Why ball upwards transfer units can not be used as ball down facing?

main ball downwards transfer unit
main ball downwards transfer unit

Ball transfer units are divided to different types, like pressed metal series, machined heavy duty series, stainless steel series, plastic series, spring shock load series, ball downward series.The purpose of design ball transfer unit is handling and transmit parcels, goods, cargo etc. So you can often see them in airport, factory facility.
Some one also wants to use them as ball caster considering on it’s 360 degree oriental movements.But, it must choose the special design ball downward models.If there are salesman tell you choose normal cheap ball upward model to use as ball downward, just the loading capacity is half or lower, remember, that’s wrong and you will get lose if using them.

Now, lets see picture to know why:
sub-balls-structure
Below is a photo showing different structures of ball upward and downward transfer units.Them are quite different on the sub-balls arrangement and inner design.Here is a testing picture showing a upward ball transfer unit used as ball downwards:

IMG_20160503_102946
The reason is there will be no enough sub-balls supporting main ball when running, and them will be forced to stuck in the space between main ball and shell.

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RTW Machined Steel Cylinder Track Rail Wheel

Machined steel track cylinder wheels

furnace wheel
furnace wheel

Material: Carbon steel #45+Bearing

Bearing: ball bearing without seal

Finish: Heat Harden

Applications: Industry drying oven, Production transmit line, Small railway truck, etc.

machined wheel
machined wheel
Model d D Lt Bearing Loading Capacity
RTW15SC 15 70 26 6004 x1 300kgs/660lbs
RTW20SC 20 75 27 6005 x1 350kgs/770lbs
RTW25SC 25 80 28 6006 x1 400kgs/880lbs
RTW30SC 30 90 30 6007 x1 450kgs/1000lbs

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CTW Machined Single Flanged Steel Track Wheel

Machined steel track wheels

steel track  wheel
steel track wheel

Material: Carbon steel #45+Bearing or Harden steel GCr15(SUJ2)

Bearing: None bearing with greased, Needle Roller Bearing or Bronze Bushing with oil greased

Finish: Heat Harden or Painted

Applications: Industry drying oven, Production transmit line, Small railway truck, etc.

flange track wheel
flange track wheel
Model d Lt D fD Rt Wt (3) Bearing Max. Speed Load Capacity@max speed
CTW12SF-N 12 55 125 150 38 50 No HK1214 x2 4000rpm 650kgs/1400lbs
CTW15SF-N 15 55 125 150 38 50 No HK1514 x2 3000rpm 780kgs/1700lbs
CTW20SF-N 20 55 150 175 38 50 No HK2014 x2 2500rpm 860kgs/1900lbs
CTW25SF-N 25 80 200 225 57 75 No HK2514 x2 1900rpm 1100kgs/2400lbs
CTW30SF-B 30 60 125 150 38 50 Yes FB092H303455 1200rpm 260kgs/570lbs
CTW40SF-B 40 60 125 150 38 50 Yes FB092H404455 950rpm 340kgs/750lbs
CTW45SF-B 45 60 125 150 38 50 Yes FB092H455055 850rpm 380kgs/830lbs
CTW50SF-B 50 70 125 150 38 50 Yes FB092H505555 750rpm 500kgs/1100lbs
CTW25DF-S 25 80 150 180 50 75 No Oilless 253580 350rpm 1500kgs/3300lbs
CTW30DF-S 30 80 200 230 50 75 No Oilless 303880 300rpm 1800kgs/3900lbs
CTW35DF-S 35 110 200 230 65 100 No Oilless 3545110 250rpm 2100kgs/4600lbs

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