Section 1 Castings for propellers

1.1.1 This Section gives the requirements for copper alloy castings for one-piece propellers and separately cast blades and bosses for fixed pitch and controllable pitch propellers (CPP). These include contra-rotating propellers and propulsors fitted to podded drives and azimuth units.

1.1.2 These castings are to be manufactured and tested in accordance with the appropriate requirements of Chapters Ch 1 General Requirements and Ch 2 Testing Procedures for Metallic Materials and the specific requirements of this Section.

1.1.3 As an alternative to Ch 9, 1.1 Scope 1.1.2, castings which comply with National or proprietary specifications may be accepted provided that these specifications give reasonable equivalence to the requirements of this Section or alternatively are approved for a specific application.

1.1.4 The appropriate requirements of this Section may also be applied to the repair and inspection of propellers which have been damaged during service.

1.1.5 Generally, survey and certification are to be carried out in accordance with the requirements of Ch 1 General Requirements.

1.2.1 All castings are to be manufactured at foundries approved by Clasifications Register (hereinafter referred as 'LR').

1.2.2 The pouring is to be carried out into dried moulds using degassed liquid metal. The pouring is to avoid turbulent flow. Special devices and/or procedures are to be used to prevent slag flowing into the mould.

1.3.1 All castings are to be free from surface or internal defects, including cracks, hot tears or other imperfections, which would be prejudicial to their proper application in service.

1.3.2 Minor casting defects which may still be visible after machining, such as small sand and slag inclusions, small cold shuts and scabs are to be suitably removed by mechanical means such as chipping or grinding.

1.3.3 The removal and repair of defects are dealt with in Ch 9, 1.9 Rectification of defective castings and Ch 9, 1.10 Weld repair procedure.

1.4.1 The chemical compositions of samples from each melt are to comply with the manufacturing specification approved by LR and also with the overall limits given in Table 9.1.1 Chemical composition of propeller and propeller blade castings. In addition to carrying out chemical analysis for the elements given in the Table, it is expected that manufacturers will ensure that any harmful residual elements are within acceptable limits.

1.4.2 The use of alloys whose chemical compositions are different from those detailed in Table 9.1.1 Chemical composition of propeller and propeller blade castings will be given special consideration by LR.

1.4.3 The manufacturer is to maintain records of all chemical analyses, which are to be made available to the Surveyor so that he can satisfy himself that the chemical composition of each casting is within the specified limits.

1.4.4 When a melt is wholly prepared from ingots for which an analysis is already available, and provided that no significant alloy additions are made during melting, the ingot maker's certified analysis can be accepted subject to occasional checks as required by the Surveyor. If any foundry returns are added to the melts, the ingot manufacturer's chemical analyses are to be supplemented by frequent checks as required by the Surveyor.

1.4.5  For alloys Grade Cu 1 and Cu 2, the zinc equivalent shall not exceed 45 per cent, and is to be calculated using the following formula:

where A is the algebraic sum of the following:

1 × % Sn

5 × % Al

−0,5 × % Mn

−0,1 × % Fe

−2,3 × % Ni

1.4.6 Samples for metallographic examination are to be prepared from the ends of test bars cast from every melt of Grade Cu 1 and Cu 2 alloys. The proportion of alpha-phase determined from the average of at least five counts is to be not less than 25 per cent.

1.5.1 At the option of the manufacturer, castings may be supplied in the `as cast' or heat treated condition. However, if heat treatment is to be applied, full details are to be included in the manufacturing specification.

1.5.2 If any welds are made in the propeller casting, stress relief heat treatment is required in order to minimise the residual stresses. Requirements concerning such heat treatment are given in Ch 9, 1.10 Weld repair procedure.

1.6.1 Test samples are to be cast separately from each melt used for the manufacture of propeller or propeller blade castings.

1.6.2 The test samples are to be of the keel block type, generally in accordance with the dimensions given in Figure 9.1.1 Keel block type test sample and are to be cast in moulds made from the same type of material as used for the castings.

1.6.3 The method and procedures for the identification of the test specimens, and the castings they represent, are to be agreed with the Surveyor. The identification marks are to be transferred and maintained during the preparation of test specimens.

1.6.4 Where castings are supplied in the heat treated condition, the test samples are to be heat treated together with the castings which they represent.

1.6.5 Where the manufacturer proposes test specimens to be taken from integrally cast test samples, this is to be the subject of special agreement with LR. Wherever possible, the test samples are to be located on the blades in an area lying between 0,5 to 0,6 R, where R is the radius of the propeller. The test sample material is to be removed from the casting by non-thermal procedures.

