Tunnel washers are of four general types:
- Single skin - Voss, Schultess
- Double skin
- Cherry Tree, Milnor, Poensgen
- Single and double skin -
Aqua Trac, Senking
- Batch exchange -
The configuration of a tunnel washer
and the required number of stages, size, etc. must be full and accurately specified
prior to selection and purchase of the machine. Once built it is not possible to
modify or re-configure the normal tunnel washer, i.e. change the number of stages
or wash parameters. The only system which can be changed is that which consists
of a machine assembled in a modular construction with separate, discrete components
linked together, e.g. Poensgen.
No one machine has all the desirable
features and the machine selected should comprise the maximum plus points for the
The control of the washing system,
individual wash processes and workflow must be closely allied to production planning.
The inherent flexibility available to the launderer within a washer-extractor system
is not necessarily available for the CBW system. This system cannot be adequately
controlled or monitored manually and therefore operations are invariable controlled
by their process card readers or full computer programming. The number of individual
operations required i.e. load sequencing, process design and inputs, cycle time,
press, conveyor and tumble drier interfaces makes any manual alternative method
of control impossible.
A tunnel washer does not just replace
a line of batch washers, it must be regarded as the core of a wash system. The installation
of a tunnel washer should dictate the end of "ad hoc" planning of production
through the washroom.
Planning must commence in Sorting as the tunnel washer
demands not only a constant supply of work at regular short intervals but work of
a category that will be adequately washed by the process installed on the machine.
Loading of the machine must be considered in terms of
the weight of the classification in relation to volume, the accuracy of the weight
of the load, and in the correct sequence to balance the tumbler operation.
Previously a line of batch washer-extractors has been
able to accept a variety of soiling and different classifications by having available
different processes catering for different requirements of temperature, chemicals,
water levels, time of processing and a variable number of stages within each process.
For the tunnel washer it is necessary to study how to merge these different requirements
into one average process which will process as much of the work as possible and
discard for separate washer-extractor processing, anything that does not fit. We
must also study the needs for special requirements such as Bleaching, Starching,
Softening, Anti-chlor and Souring.
Press or Hydro-extractor
The press extracts water from the work after washing
and rinsing. Inefficient use because of poor maintenance will cause production to
suffer. If the tunnel wash machine is being run on a reduced time cycle to produce
more work, an increase of moisture retention can occur with possible further delay
implications during the drying operation. It is also now possible to obtain a pass-through
high speed hydro-extractor unit as an alternative to a press unit. The choice of
moisture removal system will depend on production requirements.
These must be balanced to the machine cycle time, otherwise
production suffers. Production planning must therefore take account of the number
of tumblers and their performance.
The evaporative performance of ironers should be studied
to avoid unnecessary conditioning of work thus minimising the use of tumblers and
allowing either a shorter machine cycle time or reduced energy usage.
Above all else the batch tunnel washer has to be operated
as part of a fully integrated system with each individual element closely linked
and tuned to the requirements of the next i.e.
- sorting - a correct load at each cycle time
- tunnel washer - receives a load at each cycle time
- press unit (or extractor) - receives, processes
and discharges a load within the tunnel washer's standard cycle time
- tumble drier - receives and processes to part of
fully dry any work load presented from the conveyor and discharges this to the required
level of dryness and is ready to receive a further load from the conveyor at the
required cycle time or multiples of cycle time. It follows from the above that each
tunnel washer will require a multiple bank of tumblers to maintain effective production
without hold or pause periods occurring.
This information courtesy of Division
of Building Technology, CSIR.