Providing Industry Leading Release Agent Solutions for Transfer Molding
Transfer Molding for General Rubber Applications
The process of transfer molding of rubber involves having a "piston and cylinder” type of device built into the mold so that the rubber can be squirted into the cavity† through small holes called gates or sprues. Watch a video of this process.
For general rubber applications this process is used to produce a wide variety of end products. However, there are considerable challenges for the release agent in this process. The mold release must encourage the rubber to flow – ensuring that there are no voids in the molded surface. This is particularly important when molding high durometer rubber compounds. Chem-Trend has decades of experience working with molders of rubber and has built its reputation on understanding, and overcoming the complexities of rubber molding challenges.
A mold release agent with high lubricity† can assist in the process of rubber flow; however the release agent should not be disturbed or scoured away from the mold surface during the rubber flowing process. A balance needs to be struck between the level of lubricity that the mold release provides and its tenacity to remain attached to the mold surface. Products that form a very hard, low-transferring mold release film are highly desirable if the rubber is to be bonded to a metal part during molding. However, good rubber flow may be impeded.
The mold release must not migrate to the bond-line. Very often, mold release lubricity (for encouraging good rubber flow) needs to be sacrificed to ensure that good technical quality parts are made. Conversely, very soft rubber stocks must not be encouraged to flow around the mold too quickly. Insufficient pressure build-up within the rubber section can lead to voids or air-trapping. A less lubricious mold release – one that is more tenaciously attached to the mold surface – can assist here.
The mold release agent must not allow any anti-tack on the raw material to contaminate the mold surface, causing build-up. We compound many different elastomers, depending upon the application and the mold release needs, to handle these different compound chemistries. In cases where customers process multiple elastomers, more than one type of mold release may be required.
Over the years working on shop floors of molders of rubber via the transfer process, Chem-Trend has been able to develop a wide range of Mono-Coat® branded semi-permanent and Chem-Trend® PM type conventional products. These products help reduce waste and increase efficiency. To learn more about our experience in this area, and how that experience can help you, visit our main Rubber Molding page, or contact us to speak directly with one of our rubber industry experts.
Transfer Molding for Tire Curing Bladder Production
Transfer molding is a process that is not used to vulcanize pneumatic tires, but is used in the manufacture of the inflatable curing bladders (membranes) used in the curing process of the tire. Chem-Trend supplies a range of water-based semi-permanent mold treatment/ coatings that help keep the mold and core free of mold fouling, as well as assist in the release of the finished bladders. These mold coatings are sold to custom tire curing bladder producers as well as those tire producers who manufacture their own curing bladders.
Beyond the release agents that Chem-Trend produces for the manufacturing of curing bladders via transfer molding, we also produce a world-class line-up of products to protect the bladders and enhance the tire manufacturing process. Today’s high quality curing bladders face considerable stresses during their working lives. To help reduce some of those stresses, and prolong bladder life†, Chem-Trend has created a range of specialist Tire Curing Bladder Treatments. These are coatings that, applied to the surface of new tire curing bladders, protect their working surface against abrasion and chemical attack, significantly increasing their service life.
Protecting the curing bladder against the high level of abrasion that occurs around its contact surface with the bead areas of tires significantly improves service life. The coatings also act as a barrier to help slow down the ingress of sulfur and other compounding ingredients from the hard chafer compound that can lead to local hardening of the curing bladder. Providing a barrier to the ingress of these materials helps to further increase bladder life by reducing the tendency for this region of the bladder to crack in the vent lines – a typical cause of early bladder failure. Depending on the bladder type, curing press type, and fit to the inside of the tires, customers report increases in average bladder-life of up to 45% when using our coatings.
An additional benefit provided by many of the Chem-Trend coatings for bladder treatment, is enhanced slip. This helps eliminate the start-up difficulties often associated with new bladders and works to reduce defect levels throughout the life of the bladder.
Each product is designed to be applied to the curing bladder when it is new. Depending on the grade selected, the coating is either left to cure at room temperature or is cured by baking the coated bladder in a hot air oven. Each coating is applied only once to the surface of the bladder – there’s no need for further applications. These coatings provide protection to the curing bladders throughout their service life, helping enhance slip to improve tire uniformity and reduce defects. However, these coatings will not provide the level of slip required to ensure optimum tire uniformity and release throughout the life of the bladder. Therefore, they do not replace the need to treat the inside of the uncured tires with an inside tire paint†; they are intended to be used in conjunction with them.
Chem-Trend is a world leader in the development and manufacture of processing aids for tire production. To learn more about how our range of products and extensive knowledge of this industry can help you, visit our main Tire Curing/vulcanization page, or contact us directly to speak with one of our tire industry experts.