You can make many parts through compression molding rubber only if you know the benefits, choose suitable rubber material and understand various process parameters.
In this guide, we will highlight all the fundamental aspects you should know about compression molding rubber products.
What is Rubber Compression Molding
Compression rubber molding is special processes that uses compressive forces and heat to manipulate preformed rubber according to the specific mold design.
For a successful molding process, you must know the compressive force requirements, choose suitable mold, and understand the rubber temperature properties.
Advantages of Rubber Compression Molding
There are many benefits why you should consider compression molding for you next projects:
- It is an easier procedure
Compared to other methods of shaping and manufacturing, it is a comparatively straightforward process.
- Low tooling cost
The process does not require costly sophisticated machinery or specialized equipment; the tools and equipment needed for the procedure are significantly simpler and often require a lower cost.
- Large and thicker pieces can be produced with ease
By feeding material directly into the mold, you can produce large and thick rubber parts.
- Perfect alternative for small production
Since the tooling cost is relatively low, you can use the process for low scale production of rubber parts.
Before moving on with large-scale production, it is frequently used to generate models or samples of designs.
- Little waste
It reduces possible rubber material wastage making it cost effective process.
Limitations of Compression Molding Rubber Parts
- Not a suitable process for some intricate parts
This technique may need to be revised for some intricate components and product designs.
Usually, the flow constrains is a major issue alongside the requirement to adjust mold design.
- Compression molding process is slightly longer
Processing certain rubber parts may take a longer time.
- It is more likely to incur charges after molding.
You may experience parting line flash. Of course, this is also alongside other various unavoidable parameters that can lead trimming after compression molding process.
Factors to Consider in Rubber Compression Mold Design
The following are the factors to consider in rubber compression mold design:
- Weight
Because heavier molds need more energy, their weight may affect how well a product is produced.
As a result, the mold’s design should work to reduce weight while yet preserving the required structural integrity.
- Flexibility
The mold design should be adaptable to accommodate various part designs and forms. Applying interchangeable inserts, versatile tooling, or movable mold cavities can accomplish this.
- Vibration dampening
Vibration-dampening elements should be incorporated into the mold design to lessen the effect of machine vibration on the quality of the finished product.
The use of shock absorbers or the integration of vibration-absorbing materials can accomplish this.
- Mechanical properties
It can make it more likely that the mold will be able to adapt to the physical characteristics of the material and generate high-quality pieces.
This a long side the properties such as strength and hardness.
- Cost
Performance and financial factors should be balanced in the design of the mold. Utilizing inexpensive materials, straightforward configurations, or improved production techniques might help achieve this.
- Pressure required
The mold’s design should consider the force necessary to compress the rubber substance inside the mold chamber appropriately.
- Thermal decoupling
To avoid excessive heat transfer between the rubber substance and the mold, the mold design should consider thermal decoupling, which can result in flaws and lower the quality of the finished product,
The integration of insulating materials or the usage of cooling channels can accomplish this.
Best Rubber Material for Compression Molding
Compression Molding Silicone Rubber
Pre-catalyzed silicone rubber, made by combining silicone with powder, is the silicone rubber used in compression molding. The addition of heat makes it easier for the silicone to cure.
Through the use of a two-mill roll, pigment is combined with silicone. The element that requires a lot of labor is at play here. During this phase, there is a significant possibility of silicone contamination.
The material is weighed and shaped to the required size and layout of the item in question after it has been this way before the the-catalyzed and color added.
Compression Molding EPDM Rubber
EPDM is a synthetic rubber known for superior performance characteristics. It is easier to mold through the various convention compression molding process.
Compression Molding Natural Rubber
It’s, commonly referred to as latex, is a substance with a high degree of elasticity made from rubber plants.
Natural Rubber combines various substances, including vulcanizing chemicals, fillers, and accelerators, to enhance its qualities before compression molding.
Liquid Silicone Rubber Compression Molding
It is a two-part, platinum-cured silicone substance. It is highly resistant to aging, chemicals, and hot and low temperatures.
Liquid Silicone Rubber is compressed by mixing the components and injecting them into a heated mold.
The material is then tightly crushed while subjected to high pressure until the required shape is achieved. The finished item is removed from the mold once the substance has cooled and set.
How to Choose a Compression Rubber Molding Machine
The following are the key factors to consider when choosing the compression rubber molding machine:
- The quantity of Rubber that the product will require.
- The temperature needed to heat the Rubber to the minimal minimum.
- Minimal time is required to heat the Rubber.
- Selecting the most effective heating technique.
- Determining the amount of force necessary.
Rubber compression molding equipment required includes the following:
- Hydraulic press
- Alignment pins
- Mold cavity which can be made from steel or aluminum
- Compression molding press
- Mold plates
Recommended Compression Molding Temperature
The mold temperature for a standard rubber compression molding operation is 180°C but can vary from 140°C to 200°C.
Temperatures may vary for each rubber type as they have different heat and temperature resistance.
Recommended Pressure for Compression Molding Process
Mold pressures can range between 20 to 700 bars depending on the sort of Rubber used and the individual product being made, but the recommended mold pressure is 100 psi (700 kPa).
To calculate the compression molding pressure, multiply 4,000–6,000 psi (pressure) by the anticipated area of the part at the line of separation.
How to Determine Average Cost of Compression Molding Rubber
When determining the average cost of compression molding, the following are considered and calculated:
- Material cost
The price can change depending on the Rubber used, how much is bought, and the source.
