JR Dickens - ASME 1999

NDE Opportunities for Quality Assurance and Process Control in the Forest Products Industry

by

Robert Dickens, Ph.D. and Zhiyong Cai, Ph.D.

Temple-Inland Forest Products Corp.

Panel Products Division

Applied Research Center

NDE Opportunities for Quality Assurance and Process Control in the Forest Products Industry

Presented to

ASME NDE Engineering Division

6th NDE Topical Conference

San Antonio, Texas

April 20-22, 1999

April 20, 1999 ASME NDE Topical Conference 3

Temple-Inland -- Overview

• TIFPC is a $600 million subsidiary of Temple-Inland, Inc.– 3 operational divisions

• Forests

• Solid Wood

• Panel Products

– 20 manufacturing facilities• 6 in Solid Wood

– 5 sawmills, 1 plywood mill

• 14 in Panel Products– 4 particleboard, 4 gypsum wallboard, 3 medium density fiberboard, 1 fiber products, 1 cement

fiberboard, 1 laminating



– All operations run 24 hrs/day, 7 days/week• exception is laminating plant

– Total annual production of the Panel Products mills:• over 3.5 BILLION square feet

• enough to circle the globe 7 times!

– Temple has been expanding rapidly in the past few years . . .• 1996: started-up new particleboard mill in Arkansas

• 1996-97: renovated & expanded 3 older particleboard mills (TX, AL, GA)

• 1998: started-up new MDF mill in Arkansas; started-up new cement fiberboard mill in Waxahachie; acquired two MDF mills from MacMillan-Bloedel (Clarion, PA & Pembroke, ON, Canada)

• 1999: will complete startup of new gypsum wallboard mill in Tennessee

• 2000: ??? (potential to build another cement fiberboard plant or an oriented strandboard plant)



• All of the older mills have been upgraded to PLC control systems

• As a result of recent expansion:– 7 mills < 5 years old

– 5 mills < 3 years old

– 1 mill still under construction


High-Tech Control Systems

• Computerized control systems open up new possibilities for process improvement . . .

• . . . but closed loop processes depend on accurate measurement systems

• Individual machines can be controlled based on --– temperature

– pressure

– flowrate

– velocity

– position


High-Tech Control Systems

• But how do you measure the OUTPUT???– at present, we still rely on offline destructive testing for

quantitative measurement of mechanical properties (e.g., flexural strength, internal bond strength, modulus of elasticity)

• Disadvantages of offline testing:– time delay -- minutes to hours behind the actual process

– time consuming -- takes 1-2 technicians working around the clock

– QC test samples consume up to 1% of gross production

– small sample sizes lead to high probability of errors:• Type I error: missed defect --> shipped to customer (consumer risk)

• Type II error: false call --> product downgraded (producer risk)


NDE Already in Use

• Many of our mills already have several forms of NDE . . .– ultrasonic methods: blow/delamination detectors

– x-ray methods: density profilometers

– optical methods: NIR spectroscopic moisture measurement

– visual methods: two eyeballs and a bright light


Particleboard/MDF Blow Detector

• PB/MDF blow detector used to determine board integrity immediately after pressing– through-transmission ultrasonic technique

– operating principle: blast the heck out of the board and check to see if any sound gets through

• If YES --> board is in one piece ==> PASS

• If NO --> board has a blow or delamination ==> REJECT

– can be a headache to calibrate• too sensitive -- Type II errors -- reject good product

• not sensitive enough -- Type I errors -- defects passed to the downstream process, and possibly to the customer


Particleboard/MDF Blow Detector


X-Ray Profilometers

• X-ray profilometers used to measure density gradient through the thickness of the board– each PB & MDF plant has a desktop profilometer used to test

small QC samples

– our MDF operation in Arkansas is the only plant which has an on-line profilometer to give real-time feedback to the operator

• While density profile is an important feature of the board -- particularly for MDF -- it is not an adequate predictor of board strength

• Expensive -- desktop model costs $50,000


Infrared Moisture Detectors

• Moisture content one of the most critical variables in wood processing– depends on initial MC, mixing, drying, and blending variables

– excess moisture ==> blows

– insufficient moisture ==> delaminations

– less moisture requires longer press cycles

– moisture content can change rapidly

• On-line moisture meters utilize near-infrared sensing– reflectance characteristics of wood are related to MC

– may not be quite as accurate as oven-drying, but provides quick, continuous feedback


Infrared Moisture Detector


Visual Inspection

• Final QA check is visual -- 100% inspection– sander operator is responsible for grading the board

– at line speeds up to 140 fpm, operator only has about 3 seconds to grade each board

– assisted by bright lights and mirrors, but . . .

