The demand for waterproof safety footwear continues to grow globally, especially in mining, agriculture, construction, food processing, oil & gas, and municipal engineering industries. Compared with traditional PVC or rubber boots, PU rain boots are increasingly popular because they are lighter, warmer, more comfortable, and long-lasting.

For investors and manufacturers interested in the safety footwear market, it is important to learn about PU rain boot production technology before deciding on equipment, factory/floor layout and production capacity.

This article describes how PU rain boots are produced, what machines are essential, and why polyurethane technology is rapidly replacing traditional technologies for making rain boots.

What Are PU Rain Boots?

PU rain boots are waterproof boots made with polyurethane materials using an injection or direct pouring process. PU boots are usually far superior to PVC boots since they have a microcellular foam structure that makes them much more flexible, and wear resistant, apart from having better insulation properties.

PU boots are widely used in:

• Mining
• Cold weather environments
• Food factories
• Agriculture / farming
• 建設
• Chemical plants
• Oil & gas

Leading safety footwear brands are gradually adopting double density PU technology for its advantages in improved comfort and durability.

Main Advantages of PU Rain Boot Technology

Light Weight Structure

Foam density of polyurethane makes it a lot lighter than rubber, and PVC, giving the finished boots lower density on the whole. Both farmer and factory workers can wear PU boots longer without the feeling of fatigue.

Better Thermal insulation

PU materials are cold insulating in a remarkable manner as compared to other materials, viz., rubber and PVC, PP, etc. PU rain boots are, therefore, largely used in winter friendly environment, and in cold storage operations.

Enhanced Comfort

The structure of rigid flexible foam within the boot serves to absorb any shock as you walk, improving comfort for long periods of working on your feet.

Excellent Chemical Resistance

Modern formulations of PU demonstrate strong resistance against oils, chemicals and abrasion.

Longer Service Life

High quality PU rain boots will often outlast traditional PVC in harsh industries. The production of basic PU rain boots, will typically include the following steps:

1. Raw Material Preparation

Most common principal raw material components Polyol Isocyanate Colour paste Purpose Banana smoothies have not been convinced to do much. “make my smoothie for me, or heat me a cup of joe once in a while.” Additives Blowing agents

It is imperative that proportioning of the individual ingredients is accurately controlled to ensure foam density, flexibility and hardness characteristics are constantly maintained, together with the quality of the finished product. Nowadays, most factories incorporate automatic feeding and dosing system throughout to enable stable production.

2. Mold Preparation

Boot molds are cleaned and applied with a mould release as required. Good control of mould temperature is necessary as it can affect amongst other things, surface quality of the foam and structure of the foam. These factors can affect the final appearance of the product and cause difficulty with demoulding operations. Moulds are often made from aluminium to improve heat transfer and to give a longer life.

3. PU Injection or Pouring

A mix of polyurethanes is injected through a PU mixing head into a boot mold. This is by far the most important section of the entire production process. The mixing system should ensure the right ratios and pressure, stable reaction, and mixing performance as well as foam characteristics. Many factories employ rotary type PU injection machines to increase efficiencies.

4. Foaming and Curing

The injected PU material is a mix that undergoes a chemical reaction resulting in expansion within the mold.-stage, the following occurs:

• The structure of the foam takes shape
• The density is stable
• The shape of the finished boot is formed

Special care should be taken in the curing time to avoid deforming the boot or pulling or causing the boot to shrink.

5. Demolding

After curing, workers “unmold” the ready work boot from the mold. A good design of molding machine helps lessen damage to boot during demolding, and increases line speed.

6. Trimming and Finishing

The extra amount of “flash”, or material left over from the original mold diet is trimmed back, and the boot is checked for:

• Surface defects
• Air bubbles
• Uniform coloration
• Sole bonding
• Accuracy of weight

In some factories, printing, logos, or finishing the sole for anti-slip finishes is done at this point in the process for the individual work boot. Making a high quality PU rain boot.

Double Density PU Rain Boot Making Process

Entering into the whole of the process, the Double Density PU rain boot is among the most popular of the new “premium” safety footwear. As the words suggest, DDPU involves two densities of latex -a softer PU injected to make a midsole of comfort and a hard injection for the bottom of the shoes. The advantages of this method of manufacture include:

• Better cushioning shock absorption
• Better anti-slip performance than all rubber boots
• More comfortable in the foot for the wearer
• Life and wear of the sole is improved

It is for this last reason that many factories now choose to use only double density PU shoe machines for their whole range of production of shoes, especially for export. The increasing demand for premium safety boots in the international market is responsible for this development.

