Mechanical Engineers Data Handbook Episode 10 pot

MANUFACTURING TECHNOLOGY 215 Positions of welding In addition to 'flat' welding, which is the ideal position, three other positions are used: horizontal, vertical and overhead. If one member is vertical and one horizontal the position is called horizontal-vertical. In the last case a number of passes must be made to overcome the tendency for molten metal to run out. (See figure.) 5.12.9 Welding terminology, throat size and allowable stress Welding practice The relevant British Standards are BS 4360: Part 2, BS 639, BS 1719, BS 1856, BS 2642, BS 449 and BS 499. Included Butt weM Effective throat size (r=throat thickness, L=leg length) Horizontal vemcai Overhead Horizontacvellical Leg length f i Root / Weld face Excess weld metal % Throat thickness e = included angle Fillet weld Fillet angle, 0 (") 60-90 91-100 101- 106 107-1 13 114-120 tlL 0.7 0.65 0.6 0.55 0.5 216 MECHANICAL ENGINEER’S DATA HANDBOOK Allowable stress for welded structural steels \ Grade 43 50 55 Stress (N mm-’) 115 160 195 5.13 Limits and fits It is impossible to make components the exact size and an allowance or ‘tolerance’ must be made which depends on the process and the application. The tolerance results in two extremes of size which must be maintained. The tolerances of two fitting parts, e.g. a shaft in a bearing, determines the type of ‘fit’ and makes interchangeability possible. British Standard BS 4500: Part 1 : 1969, ‘IS0 Limits and Fits’, gives a comprehensive system relating to holes and shafts; it can, however, be used for other components, e.g. a key in a keyway. 5.13. I Terminology Taking the example of holes and shafts, there is a ‘basic size’ and then maximum and minimum sizes for each, their differences being the tolerances. Their differences from the basic size are called the ‘maximum and minimum deviations’. Upper deviation Lower deviation Minimum limit Basic of size size E-+ Tolerance Minimum limit of size Maximum limit 01 size nca Maximum limit of size Basic size r deviation r deviation Maximum Minimum Maximum mum rance Clearance fit Transition lit Interference fit MANUFACTURING TECHNOLOGY 217 Types of .fit 5.13.2 Selected Fits The fit describes the manner in which two parts go together. A ‘clearance fit’ means that the shaft will always be smaller than the hole. An ‘interference fit’ means that the shaft will always be larger than the hole and a fitting force will be necessary. A ‘transition fit’ means that there may be either clearance or interfer- ence. Tolerance BS 4500 gives 18 ‘tolerance grades’ numbered ITO1, ITO, IT1, IT2, up to IT16. The actual tolerance depends on the size of the component (see table below). BS 4500 ‘Selected Fits’ Gives a much smaller range of fits, the hole tolerance is denoted by the letter H and the shaft by a lower-case letter (see table). For conventionally manufactured parts, the five fits given are usually sufficient (see table). selected fits (Bs 4500) Hole H7 H8 H9 H11 Shaft cll d10 e9 fl g6 h6 k6 n6 p6 s6 Reduced range of fits for conventionally manufactured prts _______~ ~~ Type of fit Shaft tolerance Hole tolerance Description of fit Clearance fl Clearance g6 Transition k6 Interference P6 Interference s6 H8 H7 H7 H7 H7 Running Sliding Keying Press Push or shrink 5.13.3 drawing Preliminary design drawing Example of symbols and sizes on It is convenient to use symbols, e.g. 45 mm shaft and ‘transition’ fit. Tolerance is given as: 4 45H7/k6. Production drawing For a 30mm diameter shaft, fit H9/d10: Hole maximum limit of size= 30.012 mm Hole minimum limit of size = 30.00 mm Therefore tolerance = 0.012 mm. Shaft maximum limit of size = 30.015 mm Shaft minimum limit of size = 30.002 mm Therefore, tolerance = 0.01 3 mm On the drawing these parameters would be given as (rounding off to nearest 0.01 mm): Hole: 30.01 Shaft: 30.02 30.00 30.00 ~ Engineering materials 6.1 Cast irons ~~~ ~ 6. I. I Grey iron Grey iron is so called because of the colour of the fracture face. It contains 1.543% carbon and 0.3-5%0 silicon plus manganese, sulphur and phosphorus. It is brittle with low tensile strength, but is easy to cast. Properties of some grey irons (BS 1452) Tensile Compressive Transverse Modulus of strength strength strength Hardness, elasticity Grade (Nmm-2) (Nmm-*) (Nmm-’) BHN* (GN m-’) 10 160 620 2W370 160-180 76-104 17 260 770 450490 190-250 110-130 24 370 1240 620-700 240-300 124145 *BHN = Brinell hardness number. 6. I .2 Spheroidal graphite (SG) iron This is also called nodular iron because the graphite is in the form of small spheres or nodules. These result in higher ductility which can be im- proved further by heat treatment. Mechanical proper- ties approach those of steel combined with good castability. Properties of some SG irons (BS 2789) Tensile 0.5% permanent Minimum strength set stress Hardness elongation Grade (Nmm-2) (Nmm-2) BHN* (%) SNG24/17 370 SNG37/2 570 SNG47/2 730 230 390 460 140-170 17 210-310 2 280-450 2 *BH = Brinell hardness number. ENGINEERING MATERIALS 219 6. I .3 Malleable irons These have excellent machining qualities with strength similar to grey irons but better ductility as a result of closely controlled heat treatment. There are three types: white heart with superior casting properties; black heart with superior machining properties; and pearlitic which is superior to the other two but difficult to produce. Properties of some maUeabie irons Minimum Yield tensile point strength strength Hardness, Elongation Type Grade (Nmm-2) (Nmm-2) BHN* (%) White heart, W22/24 310-340 180-200 248 (max.) 4 BS 309 W24/8 340-370 200-220 248 (max.) 6 Black heart, B18/6 280 170 150 (max.) 6 B22/14 340 200 150 (max.) 14 Pearlitic, P28/6 430 143-187 6 BS 310 B20/10 3 10 190 150 (max.) 10 - BS 3333 P33/4 460 - 170-229 4 *BHN = Brinell hardness number. 6. I .4 Alloy irons The strength, hardness, wear resistance, temperature resistance, corrosion resistance, machinability and castability of irons may be improved by the addition of elements such as nickel, chromium, molybdenum, vanadium, copper and zirconium. 6.2 Carbon steels 6.2. I Applications of plain carbon steels These are alloys of iron and carbon, chemically combined, with other elements such as manganese, silicon, sulphur, phosphorus, nickel and chromium. Properties are governed by the amount of carbon and the heat treatment used. Plain carbon steels are broadly classified as: low carbon (0.05-0.3%C), with high ductility and ease of forming; medium carbon (0.3-0.6%C), in which heat treatment can double the strength and hardness but retain good ductility; and high carbon (> 0.6%C), which has great hardness and high strength and is used for tools, dies, springs, etc. 220 MECHANICAL ENGINEER’S DATA HANDBOOK Applications of plain carbon steels %Carbon Name Applications 0.05 Dead mild 0.084. 15 Mild 0.15 Mild Case carburizing type 0.10-0.30 Mild Steel plate, sections, structural steel 0.254.40 Medium carbon Bright drawn bar 0.30-0.45 Medium carbon High tensile tube, shafts 0.40-0.50 Medium carbon Shafts, gears, forgings, castings, springs 0.554.65 High carbon Forging dies, springs, railway rails 0.654.75 High carbon Hammers, saws, cylinder liners 0.75-0.85 High carbon Chisels, die blocks for forging 0.854.95 High carbon Punches, shear blades, high tensile wire 0.95-1.10 High carbon Sheet, strip, car bodies, tinplate, wire, rod, tubes Sheet, strip, wire, rod, nails, screws, reinforcing bars Knives, axes, screwing