– . . . 3 seconds isn’t long to inspect 64 sq. ft.

• The heat is on the operator to provide consistent and accurate grading . . .

• . . . but even under the best conditions, the probability of a Type I error is about 20-30%


Some Recent Developments of Interest

• QNDE is no stranger to the forest products industry, e.g.:– 15 years ago Weyerhaeuser developed an on-line ultrasonic device

to measure internal bond of particleboard• utilized pitch-catch, rolling wheel transducers mounted above and below the

production line

• the device was deployed into four particleboard plants about 10 years ago

• word on the street is that no other installations were attempted, and that the original four installations are no longer in use (we don’t know why)

– 2 years ago a commercial manufacturer of blow detectors announced an “add-on” to their standard blow detector:

• basically, a computer with a neural network (black box)

• the vendor was eager to install the device in one of our MDF plants, but when we started asking questions, the communication came to a sudden halt



• No commercially available systems are known besides the “add-on” to the blow detector

• NIR techniques are starting to get warm:– spectral absorption is sensitive to more than just moisture --

evidently, changes in wood chemistry can be detected and related to product quality

– one plant in Sweden uses NIR to improve the consistency of their product

• spectroscopy performed on dried wood prior to resin addition

• authors claim that NIR feedback helps them know when/how to adjust the process to compensate for variations in the constituent wood



• NIR techniques will be the focus of a full-day technical track at the upcoming Forest Products Society meeting – at least six NIR papers are scheduled to be presented

– the handwriting is on the wall!


Why Keep Trying?

• NDE technology continues to improve

• Numerous controlled lab studies have shown promising results with respect to QNDE, and

• QNDE has many potential benefits

• The remaining challenge is to overcome the hurdle of transferring technically feasible methods from the lab to the plant!


What are the Overall Benefits of QNDE?

• reduced process variability– lower process targets

– reduced material and energy requirements

• reduced downfall and reject– less frequent destructive tests

– more timely operator response to changes in the output

– lower risk of Type I errors (defects propagating downstream)

• Improved utilization of press time– increased production capacity (press is usually the bottleneck)


What are the Overall Benefits of QNDE?

• Reduced risk of Type II errors– improved customer satisfaction (more consistent product)

– fewer product claims

• Reduced cost of quality– reduced labor required for destructive testing

– less time spent retesting product “on hold”

– reduced labor required for testing and ruling on product claims

– reduced “rework” by sales force and plant personnel (making peace with dissatisfied customers)


Benefits of QNDE for Continuous Process Improvement

• QNDE would provide rapid feedback to plant operators for making ongoing improvements in the process– easier to observe and understand the relation between process

inputs and the final product


Where are the Greatest Potential Benefits?

• Particleboard/MDF– 1.1 billion square feet per year– relatively high quality costs

• downgrade & reject

• complaints & claims

– QNDE needs to focus on improving the consistency of the product

• Gypsum wallboard– 2.1 billion square feet per year– much lower quality costs than PB/MDF

• less downgrade

• fewer claims

– QNDE needs to focus on improving the efficiency of the process


Where are the Greatest Potential Benefits?

• Exterior siding products (wood-based and cementitious)– 0.3 billion square feet per year

– relatively low quality costs

– QNDE may be useful either for quality assurance or process improvement


Where Do We Start?

• Air-coupled ultrasound appears to have the highest likelihood of success for on-line QNDE– avoids the major headaches associated with coupling

• can’t use liquid coupling

• wheel coupling is also problematic

– air-coupled ultrasound has benefited from recent improvements in transducer design and electronic instrumentation

• Our goal:– during the next few months, prove the feasibility of air-coupled

ultrasound under lab conditions

– by early 2000, deploy a passive system into one of our production operations


QMI Air Scan


Concluding Remarks

• Various forms of NDE are already in use in our mills

• The potential benefits of QNDE are enormous

• Technical hurdles remain, but continued advances in NDE technology mean we’re getting a little closer every day

JR Dickens - ASME 1999

Documents

greatest potential

coupled ultrasound

process control

quality assurance

recent developments

process improvement

nde opportunities

plant