Molding is a manufacturing process that uses a mold - the latter being a solid container used to give shape to a piece of material. It is a forming process. The form is transferred from the mold to the material by...
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Here is everything you need to know about rubber tubing and its use.
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Rubber tubing, also known as rubber hose or rubber piping, is made of natural and synthetic rubber and is used to circulate and transport liquids and gases for household and industrial uses. The natural or synthetic rubber materials used for the manufacture of rubber tubing make it extremely flexible, dependable, and resilient for use in hydraulic and pneumatic equipment as well as food processing and medical applications.
Rubber tubing can be produced in a wide variety of tube diameters and wall thicknesses. It is this versatility that has made it adaptable for use in many unique and specialized industrial applications.
Rubber tubing is distinctively different from other tubing because of its rubber content, which is an elastomer that has high strength and durability as well as being able to be stretched and deformed without being permanently damaged. This is mainly due to its flexibility, tear resistance, resilience, and thermal stability.
Rubber tubing is produced using one of two processes. The first method is the use of a mandrel, where rubber strips are wrapped around a pipe and heated. The second process is extrusion, where rubber is forced through a die.
The rubber used to manufacture rubber tubing using the mandrel process is delivered for production in rolls of rubber strips. The thickness of the walls of the tubing is determined by the thickness of the sheets. The color of the tubing is determined by the color of the roll. Though color is not necessary, it is used as a method of deciding the classification and final use of the rubber tubing.
To make the rubber pliable for the production process, it is run through a mill that heats the rubber strips to soften and smooth the rubber to ensure that it has an even texture.
The soft and pliable rubber is moved to a cutting machine that cuts it into strips of equal width to fit the width and thickness of the size of the rubber tubing to be made.
The strips that have been created in cutting are sent on to the mandrel. Prior to wrapping the strips on the mandrel, the mandrel is lubricated. The diameter of the mandrel is the exact dimensions as the bore of the rubber tubing. As the mandrel turns, the rubber strips are wrapped around it at an even and regular pace.
The wrapping process may be repeated to reach the desired thickness of the rubber tubing.
After the tubing has reached the exact thickness, a reinforcement layer is added that is made of a high strength synthetic material that has been rubber coated. The selection of the layer is determined by the amount of pressure the rubber tubing may endure. In some cases, for extra strength, the reinforcement layer may have wire added.
The final layer of rubber stripping is its outside covering.
Once all the various layers of rubber strips have been applied, the full length of the completed tubing is wrapped in wet nylon tape. The tape will shrink and compress the materials together. The result of the tape wrapping is a textured finish on the outside diameter (OD) of the tubing that becomes an asset and benefit for applications where the tubing will be used.
The tubing on the mandrel is placed in an autoclave into which steam is fed at high pressure. The steam and heat initiate the vulcanization process, a chemical reaction that cures the rubber and makes it elastic.
One end of the tubing is tightly sealed to create pressure. A hole is made in the tubing for water to be pumped in to separate the rubber tubing from the mandrel. The rubber tubing is easily slipped off the mandrel, has its ends trimmed, and is cut to the desired lengths.
The extrusion process involves forcing rubber through a disc shaped die. Rubber tubing made by the extrusion process uses a soft unvulcanized rubber compound. Parts produced using this method are soft and pliable, which are vulcanized after the extrusion process.
The extrusion process begins by having the rubber compound fed into the extruder.
The rubber compound slowly leaves the feeder and is fed to the screw that moves it along toward the die.
As the raw rubber material is moved along by the screw, it is forced through a die in the exact proportions to the diameter and thickness for the tubing. As the rubber moves closer to the die, there is an increase in temperature and pressure, which causes the extruder material to swell depending on the type of compound and hardness.
Since the rubber used in the extrusion process is unvulcanized, it has to undergo some form of vulcanization once it has been through the extruder. Though treatment with sulfur was the original method for vulcanization, other types have been developed by modern manufacturing, which include microware treatments, salt baths, or various other forms of heating. The process is necessary to shrink and harden the finished product.
The vulcanization or curing process can be seen in the diagram below.
