How to carry out waterproof product mechanical design?

Product mechanical engineers have definitely been exposed to the issue of how to carry out waterproofing product mechanical design. Before officially explaining how to carry out waterproof product mechanical design, we should firstly know the IP rating (waterproof level).

IP rating

The IPX waterproof level is divided into 8 levels, ranging from IPX-1 to IPX-8, and the waterproof ability increases in turn. The IPX waterproof rating is listed below for reference.

IPX-0 has no waterproof protection

IPX-1 equipment can provide waterproof protection equivalent to 3-5 mm/min rainfall for 10 minutes under normal operating conditions.

IPX-2 is basically the same as IPX-1, but it can pass the waterproof test of 15 degrees upturned in all directions.

IPX-3 60-degree angle splashes waterproof protection, provides 10 liters / second flow rate for 2-5 minutes, and waterproof protection of 80-100n/m pressure.

IPX-4 is basically the same as IPX-3 but can provide all-around and angular splash protection.

IPX-5 waterproof protection from all directions and angles, providing waterproof protection at a flow rate of 12.5 liters/sec for 2-3 minutes and pressure of 30n/m.

IPX-6 waterproof protection against large waves can last 2-3 minutes against a depth of 3 meters underwater, a flow rate of 100 liters/min, and a pressure of 100n/m.

IPX-7 can be immersed in 1 meter of water for 30 minutes.

IPX-8 is completely waterproof and can be used continuously in water for a long time.

There are many common waterproof products in life, such as smartwatches, electric toothbrushes, and most beauty electronics products. So how should the waterproof structure for these products be designed? Below we will introduce some common waterproof mechanical designs:

O-ring waterproof:

The selection of O-ring materials are:

Silicone ring (industrial products)

Features: high-temperature resistance, oil resistance, low-temperature resistance, non-toxic and tasteless, etc.

Nitrile rubber (NBR)

Features: anti-aging, oil and wear resistance, etc.

Fluorine rubber (FKM)

Features: high-temperature resistance, oil resistance, chemical resistance, etc.

PTFE

Features: Corrosion resistance, wear resistance, high-temperature resistance, low-temperature resistance, aging resistance, high-pressure resistance, organic solvent resistance, etc.

Polyurethane

Features: wear resistance, high-pressure resistance, aging resistance, hydrolysis resistance, etc.

Product overmolding (double injection) waterproof:

The product is overmolding (double injection) waterproof, which means that the product is is injected through two molds. Many people do not understand the overmolding (double injection) mold and do not know what the product will look like after it comes out. You can imagine that our product has 2 layers (one layer is plastic and the other is soft rubber). Their combination is that the soft rubber is wrapped on the hard plastic to achieve an adhesion effect.

Bicolor molding (double-material injection injection)

A bicolor molding (double injection) mold is a mold in which two plastic materials are injected into the same injection molding machine and molded two times, but the product is only released once. Generally, this molding process is also called double-material injection molding, which is usually completed by a set of molds and requires a special overmolding injection molding machine. Bicolor molding (double injection) first injects hard plastic and then injects soft rubber. The front mold is inconsistent, and the rear mold is the same. During the injection molding process, the rear mold needs to be rotated 180 degrees.

Overmolding (overmolding):

The two plastic materials are not necessarily injected into the same injection molding machine but are molded two times. After the product is taken out from one set of molds, it is put into another set of molds for the second injection molding. Generally, this injection molding process is usually completed by 2 sets of molds, without needing a special two-color injection molding machine.

Ultrasonic structure waterproof:

Many mechanical engineers who have just entered the industry have only heard of ultrasonic structures and have not learned much about them, so I will give you a brief explanation here. The main focus of the ultrasonic structure is the design of the ultrasonic line. The ultrasonic line can be made into one or two ultrasonic lines. The ultrasonic line can be made as a whole or can be broken, but the whole line must not be disconnected if it is to be waterproof. The design of the welding surface of the ultrasonic line is common in the following structures: Step welding surface, groove welding surface, bite surface welding surface, crisscross welding surface, etc. The groove welding surface mechanical design can prevent glue overflow and can provide the function of alignment during assembly. However, this form of ultrasonic structure cannot be too thin for the material thickness. It is not recommended to use this form of welding surface for products that are too thin, and it is recommended to use a structure in the form of a stepped welding surface for products that are too thin. 

In product mechanical design, an ultrasonic structure usually is not the priority. because the defect rate of ultrasonic products in the production process is much higher than that of other products. Once the ultrasound is poor, it means that the shell is scrapped. Ultrasonic structures are commonly found in mobile phone chargers, car chargers, and other products

Waterproof breathable membrane (waterproof mesh)

Many people have not heard of the material of the waterproof and breathable membrane. In fact, this material is often encountered in the process of making structures. This material is generally used for horn holes, microphone holes, and other structures to carry out such a waterproof design. There are also many people who are curious about how this product is made when they see this product. In fact, these materials are all die-cut parts. What I want to explain is that the waterproof and breathable membrane can be brushed with 3M glue to facilitate our assembly and fixation. Some people may not have seen it, so there is such a question. Let me explain to you here.

3M glue waterproof

3M adhesive is waterproof. Many people may have doubts, how is 3M adhesive waterproof? In fact, there are many models of 3M adhesive, of course, the price is definitely different. Double-sided tape is classified by substrate:

Double-sided adhesive for non-woven substrates (composed of double-sided coated acrylic adhesives for non-woven substrates): such as 3M9448, 3M9080, 3M9075, etc.;

Double-sided tape without base material (directly coated with acrylic 3M acid glue): such as 3M467, 3M468, 3M9473, etc.;

PET substrate double-sided tape (composed of PET substrate coated with acrylic adhesive on both sides): such as 3M9495MP, 3M9795B, 3M9495LE, etc.;

Double-sided adhesive on foam substrate (composed of double-sided coating of acrylic adhesive on foam substrate): such as 3M4920, 3M4026, 3M4032, etc.;

Hot melt adhesive film: such as 3M615, 3M668, 3M669, etc.;

High-temperature resistant tape: such as 3M244, etc.;

3M double-sided tape is widely used in computers, mobile phones, communications, household appliances, audio-visual equipment, automobiles, and other products.

 

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