Selection and replacement technology of vertical injection molding machine hydraulic oil

Date：2014-06-03 14:11:52

        Hydraulic oil is an important medium of energy transfer hydraulic systems , lubrication and cooling . Its main role is to pass a point in the hydraulic system of the force applied to the other parts . It also has a lubricating , cooling and rust effects. Reliability, accuracy and flexibility of the hydraulic system operation depends on the device in addition to the design of hydraulic components , materials and performance, to a great extent dependent on the selection and replacement of hydraulic oil technology .
        Plastic injection molding machine injection molding process, temperature, pressure, flow and other process parameters need to be controlled according to the molding requirements to ensure product quality. To meet the pressure and flow rate can be precise, stable and continuously adjusted according to process requirements , must be prepared to maintain and repair the hydraulic system . Stability, reliability, reproducibility , sensitivity , energy efficiency and low noise performance injection molding machine hydraulic systems working directly affect the quality of injection products , dimensional accuracy, cycle time , production costs, work environment, safe operation and maintenance overhaul. Where the correct selection and replacement of hydraulic oil plays an important role . The author based on years of theoretical knowledge and practical experience were summarized .
        Category 1 hydraulic oil
        According to international regulations, hydraulic oil belongs to class L ( Lubricants and related products ) in group H ( hydraulic systems ) , and adopt a unified approach to naming its general form is : class - species numbers, such as L-HM 68, L for the category ( lubricants and related products ); HM as varieties ( with abrasion resistance, general hydraulic systems for high load ) ; 68 for the grade ( viscosity grade ) .
        Correct selection of two hydraulic oil
        2.1 Select the principle of hydraulic oil
        General requirement is no water , no mechanical impurities , corrosion and rust qualified, good anti-foam , suitable viscosity , and good abrasion resistance .
        Requirements for the choice of hydraulic oil :
        ( 1 ) have the right viscosity, viscosity variation with temperature is smaller .
        Viscosity is an important property of the hydraulic oil at the same working pressure , the higher the viscosity , the slower the velocity of the various components , while the temperature quickly , the pressure drop and power loss. Control and regulation of low viscosity hydraulic oil hydraulic system will completely offset . Due to its different geographical and seasonal changes in system temperature difference before and after the start , will change the viscosity of the hydraulic oil , the oil viscosity is required to be small with temperature changes .
        A hydraulic system can only use a limited range of a certain viscosity or viscosity hydraulic oil change can play a greater efficiency . The hydraulic pump is one of the most sensitive to changes in viscosity of the oil component . Generally , other components of the system should be based on the required viscosity pump design and selection of the fluid viscosity . Injection molding machine temperature is higher, the larger the system pressure , and therefore to choose a slightly higher viscosity of the hydraulic oil.
        ( 2 ) have good lubricating properties.
        In recent years, the development trend of hydraulic systems and components for high-power , small size , light weight and high-pressure , high-speed, high-volume , its purpose is to improve the efficiency of the hydraulic system. However, under such conditions, the oil pump and the motor , the control slide valve and the central part of the cylinder such , many in the boundary lubrication state. Boundary lubrication produce is often due to excessive load , or by other factors and the thickness of the lubricant film caused a decrease . In this case, a partial surface of a sintered friction occurs . Therefore, to prevent all types of wear, abrasion, delamination , fatigue resistance , hydraulic oil requirements with good lubricating properties .
        ( 3 ) better oxidation resistance .
        In operation of hydraulic equipment , hydraulic oil in contact with air , under the action of oxygen in the air , hydraulic oil will oxidize , deterioration , especially under high temperature and high pressure oxidation is faster , as a result of oxidation darken general performance , acid number increases, the viscosity changes or a precipitate . Will enhance an increase in acid resistance, oxidation of the viscous liquid or solid product of high molecular weight , poor solubility . The polymer precipitate in suspension , may spread to various parts of the hydraulic system , causes filter blockage , wear of components such as hydraulic pumps , reduced efficiency , prevent operation of the control mechanism . Therefore, the requirements of the hydraulic oil is better oxidation resistance .
