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Rafer: Glossary

Tailor-made conveyor chains

Fit: Assembly of a outer container part (bore) and an inner contained part (shaft). The male (shaft) and female (bore) parts have the same nominal size but different tolerances offering either positive play, clamping or uncertain play. Boring: Operation which consists of carefully machining the inner surface of a cylinder or any other hollow part. The result of this operation is known as a bore. Shaft: Mechanical member transmitting power in the form of torque and rotary movement. The cylindrical shape of this member is what gives it its name.

Pin: Straight mechanical part around which one or more other parts rotate. Its sole purpose is to guide a rotation or translation movement.
The choice of diameter is very important for pins. For correct guiding, the length must be at least twice the value of the diameter.
Chain pins are generally solid, but they can be hollow and used for attaching accessories or spacers connecting two chains operating in parallel.

Burr: Refers to unwanted excess material, often very thin, as if the material had been smudged. It is anti-aesthetic and can be sharp.

Bloom: Steel bar with a square or rectangular cross-section larger than a square of 120 mm (160 mm for certain steel industries), with variable length intended for being inserted in rolling trains referred to as finishing mills.

Bolt: Assembly member made up of a screw with a uniform thread and flat end (or threaded rod) and a nut (and optionally a washer).

Carburisation: Thermochemical treatment which consists of making carbon penetrate the surface of a steel in which the carbon percentage is too low to be hardened, in order to transform the surface into a highly-carburised steel that can be hardened.

Breaking load: Weight of the load that causes the chain to break (permanent deformation or destruction)

Key: Metal fastening inserted by force in a notch made in a part in order to rest against another part or between two parts in order to secure them to one another and prevent rotation.

Safety factor: In order to determine the breaking load of a chain, a safety factor of the force F needs to be applied.
Breaking load = F x safety factor
This factor is dependent on the operating conditions. It can range from 5 to 12, but is generally between 7 and 10. It is advisable, however, to check the joint pressure before ultimately choosing the chain, since this can be a determining factor.

Drawing coefficient (DC): Variable parameter according to the condition of the raceway, the lubrication, the diameter of the chain roller, i.e.:
-0.10 for a chain with standard rollers, good lubrication and clean raceway
-0.15 for a chain with standard rollers, uncertain lubrication and obstructed raceway
-0.20 for a chain with small rollers, uncertain lubrication and obstructed raceway
-0.33 for direct friction of the link plates on the steel raceway
-0.02 to 0.05 for ball rollers (the larger the diameter of the roller, the lower the coefficient)

Conveyor: Continuous handling apparatus in a closed circuit, providing overhead or ground-level transport of loads or materials.

Screen rake: handling apparatus for removing the refuse that builds up on the screens.

Gear teeth: Set of teeth of a sprocket wheel; generally cut; can also be flame-cut and ground for special profiles or for very large rollers.

Pitch diameter: distance between the centre of the wheel and the approximate middle of the teeth.
PD = pitch/sin(180°/no. teeth)

Ductility: Refers to the capacity of a material to deform plastically without breaking. Breaking occurs when a defect (crack or cavity) becomes critical and spreads.

Bushing: Cylindrical metal nozzle used to assemble two parts, by protecting the pin.

Hardness: For metals, defines the resistance of the surface of the sample to penetration by a harder body, for example the ball or the tip of a hardness tester.

Sluice: Structure built between two bodies of water on different levels, which allows boats to pass from one to the other and vice-versa by means of opening and closing mobile elements, doors and valves.

Elevator: Appliance or engine used to transport loads or materials vertically or on very steep slopes.

Enamelling: Depositing a vitreous, transparent or coloured layer on a metal or another substrate. The part to be enamelled is covered with pigments, in suspension in a volatile oil, and then exposed to a temperature of around 800 °C; the oil evaporates and the molten pigments are bonded to the surface. Enamelled parts have great durability, excellent resistance to scratching and chemical agents, and are easy to clean.

Spacer: Tube-shaped part intended for maintaining a constant separation between two ball bearings.

Coating: Metered mix of aggregates and filler coated with bitumen or tar, used for the top layers of pavements and for watertight covering of canals or dams.

Shoulder: Sudden change in diameter, generally in order to provide a bearing surface for another part.

Oven: Enclosure with a very high temperature and humid heat.

Excavator: Earthmoving plant provided with a bucket chain mounted on a roller track or a bucket wheel.

Threading: Consists of one or more helical grooves on a cylindrical outer surface.

Roller: Chain roller with a diameter greater than the height of the link plates. It allows the chain to roll over a flat surface. Rollers can be straight or shouldered in order to provide lateral guiding. The straight or shouldered rollers are made from treated steel.

