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EMPIRE hydraulic hoses

I.Rubber hose is a common auxiliary device in hydraulic systems, and is used to connect various components in the hydraulic system, to deliver or suction, under positive or negative pressure, materials in gaseous, liquid or solid states. Rubber hoses are widely used in various sectors of our national economy, including manufacturing, agriculture, mining, metallurgy, seafaring, aviation, road transportation and military industries.

In recent years, the rubber hose industry developed following the trends of large length, large diameter, wire-braid reinforcement and resin. The compact design and installation of industrial equipment also require smaller bending radius of rubber hoses, while changes in working environment and media delivered have raised higher requirements on resistance performance against high or low temperature, surge impacts and mediumtypes.

Driven by fast development of hydraulic technologies and ever demanding requirements on safety, environmental protection and health during material transmission and power transfer, hydraulic hose has become an indispensable supporting part and is named “blood vessel” of industry.

II. Rubber hose industry in China sticks to the Scientific Outlook on Development and has realized continuous, quick and coordinated development in terms of product species, specification and quality. According to data analysis inAnalysis Report on Investment Forecast and Production and Sales of Rubber Hoses and Belts in China 2013-2017[1], China has become the largest rubber hose producing and consuming country of the world. According to statistics by CRIA Rubber Hose and Belt Branch, the current annual production in China is 360 million m² for conveyor belts, 2.1 billionAm for V-belts and 660 millionBm for rubber hoses, which listed China as a major producer and provides chances for Chinese products to enter international markets.

III. Empire makes improvements to existing rubber hoses and belts in terms of rubber material, production technology, product performance and cost control, to cater for market needs and user requirements. Through continuous efforts on new products and new technologies, Empire rubber hoses and belts provide internationally advanced performance, and significantly improved competitiveness of our products in international markets.

(I) EMPIRE rubber hose introduction:

1.By raw materials, rubber may be classified as natural rubber and synthetic rubber.By forms, it is classified as bulk raw rubber, latex, liquid rubber and powder rubber. Latex is the colloidal state of bulk rubber with water content. Liquid rubber is the oligomer of rubber and is usually in forms of thick liquid before vulcanization. Powder rubber is the processed latex in powder form.

2.Rubber hoses may use Styrene-Butadiene Rubber (SBR) as its raw material, which is the copolymer of butadiene and styrene. SBR with 10% styrene content provides good cold property and SBR with 30% styrene provides excellent abrasion resistance. Nitrile Butadiene Rubber (NBR): It is the copolymer of butadiene and acrylonitrile. Generally acrylonitrile contentofrubber is 18%, 26% or 40%, where higher acrylonitrile content provides better resistance to oil and heat.Innerandouterrubber layers of hoses are usually made from natural rubber, SBR or Cis-polybutadiene. Oil-resistant hoses are usually made from neoprene and NBR. Hoses with good resistance to acid/alkali and high temperature are usually made from Ethylene Propylene Rubber (EPR), fluororubber or silicone rubber, etc. Recently, thermoplastic rubber became popular, such as thermoplasticpolyurethane rubber and polyester rubber, etc.

3.Types of rubbers: A principle in rubber selection for oil-resistant hoses is that in application of oil delivery, larger difference in values of solubility parameters between hose material and media tends to realize better performance. Reinforcement agent and stuffing agent: In production of black hoses, low-structure carbon black is preferred but should not be used in very large amount. Stuffing agent usually adopts high-abrasion furnace black, mixed with pottery clay powder, talcum powder, mica powder and calcium carbonate, etc. which provides good electric resistance. Vulcanization system: For hose rubber materials prepared by NBR, the vulcanization system can realize better effect in case of low-sulfur preparation.

