The Wide Range of Applications, and Molding Challenges of Rubber and Elastomers
Transportation, sporting goods, household appliances, machinery, office equipment, pneumatic tires, footwear and many other items take advantage of the flexibility of rubber. A huge variety of different rubber compounds are used in the moldings processes required to make these goods. The selection of which rubber compound to use, which process and application to employ, depends both on the function of the part as well as the environment in which the part is expected to perform. With decades of experience working with molders of rubber components, Chem-Trend has developed solutions to many of the challenges faced in these processes and applications.
Molding compounds are designed to be flexible and durable. “Rubber” is an all-embracing term for a flexible, cross-linked (thermosetting) material that can be molded into almost any shape in order to fit a specific space envelope and/or perform some kind of mechanical task. The elastomer upon which the compound is based can be one of more than fifty “species” that are characterized by the chemistry of their polymeric lattice. Some elastomers exhibit what appears to be a greater degree of “chemical aggressiveness” than others.
The mold release agent used in manufacturing must be capable of protecting the mold surfaces against the compounds that are formed, and easily releasing the part from complex-shaped molds. This is where Chem-Trend’s expertise comes into play. It may seem strange, but rubber compounds that are designed to be resistant to the most chemically aggressive environments, tend to be manufactured from compounds that present the most chemically aggressive molding challenge. These compounds are manufactured with elastomers that are commonly called special purpose, or exotic, elastomers. Moldings made from halogenated compounds, for example – especially fluoroelastomers that typically spend their entire working lives as sealing materials in hot fuel – are usually quite difficult to mold due to their inherent stickiness. The reactivity of the halogen in the compound accounts for its affinity for metal (the mold surface). The cross-linking system also plays a large part, since peroxides are often used and they, too, tend to attack the mold metal surface.
The mold release agent’s key task, in these circumstances, is to create a barrier against primarily chemical, but also mechanical attack. No matter whether the product is a conventional or semi-permanent mold release agent, it must provide the necessary barrier to prevent the rubber compound from attacking the mold surface. The mold release agent must be chosen with this primary aim in mind.
A second issue to consider in choosing a proper mold release agent is abrasion resistance. Compounds made from general-purpose elastomers are molded into products that spend their lives in air – a less chemically demanding environment. However, the environment in which these moldings live is demanding in other ways. A natural rubber motor mount, for instance, needs to resist many thousand deflections during its working life. From a molding standpoint, general-purpose elastomers tend to present a greater challenge due to the abrasiveness of the compounds, in which they are formulated. In these circumstances, the mold release needs to act as a barrier against primarily mechanical, attack.
Beyond the primary attribute of preventing attack on the mold surface, the mold release agent also must provide surface slip, or lubricity†, to the mold surface, allowing the molded part to be removed easily from the mold. The mold release must be designed to lubricate the interface between the mold and the molded part, and it is advantageous to use the least amount of lubrication necessary to perform this function. Lubrication means that there is mobility within the release agent film. However, excessive movement of the release agent around the mold during the molding process can lead to potentially defective moldings.
If an efficient barrier is provided against chemical and mechanical attack, there is no need to build-in a great amount of lubricity in the majority of cases. However, there are exceptions and these usually apply to moldings that have very complicated shape or geometry. Sometimes, a high amount of slip is needed and a necessary trade-off must be made. This is a significant challenge in developing high performance release agents. But, the rule still applies – the least slip possible, the better.
Finding the proper mold release is a balance between three factors: 1) assessing how chemically aggressive a compound might be; 2) assessing its tendency to abrade away the release film; and, 3) taking into account the product shape. Chem-Trend has, during three decades working with rubber molders, developed the proper products to meet these challenges.
Silicone Rubber Compounds
Silicone rubber compounds need special mold releases. It is normally possible to mold a carbon-based rubber with a mold release designed for silicone† rubber, however, the opposite does not hold true. Mold release agents containing any type of silicone should be avoided when molding silicone-based rubber compounds. Chem-Trend makes a comprehensive range of products for silicone rubber molding.
Solutions to Your Rubber Molding Challenges
Chem-Trend is an expert in developing and manufacturing specialized release agents and related products for the rubber molding industry. We have specific products to help address the challenges of molding rubber compounds across many different types of rubber molding processes. Our many years of experience in this industry can help you to select the right products for your process and raw materials, increasing efficiency, lowering scrap rates, improving product quality and extending tool life. To learn more about how we can help you face the challenges of rubber molding, visit our main Rubber Molding page or contact us directly and talk with one of our experts.
Special Challenges of Molding Rubber for Tire Manufacturing
An elastomer is a polymer with visco-elastic properties (usually referred to as elasticity), this term is derived from elastic polymer, and is often used interchangeably with the word "rubber", especially when referring to vulcanized elastomers. The word "rubber" is used as a generic term for the natural and synthetic elastomers used to manufacture tires. Of course, the types of elastomers used to produce various components within a given tire are thermosets (requiring vulcanization) and have been specifically selected for the physical properties they provide, e.g. resistance to tearing/chunking, specific hysteresis characteristics to provide grip etc. All of these factors have an effect on the specific release agent required for different parts of the tire manufacturing process.
Chem-Trend has been able to learn and understand the specific challenges of molding rubber into pneumatic tires through its decades of involvement on the shop floors of both its rubber molding and tire manufacturing customers. We have separate laboratories for each type of process because we understand that, although they share some similarities, they are in fact, very different processes. Rubber is a broad term, and it takes expert and in-depth knowledge of specific rubber properties and manufacturing processes to help both rubber molders and tire manufacturers improve their process efficiency, reduce scrap rates and produce high quality parts. To learn more about how Chem-Trend can help you face the challenges of molding rubber elastomer into tires, visit our main Tire Curing/Vulcanization page or contact us directly.