MIL-STD 810 Mechanical Vibration
The MIL-STD 810 mechanical vibration test standard specifies procedures for the best mechanical vibration testing. Method 528.1, mechanical vibrations of shipboard equipment, establishes requirements for environmental and internally excited vibration testing. This is testing of Naval shipboard equipment installed on ships.
Keystone Compliance is a mechanical vibration testing lab with significant MIL-STD 810 mechanical vibration testing experience. Our mechanical vibration laboratory and test engineers understand the nuances of the vibration profiles and vibe testing.
The following information is extremely technical in nature. It was derived from test method 528.1 of MIL-810H mechanical vibration compliance standard. Even though the language is from 810H mechanical vibration, it applies to previous versions of the standard. This includes MIL-STD 810G mechanical vibration.
When is Method 528.1 Applicable?
The test procedures specified herein are applicable to shipboard equipment that are subject to mechanical vibrations on Navy ships. Most Navy ships have conventional shafted propeller propulsion. However, the test can be tailored for non-conventional propulsor types such as waterjet or podded propulsors. For internal excitation caused by unbalanced rotating components of Naval shipboard equipment, use the balance procedure.
For mechanical vibrations associated with reciprocating machinery and lateral and longitudinal vibrations of propulsion systems and shafting, see MIL-STD-167-2A.
What are Best Balance Procedure Methods for Rigid Rotors?
Except for machinery operating below 150 rpm, all balancing is done by balancing equipment requiring rotation of the workpiece. This may be either shop or assembly balancing type equipment. The minimum detectable unbalance of the balancing machine used shall be below the residual unbalance specified.
The allocation ratio of unbalance between two planes of correction must not be more than 2 to 1. The amount allocated must be proportional to the distance from the other plane to the center of gravity of the rotor. This distance is then divided by the total distance between planes.
For machinery rated at lower than 150 rpm, the rotor including shaft may be balanced on two knife edges. Then apply correction to attain a static balance.
What Methods Should Be Used to Attach the Test Item for Shipboard Equipment?
For all ship vibration tests, the item is secured to the machine. This is done at the same points of attachment used to secure it to the shipboard. In cases where alternate attachment points are specified, tests shall be performed using each attachment configuration. Equipment that is hard mounted, or not isolation mounted, aboard ship shall be hard mounted to the shaker testing equipment.
For equipment designed to be secured to a deck and a head brace support, a vertical bracket is used. This simulates a bulkhead. The bracket shall be sufficiently rigid. This ensures that its motion is essentially the same as the motion of the platform on the testing machine.
For isolation mounted shipboard equipment, see below.
What Methods Should Be Used to Attach the Test Item for Shipboard Portable and Test Equipment?
There is portable and test equipment that is designed for permanent or semi-permanent attachment to a ship structure. For 810 mechanical vibration testing, equipment is attached to the testing machines the same way it is attached to the ship. Equipment that is not designed for permanent or semi-permanent attachment is secured to the testing machine by suitable means.
What Methods Should Be Used to Attach the Test Item for Achieving the Proper Orientation for Vibration Test?
Test items shall be installed on vibration testing machines in the same manner as the direction of vibration will be. So, it is installed along each of the three rectilinear orientation axes of the equipment, as installed on shipboard. These axes are: vertical, athwartship, and fore and aft.
On a horizontal vibration-testing machine, the test item may be turned 90 degrees in the horizontal plane. This is so that it is vibrated in each of the two horizontal orientations. A test item in the ship vibration lab is never installed in any other way than its normal shipboard orientation.
What Methods Should Be Used to Attach the Test Item for Isolation Mountings?
Type I testing of equipment that is installed on a shipboard on isolation mounts, is performed on isolation mounts. Or the item is hard mounted to the testing machine. This testing of an item on isolation mounts is only valid for the mount type and configuration used for the test.
Ensure the transmissibility across the mounts does not exceed 1.5. This is within the blade frequency range of 80 percent to 115 percent of design RPM.
Equipment that is tested for Type I vibrations by hard mounting to the test fixture throughout the duration of the test. This test is valid for either hard mounted or isolation mounted shipboard installations. This is provided that the isolation mounts are Navy standard mounts.
What methods should be used to attach the test item for Internal Isolation or Shock Mountings?
Equipment, like electronic cabinets, incorporate other isolation mountings integrally within the equipment box. These are tested with the internal mountings in the normal shipboard configuration or as specified.
Equipment Operation
Except as noted below, the test item shall be energized or operated to perform its normal functions. Equipment that is difficult to operate on the testing machine shall be energized and subjected to operating conditions during the test. The test item shall then be operated after the test to demonstrate that there is no damage from the test.
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There have been several versions of mechanical vibration testing procedures in MIL-STD-810 mechanical vibrations of shipboard equipment testing. Below is a list of each version and the appropriate method number: