Knowledge | 2022-07-06

Several main ways to improve the cleanliness of ultrasonic cleaning


Ultrasonic cleaning machine is widely used in hetero, micro, and high-precision parts cleaning. At present, the cleaning agents used in the ultrasonic cleaning process are mainly hydrocarbon cleaning agents and water-based ultrasonic cleaning agents. In comparison, the cleaning degree of parts and components after cleaning with hydrocarbon cleaning agents is higher, however, the water-based ultrasonic cleaning agent has its unique advantages of low cost and safe use, and is still welcomed by small and medium-sized users. The definition of cleanliness can be simply understood as the relative residual amount of impurities on the surface of the workpiece after cleaning. At present, there is no unified standard test method, because of the increasing demand for high precision assembly and high precision surface treatment, the requirement of cleanliness is higher and higher. How do improve the cleaning cleanliness of water-based ultrasonic cleaning agents? The following author shares some ways to improve the cleanliness of ultrasonic cleaning.

Using immersion block ultrasonic cleaning:

Ultrasonic cleaning of the workpiece is an advanced cleaning technology, and it is also a physical cleaning method widely used in the cleaning field. Ultrasonic cleaning is the use of immersion-block transducers to convert ultrasonic electrical signals into high-frequency mechanical vibrations that are transmitted into the cleaning fluid. Under strong Sonication, the molecules of the liquid are sometimes pulled and sometimes pressed, the formation of many tiny voids (voids), commonly known as the“Cavitation effect.”. Because the pressure difference between the inside and outside of the cavity is very wide when the cavity breaks, it has a strong impact force at a moment, when the surface of the workpiece, the slit, the inner cavity, the blind hole, the small hole and so on are subjected to this impact force, adhere to one of the various types of oil, debris, and other dirt will be peeled off. In addition to its huge energy, ultrasound also has a stirring effect, so that the cleaning fluid movement, fresh cleaning fluid constantly act on the dirt to speed up the dissolution, to achieve the goal of cleaning.

Usually using immersion block transducer, according to the cleanliness requirements of the workpiece can be used single block or multi-block layout, single or multi-slot layout. In addition, the transducer can be arranged on the inner side wall or bottom of the groove according to the shape and size of the workpiece. The temperature of the cleaning solution is generally 50 ° c-60 ° C, and the cleaning time varies from 30 seconds to 10 minutes according to the technological requirements The ultrasonic intensity is set at about 0.5-1w/CM2. Ultrasonic cleaning is especially suitable for porous objects and small parts with complex geometry, such as the crankshaft, connecting rod, piston, spring, and valve plate in compressors. The water-based parts automatic ultrasonic cleaning machine designed and manufactured by our company for a customer, its cleanliness index can reach: liquid dust content of 0.5 ~ 15mg/piece, solid dust content of 0.1 ~ 3mg/piece (more than 10 kinds of parts of material, shape water-based cleaning equipment cleanliness of the effective way shape is different, its cleanliness index is also different).

Cleaning by mechanical shaking:

At the same time as adopting the ultrasonic cleaning, according to the characteristics of the parts and the requirements of the users, mechanical shaking cleaning can be added, that is, using the eccentric wheel or cam mechanism; Cylinder vibration cleaning can also be used to make the work-piece basket up and down shaking (vibration), to enhance the cleaning decontamination effect.

Immersion block ultrasonic cleaning and mechanical shaking cleaning are suitable for immersion cleaning.

High-pressure fixed-point spray cleaning:

High-pressure spray cleaning has a powerful cleaning force, can remove stubborn adhesion to the surface of the dirt, especially for some special shapes, deep blind holes, and high cleanliness requirements of parts (such as crankcase), at the same time also has a certain removal of burr, Flash, welding slag and other functions. Compared with low-pressure spray cleaning, its cleanliness index can be increased about 3 times. The fixed-point mode is adopted to clean small holes, blind holes, and parts with a special shape that are not easy to be cleaned by the traditional mode. A rotary encoder sprocket is arranged at the driving shaft of the feeding end of the workpiece, and the rotation angle of the sprocket is arranged to adjust the movement of the conveying mechanism (which can be adjusted when the chain deforms and the pitch changes), the PLC is used as the core to control the variable frequency speed governor so that the transmission chain can start smoothly, move quickly, slow down smoothly and reach the position accurately, and the positioning accuracy of 1mm can be realized. The combination of accurate positioning and high-pressure spray can ensure the cleaning effect of high cleanliness.

