Extrusion, Rubber

Rubber Processing Methods

Dow Corning's New "In Situ"-Mixing Extrusion Technology - Increases Processing Flexibility and Productivity

Dow Corning has developed a patented “in situ”-mixing extrusion system in partnership with Colmec, SpA that allows users to mix then extrude uncolored, Silastic® brand high consistency silicone rubber compounds with color masterbatches, or various additives, fillers, and processing aids in a single step on one piece of equipment. Versus conventional practices, the system allows fabricators to increase processing flexibility by reducing raw material inventories since precolored masterbatches no longer need to be purchased, as color can be added on-the-fly. The system also can shorten production times and lower costs by up to 15% annually, while at the same time yielding excellent mixing and a very consistent product. These benefits make it easier to compress delivery times to customers and react faster to changing market demands.

The “in situ”-mixing extrusion system can be used either with conventional peroxide-cure silicone chemistry, or with increasingly popular platinum-catalyzed systems. Benefits of switching to addition cure platinum catalysts include:

* Elimination of 2,4 DCIBP cure by-products for environmental and health benefits
* Elimination of post-cure treatment for non-food applications, since cure is more complete with this chemistry
* Easy, on-the-fly changes of cure speed to meet varying processing requirements; and
* No compromise to stability and shelf life for the silicone compounds.

The new extrusion technology will be of interest to fabricators using high-consistency silicone rubber products for the wire & cable, building & construction, and automotive industries, as well as for extruding tubing and hose.

Two machine options are available for users wishing to implement the “in situ”-mixing extrusion technology. In Option 1, for customers already using a Colmec extruder, purchase of a second, 45-mm Colmec extruder with a 2:1 L/D ratio, an additional screw, and an adapter with mix zone and extruder head would complete the system. In Option 2, for customers who do not already use Colmec equipment, purchase of two Colmec extruders – e.g., one 45 mm and one 90 mm – plus the adapter with mix zone and extruder head would complete the system. Furthermore, it is possible to modify existing Colmec extruders to function like this new system.

Dow Corning holds a global patent on the machine concepts and the process. Colmec produces, sells, jointly markets, and services the equipment.

For more information about the “in situ”-mixing extruder, please contact us.

Colmec SpA has been a leading manufacturer of rubber extrusion lines for the European marketplace for the past 30 years. Headquartered in Milan, Italy, the company can be contacted at www.colmec.it.
A
Additive. Additives combine with a Silastic® silicone rubber base to enhance processing or performance characteristics of the compound.
Autoclave Vulcanization. A method of curing rubber with the use of steam.
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B
Base. A base is a silicone polymer with reinforcing fillers and process aids.
Bonding. The process of adhering silicone rubber to a substrate.
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C
Calendering. The process of forming silicone into uniform thin sheets.
Catalyzing. The addition of a curing agent to allow for heat curing of silicone rubber.
Compound. A compound is a ready-to-use blend of a silicone rubber base, fillers, modifiers, vulcanizing agents, and pigments.
Compression Molding. A process of curing silicone by use of a molding method whereby a preform is placed into one half of a heated mold and the mold is closed. Pressure is applied and the preform is forced into all parts of the mold cavity.
Crosslinking. When rubber is heated to the required temperature, peroxide decomposes to form free radicals that react with the organic groups in the silicone polymer. In an addition cured silicone rubber, the catalyst activates the reaction between the crosslinker and reactive organic groups in the silicone polymer. This results in crosslinking between organic groups. The number and position of these linkages determine the degree of vulcanization.
Curing. The degree of vulcanization of the rubber; also known as Heat Aged Curing
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E
Extrusion. Continuously forcing rubber through a die that forms it into the desired size and shape.
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F
FKM. Fluorocarbon Elastomer
FSR. Fluorosilicone Rubber
FVMQ. ASTM standard for silicone that has good oil and fuel resistivity (Fluorosilicone Rubber); VMQ is the ASTM standard for general purpose and high strength silicone rubber
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H
HCR. High Consistency Rubber (Heat Cured Rubber)
Heat Aged Curing. The degree of vulcanization of the rubber.
HVA/Hot-Air Vulcanization. A method of curing rubber with the use of hot air.
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I
Injection Molding. A process for curing or molding parts by injection of rubber into a cavity.
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L
LSR. Liquid Silicone Rubber
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M
Molding/Moulding. The method of heat curing rubber by using compression, transfer or injection molding equipment.
MQ. ASTM standard for general purpose and high strength silicone rubber; also known as VMQ
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P
Pigmenting. The addition of color to silicone.
PMQ. ASTM standard for extreme low temperature service silicone rubber; also known as PVMQ
PVMQ. ASTM standard for extreme low temperature service silicone rubber
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S
Scorch. The premature vulcanization of the rubber - before the flow of rubber in the mold is complete.
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T
TPE. Thermoplastic Elastomer
Transfer Molding. Unvulcanized rubber is placed in a chamber (called a pot), usually at the top of the mold, and the assembly is placed in a press. The press applies pressure to a piston-like plug in the open end of the pot, clamping the halves of the mold together and forcing the rubber to flow through the heated mold.
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V
VMQ. ASTM standard for general purpose and high strength silicone rubber
Vulcanization. The rubber cures when it is heated to the required temperature; peroxide decomposes to form free radicals that react with the organic groups in the silicone polymer.

Dow Corning