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The value of biannual corrugated engineering audits: biannual audits can help corrugating operations "tune up" and operate more efficiently.

Today's market is experiencing increasing levels of competition and the effects of a slack economy. Technology has made business more involved, and quality standards have definitely tightened. These conditions force companies to seek techniques to improve board quality and productivity and reduce maintenance, man-hours, and operating and overtime costs due to unscheduled downtime and waste levels.


Biannual corrugated engineering audits make this possible. The basic philosophy of an audit is to return the primary components of a corrugator to their original equipment manufacturer (OEM) condition. OEM condition is what existed on installation of the unit.

After completing an audit and correcting all the problem areas, equipment will run faster and smoother and be more productive. The results will be less downtime due to breakdowns, less waste, less expensive maintenance, decreased energy costs, consistently improved box performance, and more profits.


The evaluation consists of four basic phases:

* Coordination meeting: Before an audit begins, a team member will meet with the management team of the plant. This usually includes the general manager or owner, plant manager, corrugator supervisor or superintendent, maintenance manager, and corrugator scheduler. The meeting will establish priorities for auditing the equipment, devise a tentative schedule for the audit, and coordinate the resources required by the plant team.

* Conducting the audit: Safety is the first priority of an audit team. During the audit, at least one maintenance person, and others designated by plant management who will undergo training during the equipment evaluation, will assist. A daily meeting with assigned personnel will review joint findings and identify the combined board effects and wastes from the mechanical, adhesive, and heat deficiencies clearly identified.

* Out brief: The detailed equipment system out brief with management will apply suggested priorities on equipment adjustment, mechanical issues, repair, modifications, or upgrades and consider future equipment installations to improve board quality, productivity, and plant profitability.

* Follow up: This visit ensures that the plant has achieved the maximum benefit from the mechanical audit:

* Review completed recommendations

* Determine if corrective actions have addressed plant issues

* Assess priorities and plant requirements

* Ensure plant can incorporate audit checks into their preventative maintenance program.

Checks must be integrated into a preventative maintenance program. Every paper mill should perform these critical checks.

Operators and maintenance crews should conduct the second audit of a biannual audit. Fewer areas will require repairs and adjustments with each audit performed. This net result of the efforts of an audit team will significantly enhance production efficiency, increase production records, improve combined board quality and box performance, lower waste levels, increase competitiveness, and grow market share and profits. Depending on the condition of a corrugator, increased production can be 5%-30%, and waste savings can be 1%-5%.


The following are key tools used in an audit:

* Easy read Pi tape: This tape will accurately measure the diameter of a roll to 0.001 in. (0.0254 mm).

* Magnetic base and dial indicator: A 100-lb. pull magnetic base has an adjustable gooseneck that is more versatile than the standard model. It provides a firm hold while making measurements. A dial indicator measures the roundness of a roll. This is total indicated run-out (TIR). (See TAPPI TIP 0304-56: TIR and its impact on combined board quality.) This instrument also measures the bearing clearances (BC) of each roll. (See TAPPI TIP 0304-47: Bearing clearance checks and their impact.)

* Corrugator roll depth gauge: After zeroing and using appropriate gauge blocks for calibration, this instrument measures the chordal flute depth of the corrugating rolls. (See TAPPI TIP 0304-73: Checking coating thickness on corrugating rolls.)

* Corrugated roll biddle chrome or tungsten carbide thickness gauge: This simple instrument uses a very sensitive spring and magnet to check coating thicknesses as low as 0.0001 in. (0.0025 mm). (See TAPPI TIP 0304-73: Checking coating thickness on corrugating rolls.)

* Corrugator roll parallelism check with NCR paper: This procedure checks the parallel alignment of corrugating rolls at operating temperature. (See TAPPI TIP 0304-62: Checking the parallel of corrugating rolls with NCR.) Misaligned rolls can result in medium fracture, leaning flutes, hi-lows, and reduced combined board caliper and roll life.

* Machinist level and 100 ft. (30.48 m) steel tape: After calibration, these instruments measure the components of the corrugator for proper level and alignment. Specification maximum is [+ or -] 0.006 in./ft. ([+ or -] 0.152 mm/3048 m). Note that out of level or misaligned corrugator components can cause twist warp, loose edge bond, misalignment waste, and abnormal bearing wear.

* Stainless steel libeler gauges 1 in. (2.54 cm) long with thicknesses of 0.003-0.040 in. (0.076-1.016 mm). These can be used to check meter, applicator, and rider roll gaps to within [+ or -] 0.001 in. ([+ or -] 0.025 mm) side-to-side measurements. They can also measure single facer applicator roll pan dam wear--"C" flute = 0.0015 in. (0.038 mm), "B" flute = 0.001 in. (0.025 mm), and "E/F/G/N/O/Z" flutes = 0.0 in. (0.0 mm).

* Steel scoring rule or straight edge 18 in. (45.72 cm) long: This checks the level of a double backer's hot plates for proper leveling. The hot plates must be such that the leading edge of any plate is slightly lower than the trailing edge of the preceding plate. An acceptable level is 0.003-0.005 in. (0.076-0.127 cm) when measured hot. (See TAPPI TIP 0304-66: The impact of double backer hot plate level on board quality and how to measure it.)

* Infrared pyrometer with laser sighting: This is useful to conduct temperature audits on all steam-heated vessels of a corrugator. A target is an idle temperature of not less than 350 [degrees] F (177 [degrees] C). A high temperature variation from top to bottom may indicate a siphon placement or steam balance issue that will require fixing. (See TAPPI TIP 0304-66: Conducting a corrugator temperature audit.)

The pyrometer also is used to check the "side-to-side" temperature variation on the liners, single face web (open face), and medium at a point immediately after leaving the preheaters, pressure rolls, preconditioners, and hot plates. The maximum allowable side-to-side temperature variation on liner, medium, single face web, and combined board is 6"F (3C) measured at a constant line speed.


At this point, you can perform an actual audit. Plan to spend at least 4 hours on each machine center unless two or more audit teams with the appropriate training and tools are available. Supply the auditors with the machine specifications so they can determine immediately how closely the rolls meet specification.

Computerizing the machine specifications and audit results using spreadsheet software allows comparison of a current audit with a previous audit to track component wear and failure rates. This simple procedure will help establish "predictive maintenance failure points" and significantly reduce unplanned downtime.


Having the initiative and the staying power to complete two audits per year can keep a corrugator in OEM condition. This will allow consistent gains each year in productivity, efficiency, box performance, waste reduction, customer satisfaction, and market share.

Editor's Note: This article is an abridged version of the original. To access the complete article as well as several graphics illustrating engineering audits, please go to, click on Solutions!, and go to August Online Exclusives.

About the author: Rick Crocker is director, technical services, for Georgia-Pacific Corporation. Please contact him by email at
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Title Annotation:Practical Solutions
Author:Croker, Richard
Publication:Solutions - for People, Processes and Paper
Date:Aug 1, 2003
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