Conveyor Design Guidelines

SELF TRACKING BELT is a friction driven belt system which utilises grooved rollers at both infeed and discharge to maintain belt tracking.  The top of the belt is smooth and flat while the bottom underside has crimped lateral weft wires to align and locate the longitudinal warp braid wires.  The crimped aligned lateral weft wires align with the grooves in both the infeed & discharge rollers and any intermediate support rollers or support wear strips.  Conveyor circuit design guidelines are as below:-

Conveyor Design Circuit

Belt carry way can be supported on grooved free to rotate rollers or on longitudinal grooved wear strip rails.  See below for further details.  The return way can be supported on free to rotate parallel rollers or flat strip longitudinal wear strips.  All wear strips should be tapered down at the leading edge to prevent belt catching.



Important Note: Reverse flexing of belt will result in early belt failure.

Conveyor Set up & Adjustment

Ensure that conveyor set up is square with end rollers parallel.  Across corners dimension “Z” must be equal.

Belt tension adjustment can be operated mechanically, pneumatically, hydraulically or by gravity weighted cables over pulleys.  At all times ensure that the tension adjustment operates with a parallel guiding system.  DO NOT OVER TENSION (see below)

The SELF TRACKING BELT does not require high tension to ensure slip free drive.  Only enough tension should be applied to  the belt to prevent belt slip on the drive roller during normal production operation.

The belt tension is listed below in Newtons/mtr of belt width.
 

Warp Braid Cable Diameter	Normal Operating Tension Range	Maximum Tension
2.0mm	1500—5000 N/m of width	10000 N/m of width
2.8mm	1500—7500 N/m of width	18000 N/m of width

At elevated temperature the belt will expand at the following coefficient of thermal expansion: 1.64 x 10^-6  / °C

When designing in the length of take up adjuster the following formulae is to be used to establish belt length expansion at high operating temperature.

L₁ = L₀ [1 + (1.64 x 10^-6  (T₁—T₀))
 

L1	Belt length at temperature T1 (operating temperature)
L0	Belt length at T0 (ambient temperature)
T1	Belt operating temperature
T0	Ambient temperature at installation.

 

Grooved Roller Design

Speed as well as roller diameter have an influence on belt life.  Due to the flexibility of the longitudinal warp braid wired rollers with belt wrap can be relatively small.  It is good practice to maximise all roller diameters, however the following minimum diameters should be noted:
 

Longitudinal warp braid wire diameter.	Minimum outside diameter of grooved roller. (mm)
2.0mm	210mm
2.8mm	315mm

Belt support rollers which have no belt wrap can be smaller than the above diameters.



Belt Width (Bw) mm = [17.5 x (n-1)] + 25
Roller Width (Rw) mm = Bw + 25
Number of Grooves or Cables (n) =     Bw—25     +1
                                                                      17.5
 
Note:  If “Thick Wall” tubing does not allow a reasonable material thickness after machining then consider “Hollow Bar”.

Methods of Belt Support

Carry Way Support

There are many ways of providing carry way belt support.  Below is a series of suggested arrangements that should be considered.  When designing support DO NOT allow contact with the crimped weft cross wire positions.



Notes:- 
1) Where possible use low friction material for wear strips.
2) The belt can also be supported over a series of grooved rollers with groove dimensions similar to the drive / idle roller. See page 5.
3) Please ensure that the wear strips have a tapered down belt lead in at any point where the underside of the belt starts to engage the wear strips.
4) The spacing is dependant upon the belt load, belt weight and belt tension to limit the belt deflection across the width.

Return Way Support

Typical arrangements of return way only flat wear strip that may be considered.

Straight In-line Staggered Wear Strips


* Ensure adequate clearance between the belt edge and any frame construction to prevent belt edge contact during use.
Note: It is recommended that all wear strip surfaces are faced with low friction material where possible.



All support rollers must be free to rotate and set horizontally and perpendicular to the centre line of the conveyor / belt.  In general diameters vary between 50mm and 150mm.  They should have sufficient diameter to suit the width of the belt and application without deflection.  The spacing can vary between 900mm and 3mtrs, however to limit the catenary belt sag between rollers and belt tension minimise the spacing. The catenary belt sag between rollers also acts as a natural belt take-up mechanism.

It is also possible to use a combination of straight wear strips & free to rotate rollers.

Technical Design Data:-

Conveyor Data Requirement	Formula	Units
Drive Tension for Horizontal Conveyors (TH)	= [(WM + WB) x FC + (WB x FR)] x L	Kgf
Drive Tension for Incline Conveyors (TI)	= TH + (HI x WM)	Kgf
Additional Back Pressure Tension (TBP)	= 0.8* x (TH ….or TI for incline conveyors)	Kgf
Maximum Total Belt Tension (TT)	= TBP + (TH ….or TI for incline conveyors)	Kgf
Belt Deflection (Sag) between Cross Roller          Supports (D)	= 570 [(WM+ WB) x A2] / TT	mm

* Factor is for 180° of belt wrap around drive. This factor will increase for belt wrap angles of less than 180°

WM	Product Load (Kg/mtr of belt length)	WB	Belt Weight (Kg/mtr of belt length)
FC	Coefficient of friction for Carry Way	FR	Coefficient of friction for Return Way
L	Conveyor Length (mtrs)	HI	Height Increase for Incline Conveyors (mtrs)
A	Distance Between Cross Supports (mtrs)

Coefficients of Friction
 

Free Rotating Support Rollers	0.1
Plastic Wear Strips (lubricated)	0.1
Plastic Wear Strips (unlubricated)	0.2
Steel Wear Strips (lubricated)	0.25
Steel Wear Strips (unlubricated)	0.35

If you require conveyor design assistance then please call our Technical Sales Team.

