Patent GB-689908-A (GB)
Title: A device for gauging surface roughness, and a method of manufacturing the same
IPC: G01B21/30
Filed: 1950-03-14
Abstract: A device for gauging surface roughness (see Group XIX), comprises a series of juxtaposed standard specimens having testing surfaces differing progressively from one another in roughness over a given range, the said specimens being made of a synthetic resin of the type known as "cast resins," that is to say, resins that can be polymerized without pressure, or at low pressure, by heating, by the action of catalysts, or by the combined action of heat and catalysts. Suitable resins are phenol-formaldehyde resins prepared in an alkaline medium, resins of the acrylic type prepared by pure polymerization in the presence of catalysts of monomer bodies possessing one or two double bonds in the constitution of their molecules, and the resins obtained by the combination of melamine and formaldehyde.  The phenol-formaldehyde resin may be made by mixing together 270 grammes of phenol, 250 grammes of formaldehyde at 34 per cent and 8 grammes of ammonia at 33 per cent.  The mixture is boiled until two distinct phases are formed, the phase of greater density comprising a not completely polymerized resin containing water.  This phase is separated and heated in a vacuum on a water bath so as to free it from the dissolved water, care being taken, however, to arrest the operation while the resin is still very fluid at a temperature of 60 DEG  C.  The device is made by selecting plates of graded roughness made of steel, pressing a lead sheet on to the assembled plates under high pressure, removing the lead sheet and pouring the synthetic resin on to the negative thus obtained, the whole being then introduced into a stove until the time arrives for demoulding.  Before the impression is made, the lead sheet is carefully scraped and rolled so as to impart to it as fine a surface condition as possible.  The leaden negative preferably comprises a plurality of superposed sheets, the sheet that is to receive the impression being thin and the other sheets serving as a support for this thin sheet.  The leaden negative may be protected by a coat of varnish before it receives the synthetic resin.  An incurvation of the effective surface of the resulting article may be obtained after heat treatment by allowing one surface of the article to be exposed to the atmosphere while the other surface is shielded from the air by the mould.ALSO:A device for gauging surface roughness, (see Group XIX), comprises a series of juxtaposed standard specimens having testing surfaces differing progressively from one another in roughness over a given range, the said specimens being made of a synthetic resin of the type known as "cast resins," that is to say, resins that can be polymerised without pressure or at low pressure, by heating, by the action of catalysts, or by the combined action of heat and catalysts.  Suitable resins are phenol-formaldehyde resins prepared in an alkaline medium, resins of the acrylic type prepared by pure polymerisation in the presence of catalysts of monomer bodies possessing one or two double bonds in the constitution of their molecules, and the resins obtained by the combination of melamine and formaldehyde.  The device is made by selecting plates of graded roughness made of steel, pressing a lead sheet on to the assembled plates under high pressure, removing the lead sheet and pouring the synthetic resin onto the negative thus obtained, the whole being then introduced into a stove until the time arrives for demoulding. Before the impression is made, the lead sheet is carefully scraped and rolled so as to impart to it as fine a surface condition as possible. The leaden negative preferably comprises a plurality of superposed sheets, the sheet that is to receive the impression being thin and the other sheets serving as a support for this thin sheet. The leaden negative may be protected by a coat of varnish before it receives the synthetic resin.  An incurvation of the effective surface of the resulting article may be obtained after heat treatment by allowing one surface of the article to be exposed to the atmosphere while the other surface is shielded from the air by the mould.