Note: Descriptions are shown in the official language in which they were submitted.
= 1 - C 590 (R)
MECHANICAL DISHWASHING SYSTEM A'ID APPARATUS
This invention relates to an improved process and apparatus
for the mechanical washing of dishes. The term "dishes" is
5 used here to include all sorts of crockery, glassware, cutlery
and kitchen utensils.
Dishwashing machines wherein the dishes are placed on a hori-
-zontal rack or conveyor chain above an open reservoir or wash
tank containing a heated wash liquor comprising an aqueous
cleaning liquid and which operate by pumping and spraying said
aqueous cleaning liquid onto the dishes for a predetermined
period followed by a rinsing programme wherein the washed
dishes are sprayed with warm water, optionally mixed with a
rinse aid, are known.
Various types of dishwashing m~chines operating on the above
principle are known.
A. Sin~le tank "dump" machines
In these machines the wash liquor is dumped completely after
each wash. They operate as follows:
1. Wash tank is filled with warm water and cleaning agent is
dosed,
2. Wash cycle (circa 45 -180 seconds);
3. Wash water is drained;
4. Mach;ne is rinsed ~optional);
5. Wash tank is f;lled with fresh warm water and rinse aid is
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= - 2 - C 590 (R)
dosed;
6. Rinse cycle (circa 45 -180 seconds);
7. Rinse water remains in tank and is used for the next wash
cycle.
B. Single tank ''re-use"_machines
In these machines only part of the wash liquor i5 continuously
drained via an overflow pipe and refreshed by water from the
rinse. They operate as follows:
1. Wash tank is filled with warm or cold water (depending on
local circumstances) and cleaning agent is dosed;
2. Wash cycle (circa 20-70 seconds);
3. Wash water stays in the wash tank;
4. Rinse cycle (circa 5 -20 seconds). Rinse water from a warm
- water line at ordinary water pressure (1.5 - 3 bar) flows
into the wash tank via rinse sprayers. Rinse aid is dosed
into the warm water line during rinsingj
5. Water level in wash tank is kept constant by means of an
- overflow pipe (i.e. during the rinse cycle part of the wash
water is drained);
6. Next wash cycle can start.
C. Multitank "re-use" machines
These machines generally operate as follows:
l. Tank (pre-wash, wash and power rinse~ are filled with warm
. water,
2. Machine is switched on (all sections have their own pump);
3. Cleaning agent is automatically dosed into the wash tank
and rinse aid is dosed into the water of the final rinse;
4. Final rinse water (rinse water from a warm water line at
ordinary water pressure (1.5 -3 bar) flows into the final
rinse section via rinse sprayers, it cascades over into the
power rinse tank.
5. Water from the power rinse tank cascades into the wash tank9
and from there it cascades over into the pre-wash tank, kept
at a constant level by an overflow to the drain. The power
r;nse (- pumped rinse) prior to final rinse is necessary to
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rinse away alkalinity and soil residues from crockery be- l
cause the final rinse (with fresh warm water) is too short
to obtain alkali-free and soil-free crockery.
Some multi-tank machine types do not have a power rinse ¦
section so that the final rinse water cascades into -the
wash tank.
These machines generally operate at a relatively high wash temper- !
10 ature of about 60C and a rinse temperature of about 80C. ~j
~1
The cleaning agents used in industrial mechanical dishwashing can
be powders or liquids and are generally blends of two or more of the
following compounds: sodium- or potassium triphosphate, sodium meta- I,
silicate, sodium- or potassium hydroxide, sodium carbonate, sodium
sulphate, with or without a chlorine bleaching agent.
The current increasing demand to reduce energy and water consumption
has led investigators to a reconsideration of mechanical dishwash-ing
processes. Considering that lowering the wash water temperature
from a nominal 60C to 50C, and lowering the rinse water tempera-
ture from a nominal 80C to 60C without further changing the timing
of the machine programme involve an energy-saving of about ~5%, it
could be easily appreciated that one of the major objectives of in-
vestigators is to lower these temperatures in mechanical dishwashingprocesses. Lowering of the working temperature will also improve
working conditions in the kitchen environment.
However9 lowering the wash and/or rinse temperatures will obviously l~
decrease the hygienic safety of the process owing to reduced thermo-
disinfection and higher risk of cross-contamination. ~t
,
It is one object of the present invention to provide a process and
apparatus for the mechanical washing of dishes, whereln washing
and/or rinsing can be effected at lower -temperatures without de-
creasing the hygienic safety of the process.
- 4 - C 590 (R) i
It is another object of the invention to improve the bleaching
and h~qiene performance of mechanical dishwashing processes.
It has now been found that the above objects can be achieved by
the separate addition of a bleaching and/or disinfecting agent,
which latter agent in the further description of the invention
will also be referred to as "sanitizer".
