Flat-Top Chain Conveyors

Several other types of flat-top chains are available, but space does not permit covering them in this book. There is a series of flat-top chains that use modified no. 40 or no. 60 base roller chains and have top plates that snap on to the base chains. The plastic chains can be made from many other plastics than acetal, and there are special side-grip, high-friction, and low back-pressure, flat-top chains for unusual conveying needs. If the user has unusual needs, they should contact an ACA flat-top chain manufacturer for help with selecting the proper flat-top chain. 

Nine types of chain conveyors were described in the chapter on engineering steel chain conveyors. Most of those descriptions do not apply to flat-top chain conveyors. Most flat-top chain forms a special kind of slat conveyor, and that is the only type covered in this chapter. 

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Important diameters for standard flat-top chain sprockets are also shown in Figure 4-42 and Figure 4-43. In most cases, the barrels of the chain engage every other tooth on the sprocket, so the number of effective teeth is one-half the number of actual teeth on the sprocket. The number of effective teeth must be used to compute the correct pitch diameter. The maximum outside diameter is larger than the pitch diameter only for sprockets with 19 actual (or 9>/2 effective) teeth or more. That is one of the reasons why a sprocket in a flat-top chain conveyor should have at least 19 actual (or 91/2 effective) teeth. 

The flat-top chain conveyor must be wide enough to handle the widest object carried on it. Also, if speed is limited by other factors, two or more flat-top chains may have to be used in parallel to produce the needed ouQ)ut. This will increase conveyor width. There also must be enough clearance height to permit the carried material to pass, as well as enough clearance height in the return mn... 

Shaft center distance is often the same as the conveyor length, but sometimes it is longer. The shaft center distance may be made longer to accommodate additional loading and unloading equipment at the ends of the conveyor. Flat-top chain conveyors generally should not be more than 100 ft long. 

Ways or wear strips normally are used to support the load-carrying strands of a flat-top chain conveyor. A wide variety of materials can be used in wear strips for flat-top chains, but the most commonly used materials are listed below. 

The return strand of flat-top chain conveyors should be supported when the shaft center distance is more than about 5 ft. This is because a long unsupported return strand hangs in a catenary and can greatly increase chain pull. 

FIGURE 12-10 Side clearance in multiple-strand flat-top chain conveyors. 

Both sprockets (head shaft and tail shaft) are the same size in most flat-top chain conveyors. In this case, the chain length can be calculated using Equation 12.11 ... 

A flat-top chain conveyor is basically a special type of slat conveyor. Some of the lubrication advice for other conveyor chains also applies to flat-top conveyor chains. However, many flat-top chain conveyors have features that demand special lubrication. Flat-top chain conveyors should be lubricated whenever possible as shown in Figure 13-16. Lubrication reduces friction and chain pull, and lubrication increases the life of the chain and wear strips. 

As with other types of chain, flat-top chain needs good lubrication in the joints. Even more important, flat-top chain conveyors need good lubrication between the top plates and the wear strips. If lubrication is allowed, be sure to get good lubrication between the top plates and the product in the accumulation section. 

Water can be used to lubricate flat-top chain conveyors, but plain water should be used only if oil or a soap and water mix cannot be used. Water is not as good as oil or soap and water because of its higher friction and poorer cleaning ability. Water should only be used to lubricate plastic or stainless steel chains because water rapidly corrodes carbon steel chains. 

Sometimes no lubricant can be permitted on a flat-top chain conveyor. For those cases, a low-friction acetal chain with Nylatron comers can be used. This combination offers the lowest coefficient of friction. 

In drip lubrication, oil, soap and water, or plain water is dripped onto the chain and wear strips. As the drip rate increases, the drops turn into a stream. This is still considered to be a form of drip lubrication. Typical oil stream lubrication of a flat-top chain conveyor is shown in Figure 13-16. One must be sure that lubrication reaches all critical points in the conveyor. It is especially important to get lubrication between the chain top plates and the wear strips. 

Chapters 9 and 10 were reorganized to make the selection steps similar for all chain conveyors. Chapter 12, on selecting flat-top chain conveyors, is all new. There was nothing on flat-top chains in the first edition. This is a major addition. 

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