Bottle washers for industrial use are quite complex machines and are generally used for washing returnable glass bottles.Sometimes they are also used for new glass bottles; as they guarantee better washing of the glass bottle than a rinsing machine can do.They can wash any type of bottle coming from the production of mineral water; wine, spirits, soft drinks, fruit juices, milk, etc.Until a few years ago, only paper labels were used to label returnable glass bottles. Today, plastic labels (wash-off labels) are also used with considerable advantages from the point of view of washing; reduction of temperatures and the use of chemicals, elimination of label pulping in the water and therefore greater cleaning of the water of the bathrooms. The only drawback is the higher cost of wash-off labels compared to paper ones.
Structure Of The Bottle Washing Machine
The first big division that we are able to make is between bottle washers with a single head (single-end) and bottle washers with double head (double end).
In the first case, the entry and exit of the bottles take place on the same side. These are small to medium-sized machines that usually do not exceed 30,000 bottles washed per hour of work.In these washing machines, there is only one large single alkaline wash bath followed by a series of rinses.
The double ends are structured with the entry of the bottles; to be washed at one end and the exit from the opposite side.They are also defined as modular bottle washers given the structure of identical “modules” which follow one another and which can be present in variable numbers (usually from 3 to 5) depending on the washing needs.The working potentials are generally very high, with a capacity even higher than 100,000 pieces per working hour.
Both machines guarantee good washing; but, the machines that can give greater washing performance and guarantees are those with double heads (double end). These also have a much higher cost than the others.Each bottle washer also has a temperature gradient necessary to avoid breaking phenomena for the glass (thermal shock) due to large changes in temperature. This trend brings the containers from room temperature; (sometimes very cold if we think of bottles washed in winter and perhaps stored on yards or in unheated warehouses) to values close to 80 ° C and then bring them back to room temperature before leaving.The same goes for the alkalinity that follows a concentration gradient suited to the need to recover soda that otherwise would be lost due to dragging. The water of the first rinse positioned after the alkaline baths (or technically after the pulping) is conveyed and returned to the pre-wash tank (which also serves to give the temperature gradient) to be recovered and used again.In this case there will be a pre-wash with a certain soda content which begins to wash and detach the label as well as giving some heat to the cold bottles.
Bottle InletThe most used bottle feeding system is the harpoon one. This, through an elliptical movement; automatically brings the bottles from the accumulation surface at the entrance to the washing machine to the baskets without using any other means of pushing.High-density plastic profiles are assembled on the harpoons; which ensure the silence of the load and the delicate treatment of the bottles.They are associated with important safety mechanisms to avoid breaking bottles or baskets.Specially shaped bottles: rectangular, square, oval; require a special auger feeding system capable of managing their pitch and orientation.The bottles are thus spaced apart and brought to the loading chutes by means of a polyethene profiled pushing device.The baskets can be of different sizes depending on the size of the bottles to be treated and are designed to allow: high washability of the bottle; and their easy replacement.Usually, with one type of basket, it is possible to wash more bottle formats; but it is necessary to carefully check the positioning of the bottle inside the basket in order to wash and rinse it.
As soon as you enter the machine; the bottles are sprayed or immersed in alkaline and slightly warm water deriving from the first rinse which has the function of removing heat and soda from the bottles; leaving the pulp.In this sector, we are therefore witnessing:
As the temperature of the glass rises
Land the labels begin to get wet with the alkaline solution
Normally in this area, there are no particular problems since the solution that comes from the first rinse; has already been treated with the hardness control additive, which avoids the precipitation of salts.
Washing baths (pulp)
In these sectors, the actual washing of the bottles takes place in order to eliminate any impurities from the inside; and at the same time detach the label which will then be released from the machine with special extractors.These baths then have the function of eliminating any glue residues and last; but not least of sterilizing the bottles (reference table) given the use of hot soda.The final result of the washing therefore largely depends on this (or these) caustic baths also called “pulp”.As just said, one of the objectives of caustic washing is the removal of labels. The labels should be detached at a precise point of the machine; so that they can be extracted without breaking them and above all without pulping them.The kinetics of detachment passes through the activities carried out by the caustic bath that is expressed on the surface of the label; (to be clear on the illustrated part), wets this face (wettability of the label) and reaches the underlying glue; (positioned between the label and the bottle) dissolving it and determining its complete detachment.
