Faster curing, low compression set, no post cure liquid silicone rubber.The economies of the latest developments in liquid silicone rubber Noun 1. silicone rubber - made from silicone elastomers; retains flexibility resilience and tensile strength over a wide temperature range synthetic rubber, rubber - any of various synthetic elastic materials whose properties resemble natural rubber (LSR 1. (networking) LSR - Label Switching Router. 2. (operating system) LSR - Local Shared Resources. ) materials and process technology make feasible the replacement of not only conventional heat cured silicone rubber, but also organic rubber in many applications. It is now possible to produce parts of at least five grams, in tools with over 30 cavities, with a production cycle of as little as 20 seconds. The latest cold-runner tool and molding press technology makes it possible to produce parts with no waste and no flash. This same technology also makes possible continuous, fully automated au·to·mate v. au·to·mat·ed, au·to·mat·ing, au·to·mates v.tr. 1. To convert to automatic operation: automate a factory. 2. production. Parts can be ejected from the mold mold, name for certain multicellular organisms of the various classes of the kingdom Fungi, characteristically having bodies composed of a cottony mycelium. The colors of molds are caused by the spores, which are borne on the mycelium. into a box, ready for shipment with no need of deflashing. The combination of these factors is, in many cases, rapidly making older methods of molded mold 1 n. 1. A hollow form or matrix for shaping a fluid or plastic substance. 2. A frame or model around or on which something is formed or shaped. 3. Something that is made in or shaped on a mold. rubber part production uneconomical, despite the premium cost of the LSR material. LSR materials provide the same unique and outstanding properties of traditional silicone rubber. Among these are outstanding low temperature flexibility, excellent high temperature aging resistance and physical properties which undergo relatively little change with changing temperature. LSR materials also have excellent resistance to other environmental hazards 'Environmental hazard' is a generic term for any situation or state of events which poses a threat to the surrounding environment. This term incorporates topics like pollution and Natural Hazards such as storms and earthquakes. such as ultraviolet An invisible band of radiation at the upper end of the visible light spectrum. With wavelengths from 10 to 400 nm, ultraviolet starts at the end of visible light and ends at the beginning of X-rays. The primary source of ultraviolet light is the sun. radiation and ozone. LSR materials are excellent electrical insulators. Previous curing technology LSR materials have had good compression resistance only when given post cures of four hours at 200 [degrees] C. This is because, although the hydrosilylation curing reaction (figure 1) proceeds very rapidly, it does not rapidly go to completion. Unlike conventional silicone rubber, cured with vinyl vinyl /vi·nyl/ (vi´nil) the univalent group CH2dbondCH—. vinyl chloride a vinyl group to which an atom of chlorine is attached; the monomer which polymerizes to polyvinyl chloride; it is toxic specific peroxides, press cured LSR parts will, due to the stoichiometric stoi·chi·om·e·try n. 1. Calculation of the quantities of reactants and products in a chemical reaction. 2. The quantitative relationship between reactants and products in a chemical reaction. excess of hydrosilane crosslinker and the continued presence of active platinum platinum (plăt`ənəm), metallic chemical element; symbol Pt; at. no. 78; at. wt. 195.08; m.p. 1,772°C;; b.p. 3,827±100°C;; sp. gr. 21.45 at 20°C;; valence +2 or +4. catalyst, continue to cure after removal from the mold when subjected to high temperatures. This phenomenon is referred to as aftercure. If the part is deformed de·formed adj. Distorted in form. and heated, such as in a high temperature sealing application, the aftercure increases the compression set. [Figure 1 ILLUSTRATION OMITTED] A unique and very effective method of preventing aftercure has been developed that has been applied to a wide range of LSR products. The new generation of LSR will enable the production of parts that can behave like parts made from peroxide peroxide (pərŏk`sīd), chemical compound containing two oxygen atoms, each of which is bonded to the other and to a radical or some element other than oxygen; e.g. cured silicone rubber, but will be able to cure much faster. They will be molded in this fast, efficient operation without the need of any subsequent processing. Experimental This article will describe several studies that were undertaken during product development and during subsequent product evaluation for specific purposes. A 60 durometer Du`rom´e`ter n. 1. An instrument for measuring the degree of hardness; especially, an instrument for testing the relative hardness of steel rails and the like. grade was developed and compared to materials with previous curing technology. The specimens are 6 mm sheets, compression molded for five minutes at 165 [degrees] C. Some specimens were post cured in a circulating cir·cu·late v. cir·cu·lat·ed, cir·cu·lat·ing, cir·cu·lates v.intr. 1. To move in or flow through a circle or circuit: blood circulating through the body. 2. air oven for four hours at 200 [degrees] C, where indicated. Compression set testing was carried out in accordance Accordance is Bible Study Software for Macintosh developed by OakTree Software, Inc.[] As well as a standalone program, it is the base software packaged by Zondervan in their Bible Study suites for Macintosh. with DIN 53517, at 25% compression. Curing times In the annealing procedure could be divided into 3 stages:heating to a particular temperature, keeping for a period of time and cooling to room temperature. The curing time is the hold time of the 2nd stage. , temperatures and compression set results are given in table 1.
