The value of biannual corrugated engineering audits to your operation, Solutions! Online Exclusives, August 2003

online exclusives


Richard Croker
Technical Services
Georgia-Pacific Corporation
June 1, 2003

Editor’s note: Examples of engineering audit forms for corrugated operations are included at the end of this article.

Today’s market and customer demands are experiencing increasing levels of competition and a slack economy. Technology has made our business more involved and quality standards have definitely tightened. It is forcing us to look for techniques to improve our board quality, productivity, and reduce maintenance, man-hours, operating and overtime costs due to unscheduled downtime, waste levels.

I realize that this is a great deal to ask for in today’s environment of minimal capital expenditures but it is possible through the effective use of biannual corrugated engineering audits. Our equipment must be kept in top condition, as most of performance containerboard produced today is not as forgiving as what was produced a short decade ago. Corrugators and flexos must run at higher speeds with fewer defects. It’s no longer acceptable to have 1% to 2% defects. Automated setup equipment requires fewer defects as most boxes are packed by high speed packing machines. The target for 0 defects is now our goal. We are asked to deliver “Just-in-time” and not within normal lead times. Production levels must be high in order to stay cost competitive and we must adapt to a constantly changing market place.

The basic philosophy of an audit is to get the primary components of the corrugator back into O.E.M. (Original Equipment Manufacturer) condition. O.E.M. condition is when the corrugator was newly installed. Request your corrugator supplier(s) or supplier(s) for complete O.E.M. specifications if they are not already in your position. I can help you acquire this information when you supply the make, model, year of manufacture, and serial number of each machine center.

After completing the audit and correcting all of the problem areas identified, your equipment will run faster, smoother, and be more productive. You will have less downtime due to breakdowns, less waste, less costly maintenance, decreased energy costs, consistently improved box performance, and last but not least, MORE PROFITS, while still remaining competitive.

My Team’s Corrugated Mechanical Engineering Audit provides a full physical examination of the mechanical condition of the following production centers and their individual components:
  • Hot Plates
  • Double Backer
  • Glue Machine (GM)
  • GM Triple Deck Preheaters
  • Bridge Guide
  • Single Facer(s) (SF)
  • SF Preheaters(s)
  • SF Preconditioner(s)
  • SF Inclined Conveyor
  • Bridge
  • Roll Stands
  • Steam System

There are four basic phases of this evaluation which follow:

Phase One – Coordination Meeting
Before the audit begins, our team member will meet with the Plant’s Management Team. This usually consists of the General Manager or Owner, Plant Manager, Corrugator Supervisor or Superintendent, Maintenance Manager, and Corrugator Scheduler. This meeting will set the priorities for auditing the equipment, a tentative schedule for the audit, and coordinate the resources required by our team from the plant. If any of the audit’s downtime can be conducted in conjunction with scheduled Preventative Maintenance (PM), that is fine as long as both teams are not working on the same component. The time for each component is flexible and the longer we have the equipment, the more thorough we can be with the planned mechanical checks. Days are also flexible, but keep in mind, the day we check the glue machine, bridge guides, preheater stack, and hot plates, the corrugator will obviously not be producing board. The glue machine will have to be cleaned up and cleared of all paper before the audit can start. An operator and plant personnel must be available to start or jog the machine as required during the audit for safety requirements.

Phase Two – Conducting the Audit
Safety is the first priority of our Team. During the audit we will need the assistance of at least one maintenance person and others designated by Plant Management who will be trained during your equipment evaluation. A daily meeting with our assigned personnel will review our joint findings, and the combined board effects/wastes caused by the mechanical/adhesive/heat deficiencies identified.

