When the machine is moving on the sand, there are some factors may effects on the movement and even the process of transferring mixture from working surface to the scoop blade such as:
- Humidity
High level of humidity - saturated
Medium level of humidity 18-30%, the figure for mixture of sand and trash may easily stick on rotavator. This makes the load of rotavator heavier.
Low level of humidity, the sand is dry, easy to shovel.
Therefore, proper humidity is necessary.
- Solution:
Drainage holes on the scoop blade to decrease the level of wet for mixture.
- Structure of filtering materials
Sand: permeable to water but also poorly retains water.
Clay: more than 20% is soil, as well as other components, difficult to absorb water but holds water well, high stickiness, so it is more difficult to dig than sand.
4.2 Calculating the force effect on the process of transferring materials - The drag force of sand is calculated by the formula
FD = kh ∙ B ∙ h = 9518.992(N) (4.1) By which:
FD: drag force of sand.
kh: the coefficient of drag force.
B = 4 ∙ 7 = 28 (cm): the width of excavator bucket (there are 7 distinct excavator buckets).
h: thickness of chip sand (cm).
- The friction force of sand is calculated by the formula
FF = f ∙ (Gcosα − Pasinα) (4.2) FF = 0.4 tanφ ∙ (G ∙ n2∙ r
900 ∙ sinα − G ∙ cosα ) = 891.03 (N) By which: 𝑓 = (0.3 − 0.4) ∙tanφ : coefficient of friction
G is the total weight of mixtures on the screener Pa (N): inertial force of object caused by inertial a
From the table 3.1, I choose friction angle = 500 with 𝑓 = (0.3 ÷ 0.4) - The total force of sand acting on the scoop blade:
Ftotal = FD+ FF = 10410.02 (N)
51 4.3 Choose the tires
Weight of the machine
W = 375 (kg)
A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be moved easily facilitating movement or transportation while supporting a load, or performing labor in machines.
As the working surface of the machine is not only dry sand terrain, but also wet and rough areas which are totally different with normal road’s surface, so the installed wheels must be terrain wheel. Terrain tires are used for traction on all kinds of surfaces, including on and off-road. They combine the open-tread design of off-road tires with the good handling of street tires. This design improves the traction of the tires on off-road surfaces and even providing more load carrying capacity. These are usually more aggressive tires made for heavier trucks and more off-road use. However, these tires are noisier than regular all-season tires due to the tread design. Mechanical friction, wind and rolling resistance, and tread patterns all influence the economy. Rolling resistance could be eliminated with stiffer sidewalls and almost no tread, but the latter would also eliminate the traction.
There are variety of terrain tires such as:
- Mud-tires
The large tread blocks, which are divided by broad and deep grooves actually stops the mud from entering and sticking to the tread.
These tires are suitable for humid area and wet sand, even dry sand.
These tires are generally not recommended for on-road use due to their bare design alongside they tend to create a lot of noise and vibration at highway speeds.
Figure 4. 1: Mud tires [15]
52 - Sand tires
The sand tires or sand paddle tires are primarily employed in off-road vehicles and are purposely designed for use in dry sand.
They are patterned in a different way compared to normal ties and consist of large rubber paddles sequentially arranged and placed on a smooth rubber core. Such tires usually comprise of smaller tread blocks, which are divided by numerous narrow grooves called sipes.
Figure 4. 2: Sand tires [15]
- All-terrain tires
The all-terrain tires are mostly found on Sports Utility Vehicles (SUVs) and other four- wheel drive vehicles.
Practically, these tires are not meant to provide good grip on loose surfaces like sand, and can easily get choked in mud.
They also have abundant sipes to counter wet weather conditions.
One of the plus points with all-terrain tires is that they can be driven on paved roads, however, at the same time they are noisy and are unable to resist on high speed cornering and braking especially on the highways.
Figure 4. 3: All-terrain tires [15]
53 - Cross-ply tires
Cross ply tires, also known as bias tires, have reinforcing plies put together in erect position on the plain surface of the tire, which provides perfect rigidity to the sidewalls.
These types of tires find it hard to be mounted on single piece rims because of their hard sidewalls and hence are fitted to somewhat narrow split rims.
Figure 4. 4: Cross-ply tires [15]
In addition, there are also other tires that can be applied on the rough terrain such as wheels of tractor or crawler.
Figure 4. 5: Wheel of tractor
Figure 4. 6: Crawler
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Here, I choose mud tires as they suitable for the beach in Viet Nam, easy for find and also manufacture.
GOODYEAR 185/75 R16 104/102R
Supplier name GOODYEAR
Rim diameter (inch) 16
Addendum diameter (mm) 551
Profile (%) 75
Tire width (mm) 185
Load index (kg) 900
Allowable maximum velocity (km/h) 170 Table 4. 1: Technical specification of wheel - Meaning of parameters on wheel
Figure 4. 7: Meaning of parameters on wheel [16]
Some of characters such as “S” is the code that users have to check and figure out the exact values throughout standard tables.
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