Xiamen Better Silicone Rubber Co., Ltd
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Bellow Compression Mold, also be known as Silicone Hose Molding, Silicone Expansion Joint Mould, Rubber Boot Moulding and Rubber Flexible Bellow Mold, mainly produce silicone bellow that can isolate dust and connect components.
Bellow Compression Mold's advantage is that compare to transfer molding and injection molding, it is one of the lowest cost molding methods; In addition, it wastes relatively little material, which gives it an advantage when dealing with expensive compounds.
Bellow Compression Mold's Structures
Silicone Bellow Compression Mold includes three types: Keel Structure, Split Structure and Keel+Split Structure.
The slider mold shown in the figure is composed of a top plate, a bottom plate and two sliders. The raw material is placed on the core of the bottom plate and formed after hot pressing.
Since the slider needs to be moved manually to demold, the more time the mold is used, the rougher the trimming cut edge of the mold is rubbed, and the bellow is to form a rough edge and obvious parting line.
The silicone material is plaeced in the holes on the keel and the bottom plate, then it is heated to form the raw material. Therefore, the final bellow's parting line is located on the both sides of the longer side. The keel structure is named for its distinctive keel-shaped core. The mold is composed of a top plate, a bottom plate and a movable keel core.
The Keel + Split structure is consist of a top plate, a bottom plate, a keel and two splits. The keel is laid across the bottom plate, with sliders at both ends of it. The raw material is placed on the keel and covered to the two ends of the slider, and heated to form it. After processing is completed, it is necessary to manually pull apart the movable core at both ends and remove the keel for demoulding.
Compression Mold of Bellow Materials
| EPDM Bellow | Hardness: 30~90 |
| Service temperature: -45℃~100℃ | |
| Advantages: Excellent heat resistance, weather resistance and ozone resistance. Good water resistance, electrical insulation, resilience, low tempersture. | |
| Disadvantages: Poor air tightness, self-viscosity and mutual viscosity, not resistant to non-polar solutions. |
Neoprene Bellow | Hardness: 40~95 |
| Service temperature: -45℃~135℃ | |
| Advantages: Great resistance to exposure to the ozone, sunlight, oxidation, weather, oils, solvents, and several other materials. It is also tear resistant, is durable, and easily adheres to metals and fabrics. | |
| Disadvantages: Poor resistance to strong oxidising acids, esters, ketone and certain hydrocarbons. |
CR Bellow | Hardness: 40~90 |
| Service temperature: -40℃~100℃ | |
| Advantages: Ozone resistance, weather resistance, chemical resistance, aging resistance. Good tensile strength, elongation, adhesion and flame retardancy. | |
| Disadvantages: Poor cold resistance and storage stability, not resistant to petroleum-based lubricants. |
NBR Bellow | Hardness: 40~90 |
Normal service temperature: -35℃~100℃ Low temperature resistance type: -55℃~100℃ High temperature resistance type: -30℃~125℃( in the air); -30~150℃(in the oil) | |
| Advantages: Excellent resistance to oil and non-polar solvents, excellent bonding properties, good mechanical properties and air tightness. | |
| Disadvantages: Weather resistance and ozone resistance is not strong. |
FKM Bellow | Hardness: 50~90 |
Service temperature in Static Seal: -26℃~232℃ Service temperature in Dynamic Seal: -15℃~200℃ | |
| Advantages: Flame retardant, gas penetration resistance, ozone resistance, weather resistance, good aging resistance and resistance to chemical media. | |
| Disadvantages: Can not be used with molten or gaseous alkali metals. |
Bellow Compression Mold Surface Treatment
Sand blasting adopts compressed air as the power to form a high-speed jet beam to spray the material (copper ore, quartz sand, emery, iron sand) to the surface of the mold to be treated at high speed, remove the residual burrs and rust, and make the surface of the mold smoother. The surface requirements of the different products are different, and sand of different thickness is used. At the same time, the mechanical properties of the workpiece surface are improved, the fatigue resistance of the workpiece is improved, the adhesion between it and the coating is increased, the durability of the coating is extended, and the flow and decoration of the coating are also beneficial.
The sand blasting method is simple, so the cost is low. However, if the mold surface is sandblasted twice or multiple times, the tool edge of the mold will be damaged, resulting in more rough edges and thicker parting lines.
In the process of using chemical liquid to corrode the mesh, the liquid soaks the mold for a fixed time chemical reaction, wich is not affected by the surrounding environment. However, when the liquid corrodes the mesh, it needs to cover the non-texture area, which is difficult to operate. Moreover, the mesh life in the corrosion area of the liquid is relatively short, which can easily lead to the rapid scrapping of the mold core.
For the small mesh area that needs to be treated, there will be a dividing line between the mesh in different areas, so that the surface pattern of the products is inconsistent. In this case, chemical corrosion is suitable for products that need to form a large area of mesh.
EDM treatment is easy to operate, short time, high precision, suitable for small area of mesh processing. And the electrical spark hit out of the mesh is harder. Usually 5 Axis Machine is used for processing, so the cost of EDM is the highest.
