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Technical Glossary

Acetoxy RTV

One component RTV which produces acetic acid as by-product of cure.

Addition Cure RTV

Two-component RTV which cures with no by-product and low shrinkage. These RTV's can be accelerate with heat. 

Adhesive Failure

Loss of adhesion between the adhesive and the substrate. The adhesive pulls cleanly away from the substrate.

Alkoxy RTV

One component RTV which produces alcohol as by-product of cure. Primary use is in applications requiring non-corrosive by-product.

Ambient Temperature

The temperature of the surrounding environment.

Application Rate

The amount of uncured material per unit which can be discharged through a nozzle under pressure. Nozzle configuration and pressure are typically specified.

Arc Resistance

The time required for an arc to establish a conductive path in a material.

Bond Strength 

The amount of adhesion between bonded surfaces usually expressed in lbs./in. Also referred to as peel strength.

Breakdown Voltage

The voltage required to cause failure in an insulating material (see dielectric strength).

Capacitance

A measurement of the amount of electrical charge in a capacitor can hold. 

Centipoise

A unit of viscosity, flowability. Water rough equivalent to 1 cps, maple syrup 1,000.

Coefficient of Thermal Conductivity

A measure of the ability of a material to conduct heat. A higher number means a better heat conductor. 

Coefficient of Thermal Expansion

A measure of the tendancy of a material to expand with a temperature increase of contract with a temperature decrease. A higher numbers means a larger change up and down as the temperature rises and falls respectively. 

Cohesive Failure

Loss of adhesion because the adhesive ruptures, leaving adhesive on both substrates involved in the bond.

Compression Set

Permanent residual deformation of an elastomer after being subjected to a compressive force. If a material, after being compressed and allowed to relax, returns to 90% of its original thickness, it exhibits 10% compression set.

Condensation Cure RTV

Two-component RTV which cures by mixing base and curing agent, normally DBT. Alcohol is a by-product of cure. 

Corona

A luminous discharge due to ionization of air surrounding a conductor.

Cure Inhibition

A poisoning of the catalyst in an addition cure product, such that there is a lack of complete cure, usually at the interface between the silicone and the other material. 

Cure Time

The time it takes for a material to solidify. Attainment of maximum physical properties normally will require additional time. 

Density

Weight per unit volume of a substance. Normally expressed in lbs./gal. Specific Gravity x 8.34 = lbs./gal. Specific Gravity x 62.4 = lbs./cub. Ft.

Dielectric

Electrical insulating material; non-conductor of electricity.

Dielectric Constant

The ratio of the electrical capacitance of an insulating material to the electrical capacitance of air. Also called permittivity.

Dielectric Strength

The maximum voltage a dielectric material can withstand and still perform as an insulator. Expressed in volts/mil.

Diluent

A liquid, either solvent or oil, used to lower the viscosity of an uncured RTV and sometimes to soften the cured RTV.

Dip Coating

A process for applying a thin coating of a material onto a solid substrate by dipping the substrate into a solvent dispersion of the material and withdrawing it.

Dissipation Factor

Ratio between the permittivity and conductivity of a dielectric.

Durometer (Hardness)

The resistance of a material to indentation, typically expressed as a numerical value on the Shore A scale. The higher the number, the harder the cured material will be. View Shore Hardness Chart.

Elastomer

A material which can be elongated or compressed and regain its initial dimension.

Elongation

The amount a material will stretch before breaking. It is expressed as the percent of the original length.

Encapsulate

To surround an object with a protective material, such as a RTV Silicone.

Filler

A powdered or finely divided material blended with silicone polymer to form an RTV with improved physical properties. Typical fillers are silica and iron oxide.

Fixture

The act of holding a part in place.

Fixture Time

The time at which a material will hold a part in place. This time is application specific and varies greatly. It is dependent upon such parameters as part size and configuration, part weight, the material being used, its thickness, temperature and relative humidity.

Flash Point

The lowest temperature at which application of a flame causes the vapour above a material to ignite.

Gasket

A material placed between two adjoining parts in an assembly for the purpose of preventing the passage of gases, dust, liquids etc., into or out of the assembly at that point.

