I would like to modify my DME Sprue Bushing. What is permitted and how hard is the sprue bushing material?
DME offers a few types of Sprue Bushings: “A” series, “B” series, “U” series, “UV” Series, “LN” Series, “AR” series, “UR” series, “L” series and Performance Sprue Bushings. All but the Performance Sprue Bushings are made from steel with a base hardness of 43-45 HRc, and the “LN” series has an additional surface treatment that brings the surface hardness up to about 60-62 HRc.
The Performance Sprue Bushings are made from a copper alloy and have an additional hardened 420 Stainless steel insert. The “PSB” type Performance Sprue Bushings are directly replaceable with the existing DME “B” Series Sprue Bushings. The “PSU” type Performance Sprue Bushings are directly replaceable with the existing DME “U” Series Sprue Bushings.
Note: If you order a sprue bushing separate from your mold base, it is important to check the fit of the sprue bushing OD to your mold base OD. In some cases mold makers will need to open up the sprue bushing hole in the mold base and fit to suit. A tight tolerance of no more than 0.0004 inches clearance across the two mating diameters is recommended, as some resins will flash past 0.0005 inches clearance.
When ordering a complete mold base from DME, customers must specify if the sprue bushing is to be installed (normally the sprue bushing is shipped with the mold base but not installed). If requesting to ship the mold base with the sprue bushing installed, DME will ensure a proper fit between the sprue bushing and the mold base plates.
If it is not requested by a customer to have the sprue bushing installed into the mold base, the sprue bushing will be shipped in the crate not installed, and the mold maker will need to check the fit between the sprue bushing and mold base plates and may have to modify as described above.
Most modifications are made to the front face of the sprue bushing as mold makers add a runner channel.
Note: That the distance from the underside of the sprue bushing head to the front of the sprue bushing (at the molding surface) is slightly oversized relative to standard plate thicknesses provided by DME. If the it is requested (when ordering a complete DME Mold Base) to have the sprue bushing installed, the front of the sprue bushing will be ground to ensure proper fit. However, when ordering a sprue bushing separate, mold makers are expected to perform this secondary operation.