Elastomers

The word “rubber” refers to an extensive family of materials that are widely used in the industry as, due to their wide range of materials, they are capable of meeting various requirements. Rubber:

• is practical and adapts to movement, tolerances, hardness and temperature variations
• can be used at a wide range of temperatures, from -60ºC to +320ºC
• is an electrical insulator, conductor or anti-static
• withstands extreme environmental conditions
• is resistant to fuels, chemical agents, oils
• is fire resistant and can be self-extinguishing
• is a vibration absorber and a noise inhibitor
• is compatible with other technical materials, with which it can be combined in many different ways
• can be obtained in a wide range of colours

Dureza y suavidad

Rubber is a property that anyone can recognise simply by touching it, but to determine the exact level of hardness, specific instruments are needed as well as reference standards that will be described later.

Solid rubber has a hardness that ranges from 20 to 98 Shore A, with 20 representing the point of extreme softness and 98 constituting the point of extreme hardness.

All types of rubber can be prepared so that they cover the majority of this hardness spectrum. The exact calculation of the required hardness is fundamentally important for a piece of rubber to work correctly and perform its function (in cases where a certain deformation is required due to contact with a friction surface or when a resistance to abrasion is necessary).

Elasticity

This is the ability to deform and quickly return to its initial state, which not only allows the ability to catapult, but also to provide a constant force either under tension or under compression.

All types of rubber are naturally elastic, but the degree of elasticity varies depending on the types, as well as their lifetime, which can be limited when they are exposed to light, the ozone, etc.

Some special types of rubber remain elastic throughout their projected life, but they all relax and lose their elasticity within certain limits if subjected to constant deformation.

Resistance to temperature

Given that they belong mainly to the family of hydrocarbons, rubber has a relatively limited range of temperature resistance.

The application temperature indicates the range within which the properties of the rubber remain more or less unchanged. The material tends to harden at temperatures below the minimum shown and extremely low temperatures can cause the rubber to rupture. The material will be damaged, even destroyed, at temperatures above the stipulated maximum.

The exact operating temperature must be established so that the most suitable material is chosen to work in those conditions.

Weather resistance

The properties of some specific types of rubber can remain unchanged indefinitely when exposed to any type of atmospheric conditions (heat, cold, humidity, rain, drought); the most suitable type to resist any type of atmospheric conditions, including an ozone attack, is EPDM.

Resistance to extreme environments

All aggressive chemicals, certain food components, coolants and hydraulic oils must be considered for a proper formulation of the rubber and tested to guarantee a suitable sealing service.

All types of synthetic rubber known today have been developed with the aim of obtaining better resistance to the fuels and oils that have so notably characterised the 20th century.

In terms of performance against oils and fuels, CR has moderate resistance, NBR and VMQ have good resistance, whereas FPM, FVMQ, ACM and FFKM have very high resistance.

For rubber parts to maintain their characteristics, the environment in which they are stored is of vital importance.

Parts that are properly treated are kept unchanged for long periods of time, although it is advisable not to exceed the following limits:

• NBR – 4 years
• FPM – 10 years
• VMQ – 10 years
• EPDM – 6 years
• CR – 4 years

The following are the ideal storage conditions:

• Heat – Storage temperature between +10º and +23ºC. Parts should not be stored close to heat sources.
• Moisture – Moisture and steam should be avoided. The optimal relative humidity of the air ranges from 65% to 75%.
• Oxygen – Equipment that emits ozone such as electric motors, electronic equipment, installations that give off sparks, halogen lights, etc... should not be located in the storage area.
• Light – Direct exposure to sunlight should be avoided. Artificial lighting with UVA ray
• Contact – During storage, particular care must be taken to ensure that the parts do not come into contact with solvents, fuels, lubricants (oils and greases), chemical substances, acids, etc. Moreover, prolonged contact with brass, copper and non-stainless steel is also harmful.
• Cleaning – If necessary, the parts must be cleaned with soap and water, without using organic solvents such as oil, benzol, turpentine, etc., and care must be taken not to use sharp, cutting or abrasive objects.
• Other precautions – It is advisable not to stretch, bend or hang the joints and not to subject them to permanent weights. If in doubt about the conditions of a part that has been stored for a long period of time, you can check the condition of the surface by gently stretching it. If the surface shows signs of cracking, it must not be used.O

The raw material is obtained by mixing a base polymer or a raw mixture with a series of additives. The choice of base polymer and additives is directly related to the type of properties to be obtained.

