Forklift stability and other technical safety issues - Monash University

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1. Stacking – with the mast vertical and forks at maximumheight, the maximum load is determined when the forkliftis tilted forward on a platform to:• A slope of 4% for forklifts of rated capacity up to 4999kg; and• A slope of 3.5% for forklifts with capacities of 5000 kgto 50000 kg2. Travelling – with the mast at full rearward tilt and forkslowered, the maximum load is determined when theforklift is tilted forward on a platform to a slope of 18%3. Stacking – with the mast at full rearward tilt and forks atmaximum height, the maximum load is determined whenthe forklift is tilted sidewards on a platform to a slope of6%4. Travelling – with the mast at full rearward tilt and forkslowered, the forklift is tilted sideways on a platform to• a slope of up to 40% for forklifts of rated capacity upto 4999 kg; and• A slope of 50% for forklifts with capacities of 5000 kgto 50000 kgdepending on the forklift capacity and maximum speedTests 1 and 2 primarily determine forward tipover stability, test 3 determines side tipoverstability when loaded, and test 4 determines side tipover stability when empty.6
AS and ISO standards - counterbalance forklift stability tests - limitationsAll the above tests are undertaken under a quasi-static situation. Hence dynamic effects suchas tyre bounce and energy due to the build up in motion that may make the forklift more likely totipover are not included.Further “it is permissible in lateral tests for one of the load wheels to lose contact with the testplatform and it is acceptable for parts of the structure or other designed features to makecontact with the test platform.” In practice this situation is likely to cause the forklift to becomeunstable if it were travelling.And for stability tests, the forks and side shift are centred (provided the side shift has a lateraldisplacement that does not exceed 100 mm for forklifts with capacities to 6300 kg and 150 mmfor larger forklifts). A sideshift of 100 mm would increase the sidewards displacement of therated load by around 1/3 rd at a 4300 mm lift height, or 25% at a 6000 mm lift height. Thispotentially would reduce side stability significantly.Rated capacity may be determined by one or more of the three tests. Hence it is possible thatsafety margins in excess of the Standards exist in respect to the other factors. It is thereforepossible that having the sideshift fully to the right or the left may not result in a lower ratedcapacity.However as manufacturers do not provide information as to which test was the limiting one inrespect of rated capacity no assessment can be made of the impact of sideshift movement onsafety margins.It is recommended that manufacturers provide customers with information as to thestability test that determined a forklift’s capacity. And it is further recommended thatstability tests be undertaken for the worst case scenario – that is for instance with theside shift in its worst positionAS and ISO standards - counterbalance forklift stability tests – tipover when stationaryData has been collected on 178 forklifts with capacities from 1 – 48 tonnes. This data has beenanalysed in respect of tipover and other safety issues.The result of stability tests one and two are that with the forklift stationary on a level surface,and the forks down:• On average the rated load could be increased by 37% without tipover;• At a minimum it could be increased by 21% without tipover; and• 80% of forklifts could have increases ranging from 33% to 60% without tipover.These data are shown in the graphs below.SAFETY MARGIN (%)140%120%100%THEORETICAL SAFETY MARGINS AT RATED LOAD -FORKLIFT STATIONARY80%60%40%20%0%0 10000 20000 30000 40000 50000FORKLIFT CAPACITY (kgs)SAFETY MARGIN (%)140%120%100%THEORETICAL SAFETY MARGINS AT RATED LOAD -FORKLIFT STATIONARY80%60%40%20%0%0 1000 2000 3000 4000 5000FORKLIFT CAPACITY (kgs)7
Page 3: 2. “Stability triangleThere are t
Page 8 and 9: AS and ISO standards - counterbalan
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Page 14 and 15: As can be seen the solid tyred fork
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Page 20 and 21: Australian Design Rules for heavy v

Forklift stability and other technical safety issues - Monash University

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