European directivesand other documents emphasis the necessity of reducing the flammability risk when using industrial fluids (hydraulic fluids, lubricants, processing fluids like those used in steel treatment and cutting etc.), especially in explosive atmosphere. Thus, “in particular, where fluids are used, machinery must be designed and constructed for use without risks due to filling, use, recovery or draining.” Risk assessment implies a complex analysis of design, equipment, procedures and operators. Thus, the same document underlines that “machinery must be designed and constructed to avoid all risk of fire or overheating posed by the machinery itself or by gases, liquids, dust, vapours or other substances produced or used by the machinery.”
Both manufacturers and users ask for tests that could certify fluid flammability characteristics,preferring ISO or ASTM standards.Many documents, including EU Directives, give recommendations to use standardised tests for estimating flammability of fluids. The evaluation of fire resistance of a hydraulic fluid cannot be done by one test only and the aspects of fire resistance have to be pointed out by several tests,including those simulating on small scale the worst scenario that could happen in real applications using hydraulic fluids. Many of these tests give a result as “pass” or “not pass”.The fluid that passed a particular test or, better, a set of tests, is included in recommendations or approvals, but these ones are specific to regional or national reglementations
TESTING PROCEDURE：
The tests were done with the help of an original equipment (Fig. 1) allowing a dedicated soft assistance in order to protect the operator and to sustain reproducibility, according to the standard SR EN ISO 20823:2004 Petroleum and related products. Determination of the flammability characteristics of fluids in contact with hot surfaces - Manifold ignition test. This test simulates an accident or the hazardous event when a fluid drops on a hot surfaces: 10 ml of fluid is dropped during 40…60 seconds on a manifold kept heated at a constant temperature, from a distance of 300±5 mm above the manifold surface. For each temperature and fluid there were done 3 tests. The highest temperature, for which the fluid does not burn or ignite, was established is the same “verdict” was obtained for all the three tests. All the temperature values given in this study have the accuracy given in Figure 2. The equipment is controlled and assisted by a PC with a dedicated soft in order to protect the operator from being near the heated zone. Figure 2 presents the display of the soft.
There are several reasons of fluid leaking:
1、fatigue of the system elements, under normal or severe exploitation (cracks, creep, ageing),or due to an adequate maintenance,
2、cyclic or accidental thermal expansions, bolts stretch;
3、changes of fluid properties due to exploitation,especially temperature rising that makes the fluid to become thinner,
4、the efficiency loss of seals and hoses in time, due to their modifications produced by long exposure to temperature or/and chemicals, but also by trapping “foreign” particles (solid,liquid, gaseous or mixtures of them);
5、screw-up operations: a controlled mounting and a preventive maintenance decrease the leak probability under functioning conditions.
It is also important to respect procedures for starting and stopping the equipment;
6、operator’s faults; regular trainings could significantly reduce these events.
There were tested the following grades of hydraulic oils HLP 68 X-Oil, HFC Prista, Shell Irus Fluid DR 46, a rapeseed oil (obtained after a dewaxing process) and an emulsion 5% MHE 46 in water as recommended by Prista producer. There were identified distinct behaviours of these fluids under the test conditions.
Shell Irus Fluid DR 46 is a tri-aryl phosphate ester fire resistant hydraulic fluid. It contains carefully selected additives to give superior oxidation and hydrolytic stability. Shell Irus Fluid DR 46 should be used in hydraulic systems operating in close proximity to potential ignition sources. This includes equipment such as die-casting machines, billet loaders, electric arc furnaces, forging presses and others operating in fire hazard situations.
PRISTA HFC is a fully synthetic fire resistant waterglycol based hydraulic fluid blended with an additive package to improve the anti-wear properties and corrosion protection of the finished product.
HLP 68 X-Oil is an optimized alloyed hydraulic oil with a high performance level and a broad field of industrial application. It especially distinguishes with good viscosity-temperature behaviour, high ageing stability and reliable corrosion protection.
Additives provide an excellent wear protection under extreme loads, too. The behaviour against sealing materials is neutral.
Prista MHE-40 is used as 5% working fluid in oil-inwater emulsion for hydraulic systems with high risk of flammability. The tests were done on the fully mineral oil and for the emulsion 5% MHE 40(vol.) in water.