Showing papers on "Peening published in 1981"

Method of peening airfoils and thin edged workpieces

Abstract: Shot peening of thin edges of workpieces which are subject to deformation damage by direct impacts is accomplished by rotating the workpiece edge near centerline through a particular angle measured from the normal to the shot streamline. The angle is sufficient to cause oblique blows on the centerline of the edge, but insufficient to cause direct impacts. Compressive stresses by the oblique blows provide residual compressive stresses along the centerline to the desired depth. The angle is calcuable from the edge radius, the depth of stressing desired at the centerline, and the depth of stressing produced by shot at a reference location. Oscillatory rotation is preferably used to obtain even peening.

Duplex peening and smoothing process

Abstract: Disclosed is a two step process of peening for workpieces having small radii fillets or fragile edges, such as gas turbine airfoils have. In the first step, relatively small size shot of less than 1 mm dia is used to impart a first peening intensity to a workpiece. This results in a first relatively rough surface finish. In the second step, shot of substantially uniform diameter in the range 1-2.5 mm is impacted with uniform velocity to provide a surface finish smoother than 30AA (10-6 inch). When fillets are peened, improved fatigue life results from the duplex process. When used on edges, where direct edge impact is avoided in the second step, deformed edges are avoided by the process. Yet the workpiece is substantially smooth and the edges have the requisite residual stress distribution.

Investigation of shot peening as a forming process for aircraft wing skins

Abstract: The technique of generating curvatures in thin sheets by shot peening is well established for forming airplane wing skins to controlled contours. Success used to depend on the peening machine operator’s skills; therefore, a systematic experimental investigation was conducted into the effects of workpiece geometry and process variables on resulting curvatures. Most of the tests were conducted on 6 x 24 in. (152 x 610 mm) 2024-T3 and 7075-T6 aluminum alloy sheets of up to 0.5 in. (12.7 mm) thickness. Shot of 0.023 to 0.066 in. (0.6 to 1.7 mm) diam was used in a wheeltype machine at speeds up to 250 ft/s (80 m/s). The radius of curvature Rof a peened specimen can be expressed as R = A + B/Swhere Sis the shot density (weight per unit area) and Aand Bare parameters which are functions of other process variables. Specimens with a length-to-width ratio of L/W =1 have equal stiffness in the Land Wdirections but developed a predominant curvature the direction of which was affected by secondary variables such as the rolling direction in the sheet. However, transverse and longitudinal radii of curvature were almost identical in thicker specimens of L/W =1/4 and could be used to predict the transverse curvatures of long workpieces peened under production conditions, as confirmed by productionscale experiments.

Influence of sub-zero and shot-peening treatments on impact and fatigue fracture properties of case-hardened steels

Abstract: High-cycle fatigue endurance limits and impact fracture strengths were determined for carburized SAE 4028 steel with and without a shot-peening treatment and for carbonitrided SAE EX55 steel with and without a sub-zero treatment at -85 °C (-120 °F). The shot-peening and the sub-zero treatments did not influence the impact fracture strengths of the steels; the impact fracture strengths of carburized SAE 4028 and carbonitrided EX55 steels were 2250 MPa (325 ksi) and 3220 MPa (468 ksi), respectively. The treatments had marked influence on the fatigue endurance limits of the steels, however. The fatigue endurance limit of carburized SAE 4028 was 730 MPa (105 ksi) without the shot-peening treatment and 1035 MPa (150 ksi) in the peened condition. The carbonitrided EX55 steel had endurance limits of 965 MPa (140 ksi) without the sub-zero treatment and only 415 MPa (60 ksi) after the treatment. The differences in fatigue endurance limits were explained through changes in residual stress patterns in the hardened cases. Shot-peening induced a compressive residual stress in the surface of carburized SAE 4028 steel, which was as high as 650 MPa (94 ksi). The residual stress in the case of EX55 without the sub-zero treatment was compressive for both the martensite and austenite phases, whereas the stress existing in the austenite after the sub-zero treatment was highly tensile. Differences in residual stresses among individual phases within the microstructure were used to explain observed changes in fracture mode.

Peened overlay coatings

Abstract: Disclosed are coatings which are improved by a special peening process. Uniform sized spherical steel shot, in the range 1-2.5 mm is impacted at uniform low velocities onto a coated workpiece. Peening intensities are in the range 0.30-0.60 mm N. MCrAlY high temperature coatings are particularly improved, with densities of the order of 99 percent. Physical vapor desposited coatings have surface finishes of the order of 30×10 -6 inch AA (Arithmetic Average) and plasma sprayed coatings have finishes of the order of 100×10 -6 inch AA compared to unpeened finishes of 50-60×10 -6 inch AA and 200-300×10 -6 AA respectively.