1.7.1 At least one tensile test specimen representative of each cast is to be prepared. The dimensions of this test specimen are to be in accordance with Figure 2.2.1 Test specimen dimensions for forgings and castings - I in Chapter 2.

1.7.2 The results of all tensile tests are to comply with the requirements given in Table 9.1.2 Mechanical properties for acceptance purposes: propeller and propeller blade castings.

Figure 9.1.1 Keel block type test sample

Table 9.1.2 Mechanical properties for acceptance purposes: propeller and propeller blade castings

Alloy designation	0,2% proof stress N/mm2 minimum	Tensile strength N/mm2 minimum	Elongation on 5,65% minimum
Grade Cu 1 Manganese bronze (high tensile brass)	175	440	20
Grade Cu 2 Ni-manganese bronze (high tensile brass)	175	440	20
Grade Cu 3 Ni-aluminium bronze	245	590	16
Grade Cu 4 Mn-aluminium bronze	275	630	18

1.7.3 The mechanical properties of alloys whose chemical compositions do not accord with Table 9.1.1 Chemical composition of propeller and propeller blade castings are to comply with a manufacturing specification approved by LR.

1.8.1 Propeller castings should be visually inspected at all stages of manufacture, and all finished castings are to be 100 per cent visually inspected by the manufacturer. The manufacturer is to draw any significant imperfections to the attention of the Surveyor. Such imperfections are to be verified in accordance with Ch 9, 1.9 Rectification of defective castings.

1.8.2 All finished castings are to be subjected to a general visual examination by the Surveyor, in addition to the visual inspection carried out by the manufacturer. This is to include internal surfaces such as the bore and bolt holes. Where unauthorised weld repairs are suspected by the Surveyor, the area is to be etched (e.g. by iron chloride) for the purpose of confirmation.

1.8.3 For the purpose of these requirements, the blades of propellers, including CPP blades, are divided into three severity Zones A, B and C as shown in Figure 9.1.2 Severity zones in all propeller blades and detailed in Ch 9, 1.8 Inspection and non-destructive examination 1.8.4 for blades having skew angles of 25° or less and Ch 9, 1.8 Inspection and non-destructive examination 1.8.5 for blades having skew angles of greater than 25°. The definition of skew angle is given in the Rules and Regulations for the Classification of Ships, July 2022, Pt 5, Ch 7, 1.1 Details to be submitted, Pt 5, Ch 7, 1.1 Details to be submitted 1.1.2. Proposals by the propeller designer for a modified zone area based on detailed hydrodynamic load and stress analysis may be considered by LR in conjunction with the requirements of the Rules and Regulations for the Classification of Ships, July 2022, Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.7 and relevant sections within the appropriate Rules set.

Figure 9.1.2 Severity zones in all propeller blades

1.8.4  Skew angles of 25° or less:

• Zone A is the area on the pressure side of the blade from and including the root fillet to 0,4R and bounded on either side by lines at a distance 0,15 times the chord length C_r from the leading edge and 0,2 times C_r from the trailing edge, respectively. Where the hub radius (R_b) exceeds 0,27R, the other boundary of zone A is to be increased to 1,5R_b.
• Zone B includes the areas inside 0,7R on both sides of the blade, excluding Zone A.
• Zone C includes the areas outside 0,7R on both sides of the blade.

1.8.5  Skew angles of greater than 25°:

• Zone A is the area on the pressure side of the blade bounded by, and including, the root fillet and a line running from the junction of the leading edge with the root fillet to the trailing edge at 0,9R and passing through the mid-point of the chord at 0,7R and a point situated at 0,3 of the chord length from the leading edge at 0,4R.
• Zone A also includes the area along the trailing edge on the suction side of the blade from the root to 0,9R and with its inner boundary at 0,15 of the chord length tapering to meet the trailing edge at 0,9R.
• Zone B constitutes the whole of the remainder of the blade surfaces.

1.8.6 In propeller blades with continuously loaded tips (CLT), the whole of the tip plate and the adjoining blade to a distance of 100 mm is to be regarded as severity Zone B, see Figure 9.1.3 Severity Zone B at continuously loaded blade tip. For propellers with diameters less than 2 m, the width of this zone may be reduced to one tenth of the propeller radius.

Figure 9.1.3 Severity Zone B at continuously loaded blade tip

1.8.7 In addition, the palm of a CPP blade is divided into severity Zones A and B as shown in Figure 9.1.4 Severity zones for controllable pitch propeller blades.

1.8.8 If a CPP blade has an integrally cast journal, the fillets of the journal and the adjoining material up to a distance of 20 mm from the fillet run-outs are to be regarded as Zone B, as indicated in Figure 9.1.5 Severity zones in integrally cast CPP blade journals. The remainder of the surface of the journal may be regarded as Zone C.