4.The reinforcement layer may be made of cotton fibers, synthetic fibers, carbon fibers of various types or rock wool or steel wires. Reinforcement materials should be determined by the desired specification, structure and working pressure, on basis of which the hose pressure capacity will be calculated. In order to meet vacuum requirements without collapse or deformation of hoses, the inner rubber layer is the innermost layer of rubber hoses and must be prepared by using special formulas to meet particular requirements and to resist chemical or physical effects by materials delivered. Such materials delivered may be solids, liquid or gas, and may be acid, alkali or neutral.If the medium delivered is solid,suitable reinforcement materials should be selected accordingly, whether fabric, braided structure, spiral structure or knitted structure is used, in order to achieve the desired reinforcement effect. For general-purpose low-pressure and middle-pressure hoses, fabric textile or fabric threads are usually used as reinforcement materials, such as fabric, fabric-braid, fabric spiral and knitted structure.

5.By reinforcement material and structures, rubber hoses may be classified as pure rubber hose (with no fabric material), fabric hose (with fabric cloth as reinforcement layer), suction hose (fabric layer covered by another layer of metal spiral wires), braided hose (braided fabric or steel wire),spiral hose(spiral steel wires or fabric as reinforcement layer), knitted hose (knitted fabric), short-fabric hose (mixed short fabric and rubber).Among them, suction hoses work under negative pressure and wire-braid or spiral wire hoses are able to stand pressure of 80~600MPa and even higher.

6.For hoses with different reinforcement layers, theproduction methods of reinforcement layers and hose forming machines are also different. In production, only extruders are required to produce pure rubber hoses which do not have any reinforcement; forming machines are required to wrap fabric reinforcement onto theinnerrubber layer to produce fabric hoses; spiral metal wires need to be wound before theinnerlayer is formed, for production of suction hoses; special braiding or winding machines are required to produce wire-braid or spiral wire reinforced hoses, and knitting machine is required to produce knitted hoses.

7. Hose forming methods includepole forming (soft or hard) and poleless forming.Pole forming is to build hose on a hard or soft pole, while poleless forming is to extrude the reinforcement layer andouterrubber layer directly on theinnerrubber layer. In order to maintain pressurized state of hoses during vulcanization process, after forming process is completed, hoses will be wrapped with wet fabric (fabric rolls soaked in water), wires or coated by lead, before they proceed to the vulcanization process. Vulcanization may be done by vulcanization tank heated directly by steam or by continuous vulcanization. Short-fabric hoses are produced by directly adding short fabric to the raw rubber material and by extruding, which has simple production process and will gradually take the place of knitted hoses and fabric hoses.

(II) EMPIREhose manufacturing process:

The manufacturing process of rubber hoses is rather complicated, because many types of equipment and materials will be required.Recently, TPE (thermoplastic elastomer) or plastics has become an alternative raw material, and can simplify the manufacturing process, but at relatively high costs, and therefore, rubber still serves the main raw material.Modern hose manufacturing process lays increasing importance to highly automated and continuous production.

1.Rubber forinner, middle andouterrubber layers is prepared according to particular formula by mixers, and is then extruded to form theinnerhose which clads a soft or hard pole coated with release agent (pole is unnecessary of liquid nitrogen refrigeration is used).

2.A thin middle rubber slice is produced byusing a calender, which, after separant is applied, will be rolled up and cut into required size.

3.A winding machine or a braiding machine is then used to braid coppered steel wire or rope onto the hose, in the meantime, the winding machine or braiding machine also applies the middle rubber layer between any two layers of coppered steel wire or rope which is strapped at both ends (previously, the braiding machine needs to applyprestress onto the coppered steel wire).

4.Theouterrubber layer is formed on the hose which then is coated with lead and proceeds with vulcanization for protection.

5.Vulcanization is realized by using vulcanization tank or salt bath.

6. Finally the vulcanization protection layer is removed and the hose is depoled, fitted with connected, and sampled for pressurization test.

(III) Precautions in EMPIRE hose manufacturing:

1.Poor sealing tightness ofinnerrubber layer may lead to invasion by high-pressure oil to the steel wire layer.

