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The effect of the additional wear due to contaminant particles may be expressed as an additive term in the basic wear relationship. It will be noted from the derivation of equations for the effect of contaminant particles on actuator surface wear and the possibility of stiction problems that a probability of damaging particles entering the gap between the piston and cylinder must be estimated. The contaminant factors involved are as follows: Hardness - The wear rate will increase with the ratio of particle hardness to actuator surface hardness. It will normally be the hardness of the piston that will be of concern. If the ratio is less than 1, negligible wear can be expected. Number of particles - The wear rate will increase with a concentration of suspended particles of sufficient hardness. Size - For wear of the piston or cylinder to occur, the particle must be able to enter the gap between the two surfaces. The particle must also be equal to or greater than the lubrication film thickness. With decreasing film thickness, a greater proportion of contaminant particles entering the gap will bridge the lubrication film, producing increased surface damage. Shape - Rough edged and sharp thin particles will cause more damage to the actuator surfaces than rounded particles. As the particles remain in the gap, they will become more rounded and produce less wear. It is the more recent particles being introduced into the gap that cause the damage. The contaminant multiplying factor can be established as follows: CCP = CH*CS*CN (9-19) Where: CH = Particle hardness multiplying factor = HP/HC Hp = Piston Hardness (See Table 9-1) Hc = Cylinder Hardness (See Table 9-1) Cs = Filtration multiplying factor = Filter size (micron) /10 CN = Particle size multiplying factor - For most applications the particle size factor will be equal to approximately 1.0. For severe conditions where the number of contaminants and particle size can be expected to increase, the particle size factor may be expected to approach a value of 2.0. 9.3.3 Temperature Multiplying Factor The effect of the temperature of the surface on the wear rate is a complicated phenomenon, because the corrosion of the wear debris at different temperatures Actuators 9-14 Revision C

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