An Explanation of Force and Labor Power

posted on: Sunday September 23, 2012

Many variables affect how much force is needed to move a loaded cart across a warehouse floor. In most cases, a fully loaded cart is the ideal move in an industrial environment because it is the most efficient. A fully loaded cart has fewer moves in a day than a partially loaded cart, which also reduces product flow traffic. So why are partial loads moved through out the day? The greatest variables are the weight of the loaded cart or the physical size of the product being moved.

Weight on a loaded cart is taken into consideration when an operator needs to push the load by hand in an industrial environment. If it is too hard to push the cart, then weight is taken off of the cart to accommodate the operator or more rest breaks are needed because of operator fatigue.

The cart construction is also a factor in how much weight the cart can carry. Carts are rated for maximum weight and if overloaded damage to cart or injury to an operator may occur. The wheels and bearings under the cart are also rated to a weight capacity. Higher capacity wheels and bearings significantly reduce the rolling resistance of the load.

The physical size of the product being moved is often times large but does not weigh a lot. If the product fills a cart then the cart needs to be moved regardless of the weight. If the product can be put on two carts that are trained together then a single move can be accomplished with double the product being moved. Several carts can be trained together to maximize efficiencies.

When moving a load across a warehouse floor two parts of the equation should be looked at. The first part is the cart assembly. The cart should be fully loaded in weight to utilize the weight capacity. If the cart is rated for 1500 lbs. of carrying capacity then it should be loaded between 1200 and 1500 lbs. to maximize efficiency. Many carts are available that can be purchased or custom built to meet a number of different needs.

The second part of the equation is the prime mover of the cart. If a production person is the prime mover of the cart then push and pull capacities are determined by forces required to move the load and the distance the load needs to travel. There are guidelines outlined by OSHA that are available for push and pull capacities. The most efficient move would be for the prime mover to utilize 80% to 100% of the OSHA guidelines. However, there is a great disparity between how much weight needs to move on a cart and the OSHA push/pull guidelines for personnel. In order to balance the two parts of the equation, cart assembly and the prime mover, they need to be rated to a similar value to maximize efficiency.

If a cart is fully loaded to 1500 lbs. then the prime mover should have capacity to move that load. A good “Rule of Thumb” to better understand what it takes to move a load is to determine how many people are needed to move a loaded cart in a warehouse. The “Labor Power” is the number of people needed to get a load moving by pushing or pulling. The “Labor Power” of one is defined as a healthy 200 lb. person with good upper body strength can push or pull 100 lbs. of horizontal force for a very short period of time. The horizontal force (push/pull) needed to move a cart loaded with 1500 lbs. of steel may be 300 lbs. which would be a “Labor Power” of 3. That would equate to three production personnel to push the loaded cart in order for it to move a very short distance.

 

1LP (Labor Power) = 1 healthy 200 lb. production worker with good upper body strength

= 100 lbs of horizontal force

A healthy 200 lb. production worker = 100 lbs of horizontal push or pull force (short

period of time)

1 LP = 100 lbs of horizontal force

 

Since it is not practical, efficient, or safe to have several people moving a single cart there are other options that will move a heavy cart. A Load Mover that is battery powered can do the pushing and pulling that is required to move heavy loads. The Load Mover is easily controlled by a single operator and is connected to the cart to be moved.

Load Mover Inc. manufactures a variety of Load Mover sizes from 200 to 1000 lbs of draw bar pu