Bucket: Type of trough with variable capacity and shape, used in a certain number of handling apparatuses (dredger, elevator, bucket loader, etc.) for digging the ground.

Cotter pin: Small metal part which is inserted in the end of certain elements so that the assembly forms a removable rigid unit. It can be used to immobilise or position a part in relation to one another, acting as a pin or a safety part (shearing in the event of an overload)

Greaser: Device which, in a machine, automatically supplies grease or lubricant to moving members.

Shot-blasting machine: Machine which blasts shot in the form of micro-balls in order to strip a surface of the material that covers it.

Seizing: Mechanical accident between two metal surfaces rubbing against one another, when metal particles come loose from one surface and scratch the other surface more or less deeply, leading to heating and welding of the surfaces in question.

Log: Trunk of a felled tree, with the top and branches removed.

Guiding / Alignment: The guiding quality of the chain during its movement as well as the alignment of the pinions that drive it are essential aspects. These elements must be checked systematically before starting up any new equipment.

Play: Space left between two parts that are not perfectly assembled. Since it is impossible to manufacture parts with perfect geometry, play is an essential feature when assembling the elements of a mechanism.

Joint: Device allowing a rotary movement to be transmitted between two shafts in which the relative position is not properly defined, incorrect or variable.

Rolling mill: Industrial facility used to reduce the thickness of a material (generally metal). It also allows the production of extruded bars (long products).

Limit of elasticity: Stress above which a material starts to deform in an irreversible manner.

Lubrication: It is advisable to grease the return slack strand of the chain. This allows the lubricant to access the centre of the chain joint. The quality of the lubricant used and the care taken when applying it to the chain can substantially affect the behaviour and service life of the chain.

Link plates: Metal plates linking the joint parts. These can be roller link plates, in direct contact with the bushings, and pin link plates, in direct contact with the pin.
Two roller link plates or two pin link plates form a chain link.

Connecting links with self-locking nuts: The two pins are riveted to a link plate at one of their ends and the other end receives a connecting link plate immobilised by self-locking nuts.

Connecting links with pinned pins: The connecting link plate is immobilised by pins to allow easier removal. For certain applications, we can deliver chains with the pin link plates pinned on one site.

Flat section: Flat surface on a cylindrical part. Hub: Central part on which the parts that will rotate about an axis are assembled. It can be offset or symmetrical (wheel with no hub = disc).

Nitriding: Thermochemical treatment leading to the formation of nitride(s), for hardening the surface of the treated parts.

Pitch: Refers to the distance between two pitch centres with consecutive axes. The pitch must be selected according to the conditions for use, the type of product to be transported, the frequency of the accessories, the available space, etc. Not all pitch values defined according to a normal series can be achieved: see the table in chapter 2 containing the preferred pitch values. Pitches with intermediate values or pitches in inches can also be produced.

Shut-down / storage periods: Certain applications may have long shut-down periods. It is of utmost importance to take every precaution possible to protect the chain from corrosion by applying a suitable lubricant.

Link plates with attachments: made by bending or in the shape of brackets added by welding or by riveting:
o M-shaped attachments with one or more holes, forming an attachment plane parallel to the link plates.
o K-shaped attachments with one or more holes, forming an attachment plane perpendicular to the link plates, with the choice of three centre-to-centre distances for the holes (K2 with short, medium and long centre-to-centre distance), the width of the attachments varying accordingly. These attachments can be made on the roller link plates or on the pin link plates, on one side or both, with a frequency and arrangement to be specified in the order.
o Special attachments can be made on request for large enough quantities

Polishing: Consists of making a surface smooth and optionally shiny. Deep link plates: Asymmetric link plates that allow the loads to be placed directly on the chain rolling over straight rollers. These chains are generally used in parallel for form a belt and distribute the loads.

Perforated link plates: With one, two or three holes, for receiving attachments or spacer bars. If they pass through the chain, undercuts will need to be made on the gear teeth of the wheels.

Weight of the table: Total weight of the section in question, i.e. the entire mobile portion: chain + rollers + pallets + accessories, etc.

Joint pressure: In certain applications, the contact pressure in the joints is a determining parameter. In fact, this pressure is responsible, with every oscillation of the chain as it passes over the wheel, for causing wear of the chain. This pressure must be monitored, in particular when the chain is used in abrasive environments, with no maintenance, in stainless-steel chains, etc.
P in N/cm²
F=tangential force in the chain in N
S=projected diametric surface, or Ø of the pin (in cm) x bushing length (in cm)

The values of P for standard chains can be:
4000 N/cm² with plenty of oil
3000 N/cm² with good maintenance and clean environment
1500 N/cm² with uncertain maintenance and dusty environment
1000 N/cm² without maintenance

Groove: Long notch, with rectangular section, dovetailed or T-shaped, made in a part.