        ( 4 ) Shear Cean qualitatively better .
        When the hydraulic oil through the pump , valves, and other porous member is subjected to intense shearing action , which may cause mechanical action in the form of two kinds of change in viscosity , i.e., at high shear rate and the temporary loss of viscosity polymer permanent damage caused by the viscosity of the thickener molecules fall , and when the hydraulic oil viscosity drops to a certain limit , you can not continue to use, need to be replaced . Therefore, the requirements of the hydraulic oil shear Cean qualitatively better .
        ( 5 ) better corrosion resistance .
        Hydraulic oil to prevent metal corrosion performance is good or bad , affect the life of hydraulic components is very large .
        ( 6 ) Demulsibility better .
        During operation of the hydraulic oil from different sources may be mixed with water , aqueous hydraulic fluids can cause metal corrosion. Mixed with water under vigorous agitation in the hydraulic oil system regulator , pumps and other components , it is easy to form an emulsion . Particularly emulsion containing dust and other dirt , hydraulic oil may cause deterioration, degradation , and generation of sludge precipitate impede thermal cooler , block pipelines and valves , reduced hydraulic oil lubrication .
        ( 7 ) anti-foaming better .
        Circulating in the hydraulic system , the hydraulic oil containing bubbles will affect the compression ratio of hydraulic oil , so that the final energy transfer unstable . Furthermore, the presence of bubbles also increases the contact area with the air hydraulic oil , hydraulic oil accelerated oxidation . When a large amount of air dissolved by high-pressure liquid cylinders, valves and other components work , most of the air is released to generate foam , and went back to the tank with oil , and then mixed with the hydraulic system , will produce power transmission lag , lost power delivery reliability and accuracy. Serious, oil will overflow tank , not the normal production .
        Cleanliness ( 8 ) oil is better .
        The reason a lot of hydraulic oil contamination , airborne dust , metal shavings , sand casting can become residual oil in the dirt . Dirty hydraulic oil will plug the hole so that less oil filter , cavitation , vibration and noise occur , but also the operation of the sliding portion difficulties affect the reliability and accuracy of movement of the sliding portion in an early stage of wear .
        ( 9 ) on the sealing material to be small.
        Sealing materials used in hydraulic systems , depending on the type of hydraulic oil varies , such as when used as a sealing material nitrile rubber hydraulic system should be selected mineral hydraulic oils , and use phosphate-based fire resistant hydraulic oil will failure. Effect of hydraulic oil on the sealing material are: swelling of the sealing material and to produce softening ; harden the sealing material . The result is the loss of sealing performance of the sealing material , causing leakage and eventually the system pressure drop , out of control , that it can not work . Therefore, the impact of hydraulic oil required for the sealing material should be small, the sealing material to be used with the system to adapt .
        2.2 injection molding machine hydraulic oil varieties selection
        Hydraulic oil based on the selection and use of the principle features of the injection molding machine , requirements for lubricants : a viscosity index of 90 or more ; 40 e dynamic viscosity 32 mm2 / s or more ; N46, N68 , etc. ; foaming pressure should not use oil . Disable different types of different grades of oil. Optional containing anti-wear agent , anti -oxidants , anti-corrosion additives in oil.
        3 Hydraulic oil pollution hazards and control
        3.1 pollution hazards
        Pollution is the hydraulic system oil is in some cases detrimental to system performance and life of the tainted dirt . Common forms of pollution have residual oil pollution own pollution, fuel tanks , tubing, components, intrusion contamination from the surrounding environment , the air , the maintenance component assembly and disassembly , as well as the system itself generates pollution. 90% of the vane pump failures are due to dirty oil caused .
        Filter blocked , causing difficulties pump suction intake air , heat pump , generating noise ; accelerated pump wear , resulting in leakage increased , resulting in lower volumetric efficiency of the pump , shortened component life , reduce oil output , resulting actuator movement slow down ; stuck or sliding spool valve wear parts , the spool failure, leading to an electromagnetic coil failure and even cause accidents ; accelerate damage to the seals ; cause deterioration of the oil mixed with water .
        3.2 Pollution Control
        ( 1 ) the appropriate choice of filters is an important means to control pollution.
        The main role of the filter that filters the hydraulic oil mixed with impurities in the hydraulic system to filter impurities in the work is completed , to ensure clean hydraulic oil . Oil filter should be based on the technical requirements of the hydraulic system, according to filtering accuracy, flow capacity , operating pressure, fluid viscosity , temperature and other conditions to select models and require periodic inspection and cleaning.
        ( 2 ) to prevent dirt from outside intrusion.
        In the process of transportation and storage of different types of hydraulic oil should be stored separately in different clean container , and affix the seal , ready to store the date of record. Choice should be stored dry and ventilated shade and avoid direct sunlight or high temperatures caused by oxidative deterioration of hydraulic oil. Best buy oil new static discharge for a few days , and then injected into the system through the oil filter .
        Hydraulic oil temperature ( 3 ) control the hydraulic system work.
        Hydraulic oil temperature is too high for hydraulics unfavorable , the high viscosity of the oil is not only dramatically changed the oil , and the oil will become stable at room temperature corrosive , accelerate oxidative deterioration , do not decompose beneficial ingredients used to shorten the life of hydraulic oil , and even excessive vaporization leaving the pump suction air , does not work. General hydraulic system operating temperature is best controlled at 65 e less.
        ( 4 ) the periodic inspection and replacement of hydraulic oil.
        At regular intervals, the system checks the oil sample analyzed the degree of pollution is in compliance with the requirements . If you do not meet the requirements , it must be replaced immediately.
        ( 5 ) whether the hydraulic fluid in use or storage , should prevent mixing of the water .
        Oil mixed with a certain amount of water will make the oil turns milky , serious or even unusable.
        3.3 selection of filters
        To oil in the oil filter to filter out contaminants are commonly used way to control oil pollution. Injection molding machines are equipped with appropriate filters . When the oil filter failure or inability to restore function , should be promptly replaced. Select filters mainly consider filtering accuracy , flow capacity and pressure conditions . Oil particles of similar size with a gap of damaging the hydraulic components , so the choice of precision hydraulic system oil filter should be less than the gap among the smallest movement of the various components of the gap size . The flow capacity of the oil filter system flows through the oil filter to determine the maximum flow .
        Typically, a period of time after the oil filter , the filter pore size becomes small, so that reducing the flow through the oil filter , oil filter pressure drop increases. The magnitude of the pressure filter is generally 0101 ~ 011 MPa. Pressure drop is too high , the energy loss is too large , and may even damage the filter, so the choice of filter, be sure to add some margin on the basis of maximum flow , so that the original oil filter differential pressure will not be too high.
        4 hydraulic oil replacement technology
        4.1 oil change steps and precautions
        ( 1 ) The hydraulic oil tank with oil change machine extraction , demolition tubing and various hydraulic cylinders, replacement of wearing seals, stringent cleaning tank and oil filter .
        ( 2 ) with a low viscosity hydraulic oil flushing , start the motor , low-speed test run .
        ( 3 ) Add a new hydraulic fluid to a predetermined position. Hydraulic oil into the front tank to be cleaned . Open the fuel tank cap, into the hydraulic oil until the oil level in the highest position of the table. After boot operation , note positive position . On a regular basis in the hydraulic oil sampling tests , under normal conditions of use , sampling once every six months . More than 80% capacity utilization equipment , sampling once every three months .
        Oil change indicator according to the hydraulic oil oil change , oil change should pay attention to :
        ( 1 ) Before replacing the hydraulic oil, hydraulic oil tank older to drain the entire system must first program to clean ;
        ( 2 ) Replace the hydraulic oil system must comply with the requirement to use oil grades , and should have been tested for specification compliance ;
        ( 3 ) new hydraulic oil into the tank after filtration , filtration accuracy not less than the filtration system accuracy ;
        ( 4 ) When refueling, note mouth drums , tank port , filters out the tubing clean.
