From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The properties and applications of laminated goods and powder mouldings, with comparative data and beam test results.
| Identifier | ExFiles\Box 61\1\ scan0241 | |
| Date | 26th April 1934 | |
| 2 The laminated class more nearly resembles metallic engineering material because it has much greater strength and toughness than mouldings, and is supplied in the form of sheets, blocks, bars, rods, angles, channels, and similar sections ready for machining into engineering components. By ignoring those plastics which soften at a comparatively low temperature we are reduced to engineering material in the form of mouldings made from a synthetic resinoid powder with a wood meal or fibrous base and synthetic resinoid bonded laminated material of paper, fabric, or asbestos base. Mineral fillers, except asbestos fibres, are little used except for temperature resistance, as they reduce the mechanical strength. POWDER MOULDINGS Powder mouldings are largely used in electrical engineering both for their mechanical convenience and insulating properties. When large numbers of component parts of the same size and pattern are required for mass assembly of such things as vacuum cleaners, small weighing machines, meters, or food-handling machinery, these mouldings cannot be excelled in exact size, appearance, wearing properties, low maintenance, and low first cost. The fibrous powder mouldings are sufficiently strong for light engineering purposes while paper or fabric base mouldings, costing a little more, can be used in place of most small metal castings. Mouldings are limited in size by the tools necessary to produce them. The largest moulded tank at present possible is little larger than the size of the radio cabinet, but much larger ones could be made if there arose a demand sufficient to warrant the capital cost of the tools. Where thousands of articles are required from the tool the cost per article becomes nominal. LAMINATED GOODS Laminated plastics more nearly approach the engineer's idea of a structural or engineering material. TABLE I PHENOLIC RESINOID PRODUCTS | CHARACTERISTIC | POWDER MOULDINGS | LAMINATED SHEET | OTHER MATERIALS | |---|---|---|---| | | WOOD MEAL BASE | WOOD MEAL WITH FIBRE BASE | GRADE I PAPER BASE IMPREGNATED | GRADE II PAPER BASE COATED | CANVAS FABRIC BASE | FINE CLOTH FABRIC BASE | GREY CAST IRON | WOOD A•F•S•H R•RED PINE | ALUMINIUM 96% CAST | | TENSILE STRENGTH LBS PER SQ: INCH | 5-8000 | 5-8000 | 9-15000 | 10-18000 | 8-14000 | 8-18000 | 20-35000 | A 9-15000 R 7-9000 | 12-16000 | | ELONGATION AT BREAK | 1/2-1% | 1/2-1% | 1-2% | 1-3% | 1/2-4% | 1/2-4% | 1/4-1% | — | 3-10% | | COMPRESSION TO CRACK. INCH CUBE | 26-32000 | 26-35000 | 36-45000 FACE UP 26-30000 EDGE UP | 30-35000 FACE UP 15-25000 EDGE UP | 35-42000 FACE UP 18-22000 EDGE UP | 30-45000 FACE UP 15-25000 EDGE UP | 70-95000 | A - 9000 R 9-11000 GRAIN VERTICAL | 10-30000 | | CONTRACTION AT 10,000 LBS PER SQ: INCH | 1-2% | 1-2% | 1-3% | 2-7% | 2-4% | 2-4% | 1/4-1/2% | — | — | | IZOD TEST FT LBS PER SQ: INCH | 1-2 | 2-4 | 5-7 FACE 2-3 EDGE | 15-23 FACE 5-7 EDGE | 20-40 FACE 10-15 EDGE | 20-60 FACE 10-40 EDGE | 1/2-1 1/2 | 5-35 | 2-12 | | MOD: OF RUPTURE RECT: BEAM ROUND B.S.S. 321 | 9-11000 | — | 15-17000 15-20000 | 14-28000 — | 16-22000 16-19000 | 16-25000 — | — | All-14000 R 6-9000 | — | | YOUNGS MODULUS LBS PER SQ. INCH x 10^6 | 1-2 | — | 3/4-1 1/2 | 1/2-1 1/2 | 1/2-1 | — | 52-54000 6-15 | 1 1/2 | 8-12 | | WATER ABSORPTION B.S.S 488 B.S.S 316 1/16 1/8 1/4 | •1-1% | •1-1 1/2% | •5% •3% •1% | 2-4% 1-3% •5-2% | •1-5% •1% | •1-3% | NONE | HIGH | NONE | | SPECIFIC GRAVITY CUBIC INCHES PER POUND | 1•38 20 | 1•38 20 | 1•38 20 | 1•38 20 | 1•38 20 | 1•38 20 | 7•2 2•8 | •8-•55 35-50 | 2•6 10•5 | The figures show them to be considerably stronger than the best powder mouldings. They can be purchased either in convenient form for machining as a finished article, and large structures can be built from them. No special moulds are required and the cost of a few machined parts of one pattern is not prohibitive as in the case of mouldings. There are two distinct grades of laminated stock. Grade I sheet is made from paper or fabric thoroughly impregnated with a solution of the resinoid, dried, and cut to size; the sheets are stacked to the thickness required and then baked to the insoluble state in steam-heated hydraulic presses. Grade I tubes are made by rolling this impregnated paper or fabric on a hot steel mandrel between hot rolls until the wall thickness is built up and then pressing in steel moulds or dies. They are known as “rolled and moulded tubes,” and are made up to 4 ft. long in any round, rectangular, or irregular section up to 4 in. diam. Grade I rods and bars are produced in