A locating ring, also known as the retaining ring, is a fastener used to locate or align the orifice of the hot or cold sprue with the through hole in a housing/bore. Locating rings are typically one time use only. The sprue orifice is normally located in the center of a sprue bushing, and the bushing is aligned in the center by the locating ring.
Locating rings are typically located in the center of a mold, but are often subject to deviation by several inches to reduce the size of the mold base. They are normally made of stainless steel, carbon steel or beryllium copper which may be characterized by various finishes for aesthetics and corrosion protection based on the settings in which they are used.
There are a handful of different types of locating rings, all of which are mounted in a counter-bore of identical depth in the top or injection clamp plate. In this section, we’ll review some of the most common types of locating rings that you can find today:
● Standard Locating Rings:
The standard type of locating ring is capable of aligning a mold to a platen properly. Despite being the basic type of locating ring, it is not very user-friendly, namely in large molds. It is only able to extend beyond the face of the clamp plate by 5/16 inches. In other words, there is inadequate bearing surface that can hold the ring in the platen-alignment hole.
● Extended Lead-in Locating Rings:
This type of locating ring has an extended or tapered lead-in, and is more commonly seen on the production floor. Unlike the standard locating rings, the positioning of the mold in the making is made faster and easier by these rings, thus reducing the likeliness of damage to the platen and the ring. Most extended lead-in locating rings can extend beyond the face of the clamp plate by 25/32 inches.
● Clamp Type Locating Rings:
This type of locating ring has a relatively smaller inside diameter in order to keep the sprue bushing from blowing back. The primary advantage of the clamp type locating ring is that it completely eliminates the need of bolting the bushings to the mold base with cap screws. As a result, there will be no exposed screws on the surface of the sprue bushing to fill up with plastic.
● Flanged Locating Rings:
The flanged type locating rings, or platen-backed locating rings, are said to be one of the best one because of the unique advantages that other locating rings do not have. Firstly, flanged locating rings provide additional support to the center of the mold by pushing the flange up against the platen. Secondly, shim can be added underlying the flange to help prevent a worn platen. Based on the amounts of shim used, a flanged type locating ring can preload the center of the mold to protect it from parting-line flash. Imagine processing a worn platen around this flash, you’d end up with a less rigid process window.
The first thing you need to consider when selecting a locating ring is to determine whether an internal locating ring or external locating ring is needed. In other words, you need to decide whether you want to retain components within a housing internally, on a shaft, or both.
Now that you’ve selected the assembly type, the next step is to determine the assembly size. You need to account for some of the most important dimensional parameters, such as the groove diameter, and the housing or shaft diameter. Your supplier or manufacturer should provide you with clear specification as to which locating ring best fits your application. Some manufacturers are able to customize your locating ring if you cannot find a suitable size ring for your application.
That said, the last step is to choose which type of ring you need as we’ve already covered in the previous section. As a matter of fact, many suppliers actually offer various combinations of different types of locating rings we mentioned in the above section. Unless you are going to request a custom made locating ring, choosing a combination of commercially available locating rings that are well-suited for your intended application is the best thing to do. When it comes to buying locating rings, do note that the cost difference among the different types or specifications of the locating rings are fairly insignificant, meaning you should emphasize on the usability rather than the affordability when it comes to acquiring locating rings.
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