The choice of the extrusion process is based on its speed and efficiency as well as the variety of tubing sizes, colors, and profiles.
The wide use of rubber tubing has led to the development of several different types of rubber to fit unique and specialized applications. Though there are many varieties of rubber, all types can be divided into natural or synthetic.
Each type of rubber has strengths and weaknesses that are determined by the characteristics of the chosen polymer. Material selection is based on the temperature of the application, chemicals involved, abrasive factors, compression, and load, to name a few.
Fluoroelastomer rubber tubing is used for high temperature environments and is resistant to chemicals, oil, and heat above 200°C. The types of FKM are divided according to their fluorine content, which can range between 66% to 70%. FKM tubing with a high fluorine content has increased resistance to fluids.
Butyl rubber tubing is used for air and carbon dioxide transfer. It has thick walls, is shock absorbent, and is resistant to oxygen degradation with a temperature use range of -30° F to +275° F. Butyl rubber is a combination of isobutylene and isoprene.
CSM is made by the chemical treatment of polyethylene with gaseous chlorine and sulphur dioxide. The treatment causes the polyethylene to become flexible, vulcanized rubber. The chlorine creates a flame resistant and oil resistant rubber.
Hypalon, the name given to CSM by DuPont, is resistant to oxygen, ozone, and harsh weather conditions. Its main use is in applications where there are corrosive chemicals or acids as well as oil and grease. It can be used at temperatures ranging between -34° C to 93° C and retains its tensile strength for long periods of time.
Natural rubber is made from the fluids of plants and trees and has exceptional mechanical properties such as impact resistance, tensile strength, resistance to abrasion, and tear resistance. It is used for applications that require the highest degree of physical properties but is not used where resistance to chemicals, fuels, oils, or solvents may be involved.
Natural or latex rubber is produced from latex that is collected from rubber trees. It is very durable and flexible, which makes it usable in environments that require high strength, elongation, and tear strength. Regardless of its many positive properties, natural rubber should not be used for applications that are outside due to it being affected by UV rays and ozone.
Neoprene rubber is a synthetic rubber made from coal, salt, and limestone. It is used in applications that require a resistance to petroleum products, sunlight, ozone, and heat. Neoprene rubber products are mainly used for outdoor applications due to its ability to withstand wide temperature variations. A drawback to neoprene rubber is its electrical conductivity, which limits it from being used in electrically charged environments.
Nitrile is a copolymer of acrylonitrile and butadiene. It has exceptional properties, which include its resistance to water, petroleum products, and fuels. Nitrile rubber tubing can be exposed to petroleum products for long periods of time without becoming brittle and retains its excellent flexibility.
SBR has the same properties as natural rubber though it is a combination of styrene and butadiene. It is resistant to solvents and petroleum products much like latex rubber but has better water resistance than natural rubber. The characteristic of SBR that makes it ideal for manufacturing is its abrasion resistance and low cost.
Silicone rubber is made from a polymer that is reinforced with silica. It can be used in a wide expanse of environments from extreme cold to very high temperatures and is flame resistant. Silicone tubing is smooth, pliable, elastic, resistant to water, and flexible.
TPE is used in applications that require resistance to harsh and dangerous substances as well as a wide variety of acids. It can handle constant bending and movement, which has made it popular for use in robotics and pumps. TPE can be severely stretched and deformed but return to its original shape without signs of wear. This quality gives it a long life of usefulness.
EPDM is a comonomer that consists of propylene, ethylene, and diene which allows it to be vulcanized with sulfur. It is highly resistant to heat, light, and ozone. When it is properly produced and mixed, it can be used as outside tubing for many years. The main feature that makes it ideal for outdoor use is its ability to withstand temperatures below -40° C. Black carbon, calcium carbonate, and plasticizers are added during the manufacturing process to help give EPDM its rubber properties.
Hytrel® rubber tubing is used where the function of the inner lining is different from that of the outer lining. It is co-extruded with PVC where the Hytrel® is extruded first, which is followed by the PVC being extruded over it. It is designed to endure harsh and stressful conditions.
