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  • Quality Drying ofHardwood LumberGuidebook-ChecklistR. Sidney BooneMichael R. MilotaJeanne D. DanielsonDean W. Huber

  • Abstract Contents

    The IMPROVE Lumber Drying Program is intended toincrease awareness of the lumber drying system as acritical component in the manufacture of quality lumber.One objective of the program is to provide easy-to-usetools that a kiln operator can use to maintain an efficientkiln operation and therefore improve lumber dryingquality. This report is one component of the IMPROVEProgram. It contains a Guidebook-Checklist for QualityDrying of Hardwood Lumber that kiln operators or own-ers can use to readily evaluate how well their operationsrate on those factors that most strongly affect dryingquality, with particular emphasis on kiln operation andmaintenance and lumber handling. Appendix 1 containsa shortened version of the checklist for easy duplicationand filing. Appendix 2 contains the same checklistitems; however, the information is arranged by dryingsystem components for convenience in checking indi-vidual components.

    January 1992

    Gen. Tech. Rep. FPL-IMP-GTR-2. Madison, Wl: U.S.Department of Agriculture, Forest Service, ForestProducts Laboratory. 56 p.

    A limited number of free copies of this publicationare available to the public from the Forest ProductsLaboratory, One Gifford Pinchot Drive, Madison, WI53705-2398. Laboratory publications are sent to morethan 1,000 libraries in the United States and elsewhere.

    The Forest Products Laboratory is maintained in coop-eration with the University of Wisconsin.

  • Quality Drying of Hardwood LumberGuidebook-ChecklistR. Sidney Boone, Research Forest Products TechnologistForest Products LaboratoryMadison, Wisconsin

    Michael R. Milota, Assistant ProfessorOregon State UniversityCorvallis, Oregon

    Jeanne D. Danielson, Supervisory Research Forest Products TechnologistForest Products LaboratoryMadison, Wisconsin

    Dean W. Huber, Program Manager, Forest Products Utilization and MarketingState & Private Forestry, Region 5San Francisco, California

    complete guidebook-checklist for drying quality hard-Introduction

    The IMPROVE Lumber Drying Program is intended toincrease awareness of the lumber drying system as acritical component in the manufacture of quality lumber.The goals of the program are to help sawmill, furniture,flooring, molding, and cabinet plant personnel improvelumber drying quality by identifying sources of dryinglosses, both grade and volume. Operation of the dry kilnis only one factor that determines lumber drying quality.Each step of the lumber manufacturing process affectslumber drying quality-from the time logs are felled inthe woods until the lumber leaves the unstacker afterdrying. The IMPROVE Lumber Drying Program isdesigned to systematically evaluate the drying operationand identify areas contributing to poor lumber productquality, both in the drying operation stage and at everyprior stage of lumber manufacture. Therefore, causes ofdrying quality losses can be corrected at their source,rather than trying to compensate for them in the kiln.

    A package of analytical tools for the IMPROVE programis under development. These tools will measure andimprove processing efficiency and product quality insawmills, veneer mills, and plywood plants. Methods willbe provided to evaluate how effectively logs are beingconverted into end products, to identify opportunities toincrease product yield and value, and to predict theresults of proposed improvements.

    One objective of the IMPROVE Lumber Drying Programis to provide easy-to-use tools that a kiln operator canuse routinely in daily work around the kilns without hav-ing to perform special studies or interfering with produc-tion. To help fulfill this objective, this report contains a

    wood lumber. The guidebook explains the impor-tance of each item on the checklist and describeshow to evaluate it. if questions arise while using thechecklist, you can refer to the guidebook for adetailed explanation. The guidebook also provides aquick reference on drying quality. Kiln operators canuse the checklist to readily evaluate how well theiroperations rate on those factors that most stronglyaffect drying quality. Particular emphasis is given tokiln operation as well as maintenance and lumberhandling. In addition to the guidebook and checklist,Appendix 1 contains a summary checklist for easyduplication and filing. Appendix 2 contains the samechecklist items but listed according to drying systemcomponents for convenience in checking individualcomponents.