Table 1 - compression set of 60 durometer materials
Compression set test temperature 150 [degrees] C
Previous curing technology
Test Press cure Post cure
duration only 4 hrs. @ 200
[degrees] C
22 hours 38% 7%
72 hours 48% 9%
168 hours 55% 13%
336 hours 64% 18%
672 hours 67% 23%
1,008 hours 68% 29%
Compression set test temperature 175 [degrees] C
Previous curing technology
Test Press cure Post cure
duration only 4 hrs. @ 200
[degrees] C
22 hours 59% 9%
72 hours 65% 15%
168 hours 68% 23%
336 hours 73% 32%
Compression set test temperature 150 [degrees] C
New technology
Test Press cure Post cure
duration 5 min. @ 165 4 hrs. @ 200
[degrees] C [degrees] C
22 hours 13% 6%
72 hours 17% 8%
168 hours 23% 14%
336 hours 30% 19%
672 hours 32% 23%
1,008 hours 36% 31%
Compression set test temperature 175 [degrees] C
New technology
Test Press cure Post cure
duration only 4 hrs. @ 200
[degrees] C
22 hours 17% 9%
72 hours 27% 16%
168 hours 34% 25%
336 hours 39% 33%
Table 2 gives the results of 6 mm injection molded specimens cured for 18 seconds and tested in the same manner. Table 3 gives the results of compression sets on 30 durometer and 50 durometer oil bleeding grades. All specimens are compression molded, 6 mm sheets, which were tested in accordance with DIN 53517, at 25% compression. Among these are low bleeding and high bleeding grades. This refers to the relative amount of oil which the specimens will exude ex·ude v. To ooze or pass gradually out of a body structure or tissue. . Table 2 - compression set, 22 hours @ 175 [degrees] C, 60 durometer LSR, 6 mm injected in·ject·ed adj. 1. Of or relating to a substance introduced into the body. 2. Of or relating to a blood vessel that is visibly distended with blood. injected 1. introduced by injection. 2. congested. molded specimens
Mold temperature 180 [degrees] C, cure time 18 seconds
Previous curing New technology
technology
59% 24%
Table 3 - oil bleeding LSR grades for electrical connector insulators
Compression set, 22 hours @ 175 [degrees] C on 2 mm sheets
press cured 5 minutes @ 166 [degrees] C no post cure
30 30 50 50
durometer durometer durometer durometer
low bleed high bleed low bleed high bleed
Previous
curing
technology 48% -- 50% 50%
New
technology 15% 16% 20% 20%
Additional cure testing of both 30 durometer high bleed Printing at the very edge of the paper. Many laser printers, including all LaserJets up to the 11x17" 4V, cannot print to the very edge, leaving a border of approximately 1/4". In commercial printing, bleeding is generally more expensive, because wider paper is often used, which is later grades was carried out on a Monsanto The Monsanto Company (NYSE: MON) is a multinational agricultural biotechnology corporation. It is the world's leading producer of the herbicide glyphosate, marketed as "Roundup". MDR MDR, n See multidrug resistance. MDR, n the abbreviation for minimum daily requirement, specifically the Minimum Daily Requirements for Specific Nutrients compiled by the United States Food and Drug Administration. 2000 rheometer rhe·om·e·ter n. An instrument for measuring the flow of viscous liquids, such as blood. . Testing was performed at 150 [degrees] C, 175 [degrees] C and 200 [degrees] C. Results are given in table 4. This was done in anticipation of a molding trial on a 15 gram part which is currently in production in a four cavity cavity /cav·i·ty/ (kav´i-te) 1. a hollow place or space, or a potential space, within the body or one of its organs. 2. in dentistry, the lesion produced by caries. tool, from which the parts are manually and individually removed. The fabricator fab·ri·cate tr.v. fab·ri·cat·ed, fab·ri·cat·ing, fab·ri·cates 1. To make; create. 2. To construct by combining or assembling diverse, typically standardized parts: must post cure the part when molded in the competitive material. New technology, 30 durometer high oil bleeding grade needed was not post cured. Table 4 - MDR 2000 rheometer testing 30 durometer, high oil bleeding grade