The fabrication and production of rubber tubing is designed to develop types of rubber tubing for specialized conditions. Though there are a variety of materials used to make rubber tubing, the grade and type of tubing is carefully selected for specialized applications, which leads to its different types.
The main concern of the food industry is tools that are safe and free of contaminants. Tubing used in the industry is required to follow very strict requirements to meet the standards of the Food and Drug Administration (FDA), which specifies the types of materials that are permitted to be used for food handling products. As with other industries, food handling equipment has to be able to withstand high pressure and temperature conditions as well as the types of acids and chemicals used in food processing.
Much like food grade rubber tubing, there are strict guidelines for the production of medical grade rubber tubing, which imposes severe design and construction requirements regarding the machining of the tubing and its ability to resist contaminants, degradation from use with chemicals, thermal damage, but have biocompatibility. The main purpose of the standards is for the protection of the patient.
The most common type of medical rubber tubing is silicone since it meets the standards established by the FDA per 21CFR177.2600. Medical rubber tubing is produced in various grades, levels of hardness, and sizes, depending on the application.
Conductive rubber tubing is used to control the build up of static in electromagnetic interference (EMI) or radio frequency interference (RFI) shielding. It is made from natural or silicone rubber and conducts electricity by the distribution of carbon or other particles in the raw material prior to fabrication.
Static electricity attracts dust that can cause sparks. Conductive rubber tubing reduces the friction that can ignite the dust. The tubing does not conduct electricity but moves or transports gases and liquids near electrically charged equipment.
Microbore tubing is designed for use in the medical industry and comes in extremely small sizes. As with any products used for patient care, it has to meet FDA requirements for sterility and materials. It is used for intravenous lines and placement in veins and arteries with strong wall construction to allow for free flow of liquids such as blood or drugs and is ultra-smooth, inert, and sterile. Microbore tubing for medical use meets the USP Class VI biocompatible requirements for medical use.
Air tubing moves pressurized air to actuators, valves, and tools. Extruding or mandrel methods can be used for the manufacture of air rubber tubing. It is constructed with an inner layer that is reinforced with fibers or a protective coating. When selecting air rubber tubing, the outside diameter (OD) determines the amount of pressure the tubing will be able to withstand. Small ODs tend to choke air flow.
Chemical rubber tubing is designed for the movement of hydraulic fluids, acids, and toxic substances. It is co-extruded such that it has an inner and outer layer. The key characteristics of chemical tubing is its flexibility, resistance to absorption, and smoothness.
Heat shrink tubing is used to insulate, protect, and repair wires to extend their usefulness. Rubbers that are used for this process are abrasion, chemical, oil and acid resistant and able to withstand temperatures between -90° F to 390° F. Heat shrink rubber tubing has a dielectric strength of 500 to 800 V/mil, which is the strength tubing can handle before it begins to breakdown. The higher the dielectric strength, the better the tubing is at preventing heat, electricity, or signal from dispersing.
Fabric, cloth, or textile reinforced tubing has three parts, which are the reinforcing material, tube, and cover. The tube is made from synthetic rubber that is resistant to abrasion, corrosion, and oils, usually NBR. The reinforcing material is made from multiple layers of synthetic material that gives the tubing a very solid and firm structure. The fabric and reinforced tubing are covered with a second layer of synthetic rubber that has the same properties as the first layer. The construction, structure, and arrangement of the materials produces a highly durable and resilient tubing.
Non-reinforced rubber tubing is used for low pressure applications such as pneumatic machinery and the food industry. It is exceptionally flexible, lightweight, durable, and can be used as lay flat tubing. Non-reinforced tubing is customizable to fit any size application with custom IDs and ODs in multiple colors. The smooth even inner surface of the tubing maximizes flow and reduces or prevents buildup.
For added strength and stability, non-reinforced rubber tubing may be cloth inserted with one or more plies of cloth, such as polyester, nylon, or cotton. The application of cloth makes non-reinforced tubing suitable for processes involving oil, caustics, and hydrocarbons.