    The guidebook-checklist is intended to be used witheither steam-heated or dehumidification kilns. It is notpractical or our intent to cover all the detailed compo-nents of the lumber drying system. We encourageyou to use the guidebook-checklist and adapt them toyour individual situations. Many other maintenanceand operating factors are also important, but thesedo not have as direct a bearing on drying quality,although they should not be neglected. Chapter 4 ofthe Dry Kiln Operators Manual (DKOM)1 containsmaintenance checklists and discusses many factorsof kiln maintenance. Kiln manufacturers can alsosupply maintenance checklists and additional infor-mation.

    1US Department of Agriculture, Forest Service. 1991. Drykiln operators manual. Agric. Handb. 188. Washington,DC: U.S. Department of Agriculture, Forest Service. 274 p.

  • Guidebook-Checklist

    The guidebook-checklist can be used three ways:(1) to make an overview of the entire kiln operation;(2) to closely check or monitor a particular kiln that issuspected of causing drying problems; and (3) to moni-tor the effects of improvements by providing a base-line for later comparison.

    The checklist is a working tool and to get the most valuefrom it, you must physically examine various equipmentand systems around the kiln. Only by actually observingthe items on the checklist can you accurately assessyour kiln operation, The checklist is arranged so thatitems located near each other can be checked together.For example, all observations of values and controlsnormally found in the control room are listed together onthe checklist, and checks of stacking and snickering aredone at the dry end. A shortened version or summary ofthe checklist (without the rating key) is given in Appen-dix 1. We suggest you make copies of this shortenedversion to write on and keep with your kiln records.

    For convenience in checking individual systems, suchas air circulation or heating, a summary of the checklistitems arranged by drying system components is givenin Appendix 2.

    Rating System

    Each item on the checklist has a rating key based ona scale from 4 (high) to 1 (low). Each level of rating isfurther described in the guidebook. The high rating of 4is intended to be attainable, but challenging, for mostof the industry. The low score of 1 indicates a strongneed for improvement. In a well-maintained and well-operated kiln, most of the ratings should be 4 and 3.

    Overviewing the Kilns

    When using the checklist as an overview, it is not nec-essary to look at all items in the same kiln. You maycomplete the checklist items relating to an empty kiln inone kiln, then do the ones related to a running kiln at asecond kiln, and check the dry end as a third kiln isbeing unloaded. This overview can be completed inseveral hours or less.

    Studying One Kiln

    Past experience or the overview checklist may suggestone particular kiln is causing drying quality problems.You can also use the checklist to evaluate that one kilnfor all steps from loading through unloading. You willhave to keep the checklist for each step of the dryingcycle as it is completed.

    Monitoring the Effectsof Changes

    If changes are made that affect the drying operation,either at the kiln or in the prior lumber handling, you canuse the checklist to monitor how these changesaffected drying quality. Rate the kiln or operation beforethe changes are made and save the checklist. Repeatthe checklist rating after the changes have been made.You can then compare the before and after ratings forthe effect of these changes.

    How to Follow the Checklist

    The checklist is arranged so that items are groupedtogether by the area of the kiln or yard where they arechecked. Begin in the kiln control room. The first seriesof questions ask about standard operating procedures.These relate to maintenance procedures and mainte-nance schedules, recordkeeping, and communications.These items should be checked regularly to preventproblems or correct them before they become serious.

    In the control room, you will be asked to check thesteam valves and controls to see that these are in work-ing order and that the desired schedule is actually fol-lowed.

    From the control room, go to the fan deck and the kilnroof. Here, you will check the fans, heating coils, andvents.

    In the kiln yard area, accurately measure the stickersand bolsters for uniform size. Use dial calipers or amicrometer, if possible, to check sticker and bolsterthickness.

    Then, find an empty kiln and check for condensation,clean reheat coils, and a good water supply to the wet-bulb. Next, turn on the steam to check the steam pipesand heating coils, and turn on the steam spray to checkit for leaks and uniform distribution of steam.

    From the empty kiln, move to a kiln that is being loaded.Check the loading practices as packages are loaded onthe kiln trucks or load supports. After that kiln is loaded,check that the package loading and use of baffles willensure proper airflow through the packages. Duringstartup, check the traps and the airflow across the wet-bulb. While the kiln is operating, check for drainage orleaks, and confirm that the fan reversals actually areoccurring.

    Finally, go to a kiln that is ready to be unloaded


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