5-7) and

/0I the white oak (kiln runs 8-10) lumber

Lu S are given in table 5 (three crosscutsas before).

The boards dried full-length (kilnO - run 11) and with no conventionally

dried control were end trimmed to ex-Figure 1.-Construction of smoothed-accelerated schedule for northern red oak. actly 8 feet, and cut into two 4-footM 148 923 pieces to expose honeycomb on inter-

nal surfaces (fig. 7). The number of(runs 3, 4), conventional drying re- reductions approach 70 percent. honeycomb checks on what were thequired 27.5 days from 89.5 to 7 per- The results for white oak (kiln runs ends and centers of the 8-foot boardscent moisture content, and the ac- 8-10) are shown in figure 6. Conven- was recorded; the results arecelerated drying techniques required tional drying required 22 days from 68 tabulated as follows:12 days from 88 to 7 percent moisture to 9 percent moisture content. Ac-content-a 56.4 percent reduction In celerated drying with steaming attime (fig. 4). 212 F required 9.7 days from 69 to

7 percent moisture content, and whenAdditional experiments-Drying steaming was at 190* F, 10 days were

time comparisons for red oak (kiln required to dry from 68 to 6 percentruns 5-7) are shown In figure 5. Con- moisture content. These are timeventional drying required 31 days reductions of about 55 percent.from 80.5 to 10 percent moisture con- Figures 5 and 6 show no practicaltent. Accelerated drying with steam- difference In drying time in the ac-Ing at 212' F required 8.8 days, from celerated techniques between steam-81.5 to 10 percent moisture content; ing at 190 ° F and 2120 F.with steaming at lg0 ° F, 8.1 days The lumber in full 8-112-foot lengthswere required to dry from 80.5 to 10 dried from 90.9 to 6 percent moisturepercent moisture content. These time content in 12 days.

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Page 8: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

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Page 9: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

Number of honeycomb Percent of exposed ends-checks

(End of 8-ft board) (Center of 8.ft board)

0 72.1 85.5 Ward (14, 15) and McMillen, Ward.1 12.9 7.8 and Chern (6) are making significant2 4.9 4.4 progress with this natural variability3 1.5 1.0 approach to oak drying. Their4 3.0 0 research is finding a correlation be-5 or more 5.6 1.0 tween an infection of certain bacteria

in the living tree and the occurrenceDiscussion of Results research does not answer these ques- of honeycomb and ring failure during

tions; it does show that substantial drying. If this infected oak lumber canBased on the results of this work, reductions in the drying time of 4/4 be identified and segregated by a

the accelerated schedule can dry oak oak lumber may be nearer to realiza- method that is practical on a produc-from green to 6 percent moisture con- tion than has been thought and can tion basis some of the "naturaltent in a range of 9 to 12 days. This is provide added impetus to define the variability" will be reduced, and eachabout one-half the time normally re- wood characteristics that separate segregation can be dried according toquired by conventional schedules. unacceptable from acceptable quality, the limits of its tolerance.Heat losses would therefore be re-duced by about one-half; becauseheat losses account for 20 to 33 per- 230 -cent of the energy consumed in kilndrying (11), a net reduction of approx- 220imately 10 to 15 percent (minussteaming requirements) may be realiz- .' 2/0 -ed by utilizing the accelerated Ischedules.20

The results of comparisons for 200quality are not as clearly defined as IU1those for drying time. Some com- , /90-parisons for quality showed no ap- S SCHEDULES:parent significant detrimental effect q /80 -__SEU SMOOTHEDresulted from the accelerated drying; Qt 'SMother comparisons did show a LAJ /70 - McMILLEN'S ACCELERA TEDdetrimental effect. Some oak ap-parently will tolerate this type ofrapid drying and maintain good quali- IA_ 1ty, and some oak will not tolerate it ,without developing surface and inter- /50 -val checks. /a

Although the results of this / 40 -research indicate the percentage of (4boards with drying defects may not . /30 --be too large, the uncertainty of thequality and the high value of oaklumber warrant caution in applying C 120 --

these accelerated schedules.In 1970 Rietz (8) also observed that //O

4/4 oak could be dried rapidly with aminimum of degrade. In kiln-drying J I I I I 2 O Ifrom green to 7 percent moisture con- 70 60 50 40 1301201 /0tent in 12-1/2 days, he noted only 20 MOISTURE CONTENT (PCT)minimal surface checking and 2,honeycomb. Conversely, those intouch with industrial drying of oakare aware that honey comb issometimes observed even after kiln J /0drying by relatively mild conventionalschedules.