- Labor cost
Compression molding costs cover the workforce needed to run the machines and the process.
The intricacy of the level of expertise and the part design necessary to operate the machinery can affect this.
You can get the labor cost by dividing the operator’s hourly wage by the time needed to make the parts.
- Tooling cost
The difficulty of the mold size and part design will determine how much the tooling will cost.
- Overhead cost
Administrative charges, utilities, rent, and insurance are overhead expenditures incurred when a business operates.
One can multiply the total overhead costs by the total number of units produced for a particular time to get the overhead price per unit.
Importance of Compression Molded Rubber Prototypes
Molding tools that are widely used are prototypes. These pieces of equipment are of the same caliber as the set of molds, but they have a shorter lifespan and a simpler design.
Prototypes enable the fabrication of parts in high-quality materials for a prototype series or a preliminary production run without requiring a substantial initial investment.
The following are the importance of compression molded rubber prototypes:
- Accuracy
Prototypes of compression molded Rubber have excellent precision and accuracy, offering a nearly perfect picture of the finished product. Before large-scale production starts, designers can find and fix potential design faults or problems.
- Quick turnaround
Prototypes of compression molded Rubber may be made fast, giving manufacturers more time to test and improve their creations. By shortening the development process, money and resources are ultimately saved.
- Cost-efficient
Prototypes made of compression-molded Rubber are reasonably affordable. Therefore, it is a cost-effective choice for small firms or start-ups to test their concepts and designs before spending money on mass manufacturing.
How Compression Molding Rubber Works
Step 1: Design Mold for Compression Molding Rubber
Start by designing the mold. In most cases, the mold are made through CNC machining process.
After which you will apply the necessary surface finish and other secondary operations such as hardening. Generally, the molds for molding rubber are either steel molds or aluminum molds.
Among the key considerations during mold design for compression molding rubber include;
- Possibility of flash
- Overflow grooves
- Cavity placement
- Pin alignments
- Allowances
Step 2: Prepare Rubber for Compression Molding
You can process many rubber materials such as:
- Silicone
- EPDM
- Viton
- Nitrile
- Butyl
- Natural rubber
- SBR, etc.
During this stage, you will make the rubber preform. This is basically an uncured rubber form. You will choose a preform that works best for your rubber compression molding process.
You must consider both the size and tolerance at this section.
Step 3: Perform Actual Compression Molding on Rubber
Start by preheating the mold. Next, you will place the rubber preform in the mold ready for compression molding.
Using a suitable press, apply reasonable pressure on the heated rubber preform. The pressure will force the rubber to conform to the desired shape.
Once the shape is formed, open the mold to remove the compression molded rubber part. You can then subject the compression molded part to various finishing operations.
Remember, the temperature, pressure and time for compression molding rubber will depend on the material type and parts you wish to process.
Common Rubber Compression Molding Defects & Solutions
When compression molding rubber, there are several factors to take into account. The defects occur as a result of the following causes:
- Fillers for elastomers
- Ineffective Treatment
- Insufficient Cavity Fill
The following are the defects caused by the above reasons in rubber compression molding:
- Shrinkage
Shrinkage may be brought on by incorrect curing, cavity shape, and other factors.
- Chips
Inadequate tooling, mold flaws, and careless handling might produce chips.
- Blisters
Blisters are frequently brought on by inadequate cure or moisture.
- Flow lines
Too much heat causes flow lines.
- Discoloration
This defect is brought on by contamination or badly blended pigments.
- Short moldings
Inadequate component charge, reduced pressure or closure rates, and improper material distribution can result in short moldings.
The following are the solutions to compression molding defects:
- It is vital to guarantee that the compression pressure is set properly and that the mold is designed properly.
- Check that the cooling process is effectively managed, the material is dispersed appropriately inside the mold, and the mold is constructed with the proper features.
- It’s crucial to check that the mold is adequately vented and the temperature is managed.
How Compression molding vs. Injection Molding Rubber Compare
- The ability to control better tolerances, which may be required for specific products, is a benefit of rubber injection molding.
- Rubber compression molding is comparatively cheaper with less expensive tooling, while rubber injection molding is perfect for high-volume runs.
- Due to its intricate design, injection molding of Rubber is more expensive, but compression molding of Rubber is excellent for big items in the low- and medium-series.
- Best for large parts
Comparing other rubber molding processes:
| Compression Molding | Rubber Transfer Molding | Rubber Injection Molding |
| Best for simple or less intricate parts | Enjoy the benefits of compression and injection molding rubber | You can control accuracy and tolerance |
| Suitable for large rubber parts | Can handle large processes – more preferably those that require secondary processing | For tiny and more accurate rubber parts, its work well |
| Economical due to low tooling cost | Allows for design flexibility | Slightly costly but best for high quality parts. Besides, the design is more complex |
Compression Molded Rubber Parts
The following are the compression molded rubber parts:
- Compression Molding Silicone Rubber Keypad
- Compression Rubber Molded Boots
- Bumpers
- Anti-vibration pads
- O-rings
- Grommets
- Vacuum filters
- Tubing
- Rubber-to-metal bonded products
- Goods made of extruded Rubber
- Products for reducing vibration, such as bushings, isolators, couplings, and mounts
Conclusion
Compression rubber molding is a versatile process you can use to make many parts and components. All you need is a thorough understanding of the main processes and choosing the right rubber material.
For all your rubber compression molding, contact Lindas now.