Electrical Sicssor Lift

You will need the ~same sized motor for hydraulic or electric and a geat mechanisms match them. If the gear mechanism is lossier than the hydraulic system you may need a larger motor.

Hydraulic is probably cheaper as for 4 tonnes all the mechanics will be quite costly?

Why do this?

I could make a better suggestion if I had more information.

Capacity?

Safety Factor? (20%, 50%, etc.)

Lift height?

Cycle time?

Voltage?

Control?

And out of curiosity, why change from hydraulic actuation?

Stresses in the scissor lift members will be the same regardless of how it's actuated, so why worry about that? Forces on an electric actuator will be the same as a hydraulic one, given the same payload.

To determine what the forces are for the hydraulic actuator, measure and plot the pressures in the cylinder multiplied by the area of the piston. I think you will find that they start out very high and decrease as the mechanical advantage becomes greater as the lift rises. This can be done inexpensively by inserting a dial pressure gauge in the line to the cylinder.

An electric actuator will have to produce the same forces. DC motors can handle short periods of overload but not like a hydraulic system which may start out by producing 12,000 kg force (for example) reducing to near whatever the gross weight (4000 kg for example) is as the hydraulic cylinder approaches the direction of travel.

You should also consider the safety issue involved here. Placing check valves on the hydraulic cylinder prevent the lift from falling when no power is present. The same can be done with a mechanical brake. However, if you spring a leak in a hydraulic line, the lift comes down only as fast as pressure is lost. If a mechanical brake fails, it may come down much faster.

Most cylinders on lifts are ported to restrict fluid flow.

An electric brake is not needed if a worm-gear drive is used. It tends to self lock if the worm to gear ratio is high enough.

thank you all for these replies

i will try to answer some of your answers.

first i am trying to change it to electrical because it is not working very well with the hydraulic and there are alot of leackage in the oil pipes and it is too much dirty.

now i am trying to make a new one not modify the old one so i have to design from the begining so i need the stresses to change the dimension of the old one .

and what should i do after the stresses just select material and saftey factor and take the maximum stress in each one the find the area.

this what i need.

thank you.

Ahhh . . . When designing a new one to use electric actuator, try a different method or mechanism to do the lifting. Because hydraulic actuators are capable of very high forces, the linkages and basic design is different than a machine using electric motors, which can't be overloaded to a large extent.

If the hydraulic machine is rated for close to the loads you handle, then the basic scissor lift members are probably close to the required dimensions and strength for that load. If it's capable of lifting much more than you require, then the members will be larger than necessary. A structural engineering handbook will give you information for choosing sizes of steel members as well as beam formulas and examples of calculations, which there is more to than what is practical to transfer to you in this forum.

Can you visit a place that has or sells electric lifts? See what others have done.

Rashad,

There are many manufactures of scissor lifts.

If you answer the questions in my previous post I will be able to tell you who makes a suitable unit.

Otherwise, fix the old one!

If you want electric, there are many manufactures of "screw actuators" that can be used to replace existing hydraulic cylinders.

Of course screw actuators are about 10 times the cost of hydraulic cylinders of the same capacity.

It appears to me that your main problem is something called "lack of maintenance."

Save a lot of time and money and fix the hydraulics.

Your choice!!

Hi rashid:

You should also take fatigue into consideration, as well as any notches or holes as this instills a greater stress on the part than just removing material. It is the location where stress fractures will begin.

Devices that lift people or travel overhead where people are involved typically require a safety factor of 10.

mechtech