 

Self Tracking Belt Installation Guidelines

Friction Driven - Pin & Endless Seam Joint

Preparation

Before installing a new belt, always check the conveyor structure;
· Shafts to be at 90° to direction of travel, and horizontal.
· Rollers to be free to rotate
· Belt supporting surfaces are smooth and level with adequate belt edge clearance.  Check that there are no parts of the structure that can catch the belt.
· If a take-up mechanism is fitted, ensure that it is functioning correctly.

Installation Procedure

 

Tools you will need:

· Safety glasses · Flat end pliers · Side cutting pliers · Needle Nose Pliers · Cable ties/soft wire/rope (optional) · Pulling rope (optional—for long new conveyor installations) · Necessary tools for conveyor belt take up adjuster · Welding set to complete the belt edge at the pin join strand.

Important Note

The following procedure is for a “Pin Joint” process only.  “Endless Seam” join belts can only be fitted to a conveyor with a special design to enable fitting from the conveyor side.

· Please note that the belt length is predetermined and should be ordered as a fixed length to suit the conveyor.  It is not possible to adjust the belt length during installation.
· The top of the belt is smooth whilst the underside of the belt has formed “V” sections in the cross wires to locate in the grooves of the grooved drive & idle infeed rollers.
· There is no direction of travel as both ends of the belt are identical.

 
1. First ensure that the electrical supply to the conveyor is turned off and the power supply locked out.
2. Release any conveyor belt tension take up mechanism to allow maximum adjustment during installation.
3. The belting should be pulled through the conveyor circuit until the two ends meet.  There are 2 approaches to this:

a. The first being when a belt is replaced for a belt in situ on the conveyor.  In this instance drive the existing belt to a position where the join pin is assessable at the infeed non-drive end of the conveyor.  The existing join pin is cut at its ends and withdrawn.  The new belt is then temporarily attached to the lagging end of the old belt by means of a connecting pin laced through the opposing braid wire loop ends of the new and old belt. By means of supporting the new belt roll you will be able to carefully drive the belt (operate at slow speed) into the conveyor using the existing belt – always maintain suitable belt tension to ensure there is no belt slip on the drive roll.  Whilst the belt is being driven in the old belt should be collected as it exits the underside at the infeed end and layered carefully onto a pallet or suchlike for disposal.
Then continue from step 4.

b. The second when a new belt is fitted to a conveyor where there is no existing belt (such as a new installation) then the belt will have to be fed through the conveyor circuit by hand. Position the replacement belt at the infeed with the smooth surface uppermost. The underside “V” forms of the belt are to align with the grooves of the infeed and drive rollers. For long conveyors you will need to attach a steel bar to the leading braid wire loops with cable ties or suchlike (see below). To this bar then attach a pulling rope which is first fed through the conveyor to the discharge.  From here the belt can be pulled through the carry way part of the circuit.  Once the lead edge of the belt is at the discharge end the rope should then be fed back through the return way of the belt circuit to the infeed end.  It can then be pulled (maybe with slow speed drive assistance) to the infeed end. 
Then continue from step 4.


4. The two opposing ends of the belt are then pulled together. Remove the drilled pulling bar assembly.  Push the connecting wire through the opposing loop ends as shown.



5. The connecting wire should then be cut to length and welded to the corresponding cross wire at the edges.
6. Check that the “V” sections on the belt underside are aligning with the grooves in the drive & idle infeed rollers.
7.  Re-tension the belt enough to maintain adequate drive without over tensioning the belt.
8. Check there are no belt parts or tools left on, or in the conveyor.
9. Remove power lock off and then start the conveyor and test run under slow running conditions before running at normal operating speed.

· Longer belts may be supplied in sections and therefore multiple belt joins will be necessary.
· Extra care should be taken when installing a belt with “Bent Up Edges”.
 

Joining Methods

 

Pin-Joint

This is the preferred joining system. The leading and trailing ends of the belt feature pre-formed loops, through which a pin is inserted. The belt can then be easily and quickly joined and disassembled on the machine







 

Endless Seam

The belt is supplied endless, with the warp cables interwoven to create a seam. This system is used when uniform openings are required down the length of the belt. This joining method requires that the belt be fitted on the machine from the side and therefore a special machine design is required.







 

Edges

Weft wires are plasma welded together in groups of 2 or 3 wires. This prevents shifting of the weft wires and damaging of the edges.

Maintenance

Cleaning:

Whenever required, Self Tracking Belt can be cleaned with compressed air, spray nozzles or brushes.  The grooves in pulleys and rollers can be cleaned using spring loaded scrapers.

Preventative Maintenance:

Preventative maintenance consists of regular inspection of the belt:
 

• Check the joint of the belt for cable damage
• Check the sides of the belt for edge damage
• Check the grooves for accumulation of product
• Check the functioning of the support rollers
• Check the wear on the support strips.