Pros and Cons of Pallet Racking

Posted byd5admin December 1, 2010

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Pallet storage strategies for warehouses

Depending on a number of factors including budget, SKUs, turns and picking requirements, the storage strategy for a warehouse would differ.  Below is a guide to help warehouse managers decide on what storage strategy is best for his/her operation.

BULK STACKING PALLETS

The most inexpensive storage strategy from a capital investment point of view is Bulk Stacking.

The positive points for bulk stacking include:

• Low up front investment required
  • Only the actual warehouse space is needed
• Good for multiple pallets of like product.
• Good for shipping lanes going in a single destination
• Good density for low roof warehouses (12 ft to 16 ft clear)
• Pallets are accessible for pallet trucks at ground level

The weaknesses of bulk stacking storage include:

• Crushing and leaning of product is a problem
  • Typical maximum storage heights of 2 or 3 pallets high is common
  • More expensive corrugate is required to protect product
• Not recommended as a case picking media
• Driving into long lanes can be slow and stressful for forklift operators
• The possibility of pallets collapsing exists.
• Low use of warehouse cube (not optimized for space)

SELECTIVE RACKING

The simplest type of racking, it is made up of beams, frames and spacers.  It sometimes includes wiremesh decks or pallet supports, but not always.  Budget $75 per pallet stored for this type of racking.

The strengths of single deep selective rack are:

• Common parts, easy to source.
• Easy to assemble.
• Can be moved around and used in multiple configurations including: wide aisles (sitdown trucks), narrow aisles (reach trucks) and very narrow aisles (turret trucks)
• Many accesories like carton flow and pushback modules can be added to modify use.

The weaknesses of this type of storage include:

• Lower density than other types of racking.
• Tall 5″ beams means loss of cube for carton picking.
• Roll form rack is susceptable to damage from unguided lift trucks.  It gains much of its strength from the shape that it takes.  Change the shape through an impact with a forklift and its capacity is reduced considerably.
• One size fits all does not take into account the fastest moving SKUs and the volume they represent.
  • Given 50% of volume is represented by 10% of SKUs, there is not sufficient density using this rack.
  • Given 80% of SKUs is represented by 20% of cubic volume, this style of racking consumes too much space to store small quantity SKUs.

DOUBLE DEEP RACKING

Designed for use with a deep reach fork truck, it is simply selective racking doubled up into sections of four pallets deep accessible from two aisles.  Budget $85 per pallet stored for this type of racking.

The strengths of Double Deep rack:

• Common parts, easy to source.
• Easy to assemble.
• Requires one of two design strategies to work with the baselegs of the deep reach truck.
  • Raised rack with clearance for the 5″ high baselegs or
  • A longer beam to accomodate the width of the 5″ wide baselegs to straddle the pallet at ground level.  The beam usually needs an additional 7″ of side spacing between pallets stored on the beam, ie. 21″ additional on a two-pallet wide beam.
    • special attention should be paid to the baseplates in seismic zones
• High pallet storage density using standard racking.
• Relatively low cost storage solution as selective racking is inexpensive compared to other types of higher density racking.

The weaknesses of Deep Reach storage include:

• Visibility storing and retrieving pallets at height is difficult without a fork-mounted camera.
  • lack of visibility can add to rack and product damage or
  • reduced productivity due to slow pallet transactions.
• Selectivity is only 50%
  • product can be buried and lost without a good inventory location tracking system.
• Not a good system for case picking due to the need to bring pallets forward using a Deep Reach Truck.
  • Using push-back racking or carton flow racking at the ground level helps to support this weaknesses.
  • Create a taller bay at ground level to allow pallet trucks to index product forward.
    • Care must be taken to ensure pallets are perfectly straight so that the deep reach truck can straddle it and still access higher level pallets.

PUSH BACK RACKING

Designed for use with a deep reach fork truck, it is simply selective racking doubled up into sections of four pallets deep accessible from two aisles.  Budget $175 -$350 per pallet stored for this type of racking.

