Hydraulic Hose Assembly Cleanliness

Transcription

1 Hydraulic Hose Assembly Cleanliness Amit Shinde Senior Engineer Eaton India Engineering Center Pune, India Hemant Sonawane Manager Engineering Eaton India Engineering Center Pune, India Jody Taylor Manufacturing Engineer Eaton Van Wert facility Ohio, United States Did you know that more than 80% of hydraulic failures come from contaminated oil? Dirty hoses and tubes can be a major part of the problem. Today's hydraulic systems operate at higher speeds and are therefore vulnerable to lower levels of contamination. There was a time when hydraulic pressures were much lower than they are today. Clearances between internal metal to metal surfaces were not as tight. And we were more concerned about contaminants we could see. We now need to be concerned about dirt and other contaminants that we cannot see, including particles as small as 2 to 5 microns. That small of a measurement is hard to comprehend. This paper highlights the importance of hydraulic hose assembly cleanliness & key factors which should be considered during manufacturing of a general hydraulic hose assembly so that it successfully meets the stringent cleanliness requirements of a critical hydraulic hundreds of feet of hydraulic hose. In addition to carrying hydraulic fluid, these hoses are also storing and carrying contaminants. Even before a breakdown, contaminants in fluid can reduce system efficiency. A less efficient system is a less productive These productivity losses can go undetected because efficiency loss is gradual. In hydraulic systems, for example, efficiency can drop as much as 20 percent before the operator detects a change in operation. That's losing a day of productivity each week. Even high efficiency filters do not remove all contaminants. Contamination can affect any machine with hydraulic capabilities. One track that runs faster than the other track on a tracktype tractor can be a sign of contamination. Equipment operators also see other common effects of hydraulic system contamination including cylinder drift, jerky steering, slower performance, erratic operation, shorter service intervals, higher operating costs, lower productivity and possibly catastrophic failure. Fig.1: Critical Hydraulic Applications Why contamination control is critical in hydraulics system? What happens to clean oil when it travels through newly installed hoses and tube assemblies that have not been cleaned? The particles of contamination from the cutting, crimping, bending and flaring process create a problem that will cause premature wear and system failure. It is imperative to protect your equipment from hydraulic contamination. Premature wear and system failure can be greatly reduced by the installation of clean hose and tube assemblies. Whether it's an excavator, backhoe, tractor, or any other piece of heavy machinery, it contains What are some of the hose assembly cleanliness requirements from mobile & industrial platforms in hydraulics industries? Below are examples of recommended cleanliness levels of hose assembly products for various applications: These requirements vary greatly based on hose assembly location & application in hydraulic Overall the contamination particle size ranges from 50 to 1200 microns & contamination mass from 8 to 50 mg per m^2 for different hose assemblies. Turbo and lube oil assemblies located in internal oil supply lines need to have system with maximum particle size less than 50 microns & max mass of 10 mg/m^2. Mobile products and off-road equipment, components that conduct or store vehicle hydraulic fluid in a hydraulic or hydrostatic system: Upstream of the Filter on Hydrostatic Applications up to 800 microns & downstream from the Filter for Hydrostatic or Sensitive System Applications. 1

2 Component surfaces in contact with high pressure fuel or oil system are allowed to have particle size up to 150 microns. Component surfaces in contact with filtered lubricating oil or filtered fuel 500 microns Internal surfaces of Intercoolers, Intake piping and component surfaces in contact with lubricating oil, inlet air, and exhaust gas & HVAC hose assemblies 1200 microns Fuel hose electro-hydraulic control valve systems 150 microns Hydrostatic hose assemblies with particle size up to 500 microns & max mass of 5 mg/l. How do we measure the cleanliness of a hose? The following ISO specifications are the main industry specifications involving hose assembly cleanliness. Typical methods of extraction involve sloshing a liquid solvent back and forth through a completed hose assembly and then pouring it through a filter to isolate the contaminants. Contamination particles are usually sized using a metric unit of measure called a micrometer, otherwise known as a micron. ISO 4407 (Maximum Particle Size Analysis) Maximum particle size is an analysis on the maximum particle size that is found in the sample fluid. A microscope is used to size individual pieces of contaminant. Customers may specify that the cleanliness level have a maximum particle size, for example 500 microns. Particle size is important in reference to maximum clearances of hydraulic components. ISO 4406 (Particle Size Distribution) Particle size distribution is a reporting method to gauge both the size and number of contaminant particles in a known quantity of fluid. A fluid sample is either taken directly out of a hydraulic system or a known quantity of fluid is used to dislodge contaminants out of a hydraulic component (in this case a hose assembly). This fluid is run through a particle counting instrument to size and count contaminant particles. ISO 4405 (Gravimetric Measurement) Gravimetric measurement is a reporting method that references the total mass of contaminant found in a hydraulic component. This total mass measurement is then normalized by the total internal component surface area of a hydraulic component. It is important to understand that there is absolutely no correlation between cleanliness levels of gravimetric vs. size/distribution methods. A clean hose by weight (gravimetric) may have many small, lightweight particles that result in a worse level of cleanliness using the particle distribution analysis methodology. ISO 3938 specifies methods for reporting data relating to contamination levels of fluids used in industrial, mobile and marine applications. General cleanliness testing method Standard cleanliness testing, as it relates to maximum particle size and contaminant mass, is done by using either DI water or a petroleum based solvent to remove the contamination from the ID of the assembly, the fluid is pre filtered through a 5μm filter. This is done by partially filling the assembly, plugging the ends and agitating or by flushing the fluid through. The fluid is then poured through a 5μm Millipore patch by means of a vacuum, dried, weighed for mass and inspected under magnification. Fig 2: Cleanliness measurements Where does such a contamination come from? It's often there from the very beginning. Large amounts of contamination are introduced at the time of hose and tube installation on hydraulic machinery. Hose cutting process: A major contributor to hose assembly contamination occurs during cutting of the hose to length, typically done with a circular saw. As the saw blade cuts through the hose, particles of hose tube, reinforcement, and cover are thrown into the open hose end. This cutting debris is typically limited to a few inches of hose length at the ends. Different cutting processes can affect the amount of debris that is deposited in the ends of the hose. The cutting method is selected based on the hose construction. For a hydraulic hose having metal wire braided 2