The resulting product is a non-vulcanised compound. The quantity of additives used on the base polymer varies from 20% to 130% as a percentage of the weight and always includes the following types:

• Accelerating agents – Chemical agents that change the speed and reaction time to vulcanisation (e.g., sulphur).
• Plasticisers – To facilitate moulding or allow specific properties to be obtained (e.g., paraffin).
• Inert fillers – Inert chemical materials used to increase mass (e.g., calcium carbonate).
• Activators – Active chemical materials that allow the binding of the molecular chain (e.g., zinc).
• Reinforcing fillers – Materials that increase the strength and/or resistance of the compound (e.g., black carbides).
• Pigments - Used to obtain various colours (e.g., iron oxide).
• Anti-degrading agents – Chemical substances that increase resistance to an ozone attack.
• Process finishes – Resins, soaps, etc.

The compound is produced by repeatedly mixing the raw material with the relative additives, either in a Banbury mixer or an open mixer. The Banbury mixer is operated by two rotors inside a closed box. The open mixer adopts two rotating cylinders that work together with the ingredients.

The raw material is the essence of every correct supply. The formulation of the compound must lead us to achieve the required resistance characteristics and a production that allows the finished parts to be manufactured at market prices.

Having analysed and determined the type of component that meets these primary requirements, the control to ensure that the compound remains constant becomes essential.

This is only possible through a prior control of the ingredients and a continuous high-quality control of each batch of compound. Each batch represents the quantity obtained by each mixing operation and ranges between 50 and 100 Kg.

At JIOrings, we pay particular attention to the identification and traceability of our products. We also offer a wide range of compounds and mixtures to our customers, whose properties are detailed in the technical sheets. Upon request, we can also supply the IMDS (International Material Data System), which breaks down the composition of the compound.

