Recently, one of our sales engineers made a trip overseas to help in a process test utilizing one of our 5” Continuous Processors (CP). The machine was being used to process a Sheet Molding Compound (SMC) consisting of calcium carbonate, thickener, epoxy resin, peroxide, and 1” chopped fiberglass strands. The goal for the SMC was to add 25-33% (a finite percentage of) fiberglass into the mix during the process and then mold it as it discharged from the CP.
A typical process for a SMC is to add (drop) chopped fiberglass into a mold containing a resin paste. Fiber is added to SMC to add strength and weight reduction. Then, after the fiber has ‘settled’ into the resin paste, a second sheet of resin is placed over top – thereby encapsulating the fiber between the two sheets. By utilizing a continuous processor, the fiber can be better distributed throughout the resin mixture and dropped in to a mold directly from the machine – eliminating the two step process.
Utilizing two loss-in-weight feeders, the calcium carbonate and thickener were introduced into the processor directly above twin co-rotating feed screws at the feed end. A gear pump was used for the resin blend which was added into an injection port on the top barrel about 3 inches forward of the feed inlet. The fiberglass was then introduced in to the process two thirds down the barrel at a vent port that was about three inches in diameter. The fiberglass feeder consisted of a double row chopper gun with a moving belt about six inches wide – both controlled by a potentiometer. The combination chopper/belt feeder was highly effective for this application and performed without problem the entire test.
Due to maximum limitations of the resin pump in use, the test was begun running at roughly 100 lbs. of product per hour. Afterward, there were a couple of issues that needed to be addressed in order to continue with the test. One of the first issues was the paddle arrangement in the test machine was found to be ‘loose’ and needed to be tightened. Secondly, the supply amperage was too low to allow the machine to start. After locating another disconnect, the machine operated as purposed. Additionally, the small diameter of the vent port – for introducing the fiber – was an ongoing problem throughout the test. This would need to be addressed before actual production could begin.
Shortly after the test began, it was discovered that the discharge end of the machine became hot enough to ‘kick off’ the peroxide causing the product to begin to harden in the vessel. A firm understanding of the CP led our sales engineer to check to see if the packing glands had been correctly installed. As suspected, they were running above 180 F. With instruction from our engineer, the barrel was disassembling, and the client was shown how to pack the machine so that it would not get hot. Additionally, the glands were measured to make sure they never exceeded 125 F.
The next two days, 20 panels were made with glass loading between 25-33%. The panels themselves indicated excellent strength and surface finish. The customer commented that they have been looking for a machine that can do what our CP can do for several years. Their previous method of running their material through two extruders had caused the panels to crack and break very easily. Without the expert knowledge of a Readco engineer on-hand who understood the intricate capability of the machine, it is highly possible that the test could have been a failure. Instead, with a few minor adjustments, Readco was able to demonstrate the full versatility of the CP while meeting and exceeding our customer’s expectation.