Classification and Structure of Rubber Molds

Classification and Structure of Rubber Molds

With the development of China's rubber product industry, the variety and production volume of rubber products have been increasing, driving the shift from traditional empirical design to theoretical calculation design for rubber mold design and manufacturing. This shift is particularly pronounced with the continuous improvement of rubber production equipment and manufacturing processes, resulting in a growing number of rubber molds. The manufacturing level and complexity of these molds have also increased, emphasizing the need for high efficiency, automation, precision, and long lifespan in the development of rubber molds.

I. Classification of Rubber Molds

Rubber molds can be classified based on their structure and the production process of the products as follows:

1. Compression Molds

   Also known as ordinary compression molds, these molds involve placing pre-processed rubber compounds with specific shapes and quantities into the mold. The mold is then subjected to pressure and heat in a flat vulcanizing machine. The rubber material cures under pressure and heat.

   Features: These molds have a simple structure, high versatility, wide applicability, and are easy to operate, making them prevalent in the production of rubber molded products.

2. Transfer Molds

   Also known as transfer molds or injection molds, these molds are used for rubber materials that are pre-processed, have simple shapes, and are provided in limited quantities. The rubber material is placed in the mold cavity and cured by transferring pressure through a plunger and injecting the material through a gating system into the mold cavity.

   Features: These molds are more complex than regular compression molds. They are suitable for manufacturing thin-walled, long, and easily bent products that cannot be efficiently produced by conventional compression molding. Products produced with these molds exhibit good density and superior quality.

3. Injection Molds

   Injection molds are used to inject pre-heated, plasticized rubber materials into the mold cavity, where they are shaped and cured.

   Features: These molds have a complex structure and are suitable for large, thick-walled, thin-walled, and complex-shaped products. They offer high production efficiency, stable quality, and the ability to automate production.

4. Extrusion Molds

   Extrusion molds are used to produce various rubber profiled semi-finished products with different cross-sectional shapes through a head mold. These semi-finished products are then used for subsequent shaping or vulcanization in a vulcanization tank.

   Features: High production efficiency, stable quality, and the capability to automate production.

II. Structure of Rubber Molds

1. Sprue (or Flow Channel): To ensure that the rubber material completely fills the mold cavity, a surplus of material is often required. This excess material is stored in channels surrounding the mold cavity, known as sprues or flow channels.

2. Vent Holes: Air trapped inside the mold cavity can lead to defects like air bubbles, surface blemishes, or incomplete filling. Therefore, proper venting is essential. While some air can escape through the parting line gaps, additional small holes, known as vent holes, may be added to facilitate effective air removal.

3. Demolding Ports (also known as Knockout Ports): Demolding ports should not be too deep or have large bevels. In the case of paired demolding ports, each set should be symmetrical with respect to the mold center and positioned as close as possible to the locating pins. Generally, they do not require angular channels, but molds for thin products with shallow cavities may use them to facilitate easier demolding.

4. Handles: Rubber compression molds come in fixed and movable types. Fixed molds are operated mechanically without removing the mold from the press, whereas movable molds, particularly for ordinary compression molds, are usually operated manually. For ease of handling, molds that are relatively heavy (typically over 6 kilograms) may have handles installed. Handles make the molds more convenient and safer to move but also increase the footprint required. Smaller molds may not have handles.

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