Accordingly, in one aspect the invention provides a process for
the mechanical washing of dishes, wherein said objects are placed
on a horizontal rack or conveyor chain over an open reservoir or
wash tank containing a wash liquor comprising an aqueous cleaning
liquid which is pumped and sprayed through spraying devices
placed over and/or under the rack or conveyor chain onto the
dishes, subsequently foll.owed by a rinse cycle wherein said
washed dishes are sprayed wîth water optionally mixed with a
rinse a~d through spraying devices placed over and/or under
the rack or conveyor chain, characterized in that a bleaching
and/or disinfecting agent is introduced into the cleaning liquid
line to the spraying devices and/or direct into the wash liquor
in the tank before the start of the rinse cycle, thereby con-
trolling the amount of sanitizer in the cleaning liquid at a
suf~icient strength.
In another aspect of ~he invention an apparatus for the mechan-
ical washing of dishes is provided, comprising an open wash
liquor tank, a moving or sta~ionary horizontal rack for articles
(dishes) to be washed placed above the wash liquor tank, a pump
connected to the wash liquor tank for spraying wash liquor onto
the articles through spray anms situated above and below the
rack, an overflow to maintain the wash liquor level in the tank, `
and optionally a heating element mounted in the tank for heating
the wash liquor, characterized in that there is provided a
device for injecting a bleaching and/or disinfecting agent into
: ~5 the wash liquor.
. ~ ` Said injection-device can be connected to the wash liquor line
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at a point before or where the flow is split between the upper
and lower spray arms, or direct to the was liquor tank.
Preferably the injection points are provided with a one-way
valve.
Bleaching and/or disinfecting agents usable in the present in-
vention are, for example, alkalimetal hypochlorite and hydrogen
peroxide. Also peroxy acicls or peroxy acid precursors can be
used. Depending on the manner of dosing, the sanitizer may be
used in any physical form for convenient dosing, e.g. a liquid
or a solid. If alkalimetal hypochlorite is used, it is prefer-
ably introduced in the form of an aqueous solution at a concen-
tration of about 6 -12% by weight. A preferred alkalimetal
hypochlorite is sodium hypochlorite.
If hydrogen peroxide is used, it is introduced as an aqueous
hydrogen peroxide solution, for example at a strength of about
3 -60% by weight.
Hitherto separate addition of hypochlorite in mechanical dish-
washing systems has been suggested via the rinse water. However,
in most countries addition of hypochlorite or any other oxida-
tive disinfectant to the final rinse water is prohibited by law,
owing to the risk of the formation of undesirable residues on
washed articles.
The present invention avoids the above risk and is safe in this
respect.
The technical problem to solve is how and when to dose the
bleaching and/or disinfecting agent solution of a fixed concen-
tration to obtain the most cost-effective bleaching and/or dis-
infecting action. The reduction of hypochlorite, for example
by organic soil in the wash liquor, will mean that, in order to
maintain a constant active chlorine level, a regular dosing of
hypochlorite would be needed but at a rate which varies with its
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- 6 - C 590 (R)
^reduction by the organic soil present in the wash liquor. It
was found that for a satisfactory bleaching and sani~izin~ ef
fect the active chlorine content in the wash liquor should pref-
erably be maintained at a level of at least 30 ppm per litre,
particularly at a level within the range of 30-50 ppm per litre.
It is easier to maintain this constant level if the bleaching
and/or disinfecting agent is dosed during the wash process in
pulses~ preferably at leas-t 30 seconds before the start of the
rinse cycle, the amount being calculated on the basis of the
amount of rinse water per rack or per hour and adjusted by
means of the pulse frequency of the pump.
For example, in a single tank machine, having a wash tank con-
tent of 50 litres and a rinse water adjusted at 2.5 l/rack, this
turns out to be approximately 625 9 of hypochlorite solution
(6% active chlorine) per 200 racks washed (i.e. 1.1 9 sodium
hypochlorite/li-tre).
To ensure that sufficient active chlorine or active oxygen is
present in the liquor, the dosing pump for the bleaching and/
or disinfecting agent may be activated by push button to deliv-
er an extra "initial dosing" (i.e. a dose, yielding at least
30 ppm active chlorine level in a fresh liquor). In addition
an extra amount of sanitizer may be needed to allow for varia-
tions in the intervals between two wash processes and in the
soil l~ad or soil composition.
Preferably a main wash product that contains more sequestrant
than ~ost conventional mechanical dishwashing products is used
to improve the hygienic safety of the process even further.
Both powder and liquid cleaning products can be used in the
proce~s of the invention. The powder product may be dosed
via any commercially known "powder dosing" system, e.g. an
overflowing reservoir system, and the liquid product may be
dosed by a suitable pump. The product concentration can be
kept ~ithin acceptable limits via a conductivity cell in the
wash liquor and controller. Advantageously the aqueous clean-
ing liquid in the wash tank is kept at a strength at least
- 7 - C 590 (R)
equivalent to 500 mg/litre sodium triphosphate per 1 mole M 3
water hardness and 200mg/litre NaOH.
