Hydraulic Drive Question 1

[spd748]

I am in the process of designing a hydraulic drive for a circular saw mill. I have most of the numbers worked out except one. I can't seem to calculate the torque required to move the carriage. The specs are as follows:

I need to move a 5000 lb (maximum total mass)carriage along a flat plane at a maximum velocity of 325 fpm. The carriage rides on steel roller bearing wheels which in turn ride on a steel track so friction should be minimal. The carriage is pulled by a cable which is wrapped around a 13" steel drum. The drum is mounted on a shaft which will be turned by a hydraulic motor. I would like to keep acceleration/de-acceleration rates to a minumum to allow the system to start and more importantly stop the carriage quickly. I ran the specs through a couple of formulas that I have but the torque requirement that I come up with sounds way too low. I suppose that I need an independent opinion on the matter. Thanks in advance for any information that respondents may offer.

 

[spd748]

Ed,

Is there some reference material that you can suggest I read on the design of hydrostatic systems? I know that reading a book won't make me a hydraulics engineer however it may at least give me an understanding of those type of systems.

 

[spd748]

Ed,

The picture is of a mill similar to mine. The design and operation of the drive system is the same. You are correct. High production is not a primary concern. I would however like to make the system as reliable as possible. My mill is designed to produce ~8-10k board feet per day. On a good day where nothing goes wrong and my back holds out I produce ~6k board feet. This mill is a part time job/hobby. My purpose in converting to hydraulics is to ease the work load. As it is, everything on the mill is manual. I've built a live log deck and chain type log turner to assist with the heavy work. A hydraulic drive would allow for on the go carriage speed changes to compensate for changes in cutting conditions. As it is, there is no practical carriage speed adjustment other than allowing the belts to slip.

 

[unclesyd]

This mill will solve all your problems with speeds, feeds, and horsepower.
You must watch the movie.

http://www.doublecut.com/sawmill_detail.asp?mill=14

Look at the lower right side of this page there are a few formulas that may help.

http://www.thinkerf.com/FreeLit.htm

Sawyers information links galore

http://www.xmission.com/~sherwin/sawyer1.htm

 

[maytag]

Don't have any idea where you are located but if you are in the farm belt you might try a tractor/combine/cotton picker salvage yard. Most all the modern day combines and cotton pickers are hydrostatic drive and you can probably pick up a complete hydrostatic drive relatively cheap. Not doing any calcs as I don't have the time I believe if a motor and pump will propel a 30,000 lbs combine thru mud it will drive your saw.

Good luck,
Maytag

 

[EdDanzer]

This link will provide some information about hydrostatic drives.

http://hydraulics.eaton.com/products/pdfs/E-PUPI-MC002-E.pdf

The carriage drive I worked on used a lever on the swash plate to control speed and direction. You can use an open center variable volume piston pump into an electrically controlled directional control valve driving a 10000 series Charlynn to reduce costs. The pump volume (speed of travel) would still be controlled by a lever and a switch for direction of travel.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[desertfox]

Hi spd748

I eventually found this article on cutting forces although its cutting trees from S.America, maybe we can use some info from here to help get the additional force while sawing.
Have a look and let me know what you think.

http://www.fpl.fs.fed.us/documnts/fplrp/fplrp567.pdf

desertfox