Dairy Engineering

Module 2. Bottle & cans washing and CIP cleaning equipment

Lesson 5
DESCRIPTION, WORKING AND MAINTENANCE OF CAN WASHERS STRAIGHT - THROUGH CAN WASHER

5.1 Introduction

Milk is procured from villages in cans, and brought to the Dairies or Bulk milk collection centers. At dairies, if the collection through cans is in large quantities, the cans have to be cleaned using mechanical means. If the quantities are less, then it can be done manually, using can washing trough and mechanically operated brushes and steaming blocks. The mechanical can washers are again two types. The smaller capacity ones are Rotary can washers, whose capacity is 3 to 5 cans/min, while the larger capacity ones are Straight-through can washers, whose capacity is about 12 cans/min.

5.2 Hans Washing or Can Scrubber

This method is adopted in all milk chilling centres where less number of cans is to be washed. One man can operate this unit conveniently.
Construction of can scrubber is shown in figure and described below:

1. The scrubber machine is made of 10 SWG G.I. sheet or M.S.sheet with totally galvanised.
2. The machine is painted with 'epoxy' paint to avoid corrosion.
3. The can scrubber consists of a tank in which two revolving nylon brushes are mounted on shafts.
4. The extension of shafts are properly encased in sealed enclosures and provided with suitable bearings and lubrication points.
5. Gland packing is used to avoid the leakage through the shaft.
6. A stationary nylon brush is fitted with a bracket on the inner wall for cleaning outside of the cans.
7. Side stationary brush is changeable. It can be fitted on either side of the inner wall.
8. Cylindrical nylon brushes, revolve at a low speed, i.e., 80 to 100 rpm, in opposite directions by a motor and reduction gear unit, give thorough and effective cleaning action on either side of the can..
9. Steam and water connections are given to the tank for making warm water for washing operation.
10. At the bottom of the tank a drain valve is fitted for easy draining and cleaning of the tank.

5.2.1 Preparation: Can scrubber is prepared for can washing as follows

1. Check the oil level in the gearbox and lubricate the chain over the sprockets for the brushes.
2. Check the rotation of the brushes.
3. Clean the tank and close the drain valve.
4. Open the water valve and fill the tank to the marked level.
5. Add. 0.8% washing soda and 0.2% tri-sodium phosphate to the water.
6. Open the steam valve and raise the temperature of the detergent solution to 55°C.
7. Start the rotating brushes by switch on the drive motor.

5.2.2 Washing Operation: Washing operation is done as follows

1. First of all can is pre-rinsed with warm water at about 40°C both from inside ­and outside.
2. Then can is inserted on the top rotating brush and brushed thoroughly from both sides for 10 seconds.
3. Then can is taken out and rinsed with hot water at about 60°C.
4. Final rinsing, sterilization and drying of can are carried out on the steaming block.

5.3 Steaming Block

Steaming block is always used with can scrubber for final rinsing and sterilization of washed cans. The construction of steaming block is as below:

1. The stationary part of steaming block is made of cast iron material and the working parts are of stainless steel.
2. At the base water and steam lines are connected through spring loaded valves and the valves are operated by the pedestal levers.
3. A steam mixing battery is fitted inside the vertical column.
4. The top portion has a concave surface on which a spray nozzle, drain hole, and seat rests for can mouth are provided.

5.3.1 Operational precautions

1. Steam supply should be given through a steam mixing battery to avoid vibration.
2. If the brushes do not rotate, check the direction of rotation and correct it or tighten the idler wheel, provided on the chain, as required.
3. It will be hard to insert the can on a new brush. Do not cut the nylon bristles to reduce brush diameter in order to reduce the worker's labour. If this is done, the scrubbing and cleaning will be ineffective.
4. Periodically check the lubrication and alignment of gearbox and sprockets to avoid any breakdown.

Fig. 5.1 Steaming block

5.4 Rotary Can Washer

Rotary can washer has a revolving platform, with holes on which the cans can be placed in an inverted position. As the revolving platform moves intermittently, the inverted can is jetted by various solutions, as shown in Fig. . Under the platform, a series of tanks, containing washing solutions will be provided. These solutions are forced at high pressure, by centrifugal pumps, through jets placed below and to the sides of the cans. The liquid returns through the platform grating to the respective tanks. The platform is rotated intermittently to ensure that each can receives a constant period of treatment over the jets.

The sequence of operations preceding simultaneously are

(1) loading of can in vertical inverted position
(2) rinsing with warm water (which is drained),
(3) drainage of rinse water,
(4) treatment with detergent solution at high pressure ( at 65 to 70 ⁰C) to soak, loosen and dislodge milk film from can surfaces,
(5) drainage of wash solution back to detergent tank,
(6) hot water rinsing at 65 to 70 ⁰C,
(7)and (8) blasting with dry saturated steam,
(9) drying of steam condensate with hot air blast, and
(10) unloading of the can, inverting and placing the lid on the can.

The can washer is provided with a stationary canopy with chimney to take away the exhaust steam. The capacity of washer is suitable for small chilling centers, and can wash about 3 to 6 cans / min. The same operator can load and unload the can, thus saving man power.

Fig. 5.2 Rotary can washer

5.5 Stright Through Can Washer

5.5.1 Principles of operation

Straight through can washer carries the cans through the washer in a straight line by means of a continuously moving conveyor or slide along rail as they move intermittently from one jetting position to the next. The driving unit moves the can forward from one position to the next at regular intervals.

