Extruded Products

Types of hoses
Tread tire (tire tread)
Sidewall tire (the side part of the tire)
Sealants
Profiles and strips
And all products that are continuous in nature.

Classification of Extruders Based on Feeding

Extruders are classified into two categories based on the temperature of their feed materials necessary for operations:

Hot feeding extruder
Cold feeding extruder

Typically, the feed required for hot extruders used in the rubber industry is pre-heated through separate operations. In conventional hot extrusion methods, a screw is usually used for this operation. Cold extruders work using a rubber strip or granulated rubber at ambient temperature. Secondly, extruders can also be classified based on their applications.

Many machine factories want their systems to be able to efficiently process various mixtures with different mixing processes. Here, the focus is on minimizing die change time and returning the machine to appropriate operating conditions, as well as ease of cleaning necessary to minimize contamination from compound changes. When a machine is expected to run for a long time with rubber compounds that have limited fluidity and flow properties, screws and dies can be designed to ensure a high output of materials while maintaining good dimensional control. Additionally, despite slight variations in feed materials, the feeding section, traction belt, and control system can be selected to achieve suitable dimensional control.

The main physical difference between cold and hot extruders lies in their length-to-diameter ratio of the screw. In the case of hot machines where a significant amount of energy is required to heat and plasticize the rubber mixture on the screw, the function of the extruder screw is solely to convey and apply pressure. This results in machines being smaller with screw lengths ranging from 3d to 5d relative to their diameter.

In addition to the functions of conveying and pressurizing through the screw, in cold extruders, the screw must perform the mechanical tasks needed to raise the temperature and achieve the desired heating of the rubber, as well as ensure the plasticity of the materials upon exiting the die. This requires screws to be longer, typically ranging from 9d to 15d, and in some applications, even larger screws may be used.

Cold extruders have widely replaced hot types in production lines. This replacement has occurred mostly in lines designed for long-term operation or high precision in dimensional measurements. These machines, owing to significant advancements as a result of a variety of developed designs and knowledge of working techniques, have played a pivotal role in capturing market share in machinery.

Components of a Cold Feeding Screw Extruder:

Hopper: This is where the mixture (materials) enters the extruder. Depending on the feeding type, the shape of the hopper varies.

Two important factors regarding the hopper:

Hopper Size
Uniformity of Feeding

Uniform feeding leads to the production of uniform products.

Shell or Body of the Extruder:

This is a metallic cylinder that surrounds the screw. Inside this cylinder, holes are designed to allow cold and hot water to pass through to control the temperature of the extruder. If the temperature of the mixture is not controlled, it can become overheated, leading to burnt or scorched output products.

Screw:

In a cold feeding extruder, as the name suggests, the rubber mixture is fed at ambient temperature. The feed may be in the form of strips or pellets, and the screw must provide sufficient mechanical energy to soften the mixture and overcome the back pressure of the die. In designing the screws used in cold feeding extruders, specific considerations are necessary. To ensure adequate mastication occurs, the height of the screw blade should be low, and the length should be long. A simple extruder screw consists of three sections: feed section, conveying or measuring section, and compression section.

Each section of the screw has its own role. The feed section transfers materials from the feed hopper. The conveying section heats and mixes the materials, while the compression section ensures uniformity and creates the required pressure to push the materials through the die. There is temperature control within the screw as well, with channels constructed within the screw that allow water to flow through for temperature regulation. The speed of the screw has a significant impact on the temperature within the extruder; with a fixed amount of feed, increasing the screw speed results in a higher output temperature from the extruder.

The ideal speed in screw extruders:

Is the maximum speed allowing the rubber to be received from the feed without accumulating in the hopper.

Die:

The die is the component that sits on the head and shapes the mixture as it exits into the desired form. Generally, designing a die requires considerable skill and experience.

Rubber Extruder Machine

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