1.8.9 Hubs of controllable pitch propellers are to contain a Zone A region at each blade port as shown in Figure 9.1.6 Severity zones for controllable pitch propeller hub. The remainder may be regarded as Zone C.

1.8.10 On completion of machining and grinding, the whole surface of each casting is to be subjected to a liquid penetrant inspection in accordance with a procedure acceptable to LR.

1.8.11 All liquid penetrant inspections on Zone A areas in the finished condition are to be made in the presence of the Surveyor.

Figure 9.1.4 Severity zones for controllable pitch propeller blades

Figure 9.1.5 Severity zones in integrally cast CPP blade journals

Figure 9.1.6 Severity zones for controllable pitch propeller hub

1.8.12 Liquid penetrant inspections on Zones B and C are to be performed by the manufacturer and may be witnessed at the Surveyor’s request.

1.8.13 The surface to be inspected shall be divided into reference areas of 100 cm². The indications detected shall, with respect to their size and number, not exceed the values given in Table 9.1.4 Allowable number and size of liquid penetrant indications in a reference area of 100 cm2. The area shall be taken in the most unfavourable location relative to the indication being evaluated.

1.8.14 Indications exceeding the acceptance standard in Table 9.1.4 Allowable number and size of liquid penetrant indications in a reference area of 100 cm2 shall be repaired in accordance with Ch 9, 1.9 Rectification of defective castings.

1.8.15 All defects requiring repair by welding in new propeller castings are to be recorded on sketches showing their locations and dimensions. Copies of these sketches are to be presented to the Surveyor prior to repair.

1.8.16 Where repairs have been made either by grinding, straightening or welding, the repaired areas are to be subjected to dye liquid penetrant inspection in the presence of the Surveyor, regardless of their location and/or severity zone.

1.8.17 Where no welds have to be made on a casting, the manufacturer is to provide the Surveyor with a statement that this is the case.

1.8.18 Where it is suspected that a casting contains internal defects, or where deemed necessary by the manufacturer or Surveyor, further volumetric NDE should be carried out, where practical, in the form of radiographic and/or ultrasonic testing. The acceptance criteria are to be agreed between the manufacturer and LR in accordance with a recognised standard. ASTM E272 (Severity Level 2) or equivalent is to be the radiographic acceptance standard for copper alloy castings.

1.8.19 Due to the attenuating effect of ultrasound within cast copper alloys, ultrasonic testing may not be effective in some cases, depending on the shape/type/thickness, and grain growth direction of the casting. Generally, ultrasonic testing of Cu 1 and Cu 2 grades is not effective. For Cu 3 and Cu 4, ultrasonic inspection of defects may be possible and effective ultrasound penetration into the casting is to be practically demonstrated on the item. This would normally be determined by way of back-wall reflection, and/or target features within the casting. In the absence of any proposed acceptance standard by the manufacturer, UT acceptance criteria is to comply with the requirements of Ch 4, 4.6 Non-destructive examination 4.6.2.

1.8.20 Advanced NDE methods, as described in Ch 1, 5.11 Advanced NDE methods, may be applied to Cu 3 and Cu 4 copper alloy castings for propellers, as appropriate to the material type, thickness, complexity and geometry, as a substitute for, or complementary to conventional ultrasonic or radiographic testing.

1.8.21 The measurement of dimensional accuracy is the responsibility of the manufacturer but the report on dimensional inspection is to be presented to the Surveyor who may require checks to be made and to witness such checks.

1.8.22 Static balancing is to be carried out on all propellers in accordance with the approved plan. Dynamic balancing is necessary for propellers running above 500 rpm.

1.9.1 The rectification of defective propeller and propeller blade castings is to be carried out in accordance with the requirements given in Ch 9, 1.9 Rectification of defective castings 1.9.2 to Ch 9, 1.9 Rectification of defective castings 1.9.11.

1.9.2 Where, in the surface of the end face or bore of a propeller boss, local pores are present which do not themselves adversely affect the strength of the casting, they may be filled with a suitable plastic filler after the appropriate preparation of the defective area. The foundry is to maintain records and details of all castings which have been so rectified.

1.9.3 Where unacceptable defects are found in a casting, they are to be removed by mechanical means, and the surfaces of the resulting depressions are subsequently to be ground smooth. Complete elimination of the defects is to be proved by adequate liquid penetrant inspection.

1.9.4 Shallow grooves or depressions resulting from the removal of defects may, at the discretion of the Surveyor, be accepted provided that they will cause no appreciable reduction in the strength of the castings and that they are suitably blended by grinding.