2.Poor air tightness ofouterrubber layer may lead to rusting or corrosion of steel wires.

3.Uneven wall thickness, especially of theinnerrubber layer may cause very bad influence on hose products.

4.Improper vulcanization, such as undercuring or overcuring, may lead to failure to meet requirements on hose features and functions.

5.In the braiding or winding process of steel wires, failure to follow process requirements on braiding angle (54°44′) or tightness will cause extra deformation (extension, shortening or bending deformation) of the hose when it is in use (pressurized).

6.Measure should be taken to avoid insufficient adhesion between rubber layer and steel wire layer.

(IV) In the manufacturing process of HP hose assembly, many factors may have influences on the final product quality, and Empire will take strict control throughout the manufacturing process.

1. Controls and testing of HP hoses:

The hoses for use in HP hose assembly will be tested in according to related technical standards, to ensure all technical performance indicators and requirements of hose assemblies are met. Attentions should be paid to:

(1) Dimensions and actual deviation of hoses. There may be slight deviations in the inner and outer diameters ofhoses and outer diameters of reinforcement layer, and if such deviation is larger than the allowed range, it can hardly ensure balance between hose connectors and crimping tightness, therefore it cannot ensure quality of hose assembly. As such, strict inspection should be made to the I.D. of hoses for use in hose assemblies and O.D. of the reinforcement layer, but requirements on hose O.D. may be relaxed to certain extent.

(2) Deviation of hose wall thickness. Decenteredinnerrubber layer and overlapping width of middle rubber layers may result in extra deviation of hose thickness. Extra deviation of wall thickness will affect the hose tightness and uncoupling strength and may event result in deflected connectors. Therefore, strict control must be realized on hose wall thickness, and it should be especially careful if wall thickness deviation is larger than 0.5mm.

(3) Inter-layer adhesion. High quality hoses should realize very good integrity, which means good adhesion between structure layers of the hose. Various layers should tightness combined into an integral structure, so that the technical requirements on assembly and crimping process of connectors will be met, ensuring satisfactory performance of hose assembly. The adhesion between different hose layers shouldbein no case lower than the required level in related standards, and hoses with high adhesion performance should be used in manufacturing of hose assembly.

(4) Hose appearance. Hose appearance cannot be ignored, because it not only influences the appearance quality of hose assemblies but also affects its application. Some defects, such as bubbles, air holes or mechanical wear may expose the reinforcement layer and cause rusting, which reduces the hose pressure capacity and has direct impact to service life of hose assembly and may even cause accidents in use. As such, careful appearance inspection should be made to hoses and those with defects that may affect the hose assembly performance should be rejected.

2. Quality control on connector metal parts:

Strict quality inspection must be made before assembly to the connector tube, sleeve and connecting and sealing parts. In inspection, the hose dimensions, tolerance fitting and machining precision should meet requirements in the connector drawings, inspections must also be made to interchangeabilities of connectors and connector compatibility with hose used, besides, special inspections should be made to the smoothness of connector tube and of edges and corners. If any sharp edge or burr is found on the connecting metal part, such connector must be reworked before use for any purpose, otherwise, it will significantly reduce the performance and service life of the hose assembly. Some potential defects in the steel materials used for connector metal part production cannot be identified in visual inspection, but radial breakage or axial cracks may occur during connector fitting or crimping process or during hydraulic tests. Therefore, strict testing should be made to connector metal part one by one in a same batch, to eliminate potential risks.

3. Strict control on operation quality in manufacturing process:

Many manual operations are involved in manufacturing process of HP hose assembly, over which Empire realizes strict quality control, to minimize impacts human factors.

(1) Hose length measurement and cutting. Efforts are made to realize accurate measurement of hose length, but special attentions are also made to bending of hoses. Within the required length range, it is preferred that hose products are slightly longer rather than shorter, because as a result of internal pressure, the hose tends to be shorterthan its nominal length. If a hose is short, even though it can be fitted with the connector, it is still subject to a tensile stress during its use, which reduces the service life of such hose.