Factors of the process
The type of glue used, the percentage of soda present in the bath, the operating temperature; the quality of the paper, the colours used and the possible presence of waxy coatings are the factors that influence the process. In general terms, we can standardize the above by saying that:
The glues in use today are mostly of a starch-casein nature with a good possibility of removal in soda solutions; starting from the concentration of 1% as long as this is able to come into contact with the totality of the glue layer present.
The activity of the soda in solution is substantially expressed in the range between 1.5% and 3%, even if normally above 2% the viscosity of the solution increases; thus reducing the effect and the degree of removal. Exceeding this value (2%) therefore determines a substantial increase in costs without bringing a real benefit to activity.
Temperature plays a fundamental role in the label removal processes. Below 60 °C; labels are not removed in the working time of the bottle washer. However, the removal of good quality labels is carried out at 80 °C.
Structure of the label (quality of the paper, colours, waxy coatings, etc.) should be studied a priori in order to reduce the problems of detachment. For example, it is optimal to try to avoid the presence of heavy metals brought by certain colours; to have a decent paper quality that avoids pulping in the detachment phase, to reduce the presence of waxy coatings or the presence of areas with poor wettability.Further, reduces detachment. In general, it would be optimal to use labels that are "wettable" or that allow; in the contact time provided by the machine, the possibility of crossing the upper face in away uniform.
All bottle washers are equipped with a system label extraction two-stage.In the first stage, which begins its action after a caustic treatment time equal to about 40% of the total caustic treatment time; a current of caustic solution (generated by the different levels of two communicating tanks) hits the bottles, removing about 30 % of labels present.The current, at this point full of removed labels, is guided by the machine structure to a filtering mat that crosses the whole machine transversely; and, leads the paper residues to the outside.In the second stage, positioned at the end of the caustic treatment, a multitude of high-pressure sprays, emitted by easily removable nozzles for easy maintenance and internal cleaning, hit the bottles; removing the remaining 70% of the labels. The removed labels are then brought to fall on the aforementioned carpet; which leads them outside the machine.Inside the pulp, a possible critical phase is represented by the exit area of the bottles from the washing solution (out of the pulp) as it is essential that the bottles, which are hot; do not dry due to the effect of too high temperature or due to the very high stops (low speed of movement or stops for various problems).
Drying accentuates the corrosion phenomena of the soda against the glass; then causing blurred areas on the washed bottles and the presence of substantially irreversible white spots (white bottles).If this situation arises, it will be necessary to check the choice of the most suitable additive; and, contact the manufacturer to verify the possibility of increasing the number of spraying ranks.In this area are also the labels extracted, which is considered correct if most of them come out of the second module, otherwise, there is:
A too fast extraction if the extraction takes place in excessive quantities from the first module. This situation could lead to pulping of the labels with cellulose fibers in circulation to clog the filters and with the possibility of fine dragging at the bottom of the rinse (pieces of label remain in the washed bottles). In this situation, it is necessary to check that the concentration of soda and additive are not too high.
A too slow extraction with consequent exit of the labels in too high quantity beyond the second module. The problem may be that the delayed detachment brings the labels out of the machine and traces of glue remain on the glass. In this case it is necessary to check the working parameters of the machine and above all the temperature and the additive to the soda.
Pre rinse or first rinse
In bottle washers, there is now more and more a sector dedicated to reducing the alkalinity and above all to recovering this; and part of the heat, in order to be able to reuse it again in pre-macerations.This section, therefore, has the purpose of facilitating the elimination of soda and therefore improving rinsing; and controlling the precipitation of inorganic salts (limestone).We normally speak of a "static tank" and will be treated differently depending on how the circuit moves inside it. We will distinguish two different situations:
If the tank is loaded in the morning and emptied in the evening without adding fresh water; there will be a progressive increase in alkalinity and therefore we will have to treat it as a normal washing bath. We will add the same additive to the soda or even the additive of the rinses.
If during work there is a constant replenishment of fresh water so as not to increase the alkalinity; the bathroom must be treated as a normal rinse and provide for the dosage of the sequestering agent in a quantity proportional to the water that enters (dosage on the water supply line).
