The liquid-silicone-rubber market is evolving, with advances in materials and equipment as well as shifting reasons for designers and manufacturers to consider the material.
Material, manufacturing and processing experts explored LSR issues at a recent symposium at Engel Machinery Inc.'s Corona technical center.
Wacker Silicones, 2KM, Gayson Silicone Dispersions Inc., M.R. Mold & Engineering Corp. and Engel were among the symposium presenters.
Gregory Dull, a marketing manager with Wacker Silicones, discussed LSR market trends, the potential for LSR to replace isoprene in a few places and the possibilities for silver-based antimicrobials.
People are looking for LSR for larger parts in smaller volumes and for replacement or new parts, he said. Originally, LSR was used for high volumes of small parts. Now, the trend toward smaller volumes of larger parts is growing.
Dull said some original equipment manufacturers are exploring LSR as a replacement for the chemical polyisoprene, possibly in the medical market.
Goodyear Tire & Rubber Co. of Akron, Ohio, and other firms use isoprene monomer mostly to produce a synthetic version of natural rubber.
Isoprene is a clear polymer with more resilience than LSR, he said. Tests at Wacker Silicones indicate LSR may lack the resilience and self-closing capacity to survive multiple needle penetrations a necessary function in the medical industry.
LSR is finding more use in antimicrobials. Some silver-based antimicrobials are showing promise in reducing bacteria growth in products made from LSR, Dull said.
Dull mentioned Dow Corning Corp. of Midland, Mich., and Momentive Performance Materials Inc. of Albany, N.Y., as two of Wacker Silicones' competitors in the LSR market.
Bob Bradley, co-owner of Gayson SDI of Barberton, Ohio, said that while LSR's viscoelasticity and temperature adaptability once drove use of the material, now LSR's texture and inertness are additional drivers.
I have seen a shift in the LSR market over the last eight to 10 years, Bradley said. He predicts more changes in the pipeline.
Gayson SDI offers more than 30 standard colors and has developed more than 10,000 colors for LSR; high-consistency silicone rubber, known as HCR; and room-temperature vulcanizing silicone, known as RTV. Bradley said that it is physically impossible to match some colors and that highly filled LSR may interfere with a batch's colorability.
For about a decade, Gayson SDI has developed LSR additives for heat-stabilization, mold-release, scent, antimicrobials and other applications. While in the early stages, Gayson SDI has been developing dispersions for a number of chemical additives in silicones [that] we offer in HCR silicones for use in LSR, he said.
Gayson SDI supplied scent-containing silicone that was used to manufacture vanilla-flavored baby-bottle nipples for an undisclosed consumer-products firm.
In addition to scent, Silcosperse-brand chemical-additive dispersals may include magnesium oxide, cerium hydrate or antimicrobial substance, but no curing agents, Bradley said.
I want to take away the fear of using color with LSR, Bradley said, noting that 95 percent of LSR medical applications use clear material, although your parts no longer need to be clear. Use of color in silicone connectors, for instance, can help speed medical processes in an operating room and potentially prevent errors.
With temperature versatility, LSR is finding applications for consumer kitchenware and bakeware products. At a nearby tabletop display at the symposium, for example, M.R. Mold distributed samples of freestanding LSR cupcake baking cups.
Bradley encouraged product designers to think outside the box for color use with potential applications involving delivery services, credit cards and the Internet.
Gayson SDI was founded in 1981 and employs 25. The dispersion house supplies Silcopas-brand coloring for LSR and RTV silicones, and Silcosperse-brand silicone modifiers, but does not function as a material formulator.
Pigments are not dissolvable in silicone and must be dispersed, Bradley said. Dispersion breaks down pigments to primary particle size and evenly distributes them through the silicone carrier to achieve consistent particle size.
Bradley said competing silicone dispersion firms include Holland Colour NV of Apeldoorn, Netherlands, with a U.S. location in Richmond, Ind., and Pan Technology Inc. of Carlstadt, N.J.
Engel's Steve Broadbent dwelt on the characteristics of two-component injection molding machines, but he urged caution.
Thoughts about a two-component machine should prompt a processor to ask: Does the program warrant the capital expense of a specialty machine? said Broadbent, project engineer for elastomers with Engel in York, Pa.
The additional injection unit, extend-machine frame and injection-control software can add as much as $100,000 to the base machine price, and the transfer method, robot or rotary device can add another $35,000-$45,000, Broadbent said. Further, two-component tools tend to be very expensive.
Two-component technology is widely accepted in Europe and gaining popularity in the North American market, Broadbent said. Once customers get past the initial fear of the technology, it will move faster.
Wacker's purchase of a Victory press will allow a customer to get up close and review the process and technology, Broadbent said.