The flexibility and adaptability of rubber tubing has made it an essential for use as a component in several industries. Rubber tubing is highly resilient and dependable as well as long lasting. These qualities make it ideal for use in homes for transfer of water and chemicals and in industry for applications involving hydraulic fluids and chemical processing.
Rubber tubing in the auto industry is referred to as hose and tubing. It is used as fuel lines, radiator hoses, for supplying lubricants, and part of cooling systems. The smooth operation of automobiles depends on rubber tubing being in excellent condition. Since rubber tubing has a long life span and history of dependability, it is the most widely used method for movement of fluids in automobiles.
There are several varieties of rubber tubing used in agriculture. It is used to transfer grain, collect debris, and provide ventilation. Each application requires a specially designed tubing. Flexible tubing is used to move abrasive materials such as animal feed, grain, and manure. A major use for agricultural tubing is for ventilation to ensure proper airflow for livestock. Agriculture rubber tubing is required to be chemical resistant due to the wide variety of chemicals used for food production and feeding.
The special conditions of air transport require rubber tubing that can withstand harsh weather conditions, radical pressure changes, and wide temperature variances. Flexible tubing or hose is used in aircraft for fluid systems to connect moving parts with stationary ones in locations that are subject to vibrations. Additionally, rubber tubing is used as a connector between metal tubing.
To meet the required strength, durability, and reliability for aerospace, synthetic rubbers are used to manufacture aircraft rubber tubing, which include neoprene, butyl, and EPDM. The psi for aircraft tubing varies between 250 psi to 3000 psi.
Rubber tubing for food processing is extremely critical and has to be manufactured to meet the rigorous standards set by the FDA. One of necessary properties of food grade rubber tubing is the avoidance of kinking and the accumulation of contaminants or sediments to ensure easy flow and flushing. The walls of food grade rubber tubing are thick to prevent kinking, but the tubing is lightweight and flexible. Since food products produce acids and chemicals, food grade rubber tubing is resistant to those materials as well as alcohol and alkali. It is produced using a purity process to avoid the transfer of tastes and odors. Food grade rubber tubing is used with water, air, beverages, and dairy products.
There is a wide variety of tubing and hoses that are used for marine applications, which can be seen in the diagram below. Water hoses are used to pump engine cooling water, flush toilets, and cool air conditioning. Drainage hoses are found in the cockpit, sink, or shower and are resistant to kinks and abrasions. Drinking water hoses are made to FDA specifications to avoid bad tasting water. Other hoses include bilge pump and sanitation hoses, which have to be rugged for constant use.
Medical and pharmaceutical grade rubber tubing is normally produced using some form of synthetic rubber with silicone being the most common, which has very few compounding agents. The quality of medical and pharmaceutical grade rubber tubes includes having been tested as implantations in animals and humans, manufacturing conditions in adherence to FDA regulations, and exceptional quality control.
Medical grade rubber tubing is used to make feeding tubes, catheters, implants for long and short-term use, and syringe pistons. The Center for Devices and Radiological Health (CDRH), under FDA oversight, regulates medical and pharmaceutical grade rubber tubing.
The required properties for medical and pharmaceutical grade rubber tubing are odorless, non-toxic, inert, temperature stability, and superior chemical resistance. A key to meeting FDA regulations is the choice of materials used in the manufacturing process and the vulcanization or curing method.
Any industry that requires the transmission, movement, or transport of liquids or gases depends on rubber tubing as an integral part of their operation.
Though rubber tubing has a variety of applications, to enhance its usage life and ensure its reliability, it needs to be cared for properly. To prevent damage, such as leakage, cracks, smells, or deformation, rubber tubing should be checked regularly and maintained.
Rubber is soft and flexible, which makes it susceptible to tearing and wear. The majority of rubber tubing has a protective layer or coating applied. Though this offers extra protection, it does not rule out the fact that the tubing can be damaged. Rubber tubing should be stored in an uncongested area that is clear of debris, dirt, moisture, and harmful materials such as metal tools or tools with blades.
