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Title / Control all MD and CD warp during paper changes for fibreboard manufacture
Level / 4 / Credits / 10
Purpose / People credited with this unit standard are able to: define diagonal warp and describe its causes; demonstrate knowledge of the actions needed to remove or reduce diagonal warp; control machine directional (MD) and cross directional (CD) warp at changes of paper; take proactive measures at the times of paper changes to minimise warp occurring; rectify MD and CD warp; work in collaboration with other corrugator crew in accordance with workplace practices; and follow safety requirements for the equipment being used.
Classification / Fibreboard Packaging > Fibreboard Manufacture
Available grade / Achieved
Entry information
Critical health and safety prerequisites / Unit 340, Demonstrate knowledge of safe working practices in the printing and graphic pre-press industries, or demonstrate equivalent knowledge and skills.
Recommended skills and knowledge / Unit 21620, Correct faults in a single face web for fibreboard manufacture, or demonstrate equivalent knowledge and skills.
Explanatory notes
1All workplace practices must meet any applicable and recognised codes of practice, and documented workplace health, safety, and environmental procedures for personal, product, workplace health, safety, and environmental matters, and the obligations required under current law including the Health and Safety in Employment Act 1992, Hazardous Substances and New Organisms Act 1996, Resource Management Act 1991, Privacy Act 1993 and their subsequent amendments.
2Workplace practices refer to the documented procedures for the equipment and/or workplace.
3‘Cross Directional’ and ‘Machine Directional’ are abbreviated to CD and MD where these terms occur.
4Diagonal warp is referred to in some workplaces as ‘twist warp’ or ‘propellor warp’.
5‘S warp’ is not diagonal warp, but is a variant of cross directional warp where differing degrees of warp are present across the one board width. ‘S warp’ is not addressed in this unit standard.
6As equipment configuration and sophistication varies between workplaces, general control over warp is achieved by varying proportions of direct control over the different corrugator work stations, and by co-ordinating the efforts of other operators at these work stations.
7The process for defining and calculating warp percentages for the purposes of assessment is as follows: when a warped board is laid on a level surface so as to form a shallow arch, the maximum vertical deviation from the horizontal is expressed as a percentage of the board dimension that forms the arch. Warp is assessed at take-off, and thus excludes ‘post warp’.
8Actions and measures available as listed at explanatory note 10, and referred to elsewhere may be taken in any combination or sequence which is in accordance with workplace practices and equipment specifications and configuration.
9Where referred to, ‘plant listed maximum speed’ is that determined by each workplace as appropriate for specific production conditions taking into account paper grades, flutes, run length and chop length.
10Actions available to prevent, minimise or rectify warp are as follows:
(For CD warp)
Adjustments to:
–adhesive application levels
–wraps at bridge single face pre-heater
–wraps at double backer liner pre-heater
–hot plates temperature
–platen section pressure
–wraps at single facer liner pre-heater
–wraps at single facer medium preconditioner
–amount of loops on bridge.
Use of:
–double backer water sprays
–main belt steam showers
–single facer medium steam showers
–single facer water sprays.
(For MD warp using double backer and platen section) Tension control actions:
–cleaning hot plates
–adjustment at any or all of double backer liner pre-heater brake, bridge single face pre-heater brake, bridge brake, double backer liner brake
–changes to paper lubrication systems, paper guides, bridge single facer vacuum level.
(For MD warp using single facer)
Adjustments to:
–amount of loops on bridge
–single face liner brake.
Outcomes and evidence requirements
Outcome 1
Define diagonal warp and describe its causes.
Evidence requirements
1.1Diagonal warp is defined in terms of the axis of the warp running diagonally across the board.
1.2The conditions of reel stock that might cause diagonal warp to occur are described.
Rangeincludes but is not limited to – fibre orientation, slack edges in reel, paper grammage or calliper not within specification.
1.3Tension inequalities that might cause diagonal warp are described.
Rangeincludes but is not limited to – slack edges in reel, reel stands out of line, wrap arms not level, rollers not parallel, misalignment of top belt, uneven pressure roller pressures.
1.4Moisture variations that might cause diagonal warp are described.
Rangeincludes but is not limited to – varying moisture levels across the paper width, uneven adhesive application, uneven heat application.
1.5Equipment faults that might cause conditions leading to diagonal warp are described.
Rangeincludes but is not limited to – reel stands, wrap arms, rollers, top belt.
Outcome 2
Demonstrate knowledge of the actions needed to remove or reduce diagonal warp.
Evidence requirements
2.1Tension control actions are listed and their effects described in accordance with workplace practices and equipment configuration.
2.2Moisture control actions are listed and their effects described in accordance with workplace practices and equipment configuration.
