Introduction

Rubber is one of the most used raw materials across different industries. Both natural and synthetic rubber is used extensively to make everything starting from the tiniest of home goods to massive structures used in industries. There are different types of rubber molding used in producing rubber components, and the features of the product would depend on the manufacturing process and the type of molding chosen.

Did you know that India is the fourth largest consumer of rubber? According to sources, the per capita consumption of rubber is 1.2 kg. The Indian Rubber Industry states that rubber manufacturing companies in the country produce more than 35,000 different rubber products. All these products use one of the below molding types to be manufactured.

Here are the three most popular types of rubber molding used by industries to create rubber components and products.

Rubber Injection Molding

Rubber injection molding is probably the most straightforward and commonly used type of rubber molding chosen by manufacturers across the world. As the name specifies, this type involves injecting a rubber compound into a mold and keeping the mold under high pressure for the component to get shape.

There are four sub-components of rubber injection molding.

1. Organic rubber injection

Organic rubber injection starts with prepping the rubber component by stripping and mixing it before feeding it into the screw. As a result, there is no need to preheat the rubber and the completion type reduces too.

2. LSR injection

Liquid Silicone Rubber (LSR) injection is a type of liquid injection method used specifically for silicone rubber. Parts of liquid silicone are sent into the injection unit. This is cured and injected into the mold.

3. Thermoplastic rubber injection

Thermoplastic rubber injection is a process of using thermoplastic elastomers, also known as TPEs, to create molded components in. This type of rubber molding process needs high temperatures to work and that is one challenge in using TPEs. However, with TPEs, the manufacturer can avoid the initial tasks of mixing and vulcanizing.

4. Custom rubber injection molding

This is a completely customized process where the manufacturer decides every single aspect of injection molding, starting from the raw material used, the injection molding process, and the temperature and pressure decided based on customer requirements.

Advantages of rubber injection molding

• Lower costs – injection molding is usually cheaper to achieve, and that makes it a preferred type of rubber molding.
• Easier process – rubber injection molding is a straightforward process that does not involve many complicated steps, and this is also an advantage of using this over other types of rubber molding.
• Better precision – in case smaller and more intricate parts are to be produced, the best choice in the list of different types of rubber molding is rubber injection.

Disadvantages of rubber injection molding

• Higher setup costs – while the cost of producing rubber components is lower for rubber injection molding when it comes to the setup costs, this involves more initial expenses. The cost of the production machinery is higher too.
• Generation of waste – the process of producing rubber using this type of rubber molding generates more amounts of waste that can be avoided when other types of molding processes are used.

1. Compression Molding

Compressing molding is also one of the popular types of rubber molding used in creating rubber components across different industries. As the name suggests, this process uses compression to create the structures.

Preheated materials are poured into the mold or cavity, and the mold is then closed and compressed at a certain temperature and pressure. Usually, hydraulic pressure is used to achieve the effect.

The compression is applied for a specified period of time, and then the formed structure is removed.

A compression unit usually consists of the following parts.

1. A movable top half of the mold
2. A fixed bottom half of the mold
3. An ejector pin to remove the finished product

Advantages of compression molding

• Low initial setup cost – the initial cost of setting up is quite low, compared to other types of rubber molding.
• Works for low-volume production – the cost of production does not increase, even for low-volume outputs.
• Works best for large components – large components can be easily produced using this method.

Disadvantages of compression molding

• Low dimensional tolerance – this type of rubber molding does not work well for components that are small and intricate. Precision molding may be needed for certain components where even the smallest of shape changes may be detrimental. In that case, compression molding cannot be chosen.
• High wastage production – there is high wastage produced with the production process.
• High production time – the time taken to produce components is high, as there is a considerable waiting time after compression.

2. Transfer Molding

Transfer molding is another of the popular types of rubber molding that produces rubber components of different types. There are two major halves of the mold. The upper half has a cavity where the raw material needs to be placed.

The upper half comes with a plunger that can be used to push the raw material through a narrow cavity.

The raw material goes to the heated mold through this cavity and takes shape. Once the product cools down and is vulcanized, it can be extracted through the bottom half by removing the ejector pins.

Advantages of transfer molding

• High dimensional tolerance – as long as the mold is shaped right, the final product can be designed to have high dimensional tolerance.
• Metal-rubber bonding – this technique can be used to create precise and high-quality metal rubber bonding designs.
• Easy molding process – the overall process of molding is straightforward and easy, saving time and effort.

Disadvantages of transfer molding

• High initial costs – the initial setup costs for this type of rubber molding are pretty high.
• Additional finishing processes – the final product must go through additional deflashing techniques to be completed.
• Additional prepping time – the raw material needs to be cured for a specific amount of time before it can be molded. This increases the overall cycle time of production.

3. Rubber Molding with Arvico Rubber

Arvico Rubber is your favorite rubber component manufacturer, and we specialize in using all these three types of rubber molding to create components based on your specifications.

Arvico Rubber comes with 55+ years of experience in this industry, and some of the components we specialize in are gaskets, diaphragms, seals and sleeves, expansion joints, O-Rings, and bearing bushes.

We understand how important dimensional tolerance and quality are to our clients, and that is why we always have prep meetings to understand the requirements completely before accepting projects.

