11 - ericssonhistory.com
11 - ericssonhistory.com 11 - ericssonhistory.com
Corrugating Machine The aim in the development of this machine was that it should be easy to transport and install, easy to handle, and be easily adjustable for different duct diameters. The result is the corrugating machine LVA 29901 (Fig. 1) which works on the following principles. • The duct, firmly clamped in the machine, is caused to rotate. • The duct is heated along a helix by five pointed flames from burners placed on a carriage which runs along the duct. • The duct is subjected to a continuous axial pressure. As these operations take place simultaneously, a helical corrugation is produced along the duct. The speed of rotation, the heating capacity of the flames and their distance from the duct, the speed of the carriage and the axial pressure must be adjusted to the duct diameter and wall thickness in order to produce the desired corrugation. Fig. 1 Corrugating machine LVA 29901 34
The corrugating process shortens the plastic duct by 6-7 %. The machine requires a space of 1.5 X 8 m indoors or outdoors. In the latter case the site must be well protected against rain and wind. Indoors the machine is bolted to the floor. No special foundation is required. The machine corrugates between 7 and 8 ducts per hour. One man can look after three machines. This means that the production per man and eighthour shift is about 1000 duct metres of corrugated plastic duct, for which about 180 non-corrugated 6 m ducts are required. The machine is driven via a rectifier from a single-phase commercial lighting supply and has tappings for 110-240 V. The power requirement is about 0.2 kW. The burners are fed from a LP gas cylinder placed on the carriage. The LP gas cylinder suffices for about three days of operation. Corrugated Ducts Corrugated ducts have the following advantages compared with noncorrugated. • Their radial rigidity is several times greater. The wall thickness can therefore be reduced, so allowing the use of cheaper ducts. Fig. 2 Corrugated plastic duct • A considerably better lateral flexibility is obtained, which permits their use in curved conduit. The minimum radius of curvature for a noncorrugated 90 mm duct is about 10 m, for a corrugated about 2.5 m. This results not only in a smaller number of manholes, since the conduit can follow curved streets and be taken round obstructions, but it also means that the cross-section can be changed between two manholes. The group of ducts can be divided 10—15 m before the manhole for example, one half being taken along one side of the manhole and the other half along the other side (Fig. 3). This has the great advantage that the cables can pass straight through the manhole along the two sides, an especially important point with heavy plastic cables, which are difficult to bend and are much more elastic than lead-sheathed cables. • The longitudinal flexibility increases, which is an important point in conjunction with the embedment of ducts in a manhole wall or the like. As the expansion of the plastic duct is considerably greater than that of the surrounding soil, it is very difficult to embed a non-corrugated duct without the risk of strain caused by even moderate fluctuations of temperature. These strains are liable to produce untight inlets to manholes. The corrugated duct, on the other hand, functions like a concertina and the ends of the plastic ducts can be embedded without risk of tensile strains. Fig. 3 Division of a group of ducts when passing through a manhole 35
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Corrugating Machine<br />
The aim in the development of this machine was that it should be easy to<br />
transport and install, easy to handle, and be easily adjustable for different<br />
duct diameters. The result is the corrugating machine LVA 29901 (Fig. 1)<br />
which works on the following principles.<br />
• The duct, firmly clamped in the machine, is caused to rotate.<br />
• The duct is heated along a helix by five pointed flames from burners placed<br />
on a carriage which runs along the duct.<br />
• The duct is subjected to a continuous axial pressure.<br />
As these operations take place simultaneously, a helical corrugation is produced<br />
along the duct. The speed of rotation, the heating capacity of the flames<br />
and their distance from the duct, the speed of the carriage and the axial pressure<br />
must be adjusted to the duct diameter and wall thickness in order to<br />
produce the desired corrugation.<br />
Fig. 1<br />
Corrugating machine LVA 29901<br />
34
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