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Defence, R & D

Case study of DRDL
The sample rack assembly passed all the Type Approval tests at first trial. From the time that the design work was taken up it took more than a year before all the tests could be completed on the sample model. After these tests had been passed successfully, 108 cabinets were manufactured and delivered to the DRDO organization. After the equipment integration and hot staging had been completed, a team was sent for the dismantling and unpacking of the equipment. Thereafter, when the units were dispatched to the sites, the President team was sent to each of the sites in turn to assist in the re-assembly of the kits inside the sea buoys.

The DRDO team, as well as the Naval authorities, were fully satisfied with the end product and APW President was left very much richer by the experience gained.

The Company
The customer is a leading member of the Defence Research and Development Organisation (DRDO). This unit provides specialized defence equipment required by each of the three services of the Indian Military i.e. the Air Force, the Army and the Navy.

The Problem
The project in question was of a classified nature. Due to this security aspect full details were never forthcoming and an acceptable solution had to be worked out despite this limitation. It involved specialized transmitter and receiver equipment that had to be housed in 19 racks. These transmitters and associated equipment were to be placed inside sea buoys which would be anchored outside key harbour entrances. The sole entry into these buoys is a circular hole which permits only one person to enter the buoy at a time. Inside the buoy there is a platform on to which the 19 rack is to be grouted on shock absorbers.

A number of these buoys were already in place outside the harbours along the western and eastern coasts of the country. This meant that after installation of the equipment in the cabinets, and the testing at the DRDL test facility, everything would have to be dismantled and shipped to the sites. Thereafter the individual parts would need to be taken inside the buoy, one-by-one, and the entire rack assembly re-erected inside the buoy. After this the transmitter and receiver equipment would be installed and integrated once again as per the layout diagram provided by the Naval authorities.

The Solution
After several rounds of discussions with the DRDO personnel and the Naval project team we decided on the following :

• To use a mix of aluminium profiles from the tried and proven Series 10 and Series 12 family of cabinets. A robust aluminium frame was necessary to meet the rigidity criteria and vibration specifications, as well as to combat the corrosion problem posed by the sea atmosphere.

• All parts such as covers, doors and other panels would need to be made from aluminium and the fasteners would have to be of stainless steel only. Non-magnetic material had to be used exclusively.

• Suitable gasketing had to be incorporated so that the cabinet sealing was to a protection level of IP55.

• All external parts such as covers, doors and other panels, as well as the frame members, would have to be powder coated in a combination of RAL 7035 and 7037 using polyurethene powder so as to protect against the sea atmosphere.

• The design of the top cover was critical as it had to incorporate a dome for entry of a cable having a large circular connector. But it was also necessary to ensure that water dripping from above would not enter the cabinet. Aluminium welding had to be used extensively.

• In order to meet the rocking movement caused by the waves and other vibrations due to heavy seas, the cabinet would have to be grouted to the floor of the buoy on four shock mounts. These were chosen on the basis of the load to be supported, as well as the nature of the vibrations. In addition, two shock mounts were placed at the top rear face of the cabinets and these two corners of the cabinet were fixed to the bulkhead via these shock mounts.

• The airflow design was critical and special provisions had to be made owing to the nature of the heat load. The special requirement here was that the maximum heat dissipation would occur only in bursts of fairly short duration, whereas most of the time the equipment would be in an idle state, generating little heat. Thus the airflow had to be designed to handle the peak load without allowing heat build-up within the cabinet. What complicated the problem was that the only access for air entry was from the front of the cabinet, at the bottom, as the rest of the cabinet was fully occupied by the equipment. But the air so introduced had to be expelled upwards at the rear of the cabinet as this was the only path available, leading to the exhaust vent, which was at the top of the cabinet. Therefore a Cross-flow fan module with a centrifugal impeller was selected. This was fitted into a special compartment at the bottom rear of the cabinet, utilizing 4U of space. Special ducting was provided so that the air could be drawn in from the front through a filter and then ducted to the cross flow fan. And all this had to be done without compromising the IP55 sealing of the cabinet.
















The Benefits
The sample rack assembly passed all the Type Approval tests at first trial. From the time that the design work was taken up it took more than a year before all the tests could be completed on the sample model. After these tests had been passed successfully, 108 cabinets were manufactured and delivered to the DRDO organization. After the equipment integration and hot staging had been completed, a team was sent for the dismantling and unpacking of the equipment. Thereafter, when the units were dispatched to the sites, the President team was sent to each of the sites in turn to assist in the re-assembly of the kits inside the sea buoys.

The DRDO team, as well as the Naval authorities, were fully satisfied with the end product and APW President was left very much richer by the experience gained.
Products Used

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