Performance: Coefficient that takes into account the performance of the members installed between the motor and the control shaft: coupler, reduction gear, chain drive, etc.
These coefficients are obviously cumulative. Furthermore, a coefficient of 1.05 is applied to every new 180° winding. This corresponds to losses due to the movements of the chain joints, to their placement on the wheels and to the rotation of the assembly made up of the wheels and shafts. Minimum tensile strength: It is spread out, according to a series based on normal numbers, from 20 to 900 kN

Rivet: Permanent assembly element. It is shaped like a cylindrical rod, generally made of metal, solid or hollow, provided at one of is ends with a head, in other words, a part with a larger cross-section.
The other end is flattened and widened by crushing, in order to secure the elements to be riveted together.

Washer: Small pierced disc placed between a screw or a nut and the part to be clamped in order to transmit and distribute the clamping force on the part.

Sprocket wheel: Circular member for transmitting movement by means of the teeth provided on its perimeter. The sprocket wheel transforms rotation movement into translation.
The wheels used with conveyor chains are made from mechanically welded steel or cast iron.
The gear teeth are normally foundry mill-cut or flame-cut but, on request, they can be delivered with trimmed gear teeth, which is mandatory when using bush chains.
The hubs are offset from the plane of the gear teeth unless the specifications state the special need for a symmetric hub. The wheels can be supplied bored and grooved. In the event of inserting a taper key in the offset hub, the key must enter on the side of the gear teeth unless specified otherwise.

Roller: Small cylindrical rotating part made from steel that is very hard, case-hardened or quenched or subjected to any other treatment and perfectly polished, used in mechanical construction, in bearings. Rollers protect the bushings and prevent the wear of the gear teeth.

Ball bearing: The purpose of a bearing is to reduce friction between two rotating parts. Thus, a bearing reduces the heat caused by rotation.
A bearing can also be used to reduce an alignment fault between two parts.
Several types of bearing exist: ball bearings, roller bearings, needle bearings.

Silo: A container for storing loose material. Tension: Called "slack strand adjustment", since a chain should not be tight. This adjustment makes it possible initially to absorb the joint plays and then to compensate for lengthening caused by wear. Excessive tension generates a considerable increase in joint pressure and leads to premature wear of the chain.

Tolerance: Inevitable inaccuracies of the manufacturing process mean that parts may not conform strictly to the dimensions established beforehand in the blueprint. We are therefore required to state that the dimensions actually produced are comprised between two limit dimensions, which are compatible with correct operation of the part. The difference between these two dimensions is what is known as tolerance.

Wire mill: Continuous rolling train specialised in the production of machine wire (semi-finished product intended for transformation). The facility is 300 to 400 m long.

Heat treatment: When applied to a metal part, it consists of causing the part to undergo structural transformations through predetermined heating and cooling cycles in order to improve the mechanical features: hardness, ductility, limit of elasticity, etc.

Hopper: Large stacking hopper intended for storing and then dispensing a bulk material (grain, sand, etc.) by gravity.

Vibratory finishing: Consists of polishing and deburring techniques. Its ingredients include abrasive elements (ceramic, porcelain, plastic, metals), chemical additives and, of course, the devices that generate the movements (vibrators, centrifuges, etc.). Rafer uses pyramidal pebbles to clean its mechanical parts.

Fixing screw: Commonly referred to simply as screws, these are mechanical members which comprise a threaded rod and a head. They are intended for fixing one or more parts together by pressure.

Galle chain:
Galle chains are made up of straight or hollowed-out link plates and shoulder pins. The shoulders of the pins maintain the separation between the link plates and allow them to mesh with the pinion. The chains can have single, double or triple link plates according to the required tensile strength.
Galle chains can transmit forces ranging from several hundred newtons to more than one thousand kilonewtons, while their speed should not exceed 20 m/min.
Galle chains are used for low-speed transmissions (drawing bench) or to provide to and fro movements (goods lift, dam valves, etc.).
They can therefore be used to transmit considerable forces with reduced space requirements.
The simplicity of their design allows them to be used for applications in difficult environments (outdoors, temperature, etc.)

Block chains:
Block chains offer high tensile stress with reduced space requirements. They can be used for handling heavy or abrasive bodies or when violent impacts are foreseeable (drawing bench, for example).
To increase the useful life of the chain (improved wear resistance), the blocks are sometimes bushed

Roller chain:
Single-strand chain:
Double-strand chain:
Triple-strand chain:
Multi-strand chain:
Solid-pin chain:
Hollow-pin chain:
Chain with L-shaped links:
Chain with cast-iron links:
Bush chain: Smooth roller:
Shoulder roller:
Quick attachment:
Pinned quick attachment:
Attachment with nuts:
Control wheel:
Idler wheel:
Mechanical table: