DME Molding Supplies (Madison Heights, MI) has expanded its line of MRO products to include Mini-Shut Automatic Nozzle Tips. These low-cost tips shut off the flow of plastic into a mold to prevent drooling and stringing without requiring mold decompression.

There are several methods molders currently use to prevent drooling and stringing, but they're often expensive, complicated and unreliable according to the vendor. The patented, simple design of the Mini-Shut enables molders to eliminate the variables and produce consistent shots without drooling.

"The Mini-Shut fits a niche in the market as low-cost way of stabilizing the injection process and eliminating many surface imperfections on parts," said Jim Hunt, manager of DME Molding Supplies. "Competitive products cost several thousand dollars. Mini-shut is only a fraction of that."

Typically, when plastic is injected into a mold and the mold opens, plastic continues to drool out of the nozzle. This presents significant challenges to a molder as it can create imperfections in the next part. A common method of counteracting drool is with mold decompression - retracting the screw to relieve pressure at the nozzle tip. However, this process drops the pressure in the barrel and creates the potential for short shots. When the molder tries to make the next part, there is often not enough plastic in the barrel to fill the mold completely. When retracting the screw, the molder also has to control the melting process, a complicated endeavor.

"Control of the melting process depends on a number of factors, including the proper screw and NRV design, and setting variables such as back pressure, barrel temperature, screw speed and melt decompression," said Hunt. "It often produces stringing, part imperfections created because of the varying temperatures."

The Mini-Shut eliminates the need for mold decompression by the simplicity of its design. After a molder shoots the part, the nozzle itself doesn't have enough pressure to continue drooling plastic. There is no need to retract the screw, but there is plastic waiting at the tip to shoot the next part.

Another method molders often use to eliminate drooling is with spring-loaded shut off nozzles. Typically costing between $1,000 and $2,000, these parts use an internal pin that wears over time and must be replaced. The Mini-Shut's simple design with internal springs arranged in a certain pattern shuts off the flow of plastic to that tip. The Mini-Shut is a better alternative because it contains no moving parts, minimizing maintenance and downtime.-[email protected]