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General comments on design function
Definitions: mold. 1) A hallow form or matrix into which a plastic material is placed and which imparts to the material its final shape as a finished article. 2) To impart shape to a plastic mass by means of confining cavity or matrix. A side: 1) Hot half, stationary side, cavity side 2) the side of the tool which typically does not contain the ejector housing and is mounted to the stationary platen.
In most tools the A Side (half) of the tool is the cavity side, and the B is the core side, thus allowing for the plastic part to shrink onto the core and be withdrawn from the cavity and ejected. By most one is talking approximately 85% of the tools built have some sort of cavity detail which than requires a core from the B.
The A side of the tool is typically mounted to the Stationary side of the Clamp mechanism and incorporates the sprue and or some part of the feed system from the press in or through it. For example in a 2-plate mold it may only be the sprue bushing, while in a 3-plate mold the entire runner system is cut into the X plate behind the A plate and in a hot runner system the entire manifold and drop are usually retained in the A side of the tool. It is important to reminder that there are always exceptions to the rule, and the author has been part of many of those.
At a minimum the A side contains, the A plate (cavity plate), leader pins or leader bushings, sprue bushing, locating ring. In this particular scenario the top clamp plate is not listed as the slots for mounting are found in the A plate directly. In a typical A-side all the above plus a top clamp plate would be involved.
The locating ring is the ring around the sprue busing hole which locates the mold onto the platen. A platen has a large center hole where the nozzle extends through so as to contact the sprue bushing. This locating ring alienage's the mold, while centering the sprue bushing to the platen opening so as to center the sprue bushing to the nozzle of the machine. Please note the comment sprue bushing to the nozzle of the machine, as in some rare cases the sprue bushing is not centered in the mold base but off set. This ring than also allows for positioning the mold into the platen and acts as a pivot to level up the mold. In this the ring must be as close to the same diameter as the opening in the platen which is a standard.
The locating ring is a sleeve/ contoured plate of material which is located typically in the top clamp plate by a slight recess and then held in place by bolts. The ID may be minimally the same as cut into the mold for the sprue bushing and the OD has a chamfer on the upper side so as to allow easy placement into the platen. Note that there are many different configurations for its design and possible other functions. If one is to use insulation sheets on a mold, than there are taller locating rings which shall allow for engagement of the locating ring into the platen for set up.
The A side also has the leader pins** / bushing located in it. The function of the leader pins / bushing is to guide the mold halves together and in some cases they may be (pins) extremely long as some may state that the leader pins are to be the first contact for the two mold faces. Thus if a tool has deep cavities meaning the cores are long than the leader pins would be as long from the face of the A plate plus an additional amount for safety**. Please note that correctly used the leader pins would be on the side of the tool with cores and be again longer than the cores thus to always protect them (cores) from damage.
The leader pins/ bushings are spaced on the outer perimeter of the tool and while three of them are uniform in location one is off-set so that the tool may be only assembled in one way. This prevents the tool from being damage should it be hung in halves and that someone has not noticed the typically 00 marking on one corner of the plates for alignment.
**Note, depending on style and manufacture leader pins and bushings are on either the A and or B side of the tool. If one uses the idea that the pins should protect the cores than they would be located always on the core side. In some cases this is not possible due to other issues in which case care has to be taken so as not to damage the cores and or projections.
Since it was mentioned that not all 2- plate tools may use a top clamp plate, it should be stated that the use of the top clamp plate while primary for mounting to the press it is also used to retain the inserts for cavities in the A plate. If in fact an insert is manufactured (such as in a class 101 tool) it must be retained into the A plate. In most cases this is done through the back of the A plate, in such a way that the there is a step in the A plate to hold the shoulder of the insert and the top clamp plate than compresses the bottom of the insert to the shoulder and sometimes an O-ring seal.
Plate thickness is usually the cavity depth plus an amount for safety under the cavity, one is not looking at bending strength of the plate as they are usually stacked 100% contact to a top clamp plate and or multiple plates so bowing is not a function of the A side of the tool. In those cases where a hot manifold is used this changes and plate thickness now becomes an issue. What is meant is that steel may bow and warp if too thin for the force applied within the tool. In steel a simple rule of thumb is that a single plate of the thickness of 2 plates is stronger than the 2 plates in this aspect, thus it is always better to go thicker than to stack thinner plates together, (more on this aspect later).
SLSILVEY
07042014
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