Key Machines Used in a PU Rain Boot Component Piece Production Line

A typical PU rain boot production line will include the following machines:

• PU Injection Machine
• Rotary Production Line
• Mold Temperature Controller
• Raw Material Feed System
• Air Compressor System
• Cooling system
• Trimming and finishing machines and equipment

The Significance of PU Mixing Head Technology

Commonly referred to as the ‘heart’ of a PU machine, the quality and efficiency of this piece of equipment has a direct impact upon :

• Uniformity of foam, and stability of product
• Material waste, and production efficiency

Poor mixing may result in:

• Non-uniform density, and unstable product
• Air bubbling during production, and loss of strength
• Poor adhesion in joint hem

This is why specialist ‘PU’ machinebuilders pay particular attention to equipment of this type.

Sound Factory Layout for PU Rain Boot Production

A well-planned factory layout leads to improved:

• Production efficiency
• Flow of material
• Safety of workers
• Facilities for future enlargement

In a typical PU rain boot factory there will be a number of distinct departments:

• The raw material storage
• Injection moulding fittings area
• Mould room
• Cooling and curing room
• Finishing shop
• Quality control
• Packaging

Hygiene, and suitable climate conditions of temperature and air conditioning, is equally important because ‘PU’ materials are very sensitive to climatic variations.

The Trend Towards Automation in PU Rain Boot Production

The trend today in the manufacture of PU rain boots is towards factory automation as far as possible. Examples of modern automatic upgrading are:

• Automatic feeding inward
• Automatic handling of moulds
• Servo-applied injection
• PLC
• Remote trouble-shooting
• Collected production data

Automation implies reduction of labour costs and increased consistency and daily production.

Common Hazards of PU Rain Boot Production

Foam Shrinkage

This is frequently the result of erratic mixing ratios or incomplete curing.

Puddling on surface

This effect may be due to moisture, or poor mixing.

Non-uniform density, and poor product stability

Moulds not releasing properly

Cause: usually due to poor release agent application or problems with the mould temperature.

Resolution: Dispatching experienced technical support to work on this, and training moulding operators. Video. (392)

Why are Turnkey PU Rain Boot Projects Gaining Popularity

More and more investors are opting for turnkey PU production projects since it greatly simplifies the requirements for building the factory and lowers the technical risks.

A complete turnkey solution may include:

• Factory layout design
• Machine manufacturing
• Mould design
• Raw material formulation support
• Installation and commissioning
• Operator training
• After-sales technical service
• Troubleshooting support via video camera

By adopting a turnkey solution, new manufacturers can start making a profit much faster and also avoid costly mistakes in the startup period.

The Technology of PU Rain Boots How it is changing

As a result of competition between manufacturers, the footwear industry in the PU industry is moving towards:

• Lower energy costs
• More environmentally sustainable chemical formulations
• More intelligent automation
• Weight saving in relevant components in footwear
• More rapid production speeds

Cloud technology to monitor and improve production efficiency is being more widely adopted.

Bio-based polyurethane materials and solvent free processing technologies are more in demand by the international market.

Those manufacturers bold enough to embrace the technologies available today will almost certainly be stronger in the future safety footwear market.

FAQ

1. Are PU rain boots better than PVC rain boots?

Yes, PU are lighter, warmer and more comfortable to wear. They maintain better flexibility and longer service life particularly in arduous industrial work.

2. What is the production capacity of a PU rain boot line?

This depends on how the machines are designed and their levels of automation. Fully automatic rotary PU rain boot lines can produce several thousand pairs per day.

3. How long does it take to set up a PU rain boot factory?

For a complete turnkey project this will take several months, including factory preparation, machine installation and testing and operator training.

4. What industries wear PU rain boots?

Commonly found in mining, agriculture, construction, fishing, oil & gas, food processing, and cold storage etc.

5. What is the difference between single density and double density PU boots?

Single density boots form part of a PU materials family, which has one single PU layer. Double density boots have two layers of PU with one being much softer, and the other much harder.

6. Can old PU shoe machines be retrofitted?

It is perfectly possible to update many of the old PU shoe machines with better control systems, a more modern mixing head and improve automation for greater process efficiency and product quality.