Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Patent
1983-02-07
1985-07-23
Myracle, Jerry W.
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
73644, 73801, G01N 2202
Patent
active
045302464
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to methods and apparatus for identifying as fractured an article of brittle material, or articles of brittle material in a succession of generally-similar articles, the invention being concerned primarily with the automatic inspection of brittle articles in industrial manufacturing processes. Such a process may comprise the manufacture of the brittle articles themselves, or for example other processes such as the filling of the articles where the articles are in the form of containers.
The term "fractured" and any reference to a fracture herein, where the context permits, are to be understood to refer to any structural fault, within the brittle material itself, such that, if a suitable force is applied to the material so as to set up in the material a stress (which may be compressive, tensile or torsional, and which may be linear or in the form of a hoop stress), the effect of such stress will be to enlarge the structural fault rather than a mere change of dimensions by way of strain. Such faults may take the form of a crack, a chip, a bubble or other flaw in manufacture, such as to produce a weak zone or stress raiser in a manner not contemplated during design of the article.
The term "brittle" is to be interpreted in this light also, i.e. a "brittle" material as referred to herein means a material in which such a fault, if pre-existing, will tend to propagate upon internal stress being induced. Examples of such materials include glass, ceramics and many plastics materials.
Articles to which the invention is applicable include (by way of non-limiting example): glass containers such as bottles, jars, flame-sealed ampoules or laboratory glassware; fine glass articles such as decorative lead-crystal glassware; ceramic articles such as pottery, earthenware, porcelain or china; ceramic components such as insulators for spark plugs or other purposes, bearings and refractory components for industrial or similar uses; moulded plastics components such as cases for electronic equipment; plastics bottles and other containers made of plastics.
BACKGROUND OF THE INVENTION
The inspection of brittle articles may be carried out in a number of different ways, of which simple visual inspection is perhaps the most common. Apart from visual inspection, there are on existence, or there have been proposed, automatic or semi-automatic techniques for inspecting glass bottles and jars so as to detect flaws such as cracks. Such techniques are generally optical in nature and rely on light-scattering phenomena.
In connection with fine, hand-made circular glass and ceramic ware, particularly articles such as vases, bowls, drinking glasses, cups, plates and the like, it is common practice to test the finished article (after firing in the case of ceramics) for soundness by applying a light, sharp impact with the fingers, so as to cause the article to resonate with an audible note. The skilled operative can tell from the quality of this note whether there is any fault in the article. The principle of using resonant vibration in the audio range, produced by impact, is applied to a proposal for repetitive industrial inspection of one specific product, viz. plastics-coated glass bottles, contained in the United Kingdom patent (GB-A-1416082) granted to Dart Industries Inc. In the method described in GB-A-1416082, a positive impact force is applied to the bottle, and the intensity of the vibrations within the audio range 50 Hz-10,000 Hz, emitted by the bottle after a predetermined lapse of time, is then detected, by means of a transducer in contact with the bottle, and measured. In a good bottle, i.e. one having no cracks, the intensity after the pre-determined time lapse is known for any particular design and size of bottle and a given impact force, so that this value of the intensity may be used as a datum. If the bottle is cracked, the resonance will be damped by the crack; therefore if the intensity after the predetermined time lapse is significantly less than the datum value, the bottle
REFERENCES:
patent: 3924456 (1975-12-01), Vahaviolos
patent: 4077254 (1978-03-01), Mercer, Jr. et al.
patent: 4089224 (1978-05-01), Scott et al.
patent: 4090400 (1978-05-01), Vahaviolos
Grime David A.
Knight Malcolm R. M.
Pitman Kelvin G.
Metal Box Public Limited Company
Myracle Jerry W.
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