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Mechanical Engineers Data Handbook Episode 10

Tham khảo tài liệu 'mechanical engineers data handbook episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | MANUFACTURING TECHNOLOGY 215 Positions of welding In addition to flat welding which is the ideal position three other positions are used horizontal vertical and overhead. If one member is vertical and one horizontal the position is called horizon tai-vertical. In the last case a number of passes must be made to overcome the tendency for molten metal to run out. See figure. 5.12.9 Welding terminology throat size and allowable stress Welding practice The relevant British Standards are BS 4360 Part 2 BS 639 BS 1719 BS 1856 BS 2642 BS 449 and BS 499. Bull weld e included angle Fillet weld Effective throat size t throat thickness L leg length Fillet angle 6 60-90 91-100 101-106 107-113 114-120 tỊL 0.7 0.65 0.6 0.55 0.5 216 MECHANICAL engineer s data handbook 5.13 Limits and fits It is impossible to make components the exact size and an allowance or tolerance must be made which depends on the process and the application. The tolerance results in two extremes of size which must be maintained. The tolerances of two fitting parts e.g. a shaft in a bearing determines the type of fit and makes interchangeability possible. British Standard BS 4500 Part 1 1969 ISO Limits and Fits gives a comprehensive system relating to holes and shafts it can however be used for other components e.g. a key in a keyway. 5.13.1 Terminology Taking the example of holes and shafts there is a basic size and then maximum and minimum sizes for each their differences being the tolerances. Their differences from the basic size are called the maximum and minimum deviations . Basic size Minimum limit of size Minimum limit of size k I Lower deviation 4- Tolerance MANUFACTURING TECHNOLOGY 217 Types of fit The fit describes the manner in which two parts go together. A clearance fit means that the shaft will always be smaller than the hole. An interference fit means that the shaft will always be larger than the hole and a fitting force will be necessary. A transition fit means that there may be either .