By Chris Ryan, ChemSpec Technical Sales Manager
(originally published on ARPM Blog, on January 8, 2015: http://www.arpminc.com/rubber-industry-forum/article84.htm.
During the molding cycle, rubber compounds produce by-products that are given off as rubber fume and residues on the mold surfaces. If the residues are allowed to remain on the mold they gradually build in thickness and will eventually cause molding defects in the finished rubber parts. This is what is classically defined as “Mold Fouling.” Other causes of mold fouling occur with the oxidation of portions of the rubber part, either from contact with trapped air pockets, or from the incomplete part stripping off the mold at the end of the cycle.
Rubber part defects then arise through physical dimensional changes to the mold by marring the component surface or through adhesion between the residue and the cured rubber part; causing lumps and imperfections to the finished molded parts. Consequently this increases product scrap rates.
So how do you go about minimizing this problem of mold fouling?
First, ensure that the mold is cleaned on a regular basis. Clean properly and apply an anticorrosion lubricant before storing molds to ensure that the mold doesn't rust and cause pitting to the mold surface. Rust pitting will require the molds to be cleaned more often lowering production life. Companies like Muench-Chemie produce very good anticorrosion lubricants designed to negate, or at least minimize, these issues.
Secondly, after the mold is cleaned and before it goes back into production, its best to apply a coating of semi-permanent mold release agents. The mold operator can then apply a touch-up mold spray as needed to eliminate the parts from sticking, which will allow the parts to be de-molded more easily and help reduce cycle times to decrease the chance of mold fouling. Again, companies like Muench-Chemie offer excellent external mold release agents designed to help with these issues.
Moreover, internal mold release agents can also be helpful to reduce mold fouling. There are various chemical process aids that act as mold release agents that become surface active only during rubber curing. The most effective and commonly used chemicals that are used in this manner are structures of fatty acid soaps and amides. Performance Additives’ Ultra Lube 160 is highly effective in most compounds and is an outstanding internal release agent for molding applications. This product helps condition the metal molding surfaces, allowing for easy de-molding and significantly decreasing the residue that causes mold to begin fouling. Other primary amides, such as Performance Additive’s Ultraplast TP-05 and TP-06, also may greatly improve mold release characteristics.
By utilizing these internal release agents anddecreasing the residue to the mold surfaces, the mold can then stay in service much longer before cleaning, greatly improving production.
For follow-up questions on this topic, contact your respective sales representative or Marketing Manager Chris Wagner (cwagner@chemspecltd.com).