• Specific weight or Density – This is the mass per unit volume that is measured by weighing the sample in air and water. The international standards are ASTM1 D 1817, ISO 2 2871 and BS3 903A1. The measuring instrument is the density meter.
• Hardness – This refers to the resistance to the penetration of a certain blow under a specific load. Normally, 3 scales are used: IRDH (International Rubber Hardness Rating), SHORE A (from 20 to 90º Sh A), SHORE D (for materials with a hardness > 90º Sh A). The international standards are ASTM D 2240, ASTM D 1415, ISO 48, ISO 1400 and ISO 1818. The measuring instrument is the durometer.
• Tensile strength – This is the force per unit area required to break the rubber by traction. The international standards are ASTM D 412 and ISO 37. The measuring instrument is the tensile tester.
• Compression Set – This is the percentage of “no recovery” in the elastic deformation, referred to an initially applied deformation. The specimen is compressed to a certain fixed height (the usual case is 75% of the initial height) at a given temperature and for a fixed period of time. The specimen is then released and left to recover for 30 minutes. The Compression Set is measured by the thickness obtained after the rest period. The international standards are ASTM D 395 and ISO 815. The measuring instruments are the calibre, heater, clamp plates and comparator.
• Elongation – This is the length to the breaking point expressed as a percentage of the original length. The international standards are ASTM D 412 and ISO 37. The measuring instrument is the tension gauge.
• Modulus – This is the force per unit area required to elongate the specimen to a percentage of its original length (e.g., 100%, 200%). The international standards are ASTM D 412 and ISO 37. The measuring instrument is the tension gauge.
• Tearing force – This is the force required to tear a specimen. The international standards are ASTM D 624 and ISO 34. The measuring instrument is the tension gauge.
• Permanent Set / Return Set – This is the percentage variation between the original length and the length obtained after the specimen has been stretched for a fixed period of time and left to rest. The international standards are ASTM D 412 and ISO 2285. The measuring instruments are clamps.
• Resistance to fluids – This is the variation in volume due to the effect of the specimen coming into contact with the fluid under study. The volume variation is measured by calculating the weight of the rubber sample in air and water before and after it has been exposed to the liquid under study for a given time and at a given temperature. The international standards are ASTM D 471 and ISO 1817. The measuring instruments are a water bath, tension gauge, comparator and density meter.
• Chemical resistance – This is the variation of the properties (e.g., hardness, tensile strength, elongation) caused by the rubber specimen coming into contact with chemical substances under certain conditions. The international standards are ASTM D 471 and ISO 1817. The measuring instruments are furnaces and all those mentioned above.
• Rebound elasticity / Resilience – This refers to the rebound expressed as a percentage of a well-defined body (normally a type of hammer) that is thrown against a defined specimen. The international standards are ASTM D 1054, ASTM D 2632 and ISO R 1767. The measuring instrument is the rebound.
• Weather resistance – This refers to the variation in the physical-mechanical properties of a sample after being exposed to well-defined atmospheric conditions. It is measured as a percentage variation of the variations measured before and after exposure. As it is a fairly subjective test, it is necessary to accurately determine the exact exposure conditions (time of year, geographical area, angle of exposure, etc.). The international standard is ASTM D 1171. The measurement instrument is the climatic and ozone chamber.
• Resistance to ozone – This refers to the time it takes for a specimen to break under certain conditions of exposure to ozone or to the degree of breakage resulting from this exposure to ozone. Ozone causes the breakage of rubber. This test calculates the degree of resistance to this effect and can be carried out under various conditions in terms of the elongation of the specimen and the ozone concentration (usually 50 pphm), and there are various ways to check the condition of the specimen (by eye or with magnification). The international standards are ASTM D 1149 and ISO 1431/1. The measuring instrument is the ozone chamber.
• Resistance to low temperatures – This refers to the ability of a specimen to react to low temperature conditions. There are several methods that are generally divided into two basic groups: those that measure embrittlement after an impact test and those that measure the modulus of the material at low temperatures. The international standards are ASTM D 2137, ASTM D 1053, ASTM D 1329 ISO R 812 and ISO 2921. The measuring instruments are the embrittlement point and the shrinkage temperatures. .
• Resistance to ageing – This refers to the percentage variation in the characteristics of a certain specimen, measured before and after ageing at set temperatures. The international standards are ASTM D 573 and ISO 188. The measuring instruments are furnaces and all those mentioned above.
• Resistance to abrasion – This refers to the loss of mass of a specimen subjected to particular conditions of wear by abrasion. The international standard is ASTM D 394. The measuring instrument is the abrasion gauge.

This is a classification system that defines the quality values of a component. As an example, our compound NB701215-134691 is detailed below.

M2 BG 714 B14 EA14 EF11 EF21 EO14 EO34

Basic requirements: M2 BG 714

• M = Values in SI units
• 2 = Degree of quality
• B = Type (determined by heat resistance)
• G = Class (determined by resistance to swelling) 7 = Hardness at Shore A (70 +/-5)
• 14 = Resistance to traction (14 MPa)

Additional requirements:

• B = Permanent deformation (compression set)
• 1 = Test duration of 22 hours, solid specimen 4 = Test temperature at 100ºC
• EA 1 =Swelling in distilled water, test duration of 70 hours 4 = Test temperature at 100ºC
• EF 1 = Swelling in Fuel A (iso-octane), test duration of 70 hours 1 = Test temperature at 100ºC
• EF 2 = Swelling in distilled water (iso-octane: toluene/70:30), test duration of 70 hours 1 = Test temperature at 23ºC
• EO 1 = Swelling in oil ASTM no. 1, test duration of 70 hours 4 = Test temperature at 100ºC
• EO 3 = Swelling in IRM 903, test duration of 70 hours 4 = Test temperature at 100ºC