3 design verses hose having multilayered spiral wire construction would differ greatly. Dry cutting: This method generates more dust and debris and puts debris into motion more than wet cutting. Wet cutting: Water or other liquid lubricant is used and not only lengthens the service life of the saw blade, but the liquid suppresses dust and debris movement thereby reducing the amount of cutting contamination introduced inside the hose. particle debris, but also fine particles of the abrasive blade itself are added to the mass of potential contaminants flying about. Lube used during assembly of fitting into the hose for ease of insertion could also add to contamination. We have found the use of & amount of assembly lube generally affects the cleanliness of the assembly. Eliminating the use of lube in conjunction with the other parameters improve the cleanliness. Internal surface area of hose coming into contact with the fluid gives the relative idea about the contamination levels. Longer length hoses are difficult to clean. Hose internal diameter - D & length - L constitutes the internal surface area. Internal surface area, A = πdl Fig 3: Hose cutting traditional way Fig 4: Recommended hose cutting A combination of blowing air through the hose during cutting to direct debris away from the cut hose ends and vacuum to remove debris away from the work area can minimize contamination that occurs during cutting. The saw blade can also make a significant difference in the amount of cutting debris that is generated. A sharp blade will cut more quickly and smoothly and generate less debris. Saw blades should be kept sharp and clean. For wire-braided hose, serrated or scalloped blades cut hose better and faster. They also remain sharp longer since the blade can be reversed, positioning the other side of the notch for cutting. These blades are not recommended for cutting spiral wire reinforced hoses as they become dull rather quickly. Abrasive blades are recommended for cutting spiral wire reinforced hoses. The drawback is that not only do they produce more dust and hose Hose assembly storage & packaging A lot of our focus goes around the fabrication process & equipment being used to produce a quality hose assembly. At the same time the conditions under which it is manufactured, handled & stored seldom gets the attention. Being aware of particular fabrication environment is as important as contamination sources. Taking steps to avoid contamination in the first place will also assist in providing clean hose assemblies to your customers. Hoses and couplings should be stored in a clean, dry environment. Hoses should have the ends capped or remain in shipping cartons or sealed in plastic wrap. Couplings should be kept in sealed bags, boxes, or closed bin drawers until they are to be used. Completed, cleaned hose assemblies should have the ends capped or be placed in sealed bags or shipping boxes until they are attached to equipment and put into use. What are the most commonly used hose assembly cleaning techniques in market Even after concerted efforts to control hose assembly contamination during fabrication, there will still be a certain level of contaminants present inside the hose. These contaminants should be removed prior to attaching the couplings to the ends of the hose as they can become trapped between the hose coupling and the hose inner tube where they are not easily removed. Later, when exposed to pressure, vibration, flexing and the dynamics of hydraulic hose applications, they can be released into the hydraulic fluid inside the hose. As a result, it is recommended a post fabrication cleaning process be used. 3

