Rubber compression molding involves placing preformed rubber material into a heated mold cavity. Closing the mold applies pressure and heat for a specified duration, catalyzing the material’s hardening. The mold, featuring male and female components, determines the final shape. Excess rubber flows into overflow grooves, facilitating trimming. Heat catalyzes material hardening, pressure fills the cavity, and time ensures complete curing.

Essential Components of a Compression Mold:

Upon examination of a compression mold, various essential elements contribute to the effective molding of a rubber product. As depicted in the accompanying illustration, a typical compression mold comprises:

  • Top and Bottom Plate
  • Alignment Pins and Bushings
  • Mold Cavities
  • Flash/Overflow Groove

The Process Of Mold Making:

Design Process:

Expertise is crucial in navigating the design phase, ensuring accurate part production and minimizing the likelihood of tool revisions.

Metal Block Acquisition:

Procuring and receiving aluminum or steel blocks for subsequent machining.

CNC Machining:

Employing computer-controlled cutting tools to shape mold elements, including cavities and overflow grooves, by removing material from the metal blocks.


Fine-tuning the tool to guarantee the mold’s surface yields the desired rubber surface during the molding process.

Mold Hardening:

Subjecting the mold to a controlled heating and cooling process to enhance durability.

Selecting Mold Plate Material: A Comparison of Steel and Aluminum:

When it comes to compression molds, the choice typically boils down to either aluminum or steel. Each material has its own set of advantages and disadvantages, making them suitable for specific scenarios. Here’s a fundamental overview of both materials to provide a clearer understanding of when and why each is selected.


Steel Molds:

The predominant choice for compression molds is hot-rolled steel (HRS). This type of steel undergoes a heat-forming process followed by controlled cooling, resulting in enhanced thermal stability. Unlike cold-rolled steel, HRS is less prone to warping when exposed to standard molding temperatures. Rubber molders prefer hot-rolled steel due to its reliability and resistance to deformation under higher molding temperatures.


Aluminum Molds:

While aluminum is considered a soft metal, making it less durable for prolonged production use, it shines in prototyping and low-volume runs. The softness of aluminum makes it easier and faster to machine, facilitating a finer surface finish. However, its soft nature requires careful consideration of clamping pressure to avoid damage from crushing forces between the plates. Despite its limitations in durability, aluminum remains an excellent choice for specific applications, offering efficiency in prototyping and shorter production runs.

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