Page 172 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
150

Figure 7.3 Chain joint construction.

The variables in a roller chain are pitch p, roller diameter d , pin diameter d ,
1 2
width between inner link plates b , link plate thickness t, the number of links L and
1 p
strand spacing p for a multiple-strand chain, as illustrated in Figure 7.2. Pitch is the
t
centre distance between corresponding hinges of adjacent links, which identifies the
dimension of a roller chain. The larger the pitch, the larger the chain size and the greater
the power transmission capacity of a chain. The width between inner link plates b is
1
an internal dimension corresponding to the width of sprocket tooth. Usually, an even
number of links with straight links is preferred, as an odd number of links needs an
offset link that may introduce additional bending stress when forming a loop chain, as
illustratedinFigure7.3.

Roller chains are standardized products, with the pitch as a base for all other dimen-
sions. Standardization organizations worldwide have issued standards, for example,
ANSI/ASME B29.1-2011 [6], ISO 606:2015 [7], GB/T 1243-2006 [8] and so on, which
give standard dimensions for chains and sprockets to ensure interchangeability. An
identification code is adopted to facilitate specifying and ordering. In the ANSI/ASME
standard, the digits (other than the final zero) indicate the pitch of chain in eighths of an
inch [1]. For example, the number 100 chain has a pitch of 10/8 in. In GB/T 1243-2006
standard in China, the designation is indicated by chain number, number of strands
and number of links plus the Standard No. The chain number indicates the pitch of
chain in sixteenths of an inch. Chain number is usually followed by a serial number
A or B.Serial A is used in America and many other countries, while serial B is mainly
used in European countries. Both serials are available in China. For example, 08A-1-86
GB/T 1243-2006 indicates a serial A single-strand chain with a pitch of 12.7 mm and
86 links under Standard GB/T 1243-2006. More detailed specifications can be found in
relevant references [6–8].
Silent chains are named because they operate more smoothly and are quieter than
conventional roller chains. A silent chain is made from a series of toothed link plates
pinned together across the width of chain to permit articulation. The teeth of links
may have straight-sided or involute profiles. Power is transmitted through engage-
ment of chain teeth with sprocket teeth. Compared with roller chains, silent chains
can operate at higher speeds and carry greater loads, yet they are more expensive
and heavier.