Mold Base Terminology - S

Socket Head Screws: This is the type of screw that is the most common method to hold plates and components in the mold base together.; Molder friendly tip - The placement and size of the screws can be very subjective. The designers have rules of thumb they use in design so they don't spend a lot of time in making arbitrary decisions. The placement of the center of the screw should be no closer than the diameter of the body of the screw. For example the placement of the center line of a .5 screw should be no closer to the edge of a piece of steel than .5 the depth of the tap should be 1.5x the body diameter. To ensure that the screw will have the maximum 1 times (X) the diameter engagement the tap depth should always extend beyond the bottom of the screw hole by at least .12 to keep from cross threading the screw threads. A torque wrench should be used to tighten screws to the proper tightness to maximize the life of the screw and prevent broken screws.
Shipping Straps: These keep the mold halve together when putting a mold in the press. If the straps are painted orange they will not be easily misplaced. The mold should also have mounting holes in the mold base to store the straps while the mold is in use in the press. This small oversight in the design can cost the molder time looking for the shipping straps when it comes to taking the mold back out of the press.
Shrinkage: The decrease in dimension of a molded part through cooling.
Slides: Moveable steel sections of the mold containing part of the cavity that are slid out of the way to allow the part to be removed.
Sprue: The channel or feel opening for the passage of material from the nozzle of the injection molding cylinder to the runners of the mold. The plastic piece is formed in this channel.
Sprue Bushing: This is a bushing that interfaces with the injection press nozzle and connects to the runner in the plate. The sprue bushing is considered the primary runner channel and will set the cycle if it is too large. It has a nozzle the radius to match the molding press injection unit. The sprue bushing that contains the first leg of the runner. The sprue bushing can cause some problems if the wrong orifice size is used. The orifice size should always be at least .015 more than nozzle orifice to ensure there would be no undercut. In addition the nozzle radius must match the sprue bushing radii. Failure to match these two surfaces can result in a nozzle leak at the press and phenomena called a beehive will form around the nozzle costing hundreds of dollars in ruined heater bands. Beginning size orifice is determined by the amount of cavities and the gate size used in the mold. A small effective radius gauge is a good investment in the technician's toolbox that properly identifies the radii. The two most common nozzle radii is.5 or .75 radii. Misalignment of the injection unit with the mold can also cause problems. In the Avaya plant a "machinist" would fix this.
Sprue Gate: The passageway through which the resin melt flows from the nozzle to the mold cavity.
Sprue Puller Pins: These are the pins in the center of the mold used to pull the sprue away from the nozzle. They have an undercut just below the parting line that is used to ensure that the orifice of the sprue is pulled away. If the pin is too large it will cause the undercut to be larger than necessary and can increase the molding cycle because it must solidify before ejection.
Sprueless Molding: Mold design in which the sprue and runner system is insulated from the hot mold to prevent heating of the thermosetting resin in the sprue and runner. May also be referred to as hot runner molding of thermoplastics and cold runner molding for thermoplastics.
Stack Mold: This is a special mold construction that allows the mold to take advantage of opposing forces of projected area. If you are unfamiliar with how projected area us calculated let's time here to explain, because it is this principle that gives stack molds their reason to exist.
Stripper Bolts: These are used to limit plate travel. The length of the bolts is given from the bottom of the head to the end of the body. The tapped hole is always smaller than the body. The placement of the stripper bolt follows the same rules as the screws. The most common problem with stripper bolts that are used in plate sequencing is that they will frequently come loose and need to be tightened. The designer should be aware of this and try to place them as close to the outside edge for easy accessibility to the technician. The majority of mold crashes that have plate sequencing using stripper bolts come from neglect of the mold technician not checking the stripper bolts.; Molder Friendly Tip: You can use a simple technique of painting a line on the head of the stripper bolt and one on the plate once they are tightened and you can visually check each bolt during the shift P.M. This will prevent a mold crash form bots that will work there way out and cause an uneven pull if they are used in plate sequencing.
Stripper Plate Mold: In the case of a typical stripper plate mold the ejector system would not be necessary. This would eliminate the need for a rails, ejector retainer plate, ejector bottom plate. The stripper plate is used to mount the stripper ring in the mold base. This plate is usually on top of the core plate and will have the leader pin and bushing guided to prevent premature wear on the stripper and cores.
Support Pillars: These round ground posts are used to support the plate above the ejector housing. The functions of support pillars are to help prevent the plate deflection caused by injection molding pressure. Without this support along with thickness of the support plate the mold can bow under injection pressure and cause flash. When a mold has had some use the support pillars will hob into the plates and lose their effectiveness. As a result this usually shows up as flash in the center of the mold. They normally have a .002-inch preload to them to ensure that the support plate will not flex during use. They are most effective when placed in the center of the mold. Support Plate- This plate used to keep the core plate from deflecting during injection. This plate is usually the thickest plate in the mold base, because it has to keep the mold from flexing during injection. The unsupported side of the plate has the ejector plates space underneath it and can easily deflect if there is not enough thickness. It also provides a base for the cores to sit on and provides space to feed the water lines to the cores.
Sucker Pin: This is a pin with an undercut that is directly above a cold runner drop. It is used to de-gate the runner from the part. If the undercut is too sever the material will chip or flake and will lodge in-between the runner plate and cause damage.
Surface Grinder: This a machine with a rotating grinding wheel that is used to finish flat surfaces, forms, side walls, slots, shoulders, and heels. It primarily used for mold plates or finish grinding of hardened tool steel.

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