Storage methods depend on the physical characteristics (size, weight, shape) of the product and also on the volumes to be stored or handled. The other variants are brittleness and crushability in case of fragile products. The type of material handling system (manual or automatic) calls for installation of a tailor-made system. However, following are the most commonly used material storage systems.
1. Block Storage
This is the simplest type of storage method and does not attract any financial investments. Boxes, cartons or sacks containing the material are stored in the spread or stacks formed in the area assigned for storage. Stacking is done on the floor or on the wooden platform. However, block stacking has limitations on the stack height due to following reasons:
- Load bearing capability of the package (box, carton, container) at the bottom of the stack
- Sensitivity of the product inside the pack to load
- Ease in loading and unloading.
Public warehouses normally adopt this type of storage method due to a wide variety of the products they are storing and their facilities are designed for the most generalized cargo storage and handling. Boxes of consumer durables such as TV, Freezer and Washing Machine are block stacked to the extent of one to four layers depending on the size and weight of the box (Figure 6.3).
Food grain sacks are normally block stacked. The sack is 2 feet wide and 3 feet long jute or polyethylene bag, which contains 100 kilograms of food grains, is stacked maximum up to 15 layers for safe storage.
2. Racking System
Racks are used for storage of items longer in length, small containers and boxes and pallets etc. As the weights of these unit loads are beyond human handling capacity, the mechanical material handling equipments are normally used for storage and retrieval operations.
The racks may further be divided into two types such as stationary and portable. The stationary rack structure is built by getting support from wall and roof of the warehouse building. The only limitation to the height of the stationary rack structure is roof of the building and vertical reach of the material handling equipment. The racks can be designed for getting good use of vertical storage space of the building. The stationary racking system ensures excellent storage density for the given space for the uniform size of the unit loads. The racking system is commonly used in warehouses where the uniform unit loads in volumes are required to be stored. In the stationary type, for getting higher storage density, the drive-in types of racks are widely used. The structure consists of stationary racks with rails for moment of pallets or boxes, which can be pushed deep into the rack width or length.
The drive-in racks closed at one end are suitable for last in and first out (LIFO) inventory technique, while racks, which are open at both ends may be used for FIFO (first in and first out) technique. The advantage of this system is higher storage density and throughput.
Portable racks are self-contained structures with number of decks, which can be stacked one on the other during loading and can be knocked down to conserve space. The system of movable aisle is commonly used for high-density storage, when the quantities handled are high but the storage and retrieval activities are on lower ebb. The structure consists of rows of racks installed on the carriages or platforms. The racks can be moved back and forth or sideways to have desired aisle gap between the racks where from material is to be stored or retrieved as and when required (Figures 6.4-6.9).
3. Shelving System
Shelving systems are in use for non-palletized or non-uniform type of loads. The material is stored and retrieved in the shelf manually. These shelves are close or open type depending on the product configuration. Size of the unit shelf opening can be changed using dividers and modular drawers etc. The structure can be easily modified to suit the desired functionality by incorporating various accessories (Figure 6.10).
Shelving is the most flexible and cost-effective storage structure, which is available in modular configuration to suit storage volumes and product configurations.
Pallets are specially designed platforms for storage of goods with a view of moving the whole load by forklift, wherever it is required. These are widely used in-house material handling. The pallets can be broadly classified into two groups (Figure 6.11):
- Sturdy multiple reusable pallets
- One-way non-returnable pallets
Multiple-use pallets are used in physical distribution system. These are sturdy in construction and are durable.
The other types of pallets are one-time use pallets. These are non-returnable type and used in sea or air shipments. Pallets are made out of wooden, metal or plastics (see Chapter 9 for details) depending on the product, type of load and the working conditions. The most common material is wood. The standard sizes of pallets in use are 40 inch X 48 inch. The goods are stored on the pallets loose or strapped with metal strips for disallowing goods movement during transit. The pallets are available with either two-way entry or four-way entry construction. The two-way entry allows the forklift to handle pallet from two sides, while the four-way pallet allow forklift to handle it from four sides.
