MPS New All Polymer Concrete Boxes

The Sweetwater facility has been manufacturing underground utility enclosures since 2003. In the early days, units were small in size but, to be a viable industry competitor today, there are four sizes that a manufacturer must supply - 1324, 1730, 2436 and 3048. These numbers represent the nominal size of the enclosure cover in inches. In addition to manufacturing these four sizes, it is imperative that the covers are interchangeable with other manufacturers. Dimensions are governed by the Western Underground Guideline 3.6.

Over the next couple of years, production expanded into various depths of these sizes and, when an opportunity presented itself for other sizes, tooling was purchased. As the company grew, the demand for larger enclosure sizes was growing and, to fit this need, the vault was developed. This consisted of four fiberglass panels that are assembled into a box and then a top ring, corner posts and bottom ring are cast onto the panels to make the final unit. This is a creative way to utilize the same top and bottom ring molds to manufacture a variety of depths to suit the customer’s needs. This manufacturing process presents an inventory issue for panels or waste when a panel is cut to make a shorter vault. While this process is an excellent way to make an enclosure, there are more cost-effective ways to make a unit with a set depth dimension.

In order to manufacture larger all polymer boxes, larger molds are necessary and more space is required. This was not possible at the original Sweetwater location. Now that we have moved into the new location and developed a production line that can handle the larger units, we have begun to design and purchase tooling for the larger monolithic polymer concrete units.

The first such mold arrived in 2015 and was put into production. This unit is a 366036, which translates to a 36" wide by 60" long by 36" deep. The cover molds can make a variety of covers with three different load ratings, depending on the customers’ requirements. The covers are also complete with a polymer tongue and groove at the intersection of the two halves to help mitigate the entrance of dirt into the enclosure and to keep a child from shoving a piece of wire between the two covers and getting shocked, in the event that there is electrical equipment housed in the enclosure. This enclosure is being manufactured with a savings in excess of 20% when compared with a vault of the same size.

A number of constraints were addressed with the new design to make sure it could be manufactured with the minimal amount of labor and materials and also to address the commercial aspects of the box design.

The mold was developed to clamp and open with hydraulic cylinders, thus utilizing the central hydraulic system at the new location. The mold was also equipped with a pouring lip to help minimize spillage of the material when it was placed into the mold. The handling arbor for the hat portion of the mold is removable, making the entire top surface of the mold accessible for the caster. All of the radii are at least 1", providing a surface that is more conducive to apply the fiberglass cloth and help it remain where it is placed. Fiberglass cloth has a memory and it wants to remain flat, if at all possible. Providing smooth transitions make rework of the glass virtually a thing of the past. The ribs on the outside of the box have also been revisited and redesigned. They have the same taper as the sidewall of the box. The seal for the mold was designed to be an integral part of the core instead of the hat, which makes it easier to inspect and replace. A groove was machined into the core to accept standard gasket material and the depth was set to ensure a proper seal while minimizing any excess flash that is required to be removed after the box is de-molded.

On the commercial side, the product was designed to be molded with a finished top lip surface that will always be seen by the customer and the public. The ribs were scalloped to enable the boxes to stack, even at a depth of 36". This is a first for this depth of box in the enclosure industry. This is a feature that is extremely important to contractors during an installation when they need an enclosure with additional depth. With other manufacturers, they need to buy additional products to get to the same depth. All products that are either being developed or retooled will be designed with all of these features. Eventually, the entire product line will be available with these capabilities.

There are a total of seven different products that have been chosen for development to complement the existing vault line, which will all be available in 2016. 

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