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Manifolds for Mold Cooling Water

"This article first appeared in the June 2001 issue of Plastics Auxiliaries magazine."

Russ Longley
Consultant
Burger Engineering, Inc.
Olathe, Kansas

Manifolds are common auxiliaries in a plastics injection molding shop. They are key components of mold water cooling circuits. Their primary function is to route cooling water from the tower or chiller to the water passages in the mold, then collect the warmer water leaving the mold, at turbulent flow rates, and return it to the external cooling water loop.

Expressed more colloquially, manifolds can be used so the tangled sphagetti-like cooling water hoses located around a press can be neatly arranged. We have all seen examples of in-house plumbing art. Sometimes it is fashioned like a Christmas tree of pipe, that has been decorated with an array of nipples, tees and various hose connection fittings. These home-made contraptions are prone to leak and the hose connections near the plugged end may have far less pressure and flow than the ports closer to the supply inlet. True costs are seldom known.

In contrast, manufactured manifolds are engineered products that provide a convenient means to neatly arrange multiple water hoses. More importantly, they are designed to supply the mold water passages with adequate cooling water, then collect the warmer turbulent water flowing from the mold and return it to the external cooling water loop. Properly sized supply and return manifolds keep the backpressure effect from the return manifold leg of the cooling loop to a minimum.

Pressure drops and flow rates at the various ports are dependent upon a number of factors, such as, which ports are open or closed, supply pressure, inlet and port sizes, port spacing and length of manifold, etc. Detailed application and design engineering are beyond the scope of this article.

Direct benefit from the proper use of engineered manifolds is proper hook-up, adequate mold cooling and reduced mold set-up time. Collateral benefit is enhanced shop safety. For example, because water hoses are neatly arranged off the shop floor, housekeeping is improved and there is less chance for an operator to trip and sustain injury while working close to the machine frame.

Depending upon machine design and operation, smaller bore manifolds are often used as pneumatic headers. Rigid or flexible lines are connected to them and routed to air-operated machine components.

Manifolds come in various shapes, sizes, materials and colors. When populated with auxiliary products, such as, ¼ turn ball valves, flowmeters, temperature indicators, and mold temperature regulators, they appear like spiny creatures.

Depending upon molder preference and application requirements, manifolds can be mounted on the machine frame, a mold heater-chiller cabinet, the tool or located on the floor alongside the press.

Common materials of construction for manifolds are aluminum, carbon steel, stainless steel, brass and plastic compounds. Aluminum manifolds are typically extruded through proprietary dies, although smaller pipe sizes can be cost effectively machined from bar stock. Costly scrap is the downside of this design.

Stainless steel manifolds are typically fabricated from 304 square tubing. Pipe fittings for supply, return and distribution ports are welded to the tube. SS manifolds are often specified for highly corrosive cooling water applications.

Common supply and return connection sizes are ¾, 1, 1¼, 1½ and 2-inch NPT(F). Port sizes are typically 3/8, ½, ¾ or 1-inch NPT(F). Though less common, NPT(M) is used on some applications, primarily for plumbing accommodation. Optional quick connect fittings and hose barbs are also popular with molders, particularly when custom molding operations require frequent tool changes and set-ups. Occasionally molders specify that manifolds be installed directly on the mold when new tooling is ordered. This arrangement can reduce or eliminate port hoses. O-rings seal the direct connections between the port openings in the manifold base and the water passage openings in the tool.

Most aluminum manifolds are color anodized after machining to provide corrosion resistance from the cooling water. Typical color choices are red, blue, black or clear. Red and blue anodizing are the most popular because of the convention; blue denotes cooler supply water and red the warmer water returning from the mold. Color coding reduces the chances of incorrect water hose hook-up after a tool change and set-up. One manifold manufacturer uses labels instead of color coding to depict supply and return water lines.

Design features suggest some product differentiation and resultant brand preference. For example, Burger Engineering, Inc. has added value to its aluminum manifolds by incorporating a sliding dovetail lock design so multiple manifolds can be locked in parallel. This feature facilitates mounting and the connection of multiple water hoses. This company also offers modular fiberglass-reinforced nylon manifolds with integral port valves. This unique design allows up to sixteen supply-return port pairs to be ganged and secured with "all thread" rod.

Less than a handful of manifold manufacturers supply 75-80% of the served market. It is difficult to sort and rank this group because of private labeling by catalog vendors, resellers and OEM’s. The remainder of the market is supplied by local “fab” shops and in-house fabrication. Interestingly, this latter segment accounts for a significant number of manifolds that have been in-use on MRO (molding shop) applications for many years.

Aggressive cost reduction programs are driving OEM (machine builders) and new MRO accounts. Consequently, both are showing preference for engineered products that are offered as standard catalog items by manifold manufacturers. Customized special manifolds are specified, as necessary, to satisfy specific application requirements. Manufactured manifolds tend to have a lower true cost of ownership.

 

Summary

Manifolds get less play than many of the more sophisticated auxiliaries in the plastics injection molding market. Despite this, their usefulness is legend.

Buying trends for new OEM and MRO applications favor engineered products that are produced by established manufacturers versus local or in-house fabricated manifolds. Predominant purchase drivers appear to be price and delivery. Anodized aluminum is the material of choice for water manifolds on most mold cooling applications. They are lightweight and are easily customized. They have high burst pressures and low true cost of ownership.

Molders are on a continuous quest to enjoy the real benefits of shorter cycle times and increased overall efficiency that the manufacturers of new molding machines claim. The importance of proper cooling water flow to and from the mold is well understood. They know that despite the brandname or age of the press, unless cooling water is delivered at the proper flow rates through supply manifolds to the tool and return manifolds from the tool, it is unlikely that good parts will be consistently molded.

It is a generally accepted rule of thumb that the mold cooling phase accounts for approximately 75% of a molding cycle. Consequently, more attention is being focused on manifolds and the part that they play in the important work of supplying and returning mold cooling water.

Cooling water flow can be controlled with simple hand-operated ¼ turn ball valves, fast-acting, pulsed solenoid valves or more sophisticated proportional valves that are commanded by a PID microprocessor based controller. Despite this, it is forecast that the simple manifold will be around to do its share of the "heavy lifting" for a very long time.

Smartflow invites your inquiries for cooling water manifolds and comments regarding this article
at 1-800-764-3518.