Most of the waterproof products are just the upper and lower shell waterproof, key waterproof, battery waterproof, sensor leading out part waterproof, commonly used waterproof method mainly glue, ultrasonic, insert, install O-ring.
The main reasons for poor waterproof are: plastic deformation, waterproof surface is not in a tension, O-ring preloading is too loose or too tight. The structure stiffness is not enough, the screw distribution is uneven, the sliding teeth and so on.1 塑胶变形的弊端是明显的，防水的方法也很多，如改进胶口，改运水，做加强骨等，对于部分产品，引起变形主要原因还是由于受外形限制以致于上下曲面分型，或内部空间太小导塑胶件壁厚变化太大引起的
As shown in Figure 1, the product is prone to deformation due to the influence of plastic residual stress. If this kind of product is to be waterproof, in addition to increasing the reinforcement bone, increasing the demoulding slope and increasing the ejection position at the relevant position, it is necessary to make the product just formed, make the fixture positioning, and make natural cooling in warm water to reduce the residual stress. Of course, if the product shown in the figure needs to be waterproof, it doesn't have to be made into the upper and lower cover structure as shown in the right side of Figure 1. Harris Co., Ltd. just gives a similar example here.
As shown in Figure 2, the product has a shell outside the transparent mirror. If it does not need to be waterproof, the structure in the left figure can still be used although it has a little deformation. If the transparent mirror and the back shell need to be waterproof through the O-ring, hiris engineers suggest that it is best to use the hook in the right figure. Wrap the LCD and PCB with 0.15 metal cover and screw them on the fixed lens. The plastic deformation is less.
2. The waterproof is not on the same surface, as shown in the figure, the surface of O-ring is an irregular surface. When the upper and lower cover the whole shell, the waterproof line is not easy to be continuous. This kind of fireproof effect is not very good, and the ultrasonic treatment effect of similar shape is not ideal. We should try our best to avoid it and ensure that the waterproof line is continuous, Try to make the waterproof line a single shape intersecting with one side.
In the section 3a-a in Fig. 3a, whether the O-ring is placed or the supergene treatment is carried out, the part contacted up and down by Harris Automation Co., Ltd. is called the waterline.
Uneven screw distribution or sliding teeth, uneven screw distribution will lead to O-ring preloading too tight or too loose, O-ring local cloth loose, of course, will lead to poor waterproof, but it is not the tighter the better, too tight will exceed the yield strength of O-ring, when the product after high and low temperature, will reduce the elasticity of application.
After the self tapping screw slides, it will lead to insufficient coupling force and poor waterproof. How to remove the structure is recommended
For some products, the internal space is generally small, and there is almost no place to add reinforcement, so the necessary wall thickness should be increased
As shown in the figure, the lens is fixed on the bottom shell by the fixed screw. In figure a, the screw hole is too close to the edge, and the thinnest part of the plastic is only 0.8mm. From the rubber inlet shown in the figure, there will be a fusion surface where there is screw hole. Although the front mold temperature is raised to make the water inclusion invisible, the fusion surface still exists. When the plastic is tested at high and low temperature under stress, the plastic will have a fusion surface, It is easy to fracture. It is suggested to change the threaded hole to B drawing to ensure the minimum wall thickness of at least 1.5mm
Through the analysis of the above poor waterproof phenomenon, we can discuss the waterproof structure of some products.
2. Waterproof of battery door
3 key waterproof
The key combination in Figure 9 has been used in many watch products, generally reaching ip46 grade. The waterproof effect meets most requirements, and the volume is small. In many watch accessories manufacturers, it is produced as finished products, and can be selected from various specifications such as length, maximum outer diameter, waterproof grade, etc. When the product space is small, this kind of structure is recommended.
The key waterproof method shown in Figure 10 can be used when the internal space of the product is enough. The silicone key is directly screwed on the plastic cover with PCB board. In this structure, the screw posts should be evenly distributed. Because the plastic, key and PCB board are elastic, the structural rigidity of the plastic and circuit board should be ensured, and the elastic change should be ensured on the key as far as possible, The thickness of the plastic wall should not be thin, the screw column should have a reinforcing bone, there should be enough bolts to fix the circuit board, the material of the circuit board should be plywood and rigid fiberboard as far as possible, and the thickness should be more than 1.0 mm. If necessary, a steel plate can be padded in the circuit board and keys.
4. Waterproof of outgoing line
Because some lead out parts of electrical appliances need to be processed separately and connected with circuit board, this structure adopts box structure, that is, the components of each part that need to be waterproof are assembled separately, and then several parts are wrapped together by outer cover, as shown in FIG. 11 and 12, the product is composed of mask, front cover and back cover components.