Shot peening apparatus

Abstract: In apparatus for shot peening, gravity is used to accelerate uniform sized steel shot, and thereby impart a combination of good surface finish and uniform compressive stresses to workpieces. It is especially useful for finishing gas turbine airfoils. Shot is introduced into the peening enclosure (28) through a gate (40) at near zero velocity. It is then accelerated along a streamline (31) toward the workpiece (18) with uniform velocity. The workpiece, positioned along the streamline, can be manipulated in three rotational modes: oscillatory rotation to uniformly peen contoured surfaces of a workpiece, periodic incremental rotation to peen different sides of a workpiece; and, tilting motion to enable peening of shoulders (22). The apparatus is especially suited to peening fragile workpieces such as gas turbine airfoils (18). A diverter plate (44) intercepts the shot stream at times when repositioning of a fragile workpiece is undertaken. Thus, possibly damaging impacts are avoided and steady state operation is able to be promptly resumed.

Method of peening the inside of a small diameter tube

Abstract: A method for peening a portion of the inside of a small diameter heat exchanger tube by inserting a rotating shaft having a peening strip affixed thereto, orbiting and reciprocating the shaft as it rotates, and maintaining this operation for a predetermined length of time to relieve residual tensile stresses in a portion of a tube installed in a heat exchanger.

The uniformity of shot peening induced residual stress

Abstract: Two rectangular samples of ASTM SA 508 Class 2 steel, stress relieved and shot peened to 14-16A intensity, were examined in detail to determine the principal macroscopic residual stress distribution. The uniformity of the shot peening induced macroscopic residual stresses with orientation in the plane of the surface and as a function of depth were examined and compared. The microscopic residual stress (plastic deformation) distribution was determined as a function of depth, and compared for the two samples. The calibration technique to determine the single crystal elastic constants in the (211) direction and verification of the values obtained by comparison with mechanically measured applied stress are discussed. The results indicate variation in the magnitude of the subsurface compressive macroscopic residual stress with direction in the plane of measurement for either sample of less than 12 ksi. The mean value of the macroscopic stress distributions for the two samples examined differed by less than the same amount at any depth examined. The microstress distribution was found to vary essentially linearly as a function of depth, reaching a negligible amount immediately beneath the microscopically compressive surface layer. The microstress distributions in the two samples examined were identical within the limits of experimental error.

Improving the Fatigue Strength of Fillet Welded Joints by Toe Grinding and Wire Peening (Report 1)

Abstract: Various mechanical methods of improving the fatigue strength were investigated by testing the base plate and cruciform fillet welded joint specimens of 40 kg/mm2-80 kg/mm2 class steels. The results obtained are summarized as follows:1) If a peening condition is suitable to a material, the compressive residual stress induced by peening increases as a yield strength increases. As the ratio of applied cyclic stress range to absolute value of the compressive residual stress decreases, the waste of compressive residual stress by applied cyclic stress decreases and the effect of improving a fatigue life (strength) increases. Therefore, the peening effect can increase with incresaing the yield strength of material.2) It is possible to consider that a suitable condition of peening is to add the compressive residual stress as large as a yield strength of the material used, and that ari over peening ravages a surface, and may rather result in a reverse effect.3) As a result of increasing the yield strength of a weld toe and inducing. the compressive residual stress to a weld toe, by peening., a root failure occurs sometimes in the case of non-load-carrying type cruciform, fillet welded joint similarly in thee case of load-carrying type fillet welded double tee joint. Therefore, it is necessary to consider the critical leg length according to a treating condition of a weld toe, in a joint design.

Orbital tool assembly for forming rivet heads

Abstract: An orbital tool assembly for forming rivet heads has a housing attached to a driven member rotatable upon a first axis, the housing having a bore along a second axis at an acute angle to the first axis. A head having an axis coincident with the second axis and including a fluid pressure chamber is retained within the housing with bearings interposed. A coaxial driver on the head has a plurality of bores parallel to the second axis in communication with the pressure chamber, and mounts a reciprocal peening tool holder in each bore, supporting an axial peening tool. An anti-rotation arm at one end extends at right angles to the driver and is secured thereto with its other end engaging a bracket, the arm being free for rocking movements in a plane passing through the first and second axes. Rotation of the head oscillates the peening tools in the rocking plane, the peening tools being in operative engagement with unheaded rivets.