the same way by rolling on a wire which is withdrawn before moulding and all sections of bar, angle, channel, etc. can be produced in a similar way. Grade II sheet is made from paper or fabric coated on one side with treadle-stage resinoid or thick solution. The fibres of the paper are not thoroughly impregnated and the sheet is more absorbent, does not machine so cleanly, and is more liable to delaminate. It usually has a good polished surface. Grade II tubes are more obviously of this paper-sandwich construction because they are not compressed like the sheet product after rolling and coated with a coat of varnish. Their machining properties are poor but tubes or cylinders up to several feet in diameter are made for electrical transformer insulation and their electrical properties are for this purpose and for large high-tension bushings are better than the Grade I quality, if they are sealed against moisture. Round rod can be made by turning strips of Grade II sheet but it has only a small use because the laminations are in the wrong direction for most purposes and it is too absorbent. Its circumference is all “end of the grain” or edge of the sheet, and the edge is the most absorbent place on the sheet surface. A large range of quality of laminated stock can be made by varying the type of paper or fabric base, by impregnating or coating it, by varying the proportion of resinoid to base, the type of resinoid, the pressure, time, and temperature of curing. Table I gives ranges for usual commercial qualities and an attempt has been made to compare these materials with cast iron, wood, and aluminum. Notes on Table I.—Tensile strength: The lower figure represents the lowest specification test and the upper represents good average quality. Izod test: Research is still required on this test as applied to brittle or fibrous materials but the figures are a fair guide. Figures for most tests on timber depend largely on seasoning and moisture content. Edgewisc tests on laminated are decidedly lower than flatwise, yet square beams have practically equal breaking load in either position. Modulus of rupture: The figure depends upon the conventional value for Z. The figures for the round B.S.S. 321 cast-iron bars are compared with tests on rolled and moulded rods made from paper and fabric base of specification size. Young’s modulus: These figures are not quite satisfactory as the tensile or compression and the transverse beam figures are different but they are a reasonable guide. Water absorption: The figure for percentage weight gained in 24 hours depends on the size of test piece. As most of the absorption is through the cut edges of laminated, the small B.S.S. 316 test piece of 1 1/2 in. sq. X thickness of sheet exaggerates the absorption. 3 BEAM TESTS There is no complete impregnation of the ultimate fibres by the phenolic resinoids and the resulting mixture of highly compressed but comparatively soft cellulose particles or fibres with planes of resinoid or resinoid-cellulose complex, makes a Brinell test, for example, of little value. The small slip or creep in the fibres themselves, especially in laminated stock, makes the interpretation of beam tests difficult and considerable experiment is still necessary. Table II gives approximately the flexibility and strength of Grade I paper base used for switchboard panels, operating levers, and tension members. Fig. I gives particulars of a test on a fairly tough type of canvas base stock used for gear wheels and it is obvious that they are materials of practical utility. Although these laminated goods can be varied in manufacture to give considerably higher or lower flexibility, tensile or impact strength, it is not always possible to combine all the desired values in one sample. For specification purposes, a proof test is always preferable. [GRAPH: FIG. 1] Title: BEAM TEST Info: W. TYPE CANVAS BASE. 1.5" (ML.590) SQUARE BEAM ON 4" CENTRES, LOADED AT CENTRE AT 1/8 IN. PER MIN. Annotations: EDGEWISE MOD: OF RUP: 21,650 FLATWISE MOD: OF RUP: 21,200 APPROX: ELASTIC LIMIT. TENSILE - 14,700 COMPRESSION FLATWISE - 42,000 COMPRESSION EDGEWISE - 20,000 TABLE II Grade I laminated phenolic resinoid sheet (paper base) 1 1/2-in. wide strips, 1/4-in. thick loaded in centre on 1/2-in. face (rough averages) | | 6-in. span | 12-in. span | |---|---|---| | Load at elastic limit | 54 lb. | 34 lb. | | Deflection | 0•125 in. | 0•50 in. | | Breaking load | 150 lb. | 170 lb. | | Maximum deflection | 0•45 in. | 1•7 in. | | Modulus of rupture | 17,200 | 15,770 | | Young’s modulus | 1,200,000 | 1,150,000 | The tensile strength of these assorted samples varied from 11,000 to 18,000 lb. per sq. in. and the compression tests edgewise on 1-in. cubes from 22,000 to 27,000 lb. per sq. in. | ||