NO813231L - PROCEDURE FOR MECHANICAL DISHWASH, AND DISHWASHER. - Google Patents

Abstract

Method and apparatus for mechanical washing in which the objects to be washed are placed on a horizontal stand or a chain conveyor over an open reservoir or a washing tank containing a washing bath comprising an aqueous cleaning liquid which is pumped and sprayed through spraying devices placed above and / or or under the rack or chain conveyor of the articles to be washed, followed by a rinsing cycle in which the washed articles are sprayed with water optionally mixed with a rinsing aid, through spraying devices placed above and / or under the rack or chain conveyor, whereby a bleaching agent and / or disinfectant ("sanitizer") is introduced into the cleaning liquid line of the spray devices and / or directly into the washing bath in the tank before the rinsing cycle starts, whereby the amount of "sanitizer" in the cleaning liquid is regulated to a sufficient strength.The energy-saving process and the apparatus can be used for lower washing and s cooling temperatures without compromising hygienic safety.

Description

The invention relates to an improved method and apparatus for mechanical dishwashing. Dishware includes all kinds of stoneware, cutlery and kitchen utensils.

Dishwashers where the dishes are placed

a horizontal stand or a chain conveyor above a

open reservoir or a washing tank containing a

heated washing bath which comprises an aqueous cleaning liquid and which is operated by pumping and spraying said aqueous cleaning liquid on the objects for a predetermined period of time, followed by a rinsing program where the washed objects are sprayed with hot water, possibly mixed with a rinsing aid, is known .

Different types of dishwashers which work according to the above-mentioned principle are known.

A. Simple tank "dump" machine. is

In these machines, the washing water is completely dumped after each wash. They work in the following way: 1. The washing tank is filled with hot water, and detergent is dosed; 2. Wash cycle. (about 4 5-18 0 seconds); 3. Drain the wash water; 4. The machine is rinsed (if necessary); 5. The washing tank is filled with fresh, warm water, and rinse aid is dosed; 6. Rinse cycle (approx. 45-180 seconds); 7. The rinse water remains in the tank and is used for the next wash cycle.

B. Single tank "reuse" machines

In these machines, only part of the washing bath is drained continuously via an overflow pipe and refreshed with water from the rinse.

They work in the following way:

1. The wash tank is filled with hot or cold water (depending on the local circumstances), and detergent is dosed; 2. Wash cycle (approx. 45-180 seconds).; 3. The wash water remains in the wash tank; 4.. Rinse cycle (approx. 5-20 seconds). Rinsing water from a hot water line. at normal water pressure (1.5-3 bar) flows inside the washing tank via rinsing shower heads. Rinse aid is dosed into the hot water system during rinsing; 5. The water level in the washing tank is kept constant by means of an overflow pipe (i.e. that during the rinse cycle part of the washing water is drained);

6. The next wash cycle can start.

C. Multi-tank "reuse" machines

These machines generally work in the following way:

1. The tank (prewash, wash and power rinse) is filled with hot water; , 2. The machine is switched on (all sections have their own pump); 3.. Detergent is automatically dosed into the wash tank, and rinse aid is dosed into the water for the final rinse; 4.. Final rinse water (rinse water from a hot water line at normal water pressure (1.5-3 bar) flows into the final rinse section via rinse shower heads; it flows over into the power rinse tank. 5. Water from the power rinse tank flows into the wash tank, and from this it flows into the prewash tank, is kept at a constant level by means of an overflow to the drain. The power rinse (= pump rinse) before the final rinse is necessary to rinse away alkalinity and dirt residues from stoneware. because the last rinse (with fresh, warm water) is too short to achieve alkali-free and dirt-free stoneware.

Some multi-tank machine types do not have a power rinse section, so that the last rinse water flows into the wash tank.

These machines generally work at a relatively high washing temperature of approx. 60°C and a rinse temperature of approx. 80°C.

The cleaning agents used in industrial mechanical dishwashing can be powders or liquids and are usually mixtures of two or more of the following compounds: sodium or calcium triphosphate, sodium metasilicate, sodium or potassium hydroxide, sodium carbonate, sodium sulfate, with or without a chlorine bleach.

