Document jB8NjmoReEDewDzxa3EzQ1G69

i nnnn UCILJ4J un it ia ! FpoM ' J. W. ROBERTS, Ltd. Armley To K.A. Morlin/r 5so., Turner 1>os. Asbestos Co.,l.td., ROCHDAI.n ou" "*' HLD/'.VI. oum Rcr. Confidential 2Cth January, 1954 Dear Mr. Morlinr, Snraved Rock V/ool As requested by you, T have oleasure in enclosing copy of memorandum, which has been circulated by me only to those whose initials are indicated thereon. o o i >nnn n # ouJ uuu u # #C iarte i * rgs/nam/anm/ngp/jw GAW C0NTID5NTTAL SPRAYED ROCK WOOL The substitution of rock wool for sprayed asbestos was first attempted by our American imitators and former sub licensees when we stopped supplies of fibre to K.& M.Co. At least a dozen firms in the United States are carrying out sprayed applications with a mixture of rock wool and a small amount of asbestos fibre to reinforce the coating. Attempts to spray rock wool have also been made on the Continent of Europe, and it is interesting to note that some of our indirect customers have been chiefly concerned because, whilst appreciating the advantages of a blown-on method, they object to the high cost of asbestos fibre. Such a case is that applying at the Elsinore Shipyard, Denmark. Some years ago the Stillite Company, Co. Durham, had in mind using pelleted rock wool for spraying purposes, but discontinued this when we showed a direct interest in their material. T.A.C.Co. and the Atlas Asbestos Company, both appreciating the need for a low-priced form of building insulation to enable their single-skin structures to compete with the more orthodox type of building in cold climates, made a study of the matter, but no doubt being influenced to some extent by our own objection to the idea, eventually abandoned it. Our own efforts to incorporate rock wool with asbestos fibre in order to produce low-priced adulterated blends, have not been too successful, the economies resulting being largely . absorbed by overhead charges, coupled with the fact that these rock wool mixtures are heavy, so that the saving in price per ton is out-weighed by the increased amount required to cover unit area. * Our view that the spraying of pure rock wool was not a satisfactory proposition either as regards ease of application or of the resulting coating, is based on the above plus the fact that all the varieties of rock wool available in the past are unsuitable for spraying owing to the high surface tension or water-repallenet* of the fibres, so that they do not absorb the water used in the spraying process fast enough to facilitate . spraying. nmnn o r o tfDuD ' uulju u .# < iO ij ; 2 The only exception to this rule of which we have been aware until recently, is that of "Vetra" rock wool produced by the Derbyshire Stone Company. This is a washed rock wool, priced at some 50 per ton and delivered wet, so that the price, together with the difficulty in drying the fibre, resulted in loss of interest on our part. This fibre, however, does spray .more readily than the earlier grades, when suitably prepared. Quite recently Grunsweig k Hartmann of Germany patented a.new form of fibre made from basalt rock, which they describe as "Silanwolle", also taown as "Basilan". ana now being produced in Sweden as "Bergull", and by the Cape Asbestos Company in Scotland as "Rocksil", the latter being distributed by William Kenyon k Sons. This is much more like glass fibre, being longer, stronger and more resilient - in fact it is quite a different product to what is known as "rock wool". and, so far as we are concerned, must be studied on an entirely different plane, namely that of a bulking medium for our own asbestos fibres, necessitating a new type of equipment not yet available at Leeds* A machine similar to a Willey, as used for opening card waste, shows most promise. . . Owing to the high resiliency and greater mechanical strength of these fibres, permitting of more severe blending treatment, it is hoped to be able to bulk up such lower-priced fibres as Dublin Amosite to give covering capacities of cement- > bonded fibres in the order of 9-oz. to the sq.ft. 1-in. thick, I at a Works cost of approximately 46 per ton of a mixture con- A sisting of 75 parts asbestos, 25 parts rock fibre, and 40 parts l< cement* Preliminary trials indicate that this mixture sprays well. Even more recently a new variety of rock wool has, so we are told, been developed in France specifically for spraying* This Is produced by the Soclete des Hauts Foumeaux de Saulnes under the trade mark "Pyrolaine". It is a very short, perfectly white fluffy fibre, with excellent water-absorbing properties* Careful examination of this has shown that the diameter of the fibres is less than 25% of that of American rock wool or other common varieties on the market, and clearly the process of manufacture has been materially modified. Nevertheless, in producing this very fine fibre much the same proportion of very fine "shot" results. The fibre itself, being readily"soluble in acid, can be removed in the laboratory, to reve&l some 68% by weight of "shot" resembling very fine sand. Again, our laboratory tests clearly show that this fibre contains a high proportion of calcium sulphide, which is a great disadvantage so far as the corrosion of metals is concerned. 3 Our first attempts to spray "Pyrolaine" were not too successful owing to the very fluffy nature of the product and the'somewhat compact lumps in which it was received. More recently, by pre-opening in one of our damping drums (without damping it), it has been found that "Pyrolaine" can be fed and blown through one of our spray machines fitted with a 2-in. gun and hose, quite readily, but even so the fibre is very light and much of it escapes to atmosphere during spraying. A great improvement in spraying properties results if some short white asbestos fibre is mixed with the "FyrolaineM in the opening process. Because of the very soft nature of the fibre, a soft coating results, and likewise, by suitable handling, it can be trowelled perfectly smooth to give a pleasing surface. "Pyrolaine" has no self-bonding properties, and is at present being sprayed by our imitators in conjunction with silicate of soda solution, which is cheap but has many faults. Dilute synthetic rubber emulsion would give a much better felt somewhat more economically than P.V.A, emulsion, but both add appreciably to the cost of material. If one part by weight of a self-bonding fibre such as LW.10 (consisting of equal parts of No.U Rhodesian crude and cement), is mixed with 2 parts-"Pyrolaine", a good tough coating that adheres well to masonry is readily produced, but if trowelled smooth it gives a somewhat reflective surface. Again, because of the very fine nature of the fibre it does not resist heat as well as normal rock wool or asbestos fibre, tending to fuse at around 1000C., indicating that it is not very suitable for fireproofing. The more we consider the possible development of "Pyrolaine" the more does it seem that its main outlet will be in the acoustical field, more particularly where soft coatings are no detriment, and where good low-frequency absorption is required. Lack of mechanical strength discounts the value of these coatings for use in railway carriages, ships, etc. At Fr.35 per kllc delivered in France, the fibre is fairly attractive provided no large amount of overheads is involved in further handling. Covering capacity is of the order of 1-lb. per sq.ft. 1-in. thick. Importation to Great Britain would involve-10- customs duty plus charges and freight, resulting in a delivered cost at Armley via London, of 44 2* o per ton. which is approximately what ve estimate the cost of the Dublin Amosite cisn rock fibre will work out at, this having a very much better covering capacity which will more than hold its own in competition. Nevertheless, the white colour of "Pyrolaine" may enable us to use it for surfacing acoustic coatings, and our investigation is proceeding on these lines. NLD/WL 20.1.54 N.L. Dolbey