Product category:
Seals, gaskets, bushes, etc
News Release from: Dow Corning | Subject: Silicone sealant
Edited by the Manufacturingtalk Editorial
Team on 15 June 2007
Reactive hot melt silicone sealants save
time
Dow Corning discusses how reactive hot melt silicone sealant technology can save appliance manufacturers time and money.
Choosing the wrong type of sealants can be a costly mistake for appliance manufacturers, who need to make seals that are flexible, long lasting, able to retain liquids and solids, prevent heat loss, and provide noise insulation Aesthetically, manufacturers also need to improve the visual appearance of their product's components by filling in the naturally occurring gaps
This article was originally published on Manufacturingtalk on 21 Nov 2006 at 8.00am (UK)
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Hot melt sealants improve productivity
Hot melt technology combines the instant green strength of a pressure sensitive adhesive with the high performance of a crosslinked silicone sealant.
In-situ-mixing extrusion fine-tunes compounds
Dow Corning's system helps to fine tune compounds with fillers, processing aids, colorants in one step on one extrusion machine, to reduce costs and delivery times.
Appliance component sealing has typically been accomplished with adhesive tape or liquid sealants.
Each has drawbacks: tape does not require expensive equipment and allows the product to be processed immediately; but it is labor-intensive, consistency and quality of application can be an issue, and rework is time-consuming.
Sealants provide superior performance but they often squeeze out when parts are pressed together, compromising the seal and requiring an additional clean-up step.
Further reading
Silicon rubber compounds suit extrusion
A new line of platinum-cured silicone rubber compounds, suitable for extrusion applications, offers improved mechanical performance and more accurate cure rates than peroxide-cured rubber.
Large investment increases fluorosilicone capacity
Dow Corning has significantly increased its fluorosilicone capacity with the start up of a new specialty silicone intermediates plant at its manufacturing complex in Midland, Michigan.
Food approved lubricants range expanded
Dow Corning's UK and Ireland Channel Partner, RW Greeff has announced the launch of the extended Molykote range of food approved industrial lubrication products and services.
More importantly, the parts must be set aside after sealing to allow the material to cure, taking time and space.
Of the various liquid sealants available, silicone has emerged as the gold standard due to its excellent moisture protection; UV, ozone and chemical resistance; and unique temperature cycling capabilities.
Silicone is generally more expensive than most organic materials, but the life of silicone is longer and could prevent future problems that could occur with a less costly material.
In addition, the ability of silicones to bond dissimilar materials has enabled the production of many appliance designs that would have been impossible or cost prohibitive to develop through the use of mechanical fastening methods only.
For the appliance manufacturing process, though, silicone performance has come at a price.
Traditional silicones take time to cure, so product lines can proceed only at a rate that is consistent with the "holding ability" of the sealants.
Improvements to production rates can be achieved by using two-component sealants, which can take the bonding time from 24 hours to 4 hours.
But in today's competitive environment productivity improvements and lean manufacturing are essential for continuous reduction in total manufacturing costs.
A new generation of reactive hot melt silicone sealants has recently been developed combining the best features of both adhesive tapes and liquids.
Like a traditional hot melt material it is applied at elevated temperatures (120 - 130degC) and green strength develops as it cools.
The low heat capacity of silicone reactive hot melt lets the material cool very quickly with a subsequent increase in viscosity.
Within 30 seconds after application the material cools, and the viscosity rises, to give "instant bonding".
The adhesive bond strength is from both the viscosity rise and the pressure sensitive adhesive (PSA) character of the material.
The PSA is "built in" to the product to maximise the green strength and allow for increased production rates in appliance manufacturing.
The strength of the silicone PSA is two to six times greater than traditional PSA's on bonding tapes, so many mechanical fasteners that may have been needed to fix parts in place are no longer be necessary.
Flexibility in the Assembly Process: unlike other hot melts this material has 15 minutes of working time.
So once the material is applied, and even though it cools, the bonding strength is maintained for 15 minutes.
This allows for flexibility in the assembly process, and forgiveness during process upsets.
Once the parts are assembled the silicone hot melt begins to cure using moisture in the air, the same as traditional one-part sealants.
Once the material cures it forms a durable, elastomeric bond that is able to withstand a wide service temperature range while maintaining adhesion and flexibility.
This patented, solvent-free, ultra clear, neutral curing material is 100 percent silicone.
The volatile organic content (VOC) is 15 grams per liter making it exempt from the VOC regulations in California, the strictest in the nation.
In addition, the product is non-hazardous, non-corrosive and worker friendly, too.
The true value to the appliance manufacturer comes from productivity improvements with decreased cycle time, reduced labour (from tapes and mechanical fasteners), and reduced holding time to cure the sealant (reduced working capital), which results in a lower total manufactured cost.
Reactive hot melt silicone sealants are best-suited for automated and semi-automated technology, whereby the silicone is melted in a drum or pail by a heated plate, then forced into a metering device, through which a perfectly formed, seamless sealant bead is applied to the parts being manufactured.
All these operations are controlled by a micro-processor.
Many manufacturers who already enjoy the productivity and consistency benefits of automation and understand the longevity and durability benefits of wet-glazed products may be able to switch to the new hot melt system with only a small investment in new equipment, such as new pumps.
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