Our design team can produce molds with 100% precision, and all finished products go through multiple levels of quality testing before reaching our clients.

Whatever type of rubber molding you want for your components, we get that done in the quickest possible time. Please get in touch with our expert consulting team to know how we can help improve the quality of your manufacturing process with our components.

The tensile strength of rubber is a very important factor that determines the quality of the polymer chosen. Tensile strength tests are also part of quality checks to determine whether a finished polymer product is of expected quality.

Tensile strength determines how much load rubber can handle before breaking up or getting damaged. As someone using rubber components, you should be aware of the tensile strength of rubber to ensure your machinery or part works according to specifications.

What is Tensile Strength?

By definition, it is the maximum force that a material can handle (rubber, in this case) before it breaks down. The unit of tensile strength is pounds per square inch (psi). The tensile strength can also be denoted as Mpa (Megapascals).

Different types of rubber have different kinds of tensile strengths, and manufacturers may be asked to choose the type of rubber depending on the strength they need.

Why know the Rubber Tensile Strength? 

Rubber is a flexible and moldable material. When you keep putting pressure on the material, after a point in time, the fibers of the material will break, causing damage. Knowing the tensile strength of rubber will help in knowing the exact point at which this breakdown will occur.

There are three basic types.

1. Yield strength – This is the maximum force the rubber can handle without going through permanent deformation. For instance, when a rubber band is stretched to a particular point and left free, it returns back to its original shape. That’s the yield strength.
2. Ultimate strength – This is the tensile strength of rubber very close to the breakdown point. Any force beyond this may cause breakage of the material.
3. Breakdown strength – This force will cause permanent deformation or damage to the rubber material.

How Does Tensile Impact Product Performance?

Multiple rubber components like valves, seals, and diaphragms may be used in machinery. These components play several roles, including sealing, friction reduction, leakage protection, or vibration suppression.

One inferior quality rubber seal with low strength may cause hazardous leakages and harm people and property in a matter of seconds. A low-strength valve may get damaged and break down when there is an inflow of erosive fluids, leading to productivity loss.

Let’s consider a simple rubber valve fitted in tires to control air pressure. The valve must handle the internal air pressure for it to work for long. Air valves with low strength may need to be replaced more often, bringing down the quality of the product.

Finding the Tensile Strength of Rubber

Two common test methods are used in finding the tensile strength of rubber.

1. Dumbbell cut-out method – In this method, a small piece of the sample rubber is cut into the shape of a dumbbell. The cut-out should be between the thicknesses of 1.3 mm and 3.3 mm. The sample will now be stretched until it breaks. The force applied and the elongation shape will be noted down, and the tensile strength will be calculated.
2. Ring cut-out method – This method is similar to the first method except that the sample will be in the form of thin rings. These rings would be stretched, and the force applied and elongation shape will be noted to calculate the tensile strength.

How Does the Rubber Strength Vary Between Different Types of Rubber?

The physical properties of different types of rubber change their tensile strengths too. The polymer chains and the crosslinks that make up a material decide how strong the final rubber will be.

Synthetic rubber can be created using a mix of different polymers and additives to make them exceptionally strong and of high tensile strength of rubber.

The following are the tensile strengths of different types of rubber, as marked by Arvico Rubber experts.

As you can see, PTFE rubber (Polytetrafluoroethylene rubber) is the strongest in terms of tensile value. Natural rubber also has a good tensile strength of 22. Materials like silicone, Viton, and nitrile fall under the bottom three in terms of tensile strength.

How to Change the Strength of Rubber?

Naturally, different types of rubber come with different tensile strengths. However, you can change the tensile strength of a particular polymer by mixing in different fillers with different chemical properties to the polymer while producing it.

Do remember that the tensile strength change with different scenarios. While in normal state, natural rubber has a higher tensile strength than silicone rubber, when these materials are heated, the tensile strength gap reduces between these two types of polymers.

How to Test the Tensile Strength of an Existing Rubber Component?

Let’s say you ordered a million pieces of rubber valves, and the rubber component manufacturer gave you some samples to check out.

It is important for your team to find the tensile strength of rubber used in making the component before giving the go-ahead for the rest of the component manufacturing.

The easiest way to do this is to use either the dumbbell cut-out test or the ring cut-out test. A small part of the component can be cut or molded into either of these shapes, and the tensile test can be conducted.

If possible, ask the manufacturer for a raw piece of the polymer to conduct the test, which may give more accurate results. It is always recommended to get the tensile test done and not depend on the values that the manufacturer mention, especially when the order is large.

Takeaways

Knowing the strength of the rubber used in creating your components will help you use the component in an effective manner. While higher tensile strength is usually considered beneficial, you need to remember that polymers with high tensile strength may have other limitations, like a high oxidation rate or being erosion-prone.

We at Arvico Rubber start all client discussions with a clear mention of all essential features of the polymer of choice, including its tensile strength. We can also help clients choose the right polymer from the different types of rubber materials that we offer, depending on their component usage and specifications.

If you would like to know more about tensile strength of rubber and other component offerings and our success stories, please get in touch with us at info@arvicorubber.com. You can also check our expansive product portfolio online and place orders for custom-engineering products of different specifications.