1.9.5 Welded repairs are to be undertaken only when they are considered to be necessary and approved by the Surveyor. In general, welds having an area less than 5 cm² are to be avoided.

1.9.6 All weld repairs are to be carried out in accordance with qualified procedures by suitably qualified welders, and are to be completed to the satisfaction of the Surveyor. Records are to be made available to the Surveyor.

1.9.7 Welding is generally not permitted in Zone A and will only be allowed after special consideration.

1.9.8 Prior approval by the Surveyor is required for any welds in Zone B. Complete details of the repair procedure are to be submitted for each case.

1.9.9 Repair by welding is allowed in Zone C provided that there is compliance with Ch 9, 1.9 Rectification of defective castings 1.9.5 and Ch 9, 1.9 Rectification of defective castings 1.9.6.

1.9.10 The maximum area of any single repair and the maximum total area of repair in any one zone or region are given in Table 9.1.3 Permissible rectification of new propellers by welding.

1.9.11 Where it is proposed to exceed the areas given in Table 9.1.3 Permissible rectification of new propellers by welding, the nature and extent of the repair work are to be approved by the Surveyor before commencement of the repair.

Table 9.1.3 Permissible rectification of new propellers by welding

Severity zone or region		Maximum individual area of repair	Maximum total area of repairs
Zone A		Weld repairs not generally permitted
Zone B		Defects that are not deeper than (t/40) mm or 2 mm, whichever is greater, below the minimum local thickness are to be removed by grinding. Defects which are deeper than allowable for removal by grinding may be repaired by welding.
Zone C		60 cm2 or 0,6% x S whichever is the greater	200 cm2 or 2% x S, whichever is the greater in combined Zones B and C but not more than 100 cm2 or 0,8% x S, whichever is the greater, in Zone B on the pressure side
Other regions (see Note)		17 cm2 or 1,5% area of the region whichever is the greater	50 cm2 or 5% × area of the region whichever is the greater
where	t = minimum local thickness in mm
	S = area of one side of a blade = 0,79
	D = finished diameter of propeller
	B = developed area ratio
	N = number of blades
Note Other regions include: (a) the bore; (b) the forward and aft faces of the boss; (c) the outer surface of the boss to the start of the blade root fillets; (d) the inner face of a CPP blade palm; (e) all surfaces of CPP nose cones; (f) the surfaces of integral journals to CPP blades other than the fillets.

1.9.14 Areas which are prepared for welding are independent of their location and are always to be assessed according to Zone A. The same applies to the welded areas after being finished by machining and/or grinding.

1.10.1 Welding is to be carried out under cover in positions free from draughts and adverse weather conditions.

1.10.2 The manufacturer is to submit a detailed welding procedure specification covering the weld preparation, welding parameters, filler metal, preheating, post-weld heat treatment and inspection procedures.

1.10.3 Before welding is started, Welding Procedure Qualification tests are to be carried out and witnessed by the Surveyor. Each welder is to be qualified in accordance with the requirements of Ch 12, 5 Welder qualification tests.

1.10.5 Defects to be repaired by welding are to be removed completely by mechanical means (e.g. grinding, chipping or milling). Removal of defects in accordance with the requirements for Zone A is to be demonstrated by liquid penetrant inspection in the presence of the Surveyor. The excavation is to be prepared in a manner which will allow good fusion and is to be clean and dry.

1.10.6 Metal arc welding with the electrodes or filler wire used in the procedure tests is to be used for all types of repairs. Welds should preferably be made in the downhand (flat) position. Suitable preheat is to be applied before welding, and the preheat temperature is to be maintained until welding is completed.

1.10.7 When flux coated electrodes are used they are to be dried immediately before use, in accordance with the manufacturer's instructions.

1.10.8 All slag, undercuts and other defects are to be removed before the subsequent run is deposited.

1.10.9 With the exception given in Ch 9, 1.10 Weld repair procedure 1.10.10, all weld repairs in areas of solid propellers exposed to sea-water, and all repairs to separately cast blades, are to be stress relief heat treated.

1.10.10 Stress relief heat treatment is not mandatory after welding Grade Cu 3 castings in Zone C unless a welding consumable susceptible to stress corrosion (e.g. complying with the composition range of Grade Cu 4) is used. All welds in Zones A and B however, must be stress relieved by heat treatment, regardless of alloy.

