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Grommet Compression Molding, also be known as Wire Grommet Mould, Firewall Grommet Moulding and Cable Grommet Mold. Grommet is used to protect wires, cables, pipes or other items that need to pass through metal, plastic or other material so that these items will not easily damage the surface.
Grommet Compression Molding's advantage is that it can form different sizes and complex parts. Moreover, compared with other methods such as 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.
Grommet Compression Molding Structure
Grommet Compression Molding includes Keel Structure, Split Structure and Three-layer Plate Structure.
Grommet Compression Molding Keel Structure
The grommet compression molding keel structure is usually used to produce silicone rubber products with higher hardness or depper undercut. When the hardness of silicone exceeds 55 Shore A, the stronger hardness causes lower tensile property, which is easy to cause damage to the grommet during demolding.When the undercut of the grommet is deep, the structure of the keel structure is better to demold.
This structure makes the parting line located on both sides of the grommet, which is suitable for products with high material hardness, deep undercut and low surface requirement.
Grommet Compression Molding Three-layer Plate Structure
The grommet compression molding three-layer plate structure consists of top plate, middle plate and bottom plate. This structure usually used to prduce grommet with lower hardness and shallow undercut. When demoulding, in order to avoid grommet deformation, the middle plate is usually inverted and then demoulded or demold the grommet from the front of the middle plate through the hole to the bottom plate. For the grommet, generally choose to use the three-layer plate structure, because it can achieve multiple holes at the same time for production, improve production efficiency, reduce production costs, so the product unit price is lower. Compared with the keel structure and the split structure, the three-layer plate structure enables the parting line of the grommet to be located in a more hidden position: the undercut and the bottom of product. For products that need a more perfect surface, the three-layer sutrcture is a good choice.
Grommet Compression Molding Split Structure
Grommet Compression Molding Split Structure is consists of top plate, bottom plate and sliders. This structure is also suitable for products with deep undercut and high hardness. The raw material is placed above the groove of the slider and heated to form. Remove the slider manually, and the product can be easily demolded, without deformation or damage to the product. At the same time, the parting lines formed by the structure are located on both sides of the product. This structure forms a parting line on the surface of the product, uaually located on the side of the product. In addition, the split structure can meet some of the requirements of the parting line. For products with high hardness, deep undercut or some requirements for parting lines, the split structure is one of the good options.
Compression Molding of Grommet Materials
EPDM Grommet | Hardness: 30~90 |
Service temperature: -45℃~100℃ | |
Advantages: Excellent heat resistance, weather resistance and ozone resistance. Good water resistance, electrical insulation, resilience, low temperature. | |
Disadvantages: Poor air tightness, self-viscosity and mutual viscosity, not resistant to non-polar solutions. |
CR Grommet | 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 Grommet | 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 solevents, excellent bonding properties, good mechanical properties and air tightness. | |
Disadvantages: Weather resistance and ozone resistance is not strong. |
FKM Grommet | 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. |
HNBR Grommet | Hardness: 55~90 |
Service temperature: -40℃~150℃ | |
Advantages: Good oil resistance, heat resistance, excellent ozone resistance, high compression and permanent deformation resistance. High strength, high tear performance, wear ressitance. | |
Disadvantage: Poor electrical properties, poor flame resistance, and it can easily be damaged by aromatic oils and polar organic solvents. |
Grommet 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 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, which 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.
Grommet Compression Molding, also be known as Wire Grommet Mould, Firewall Grommet Moulding and Cable Grommet Mold. Grommet is used to protect wires, cables, pipes or other items that need to pass through metal, plastic or other material so that these items will not easily damage the surface.
Grommet Compression Molding's advantage is that it can form different sizes and complex parts. Moreover, compared with other methods such as 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.
Grommet Compression Molding Structure
Grommet Compression Molding includes Keel Structure, Split Structure and Three-layer Plate Structure.
Grommet Compression Molding Keel Structure
The grommet compression molding keel structure is usually used to produce silicone rubber products with higher hardness or depper undercut. When the hardness of silicone exceeds 55 Shore A, the stronger hardness causes lower tensile property, which is easy to cause damage to the grommet during demolding.When the undercut of the grommet is deep, the structure of the keel structure is better to demold.
This structure makes the parting line located on both sides of the grommet, which is suitable for products with high material hardness, deep undercut and low surface requirement.
Grommet Compression Molding Three-layer Plate Structure
The grommet compression molding three-layer plate structure consists of top plate, middle plate and bottom plate. This structure usually used to prduce grommet with lower hardness and shallow undercut. When demoulding, in order to avoid grommet deformation, the middle plate is usually inverted and then demoulded or demold the grommet from the front of the middle plate through the hole to the bottom plate. For the grommet, generally choose to use the three-layer plate structure, because it can achieve multiple holes at the same time for production, improve production efficiency, reduce production costs, so the product unit price is lower. Compared with the keel structure and the split structure, the three-layer plate structure enables the parting line of the grommet to be located in a more hidden position: the undercut and the bottom of product. For products that need a more perfect surface, the three-layer sutrcture is a good choice.
Grommet Compression Molding Split Structure
Grommet Compression Molding Split Structure is consists of top plate, bottom plate and sliders. This structure is also suitable for products with deep undercut and high hardness. The raw material is placed above the groove of the slider and heated to form. Remove the slider manually, and the product can be easily demolded, without deformation or damage to the product. At the same time, the parting lines formed by the structure are located on both sides of the product. This structure forms a parting line on the surface of the product, uaually located on the side of the product. In addition, the split structure can meet some of the requirements of the parting line. For products with high hardness, deep undercut or some requirements for parting lines, the split structure is one of the good options.
Compression Molding of Grommet Materials
EPDM Grommet | Hardness: 30~90 |
Service temperature: -45℃~100℃ | |
Advantages: Excellent heat resistance, weather resistance and ozone resistance. Good water resistance, electrical insulation, resilience, low temperature. | |
Disadvantages: Poor air tightness, self-viscosity and mutual viscosity, not resistant to non-polar solutions. |
CR Grommet | 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 Grommet | 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 solevents, excellent bonding properties, good mechanical properties and air tightness. | |
Disadvantages: Weather resistance and ozone resistance is not strong. |
FKM Grommet | 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. |
HNBR Grommet | Hardness: 55~90 |
Service temperature: -40℃~150℃ | |
Advantages: Good oil resistance, heat resistance, excellent ozone resistance, high compression and permanent deformation resistance. High strength, high tear performance, wear ressitance. | |
Disadvantage: Poor electrical properties, poor flame resistance, and it can easily be damaged by aromatic oils and polar organic solvents. |
Grommet 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 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, which 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.
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