Rubber molders should examine their processes closely to ensure they not only are making quality components but produce them efficiently as well.
A multi-deck cold runner mold system might be a solution for molders trying to utilize the greatest amount of capacity in their machines and reduce waste, said Walter Koroluk of St. Mary's, Ga.-based TechShop International.
Koroluk talked about the advantages and disadvantages of multi- and single-deck setups in various cold runner systems in his presentation, ``Maximizing Your Injection Molding Machine's Capabilities,'' given during the International Rubber Molding Conference. The event was held April 5-6 in Dearborn, Mich.
Koroluk compared three processes in looking for the most effective way to reach a molder's objectives: a horizontal cold runner system with a single-deck mold; a horizontal cold runner system with a two-deck mold; and a vertical cold runner system with a four-deck mold.
He assessed the systems producing an EPDM rubber bracket product with a single-part weight of 0.03 pounds, hardness of 55 to 60 Shore A, with a yearly sales volume of 3 million parts. The process objectives were to keep the scrap rate below 2 percent, staff the press with one operator, utilize a cold runner system to minimize rubber compound waste and keep a uniform product compression set, Koroluk said.
The production ``up time'' would be based on a 24-hour day and 220-day year, he said.
In the first case, the horizontal cold runner system with a single-deck mold took 166 days of production to finish the job, had a cycle time of five minutes and yielded rubber waste percentage of 0.1.
The system has a low mold investment and utilized a simple cold runner process, but productivity was relatively low, the waste per cavity was high, and it did not take advantage of the machine's injection capacity, Koroluk said.
The horizontal cold runner system with a two-deck mold took 88 days of production, a cycle time of 5.33 minutes and a rubber waste percentage per cavity of 0.15, he said.
The production level was higher than the single-deck mold, but the mold cost was larger and, like the single-deck mold, it didn't take advantage of the machine's capacity, he said.
The vertical cold runner system with a four-deck mold, which Koroluk recommended, took only 53.7 days to finish the job, had a cycle time of 5.66 minutes and had a rubber waste per cavity percentage of 0.08. The major advantages for the system outweighed the disadvantages, with the highest production level and lowest waste per cavity among the three being compared and it took advantage of all aspects of the injection machine's capacity, Koroluk said.
Multi-deck mold and vertical cold runner systems also have a number of other benefits, including better balance between decks, decreased material waste in each injection, dimensional uniformity throughout the process and dimensional stability of the molded part, he said. The setup is applicable to different products and rubber compounds and adjustable for different injection distributions and varied numbers of decks.
The main downside was the mold is more complex, which takes longer to set up and may require a higher allowance of clamping force on the press, Koroluk said.