Competitive New
material technology
MDR 2000 rheometer at 150 [degrees] C for 3 minutes
[TC.sub.10], minutes 0.24 0.15
[TC.sub.50], minutes 0.31 0.21
[TC.sub.90], minutes 0.39 0.24
S' at MH, N-mm 476 622
S" at MH, N-mm 102 10
Tan delta at MH 0.214 0.016
MDR 2000 rheometer at 175 [degrees] C for 3 minutes
[TC.sub.10], minutes 0.16 0.12
[TC.sub.50], minutes 0.21 0.16
[TC.sub.90], minutes 0.26 0.18
S' at MH, N-mm 569 623
S" at MH, N-mm 38 9
Tan delta at MH 0.067 0.014
MDR 2000 rheometer at 200 [degrees] C for 3 minutes
[TC.sub.10], minutes 0.13 0.11
[TC.sub.50], minutes 0.17 0.13
[TC.sub.90], minutes 0.22 0.15
S' at MH, N-mm 572 598
S" at MH, N-mm 15 7
Tan delta at MH 0.026 0.011
Samples of a competitive 30 durometer high oil bleeding grade and the new curing technology 30 durometer high oil bleeding grade were press cured in 2 mm sheets and plied plied 1 v. Past tense and past participle of ply1. for compression testing in accordance with ASTM ASTM abbr. American Society for Testing and Materials D395, method B, 25% compression. The press cure time was five minutes and the temperature was 166 [degrees] C. Results are given in table 5.
Table 5 - 30 durometer, high oil bleeding grade
Compression set, 22 hours @ 175 [degrees] C
on plied disks cut from ASTM slabs, press cured
5 minutes @ 166 [degrees] C, ASTM D395, method
B, 25% compression
Competitive material New technology
57% 15%
ASTM slabs, 2 mm thickness thickness (thik´nes) a measurement across the smallest dimension of an object. triceps skinfold (TSF) thickness of the new curing technology 30 durometer, high oil bleeding grade were press cured for five minutes at three lower temperatures; 116 [degrees] C, 132 [degrees] C and 149 [degrees] C. Specimens were plied for compression set testing which was carried out for 22 hours at 177 [degrees] C. The results of this testing are given in table 6. Table 6 - low temperature press cures on ASTM slabs, 30 durometer, high oil bleeding grade
Press cure time and temperature Compression set
22 hours @ 175 [degrees] C
5 minutes @ 116 [degrees] C 22%
(240 [degrees] F)
5 minutes @ 132 [degrees] C 15%
(270 [degrees] F)
5 minutes @ 149 [degrees] C 18%
(300 [degrees] F)
Large dumbbells of the new curing technology 30 durometer, high oil bleeding grade were injection molded on an Arburg Allrounder 210-270-500. The dumbbells size and shape are shown in figure 2. The cure times given are a combination of hold time and cure time on the machine. They therefore represent the time from end of screw screw, simple machine consisting essentially of a solid cylinder, usually of metal, around which an inclined plane winds spirally, either clockwise or counterclockwise. forward motion to mold opening. Very short times could not be obtained due to the need to cure a large sprue sprue, chronic disorder of the small intestine caused by impaired absorption of fat and other nutrients. Two forms of the disease exist. Tropical sprue occurs in central and northern South America, Asia, Africa, and other specific locations. prior to mold opening. [Figure 2 ILLUSTRATION OMITTED] Two squares were cut from either end of each dumbbell Dumbbell An investment strategy, used mainly for bonds, where holdings are heavily concentrated in both very short and long term maturities. Notes: This is also known as a barbell, charting on a timeline gives the appearance of a barbell or dumbbell. . The cut squares were stacked Stacked is an American television sitcom that premiered on Fox on April 13, 2005. On May 18, 2006, Stacked was cancelled, leaving five episodes unaired in the United States. The last episode aired on January 11, 2006. four high for conducting the compression set. The gate ends versus the dead ends were kept separate. The compression sets were 22 hours duration at 177 [degrees] C. The results are given in table 7. Table 7 - 30 durometer high oil bleed, new technology injection molded specimens
