For the determination of standard throwing power, please refer to JB/T10242-2001.
There are many methods for measuring throwing power, such as steel pipe method, gap method, box method, parallel plate method and V-shaped method. The “FAW steel pipe method” is commonly used in CHINA, which is a method for measuring the throwing power of the electrophoretic paint bath solution improved on the basis of the Ford steel pipe method.
The way to measure the throwing power at the coating production site is to measure the thickness of the coating film on the surface facing the electrode and away from the electrode, and to disassemble the coated object for observation. If the film thickness of the inner surface reaches 2/3 of the outer surface (facing the electrode), the throwing power is excellent, 1/2 is good, and the film thickness is extremely thin or the bottom is exposed, then the structure of the coated object should be improved. Measures such as opening process holes or installing auxiliary electrodes can solve the problem of swimming coating quality in the inner cavity.
The penetration power is also expressed by the penetration depth (cm) of the steel pipe.
When the steel pipe method is adopted, the steel pipe is 220mm long and 20mm in inner diameter, and a 230mmx 15mmXlmm steel bar is inserted inside, and the lower end is flush with the steel pipe and connected with the steel pipe wire. Steel pipe immersed in electricity
Swimming coating solution 2oOmm, deposited under suitable electrophoresis conditions for 3min. After the deposition is complete, the steel bar is taken out, washed and dried, and the deposition on the steel bar shows three states. As shown in Figure 21-8, the throwing power is represented by the ratio of the height of the coating film deposited on the steel bar to the height of the soaked liquid:
The steel tube in this method can also be plastic tube or glass tube. The steel tube method is suitable for the measurement of high throwing power, and the specifications of the steel tube and the inserted steel bar can also be slightly different.
The throwing power of the cathodic electrophoretic coating is generally above 75%~80%, and the throwing power of the anodic electrophoretic coating is lower, preferably no more than 70%. For workpieces with anti-rust requirements for the inner cavity, cathodic electrophoretic coating should be used.
Determination of Threshing Power by Parallel Plate Method
The parallel plate method is used to measure the throwing power using multilayer plate electrodes, in which all the plates are parallel. Five 15ommx15omm steel plates can be used in the experiment, the interval between the samples is 1mm, the whole group of samples is parallel to the auxiliary electrode, and the center sample is 30mm away from the cathode, as shown in Figure 21-9. Turn on the power, take it out after electrophoresis for 3 minutes, and weigh it after drying. Calculate the average deposition amount per plate according to the following formula.
V-shaped method
The V-shaped method is to use two flat plates to form a narrow V-shaped piece, the lower part of which is connected together, and the upper part is kept at a certain distance. After the film is formed by electrophoresis, check the area coated with the film on the inner surface, as shown in Figure 21-10.
The smaller the paint-free area shown in Figure 21-10, the better the throwing power. But this method can only explain the problem qualitatively rather than quantitatively.
