Operation and maintenance of polyurea spray machine
Polyurea sprayer connection
At the spray site, the polyurea spray machine includes many components such as H3500 main engine, PK2 spray gun, material extraction pump, supply pipe, A component, R component, heating hose, etc., which must be reasonably connected to ensure the smooth completion of the spray operation.
Air from the air compressor must pass through the air dryer. Two feeding pumps are inserted into the industrial vats containing the A component and the R component respectively. The material enters the main machine from the feeding pump with the feeding pipe, and the volume ratio of the precision metering pump in the main machine is controlled to 1:1, while accepting Heating and pressurization of the main unit. Subsequently, the material flows out of the main machine, passes through the heat-insulating hose, reaches the spray gun, and after igniting the trigger, passes through the filter screen in their respective directions and collides with the high-pressure in the mixing chamber, and then ejects at a high speed to receive compressed air at the nozzle to form a uniform fan shape. Or round material surface, sprayed onto the steel tube to form.
Field operation of polyurea spray machine
Polyurea spray machine has complex structure, complicated connection and many operation steps, and any error in any step of the whole spray process may cause the equipment to be directly scrapped. Therefore, the equipment operation steps must be standardized and determined throughout the spray process. After repeated spray tests, the on-site operation steps of the spray equipment were determined, and the operation was carried out in strict accordance with the set operation steps to ensure the normal operation of the spray test.
Polyurea sprayer maintenance
When the polyurea spray machine is not working for a long time, in order to prevent the A and R material vats and the pump from coming into contact with the humid air to crystallize, solidify and deteriorate, it is necessary to remove the A and R pump from the 200L vat and insert it. In the protective cover with the cleaning agent, the barrels of the A and R materials are simultaneously filled with nitrogen for storage. Turn off the main engine, but do not close the air compressor and the A material, R material feed ball valve.
When the feed pump is working normally, the DOP washing liquid is used to finish the construction (experiment), and then the DOP is used for circulating cleaning. After the cleaning, the residual liquid is sealed in the feed pipe. During the cycle cleaning, the washing liquid was washed twice with a washing liquid of 20 kg and a pressure of 3 to 5 MPa for 30 minutes. Cover the machine protective net cover and store the fixed warehouse.
Determination of the spray process
Polyurea coatings use high temperature, high pressure, and impact impingement mixing processes. Therefore, whether the reaction is complete and the performance is excellent during the spray process depends largely on the correct determination of the spray process. The determination of the spray process mainly includes the determination of two key parameters: spray temperature and spray pressure.
Determination of spray temperature
In the spray process of polyurea coatings, increasing the temperature is very advantageous for improving the spray effect. At the same time, the temperature sensitivity of the reaction temperature constant of the polyurea coating is low, so the elevated temperature does not cause a sharp increase in the reaction rate, but the mixing and fluidity of the A and R materials are improved due to the significant decrease in the viscosity of the material. Apparently, it seems that the warming has made the reaction more gradual. The actual temperature is controlled at 70 ~ 75 ° C. The hose is heated to ensure that the temperature of the A and R materials does not decrease with the extension of the transmission distance during the material transfer, thereby increasing the viscosity of the system and resulting in poor mixing. Therefore, the heating temperature of the hose should be basically the same as or slightly higher than the temperature in the main heater, and is usually set at 75 °C. In addition, the temperature of the hose rises slowly compared to the temperature of the main heater, so the hose is generally heated to facilitate operation.
Determination of spray pressure
Polyurea coatings are mixed at high pressures, so increasing pressure has a significant benefit to the performance of the overall system. After the pressure is increased, the atomization effect is better, the rough surface of the coating surface and the orange peel phenomenon are also obviously disappeared; but the disadvantage is that after the pressure is increased, the anti-splash phenomenon of the spray is aggravated, and it is necessary to further strengthen the shielding of the non-spray area and the construction personnel. Protection, which brings greater safety risks to the entire construction process. After the experiment, it is considered that the spray pressure of the polyurea coating is between 2,000 and 3,500 psi.
Adjustment of spray pressure difference
For polyurea coatings, the most ideal mixing effect is: A, R materials have the same density, uniform heating temperature, and consistent spray pressure to ensure equivalent reaction of polyurea coatings. However, in practice, since various physical properties such as density and viscosity of A and R materials tend to be different, it is difficult to achieve ideal mixing. It is reflected in the operation that when spray, the spray pressure difference between A and R materials is difficult to adjust to zero.
Special attention should be paid to the pressure difference between component A and component R when spray. When the pressure difference is less than 500 psi, uniform mixing of the two materials can be ensured. When the pressure difference is greater than 500 psi, the material must be re-adjusted to ensure uniform mixing of materials. And ensure that it is not cured in the gun.
Therefore, in the actual spray process, according to different polyurea coating formulations, the actual adjustment of the pressure difference between the A and R materials is an important step in the preparation of high performance polyurea coatings.
When preparing for spray, first spray two sheets of polyurea board. During the test spray, observe the discharge pressure gauges of A and R materials, and calculate the pressure difference between the two. If the pressure difference between the two is greater than 500 psi, the spray should be stopped immediately and the pressure adjusted.
The method of adjusting the pressure of the polyurea sprayer is to adjust the heating temperature of the A and R materials. Generally, the heating temperature of the A material is raised, the heating temperature of the R material is lowered, and then the spray operation is repeated, and the pressure difference is re-observed until the pressure is within 500 psi, preferably within 200 psi. It is worth noting that neither raising nor lowering the temperature should exceed the temperature range of 70 to 75 °C.