taps and dies, milling cutters Properties of carbon steels (BS 970) Composition (%) Mechanical properties Tensile strength Elongation Hardness, Type C Si Mn (Nmm-’) (%) BHN* Applications, etc. 070 M20 0.2 - 0.7 400 21 150 070 M26 0.26 - 0.7 430 20 - 080 M30 0.3 0.8 460 20 080 M36 0.36 - 0.8 490 18 - 080 M40 0.4 0.8 510 16 080 M46 0.46 - 0.8 540 14 - 080 M5O 0.5 0.8 570 14 216 M28 0.28 0.25 1.3 540 10 165 165 180 180 205 205 180 Easily machinable steels suitable for light stressing. Weldable Stronger than En2. Good machinability. Weldable Increased carbon improves mechanical properties, but slightly less machinable Tough steel used for forgings, nuts and bolts, levers, spanners, etc. Medium carbon steel, readily machinable Used for motor shafts, axles, brackets and couplings Used where strength is more important than toughness, e.g. machine tool parts Increased manganese content gives enhanced strength and toughness ENGINEERING MATERIALS 22 1 Properties of carbon steels (E 970) (continued) Composition (YO) Mechanical properties Tensile strength Elongation Hardness, Type C Si Mn (Nmm-*) (YO) BHN* Applications, etc. 080 M15 0.15 0.25 0.8 460 16 - Case-hardening steel. Used where wear is important, e.g. gears and pawls 060A96t 0.99-1.0 0.14.7 0.5-0.7 1300 - 500 High carbon spring steel *BHN =Brinell hardness number. tTo BS 950. Tempering temperature and clolour for carbon steels Temperature ("C) Colour Application _____~ 220 Pale yellow Hacksaw blades 230 Light yellow Planing and slotting tools, hammers 240 Straw yellow Milling cutters, drills, reamers 250 Dark yellow Taps, dies, shear blades, punches 260 Brown-yellow Wood drills, stone-cutting tools 270 Brown-purple Axe blades, press tools 280 Purple Cold chisels, wood chisels, plane blades 290 Dark purple Screw drivers 300 Dark blue Wood saws, springs 450-700 Up to dark red Great toughness at expense of hardness 6.3 Alloy steels 6.3. I Classification Alloy steels differ from carbon steels in that they contain a high proportion of other alloying elements. The following are regarded as the minimum levels: Element YO Element YO Element O/Q Aluminium 0.3 Lead 0.1 Silicon 2 .o Chromium 0.5 Manganese and silica 2.0 Sulphur and phosphorus 0.2 Cobalt 0.3 Molybdenum 0.1 Tungsten 0.3 Copper 0.4 Nickel 0.5 Vanadium 0.1 222 MECHANICAL ENGINEER’S DATA HANDBOOK Alloy steels are classified according to increasing proportion of alloying elements and also phase change during heating and cooling as follows: low alloy steels medium alloy steels high alloy steels and according to the number of alloying elements as follows: ternary - one element quarternary - two elements complex - more than two elements 6.3.2 General description Chromium A range of OM%, improves wear, oxidation, scaling resistance, strength and hardenability. It also increases high-temperature strength, but with some loss of ductility. Chromium combines with carbon to form a wear-resistant microstructure. Above 12% the steel is stainless, up to 30% it is used in martensitic and ferritic stainless steel with nickel. Cobalt Cobalt provides air hardening and resistance to scal- ing. It improves the cutting properties of tool steel with 8-10%. With chromium, cobalt gives certain high alloy steels high-temperature scaling resistance. Low alloy steels Copper These generally have less than 1.8% nickel, less than 6% chromium, and less than 0.65% molybdenum. The tensile strength range is from 450-620 N mm-’ up to 85O-lOoO N mm-2. Medium alloy steels These have alloying elements ranging from 5-12%. They do not lend themselves to classification. They include: nickel steels used for structural work, axles, shafts, etc.; nickel-molybdenum steels capable of being case-hardened, which are used for cams, cam- shafts, rolling bearing races, etc.; and nickel- chromemolybdenum steels of high strength which have good fatigue resistance. High alloy steels These have more than 12% alloying elements. A chromium content of 13-18% (stainless steel) gives good corrosion resistance; high wear resistance is obtained with austenitic steel containing over 11 YO manganese. Some types have good heat resistance and high strength. 