It is normally composed of three or four sections and has the task of eliminating the residues of soda; washing detergents and of making the bottles come out in at least drinkable conditions.To do this, the last rinsing ramp is normally fed by the same water which will then be bottled; and in any case by water with drinking characteristics.The problem in this sector is represented by the hardness of the water; which precipitates calcium carbonate (limestone) due to the alkalinity present and/or the temperature of the bottles.If the water is not softened, limescale precipitation must be avoided by adding a suitable sequestering additive; in a concentration proportional to the volume of water in circulation and the hardness present.The bottles come out of the caustic baths practically sterile. The rinsing area, on the other hand, is a very favourable area for microbial growth due to the presence of water; a suitable lukewarm temperature and pH towards neutrality.In this sector, it is necessary to avoid substantially sterile bottles undergoing re-pollution phenomena; with a microbial load so high that it cannot then be eliminated by the last potable rinse.For this reason, it is necessary to add in the second rinse or in the penultimate a biocide formulation that sanitizes the bottle internally and that; ending up in the tanks, keeps the microbial load controlled (bacteriostatic action).
The bottle rinsing system is based on the use of nozzles often self-cleaning directed in a radial direction with respect to each row of baskets; the self-cleaning effect, and the consequent elimination of the disassembly and cleaning operations; are guaranteed by their rotation which allows an inversion of the water flow and the continuous removal of dirt particles from the spray channels.The direction of the sprays allows the perfect washing of the bottles, first being hit an internal side of the bottle; then the bottom and finally the opposite internal side.On the side of each row of jets there is a star that allows the perfect synchronisation between jets and bottles; even following the possible elongation of the chain.Correct rinsing is essential in order not to find very dangerous soda residues in the bottle if then ingested with the product.
The opening of the unloading pallet allows the bottles to be transferred from the baskets to the cams which; with their elliptical movement, accompany the bottles along the unloading chute until they are placed on the unloading conveyor belt.The chutes and the exhaust cams are made of high density polyethylene to ensure silence and high durability.A special mention must necessarily be made for this section of the bottle washer. The presence of humidity and steam, the neutral pH; the warm environment are factors that predispose the microbial development.It will therefore be necessary to foresee and carry out cleaning and sanitizing treatments of the internal head; and, also of the external surface on a daily basis in order to avoid the establishment of possible points of microbial contamination.In this area, bacteria, yeasts and moulds can easily proliferate and just as easily contaminate the clean and sanitized bottles at the outlet.
All bottle washers can be equipped with a special device installed in the loading and unloading area; designed to reduce the noise level and allow better safety conditions for operators.
Working in a washing machine with temperatures ranging between 60 °C and 80 °C; an adequate insulation system can considerably reduce the energy consumption of the machine.On the machines it is possible to mount a total or partial insulating system; made with polyurethane panels (high thickness); supported on the edges by stainless steel sheets; able to guarantee an energy-saving close to 20% of the total energy consumption of the machine.
Cleaning of wastewater
In order to increase the life cycle of the pulp bath, there are two different filtration and recycling systems of the pulp tank solution:
SEDIMENTATION TANK: at the end of the working day the solution is sent to a sedimentation tank; in which the filtration takes place which can be carried out in medium-low pressure or high-pressure conditions.
VIBRATING SCREEN: during the operation of the machine; the solution is continuously sent inside a separator, where it is filtered by means of a net that retains all the glass and paper particles; the filtered liquid is then continuously returned to the pulping bath.
Washing with acid sector machine
Some washing machines have a sector located between the caustic wash and the final rinse with an acid spray inside the bottles.This sector aims to refine the alkaline washing by completely eliminating any inorganic residues present in the bottle.Of course, there will also be a rinsing phase before the acid spraying to partially reduceAlkalinity.The acid normally used is based on formulations containing nitric acid; which will act as a passivation for the steel surfaces.This sector does not present particular problems other than a periodic antimicrobial control for the possible formation of molds; which we know prefer environments with acidic pH.