Generally, molders using this technology are very secretive.
Clamping-unit options include the hydraulic center ram and the electric toggle, either being available with a tie-bar or tie-barless design. Choices for the injection unit configuration include a vertical, piggyback or L-shaped position.
A two-component machine with a piggyback configuration keeps the same floor space requirement, but it imposes limited access to injection units for maintenance, Broadbent said.
Use of the vertical configuration eases access to both injection units but may interfere with robotic or automation devices.
The transfer method for two-component molding may include robotics, a rotary table or indexing plate or core. Part geometry and the feasibility of machine-to-machine transfer are factors in selecting a method.
Broadbent said LSR micromolding controls exist within a complete cell for certain optional equipment.
In an equipment demonstration between the May 6 symposium sessions, Engel molded light-green flapper valves of Wacker's health-grade Silpuran-brand LSR 6000/50 on an all-electric, 55-ton E-max press with a 12-millimeter screw and a 2KM PFM servo-cartridge feeding system with an 8-mm static mixer. M.R. Mold manufactured the four-cavity tool with four heating zones, a cold-runner system and a water-cooled manifold that protects the silicone from unnecessary heat. The cycle time was 16 seconds.
Engel plans another demonstration of the machine during Canon Communications LLC's medical design and manufacturing show Oct. 13-14 in Minneapolis.
Engel Machinery's parent firm is Engel Holding GmbH of Schwertberg, Austria.
In other LSR-related developments at the symposium:
* The fabrication laboratory of Wacker Silicones is slated to become the first material supplier in North America with an Engel two-component, Victory-brand press with a horizontal LSR injection unit and a tie-barless clamping unit. Delivery of the 100-ton press is anticipated in late 2010 or early 2011.
Also, Wacker's lab in Adrian, Mich., will obtain a two-component LSR mold.
Once the Victory 200H/200V/ 100 combi is operational, Wacker will be the first supplier in the U.S. to install this type of Victory press, Dull said. It will allow our technician to use and become familiar with LSR processes and enable our customers to learn and possibly do mold trials in a production-type environment. The press is a standard Engel offering.
The Michigan site is part of the global silicones division of Wacker Chemie AG of Munich.
* 2KM, which now offers a 12-diagonal-inch operator touchscreen with 2KM software on mixing and metering equipment, in June will bring its all-electric SilcoStar E-flow LSR metering and mixing system to the North American market.
Operators want to see a digital readout in color, said Gary Bauer, managing director with 2KM North America Inc. in Parry Sound, Ontario. A programmable logic controller will manage screen content. A customer can specify either the 2KM touchscreen or another display system from Siemens AG's industry sector.
Parent company 2 Komponenten Maschinenbau GmbH of Marienheide, Germany, completed work on the variable-mix-ratio SilcoStar E-flow electro-serve unit in early 2010 after beginning development in mid-2009.
2KM promotes its all-electric Process Flow Mix cylinder concept for metering LSR use. 2KM introduced the PFM idea during 2009.
Modular design systems such as the 2KM PFM system provide solutions for special needs, Bauer said. Advanced metering systems provide better solutions for requirements of precision and control smaller shot sizes, pigments and additives needed for self-bleed, shear [and] tear requirements.
* M.R. Mold & Engineering of Brea, Calif., has developed a quotation sheet that is customized for silicone mold specifications.
Among the requirements is Choose an appropriate-size molding machine and convey that in the quote, said President Rick Finnie.
Other variables needing definition include mold material and style, parting-line selection, floating center plate activation, gate location and style and ejection method, such as pop-up cores, air poppets, mold sweep or end-of-arm tooling.
Finnie said he requires two-dimensional part drawings to prepare a bid. [Three-dimensional] part models do not reflect tolerance, he said.
Finnie identified the characteristics of low compression set, fast cure cycles, stability and extreme-temperature resistance as reasons LSR is suitable for production of high-quality parts.
Highly polished surfaces will leave silicone with a shiny finish, he said. However, silicone will stick to polished surfaces. Silicone releases best from matte or textured finishes.
Some laser etching occurs, although M.R. Mold has not purchased a laser etcher yet, Finnie said.
One M.R. Mold customer did not like laser etching, he said.
Regarding coating or plating of a mold for processing silicone, Finnie suggested use of a niche version of DuPont Co.'s Teflon synthetic fluoropolymer or the Nibore high-lubricity composite of electroless nickel and boron nitride particles from Bales Mold Service Inc. of Downers Grove, Ill.
Finnie opened M.R. Mold in 1985 with one employee. Now, the firm employs 25 and, within its facility, has a 4,000-square-foot technology center with three company-owned molding machines.
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