When rubber tubing is in use, it is important to follow the manufacturer‘s recommended handling procedures. When it is attached to a source or piece of equipment, only appropriate connectors should be used. Force or stress should never be applied since they may weaken the tubing. When moving rubber tubing from one work location to another, it should be carried or transported on a cart. Dragging of tubing can be abrasive and cause wear to the protective layer. Crushing, standing on tubing, or bending it to cut off flow should never be attempted.
Every rubber tubing is manufactured for a specific purpose. It is designed for a certain flow rate and pressure gradient. Exceeding the tubing‘s rated specifications can cause it to burst or erupt. The main determining factor for ensuring the appropriate usage levels are maintained is to know the materials used to manufacture your rubber tubing. Different materials react differently to pressure, which is determined by the material‘s tensile strength, the maximum pressure rubber tubing can withstand. Putting chemicals in a watering tube will weaken the tube and may cause leaching.
The cleaning schedule for rubber tubing depends on its amount of use. For light usage, rubber tubing can be cleaned every six months but must be inspected at shorter intervals. Manufacturers supply instructions regarding the care of rubber tubing, which includes when and how to clean it.
Prior to washing your rubber tubing, it should be inspected for possible leaks or cracks. These damages should be repaired before cleaning. Rubber tubing should be washed with lukewarm water using a mild soap solvent. All dirt, chemicals, and debris should be scrubbed away. To prevent cleaning substances remaining on the tubing, it should be rinsed thoroughly. Drying is completed with a soft towel. Rubber tubing should never be left to dry in the sun or through the use of forced heat.
Where rubber tubing is stored can have a significant impact on its usefulness. Some of the factors that influence or damage rubber tubing in storage include temperature, ozone or UV conditions, and abrasions.
Temperature: There are two types of temperature that influence rubber tubing, which are the temperature of liquids passing through the tubing and the outdoor and indoor temperatures. If the temperature is too hot or cold, the tubing will lose its usefulness.
Ozone and UV: Sun and ozone levels can do significant damage to rubber tubing such as creating cracks or dry rot. Rubber tubing for outdoor use should be thoroughly tested before being put into use.
Abrasion: If the rubber tubing is handled frequently or dragged over rough surfaces, it can suffer erosion or mechanical wear. This can be prevented by using rubber tubing made of more durable materials.
Only rubber tubing that is designed for chemical contact can withstand chemical exposure. Rubber tubing that can potentially come in contact with toxic substances should be rated to handle such exposure.
Rubber tubing comes in a wide array of sizes, configurations, grades, and purposes. The type of tubing should be selected to fit its application with the correct durability and characteristics.
Rubber tubing falls under the guidelines of the International Organization for Standardization (ISO). Tubing for food, medical, and pharmaceutical purposes are regulated by the ISO standards and the Center for Devices and Radiological Health (CDRH), a branch of the FDA, as well as the United States Pharmacopeia (USP).
ISO standards are guidelines for hoses and hose assemblies. The regulations cover:
The numbers of the regulations begin at ISO 1307:2006 and ISO 1402:2009 and continue to ISO 28702:2008 and ISO 30013:2001.
FDA 21CFR177.2600 is in regard to materials that come in contact with food but are not added to the food. It includes a list of elastomers, vulcanization materials, accelerators, retarders, activators, antioxidants, plasticizers, fillers, and emulsifiers. The list specifies what materials are GRAS, generally recognized as safe.
The regulations further describe appropriate extraction methods with a definition of the number of milligrams per square inch. Included is a list of approved rubber products, which are acrylonitrile-butadiene copolymer (Buna), silicone, polytetrafluoroethylene, and ethylene propylene diene monomer.
The sanitary qualifications cover every potential piece of equipment that may come in contact with food including tubing, hoses, gaskets, o rings, and seals.
USP Class VI is the method used to determine the biocompatibility of a material. The USP has six classifications for biocompatible materials with Class VI being the most rigorous. It certifies that materials used are not harmful and will not have any long term effects on the body by allowing chemical leaching. The USP is responsible for overseeing the safety and quality of medical devices and food.
The CDRH is responsible for oversight of the manufacture and safety of medical devices. It further regulates non-medical equipment that release electromagnetic radiation like cell phones and microwave ovens.
The CDRH has three classifications:
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