6.3.3 Effect of alloying elements Aluminium This acts as a deoxidizer to increase resistance to oxidation and scaling. It aids nitriding, restricts grain growth, and may reduce strength unless in small quantities. The range used is 0-2%. The typical range is 0.24.5%. It has limited applica- tion for improving corrosion resistance and yield strength of low alloy steels and promotes a tenacious oxide film. Lead Up to 0.25% is used. It increases machineability in plain carbon steels rather than in alloy steels. Manganese The range used is 0.3-2%. It reduces sulphur brittle- ness, is pearlitic up to 2%, and a hardening agent up to 1 Yo. From 1-2% it improves strength and toughness and is non-magnetic above 5%. Molybdenum The range used is 0.3-5%. It is a carbide forming element which promotes grain refinement and in- creases high-temperature strength, creep resistance, and hardenability. Molybdenum reduces temper brit- tleness in nickel-chromium steels. Nickel The range used is 0.3-5%. It improves strength, toughness and hardenability, without affecting duc- tility. A high proportion of it improves corrosion resistance. For parts subject to fatigue 5% is used, and above 27% the steel is non-magnetic. Nickel promotes an austenitic structure. ENGINEERING MATERIALS 223 Silicon The usual range is 0.2-3%. It has little effect below 3%. At 3% it improves strength and hardenability but reduces ductility. Silicon acts as a deoxidizer. Sulphur Up to 0.5% sulphur forms sulphides which improve machineability but reduces ductility and weldability. Titanium This is a strong carbide forming element. In propor- tions of O.2-O.75% it is used in maraging steels to make them age-hardening and to give high strength. It stabilizes austenitic stainless steel. 6.3.4 Typical properties of alloy steels Typical properties of alloy steels Tungsten This forms hard stable carbides and promotes grain refining with great hardness and toughness at high temperatures. It is a main alloying element in high speed tool steels. It is also used for permanent-magnet steels. Vanadium This is a carbide forming element and deoxidizer used with nickel and/or chromium to increase strength. It improves hardenability and grain refinement and combines with carbon to form wear-resistant micro- constituents. As a deoxidizer it is useful for casting steels, improving strength and hardness and elimina- ting blowholes, etc. Vanadium is used in high-speed and pearlitic chromium steels. Tensile Fatigue strength limit Corrosion Machine- Content Type Specification (Nmm-’) (Nmm-’) Weldability resistance ability Formability Low 1 %Cr, Mo 709M40 1.75%Ni,Cr,Mo 817M40 4.25%Ni,Cr, Mo 835M30 3%Cr, Mo, V 897M39 5%Cr, Mo, V AISI HI 1 Medium 9%Ni, Co HP9/4/45 Republic Steel Vascojet MA Vanadium alloy steel 12-14%Cr 410S21 Cr, W, Mo. V High 13%Cr, Ni, Mo 316S12 19%Cr,Ni, Mo 317S16 15%Cr, Ni, Mo, V ESSHETE 1250 S. Fox 17%Cr,Ni AISI 301 17% Cr, Ni, AI 14%Cr, Ni, Cu. REX 627 15%Cr, Ni, Mo, V AM 355 Allegheny 18%Ni, Co, Mo 300grade 18%Ni, Co, Mo 250grade 1717 PH Armco Mo, Nh Firth Vickers Ludlum maraging INCO 1240 540 1550 700 1550 700 1310 620 (1780) 2010 850 (A2630) (A1880) 1390 - 1850 1160 340 2320 960 (A3090) 620 260 650 260 590 - 740 280 (CR 1240) 1480 - 1470 540 1480 740 1930 1700 660 PHIFHTR PHIFHTR P H F H T R PH/FHTR PH/FHTR FHTR PJFHTR PHJFHTR G G GJFHTR F F FHTR FHTR GIFHTR GIFHTR PR PR PR PR PR PR F PR G G GJHT F F F F PR PR F/HTR P/HTR PWTR PIHTR P/HTR WHTR FJHTR PIHTR F F F F F F F F F F F F F F F F F G G ~ G G F F P P maraging A = ausformed, MA = martempered, CR =cold rolled, P = poor, F = fair, G = good, PH = preheat required, PR = protection required, HT = at high temperature, HTR = when heat treated, FHTR=final heat treatment required. 