We will check the following:

  • Rolls for wear
  • Coating thickness, flute depth, parallelism, and operation of corrugated rolls.
  • Steam vessels for proper temperature.
  • Proper siphon operation/position.
  • Steam supply/return legs and traps for proper operation
  • Liner and medium for proper temperatures and side-to-side temperature variations.
  • Hot plates, glue machine, preheater stacks, bridge guides, single facers, preheaters, preconditioners, roll stand, and splicers will all be checked for proper level and alignment.
  • All rolls for run out (Total Indicated Run out – TIR)
  • All roll bearings for wear (Bearing Clearance – BC)
  • All roll gaps for parallism
  • Fingers/Clean-out clearance and performance
  • Splicer operation
  • Roll stand operation
  • Adhesive performance – viscosity, pH, gel point, total oven-dry percent solids, and WPA/WRA resins.
  • Equipment upgrades

Phase Three – Out Brief
The detailed equipment system out brief with Plant Management will apply suggested priorities on equipment adjustment, mechanical issues, repair, modifications, or upgrades along with future equipment installations to improve board quality, productivity, and plant profitability.

We also discuss specific serious mechanical issues:

  • How issues contribute to current plant problems.
  • How corrective actions will eliminate plant issues.
  • Equipment improvements and upgrades.
  • Typical areas of improvement:
    • Increase productivity
    • Decrease waste
    • Decrease downtime
    • Decrease overtime
    • Decrease energy costs
Phase Four – Follow-Up
This visit enables the plant to ensure they have gotten 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.

A possible schedule for a typical double wall plant would be as follows:

Monday Quick familiarization tour of the plant
1 Hour meeting to plan audit
Tuesday Initial survey of equipment/audit preparation
8 a.m. – 12 p.m. – Audit SF #1
1 p.m. – 5 p.m. – Audit SF #2
Wednesday 8 a.m. – 11 a.m. – Review of findings and training videos for maintenance/other assigned personnel.
12 p.m. – 5 p.m. – Glue machine/Bridge Guides/Preheaters Stack/Hot plates/Double backer.
Thursday 8 a.m. – 12 p.m. – Audit SF #3
3 p.m. – 5 p.m. – Out brief with GM, PM, MM, Corrugator Supervisor, other plant personnel as appropriate.

NOTE: In order to make this an on-going dynamic exercise, you have to have the people who run the machine do this work and be taught these vital techniques. After all, who knows more about how this machine runs and its problems than the crews who run it day-after-day? I firmly believe that after each day’s audit efforts we need to come back to the classroom and discuss what we have found. It is pivotal to the plant’s future that we discuss why certain components have to be repaired or replaced as soon as possible. I think the most important thing you have to do is start to integrate some of these checks into your preventative maintenance program. Some of these critical checks should be performed in every PM.

Maintenance certainly has to be fully involved during the corrugator audit but the basic audit should be performed by the personnel that run the machine. This not only gives them ownership in the equipment that they run, but they will take better care of it to insure that it runs better, consistently. Everyone wins!!

The second audit of your biannual audit should be conducted by your operators and maintenance crews. You will find fewer areas that will require repairs and adjustments with each audit performed. This net result of your team’s efforts will significantly enhance production efficiency; growing production records; improved combined board quality and box performance; lower waste levels; an inability of your competitors to compete against you, and most importantly growing market share and profits.

We estimate an increased production level of 5 to 30+% and a waste savings of 1 to 5+%, depending upon the corrugator’s condition. It is also dependant upon how much you are willing to spend to bring the corrugator back into O.E.M. condition.

Are you ready to make the biannual audit work for you?
Can you picture yourself as the leader of the pack?
Are you ready to get fully involved and make this simple process work for you?

Once you decide to move forward, you will need the tools, training, and engineering forms necessary to conduct the audit. I have attached a list of tools required and some sample engineering audit forms to be used as a guide to develop your own in-house forms.

We want to make sure that all the machine’s rolls are the correct diameter, proper crown, roundness, level, and paralleled. We want to insure all bearings have minimum clearances. Before going further, I would like to explain the tools used in the audit along with the O.E.M.’s maximum allowable specifications.

Easy Read Pi Tape
In this instance Pi stands for 3.14- the arc of a circle. It will accurately measure the diameter of a roll to one thousandth of an inch (.0254mm). These measurements are necessary for the kind of work we do with your equipment. We use the Pi tape to evaluate proper roll diameter, roll wear, and crown. Spec +/- .001” (.0254mm).

