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U.S. 800-626-6653


Canada 800-387-6600


Mexico 442-713-5666



Special-Purpose Machines

Mold action and ejection requirements will often dictate the

use one of three special-purpose mold bases instead of the

simpler A- and B-styles.

One of these is the X-style, or stripper-plate, mold base.

Sandwiched between the “A” and “B” plates, its stripper

(“X”) plate engages the edge of a part and pushes it off the

core. Typically, the X-style sees use with round parts like

cups, caps, and containers. This style of mold base comes

in both five- and six-plate styles- -with the six-plate version

including a support plate.

The AX-style mold base is used for parts requiring core detail

in the cavity side of the mold. When the mold opens, that

core detail is pulled so that the part remains on the ejector

side of the mold. The AX-style is essentially an A-style mold

base with an “X-1” plate, located between the “A” and “B”

plates but attached to the top half of the mold so that it can

pull the part off the core detail.

The “T” style, or three-plate, mold base is used when the

molder would like to separate the part from the runner in

the tool. “T” series mold bases consist of an “A” clamping

plate, “X-1” plate, “X-2” plate, “B” plate, and the ejector

assembly and housing. Unlike the other mold bases, the “T”

series operates with two parting lines. The first parting line,

which occurs between the X-1 and X-2 plates, separates the

part from the gate prior to opening the main parting line. The

main parting line then opens and the X-1 plate is actuated to

pull the runner from the sprue-puller pin, thereby freeing the

runner and allowing it to be ejected separately from the part

being produced.

See page 11 for illustrations of standard mold base types.

Choosing A Steel

Steel selection is an important aspect of specifying the right

mold base. Generally there are four standard grades of steel

available. See page 8 for mold and die steel descriptions.

Molding Machine Considerations

After you’ve picked the right style and steel for your mold

base, it’s time to consider variables related to the molding

machine: the locating-ring style, sprue bushing, and

clamp slots.

The mold maker must select the type of locating ring that

will match the platens of the machine in which the mold will

be running. Locating rings are available in a wide variety of

configurations to fit most injection machines, but the most

common locating ring has a 3.990 in. outside diameter.

Sprue bushings must also match the machine, so be sure to

determine the proper orifice and radius of the sprue bush-

ing so it will match the machine nozzle. The most common

type of sprue bushing is made from 6145 steel that has been

hardened, ground, and polished for sprue release. In some

applications it is desirable to use a high-conductivity

copper-alloy sprue bushing.

These “high-performance” sprue bushings can cool the sprue

quickly when either the sprue weight is greater than the part

weight, or a rigid target is needed for a robotic sprue picker,

or when scrap would result from a hot sprue coming in

contact with a finished part. High-performance sprue bushings

are fully interchangeable with the standard bushings.

A number of different clamp-slot styles are available.

Whatever the style, make sure it’s compatible with the

thickness of the top clamping plate on your mold base

(ACP, “A” plate, or AX plate).

Finally, the molder needs to determine the correct mold base

height in relation to the maximum space available in the

press. A mold base that won’t run in the appropriate size of

press can turn potential profit into loss. In addition, be aware

of the maximum stroke required to eject the part for the mold.

Mold Bases and Plates

Mold Bases and Plates


Mold Bases: What Every Molder Should Know

“High-performance sprue bushings cool

the sprue quickly when either the sprue

weight is greater than the part weight,

or a rigid target is needed for a robotic

sprue picker …”