Tooling Product News

Reducing Cycle Times, Increasing Productivity using Innovative Mold Cooling Technologies

By Terry L. Schwenk

There have been several innovative technologies introduced over the past few years: gas, assist, turbulent flow, pulse cooling, conformal cooling, heat pipe technology and the use of BeCu or copper alloys. All in an attempt to improve plastic molded parts cycle times, resulting in increased productivity and reduce manufacturing cost. All of these technologies have produced incremental improvements. Heat pipe technologies seemed to have the greatest potential, but failed to give complete benefits in all situations. In 2006 at NPE in Chicago, I had the pleasure of viewing a demonstration of a cooling technology developed in Australia, from a company called Ritemp. I was very impressed with the simplicity and how they had addressed all the deficiencies normally associated with heat pipe technology.

Ritemp™ mold cooling technology’s primary objective is to overcome one of the key problems with the molding process; namely variations in the surface temperature of the mold. Ritemp™ provides highly uniform mold temperatures regardless of part geometry with hot spots completely eliminated.

How Ritemp™ works
Ritemp™, a patented technology developed and tested over 30 years, simplifies the design and manufacturing requirements of mold cooling by replacing gun drilled water lines with a “cooling chamber” or water pocket that completely envelops mold cooling surfaces. The water chamber ensures even heat distribution without the engineering compromise often limited by gun drilled water lines or conformal cooling circuits... The chamber is a sealed unit, partially filled with water mixed with a foaming agent. A vacuum is pulled on the sealed chamber, creating an environment for the water to go through a phase change at low temperatures. You see Ritemp has capitalized on some unique properties of water.

Specifically the latent heat of vaporization and latent heat of fusion. Specific latent heat of vaporization is the amount of heat required to convert a unit mass of a liquid into vapor without a change in temperature. All liquids have various heat capacity. High heat capacity is the ability of an object to absorb energy with little temperature rise. The specific heat of liquid water in calories is 1.0 calorie/gram degree Celsius. However when a liquid goes through a phase change its ability to move heat dramatically increases. For water at its normal boiling point of 100º C, the specific latent heat of vaporization is 540 Calories/g. This means that to convert 1.00 gram of water at 100º C to 1.00 gram of steam at 100º C, 540 grams of heat must be absorbed by the water. Conversely, when 1 gram of steam at 100º C condenses to give 1 gram of water at 100º C, 540 calories of heat will be released to the surroundings.

Energy Involved in the Phase Changes of Water

The data for the vaporization phase change presumes that the pressure is one standard atmosphere. By creating a vacuum, the temperature at which the phase change occurs is lowered. This condition actually improves the heat capacity water can carry when going through a phase change at room temperature. The amount of calories needed to heat the water to 100 degrees Celsius isn’t required leaving it available. This amount is approximately 83 calories. So water going through a phase change at room temperature can carry is 623 calories/gram.

So in the environment of a sealed chamber under vacuum, as you start the molding process, the hot plastic warms the mold steel causing the water temperature in the chamber to rise, resulting in boiling or vaporization of the liquid, (phase change). Using heat exchangers, water vapor is condensed back into a liquid, (phase change) and recycled throughout the chamber. Water and or coolant flow to the condenser is controlled by a Ritemp™ mold temperature control that senses and adjusts water flow through the condenser to regulate phase change resulting in temperature control of the chamber. The benefits range from lower operational and design/manufacturing costs to significant productivity gains.

The Ritemp™ Solution and Benefits

Cooling chamber surrounds part providing uniform cooling and heat control.
Air is evacuated from the cooling chambers before processing allowing water to boil at very low temperatures.
The resultant vapor rises to the top of the mould where it is condensed by specially designed heat exchangers.
The water will always boil where it is hottest and condense where it is coolest.
Heat is extracted from the mold by converting it to “Latent Heat of Vaporization.”
This process ensures that the temperature throughout the mold is evened out automatically so that a high degree of uniformity is maintained.
The need for running multiple cooling circuits at different temperatures is eliminated.
Since oxygen is not allowed into the cooling process chambers, corrosion is not possible and eliminated.
Heat and cooling control using Ritemp™ Mold temperature Controller

Top Ten Ritemp™ Benefits

Increased profitability for molder and mold maker
Faster Cycle times
Lower part reject rates
Mold corrosion eliminated
Reduced or eliminated part distortion
Reduced mold manufacturing costs
Reduced mold engineering costs
Condensation issues eliminated- mold does not “sweat”
Reduced energy costs
Reduction in maintenance costs with increased up time

The Ritemp™ Mold Temperature Controller

The controller turns the coolant supply on and off in response to the mold temperature.
Control is Closed Loop. A sensor, positioned in each chamber, accurately measures the temperature of the system.
When required it can also control a heating element for preheating the mold.
Two zones are standard and meet most applications. A six zone controller is also available.

Electrical Part Sample Application

In this particular application, the challenges presented were multi faceted. The end user had a requirement for increased part production to meet market demand, sustainable part quality over several million shots annually and reduced costs. The existing 2 cavity production mold produced a 15 gram electrical box (pictured) with a 1.5 mm critical wall thickness dimension running Noryl material. The cycle time was 18 seconds. Ritemp™ was used in the design and manufacture of a new 4 cavity production tool running the identical part.

The Ritemp™ results
The new 4 cavity tool runs 13 second cycle time (28% reduction) and has produced 7 million parts without fail to date (Dec.2006). Further to this, Ritemp exceeded expectations in that the new tool can actually run at a 10 second cycle time but is currently limited by downstream handling equipment.

Terry Schwenk is the founder of Process and Design Technologies, Inc., a firm created to provide plastics companies with complete optimized processing solutions through efficiencies gained in engineering, manufacturing and processing. Terry has over 34 years of experience in the plastics industry, including more than 23 years of specialized experience in hot runner technology and tooling. An active member of SPE and a Past Chair for Mold Making & Mold Design SPE division, Terry has an associate degree in Business Administration and is accredited with several patents. He can be contacted by emailing him at tschwenk@processdesigntech.com or by visiting www.processdesigntech.com.

Ritemp Technologies Pty. Ltd.
1084 South Road Edwardstown SA 5039
PO Box 338 Magil SA 5072
Telephone: + 61 8 8374 4633 | Fax: +61 8 8299 0892
Email: info@ritemptechnologies.com

SWM and Associates (Distributor for Americas)
P.O. Box 607,
Burlington, Ontario
Canada L0P 1G0
Tel/ Fax.: 905.319.0013
www.swm-associates.com
Scott W. Molnar, President
Cell: +1.416.786.2663
Email: scott.molnar@swm-associates.com

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