Washing is extremely important to obtain washed bottles and above all free of any other visible but also invisible contamination such as microbial type.The general sense of this washing tells us that at the exit of the bottle washing machine; the bottles must always have a degree of purity equal to the water conditions of the last rinse; (basic concept for any mechanical washing procedure).The washing of the bottles and above all the success of this process depends on many factors, which must necessarily take into account the type of machine present; the type of bottles to be washed and the structure/composition of the labels to be removed.In succession, the choice of the most optimal chemical formulations; the correct application of the same and the ability to read the “signals” shown by the bottles after washing are essential requirements for obtaining correct cleaning and sanitizing of the glass containers.The general and theoretical technological aspects that are present in a bottle washer are many; and, represent the starting point for managing the washing cycle in the best possible way.
It is possible to identify a series of critical aspects that will always be evaluated when we begin to “study” a bottle washer. In particular, if we follow the bottles in their washing cycle, we will have:
Evaluation of the correct detachment of the labels from the surface of the bottle.
The evaluation of the correct extraction of the labels that have been detached from the machine.
Evaluation of the correct removal of dirt residues from the inside of the bottles understood both in terms of dirt caused by the dried residues of what has been its contents; (especially in soft drinks and wine), and in terms of possible foreign bodies (insects, larvae and eggs of insects, mold, etc.)
On the effective alkalinity waste reduction rating on the glass before arrival at stations rinse. The methods of this abatement determine the choices to be made for the treatment in these areas.
Evaluation of the type of water in place in order to make the most correct choice on the sequestering agents to be used.
Evaluation of the final microbiology of the bottle and possibly a choice of the most appropriate sanitiser.
The correct application of these evaluations then translates into the final observation of the washed bottle which must be clean; without the presence of residual glue or traces of residual labels and with a film of water that covers the entire external surface homogeneously, of glass.When the bottle is overturned, only two or three drops of water should come out; indicating an excellent dripping and therefore a correct orientation of the spray nozzles.
Sterilization of bottles
At the end of drying, the glass must remain bright and without streaks and by checking with phenolphthalein/litmus paper; the effective rinsing must be verified (pink colour in case of residual alkalinity).It is then possible to carry out analytical checks on the state of hygiene of the container in its internal part; through microbiological analysis, in order to verify its correspondence in terms of the law.The correct operation of a bottle washer passes; through the optimization of three well-defined parameters that must necessarily be evaluated and optimized. These elements are:
Concentration of caustic soda (alkalinity) in washing baths
Land operating temperatures of the solutions washing
the contact time between caustic and bottles solutions (movement speed of the baskets)
These three intersected parameters are also able to ensure the certainty of an excellent washing and of the reduction of the microbial component inside the bottle.There is a reference table with which it is possible to confront to be able to obtain precise directions in order to obtain the “sterilization of bottles”These three parameters are, however, also essential to obtain the correct separation of the labels without that these may undergo phenomena of pulping.The working speed of the machine (the travel time of the bottles in the machine between the moment of entry and exit) and the working temperature (between 70 and 90 °C); the choice of the concentration of soda and type of additive to be applied (or of the soda-based formulation) becomes important for the result that can be obtained.
The chemical formulations that are normally used inside a bottle washer are:
Additive to caustic soda to facilitate the detachment of labels.
Additive to soda for the control of foam in caustic baths, often caused by the presence of glues of casein origin.
Alkaline formulation to be applied as an alternative to the soda system (NaOH) + additives.
Sequestering additive to control the hardness of the water in the rinsing baths Sanitizing.
Formulation for the treatment of the bottle at the outlet and to keep the rinsing tanks in suitable bacteriostatic conditions.
In addition to these, there is the possibility of resorting to further formulations capable of increasing the washing performance; so we will have:
Additives to enhance the detachment of labels.
Additives to increase the detergent capacity in the presence of dirty details such as moulds, dry dirt skins.
Acid additive to lower the pH and therefore reduce the alkalinity of the first rinse.
The activity of soda can be helped by chemical formulations able to soothe and reduce the negative effects present in caustic baths; effects determined above all by the inorganic components (water salts, metals deriving from the labels themselves, etc). And from the organic ones always arriving with the bottles returning (glue, generic dirt, etc.)The most important elements are certainly the sequestering additives and in some ways; the antifoams dosed only when necessary.Less important are the additives with surfactant action; whose usefulness has been increasingly reduced over time to the advantage of the use of sequestrates.
