6
Material Storage Systems: For Space Efficiency and Storage Density
After reading the chapter, the students should be able to understand:
- Material storage principles
- ‘Unit Load’ storage
- Material storage method
- Design of storage system
Storage is one area of the supply chain that can provide increased efficiency, cost savings and other benefits. Storage is the driving force for every business, however large or small, needing space for product storage, employees, manufacturing plant and documentation. Proper utilization of space makes your business more efficient. Material storage system needs a close interface with the material handling system in order to reduce the cost of space, material handling and product damage.
Correlating equipment control with information control is the key to material control. Material control means pinpointing exactly where material is located, knowing its status, and being able to get it where it’s needed, exactly on time.1
—Jurgen Conrad
6.1 INTRODUCTION
Storage of material may be done in a variety of ways. However, some materials are more of a concern than others. The ultimate goal of any material storage system is to have ease in material placement and retrieval, ensuring space efficiency and minimum time in tracking, tracing and pickup. With advances in technology, the inventory manager can build storage space with higher storage density so as to have higher warehouse occupancy. Proper selection of storage system can result in effective use of warehouse space and efficiency. A well-designed storage system will reduce the requirement of warehousing space. In an automated storage and retrieval system, often smaller and frequently inventoried and retrieved parts are used. This type of system is self-contained and uses travelling shelves and bins, usually carried in vertical configuration. Normally, the storage system should occupy 70 per cent of space in the warehouse, leaving 30 per cent as open space for movement of people and material handling equipments. However, in a fully automated warehouse this ratio varies from 95 to 5 per cent. For toxic and hazardous materials, special care is must to prevent spillovers or physical contact with other materials. With stringent pollution control regulations, the build up of material storage system needs utmost attention right from the designing stage. Planning the inventory system and proper flow is necessary to ensure the best storage solution. Investments in proper development of facilities and equipment using modern techniques will pay back handsomely in terms of labour, time and money.
6.2 UNIT LOAD STORAGE
The concept of unit load is quite important from storage point of view and the movement of goods in convenient lots. The unit load is constructed by bringing together a number of individual items of identical configuration so as to build up a large load, which ensures convenience during storage and transportation.
There are many ways to unitize the goods for better storage and handling. The most commonly practised method is to build load on the raised platform. This platform is called ‘pallet’. The other method is to construct a platform to fit the load. This is called ‘skid’. Load can be in the most acceptable lot size for convenience of storage, handling and movement, depending on the physical characteristics of the product. The pallets are of standard size and are used for standard loads. However, the skids are used for non-standard loads such as long metal components or compressor/generator assembly. Other common methods of unitizing are slip-sheet and clamp load. The slip-sheet is a platform on which the load is assembled, while clamp is a load assembly on the floor with clamps placed on four sides of load for facilitating its movement using material handling equipment (Figure 6.1).
Fig. 6.1 Load unitization for storage and transportation
6.3 STORAGE PRINCIPLES
The storage system in warehouse has important bearings on the total cost and success of warehousing operations. Firms give more importance to the way the inventories are handled rather than how they are stored. Invariably in industry, investment planning is done more for handling equipment rather than the storage system (Figure 6.2).
Fig. 6.2 Material storage arrangements
In fact, efficient use of the material handling equipment is possible provided the storage system allows easy access for storage and retrieval of the inventory. A well-designed storage system is a compromise between maximum utilization of the available space and need for easy and quick access to the stored goods. In general, the following rules are followed for designing an effective storage system:
- Minimize the travel distance
- Maximize the utilization of available space
- Provide easy and quick access to the stored goods
- Facilitate easy tracking of the material
- Provide security against fire, damage and theft
- Prevent contamination and deterioration of the goods
The criteria for selecting the storage system for a particular application depends on the following factors:
Product Characteristics
The products with contamination risk require such storage facility, which will isolate them from other product groups. For example, flowers pose great risk of odour contamination. Similarly, hazardous chemicals pose risk of damage to other products or human life. Hence, design consideration for these types of products needs special attention.
Configuration
The products with uniformity in shape and size may be stored in stacks or put in the enclosure, while odd-shaped products may require open space. For example, steel sheets, billets, rods, angles, pipes etc are stored in open in the steel yard.
