Forgings for shipbuilding
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Forgings for shipbuilding

Forgings for shipbuilding

(Propeller and intermediate shafts, couplings, swing rings, rudder spindles, barrels, hubs, gear units, propeller screws). We provide production and delivery of forgings for shipbuilding.

The range of produced products is as follows: shafts, including propeller, intermediate, thrust, and stern-tube ones; rudder spindles; swing rings; coaming forgings; stern boss forgings; pipe forgings for swing-masted devices, cases, walls, barrels, pistons, gear units, couplings, jaws, etc.

Forgings weighing up to 8 tons, with a length up to 8 000 mm are made of 38CrNi3MoVA, 14Cr17Ni2, 40CrNi2MoA, 38Cr2Ni2MoA, 36Cr2Ni2MoVA, 08Cr10Ni20Ti2, 08-12Cr18Ni10Ti, St.35, 07Cr16Ni4Nb, 40CrNi, 38CrMo, 34CrNiMo6, 42CrMo4, Ck50Mod and special grades according to GOSTs (National standards) and foreign standards as well as SEW, EN, DIN, etc., and rules of DNV, LR, GL, BV, РМРС, and РР.

Pipe forgings for swing-masted devices are made of steel grade 08Cr10Ni20Ti2.

External diameter of forgings ranges from 240 to 530 mm, internal diameter from 150 to 400 mm, length up to 8 000 mm, weight up to 8 tons.

Intermediate or propeller shaft is connected to the driveshaft of a motor, away from it at an angle to the horizontal rolling axis; otherwise a propeller cannot be sunk to a sufficient depth as a result of a shallow draft.

In the point where the shaft goes through the hull, a shaft tube is mounted in order to ensure its water tightness. Bearings are fixed inside the tube to minimize resistance to the shaft rotation. In single-propeller models, the shaft tube goes through the keel. Therefore, two wood strips are glued or screwed one each side to avoid its weakening.

In multipropeller models, it is advisable to glue short plywood bars to the hull bottom in the shaft tube passage points.

Shafts are made of high-strength rod steel with a diameter of 2.5, 3.0, 4.0 or even 5.0 mm, depending on the type of a model. Shafts for high-speed models must be thoroughly balanced. Shaft tube is made of brass tube with a diameter as appropriate according to the bearing size. In order to avoid transfer of nuisance vibrations from the shaft to the hull, the shaft tube is reinforced with a special brass plate bracket on outlet of the hull.

One end of the bracket is brazed to the shaft tube; the other one screwed to the hull of the vessel. Bearings, usually friction ones, are installed at both ends of the shaft tube.

Friction bearings are easily made of bronze tubes (or rather their sections). Ball bearings are quite difficult to install and adjust to fit. However, they are widely used at high-speed models, as they have frictions factors lower than those of friction bearings. All rotating parts should be lubricated/greased before launching, especially on high-speed models and models with internal-combustion engines. Installation of a plain oil cup with a ball valve will ensure continuous lubrication.

Connecting couplings are used to connect intermediate or propeller shaft with the driveshaft of a motor. They may be of various types, including rigid, flexible and joint type ones. Rigid couplings have simple construction. It consists of two pins, firmly attached to the shafts. Flexible couplings are used, where the shaft axes cannot be aligned and in order to reduce shaft oscillations. If the power transmitted is low, a plain spring soldered to the driveshaft and propeller shaft ends can be used. For greater power, installation of an intermediate washer made of flexible material - rubber or skin - would be more reliable. It is placed between the shaft flanges. If it is necessary to install the shafts at particular or alternate angles, the best way is to use joint-type couplings. Gear drives, such as reduction gear units, are used to connect two or more propeller shafts to the motor shaft. For this purpose, bevel or cylindrical gears are typically used. Shown is the simplest bevel gear drive used for operation with propeller wheels.

Propulsion systems. The most commonly used propulsion unit is a propeller screw. It consists of a hub with two (or more) blades soldered to it or as a single-piece cast. Propeller performance decreases with the increased number of blades. Two-blade propellers are installed mainly on high-speed models; three-blade ones are used on a common motor as well as radio-controlled speed vessels. Rotating propeller throws the water flow back, while the vessel is moved forward. The propeller should be mounted in the point of the deepest stern immersion in order to increase its thrust. A single-propeller drive is typically more efficient than a double-prop one. There are right-hand and left-hand propellers depending on the direction of their rotation: rightwards or leftwards (astarboard or aport), when looking in the direction of the vessel movement. In case two propellers are installed, they should rotate in the opposite directions. The blade side faced away from the vessel is called “driving face,” and the one faced towards the vessel is called “back face.” A blade of the simplest shape represents a part of helicoidal surface. Axial displacement of the blade per revolution of a propeller, if rotated in a solid body, is called a geometric pitch of the propeller.

Propeller pitch is a constant value for any point of its surface. Blade section has a winglike shape and is very thin. Fast propeller rotation is associated with the increased water inflow velocity resulted in rarefication and ebullition of water. Such ebullition, occurring as a formation of water steam-filled voids in the liquid, is called cavitation. It causes noise, vibration and propeller blade erosion thereby reducing its useful power. Therefore, a propeller rotation rate should be chosen so that it would develop speeds that cause cavitation.

Cavitation cannot be avoided at very high speeds but may be reduced at lower speeds by increasing blade faces and reducing their sections. Cavitation can also be limited by sharpening the entrance section and rounding exit edge of the blade. Propeller screws should be made of high-strength materials in order to reduce erosion. Let’s see how turning angles of the propeller blades are determined. A blade turning angle to the propeller axis should be increased with distance from the center.

The common practice is to begin with the determination of pitch and diameter of the propeller and diameter of the hub, and then proceed with graphical determination of angles. A distance equal to the propeller pitch is plotted on the horizontal line, and then distances equal to circumferences of the propeller and the hub should be plotted on a perpendicular erected from the obtained point.

The points obtained are connected with the reference point of the line to obtain angle “а,” equal to the blade turn near the hub, and angle “b” corresponding to the turn at the blade end. Intermediate angles can be found with a reasonable degree of accuracy by plotting circumferences described by the respective intermediate points of the blade.

Propellers are made of brass for standard models and of heavy-duty steels for high-speed models.

The hubs are turned out of round blanks of brass or steel, respectively. Grooves for the blades are cut on the hubs according to predetermined rake angles with respect to the shaft axis. Blades are inserted into those grooves and carefully soldered with brass or silver. The blades are made of brass or steel plates; thickness selected depending on rotation torque transferred to the propeller. Finally, they are filed and carefully ground.

Thread for the connection of the hub to the propeller should be cut before the insertion of blades. It should be noted that the direction of the hub thread should be opposite to that of the shaft rotation. In addition, a fairing of rod steel or brass should be mounted at the external side of the hub and secured with a stud screw.

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