Magnetic Base and Dial Indicator
This 100 lb. pull magnetic base has an adjustable gooseneck that is more versatile than the standard model. This may sound like overkill, but when you have four to five layers of paint to penetrate, the magnet will support a 10” to 12” (25.4 cm to 30.48 cm) extension rod necessary to reach difficult places. You will need it for a firm hold while making measurements. A dial indicator is used to measure the roundness of the roll. We call this Total Indicated Run-Out (T.I.R.). (See TAPPI’s TIP 0304-56 – T.I.R. and its impact on combined board quality.) We also use this instrument to measure the bearing clearance (B.C.) of each roll. (See TAPPI’s TIP 0304-47 – Bearing clearance checks and their impact)

Generally T.I.R.’s maximum allowable specs on rolls are as follows:

  • Cold rolls - .005” (.127mm)
  • Applicator and meter rolls – replace at .004” (.100mm)
  • Hot rolls - .005” (.127mm)
  • Preheater, Preconditioner drums - .010” (.254mm)
  • Corrugator rolls (must be out of the machine in most cases) and pressure rolls – 002” (.0508mm)
    • Note: Heated rolls should be checked when at temperature.

Generally the maximum allowable spec on a roll’s bearing clearance is as follows:

  • Cold rolls - .005” (.127mm)
  • Applicator and meter rolls -.002” (.0508mm)
  • Hot rolls, drums - .010” (.254mm)
    • Note: Heated rolls should be checked when at temperature.

Corrugator Roll Depth Gauge
This instrument is used, once zeroed, using the appropriate gauge blocks for the corrugator roll’s flute, to measure chordal flute depth (measured from the tips of two adjacent flutes to the base of the flute). This check should be accomplished cold for safety reasons. Maximum acceptable wear which will permit reconditioning are as follows: .003” (.076mm) initial coating – maximum wear is .002” (.051mm), .006” (.152mm) initial coating – maximum wear is .003” (.076mm).

Note: Rolls should be checked monthly after 60,000,000 lineal feet (18,288,000m) have been run to check for roll wear. (See TAPPI TIP 0304-73 Checking chrome thickness on corrugator rolls)

Note: Worn rolls increase take-up factor and consumes more medium.

Corrugated Roll Biddle Chrome or Tungston Carbide Thickness Gauge
This simple instrument utilizes a highly sensitive spring and magnet to check coating thicknesses down to as low as .0001” (.0025mm). This check should be accomplished cold for safety reasons. Rolls should be checked monthly after 60,000,000 lineal feet (18,288,000m) have been run to check for roll wear. See maximum wear limits listed above in the “Corrugated Roll Depth Gauge” write-up. (See TAPPI TIP 0304-73 Checking chrome thickness on corrugated rolls)

Corrugator Roll Parallelism Check with NCR (National Cash Register) Paper
This procedure is used to check the parallel of corrugator rolls when they are at operating temperature (Safety procedures must be taken to avoid burns). When the NCR strips are fed through the corrugator rolls, the flute tips leave their impressions on the NCR paper where contact occurs. (See TAPPI TIP 0304-62 Checking the parallel of corrugator rolls with “NCR”)

Note: Misaligned rolls can result in medium fracture, leaning flutes, hi-lows, and reduced combined board caliper, roll life.

Machinist Level and 100’ (30.48m) Steel Tape
These easy to use instruments once calibrated are utilized to measure the components of the corrugator for proper level and alignment. Specification maximum is +/- .006”/foot (+/- .152mm/. 3048m).

Example: A 98” (245 cm) wide corrugator’s spec is +/- .049”/8.17 feet (+/- 245cm/. 3048m) for level and for proper alignment +/- 1/8” or .125” (+/- 3.175mm). (See TAPPI article “The Machinist Level” by John R. Troyke, and “The Importance of Keeping your Corrugator Leveled and Aligned” by Richard J. Croker)

Note: Out of level or missalignent corrugator components can cause twist warp, flip up or down warp, loose edge bond, misalignment waste, and abnormal bearing wear.