2.3Knowledge that switching single facer and double backer paper reels may sometimes cure diagonal warp is explained.
2.4Machine specification checks, where diagonal warp is persistent, are explained in terms of their importance.
2.5Procedures to be followed where diagonal warp is persistent are described in terms of workplace practices.
Rangeto include the workplace practices for requesting an equipment specifications check by engineers.
Outcome 3
Control MD and CD warp at changes of paper.
Rangepaper grade, paper type, paper width, or any combination.
Evidence requirements
3.1Corrugator is operated ensuring that MD Warp does not exceed 4% at any stage or meets requirements if job specification is less than 4%.
3.2Corrugator is operated ensuring that CD Warp does not exceed 4% at any stage or meets requirements if job specification is less than 4%.
3.3Corrugator speed is not reduced below 40% of plant listed maximum, except where slitter changes enforce a greater speed reduction or when making splices on tight web corrugators.
Outcome 4
Take proactive measures at the times of paper changes to minimise warp occurring.
Rangepaper grade, paper type, paper width, or any combination.
Evidence requirements
4.1Awareness of forthcoming paper changes is demonstrated.
Rangecheck production documentation, communicate with other crew members.
4.2Proactive corrective measures to minimise the risk or effect of MD and CD warp are taken in anticipation of paper changes using actions available (see explanatory note 10).
4.3Proactive measures available to be taken are explained in terms of workplace practices.
4.4The effects of the various proactive measures available are explained in terms of workplace practices.
Outcome 5
Rectify MD and CD warp.
Evidence requirements
5.1Action is taken immediately notification is received that warp has occurred.
5.2Any warp within the control of the operator that occurs following a paper change is reduced to 2% or less within the specified period following notification.
Rangespecified period is –
(a) for workplaces operating a ‘stop order change’, 200 lineal metres of produced board, plus a further three minutes of corrugator running time;
(b) for workplaces not operating a ‘stop order change’, 100 lineal metres of produced board, plus a further three minutes of corrugator running time.
5.3The procedures to be followed in the event of failure to reduce warp to 2% or less within the specified three minutes period are followed in accordance with workplace practices.
5.4Following a paper change, any required reduction of warp to 2% or less is achieved at not less than 40% of plant listed maximum speed.
5.5Following the reduction of warp to 2% or less, no MD warp or CD warp exceeding 2% is experienced before the next paper change.
5.6The actions available to control MD and CD warp to 2% or less between paper changes are followed in accordance with workplace practices.
5.7The effects of the actions available to control MD and CD warp to 2% or less between paper changes are explained in terms of workplace practices.
Outcome 6
Work in collaboration with other corrugator crew in accordance with workplace practices.
Evidence requirements
6.1Communication with other crew is made ensuing there are no delays to production.
6.2The situation requiring action is identified and the joint action required is explained.
6.3Cooperation with other crew is demonstrated in jointly reducing MD and CD warp within the required time periods.
Outcome 7
Follow safety requirements for the equipment being used.
Rangeoperating manual, workplace practices.
Evidence requirements
7.1Equipment start up, shutdown and emergency procedures in the workplace are explained.
7.2Hazard control measures, as circulated by the company, are described and followed.
7.3Hazards or potential hazards in the workplace are identified and reported in accordance with workplace practices.
Replacement information / This unit standard, unit standard 3779, and unit standard 3786 have been replaced by unit standard 27811.This unit standard replaced unit standard 3782 and unit standard 3785.
This unit standard is expiring. Assessment against the standard must take place by the last date for assessment set out below.
Status information and last date for assessment for superseded versions
Process / Version / Date / Last Date for AssessmentRegistration / 1 / 27 April 2005 / 31 December 2015
Review / 2 / 20 September 2012 / 31 December 2019
Rollover / 3 / 10 December 2015 / 31 December 2019
Consent and Moderation Requirements (CMR) reference / 0005
This CMR can be accessed at
Please note
Providers must be granted consent to assess against standards (accredited) by NZQA, before they can report credits from assessment against unit standards or deliver courses of study leading to that assessment.
Industry Training Organisations must be granted consent to assess against standards by NZQA before they can register credits from assessment against unit standards.
Providers and Industry Training Organisations, which have been granted consent and which are assessing against unit standards must engage with the moderation system that applies to those standards.
Requirements for consent to assess and an outline of the moderation system that applies to this standard are outlined in the Consent and Moderation Requirements (CMR). The CMR also includes useful information about special requirements for organisations wishing to develop education and training programmes, such as minimum qualifications for tutors and assessors, and special resource requirements.
CompetenzSSB Code 101571 / New Zealand Qualifications Authority 2018 / / New Zealand Qualifications Aut