The ever-increasing need to reduce energy and water consumption has led researchers to reconsider mechanical dishwashing processes. If one considers that changing the wash water temperature from 60°C to 50°C, and lowering the rinse water temperature from 80°C to 60°C without further changing the time setting on the machine program, implies.

an energy saving of approx. 25%, one could easily understand

that one of the main aims of the researchers is to lower these temperatures in mechanical dishwashing processes. Lowering the working temperature will also improve working conditions in the kitchen area.

However, lowering the washing and/or rinsing temperatures will obviously reduce the hygienic safety of the process due to reduced heat disinfection and greater risk of cross-contamination.

It is an aim of the invention to provide a method and apparatus for mechanical dishwashing, whereby washing and/or rinsing can be carried out at lower temperatures without reducing the hygienic safety of the process.

It is another object of the invention to improve the bleaching and sanitizing performance of mechanical dishwashing processes.

It has now been found that the tasks mentioned above can be solved by separately adding a bleaching and/or disinfectant, the latter agent in the further description of the invention will also be referred to as "sanitizer".

Accordingly, in one aspect, the invention provides a method for mechanical dishwashing, whereby the dishware is placed on a horizontal rack or conveyor belt above an open reservoir or wash tank containing a

wash bath comprising an aqueous cleaning liquid which is pumped'

and sprayed via spraying devices that are placed above and/or below the rack or the conveyor belt on the items, followed by a rinse cycle where the washed items are sprayed with water that may have been mixed with a rinsing agent, through spraying devices • that are placed above and/or below the rack or the conveyor belt, and the method is characterized by a bleaching and/or disinfectant being introduced into the cleaning liquid line to the spray devices and/or directly into the washing bath in the tank before the rinsing cycle starts, whereby the amount

of "sanitizer" in the cleaning liquid is regulated to a sufficient strength.

In another aspect of the invention, an apparatus for mechanical dishwashing is provided, comprising an open wash bath tank, a movable or stationary horizontal stand for objects to be washed, placed above the wash bath tank, a pump connected to the wash bath tank for spraying wash bath onto the objects through spray arms placed above and below the rack, an overflow to maintain the wash bath level in the tank, and possibly a heating element mounted in the tank for heating the wash bath, and this apparatus is

characterized in that a device is provided for injecting a bleaching and/or disinfectant into the washing bath.

The aforementioned injection device can be connected to the wash bath line at a point before or where the flow splits between the upper and lower spray arms, or directly to the wash bath tank.

Preferably is. the injection points are equipped with a one-way valve.

Bleaching and/or disinfectants that are applicable

in connection with the invention, are, for example, alkali metal hypochlorite and hydrogen peroxide. Peroxyacids or peroxyacid precursors can also be used. Depending on the dosing method, the "sanitizer" can be used in any physical form for convenient dosing, for example as a liquid or solid. If alkali metal hypochlorite is used, it is preferably introduced in the form of an aqueous solution in a concentration of approx. 6-12% by weight. A preferred alkali metal hypochlorite is sodium hypochlorite.

If hydrogen peroxide is used, it is introduced in the form of an aqueous hydrogen peroxide solution, for example in a strength of approx. 3-60% by weight.

Until now, separate addition of hypochlorite in mechanical dishwashing systems has been proposed via the rinse water. However, in most countries the addition of hypochlorite or other oxidative disinfectant to the final rinse water is prohibited by law, due to the risk of forming undesirable residues on the washed items.

The invention avoids the above risk and is safe in this

regard.

The technical problem to be solved is how and when to dose the bleaching and/or disinfectant solution of a specific concentration in order to achieve the greatest cost-effective bleaching and/or disinfecting effect. The reduction of hypochlorite, for example in the case of organic dirt in the washing bath, will mean that in order to maintain a constant active chlorine level, regular dosing of hypochlorite will be necessary, but at a rate that varies with its reduction due to the organic dirt that is present in the washroom. It was found that for a satisfactory bleaching and "sanitizing" effect, the active chlorine content in the washing bath should preferably be kept at

a level of at least 30 ppm per litres, especially at a level within the range of 30-50 ppm per litres.. It is easier to maintain this constant level if the bleach and/or disinfectant is dosed during the washing process in pulses, preferably at least 30 seconds before the rinse cycle starts, as the amount is calculated on the basis of the amount of rinse water per stand or per hour and is adjusted using the pulse frequency of the pump.