4 Commonly used hose assembly cleaning methods include: Blowing shop air through the hose bore after cutting it to length. The air should be clean, dry, and filtered. Typically the pressure from the air supply ranges from 90 psi to 120 psi. Be aware that debris from the cut end of a long piece of hose can be moved to somewhere in the middle without completely removing it. The longer the hose, the more likely this is to happen. It is the most economical cleaning methods in practice & could clean general hose assemblies up to level of 800 microns. Fig 5: Air-blow process A fluid flush with liquid can be the most effective means of cleaning the hose bore. Usually this is not done until after the couplings are attached which can leave contaminants trapped between the coupling and the hose tube. It is important that the cleaning liquid must be chemically compatible with the hose tube. It must also evaporate quickly so the cleaning fluid itself does not become a contaminant. Naphtha is one such solvent cleaner. It can also dissolve other residues such as manufacturing lubricants that may adhere to the hose tube wall. Care should be taken while selecting the cleaning solvent as it might react with the surface or plating & result in flaking of surface treatments. Following the flushing process with a clean, dry, filtered air flush can promote solvent drying and further clean the hose bore. This method involves safe, responsible disposal of used cleaning fluid. However, this process is time consuming & also an expensive one. Cleanliness levels up to 150 microns & below are only possible through this method. Fig 6: Liquid flushing method Blowing a cleaning projectile such as a sponge pellet through the cut hose with clean, dry, filtered shop air, can not only remove cutting debris, but also any mandrel lubricants or other manufacturing residues. Soaking the projectile in a cleaning solvent can enhance the cleaning process. This is a very fast method of cleaning. Cleaning projectiles are most effective when used before the hose couplings are attached. As the projectile passes over the bump end of the coupling inserted into the hose bore end it could result in wiping off the collected debris and leaving it deposited there. Blowing a cleaning projectile through a finished assembly can possibly introduce new contamination into the system as pieces of the projectile can be peeled off and trapped as the projectile goes past the coupling. Using a brush and suction at the hose end can loosen and remove debris from the inside surface at the coupling end of a hose assembly where most contaminants are found. Cleanliness levels from 500 to 800 microns could be easily achieved through this method. Fig 7: Projectile cleaning Eaton contamination control products Eaton s projectile cleaning systems and CapSeal system are new additions to Eaton s family of hose assembly equipment. Eaton s FT1355 and FT1455 series projectile cleaning systems offer industry leading contamination control during hose assembly preparation. The FT1455 series projectile cleaning system is available in both a hand-held and bench mount configuration. In industry standard contamination measurement tests, the FT1355 and FT1455 series projectile cleaning systems yielded an industry leading cleanliness level of 13 to 18 in the 4µ to 14µ contaminant range per ISO 4406:99 and ISO 4405 tests. The FT1555 CapSeal system is intended to be used in conjunction with the FT1355 and FT1455 series projectile cleaning systems to prevent recontamination of hose, tube, and pipe assemblies. The FT1555 CapSeal system utilizes heat shrink 4

5 technology to encapsulate the end of a hose or tube assembly with an FT1555 CapSeal capsule. Traditional capping and plugging methods increase the possibility of recontamination, when ill-fitting caps and plugs are forced onto fittings, causing plastic particles to shear off, therefore contaminating a hose or tube assembly. Additionally, traditional capping and plugging methods require the exposed caps and plugs to be decontaminated prior to installation to minimize recontamination. Fig 8: Contamination control kit Experimental DoE on effect of factors affecting hose assembly cleanliness during manufacturing As we have seen above, there are many factors which contribute to a clean hose assembly. The hose construction, cleaning method, processing time, size of the hose, length of the hose, and kind of fitting the hose assembly is coupled with & so on. Most of the general requirement for medium & low pressure hose assemblies where permissible maximum particle size of a contaminant is greater than 1000 microns, an air blow operation would be sufficient to clean the hose. However, as the maximum allowable particle size becomes tighter or smaller, the projectile & flushing operations comes into picture. Air blow method is considered as a standard cleaning method for all hose assemblies as it is economical. It is important to establish guidelines where one of the methods meet the cleanliness requirements & is also economical for the manufacturer. Hence, an optimum process could possibly be developed by running an experimental DoE on key process factors. From the experimental analysis it is found that hose assembly cleanliness considering standard cleaning operation is function of below factors. Using these parameters, the process enhancement could be made to make the cleaning process economical & we could predict the cleanliness capability for different hose assembly designs. Conclusion: Increase demands in efficiency of industrial & mobile hydraulic equipment calls for more reliable system & related hydraulic components. Uncleaned hydraulic hose assemblies can adversely affect the hydraulic system performance. Manufacturing, assembly & storage methods play critical roles in delivering a hose which meets the cleanliness specification set by ever evolving industry requirements. Hose assembly manufactures need to optimize their operations continuously to deliver on these requirements economically through various capability studies. Bibliography: Vickers guide on systematic approach to contamination control Document No. 561 Oct EATON Contamination Control Products E- HOIN-TT032-E2 October 2015 Product specifications of key Eaton customers. ISO4407: Determination of particulate contamination by the counting method using an optical microscope ISO4406: Determination of code to be used in defining the quantity of solid particles in the fluid used in a given hydraulic fluid power ISO4405: Determination of particulate contamination by the gravimetric method ISO3938: Specifies methods for reporting data relating to contamination levels of fluids used in industrial, mobile and marine applications. H/A Cleanliness = (Internal surface area of hose -Length-ID, Air-blow timing, Airflow type, Cutting method, Lube, Hose construction). Variation in above factors affects the cleanliness levels of the hose assembly to be produced. 5