Types Of Fasteners Research Articles

Belt-Flexing Test of the Du Pont Type

Abstract In general, flexing tests are subject to large errors, some of which have been studied using a test of the du Pont belt type. An improvement in the standardization of the test conditions can be effected by using a suitably designed belt balance arm and regularly adjusting the length of the belt. The rate of cracking and also the reproducibility of the results is affected by the design of the test-piece and also by the type of fastener used. Although the error between the results on replicate test-pieces is extremely large, more important are the large errors due to lack of reproducibility of replicate molded slabs, and this variability probably arises during vulcanization. Extremely large differences can also occur between nominally identical repeat experiments. This may be due to differences in the judgment of the stages of cracking in different experiments. Graded photographs were found not to be of any value in improving the reproducibility of results between two different operators. Attention is drawn to the differences in types of cracking obtained with the du Pont and De Mattia test-pieces. It is pointed out that with the du Pont test-piece the cracking tends to develop in depth more than is the case with the De Mattia, and therefore it is more difficult to construct or use graded photographs with the du Pont test. Accepting the fact that variations in the disposition of the stages of cracking do occur between two different experiments, a method of treating flex-cracking results graphically is suggested. By this method random variations in results are ignored and the average flex-cracking results obtained. It is suggested that flexing properties may be defined by two characteristics, viz., (1) Crack initiation time, and (2) Crack propagation time, and an example of the method of determining these characteristics is given.

New Box Testing Laboratory

THE Department of Scientific and Industrial Research has set up equipment at the Forest Products Research Laboratory for testing packing-cases, boxes, etc., under stresses similar to those encountered during rail or road transport. The installation is the first of its kind in Great Britain, but several are in use in the United States, where the experience gained has considerably reduced the claims for damages paid by the railways. The plant at Princes Risborough tests both the endurance and strength of the boxes. For the former test, the cases are placed inside a large rotating drum, which revolves twice a minute, wooden baffles on the inner face causing the article to fall in different positions in turn. A moderately well-made container was found to collapse after about thirty falls, whereas one of really good design could withstand 150 or more falls. A ‘dropping machine’ tests the resistance to falls on the face, corner or edges at will, while in a further apparatus resistance to crushing can be determined. The efficiency of nailing, different types of fastenings and packings are also being investigated, and on behalf of the Ministry of Agriculture special tests are being made with the view of drawing up a standard specification for fibre-board containers for National Mark eggs. The Box Testing Laboratory will be available to manufacturers and others who wish to study possible improvements in methods of box construction and in the packing of contents to give the greatest protection. The scale of charges, and a statement of the conditions under which tests will be made, can be obtained from the Director, Forest Products Research Laboratory, Princes Risborough, Bucks.

Steam turbine blading

The paper is a review of the present position of the subject of steam turbine blading.Section (1) describes the causes and effects of corrosion and erosion. The most important materials in use are enumerated and compared.Section (2) deals with the form of the blade passage in impulse and reaction machines, and with the energy losses occurring in the blading. Some meLhods of tapering the blades are given.Section (3) details the stresses in the blades and describes the types of blade fastenings, lacing and shrouding.Section (4) gives the methods used for obtaining a large exhaust area.Section (5) deals with vibration and its causes, and shows a method of correcting for the effect of centrifugal force. The lines on which the problem is being attacked are described.Section (6) is devoted, to the methods of manufacture by-milling and by drop forging.A bibliography is appended.