1.10.11 Propeller and propeller blades are to be stress relieved within the following temperature ranges:

Soaking times are to be in accordance with Table 9.1.6 Soaking times for stress relief heat treatment of copper alloy propellers, and subsequent cooling from the soaking temperature is to be suitably controlled to minimise residual stresses and is not to exceed 50°C per hour until the temperature is below 200°C. Care should be taken to avoid heating castings in the Grade Cu 3 alloy at temperatures between 300 and 400°C for prolonged periods.

1.10.12 Stress relief heat treatment is to be carried out, where possible, in furnaces having suitable atmosphere and temperature control. Sufficient thermocouples are to be attached to the casting to measure the temperature at positions of extremes of thickness.

1.10.13 As an alternative to Ch 9, 1.10 Weld repair procedure 1.10.12, local stress relief heat treatment may be accepted, provided that the Surveyor is satisfied that the technique will be effective and that adequate precautions are taken to prevent the introduction of detrimental temperature gradients. Where local stress relief heat treatment is approved, adequate temperature control is to be provided. The area of the propeller or blade adjacent to the repair is to be suitably monitored and insulated to ensure that the required temperature is maintained and that temperature gradients are moderate. Care should be taken to select the shape of an area to be heat treated which will minimise residual stresses.

1.10.14 On completion, welds are to be ground smooth for visual examination and dye penetrant inspection. Where a propeller or propeller blade is to be stress relief heat treated, a visual examination is to be made before heat treatment, and both visual and dye penetrant examinations are to be made after the stress relief heat treatment. Irrespective of location, all weld repairs are to be assessed according to Zone A in Table 9.1.4 Allowable number and size of liquid penetrant indications in a reference area of 100 cm2

1.10.15 The foundry is to maintain full records detailing the weld procedure, heat treatment and extent and location on drawings of repairs made to each casting. These records are to be available for review by the Surveyor, and copies of individual records are to be supplied to the Surveyor on request.

1.10.16 LR reserves the right to restrict the amount of repair work accepted from a manufacturer when it appears that repetitive defects are the result of improper foundry techniques or practices.

1.11.1 The extent and procedure of straightening is to be agreed with the Surveyor.

1.11.2 Static loading is to be used for hot and cold straightening of propeller.

1.11.3 Weld repaired areas may be subject to hot straightening, provided that it can be demonstrated that weld properties are not impaired by the hot straightening operations.

1.11.4 Hot straightening of a bent propeller blade or a pitch modification is to be carried out after heating the bent region and approximately 500 mm wide zones on either side of it to the temperature range given in Table 9.1.7 Hot straightening temperatures.

1.11.5 The heating for hot straightening is to be slow and uniform and the concentrated flames such as oxyacetylene and oxypropane should not be used. Sufficient time is to be allowed for the temperature to become uniform through the full thickness of the blade section. The temperature is to be maintained within the suggested range throughout the straightening operation. A thermocouple instrument or temperature indicating crayons are to be used for measuring the temperature.

1.11.6 Cold straightening may be used for minor repairs of tips and edges of propeller blades. Cold straightening on CU1, CU2 and CU4 bronze is to be followed by a stress relieving heat treatment in accordance with Table 9.1.6 Soaking times for stress relief heat treatment of copper alloy propellers

1.12.1 Castings are to be clearly marked by the manufacturer in accordance with the requirements of Ch 1 General Requirements. The following details are to be shown on all castings which have been accepted:

1. Identification mark which will enable the full history of the item to be traced including the manufacturer’s mark.

2. Alloy grade.

3. LR or Clasifications Register and the abbreviated name of LR local office.

4. Personal stamp of Surveyor responsible for the final inspection.

5. Date of final inspection.

6. Skew angle if in excess of 25°. See Pt 5, Ch 7, 1 Plans and particulars of the Rules and Regulations for the Classification of Ships, July 2022 for the definition of skew angle.

7. The number of the test certificate.

8. Ice class symbol, where applicable.

1.13.1 An LR certificate is to be issued for each propeller, see Ch 1, 3.1 General.

1.13.2 The manufacturer is to provide the Surveyor with the following particulars for each casting:

1. Purchaser's name and order number.

2. Description of casting, to include diameter, number of blades, pitch, direction of turning, and drawing number.

3. Alloy designation and/or trade name, and chemical composition of each heat.

4. Heat or casting number.

5. Cast identification number if different from (d).

6. Details of heat treatment, where applicable.

7. Skew angle if in excess of 25°. See the relevant Rules for the definition of skew angle.

8. Final weight of casting.

9. Results of non-destructive tests and details of test procedures.

10. Proportion of alpha-structure for CU1 and CU2 alloys.

11. Results of mechanical tests.

12. A sketch showing the location and extent of welding repairs (if any).

13. Shipbuilding project number, if known.