Shelf Life
The storage system designed on first-in-first-out (FIFO) consideration.
Product Variety
The system needs to segregate the products for ease in identification during storage and retrieval.
6.4 STORAGE DESIGN—BENEFITS
Proper planning of the storage system helps in improving the efficiency of the entire logistics system. This helps in speedy movement of goods across the supply chain, which results in improving system productivity.
Space Economics
Proper design of storage scheme can result in a substantial saving on the available space, which helps in planning for additional storage load without any investment in space.
Enhance Throughput
A well-designed storage scheme will reduce the movement of material handling equipment and the idle time, resulting in significant improvement in system productivity.
Ease in Material Location and Tracking
Proper storage scheme helps in quick location and tracking of the inventory item during material pickup operation, resulting in compressed order cycle time.
Security, Safety and Housekeeping
A well-designed system will bar unauthorized access to the inventory ensuring security against theft and pilferage. The system will also reduce the accidents due to fatigue, strain and collapse of the equipment. As the number of product handlings is reduced, the risk of damage to the products is greatly minimized.
6.5 STORAGE METHODS
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.
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).
Fig. 6.3 Block storage
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.
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 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 form material is to be stored or retrieved as and when required (Figures 6.4–6.9).
Fig. 6.4 Stationary racks with rails for movement of pallets
Fig. 6.5 Stationary racking system
Fig. 6.6 Flow racks
Fig. 6.7 Cantilever racks
Fig. 6.8 Tyre storage
Fig. 6.9 Cartons
SOME CUSTOMIZED SYSTEMS
Tyre Storage
These systems are utilized for storing tyres and similar inventories with limited varieties and high volume for the purpose of efficient storage and handling. We offer customized solutions for single and multi-tier storage system incorporating optimized capacity and high safety standards.
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. We offer customized solutions for specific inventories while ensuring best standards in safety and reliability.
Cantilever Racks
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. We offer customized solutions on the basis of inventory characteristics for safe and efficient operations. 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. We offer cost effective and customized solutions with modular design and reconfigurability with multiple options for the floor surfaces. 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 your needs.
Carton/Bin Flow
These systems are ideal solutions for typical order picking operation requiring FIFO (first in first out) with high throughput. We offer customized solutions with comprehensive design comprising flow track options integrated with racking systems and high standards of reliability and consistency of operations. 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 Carousel
Vertical Carousels consist of rotating shelves that move up or down in response to your commands, delivering items to you at 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.
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).
Fig. 6.10 Shelving system
Shelving is the most flexible and cost-effective storage structure, which is available in modular configuration to suit storage volumes and product configurations.
Pallets
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
Fig. 6.11 Pallet storage
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 × 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
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).
Fig. 6.12 Wired container
Fig. 6.13 Corrugated container
Fig. 6.14 Portable-wired container
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.
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.
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).
Fig. 6.15 Silo storage
SUMMARY
A well-designed storage system helps in maximizing the utility of available space and allows ease in storage and retrieval of the goods. A good storage system provides security against fire, theft and pilferage, and prevents accidents due to fatigue, strains and collapse. The storage facility may be most general without much investment as used in public warehouse for generalized cargo or may be designed for specific requirements of products, storage capacity, automation in handling etc. The various storage methods in use are block stacking, racking system, shelve system, containers, pallets, or automatic storage and retrieval system for very high storage density and high throughput. The well-designed storage enhances the overall warehouse productivity through space economics and higher throughput.
REVIEW QUESTIONS
- Describe the concept of ‘unit load’ storage and explain how it is helping in improving the system efficiency.
- What are the different methods in use for industrial storage? Discuss their merits and demerits.
- Discuss the benefits of a good storage system.
- ‘Palletization’ is an ideal unit storage system and also aid to the transportation. Explain.
INTERNET EXERCISES
- For studying innovation and perspectives in productivity and inventory control through storage system, visit Hanel Storage System, USA, http://www.hanel.us
- Visit India’s leading ‘Material Storage’ solution providing company Godrej and Boyce Mfg. Co. Ltd. at http://www.godrej.com and find out the innovative material storage system designed by the company.
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