Choosing Manifolds For Mould Cooling
Why choose cooling manifolds
Manifolds are common auxiliaries in a plastics injection moulding shop. They are key components of mould water cooling circuits. Their primary function is to route cooling water from the tower or chiller to the water passages in the mould, then collect the warmer water leaving the mould, at turbulent flow rates, and return it to the external cooling water loop.
Expressed more colloquially, manifolds can be used so the tangled spaghetti-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 mould water passages with adequate cooling water, then collect the warmer turbulent water flowing from the mould 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 mould cooling and reduced mould 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 colours. When populated with auxiliary products, such as, ¼ turn ball valves, flow meters, temperature indicators, and mould temperature regulators, they appear like spiny creatures.
Depending upon moulder preference and application requirements, manifolds can be mounted on the machine frame, a mould heater-chiller cabinet, the tool or located on the floor alongside the press.
Common materials of construction for manifolds are aluminium, carbon steel, stainless steel, brass and plastic compounds. Aluminium 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 BSP(F). Port sizes are typically 3/8, ½, ¾ or 1-inch BSP(F). Though less common, BSP(M) is used on some applications, primarily for plumbing accommodation. Optional quick connect fittings and hose barbs are also popular with moulders, particularly when custom moulding operations require frequent tool changes and set-ups. Occasionally moulders specify that manifolds be installed directly on the mould 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 aluminium manifolds are colour anodized after machining to provide corrosion resistance from the cooling water. Typical colour 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 mould. Colour coding reduces the chances of incorrect water hose hook-up after a tool change and set-up. One manifold manufacturer uses labels instead of colour 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 aluminium 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 labelling by catalogue vendors, resellers and OEM’s. The remainder of the market is supplied by local “fabrication” shops and in-house fabrication. Interestingly, this latter segment accounts for a significant number of manifolds that have been in-use on MRO (moulding 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 catalogue 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.
Manifolds get less play than many of the more sophisticated auxiliaries in the plastics injection moulding market. Despite this, their usefulness is legend.
Buying trends for new OEM and MRO applications favour 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 aluminium is the material of choice for water manifolds on most mould cooling applications. They are lightweight and are easily customized. They have high burst pressures and low true cost of ownership.
Moulders are on a continuous quest to enjoy the real benefits of shorter cycle times and increased overall efficiency that the manufacturers of new moulding machines claim. The importance of proper cooling water flow to and from the mould is well understood. They know that despite the brand name 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 moulded.
It is a generally accepted rule of thumb that the mould cooling phase accounts for approximately 75% of a moulding cycle. Consequently, more attention is being focused on manifolds and the part that they play in the important work of supplying and returning mould 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.
This information is provided solely as a service to our customers, and in no way infers any liabilty on the part of Burger & Brown Engineering Inc, Invotec Solutions Limited its representatives, or distributors.