(2) Quality control over polish rubber. Insufficient polish rubber length will affect the fitting of sleeves and reduce the sealing length hose in the connector and compromise the sealing performance of hose assembly, however, excess polish rubber length will expose the  reinforcement layer after connector is fitted, which may easily cause rusting and damage.

(3) Strict control of measurement accuracy of hose wall thickness. Hose wall thickness is an important basis to determine the crimp fitting size, therefore, the measurement must be accurate and careful, to reduce measurement error and calculation error.

(4) Inspection and control of fitting quality of reinforced connectors. It is important to ensure correct fitting position. A very likely problem in fitting process is that the incorrect position of sleeve results in insufficient length of the fitting pipe in hose or escapee of hose from the sleeve during the fitting process, causing insufficient sealing length and compromised sealing performance. As such, sleeve must be fitted to the correct position.

4. Quality control and check in crimping process:

Crimping is a key process in hose assembly manufacturing and it is of great importance to strengthen quality control and inspection in crimping process, to ensure satisfactory hose assembly quality.

(1) Correct crimping module. In crimping module selection, the desired crimping diameter must be realized and the user must consider the fitting clearance.

(2) Crimping dimensions. On basis of hose structure, performance and connector structure, after the compression ratio is determined, the crimping dimensions must be verified through tests, especially to the first batch of products. Crimping operation is done on basis of crimping diameter of sleeve which is calculated on basis of measured hose wall thickness and selected compression ratio, then hydraulic test and connector uncoupling test are done, to check the sealing performance and the uncoupling strength of the hose.

(3) Strict control on appearance and quality of crimping. Attentions should be paid to coordination, to take control over crimping position and size, to avoid connector damages and incorrect crimping position. Re-crimping operation should be avoided.

5. Quality tests on EMPIRE HP hose assembly:

Testing of finished hose assembly is very necessary. Comprehensive inspections should be made to the model and specifications, length, fitting and sealing types, angle and direction of elbow connectors, crimping appearance and cleanness oninnersurface of hose. Tests, such as pressure test, bursting test, uncoupling test and impact service life test, should be done on randomly selected samples according to standard requirements.

(V) A series of inspections and tests should be done before the HP hose assemblies are delivered. The inspection and testing procedures of Empire HP hose assemblies are as follows:

1. Scope of application
1.1 Inspection and testing to wire-braid hydraulic hose assemblies.
1.2 Inspection and testing to spiral-wire reinforced hydraulic hose assemblies.

2.1 GB/T3683-2006 Rubber hoses and hose assemblies — wire-braid-reinforced hydraulic types
2.2 GB/T10544-2003 Rubber hoses and hose assemblies -- Rubber-covered, spiral wire reinforced, hydraulic type

3.1 500mm straight steel ruler with scale ≤1mm, and 5m flexible steel ruler with scale ≤1mm.
3.2 Vernier caliper, scale between 0 and 150mm, with precision being 0.02mm.

4.1 Sealing performance test:

4.1.1 Test pressure is determined in accordance with pressure test parameter sheet, and the test should be done three times on a testing bed for a period of 1 minute respectively, during which no leakage or damage should occur to the hose assembly.

4.2 Tensile test:
4.2.1 A 300mm hose is tested, from which air is exhausted and then pressurized to design working pressure and maintains pressurized state for 30 seconds,and thenthe pressure is discharged. The hose is marked, at least 30 seconds after pressure is discharged, on positions 125mm to a middle point between two connectors.
Then, the hose is pressurized again to the design working pressure and maintains pressurized state for 30 seconds, during which the length between such two marked positions is measured and recorded as L1.
4.2.3 Length change value△L is expressed in percentage and is calculated by using the formula:△=(L1-L0)/L0*100%, wherein, L0 indicates the length between two positions marked 125mm from the middle point after pressure is discharged. L1 - Length measured between two marked positions in pressurized state.
4.2.4 Length change should be between -4% and +2%.

