What are the selection conditions for coating solvents?

Vapor phase cleaning, the workpiece is washed, rinsed and dried in the solvent vapor layer, and the workpiece is not subject to secondary contamination, so a high degree of cleanliness can be achieved. However, if poorly managed and improperly operated, the problem of excessive solvent loss often occurs, increasing the cost of use. The following on the solvent loss is too much (especially low boiling point solvents) to do some analysis of the reasons, and put forward a number of solutions
(1) the position of the washing machine is not placed properly, there is strong air convection, resulting in excessive solvent volatilization
Solution: The cleaning machine should be avoided to be placed in the doorway, window and other places where there is a penetrating wind, as well as electric fan, air conditioning vents.
(2) Insufficient space in the upper free area of the cleaner (the distance from the vapor surface to the top of the tank), and the solvent vapors are affected by the surrounding airflow and escape.
The solution is as follows:
① This is a tank structure design issues, tank design, attention should be paid to the vapor surface to the top of the tank distance and the width of the tank ratio should be greater than 75%, the use of low-boiling point, volatile solvents and more expensive HFC-4310 solvent, the ratio should be increased to 1.2 ~ 2.0; the location of the vapor surface can be from the middle of the condensing coil or slightly below the position of the condensing coil to consider.
② can also be used double condensing tube, double condensing temperature, the upper condensing tube temperature control in -29OC, the lower working condensing coil temperature can be controlled at about 4 OC.
(3) The width of the cleaning tank should not be too wide.
(3) The vapor surface is too high, the condensation capacity is insufficient, so that too much solvent vapor escape.
The solution is as follows:
① check whether the refrigeration system is working properly, troubleshooting in a timely manner.
② such as water cooling, should check the temperature of the cooling water in the outlet, the boiling point of 45 to 50 OC between the solvent, the water temperature at the drain should be controlled at no more than 21 OC; the boiling point of 45 OC below the solvent, the water temperature at the drain should be controlled at no more than 16 OC.
(4) the vapor surface is out of control, a large number of solvent vapor escape
The solution is as follows:
① in normal operation, the vapor surface should be controlled in the middle of the condensing coil or slightly below some, can be controlled by adjusting the vapor temperature of the refrigerator or adjust the temperature and flow of cooling water.
② check the equipment temperature protection device, when the vapor surface is too high (such as refrigeration system failure), should be able to automatically cut off the power supply, stop heating.
(5) improper placement of workpieces, solvents with the workpiece out
Solution: workpiece cleaning, should make the concave down, so that the solvent can maximize the outflow, not in the concave accumulation.
(6) workpiece in the tank moving too fast, so that the solvent vapor escape
Solution: workpiece in the cleaning tank either up and down or left and right movement, the speed can not be too fast, should maintain the stability of the vapor layer, the general speed of workpiece movement should be less than 50mm/s.
(7) The height of the vapor layer is insufficient or the drying time is insufficient, so that the solvent is brought out by the workpiece.
The solutions are as follows:
① steam layer should be high enough to make the workpiece in the groove body movement, the workpiece does not reveal the steam layer.
② workpiece rinsing in the vapor layer to stay time, should be no longer condensation on the surface without solvent dripping before the end of the workpiece to leave the steam surface, in the freeze-drying area and then make a short stay in order to thoroughly dry.
(8) improper spray rinsing, increasing the solvent splash loss.
Solutions are as follows:
① spray cleaning, the position of the gun should be lower than the vapor surface 150mm, and should be sprayed downwards.
② spraying pressure should not be too high, generally less than 0.1MPa; spray the liquid stream, to multi-strand fine line flow shower is better, spraying will increase the splash loss.
(3) in the absence of the formation of a stable vapor surface is not spray washing.
(9) Improper operation procedures, increasing the evaporation of solvent loss
The solution is as follows:
① cleaning tank before heating, should be connected to the cooling water or turn on the chiller first.
② work is completed, turn off the heater first, but the cooling water does not stop or the chiller does not stop until the vapor layer completely disappeared, the solvent temperature is close to room temperature, and then stop the water or shut down the lid.
③ low-temperature control of the solvent temperature in the cleaning machine, keep the solvent temperature lower than the surrounding environmental temperature, in order to reduce the evaporation of solvents to stop working when the loss.
(10) Improper use and storage, resulting in solvent loss
The solution is as follows:
① when the washing machine is not in use, should be covered and sealed;
② long-term not in use, the solvent should be released, stored in a closed barrel;
③ Cleaning machine should have a person responsible for maintenance, pipe joints, pumps, discharge valves, filters, etc. should be frequently checked for leaks.