For example, in a single-tank machine, with a wash tank content of 50 liters and rinse water adjusted to 2.5 l/stand, this turns out to be approximately 625 g of hypochlorite solution (6% active chlorine) per 200 racks that have been washed (ie 1.1 g sodium hypochlorite/litre).

To ensure that sufficient active chlorine or active oxygen is present in the bathroom, the bleach and/or disinfectant dosing pump can be activated by push button to deliver an additional "start dpsing" (ie a dose that provides at least 30 ppm active chlorine level in a fresh bath). In addition, an additional amount of "sanitizer" may be required

to compensate for variations in the intervals between two washing processes and in the dirt load or dirt composition.

Preferably, a main wash product is used that contains more sequestering agent than most conventional mechanical dishwashing products, in order to improve the hygienic safety of the process even more. Both powdered and liquid cleaning products can be used in the method according to the invention. The powdery product can be dosed via a commercially known "powder dosing" system, for example an overflow reservoir system, and the liquid product can be dosed by means of a suitable pump. The product concentration can be kept within acceptable limits via a conductivity cell

in the washroom and regulator. Advantageously, the aqueous cleaning liquid is kept. in the wash tank of a strength ké that is at least equivalent to 500 mg/litre sodium triphosphate per mol M water-hair.ness and 4 00 mg/liter NaOH.

Under these conditions, the level of residual bacteria found in the low-temperature dishwashing process (wash temperature 50°C/rinse temperature 60°C) is close to that found in a conventional process at 60°C/80°C without hypochlorite. The combination of this alkaline bath and the use of a separate "sanitizer" additive according to the invention results in exceptional hygiene safety and provides a more cost-effective bleaching result than is possible with a conventional chlorine-containing main wash product.. •

The liquid bleaching and/or disinfectant, for example sodium hypochlorite solution or hydrogen peroxide solution, can be dosed using a diaphragm pump which is triggered by an electrical connection to the washing pump via an electrical device.

In single-tank machines with showers above and below the rack, the "sanitizer" product is preferably dosed at a point in the washing arm of the machine before or where the flow is split between the upper and lower spray arms. This initiation point with a one-way valve is chosen to reduce the delay between "sanitizer" addition and contact with the items being washed (ie to deliver a maximum instantaneous level of active chlorine or active oxygen to the items) to a minimum. It should be noted that typically the recirculation time for the wash liquid is through the wash pump. 6-10 seconds, so that dosing of "sanitizer" into the washing bath can also give fairly similar results. The dosing pump for "saniti.zing" can often be operated with a push-button for the starting dose (and intermediate bleaching if this is necessary), after which a specific volume (approx. 3 g for 6% hypochlorite solution) is dosed per stand, as this begins, for example, .30 seconds before the end of the wash cycle. This dose can be injected in pulses of 1 g, at time intervals which will depend on the duration of the washing cycle.

The rinse aid can be dosed, as in the conventional processes,

with a Venturi or electrically driven pump.

The method according to the invention not only avoids the risk of the formation of unwanted residues on washed objects, which is due to "sanitizer" one, but can also be operated at lower wash and. rinse temperatures, giving bleaching and hygienic results at least equal to those achieved with conventional high-temperature (60°/80°C) mechanical dishwashing processes. In the method according to the invention, the wash and bath temperature is preferably maintained at one level

of approx. 50-55°C, and . The rinse water temperature is kept at a level of approx. 60-65°C.

Further advantages of the invention are:

1. The level of active "sanitizer"/bleach in the washing bath can be kept more constant than when dosing via a main wash product. The required level for effective bleaching and/or "sanitizing" can be set by adjusting:

- the dosage quantity per stand and/or

- the starting dose and/or

- by manual repetition of the starting dose.

This gives better bleaching of washed items and better

disinfection of the washroom.

