Slat conveyors are used heavily throughout industry for conveying manufactured items and materials.
The range of slat types and designs developed over the years is extensive, however slats are normally attached between two chains utilising ‘K’ type attachments. Slats can be attached every pitch, creating an almost continuous slat conveyor with minimal gaps, or slats can be attached at spacing’s as required. Overlapping slat assemblies can be used to provide a fully continuous slat top, with slats attached to ‘K’ attachments on every pitch of the chain. The most common design is for the conveyor chain to carry both the slats and the product being conveyed, with outboard rollers being used for heavier applications, to help spread the bearing loads.
For heavy duty slat conveyors the slats often have furniture attached to assist with slat flex, especially at the loading point of the conveyor. Bump rails, with a small clearance below the slat, offer a cost effective solution, while more arduous applications generally have individual rolling wheels underneath the slat (either 1 off or set as a pair), with extra tracks fitted to correspond with the slat rollers. Outboard rollers on the chain (usually flanged) help to guide the assembly, even under heavy perpendicular loadings, while also supporting the weight of the slat assembly and product. By using the outboard rollers to carry the weight, the conveyor chain is only used to transmit the power and motion.
Slat conveyors can be used for simple flat/horizontal conveying, inclined conveying, swan neck conveying or conveying over complex multiple sprocket systems.
The type and design of slat is normally bespoke to the application, however some common types of slat assembly are listed below. Brooks are able to supply conveyor chains, sprockets and slat assemblies to suit virtually any conveyor applications.
Piano Hinge Slats
A continuous metal belt, fixed around the central point of a hollow pin conveyor chain. Slats interlock by a mechanism similar to that of door hinges. Interlocking curled parts are threaded with a tie rod which is locked between the chains, creating a continuous slatted conveyor. Hollow pin conveyor chain is used to allow the tie rod to pass through chain, holding both the slats and chain in position. The most common use for this design of slat is in swarf handling and food production. Optional fittings include up stands to help prevent product slippage and side plates, to contain the product within the belt and prevent product overspill on to the conveyor chain.
It is also possible to supply piano hinge belts with a meshed middle section. This type of meshed piano hinge belt is common in the food industry for drying and cooking applications, as air is able to flow through the underside of the slat.
Pressed Channel and Flat Plate Slats
An almost continual metal (or wooden) belt, fitted above the chain and providing minimal gaps between the slats. This type of slat conveyor is used for conveying large products where there is no danger of the product penetrating between the slats, either when conveying or when the slats open up around the sprockets. The slats themselves are either a steel plate, or a steel plate with 90° bent edges front and back (to provide added rigidity i.e. channel section). One common application is moving floor conveyors for car manufacture, where fittings are added to the top of the slats to interlock with the vehicles wheels. Other applications include steel fabrication i.e. moving sheet steel, or moving food products such as bread loafs.
The final design of the chain and slat assemblies depends on the products being conveyed. The slats must be thick enough to carry the required product without bending, while heavier slats increase the working loads of the conveyor, requiring larger chains and more power to drive the system. Flat top type conveyors do not generally require up stands, although side plates can be welded onto the slats to help contain the product and protect the conveyor chains.
Apron Slats and Feeders
Apron slats are similar to pressed channel conveyors, except the slats are manufactured to overlap, creating a continuous, gap free, steel topped conveyor. Often called feeder conveyors, this type of slat is usually found underneath hoppers, dragging out the material and conveying it to its next destination. These types of conveyor are generally the heaviest duty, due to the head load of the product pushing down on the conveyor and the frictional forces from dragging out the material from the underside of the hopper. For the heaviest of applications, more than two strands of chain are used, allowing the motor power to be distributed through a greater number of chains, while also supporting the middle sections of the slat and preventing bending.
Apron slats also offer a heavy duty alternative to rubber belts. The most common use of apron slats over a rubber belt is when conveying products which cause the belts to rip or split, such as recycling of consumer electrical goods which often have sharp edges. Another application, in which apron slats are used for similar reasons, is conveying raw materials such as iron ore and limestone. The ability of the slats to drag the material from underneath a hopper makes this type of system very useful for tipper truck unloading or metering a feed to other areas of the process.
The design of the slat often depends on the type of application. The most common is a flat plate with different radii on the leading and tailing edges. These radii are designed to give a slat overlap whilst conveying, but allow separation of the slats from one another when articulating around a sprocket. Another form of design is to set the ‘K’ attachments at an angle, before fitting heavy duty flat cross slats, which are longer than the pitch of the chain. The angled K attachments allow the plates to overlap one another, whilst still articulating around the sprocket
Light duty versions of these slat designs are also available for less demanding applications
Rubber Top Supported Belt
A rubber top belt conveyor generally consists of a pair conveyor chains with steel channel or box section bolted between the chains onto ‘K’ attachments. A rubber belt is then fitted down onto the top of steel channels, creating a supported rubber belt assembly. For light duty applications, rubber belts are simply run unsupported or over a smooth flat steel surface. For heavier duty applications, the supported rubber belt system is used. A supported rubber belt conveyor is generally used if there is a risk of the product becoming lodged between metal slats, for example general household waste recycling, where a wide variety of items must be conveyed.
An added benefit of using a supported rubber belt is the transmission of power through the conveyor chains, rather than the belt. This means that the belt is only required to carry the product, assisting in providing a longer life to the rubber belt, as any damage to the belt is not exacerbated by the tension of the rubber between the head and tail sprockets (this tension is taken up by the chains).
A major drawback of supported rubber belt conveyors is the flexing of the rubber gradually undoing any nut and bolts used to attach the rubber belt to the steel channel. One method to overcome this is to simply weld nuts to the underside of the steel channels. As the belt applies cycling loading to the bolts, they begin to protrude from the belt, allowing an easy visual inspection for correction and preventing nuts from dropping off on the underside of the conveyor and jamming within the conveyor chains.
Rotating and Tipping Slats
It is possible to manufacture slats which are free to articulate around a pivot point. One type of slat is a rotating slat, which is usually pivoted about its centre of gravity. The slat can either be rotated by fixtures on the conveyor structure, or more commonly the slat is free to articulate with gravity, ensuring that the slat is always horizontal.
A second type of slat is the tipping slat, which is attached to the chain on its leading edge. This type of slat is usually held horizontal by a runner down the centre of the conveyor. Where there is no runner present, the slat pivots to a vertical position, dropping the product out between the conveyor chains.
The most common application for both of these types of slats is in ovens, where the product is conveyed around multiple sprockets, increasing the residency time within the ovens.
Slats can be fitted to conveyor chains in numerous ways, such as through hollow pins, by extended bearing pins or by fixtures attached to ‘K’, ‘L’ or ‘F’ type attachments.
Roller Slat Conveyors
Roller slat conveyors utilise free rollers, mounted between two conveyor chains often on extended bearing pins and replacing solid slats. This type of conveyor is designed for larger rigid items, such as cases. With the chain running on guide rails, the free rollers may rotate allowing the object to be held stationery or be propelled at speeds greater than that of the conveyor. At the feed off point, the free rollers can be raised on guides, transferring support from the conveyor chains and accelerating the object, often onto the next conveyor.
Bespoke Slat Solutions
There are an immeasurable number of bespoke slat solutions in the market place, usually developed to suit a bespoke application where standard products are not suitable. These can range from ice scraper conveyors for fish markets, barrel conveyors in a brewery, storm screens in water processing or cooling conveyors for steel. Some of the slats simply attach over a single pitch of chain, such as for transferring large aluminium billets on deep link chains, while more complex conveyors allow the product to be re positioned while in transit on the conveyor, such as barrel washing.
If you have an existing bespoke conveyor or are looking for novel solutions during new product development, then please discuss your requirements with one of our engineers.