Fig. 5.3 Straight – through can washer

5.5.2.1 Draining

Before passing the cans to the can washer, milk, cream or any other fluid is drained out by placing the cans in an inverted position over a drip pan before it is rinsed. Few washers have arrangement of drip saver to collect the residual milk in the can. After draining of the milk the cans are automatically loaded into the can washer in inverted position. The lid of the can is also entered into the can washer for proper cleaning.

5.5.2.2 Pre-rinsing

Rinsing of can is done by passing water through the jet to clean the milk film remaining in the can at a pressure of about 1.0 to 2.0 kg/cm2 for 3-6s, so as to remove the traces of milk.

5.5.2.3 Hot water rinsing 1

Cans are rinsed by clean hot water. The temperature of hot water is maintained at about 65-70°C. Temperature should increase at successive stages, as at the sterilization and drying stage the steam and hot air temperature will be higher than 100°C.

5.5.2.4 Caustic rinsing

Caustic rinsing is done by passing the washing solution through jets at a sufficient high pressure both inside as well as outside to remove all milk and cream film inside and outside of the cans. Cleanliness of can depends on temperature and strength of washing solution. When using alkaline solution, alkalinity should be less than 0.15 percent. Caustic soda must not be used as detergent, but sodium carbonate and a corrosion inhibitor are suitable as high temperature causes the formation and deposition of milkstone on the can surface. So the optimum temperature of washing solution must be in between 65°C and 70°C for 9-18s. After Caustic rinsing the detergent solution is drained.

5.5.2.5 Hot water rinsing 2

This is done to clean the washing solution thoroughly. The water temperature in this section is about 85-90°C and this water is drained after use.

5.5.2.6 Sterilization

sterilization of can is done by passing dry saturated steam at 110°C for 5 to 10s. Steaming process sterilizes the cans and increases the can temperature which facilitates the easy and quick drying in the drying section. The temperature, heat content and moisture content of steam influences the effectiveness of steam sterilization.

5.5.2.7 Drying

The main purpose of drying is to prevent the corrosion of metal due to moisture and to check the bacterial growth. The drying operation is accomplished by blowing jet of hot air at 110°C inside the can. The moisture holding capacity of air depends on its temperature and relative humidity.

The capacity of straight – through can washers varies from 6 to 16 cans per minute. This type of washer is used in large size dairy plants. It is easily accessible for maintenance and cleaning of the inner parts. There is no recontamination of cans either by the washer or by the operator. It occupies more floor space in dairy, and requires close inspection while in operation.

The service requirements of straight-through can washer (6 to 8 cans per minute) is as follows: steam between 0.85 to 1.8 kg per can, water consumption 4.0 to 4.5 L/ can, energy between 1.0 and 2.4 kWh, to operate the machine.

Maintenance

1. The water valves should be opened, cleaned and water pressure (2.0 to 4.0 kg/cm2) should be checked. If the pressure is not sufficient it may be due to clogged jets and defective pump. The clogged jet should be cleaned and the pump should be checked for defective shaft seals, clogging and worn out parts. The pump strainer, inlet and outlet lines should be checked for the accumulation of lime and scale.

2. The can washer should be cleaned as and when necessary. All the wash sprays, nozzles and strainers should be checked and cleaned.

3. The mechanical difficulties of the can washer are caused by lack of regular and sufficient lubrication, failure to make adjustment for wear, and failure to replace worn out parts. Most of the mechanical difficulties can be avoided by proper, lubrication of the moving parts, making adjustment for wear and replacing the worn out parts immediately.

4. The temperature and pressure of the washing solution, hot water, steam and drying air should be maintained at optimum level. The proper strength of the solution is also a very important factor for proper washing.

5. Heavy scale deposits in can washers are usually the result of inadequate daily cleaning, use of hard water, and the use of solution at inadequate temperature and strength. The scales can be removed by using inhibited acid at a temperature of about 50°C.

5.6 Preventive Maintenance Schedule

Maintenance to be done	Frequency
Drain the water from can washer and clean the tanks	Daily
Clean all spray nozzles and openings	Daily
Clean the pump strainers by brushing	Daily
Clean the chain conveyor with hot water after every operation	Daily
Lubricate all the rollers, bearings, bushings, ratchet arms and chain	Daily
Check oil level in the reduction gear box	Daily
Check the function of the dosing device	Daily
Open all the shields after every operation.	Daily
Check the water line and steam line valves for leakage through glands.	Weekly
Lubricate the bearings of hot air blower and exhaust fan by lightening the grease cups	Weekly
Check the suction filter of hot air blower clean or replace, if required	Weekly
Check the leakage through pump glands	Weekly
Check steam and water valves for any leak and spray nozzles and non return valves for proper operation in steaming block	Weekly
Check oil level and smooth running of gear box in can scrubber	Weekly
Check shaft, bearings, oil seals, chain and sprocket in can scrubber, repair or replace if required	Monthly
Check the temperature sensing elements in all tanks for any scale deposition	Monthly
Check the function of the steam trap	Monthly
Check and recalibrate the temperature gauges and pressure gauges	Monthly
De scaling of can washer	Quarterly
Check all motors in can washer and scrubber	Yearly
Complete overhauling of all pumps.	Yearly