Gasket - FIPG

Formed in place gasket. In this method a one part RTV silicone rubber is applied directly onto the parts to be gasketed and cured. Thus, it is formed in place.

Gasket - Cured Bead Method

In this method, the bead of RTV silicone rubber is applied to one of the two parts to be assemble and allowed to cure before assembly. This is appropriate when frequent later disassembly will be required. 

Gasket - Wet Bead Method

In this method, the bead of RTV silicone rubber is applied to one of the two parts to be assembled and the two parts are assembled prior to cure. The is appropriate when later disassembly will be infrequent. 

Greenstrength

The internal strength of the uncured silicone rubber prior to being moved to next production process.

Impregnate

To saturate an electric motor, transformer or other device with RTV for the purpose of filling all voids between wires or other elements. 

Outgassing

Outgassing may occur in fully cured silicone parts. This phenomenon has no relationship to by-products of cure. Instead, it is a response to extreme conditions to which the part is exposed. These conditions can include high heat or the presence of a vacuum. 

Plasticizer

An ingredient added to rigid compounds to increase flexibility, elongation, or make softer.

Peel Strength

The amount of force required to peel a material off a substrate.

Polymer

A chemical chain or matrix formed by repeatedly bonding together small molecules of the same chemical structure to form a very large molecule. Dimethyl polysiloxane polymer where it can be two to many thousand.

Potting

Similar to encapsulating - to fill a container, usually containing electrical components with an RTV to provide environmental protection.

Relative Humidity

The ratio of the amount of water vapour in the air at a specific temperature to the maximum moisture vapour which can be held in the air at that temperature. Expressed as a percentage.

Reversion

The tendency of a cured RTV to return to a liquid state under exposure to temperature and humidity.

RTV

Room Temperature Vulcanizing - this mean that’s an RTV silicone rubber will vulcanize (or cure) at room temperature, from a liquid or paste state to a solid flexible rubber. A one-component RTV silicone rubber cures by a reaction with atmospheric moisture. Therefore, the cure of such products is heavily dependent on the ambient relative humidity. It is also dependent upon the ambient temperature.  Because atmospheric moisture must permeate into the RTV silicone rubber for cure and the resulting 'by-product' must escape, applications where any part of the RTV will be more than 1/4 inch away from the atmosphere should be avoided. In such instances two-component RTV silicone rubber should be evaluated.

Sealant

A material which when adhered to two adjoining parts of an assembly, prevents the passage of gases, dusts, liquids, etc., into or out of the assembly at that point.

Shear Strength

The maximum shearing force, per unit area, an adhesive bond will endure before failure. A shearing force on an adhesive bond is created when the two substrates adhered together are forced in opposite directions in the same plane as the bond. Usually expressed in lbs/sq.in. (psi).

Silicone

Any member of a family of polymeric products whose molecular backbone is made up of alternating silicone and oxygen atoms and which has pendant hydrocarbon groups attached to the silicon atoms. 

Slump

Refers to amount of movement of silicone when applied to a vertical surface. 

Specific Gravity

The ratio of the density of a given material to that of water.

Substrate

A material which provides a supporting surface for other materials. 

Tack Free Time

The time required for a one-component RTV silicone rubber to cure enough to develop a skin which is non-tacky. 

Tear Strength

The force required to propagate a tear in a material which has been nicked or cut. Expressed in lbs/ins. of width.

Tensile Strength 

The force per unit of the original cross-section area which is applied to the RTV silicone rubber at the time of rupture under tension. 

Thixotropic

Describes materials which are paste-like at rest but will flow under pressure or agitation.

Tooling Time

The time after the start of cure during which a one-component RTV silicone rubber can still be tooled or worked without harm to either adhesion or appearance.

Viscosity

A measure of the resistance of a fluid to flow normally expressed in centipoise (cps.) View viscosity comparison chart.

Volume Resistivity

The electrical resistance between opposite faces of a 1cm cube of insulating material.

Work Life

The period of time after a material is mixed with its curing agent that is will remain useful or pliable.