Selection of caustic concentration and temperature setting for the bottle washer

1. Selection of caustic concentration for bottle washing

1. Composition of the washing solution
The washing solution in the caustic tank generally uses:
a) Caustic soda (NaOH);
b) Active washing substances;
c) Additives to prevent precipitation;

2. Selection of detergent concentration
The detergent concentration in the caustic tank should be determined with reference to:
a) The degree of soiling of the bottles;
b) The nature of the labels and adhesive;
c) The labeling method (spot, line, or full-surface pasting);
d) The hardness of the working water;
e) The throughput of bottles per hour.

3. Standard values of sodium hydroxide (NaOH) for preparing caustic solution
a) Caustic I: 1.5–2.5%;
b) Caustic II: 1.0–2.0%;
c) Recommended caustic concentrations:
New bottles: 0.6 ± 0.3%;
Returned clean bottles: 2.3 ± 0.5%;
Returned dirty bottles: 2.5 ± 0.5%;
The higher the water hardness, the higher the concentration of washing additives. The total additive concentration should be controlled at 0.2–0.5% as appropriate.
In the direction of chain operation, caustic solution will inevitably be carried into adjacent liquid treatment zones, and the concentration will gradually increase automatically. Therefore, the lowest possible caustic concentration should be selected for the last caustic tank.

4. Adding caustic
a) Caustic and additives can only be added to each tank when the temperature is heated above 50°C; otherwise, foaming is likely to occur;
b) The caustic concentration in each tank can be operated with reference to Caustic I tank at 1.5–2.5% and Caustic II tank at 0.5–1.0%;
c) When adding solid (flake) caustic, Caustic I tank can be fed through the caustic hopper; Caustic II tank can be fed through the label remover section;
d) When adding liquid caustic, Caustic I tank can be fed through the reserved caustic inlet on the tank;
e) It is recommended to use an automatic caustic addition system to reduce fluctuations in caustic concentration and ensure cleaning effectiveness. For manual addition of solid flake caustic, the principle of "add frequently but in small amounts" should be followed.

5. Tank capacity
Refer to "technical parameters of each model".

II. Temperature setting

1. Heating
a) Open the main steam valve (the pressure shown on the steam pressure gauge must be maintained at a stable 0.4 MPa) and open the manual air valves for the caustic tank, hot water tank, and warm water tank;
b) When the water in the caustic tank warms to 50°C, add detergent and necessary washing additives. Generally, the NaOH content is between 1–2.5%. The soaking cleaning effect is related to the sodium hydroxide content of the washing solution, the degree of soiling of the bottles being cleaned, the temperature of the washing solution, and the soaking time of the dirty bottles. In general, higher temperature, higher caustic concentration, and longer time result in better cleaning. When starting the bottle washer, the water in Caustic I tank must be heated above 50°C before adding caustic and additives; otherwise, foaming is likely to occur. When the caustic concentration exceeds 5%, label dissolution will occur;
c) The main component of the washing solution used in the soaking tank of the bottle washer is NaOH, and appropriate additives (such as wetting agents, phosphates, defoamers, etc.) should also be added to improve washing efficiency;
d) The ideal washing solution should have the following advantages: bottles washed out meet sterilization and disinfection requirements, clean and bright both inside and outside, economical and safe, low-foaming, and non-toxic;
e) After adding detergent to the caustic tank, immediately start the label remover, and start the label-removal spray pump, caustic spray pump, hot water spray pump, warm water spray pump, and clean water spray pump. Start the main machine to circulate the bottle carriers, promoting water circulation and accelerating heating of the caustic solution;
f) When the caustic solution in Caustic I tank warms to 60°C, close the bypass manually controlled steam valve and immediately open the automatic control circuit with the pneumatic diaphragm valve. In general, control the caustic solution temperature in Caustic I tank at around 82°C;
g) After the water temperature and washing solution concentration in each tank meet the requirements, start the bottle infeed conveyor and the longitudinal infeed conveyor to begin feeding bottles. Shortly after, start the clean water spray pump to increase clean water pressure. When bottles approach the discharge area, start the bottle discharge conveyor and notify the next process to prepare;

2. Precautions
a) Only after filling each tank with water to the required level can heating begin;
b) Steam can only be supplied while the water pumps are operating continuously;
c) Steam valves should be opened slowly to avoid water hammer;
d) During heating, when opening the automatic temperature regulating valves for Caustic I, Caustic II, etc., they should be opened slowly and gradually, and should not rely on "manual" or "automatic" switch/button adjustments;
e) At the start of heating, both manual and automatic heating devices can be turned on simultaneously. When the temperature reaches 85% of the required value, close the manual heating device and allow the automatic temperature control system to control the heating;
f) While heating, start the Caustic I label-removal spray pump, Caustic I spray pump, Caustic II label-removal spray pump, hot water spray pump, warm water spray pump, clean water spray pump, label remover, and exhaust fan motor to accelerate heat exchange;
g) When washing beer bottles, the temperature difference control between caustic tanks should be set at: new bottles ΔT ≤ 38°C, returned bottles ΔT ≤ 35°C; otherwise, bottle breakage may increase;
h) Based on actual measurements, the deviation between the actual caustic temperature and the displayed temperature is approximately ±3°C;
i) The higher the caustic temperature, the better the cleaning effect. For cleaning returned bottles, temperature control is more important than caustic concentration control.