Custom Dip Molding
 Horizontal directional drilling (HDD) is becoming a preferred practice for installing pipelines, cables, water and
sewer lines, and other infrastructural elements. The trenchless
construction technique is used for drilling long distances such as
under rivers, lagoons, or highly urbanized areas, using a guided
drill for creating an arc profile.
Carlon, a division of Lamson & Sessions, Cleveland, OH, recently
rolled out a nonmetallic conduit product called Bore-Gard, designed
to meet the rigorous conditions of HDD. The conduit’s design
incorporates a seal and a locking ring to enable fast, watertight,
cement-free assembly just as the pipe is drawn through the bore.
However, to achieve a proper seal and work properly, the locking
ring system needs to remain completely dust free prior to
installation, a challenge at construction sites and directional
drilling projects where pipes sit for months, prior to use.
For most of its products, Carlon uses protective caps to keep out
dust and debris. Unfortunately, a common problem with many
protective caps is their tendency to fall off on the way to the
construction site. When a pipe arrives at a job-site without a cap,
contractors are often forced to send them back for cleaning. “The
caps we were getting from our suppliers just weren’t good enough,”
explains Craig Homberg, Carlon sales engineer. “When we asked about
ways to keep them from falling off, they could only offer to make
them smaller or increase their durometer. But the caps were already
very difficult to fit onto the pipes, and even with the changes, I
was told many would still fall off or degrade at the site.”
Homberg called one other cap supplier, StockCap, a division of
Sinclair & Rush, Arnold, MO, who suggested a custom dip molded
product. “Although dip molding has been around for more than 50
years, it’s still fairly unknown within industry,” says John Peeler,
technical director for Sinclair & Rush.
In its basic form, dip molding involves the heating of a metal mold
with the internal dimensions of the desired part. These heated molds
are then immersed or “dipped” in a tank of liquid plastisol (PVC).
The heat from the mold attracts the cool plastisol, forming the
part. The part is then extracted from the liquid, heat cured and
stripped from the mold.
Peeler says that for companies unaware that custom dip molding is an
option, finding the right protective cap be disproportionately
challenging. Other processes usually use polyethylene, which isn’t
very flexible. Moreover, the costs to make a custom cap can require
an investment of $25,000 to $30,000 in tooling costs, whereas vinyl
dip molded caps easily stretch and conform to fit most shapes, and
can be tooled for $3000 to $10,000. In addition, from a materials
standpoint, plastisol is relatively inexpensive and simple,
especially when compared to injection molding formulations. “We
develop our own formulas, in-house, specifically for applications,”
says Peeler. “Other processes would have to go to a compounder and
have them create a formulation — it may or may not work; it’s often
a lot of trial and error.”
StockCap’s in-house design team reviewed the design of the Bore-Gard
pipes to create a custom molded product with a notch on the inside
diameter of the cap, that serves as an auto-lock feature. The notch
on the cap catches on a groove on the outside edge of the pipe and
holds it in place.
The new caps worked so well that it’s now rare to find these pipes
at a job site missing caps, or with caps that are degraded or
damaged. “A better cap was one of the main design criteria for Bore-Gard,”
remarks Homberg. “If we hadn’t learned about the option of a custom
vinyl cap, we probably wouldn’t have been able to launch a great
product.”
—RM
StockCap,
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