Cure temperature 177 [degrees] C (350 [degrees] F)
Cure time (seconds) Gate end Dead end
21 22.0% 20.3%
42 18.6% 17.8%
84 20.1% 17.3%
Cure temperature 191 [degrees] C (375 [degrees] F)
Cure time (seconds) Gate end Dead end
18 18.8% 18.3%
36 17.4% 15.2%
72 17.3% 15.3%
Cure temperature 204 [degrees] C (400 [degrees] F)
Cure time (seconds) Gate end Dead end
16 20.5% 19.5%
32 18.5% 18.0%
64 19.6% 17.0%
Experimental A 45 durometer, low viscosity specialty grade material was upgraded with the new curing technology. Compression sets were conducted on 2 mm ASTM slabs, press cured five minutes at 166 [degrees] C. Samples were left with press cure only, or were post cured four hours at 204 [degrees] C. The results are given in table 8. Table 8 - 45 durometer, low viscosity specialty grade compression set, 22 hours at 177 [degrees] C
Previous curing technology New curing technology
Press cure Post cure Press cure Post cure
only 4 hours @ only 4 hours @
204 [degrees] C 204 [degrees] C
70% 11% 15% 18%
Results and discussion The data in table 1 show the dependence of post curing on the previous curing technology. Excellent compression set results may be obtained with a thorough oven post cure. The new technology offers the ability to obtain excellent compression set resistance without a post cure. Table 2 shows the results of injection molded sheets. This is evidence of the effectiveness of the new curing technology on rapidly cured injection molded specimens. In table 3, it is shown that the new curing technology is effective in oil bleeding grades. The extent of extruded oil does not appear to affect the compression set. The MDR 2000 rheometer tests in table 4 show the enhanced rate of curing versus the competitive material. During the molding trial on the 15 gram part, cycle time was reduced from 30 seconds, with the competitive material to 23 seconds with the new curing technology. Compression sets on the competitive parts could be as great as 60%. The greatest compression set on with the new curing technology was 18%. The post cure on the competitive material could reduce the compression set to less than 10%, but this has negative consequences on the bleeding properties of the parts. There is little evidence of sensitivity of curing temperature on the effectiveness of the new curing technology. Using very low temperatures, very good compression sets can still be obtained. The molding trial on the large dumbbells indicated that within the range of what is normally used for injection molding injection molding n. A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold. , neither cure time nor cure temperature have a great deal of effect on compression set. This suggests a very forgiving process for actual part production. The modified low viscosity 45 durometer material was shown to benefit from the enhancement of the new curing technology. Conclusions Previously, oven post curing of molded LSR parts was required to provide adequate resistance to compression sets. The new curing technology provides the fabricator with a method of obtaining good compression set resistance without the expense of post curing. The new curing technology has been found to provide a good measure of compression set resistance in articles cured at relatively low temperatures with fast molding cycles. These developments will provide the designers and fabricators new flexibility with many new applications where fast cycle time is necessary and outstanding performance is required. These enhancements in the material performance, coupled with the improvements that have been made with tools and presses, can make LSR the low cost, high performance alternative to organic rubber.3 |
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