Why does this contradictorybehavior occur? Is it considered just 0"natural variability" of a material ofbiological origin or will it be possibleto define causes of some of this Figure 2.-Constructon of smoothed-accelerated schedule for white oak.variability and thus reduce It? This M148 924

5

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Table 4-Smoothed, accelerated schedules for northern red oak and white ask SummaryMoisture Dry-bulb Wet-bulb EMCI Several observations are apparentcontent temperature temperature

from the results of this research. Dry-Pat OF OF Pet ing of some 414 oak lumber can be ac-

celerated to a point at which it can beNORTHERN RED OAK kiln-dried from green to 7 percent

55+ 115 111 17.5 moisture content in approximately 955 117 112 16.2 to 12 days; this represents an approx-50 119 113 15.1 imate 50 percent reduction in kiln45 120 112 13.4 time compared with that for conven-40 127 115 11.0 tional kiln schedules. Equally ap-35 132 112 8.030 136 98 4.3 parent is the fact that some 4/4 oak25 139 89 2.6 lumber will not tolerate the rapid dry-20 166 116 3.2 ing without excessive surface check-18 230 - - ing and honeycomb. This typifies the

WHITE OAK perverse nature of oak dryingcharacteristics, and leads to the con-

45+ 115 111 17.5 clusion there must be some basic45 118 113 16.2 properties or conditions inherent in40 120 114 15.135 123 114 12.7 the lumber that must account for this30 130 116 10.0 wide variation in tolerance to rapid25 136 96 4.0 drying. Future work in identifying20 148 98 2.9 these particular properties or condi-18 230 - - tions might well prove fruitful and

'EMC, equilibrium moisture content. allow for acceleration of schedules.

/00

90

80

60t-7

! CON r.ROL5,0

~40

Zs 30

A CCE1L ERA rD-/0 55.1 Pcr LESS C,,t I0

0 2 4 6 8 /0 12 14 16 18 20 22 24 26 28TIME (DAYS)

Figure 3.-Comparison of drying time of 414 northern red oak dried by convyen-tional schedule and by accelerated techniques (presurfaced, presteamed,accelerated- smoothed schedule, high-temperature dried below 18 percentMC).M 148 925

6

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IO0 -

/00

90 90

80 Z 80

~6 0L K6050- , I. '0.. ,CONTROL

Z0 K0,C0AITrROL

40- 40

20 U 20

r ~ /0-/0- 56 4 PC r LESS 0 -

0 II L _I ,

4 6 82 20 /2 26 28 /0 12 4 16 18 20 22 24 26 28 30 32

Figure 4.-Comparison of drying time of 414 northern red Figure 5.-Comparison of drying time of 414 northern red oakoak dried by conver#tional schedule and by accelerated dried by conven tional schedule and by accelerated tech-techniques (presurfaced, presteamed, accelerated- niques (presurtaced, presteamed at either 212* or 1900 F,smoothed schedule, high-temperature dried below accelerated-smooth schedule, high temperatures below18percent MC). 18 percent MC).

M148 926 M148 927

90

60

5 0

" CONTROL

30 - "-'oCo,0%

~03120 1900F O.1,

S/0 - 212"F

0 2 4 6 801/2/14/16/820 22TIME (DAYS)

Figure 6.-Comparison of drying time of 414 white oak dried by conventionalschedule and by accelerated techniques (presurfaced, presteamed at either212 ° or 190 F, accelerated-smooth schedule, high temperature dried below18 percent MC).

M148 928

'17

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2-T .

7 11-7 .

Figure 7.-Ends of oak lumber Show honeycomb (arrows indicate typical examples) after accelerated kiln

drying.