Stainless Steel Feeler Gauges 1’ (2.54cm) Long .003” to .040” (.076mm to 1.016mm)
Utilized to check meter, applicator, rider roll gaps +/- .001” (+/- .025mm) side-to-side measurements and for single facer applicator roll pan dam wear – “C” Flute = .0015” (.038mm); “B” Flute = .001” (.025mm), and “E/F/G/N/O/Z” Flutes = 0” (.000mm).

Steel Scoring Rule or Straight Edge 18” (45.72cm) Long
Utilized to check the level of the double backer’s hot plates for proper level. The hot plates must be maintained so that the leading edge of any plate is slightly lower than the trailing edge of the preceding plate. We utilize a step down spec of .003” to .005” (.076 to .127cm) when measured hot. (See TAPPI TIP 0304-66 The impact of double backer hot plate level on board quality and how to measure it)

Note: This test must be accomplished at normal operating temperature thus protective gloves must be used.

Infrared Pyrometer with Laser Sighting
Utilized to conduct temperature audits on all of the corrugator’s steam heated vessels. The pyrometer is a very valuable and safe tool to use in conjunction with an inexpensive primer gray spray paint. This paint is used to dull a heated surface to insure accurate measurements on top, and the very bottom of all steam heated rolls and hot plates. We are targeting an idle temperature of not less than 350ºF (177ºC). If the temperature variation top to bottom is high you may have a siphon placement or steam balance issue which will have to be addressed. (See TAPPI TIP 0304-66 Conducting a corrugator temperature audit)

Note: Set the pyrometer’s emissivity (reflective index) to .95 prior to use for accurate results.

The pyrometer is also used to check the “side-to-side” temperature variation on the liners, single face web (open face), and medium at a point just 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 6ºF (3ºC) when measured at a constant line speed. The measurement is taken at about the same distance from the heated vessel and inward at about 1 foot (.3m) in on each side of the sheet to insure measurement accuracy.

Note: If the “side-to-side” temperature variation exceeds 6ºF (3ºc) on “A/B/C/D/K” flutes or 3ºF (1ºc) on all micro flutes, you may have a level, alignment, or liner/medium winding issue. This may cause twist warp, flip up or down warp, loose edge bond, low ECT performance, waste, and reduced production speeds. (See attached sample “side-to-side” liner, single face web temperature audit form.)

I would like to address the matter of ordering rolls. We’ve touched on this subject earlier. It is important to set up an audit check on all incoming rolls to protect yourself. Make sure the diameter and crowns are correct and that there is no more than .0005” T.I.R. in the applicator and meter rolls. This can be accomplished by building a set of roll support stands for use in T.I.R. measurements. (Detailed drawings and parts are available if requested.) Tell your supplier that you are going to check everything he sends you and that the rolls will be returned if they don’t meet your T.I.R. spec of .0005” (.0127mm) at their cost. Supply the QEM with your specs. Do not install an out of spec roll! Causes more harm than good!

Finally, you are ready to accomplish the actual audit. Plan on spending at least four hours on each machine center unless you divide into two or more audit teams with the appropriate training and tools. Supply the auditors with the machine specs so that they can determine immediately how close the rolls are to specification. I suggest that you computerize the machine specifications and audit results on an Excel spreadsheet to compare the current audit with the past audit to track component wear and failure rates. This simple procedure will help you establish “Predictive Maintenance Failure Points” thus significantly reducing unplanned downtime.

Do you want to become the best in your business by achieving consistent gains year after year in productivity, efficiency, box performance, waste reduction, customer satisfaction, and market share?


All it will take from you to make this happen is having the initiative and the staying power to complete two audits per year thus keeping your corrugator in OEM condition! Know what you want to accomplish and keep this goal firmly in sight.

I hope this paper gives you a clear picture of what we accomplish during an audit. Please call if you need help or ask questions.

Contact the author by email at

Examples of engineering audit forms for corrugated operations.

The value of biannual corrugated engineering audits to your
The value of biannual corrugated engineering audits to your operation, Solutions! Online Exclusives, August 2003
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Author: Croker, R.