4.3 Bursting test
4.3.1 According to standard requirements, the pressurization rate between 12.5~40Mpa is 0.35~1.17Mpa/S, reaching the bursting pressure in 90 seconds. When pressure is greater than 40Mpa, a constant pressurization rate is employed to reach the final test pressure in 120 seconds.  Pressurize the hose assembly to the minimal bursting test pressure (4 times design working pressure) and maintain the pressure for 1 minute, and if no leakage or any other abnormal situation is found, it is further pressurized until the hose assembly bursts, which pressure value will be recorded as the bursting test pressure.
4.3.2 In the bursting test, if the connector is uncoupled or burst occurs within 25mm range to the connector, it is deemed as destruction of the hose assembly, in which case the bursting test may be repeated and the failure form, position and test pressure should be recorded.

4.4 Flame retardation test
4.4.1 A 300mm hose is placed on horizontally on the test stand in the test chamber, the relative position between an alcohol blast burner and the hose should be determined according to standard requirements, and the distance from outer edge of hose to the alcohol blast burner should be (50±2).
4.4.2 Adjust the flame height to 150~180mm at a flame temperature of 960±60°C. When flame becomes stable, burn the hose in the flame for 60 seconds, then remove the alcohol blast burner, and the durations of flamecombustion or flameless combustion of the test piece is measured.
4.4.3 The durations of flame combustion and flameless combustion of each hose group should be no longer than 30 seconds, and no longer than 60 seconds for any single group. The final test result should be expressed as arithmetic mean value of measured values of all three test pieces.
4.4.4 Fuel used in the tests is a mixture of 95% industrial ethanol and 5% methyl alcohol.
4.4.5 The tests are done on conditions that air flow in the test chamber has no influence on flame combustion.

4.5 Anti-static tests:
4.5.1 Insulation resistance is measured by using a high-voltage resistance meter. Voltage applied on the hose is no lower than 40V and the measurement meter should provide sufficient accuracy. The voltage on measurement meter may be set to 10V and 1×108Ω resistor is connected to the resistance meter. The test value is recorded for 1 hour and fluctuation should be within ±2%. Time response is less than 30s, to ensure resistance measurement error is within ±10%. The test piece power consumption should be no greater than 3W.
4.5.2 Test hose is 300mm in length and itsoutersurface is cleaned by clean silk or sterile gauze soaked in distilled water, and is then dried by clean cloth and stored in dry conditions for 24 hours or longer.
4.5.3 Colloidal graphite or aluminum paint is used to paint two parallel circles in 25mm width around the hose and the distance between two graphite electrodes is 100mm. Supply power to the two electrodes. The graphite surface should be even and smooth and the maximum resistance between any two points on such electrodes should be no greater than 1×105Ω.
4.5.4 The contactor is made from 25mm wide tin foil located symmetrically in a distance of 100mm. The tin foil should be in well contact with the hose and the two free ends should be fixed by clamps. 
4.5.5 The hose should be place at room temperature (25±5°C) and relative humidity of 60%~70% for at least 2 hours, and is then tested with dry surface.
4.5.6 Measurement leads should be connected to the contactors to perform the potential test.
4.5.7 Hose is placed on support plate made from polyethylene or other insulating materials and 1×1011Ω resistance should be generated.
4.5.8 Leads to the testing instruments should contact any other test piece or part, except wiring.
4.5.9 The test is done once on each test hose and the values will be recorded and expressed in Ω as arithmetic mean value of test values on all three test pieces.
4.5.10 Resistance between the two electrodes should not be greater than 25×108/d (d as nominal OD of hose).

5. Records:
5.1 All data obtained should be recorded carefully and clearly and should be authentic and accurate.
5.2 The records should be signed or sealed by test operators, to confirm and take responsibilities.

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