Perhaps You Didn't
Page 56
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Know...
THE excellent reception accorded to our first series of questions and answers on technical and semi-technical matters has prompted us to develop this feature.
To render the answers even more useful, we suggest that readers who require information of this nature should submit their queries for attention, so that others will also benefit.
It will be remembered that a member of the party depicted above is putting his problems before a Mr. Jones, whilst the others are listening-in.
What is Polarized Light?
M.P.: " I have heard remarks concerning the use of polarized light to prevent glare from headlatnps, but I find difficulty in following this new principle."
Mr. Jones: "The history of polarized light is interesting. In 1919, the wife of an American, Mr. L. W. Chubb, now director of research for the Westinghouse Electric and Manufacturing Co., East Pittsburgh, was killed because the driver of the car in which she was riding was dazzled by headlights. Mr. Chubb determined to find a solution to the problem and, in 1920, he applied for a patent for the principle in question; after 17 years of fighting, it has been granted to him.
'Polarized light vibrates in one plane and can be produced by throwing ordinary light, which vibrates in all planes, on to a polarizing screen. This may be described as ' combing ' the light, permitting vibrations in only one direction. Headlight lenses can be made of these screens, drivers may wear polarized glasses or windshields can be specially constructed to give the effect.
" In his patent, the inventor points out that transparent screens of any size can be made by sandwiching crystals of iodo-sulphate of quinine between glass or other suitable materials. The driver can see polarized light thrown by his own headlamps, but that from oncoming vehicles would be polarized in a plane 90 degrees from his own and the light would not get through the windscreen or glasses."
Features of Safety Glass.
M.P.: " I see that safety glass is now required for windscreens and outer windows facing to the front of motor vehicles. I understand that there are various forms of this glass."
Mr. Jones: " At present there are two leading classes of safety glass. The older, and that used more frequently, is a sandwich consisting of two thin sheets of glass with some transparent plastic and elastic material between e22
them Great care is required in the manufacture and in the selection of the material to which the glass is cemented to avoid the appearance of bubbles, or, later, discoloration due to the destructive action of the sun. At one time, rainbows and blisters in the glass were frequent, but now the glass is tested under ultra-violet rays to the equivalent of 20 years of ordinary service, whilst, to find the resistance to fracture, a steel ban is dropped from various heights.
" A later form is solid plate glass, especially toughened by heating throughout and then rapidly cooling only the surfaces. This puts the surfaces in tension and, if the glass receives a sharp blow, the whole piece shatters into crystalline fragments, which are practically harmless. The glass may remain in position and become almost opaque, but it can be pushed out without danger of receiving cuts."
Causes of Big Oil Consumption.
M.P.: "in an engine which uses an excessive quantity of oil, despite wellfitting pistons and rings, what would be the probable cause and what steps could be taken to improve matters?"
Mr. Jones: " Excluding the possibility of direct leaks past faulty joints, cases of excessive oil consumption for no obvious reason have been traced to 'inadequate means provided for oil, scraped from the walls, to return to the sump. In these cases enlarging the holes in the chamfer below the scraper ring at once cured the trouble.
" In another case where consumption suddenly increased for no apparent reason the cause was eventually traced to the temporary use of a cork in place of the normal crankcase breather which had become damaged."
Why Change Crankcase Oil?
M.P.: "We are advised to change crankcase oil at certain periods. Is this because the oil is wont out? What would be the possible result of ignoring such advice?"
Mr. Jones: " Oil experts tell us that oil does not wear out and therefore we may assume that the discoloration, lower viscosity and lack of lubricating properties are due chiefly to con
tamination by carbon particles, road dust and fuel. This, I think, is proved by the fact that used oil can be reconditioned for further use.
"In many industrial plants filters of this type form an integral part of the system, the oil being used almost continually, losses being made good with fresh oil.
" Whilst it may seem a waste to drain out a crankcase, in the circumstances it is an economy as, after an extended period of use the oil does lose its lubricating properties for the reasons already given."
• Tyre-tread Thickness Explained.
M.P.: " I have noticed that, in heavy vehicles, the rubber treads on the tyres are very thick, whereas, to take the other extreme, racing tyres have little rubber, yet it would seem that the latter withstand much more wear."
Mr. Jones: "You must remember that the real strength of a tyre does not lie in the rubber, but in the cord carcase. The tread rubber does little more than act as a wearing sole and assist in the prevention of skidding. When tyres have to be run at very high speeds, the mere weight of a heavy tread would cause it to strip off under centrifugal force. In tyres used on such cars as the ' Bluebird ' there is practically no rubber tread, the rubber present being little more than sufficient to bind together and waterproof the cords of fabric."
Is a Worn Tyre Liable to Burst?
M.P.: "Sometimes I have seen tyres worn until they exposed a layer of material and, occasionally, lighter rubber. Is there any danger of such a tyre bursting?"
Mr. Jones: "It is a common fallacy that this is the case. Actually, the light rubber which appears below the ordinary tread is known as the breaker strip. It is soft and acts as a cushion between the harder rubber and the carcase. It does little to increase the strength of the tyre, but, of course, there is more liability to puncture if it be exposed, as the protection of the thick tread is removed; also the tyre becomes smooth and more liable to skid on a greasy surface."