2. Presence of. active "sanitizer" at an effective level in the washroom. reduces the risk of cross-contamination due to bacteria (especially at lower temperatures, i.e. ^60°C),

and the process thus becomes hygienically safer.

Conventional mechanical dishwashing relies on high-temperature (60°/80°) automatic washing of objects with a correctly composed and dosed cleaning product. However, it is

so as to understand that there could be the development of serious deficiencies when washing a particular load of used items, which would result in'reductions- in the temperature achieved, reductions in the dosage of the product achieved,

and one part of the cycle could fail, such as the rinse. In extreme cases, it may be that more than one of these could fail.

If a serious error occurs in the process, it will undoubtedly result in someone. few items are taken out of the machine in an unsatisfactory hygienic condition. There is also the possibility that contamination introduced into the washing bath can be transferred to other objects. If much of this were to be involved, this cross-contamination could cause other washed items to become hygienically unacceptable. The invention seeks to compensate for such errors that may occur.. 3. Incompatible components in particularly liquid main wash products can be used more effectively and more economically by the separate addition of "sanitizer" according to the invention.

In the following, the invention will be illustrated with help

of examples and explained with the help of figures 1 and 2.

Example 1

Process I where a liquid detergent product is used

as a cleaning agent (see figure 1).

1. Fill the washing tank (A) with water of 50°C using the rinsing showers (B) or a separate filling tap.

2. Place the rack with dirty dishes (C) in the washing chamber

in the machine.

3. Start the washing programme.

4. Press the button for the pump (D); a preset amount

of detergent is then dosed from the storage container (E) into the washing tank (A).

5. Press the button for the pump (F) as soon as the pump is

activated by the timer (G), which is indicated by the green pilot lamp lighting up; a preset amount of bleach/"sanitizer" 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/-

"sanitizers" are showered onto the plates using the washing showers (K), which are fed from the washing tank (A) using the machine pump

(D •

7. In the last 30 seconds of the washing process, the pump is dosed

(F) a preset amount of bleach/"sanitizer" into

in the wash arm (J) or the wash tank (A); the amount is calculated on

basis of the amount of rinsing water per stand or per hour and is adjusted using the pulse frequency of the pump.

8. After the plates have been washed, they are rinsed with fresh water

water of 60°C from the water heater (M) by means of the rinsing showers (B); in order to induce faster drying of the clean dishes, a rinse aid is automatically dosed from the storage container (N) into the rinse water by means of the pump (P). 9. With each subsequent rack, the process repeats itself automatically, starting with point 6. Detergent is dosed automatically during each wash cycle analogous to what is described under point 7 for bleach/"sanitizer". 10. If the wash solution is completely dumped, the procedure must start again from point 1.

Remarks:

- In dishwashers with a separate power rinse section, bleach/"sanitizer" is dosed into the power rinse tank or the power rinse unit. - In the above process, the concentration of detergent in the wash tank is kept sufficiently high by introducing a preset amount of detergent into the wash tank at the beginning of each wash cycle. It is also possible to use a conductivity control system to maintain the detergent concentration. Such a system is analogous to that used in

process II in example 2 for powdered detergents.

- If the concentration of "sanitizer" in the wash tank during the wash - turns out to be too low (for example^lowering of chlorine concentration by splitting during a stop), an additional amount can be dosed by pressing the button for the pump

(F) .

Example 2

Process II which uses powdered detergent product which

cleaning agent (see figure 2)

1. Fill the washing tank (A) with water of 50°C using the rinsing showers (B) or a separate filling tap.

2. Add washing powder to the dosing reservoir (C).

3. Insert the rack with dirty dishes (D) into the washing chamber of the machine.

.4. Start the washing programme. ■ Detergent solution/slurry is automatically dosed from the dosing reservoir (C) into the washing tank (A). Dosing continues until the concentration reaches a preset level. This level can be adjusted with the regulator (E) which operates a solenoid valve (F) in the water supply line in the dosing reservoir (C). The regulator monitors the concentration in the washing tank using two electrodes (G, conductivity principle). The regulator has a built-in alarm circuit that drives a buzzer and/or a pilot lamp to

indicate that the reservoir must be refilled with washing powder.

The dosing system is in operation as long as the sorting machine is switched on.

5. Press the button for the pump (H) as soon as the pump is

activated by the timer (J) which is indicated by the green pilot lamp lighting up; a preset amount of bleach-

agent/"sanitizer" is then dosed from . the storage container (K) in

in the wash arm (L) or the wash tank (A).

6. The solution containing detergent and bleach/"sanitizer" is then showered onto the plates using the washing showers (M), which are fed from the washing tank (A) using the machine pump (N).

7. In the last 30 seconds of the washing process, the pump is dosed

(H) a preset amount, of bleach/"sanitizer" into the wash arm (L) or the wash tank (A); the amount is calculated on

basis of the amount of rinsing water .per stand or per hour and is adjusted using the pulse frequency of the pump (H) .

8. After the plates have been washed, they are rinsed with fresh water of 60°C from the water heater (R) using the rinse showers (B); in order to induce faster drying of the clean dishes, a rinse agent is automatically dosed from the supply container (P) into the rinse water using the pump (Q). 9. With each subsequent stand, the ■process repeats automatically, beginning with point 6. 10. If the washing solution is completely dumped, the - procedure must start again from point 1.

Remarks:

- In dishwashers with a separate power rinse section, bleach/"sanitizer" is dosed into the power rinse tank or the power rinse line. - The above procedure can also be used for liquid detergents. In such a case, the powder dosing reservoir (C). and the solenoid valve (F) not necessary-; the regulator drives a pump which doses the detergent from a storage container into the washing tank.

- If the concentration of. "sanitizer" in the wash tank during washing turns out to be too low (for example, lowering the chlorine concentration when splitting during a stop), an additional amount can be dosed by pressing the button for the pump

(H) .

Claims (9)

1. Procedure for mechanical dishwashing, ■ whereby the objects to be washed are placed on a horizontal stand or a transport chain above an open reservoir or a washing tank. which contains a wash bath comprising an aqueous cleaning liquid which is pumped and sprayed through spray devices located above and/or below the rack or conveyor chain on the items, followed by the rinse cycle' where the washed items are showered with water that may have been mixed with a rinsing aid, through spray devices placed above and/or below the rack or transport chain, characterized by the fact that a bleaching agent and/or disinfectant ("sanitizer") is introduced into the cleaning liquid .the line to the shower facilities and/or directly into the washing bath in the tank before the rinse cycle starts, whereby the amount of "sanitizer" in the washing bath is regulated to a sufficient strength. 2. Method as stated in claim 1, characterized in that an alkali metal hypochlorite is used as "sanitizer". 3. Method as stated in claim 2, characterized in that the active chlorine content in the washing bath is kept at a level of at least 30 ppm per litres. 4. Method as stated in claim 3, characterized in that the active chlorine content in the washing bath is kept at a level of 30-50 ppm per litres. 5. Method as stated in any one of claims 1 to 4, characterized in that the aqueous cleaning liquid in the washing tank has a strength of at least . equivalent. with 500 mg/litre sodium triphosphate per mol M ^ water hardness and 400 mg/litre sodium hydroxide. 6. Method as stated in claim 2, character, in that "sanitizer" is dosed into the cleaning liquid at least 30 seconds before the rinsing cycle starts. 7. ■ Method as stated in any one of claims 1 to 6, characterized in that the washing bath . kept at a temperature of approx. 50°-55°C. 8. Apparatus for mechanical dishwashing, comprising an open wash bath tank, a movable or stationary horizontal stand for objects to be washed, placed above the wash bath tank, a pump connected to the wash bath tank for showering washing liquid on the objects through shower arms located above and below the stand, an overflow to maintain the washing bath level in the tank, and possibly a heating element mounted in the tank for heating the washing bath, characterized in that a device is provided for injecting a bleaching agent and/or disinfectant ("sanitizer") ) to the washroom. 9. Apparatus according to claim 8, characterized in that the injection device is connected to the washing bath solution at a point before or there. where the flow is split between the upper and lower shower arms. •10. Apparatus as specified in claim 8, characterized in that the injection device is connected to the wash bath tank.