MA146 356

Table 5.-ComparIsons of the surface checking and honeycomb in 25 boards of red oakand white oak lumber

Surmat-iface checks HoneycombSta t Number of Total check Number of Total check

checked boards length honeycombed lengthboards

.................. ... .......................................................................................................

212'F 3 11.9 10 26.5

190 *F 9 59.5 7 11.2

Control 4 23.6 4 8.0

WHITE OAK

212*F 1 38.9 2 5.2190*F 5 20.4 1 0.8

Control 3 37.9 1 2.2

8 3.0-9-10/80

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Literature Cited1. Cuppett, D., and P. Craft.

1972. Kiln drying presurfaced 4/4 Appalachian oak. For. Prod. J. 22(6): 36-41.

2. Gaby, L. I.1963. Surface checking of white oak as related to mechanical processing.For. Prod. J. 13(12): 529-532.

3. Leney, L.1964. Checking of planed and rough red oak during kiln drying. For. Prod. J.14(3): 103-105.

4. McMillen, J. M.1969. Accelerated kiln drying of presurfaced 1-inch northern red oak. USDAFor. Serv. Res. Pap. FPL 122. For. Prod. Lab., Madison, Wis.

5. McMillen, J. M., and R. C. Baltes.1972. New kiln schedule for presurfaced oak lumber. For. Prod. J. 22(5):19-26.

6. McMillen, J. M., J. C. Ward, and J. Chern.1979. Drying procedures for bacterially infected northern red oak lumber.USDA For. Serv. Res. Pap. FPL 345. For. Prod. Lab., Madison, Wis.

7. Rasmussen, E. F.1961. Dry kiln operator's manual. U.S. Dept. Agric., Agric. Handb. 188.

8. Rietz, R. C.1970. Accelerating the kiln-drying of hardwoods. So. Lbrmn. July 1: 19-30.

9. Rietz, R., and J. Jenson.1966. Presurfacing green oak lumber to reduce surface checking. U.S. For.Serv. Res. Note FPL-0146. For. Prod. Lab., Madison, Wis.

10. Rice, W.1971. Field test of a schedule for accelerated kiln drying pre-surfaced1-inch northern red oak. Res. Bull. 595, Univ. Mass., Boston.

11. Shottafer, J. E., and C. E. Shuler.1974. Estimating heat consumption in kiln drying lumber. Life Sci. andAgric. Exp. Stat., Tech. Bull. 73. Univ. Maine, Orono.

12. Simpson, W. T.1975. Effect of steaming on the drying rate of several species of wood.Wood Sci. 7(3): 247-255.

13. Simpson, W. T.1976. Steaming northern red oak to reduce kiln drying time. For. Prod. J.26(10):35-36.

14. Ward, J. C., R. A. Harm, R. C. Baltes, and E. H. Bulgrin.1972. Honeycomb and ring failure in bacterially infected red oak lumberafter kiln drying. USDA For. Serv. Res. Pap. FPL 165. For. Prod. Lab.,Madison, Wis.

15. Ward, J. C., and D. Shedd.1979. California black oak drying problems and the bacterial factor. USDAFor. Serv. Res. Pap. FPL 344. For. Prod. Lab., Madison, Wis.

16. Wengert, E. M.1972. Review of high temperature kiln drying of hardwoods. So. Lbrmn.Sept. 15: 17-19.

17. Wengert, E. M.1974. Maximum initial moisture contents for kiln drying 4/4 hardwoods athigh temperature. For. Prod. J. 24(8):54-56.

18. Wengert, E. M., and R. C. Baltes.1971. Accelerating oak drying by presurfacing, accelerated schedules, andkiln automation. USDA For. Serv. Res. Note FPL-0214. For. Prod. Lab.,Madison, Wis.

19. Wengert, E. M., and P. G. Evans.1971. Automatic programming and control for steam-heated lumber drykilns. For. Prod. J. 21(2): 56-59.

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Page 14: FOREST PRODUCTS LAB MADISON VI ACCELERA TING THE KILN ... · Reducing kiln-drying time for oak lumber can reduce energy require-ments as well as reduce lumber in-ventories. In this

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