Thermal solutions deliver advanced temperature uniformity for molders.
Isobar super-thermal conductors can be manufactured in a variety of different sizes based on customers' molding requirements. The inner surface of the copper Isobar shell is lined with highly thermally conductive fine metallic wicking material. Both ends of the Isobar are hermetically sealed to maintain a very low level of vacuum on the inside. A small amount of environmentally-friendly working fluid resides inside Isobar's hermetically sealed shell in a liquid and vapor state (figure 1).
As heat energy is applied to one end of the Isobar, a potential difference of temperature is set up between the two ends. The working fluid inside the low-pressure shell begins to rapidly evaporate and change phase. The vapor rapidly flows from the heated end (evaporator) to the cooler end (condenser). When the warm vapor encounters cooler surfaces of the wicking material it immediately condenses, releases most of its energy and changes phase from vapor back to liquid. The liquid is then recirculated back to the other end of the Isobar by the capillary action of the wick, which functions as a solid-state pump.
The working fluid inside the Isobar is able to rapidly change phase as a result of low operating pressure. The rapid energy transfer resulting from changes in phase of the working fluid allows the Isobar to rapidly reach near isothermal conditions (uniform temperature) in a very short period of time. The Isobar is a passive device and will reach new thermal balance in the fastest possible time without any external connections when presented with new thermal demands.
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Utilizing Isobars in tool design
Molders can optimize their process by integrating Isobar super-thermal conductors in their tooling to resolve difficult processing problems due to poor thermal transfer. Because Isobars provide a high-speed, virtually isothermal path for heat energy to travel, when they are utilized in core pins they can improve part quality and productivity.
To illustrate the benefits from Isobars, two identical core pins measuring 1" in diameter and 6" long were tested with a heated platen providing a common heat source. One core pin was made of solid steel and the other was bored out to accept a 5/8" diameter Isobar. One thermocouple was mounted on the top of each core pin and multiple thermocouples were mounted along the length of each core pin. Each mold plate was heated to a temperature of 180[degrees]C.
In the test, the Isobar infiltrated core reached steady state temperature in approximately half the time required for the solid steel core (figure 2). In addition, the steady state temperature of the Isobar infiltrated core was 40% higher than the solid steel core, and the temperature variation along the Isobar infiltrated core is significantly lower than for the solid steel core (figure 3).
Isoplatens provide high levels of thermal stability to press platen applications and can be designed for electric, oil or steam heating. Integral water-cooling lines for fast process temperature changes are available on all models. The standard Isoplaten has an operating range of ambient to 250[degrees]C.
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Isoplatens utilize an engineered bi-level array of Isobar super-thermal conductors to quickly and uniformly distribute the heat energy that is provided to the platen either by oil or steam channels, or through a series of standard electric cartridge heaters (figure 4).
Isobars in the lower level of this array quickly distribute the non-uniform energy generated by the heat source of either oil, steam or electric heaters. The upper array provides a further redistribution of the heat energy residing in the Isoplaten. The combination of the two levels of the Isobar array ensures that the random point-to-point temperature uniformity of the Isoplaten is +/-3[degrees]C at typical operating temperatures over 90% of the working surface (figure 5). These benefits in thermal improvement result in faster cure time, reduced scrap rate, improved part quality, reduced startup heating time and significantly improved temperature distribution.
Isoplatens can also maintain +/-3[degrees]C temperature variation over 90% of the working surface for platens that have t-slots, mounting holes and center-injection holes.
Isoplaten's unique thermal ability to rapidly and evenly distribute heat energy permits the use of one single-zone standard temperature controller for the entire system. No special multi-zone controls and multiple thermocouples are required.
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If one of the heating elements fails in a traditional platen, a cold area immediately becomes apparent on the platen surface adjacent to that heater. When a heater fails in an Isoplaten, the distributive properties of the Isobar array rapidly transfers energy to the cold region caused by the failed heater, quickly compensating for the loss of heat energy in that region.
Isoplaten heat transfer technology benefits all customers, whether they wish to purchase French's latest hydraulic press with an integrated Isoplaten system or to revitalize an older press with the addition of custom engineered, performance-improving Isoplatens.
Twelve years ago, Vanseal, a Vandalia, IL based manufacturer of rubber seals for the automotive, medical and aerospace industries, retrofitted seven of French's competitor's presses with Isoplatens. Vanseal operates its retrofitted Isoplaten presses in addition to presses without Isoplatens. According to Vanseal process engineer, Jim Pryor, the Isoplatens are less expensive to maintain than platens heated by induction heating coils. Pryor says that the Isoplaten "maintenance upkeep is virtually nothing," resulting in significant money savings for the company. In twelve years of operating the Isoplatens, Vanseal has spent roughly $500 in total platen maintenance costs for all of its Isoplaten presses, compared to over $1,000 a year maintaining the platens on each of its non-Isoplaten presses.
In addition to the maintenance cost savings, Pryor says that the Isoplatens have performed "almost flawlessly" and yield consistent part production with less scrap, giving Vanseal additional cost savings. The 32" x 36" Isoplatens achieve a small temperature differential across the mold, compared to a 20[degrees]F temperature variation on their 24" x 24" presses without Isoplatens. The 20[degrees]F temperature differential on the non-Isoplaten presses and the temperature issues, including the center plate cooling off, especially on the front of the press, yields more scrap than when pressing with Isoplatens.
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For over 110 years, French has been a leader in the technology and quality of industrial process machinery. French offers a wide assortment of hydraulic presses, from 20 to 2,000 tons, for molding and shaping rubber and composite materials. French hydraulic presses are well known for their very low deflection, rugged construction, long life and outstanding customer payback. French also has a broad range of mechanical dewatering and drying presses for the synthetic rubber industry, with a capacity ranging from two to eight tons/hour.
French owns the exclusive license from Acrolab to sell Isobar super-thermal conductors and for the manufacture and sale of Isoplatens within the rubber molding and processing industry in North America and selected worldwide markets. Isobar and Isoplaten are registered trademarks of Acrolab.
by Tayte Lutz and Douglas Smith, French Oil Mill Machinery, and Joe Ouellette, Acrolab
Table 1--height parameter definitions Height parameter Definition Sa Arithmetical mean height Mean surface roughness. Sa = 1/A [[integral].sub.A] [absolute value of z(x,y)] dxdy Sq Root mean square height Standard deviation of the height distribution, or RMS surface roughness. Sq = [square root of (1/A [integral] [[integral].sub.A] [z.sup.2](x,y) dxdy)] Computes the standard deviation for the amplitudes of the surface (RMS). Sp Maximum peak height Height between the highest peak and the mean plane. Sv Maximum pit height Depth between the mean plane and the deepest valley. Sz Maximum height Height between the highest peak and the deepest valley. Ssk Skewness Skewness of the height distribution. Ssk = 1/[Sq.sup.3] [square root of (1/A [integral] [[integral].sub.A] [z.sup.3](x,y) dxdy)] Skewness qualifies the symmetry of the height distribution. A negative Ssk indicates that the surface is composed of mainly one plateau and deep and fine valleys. In this case, the distribution is sloping to the top. A positive Ssk indicates a surface with a lot of peaks on a plane. Therefore, the distribution is sloping to the bottom. Due to the large exponent used, this parameter is very sensitive to the sampling and noise of the measurement. Sku Kurtosis Kurtosis of the height distribution. Sku = 1/[Sq.sup.4] [square root of (1/A [integral] [[integral].sub.A] [z.sup.4](x,y) dxdy)] Kurtosis qualifies they flatness of the height distribution. Due to the large exponent used, this parameter is very sensitive to the sampling and noise of the measurement.