224 MECHANICAL ENGINEER’S DATA HANDBOOK 6.3.5 Cast high-alloy steels Composition (YO) Tensile Yield BS strength stress Elongation specification Type Cu Si Mn Ni Cr Mo C (Nmm-’) (Nmm-’)(%) - - 3 100 Austenitic - 1.0 11.0 - - - 1.0 - BW 10 manganese steel Possess great hardness hence used for earth moving equipment pinions, sprockets, etc., where wear resistance is important. 3 100 13%chromium - 1.0 1.0 1.0 13.5 - 0.15 540 3 70 15 410 C 21 steel 3100 Austenitic - 1.5 2.0 8.0 21.0 - 0.08 480 210 26 302 C25 Mildly corrosion resistant. Used in paper industry chromium- nickel steel Cast stainless steel. Corrosion resistant and very ductile. 3100 Austenitic - 1.5 2.0 10.0 20.0 1.0 0.08 480 210 22 315 C16 chromium- nickel- molybdenum steel Cast stainless steel with higher nickel content giving increased corrosion resistance. Molybdenum gives increased weldability 3 3 100 Heat-resisting - 2.0 2.0 10.0 22.0 1.5 0.4 560 - 302 C35 alloy steel 3100 334Cll 3 - 3.0 2.0 65.0 10.0 1.0 0.75 460 - Can withstand temperatures in excess of 650 “C. Temperature at which scaling occurs raised due to chromium 6.3.6 Weldable structural steel for hollow sections Mechanical properties of weldable structural steel for hollow sections (BS 4360: 1972) Tensile Yield strength strength* Elongation Grade (Nmm-’) (Nmm-’) (YO) 43c 4301540 255 22 43D 4301540 255 22 43E 4301540 270 22 50B 4901620 355 20 5oc 4901620 355 20 50D 4901620 355 20 55c 550/700 450 19 55E 5501700 450 19 *Up to 16mm thickness. [...]... 11.5/13.5 AD 465 250 700 540 450 930 10 35 - - 850 740 108 0 10 25 15 0.1 210. 2 213 0.1 210. 2 213 0.1 210. 2 213 510 25 0.1 Martensitic steel, easy to (416821) manipulate Similar to above, but (416829) harder Stainless Iron W Weldable martensitic steel S AH 2012 Martensitic steel (43 1S29) harder to work AD than stainless iron but greater resistance, especially to sea water H 770 590 100 5 Stainless Ferritic stainless... Fasteners 226 MECHANICAL ENGINEER’SDATA HANDBOOK 6.4.3 Properties of typical types BS code no Remarks Yield Tensile stress strength Elongation Condition (Nmm-2) (Nmrn-?) (YO) C Composition (YO) Ni Cr Stainless Iron 1 AD S 430 280 5 10 400 12 35 0.9-0.15 1 (max.) 11.5/13.5 0.9-0.15 1 (max.) 11.5/13.5 Stainless Iron 1 AD S 465 280 AH 850 540 430 108 0 10 - 0.14/0.2 1 (max.) 11.5/13.5 0.1 410. 2 1 (max.)... 238 MECHANICAL ENGINEER’S DATA HANDBOOK Physical properties of common engineering materials (continued) Tensile strength (Nmm-’) (GNm-’) v a P ( x 1O6K-*) (kgm-3) 150/400 130 (tension) 600/1200 (compression) 48 - 12 7200 260 170 (tension) 780 (compression) 68 0.26 11 7350 170 68 0.26 11 7350 168 100 34 0.32 20 8400 410 PS/YS 116 43 0.33 17 8800 - _ - 350-800 - - 20 1500 0.35 13.5 1420 - 100 1100 ... 70130 Brass Phosphor bronze Beryllium . 465 250 700 770 590 100 5 310 340 390 620 230 5 10 400 540 430 108 0 540 450 930 850 740 108 0 510 540 560 700 540 12 35 10 - - 10 35 - 10 25 15 25 25 20 25. Fillet weld Fillet angle, 0 (") 60-90 91 -100 101 - 106 107 -1 13 114-120 tlL 0.7 0.65 0.6 0.55 0.5 216 MECHANICAL ENGINEER’S DATA HANDBOOK Allowable stress for welded structural. 390 660 40 - - - - - - 310 850 30 108 0 1240 15 - - - - S = softened, H =hardened, AD = as drawn, AH =air hardened. 228 MECHANICAL ENGINEER’S DATA HANDBOOK 6.5 British Standard