Containers are most commonly used in manufacturing plants for in-process material handling applications. The containers are quite popular in engineering industry because they help to increase productivity, space utilization and facilitate fast material movement on the shop floor. The container is basically a cubical construction with one (top) side open for depositing and removal of the material. Different types commonly in use are as following:
Welded Wire Containers. Welded wire containers are light in weight, self-cleaning type and make it possible to view the material and allow ventilation. These containers can be stacked one above the other and ensure uniform weight for movement.
Corrugated Metal Containers. Corrugated metal containers are used in engineering industry where high strength and very high damage resistance features are required to handle the heavy metal parts.
These containers are sturdy in construction and resist abuse. These are popularly used in automobile industry for storage and movement of parts and components (Figures 6.12-6.14).
Plastic Containers. Plastic containers are moulded polymer construction similar to metal containers used for material storage, handling and shipping. These are light in weight and can be cleaned with liquids.
6. Automatic Storage and Retrieval System (ASRS)
The warehouses designed for high-rise storage due to space constrains, and operating on high throughput rate, use automatic storage and retrieval system (ASRS) along with automated material handling system. Due to automated material handling equipment the aisles are narrow leaving more space for material storage equipment resulting into high storage density.
7. Bulk Storage—Silos
These are basically used for bulk storage of material like cement, food grains and fertilizers. The products such as cement and fertilizers are manufactured in continuous process and the finished products are fed into large capacity silos until packed into small gunny or polyethylene bags for dispatch to the markets.
Similarly for the storage of very large quantity of food grains, silos are used in Food Corporation of India (FCI) godowns at selected places. A single storage capacity with silos may vary from 25,000 to 1,00,000 tonnes (Figure 6.15).
8. SOME CUSTOMIZED SYSTEMS
These systems are utilized for storing tyres and similar inventories with limited varieties and high volume for the purpose of efficient storage and handling. Customized solutions for single and multi-tier storage system incorporating optimized capacity and high safety standards are offered.
Cable Drum Storage
This system is best suited for applications for storage and handling cable drums, reels, rolls and coils of various types of inventory with provision for decoiling/recoiling and load handling. Customized solutions for specific inventories while ensuring best standards in safety and reliability are offered.
Cantilever racks have been designed for the storage of very long items like bars, tubes, timber, etc. They can be adapted to bulk store a wide range of products in a compact area, enabling immediate access and facilitating perfect stock control. The advantages are: systematic storage and retrieval for effective handling of long items; flexible, versatile and can be customized for any need; a wide range of loads can be stored irrespective of volume and weight; perfect stability under total or partial loading.
Mezzanine Floor System
Mezzanine Floor Systems are ideal for maximizing existing floor space. The usable floor space area can be doubled or trebled at a fraction of the cost of moving to a new premise. Cost effective and customized solutions with modular design and reconfigurability with multiple options for the floor surfaces are offered. Advantages are: can be customized to suit existing floor space, taking pillar positions into consideration; modular concept enables fast, easy assembly with minimal disruption; components can be quickly and easily reconfigured to meet your changing needs; reduces material handling and inventory carrying costs; wide range of components ensures flexibility in customizing solutions best suited to customer’s needs.
These systems are ideal solutions for typical order picking operation requiring FIFO (first in first out) with high throughput. Customized solutions with comprehensive design comprising flow track options integrated with racking systems and high standards of reliability and consistency of operations are offered. Advantages are: travel distances are dramatically reduced; ergonomically designed for fast and efficient access; stock rotation is automatic and accurate, and no maintenance cost.
Vertical Carousels consist of rotating shelves that move up or down in response to operator’s commands, delivering items to an ergonomically safe and convenient access window. They are ideal for storage of small industrial components, documents, discs, etc. Vertical carousals help increase storage density, throughput and efficiency while reducing inventory and required man-hours. Advantages are: uses vertical space effectively and expensive shop floor and office storage space can be used more efficiently; reduces retrieval time by enhancing picking rate and gives faster access to stored components; safe and easy to operate; protects all stored material from dust, pilferage and unauthorized access.
Source: Sople V.V (2013), Logistics Management, Pearson Education India; Third edition.
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