Under these conditions the level of residual bacteria found with
the low temperature dishwashins process (washing temperature 50C/
rinse temperature 60C) is near that found with a conventional
process at 60C/80C without hypochlorite. The combination of
this alkaline liquor and the use of a separate sanitizer addition
according to the invention results in an exceptional hygiene
security and de1ivers a more cost-effective bleaching result ~han
is possible with a conventional chlorine-containing main wash
product.
The liquid bleaching and/or disinfecting agent, e.g. sodium hypo-
chlorite solution or hydrogen peroxide solution, can be dosed
by a diaphragm pump which is triggered by an electrical connec-
tion to the ~ash pump via an electrical device.
In single tank machines with sprays over and under the rack the
sanitizer product is dosed preferably at a point in the wash
arm of the machine before or where the flow is split between
upper and lower spray arms. This injection point with a one-way
valve is chosen to minimize the delay between sanitizer addition
and contact with the articles being washed (i.e. to deliver a
maximum instantaneous level of active chlorine or active oxygen
on the articles). It should be noted that, typically, the re-
cycle time of the wash liquor through the wash pump is 6-lO
seconds so that dosing of the sanitizer into the wash liquor
can also give very sim;lar results. The dosing pump for the
sanitizer is conveniently operable by push button for the ini-
tial dose (and intermittent bleaching when re~uired), whereafter
a fixed volume (about 3 9 for 6% hypochlorite solution) is dosed
per rackg starting e.g. 30 seconds before the end of the wash
cycle. This dose may be injected in pulses of 1 9 at time in-
tervals, whlch will depend on the duration of the wash cycle.
TXe rinse aid can be dosed, as in the conventional processes,
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- 8 - C 590 (R)
with a Venturi or electrically operated pump.
The process of the invention not only avoids the risk of forma-
tion of undesirable residues on washed articles arising from
the sanitizer, but is also operable at lower wash and rinse
temperatures, producing bleaching and hygienic results that
are at least equal to the results obtained with conventional
high-temperature ~60/80C) mechanical dishwashing processes.
In the process of the invention the wash liquor temperature
is preferably maintained at a level of about 50 to 55~C, and
the rinse water temperature is kept at a level of about 60
to 65C.
Further advantages of the invention are:
1. Level of active sanitizeribleach in the wash liquor can
be kept more constant than when dosed via a main wash
product. The required level for effective bleaching and/
or sanitizing can be set by adjusting:
- the amount of dosage per rack and/or
~ the initial dose and/or
- by manual repetition of initial dose.
This makes better bleaching of washed articles and better
disinfection of the wash liquor possible.
2. Presence of active sanitizer at an effective level in the
wash liquor reduces risk of cross-contamination by bacteri~
(especially at lower temperatures, i.e. less than 60~C), hence a
hygienically safer process.
Conventional mechanical dishwashing relies upon high tem-
~erature (60/8a C) automatic washin~ of articles with a
3Q properly formulated and dosed cleaning product. It is, how
ever, conceivable that ~here could be serious faults develop-
ing with the washing of a particular load of used articles,
resulting in reductions in temperature achieved~ reductions
in the dosage of the product achieved~ and failure of one
35 ~ part~of;the cycle, for example rinsing. In extreme cases
more than one~f ~he~se might fail.
~" If a serious fault develops in the process, it will undoubt-
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edly result in a few articles being taken from the machine
in an unsatisfactory hygienic state. There is also the
chance that contamination introduced into the wash li~uor
can be transferred to other articles. If large numbers of
these would be involved, this cross-contamination could
cause other washed articles to become hygienically unaccept-
able.
The present invention seeks to compensate for such faults
that may occur.
3. Incompatible components in especially li~uid main wash
products can be used more effectively and more economically
by the separate addition of sanitizer according to the
invention.
The invention will now be further illustrated in the following
Examples and explained by way of Figures 1 and 2.
Figure 1 is a schematic general arrangement view,
partially in cross section of a mechanical dishwashing apparatus
with means for dosing a liquid detergent cleaning product in
accordance with the present invention.
. Figure 2 is a schematic general arrangement view,
partially in cross section of a mechanical dishwashing apparatus
with means for do~ing a powdered detergent cleaning product in
accordance with the present invention.
Example 1
Process I using a li~uid detergent product as cleaniny agent
(see Figure 1)
1. Fill the wash tank (A) with water of 50C by means of the
rinse sprayers (B) or a separate filling tap.
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2. Put the rack with dirty dishes ~C) tn the washing compart-
ment of the machine.