A sequestering or chelating agent is achemical compoundor oneblendof chemical compounds capable of forming forchelationcomplexmore or less stable withatomsorions. The chelating term comes fromclaws, imagining the chelator as a crab that grabs and envelops the metal ions.The sequestering action molecules, normally inserted in soda additives; have the very important function of binding the dispersed ions and salts; preventing their adhesion to the surfaces (limescale deposition) and competing with the hydroxyl bonds of the bath. They help to cleanse against moulds adhering to the inside of the bottles. They control the problem of aluminates by favouring the detachment of the label.
The classes of sequestrates used are various, even if in recent years we have mainly addressed the use of EDTA which; forming achelatedvery stable with the calciumand themagnesium is also used to prevent the formation and deposition oflimestonefrom the waters.This molecule is a stoichiometric sequestering agent capable of competing with most of the metals present. Stoichiometric means that it is an effective sequestering agent only when the sum of the bonds it is able to carry out exceeds the concentration of the metals present in the system.The fact that it behaves in this way makes it particularly difficult to calculate the optimal value to insert in the bathroom. If this value is exceeded with the incoming “dirt”, the EDTA will not be able to complete its activity and will end up under stoichiometry.This is one of the reasons that makes the exclusive use of this molecule very risky; which instead should be combined with other sequestering molecules with “threshold effect” or even better to entrust the second part of the washing to EDTA (for example in the second caustic bath); after operating in the first phase with another sequestration system (in the first bath we see a strong release in a solution of metal ions which would cancel the action of the EDTA).
The action in the second bath can therefore be more addressed to the problems of removing moulds; larvae and insect eggs and to the completion of the label detachment. A second negative aspect of the use of this sequestering agent is the corrosive action that EDTA is able to operate on the bottles in transit.Although glass is a substantially very resistant material, it is corroded by soda in the multiple washing cycles. Sequestrates increase this corrosive effect, and between them EDTA is undoubtedly the one that attacks glass the most. After this chemical attack (general opacity) the bottles moving on the conveyor belts undergo compression due to rubbing, which causes the glass to wear.On the other hand, a separate discussion should be reserved for gluconate and gluconic acid; sequestering agents with real polyfunctional activity in caustic baths. The activity of these compounds is best achieved in an alkalinity range between 1% and 3%; where they are able to intensify their sequestering, dispersing and suspending action specifically towards aluminum and its salts. Aluminum is in fact a trivalent metal that EDTA cannot bind.The “gluconates” then assist the EDTA in the eventual elimination of deposited iron (rust collar caused by the crown caps).
The function of this type of product is precisely to keep the foam that is formed by the mechanical action of the machine under control; above all due to the starch-casein glue; but also due to the presence of organic molecules transported by the dirty bottles themselves.The foam must be kept below certain levels to prevent the pumps from cavitations; that the reading probes are inhibited in their function; and, above all because the detached labels can “float” on the foam; to be extracted and not end up in the final parts of the car.
Visual Evaluation Of The Bottles
The appearance of the bottles exiting the machine indicates the quality of the washing that has just been carried out; and above all it will tell us exactly in which sector of the machine the possible defect that we have found on them comes from.
Here are some examples of defects that can be found:
Tracks of glue present on the glass are an indication of non-optimal washing baths and therefore of a problem of detachment of labels;
And labels that appear at the exit of the bottles. Also in this case it is a problem related to the washing baths;
PRESENCE a white collar on the bottle. The problem arises in the exit area from the caustic solution; with drying of the same in this sector;
White spots grouped spray. Also in this case the problem arises in the exit area from the caustic solution with drying of the same in this sector;
Bottles with homogeneous water film, but which after drying remain misted with more evident rivulets. Most likely, there is a dragging of soda because it is too concentrated or the rinsing nozzles are clogged;
Bottles with homogeneous water film, but which after drying remain misted and veiled. In this case the rinsing is not optimal due to the lack of correct control of the water hardness with consequent light precipitation of limestone. The concentration of the sequestering agent needs to be adjusted.