The strengths of push-back rack are:

• Can be used by a variety of lift trucks including Reach and Sit-down counterbalanced trucks.
  • Care should be used to have the racks be plumb and still accessible at height.
    • If a Reach truck is used, be sure to allow for passage of baselegs under the first level if lifting above 20 feet.
• Great for use with Very Narrow Aisle (VNA) equipment such as Turret trucks (Swing Reach Trucks)
  • Check push force needed against lift truck manufacturer.
  • Some VNA lift trucks are not compatible with this style of racking.  Check with your dealer.
• Increases density by reducing the need for aisles.
• Less expensive than pallet flow.
• Level carts and low profile carts are available
  • Low profile increases storage capacity.
  • Level carts reduces product damage and is compatible with some VNA equipment.

The weaknesses of push-back rack include:

• A danger of a rear-drive lift trucks climbing under itself during put-away.
• Product damage possible
• Selectivity is only 50%
  • Therefore the SKU (Stock Keep Unit) should be stored front to back.
  • product can be buried and lost without a good inventory location tracking system.
• Carts need maintenance over time.
• Some vertical height is lost due to the slope of the rails.

PALLET FLOW RACKING

Like drive-in racking, but instead of level rails, rollers are used at a pitch.  Pallets are loaded from the back which then roll (or flow) to the front of the system for picking.  Expect to pay up to $500 per pallet position.

The Pros of pallet flow rack include:

• Works great with FIFO (First in First out).
• Storage density is very high with little space lost for aisles per pallet stored.
• Great for reducing replenishment for picking.
  • Pallets can be loaded from a replenishment aisle and picked from an orderpicking aisle.  This defines traffic patterns and separates people from lift trucks.
  • Perfect for fast moving SKUs.

The Cons of Pallet Flow rack include:

• You must have good quality pallets going into the system.
  • Broken pallets with nails sticking out will get stuck in the system.  This requires someone climbing in to clear the log jam.
• The wheels and brakes in the system require maintenance over time.
• Cube is lost over the length of the system.
  • The pitch is typically 1/4″ per linear foot or 1 inch per pallet stored.
  • In a lane of 12 pallets deep stored, 1 foot of vertical storage height is lost.

DEEP LANE PALLET RACKING

There are two ways to store multiple pallets in racking (deep lane pallet storage):  put pallets in the rack and have them move inside the racking using gravity or have the lift truck enter completely (drive-in) or in part (deep reach) to store and retrieve the pallet.  Now there is a third way.

Pallet shuttle, Radio shuttle, Pallet Mole or Pallet runner are all examples of automated deep lane pallet storage.  This system has a small slave robot that enters drive-in style racking on a second rail beneath where the pallet is stored.  The robot (shuttle) lifts the pallet a few inches of the edge racking the pallet is stored on and transports it into the system.

Here is a video of an example of the technology:

 

 

 

 

 

 

 

 

 

 

 

 

 

Pros and Cons of deep lane pallet storage:

Pros:

• Almost perfect density – no aisles required.
• Eliminates crushing and leaning – full clear height can be used with no height restriction from forklift overall collapsed height of mast.
• Price per pallet stored is the lowest possible
• No honeycombing
• No rack damage – truck does not enter the rack
• Very reliable – the shuttles are very simple and require very little maintenance.
• Very fast, pallet transactions are seamless
• Density is 90% or greater
• Pallet storage is dynamic.  Pallets are conveyed in the FIFO system from inbound (manufacturing) to outbound (shipping) without the use of forklift trucks.
• Due to storage density, multiple warehouses can be consolidated into single warehouse.
• Companies save money by turning off the lighting over the racking.  Only the inbound and the out bound sides need lighting.  Warehouse is, as a result, cooler and less expensive to run.
• Unlike pallet flow, the rack and rails are level to the ground.  Therefore more storage levels may be acheived.
• Rack is only slightly more expensive than drive-in racking, therefore, this system is as affordable as push-back racking but with the ability to store at depths of 60+ pallets deep.

Cons:

• Pallets must be of good construction
• Pallet dimensions and product dimensions must be similar – multiple sized pallets cannot be stored in the same lane.
• Selectivity is reduced.  Ideally, pallets need to be of same SKU or lot or shipping destination

Please post questions and comments below.