High speed tool steel

Abstract: PURPOSE:To obtain a high speed tool steel of high abrasion resistance of which the coating layer is difficult to strip by subjecting the surface of a base material to peening by projecting steel balls to form a peened surface and a hardened layer and coating the surface thereof with a metallic compd. by a physical vapor deposition treatment. CONSTITUTION:Steel balls of about 46-50HRC hardness and about 0.3mm. sizes are projected onto the surface of a base material 5 for high speed steel tools, whereby a peened surface 3 and a hardened layer 4 removed of sharp reggedness of the machined surface are formed. Since the layer 4 has about 150- 200mum depth (b) and has hardness increased to about 100-150Hv, the layer is resistant to deformation and abrasion and has improved fatigue strength, etc. The surface is cleaned, and is improved in activity and in the adhesive strength of the coating layer. A TiN layer 2 of about 2-5mum thickness (a) is formed on the base material subjected to such surface treatment by a physical vapor deposition method, whereby the high speed tool steel having the TiN coating layer with high abrasion resistance and lubricity is obtained.

Shot peening, grit blasting make pipe steels more resistant to stress-corrosion cracking

Abstract: Shot peening or grit blasting to one of several controlled conditions is an effective means of increasing the resistance of pipeline steels to stress-corrosion cracking (SCC). Though the principal benefit is to increase the threshold stress for SCC, mill-scale removal and a good coating anchor pattern provide added benefits. Five principal factors influence the initiation and growth rate of stress-corrosion cracks in buried pipelines. These factors are susceptibility of the steel, stress level and strain rate, chemical environment in contact with the steel surface, electrochemical potential established on the steel surface, and temperature of the steel and environment system. These 5 factors are strongly interrelated in rather complex ways, but it is recognized that, for stress-corrosion cracks to grow, all 5 factors must be present concurrently and at appropriate levels. As a result, stress-corrosion cracking can be stopped or reduced by appropriately modifying any one of these 5 factors.

Preventing method for edge crack of steel sheet in cold rolling work

Abstract: PURPOSE:To prevent edge cracks of the cold rolled steel sheet, by smashing the edge of the cold rolled material widthways by a pressing roller installed between the pickling tank and the cold rolling mill or by a peening work, in order to smash fine cracks generated in the cut-out section or in the sheared section. CONSTITUTION:An edge pressing roller 6 and a push roller 10 for suppressing the cold rolled parent metal are arranged between the pickling tank and the cold rolling mill. The cold rolled parent metal 5, whose edge is trimmed by a side trimmer in order to attain a specified breadth, is clamped by the push roller 10, and the edge is pressed by the pressing roller 9 by operating the hydraulic cylinders 7 installed on both sides. As a result, the cut-out section of the edge is smashed to a smooth plane, so that fine cracks existed in the cut-out section are vanished.

Production of steam turbine rotor key way

Abstract: PURPOSE:To prevent cracking at a key way portion of a steam turbine rotor by peening the surface of the rotor key way to provide same with a compressive stress and then grinding the rotor key way surface to surface roughness lower than 5mum and a large compressive force. CONSTITUTION:A wheel pin 5 is inserted in key ways 4 of a rotor shaft 1 and a wheel 2. The surface of each key way is subject to peening treatment to provide the same with a compression stress. Subsequently, it is ground to surface roughness lower than 5mum with sand paper or emery paper to provide the same with a compressive residual stress rather than a shearing force. By such a production method, the key ways involved in connecting the rotor shaft and the wheel of a steam turbine which are used in corrosive environment can be prevented from being cracked, thereby extending the life of the rotor shaft and the wheel.

Pulsing impact straightener

Abstract: An automatic production workpiece straightener employing pulsing impact hammer peening blows on the concave curvature side of a distorted workpiece to straighten by imparting compressive stress to the surface fibers thereby permanently deflecting the workpiece in a straightening direction. As applied to rotatable shafts such as cast iron camshafts, a plurality of peening heads deliver rapidly pulsing axially spaced impact blows to cylindrical grooves in the shaft during a limited portion of each continuous revolution as required to provide straightening action with continuous or peening-interrupted automatic gauging for controlling and terminating the straightening action.