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SUPPLYING QUALITY RUBBER HOSES

by Rick Hudson

In today’s supply-chain economy, the trend is for companies to reduce and consolidate their suppliers, and our customers are no exception. A number of them have asked us if – in addition to custom-molded products, shaft seals, and O-rings – we can also supply rubber hoses. The answer is yes, we can!

We at RL Hudson have made it a priority to personally visit and inspect every manufacturer with whom we do business. During our regular trips to the Orient, we have built close working relationships with many QS 9000-registered companies. Most recently, we have developed a hose manufacturer whose capabilities and quality products are exactly what we were seeking. As a result, we can offer our customers both extruded and formed rubber hoses – either homogeneous or reinforced – all at economical prices. With that in mind, I’d like to briefly review the basics of hose anatomy and to spotlight some common hose applications.

ANATOMY Most rubber hoses are composed of three parts. The first of these, commonly known as the “tube,” is the innermost portion. As such, the tube has two functions: to contain whatever fluids are being conveyed, and to resist being broken down by these fluids. In many instances, the tube is formed when rubber is forced (extruded) through a selected profile (die) to make it a particular size. Pertinent dimensions are inside diameter, outside diameter and/or wall thickness. In some cases, straight lengths of extruded rubber may be shaped using a mandrel; this is, for example, how curved radiator hoses are made.

By itself, the tube may not have the resistance required to adequately contain pressurized fluid, especially if the fluid undergoes periodic pressure spikes (sudden increases in system pressure). The tube may need to be reinforced by fabric or wire, and this “reinforcement” (also known as the “carcass”) makes up the second (or middle) layer of most hose. In addition to helping the tube withstand internal pressure, reinforcement also helps protect the tube from outside forces.

Reinforcing fabric or wire may be applied to the tube in a number of ways, such as by braiding, knitting, spiraling, wrapping, or weaving.

The third (and outermost) layer is the “cover.” The cover's main functions are to further protect the tube from external damage and to resist environmental deterioration (such as from ozone or weather). It’s not unusual for the cover to be color-coded to aid identification or to make the hose more attractive. Decorative designs or patterns may also be incorporated (as with the patterns on garden hose). Though use of both reinforcement and a cover is common, it is also possible to have simple extruded hose with neither reinforcement nor a cover. Such hose is said to be homogeneous.

APPLICATIONS As you are no doubt aware, rubber hoses play an integral part in countless products, both large and small, in every sector of industry. Because they are flexible and can absorb vibration, rubber hoses are especially useful in designs that move and shake. For example, high-pressure hydraulic applications make extensive use of rubber hoses to contain many different types of fluid. Water-oil (and water-glycol) mixtures and low viscosity mineral oils are common.

various rubber hoses Whatever the fluid, most hydraulic hoses are produced in the manner already outlined. First comes extrusion of an oil-resistant rubber compound onto a mandrel, then application of braiding (single or double wire) by a high-speed wire braider. For extremely high pressure uses, wire may be applied in spiral layers rather than as braiding. Either way, next comes extrusion of an oil-, abrasion-, and weather-resistant cover over the reinforcement, application of a lead (or thermoplastic) sheath or nylon wrapping (to compress the hose layers), and autoclave curing. The sheath or wrapping is stripped away and the mandrel is removed following vulcanization, leaving just the tightly cured hose.

Rubber hoses are also common in automotive applications. For example, air brake systems often include rubber hoses with an oil- and grease-resistant tube made of nitrile (NBR), chloroprene (CR), or a blend of NBR and styrene butadiene (SBR). Reinforcement is typically a synthetic textile yarn with high tensile strength. The outer cover might be CR, SBR, or even chlorosulfonated polyethylene (CSM).

Another major automotive application is fuel hose. Fuel hose generally features an oil-resistant tube of NBR (sometimes compounded with polyvinyl chloride, PVC). As with air brake hose, reinforcement is likely to be textile yarn made of polyester, polyamide, or rayon. Some fuel hoses don't have a cover; when one is added, it is commonly made of oil-resistant CR or CSM. Keep in mind that, because some fuel lines can be partially or completely immersed inside the fuel tank, it may be necessary that the outer cover be as fuel-resistant as the inner tube.

Still another automotive application is radiator (coolant) hose. As previously noted, radiator hose is often factory-molded (using mandrels) into curved shapes to fit specific spaces. Ethylene propylene (EPDM) is the most common tube material. This is because EPDM offers excellent resistance to heat, hot water, and ethylene glycol, the most common antifreeze. In some instances, SBR or NBR may be used instead. Reinforcement may be applied in the form of fiber or textile. The cover may be EPDM, SBR, or CR.

Beyond hydraulic and automotive applications, rubber hose can also serve as liquid propane (L.P.) gas hose, Freon® charging hose, air hose, oxygen hose, acetylene hose, water hose, steam hose, washing machine hose, and gas pump hose.

ASSISTANCE For the past 20 years, RL Hudson has supplied sealing solutions in the form of O-rings, shaft seals, and custom-molded rubber, plastic, and polyurethane products. And, yes, we supply rubber hose products, too. As an ISO 9001-registered company, we also offer both design assistance and the highest level of quality assurance. We’ll be more than happy to help you meet the needs of your next sealing or hose application. Please don't hesitate to call us at 1-800-722-6766 if we can be of assistance.