        4.2 Hydraulic system replacement
        Hydraulic oil common faults and solutions commonly used in the injection molding machine hydraulic components include : pump , motor oil ; valve ( check valve , valve, pressure valves, flow valves, proportional control valves, servo valves ) ; hydraulic attachments, such as accumulators , filters , blocking indicator , pressure switches , pressure gauges selection switch , pressure gauge valve, the oil cooler. Leakage of the hydraulic system , especially the high-pressure oil leak , will directly affect the machine work, such as mold is not in place , the injection pressure is inadequate. Special attention is to be a one-way valve hydraulic systems requiring regular dismantling , because the one-way valves open and close frequently in high impact , collide with the valve spool , easily damage the sealing surface .
        As the hydraulic system failure is often not as straightforward mechanical failure , which caused difficulties for maintenance , but if we continue to routine maintenance , you can effectively prevent the occurrence of various failures to achieve a multiplier effect. Injection molding machine hydraulic system is toward the high control accuracy , high sensitivity , low noise , energy saving , proportional, servo , computer program direction.
        Features injection molding machine hydraulic control system : strict work according to the pilot program ; each injection cycle pressure and flow systems is according to process requirements change .
        Replacing the hydraulic oil of Example 5
        Fully automatic plastic injection molding machines , for example, the volume of 116 m3 introduced to replace the fuel tank of hydraulic oil .
        Automatic plastic injection molding machine with oil indicator. When the standard hydraulic oil impurities exceeds a set time , the oil indicator light on the front panel , then, should be completed in the product cycle , down to check the oil situation , taking replace hydraulic oil, replace the filter or clean filters and other measures to exclude failure before use. Hydraulic oil change steps are:
        ( 1 ) Purchase Shanghai refinery production of L-HM 68 6 hydraulic oil barrels ( about 1 t). Contact factory sales department , ask for certification and quality indicators single laboratory , according to a single laboratory batch sampling indicated about 1 L, sent by GB 1111811-94 quality inspection department laboratory abrasion resistance, oxidation stability, hydrolytic stability , thermal stability , filtration, shear stability and other indicators.
        ( 2 ) Prepare the cleaning of oil ( 10 # oil ) , kerosene, leather , gauze, cotton mops, empty oil drums , oil seals and other auxiliary materials.
        ( 3 ) with the oil filter to pull out the old oil tank . Removing the fuel tank , filters, relief valves, solenoid valves , etc., and clean with kerosene and replace seals . Oil cooler cleaning . Injection molding machine hydraulic system will generate a lot of heat when working , causing the oil temperature rise , oil viscosity decreased leakage increases, the consequences are unstable velocity, also causing changes in the gap between the thermal expansion coefficients of different moving parts , mechanical stuck ; in addition, the high temperature accelerated oxidative deterioration of oil. Therefore, the oil can not exceed 55e, general injection molding machines are equipped with tube -type oil cooler in order to return the oil to cool .
        ( 4 ) remove the oil tank cleaning oil . Due to larger fuel tank , the staff need to wear leather into the tank thoroughly scrub.
        ( 5 ) oiling the cursor to the highest level (H -bit ) . Trial production after 8 h , observe the oil level and fill to the cursor between the lowest (L bit ) and H bit .
        6 Conclusions
        ( 1 ) different varieties , different brands of hydraulic oil may not mix , before adding new oil and after use , should be carried out sampling tests to ensure oil quality.
        ( 2 ) work with particular attention to the oil spill problem, the oil spill would adversely affect the work , causing environmental pollution and energy losses.
        ( 3 ) strict control of the hydraulic oil temperature .
        ( 4 ) the timely elimination of leakage in the system .
        ( 5 ) regular cleaning of hydraulic system components.

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