Commonly used high-pressure spray cleaning pressure for parts cleaning is 3.5 mpa ~ 6 mpa, when there is a special need, can also choose a higher pressure or even ultra-high pressure (100 mpa) . High-pressure spray cleaning, in addition to the need to pay attention to the pressure and its high-pressure pump, high-pressure hose, and accessories, but also pay attention to the nozzle material, shape and spray distance, etc., in particular, the parts must have a reliable way of clamping, while the equipment must have more perfect shock absorption, noise reduction, and safety measures.

Set up oil-water separator:

The degreasing process is an important process for cleaning equipment. The oil contamination of the parts to be cleaned must be removed in time during the degreasing process, otherwise, the oil concentration will decrease with the increase of the number of parts to be treated, the degreasing ability will decrease continuously, and the cleanliness of the parts will also decrease, therefore, in addition to the need to regularly update the degreasing liquid, but also the need for degreasing liquid for oil-water separation treatment. When the oil concentration in the degreasing solution reaches 5-10g/L, it must be renewed, otherwise, the degreasing oil will no longer exist in the emulsified state in the degreasing solution, but will re-attach to the parts to be cleaned, thus affecting the subsequent parts to be cleaned clean quality.

The oil-water separator is a device that discharges the emulsified oil into the oil collecting barrel and after the automatic oil discharging treatment, causes the degreasing liquid after degreasing to return to the degreasing tank. The commonly used oil-water separator is mainly composed of an oil-water separation tank, pump, valve, pipeline accessories, oil collection hopper, etc. . 2.5 parts equipped with magnetic separators are often processed by grinders and other machine tools with iron powder, chips, after degreasing cleaning, these powder and chips are turbid in degreasing liquid, only through the magnetic separator on the magnetic drum or disk, can the degreasing liquid in the powder, chip suction, discharge, so that the degreasing liquid to keep clean, to improve the cleanliness of parts. The magnetic separator is mainly composed of a box body, a magnetic drum or a magnetic disk, a reducer, and a scraper.

Set up the filter circulation device:

The filtrating circulation device draws the dirtier liquid (containing insoluble matter) in the cleaning tank into the auxiliary tank for filtering, and at the same time pumps the cleaner filtered liquid in the auxiliary tank into the cleaning tank again, the device plays an important role in improving the cleanliness of parts. According to the specific requirements of the parts to be cleaned, and impregnated, spray-type cleaning methods can be set appropriate mesh number of screen plate filter, basket filter, bag filter, and filter element filter. 2.7 the installation of wind knife blowing device for higher cleanliness requirements of the parts, in the cleaning, rinsing process, often set wind knife blowing device. This is not only conducive to the final part of the drying but also to solve the surface of the part of the way to produce water spots. Because the rinsing water contains impurities, the parts are easy to leave water spots on the surface after drying, even if the use of pure water rinsing, there is a possibility of water spots. Using the wind knife blowing device, the use of wind pressure can be part of the surface of the water blowing away.

Other aspects:

1) for immersion cleaning, the structure design of the cleaning basket is also very important. The contact area between the cleaning basket and the cleaning solution is small, and the arrangement of the parts in the basket has a certain influence on the cleanliness.

2) whether it is immersion cleaning or spray cleaning, the selection of appropriate heating temperature (electric heating or steam heating), but also contributes to improving the cleanliness. Since the ability of water and organic solvents to dissolve dirt increases with temperature, raising the temperature of the solvent allows the solvent to perform its role of dissolving dirt and making it easier to remove it. Raising the temperature of the water helps to remove the alkali and Surfactants that are adsorbed on the surface of the part.

3) set up agitation device set agitation device, can improve the efficiency of separating, emulsifying, and dispersing dirt, and also help to improve cleanliness. A common agitation device is to set up an exhaust pipe in the cleaning tank. The filtered Compressed air with a certain pressure is discharged to the cleaning tank through the exhaust pipe. The bubbles that are generated rise rapidly and cause the cleaning liquid to flow, thus playing a starring role. This is one of the agitation methods to let the liquid flow.

To sum up, it is very important to adopt different cleaning processes and technology according to different material and shape parts in the design of water-based cleaning equipment.

Several main ways to improve the cleanliness of ultrasonic cleaning