3. Start wash programme.
4. Push the button of pump (D); a pre-set amount of detergent
is then dosed from the supply container (E) into the wash tank
(A)-
5. Push the button of pump (F) as soon as the pump is acti-
vated by the timer (G), which is indicated by lightening up
of the green pilot lamp; a pre-set amoun~ of bleach/sanitizer
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- 10 - C 590 (R)
is then dosed from the supply container (H) into the wash arm
(J) or the wash tank (A).
6. The solution containing detergent and bleach/saniti~er is
sprayed onto the dishes by the wash sprayers (K), which are
being fed from the wash tank (A) by the machine pump (L).
7. During the last 30 seconds of the wash process pump (F)
doses a pre-set amoun-t of bleach/sanitizer into the wash arm
(J) or the wash tank (A); the amount is calculatecl on the basis
of the amount of rinse water per rack or per hour and adjusted
by means of the pulse frequency of the pump.
~. After the dishes have been washed, they are rinsed with Fresh
water of 60C from the water heater (M) by means of the rinse
sprayers ~B); to promote quicker drying of the clean dishes, a
rinse aid is dosed automatically from the sùpply container (N)
into the rinse water by means of pump (P).
9. With each subsequent rack the process repeats itself auto-
matically, starting from 6. Detergent is dosed automatically
during each wash cycle analogous to that described under 7 for
bleach/sanitizer.
10. If the wash solution is dumped completely, the process
has to be started again from 1.
No
- In dishwashing machines with a separate power rinse section
the bleach/sanitiz~r is dosed into the power rinse tank or
power rinse line.
- In the above process the detergent concentration in the wash
tank is kept sufficiently high by introducing a pre-set
amount of detergent in the wash tank at the beginning of
each wash cycle. It is also possible to use a conducti~ity
control system to maintain the detergent concentration. ~uch
a system is analogous to that used in Process II of Example
2 for powder detergents.
~ If during washing the concentration of the sanitizer in the
wash tank turns out to be too low te.g. decrease of chlorine
concentration by decomposition during a break), an extra
amount can be dosed by pushing the button of pump ~F).
C 590 ~R)
Example 2
Process I I usin~ powder detergent product as cleaning_~ent
(see Figure 2)
1. Fill the wash tank (A) with water of 50C by means of the
rinse sprayers (B) or a separate filling tap.
2. Add detergent powder to the dosing reservoir (C).
3. Put the rack with dirty dishes (D) into the washing compart-
ment of the machine.
4. Start wash programme. Detergent solution/slurry is dosed
automatically from the dosing reservoir (C) into the wash tank
(A). Dosing continues until the concentration reaches a pre-
set level. This level can be adjusted with the controller (E)
which operates a solenoid valve (F) in the water supply line
of the dosing reser~oir (C). The controller monitors the con-
centration in the wash tank by means of an electrode (G, con-
ductivity principle). The controller has a built-in alarm cir-
cuit which operates a buzzer and/or a pilot lamp to indicate
that the reservoir has to be refilled with detergent powder.
The dosing system is in operation as long as the machine is
switched on.
5. Push the button of pump (H) as soon as the pump is acti-
vated by the timer (J), which is indicated by lighting up of
the green pilot lamp; a pre-set amount of bleach/sanitizer is
then dosed from the supply container (K) into the wash arm (L)
or the wash tank (A).
. The solution containing detergent and bleach/san;tizer is
sprayed onto the dishes by the wash sprayers (M), which are
being fed from the wash tank (A) by the machine pump (N).
7. During the last 30 seconds of the wash process, pump (H)
~ dos~s~a pre-set ~amount of bleaoh/sanitizer into the wash arm
`~~` ` ~ (L)~-or the;wash tank ~A); the amount is calculated on the basis
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- 12 - C 590 (R)
of the amount of rinse water per rack or per hour and adjusted
by means of the pulse frequency of pump (H).
8. After the dishes have been washed, they are rinsed with
fresh water of 60C from the water heater (R), by means of the
rinse sprayers (B); to promote quicker drying of the clean
dishes, a rinse aid is dosed automatically -From the supply con-
tainer (P) into the rinse water by means of pump (Q).
9. With each subsequent rack the process repeats itself auto-
matically, starting from 6.
10. If the wash solution is dumped completely, the process has
to be started again from 1.
Notes:
~ In dishwashing machines with a separate power rinse section
the bleach/sanitizer is dosed into the power rinse tank or
power rinse line.
- The above process can also be used for liquid detergents.
In that case the powder dosing reservoir (C) and the sole-
noid valve (F) are not necessary; the controller operates
a pump which doses the detergent from a supply container
into the wash tank.
- If during washing the concentration of the sanitizer in the
wash tank turns out to be too low (e.g. decrease of chlorine
concentration by decomposition during a break), an extra
amount can be dosed by pushing the but-ton of pump (H).
