Heated Platen Presses 101

Introduction

Heated platen presses give manufacturers the ability to create a temperature-controlled process environment while applying forming pressure to create components. Heated platens are thick precision machined flat plates that are brought together in a press to produce parts for use in plastic, rubber, laminate, and forestry product industries. Temperature control systems, which can be used for both heating and cooling, are integrated directly into the platens, for heat transfer directly to the material or forming molds, and can use electricity, steam, hot oil, or hot water.

 

Heated platen presses can vary in size, forming temperature ranges, and press tonnages and are usually customized to suit the specific application and the parts they are required to be produced. The performance capabilities of these presses are vast making them well suited for use in a laboratory or testing environment, as well as manufacturing facilities requiring large volume production.

Materials & Applications

The components of a platen press are largely made from structural steels for durability and to withstand multiple production cycles. The platens are most often made from either tool steel or stainless steel and can weigh several tons making them a significant component of the press. Platens are available in standard shapes and sizes, or they can be customized with specific details. Precision machined plates can be provided with cut-outs, grooves, T-slots, drilled and tapped holes and other features necessary to mount molds and also to house the heating and cooling channels.

Fig.1: Precision machined platens, with slots, grooves, and other cut-outs, to meet application requirements

Although they are built to last, care should be taken to prevent damage, such as dents or gouges to the platen surfaces as any imperfections may have a negative impact on formed parts and lead to lost time and costs for finishing operations.

 

Heated platen presses can be used to form parts in a number of applications such as;

 

Rubber molding: Molded rubber parts are formed by pressing rubber sheets or blocks into a mold cavity. The temperature and pressure of the heated platen press can be configured based on the geometry, thickness, and rubber properties.

 

Compression vulcanization: This process is similar to rubber molding, but the rubber is heated with an accelerator at high temperatures altering the molecular structure of the rubber. This helps in achieving parts with improved elasticity, resilience, tensile strength, hardness, and weather resistance.

 

UHMWPE and HDPE: UHMWPE (ultra-high molecular weight polyethylene) and HDPE (high density polyethylene) are plastics that are used in a wide range of products. They can both formed by applying intense heat to their respective base ingredients until polymerization takes place resulting in impact and chemical resistant, easy to fabricate, versatile plastics.

Fig. 2: Sheets of varying thickness of UHMWPE and HDPE can be produced with heated platen presses

Decorative laminates: Furniture surface materials and wall paneling are examples of common decorative laminates. Layers of paper and resin are bonded together with heat and pressure so the resins flow into the paper and curing conditions can be altered resulting in different surface finishes.

 

Bonding: This process is used when a smooth bond between two or more surfaces is required. A heated platen press can be used with an adhesive layer between surfaces and melting of the layer followed by controlled curing is required.

 

Industrial laminates: Varying grades of industrial laminates can be produced by fusing layers of thermosetting resins combined with a base material such as paper, cotton, cloth, or glass. Forming these layers under high temperature and high-pressure results in a material with a versatile combination of electrical, mechanical and chemical properties.

 

Wood forming: Heated platen presses can be used to make plywood, by combining wood veneers to create flat sheets, and MDF (medium-density fiberboard) panels by applying high temperature and pressure to graded wood fibers combined with binding materials.

Fig 3: MDF and plywood are common wood products formed from heated platen presses

Advanced composites: Material that is light weight and superior in strength and impact resistance are often used in the aircraft, automobile, and sports equipment industries. Heated platen presses can be used in the process of making advanced composites by combining higher strength reinforcing fibers into a resin, in a single press where pressure, temperature and vacuum can all be controlled.

Establishing Process Parameters

Developing the process for using a heated platen press is specific to the individual parts to be created and the material used. Factors such as heat distribution, temperature control, curing times, production volumes, and production rates, are just some of the variables in addition to the typical process parameters that are often considered.

Bed Size

The bed of a heated platen press can range in size from relatively small (under 20”), to large (100” and up). In addition to accommodating the largest toolset that will be used to form the actual parts, considerations for vacuum, the temperature control system, and number of heating/cooling zones could add to the overall bed size. Heated platen presses can also be customized to use multiple beds to further increase overall bed surface, and is often incorporated for press flexibility in part production, use of toolsets, and temperature control. Ultimately, it is important to choose an overall bed size and configuration that will result in a successful and efficient production process. Wide access to the bed(s) from all four sides of the press is advantageous for both automated and manual handling of materials and parts.

Fig. 4: A 225 Ton Multi-Frame Heated Platen Press

Heating Source

Heated platen presses can be equipped with different heating/cooling options each having their own individual advantages and disadvantages.

 

These options include;

 

Steam Heated Platens: These presses can provide a cost-effective heating system and is capable of providing accurate temperatures across the entire platen. Steam heated platens can be used in rubber molding, bonding and laminating particle board, and can be customized to suit the part forming requirements. They can also be used for hot water heating and cooling applications and are often insulated with high strength materials. Heating accuracy and uniformity can be controlled with both single and multi-zones for process optimization.

 

Oil Heated Platens: These platens are suitable for a wide range of rubber molding applications and can also be used in bonding and laminating. Thermal fluid transfer systems are used within the platen to control heat that can reach temperatures of 750 °F and higher. Usually machined from one piece of solid steel that can include interconnecting channels, milled, and welded along the edges, these platens are designed to prevent blockages and or leakages. The systems should be able to accommodate ease for inspection to ensure good fluid transfer flow. Larger applications using oil heated platens can be handled with larger platen sizes and including multi flow zones.

 

Electrically Heated Platens: These platens are an ideal choice for laminating, molding and bonding and can be used for forming a wide variety of materials. They are designed to provide uniform heat distribution and temperature control. Temperature ranges from 500 °F to 1000 °F are typical, and can go up to 1500 °F or higher for certain forming applications. The precision machined plates can offer features that allow for the heating elements (cartridges or strips) to be installed directly into the platen so that heat transfer is well controlled. High wattage heaters can be used for applications where rapid heating rates are required. Like the other options, multi-zone temperature control can be achieved with electrically heated platens for versatility, and sensors can be included to ensure proper temperature is reaching the appropriate zones minimizing errors in parts.

Tonnages and Speeds

The necessary tonnages and speeds for a heated platen press depend on the process and application. Rubber molding, laminates, composite and wood products will have a diverse range of requirements. For example, a typical compression molding tool may require a mold pressure of 20 tons to form its part(s). Alternatively, a laminating process that bonds layers of composite panels used for external walls may require a forming pressure of 250 tons or more. The required press tonnage will be determined by the projected area of the parts being formed and their respective materials. It is important to select a press with tonnage that suits the particular forming needs. Tonnages that are applied beyond what is required may cause excess energy consumption and tooling wear.

 

Typically, heated platen presses have forming forces that can range from 15 to 1000 tons and speeds can be configured such that closing times are rapid and close at an appropriate speed so that the tonnage is controlled. More important than the actual press speed is ensuring cycle time is minimized, and the forming pressure and temperatures are controlled, accurate and repeatable.

 

Orientation and size of the formed part may have an effect on opening speeds. Larger parts will require more space to open and thus larger machines are required which will translate to longer opening times.

Fig. 5: A 1500 Ton, with 4 daylight, heated platen press with automated loading/unloading systems

Temperature

Similar to the press tonnage, the required platen temperature, and subsequent heat transfer to molds and/or materials directly, for forming will be dependent on the needs to successfully produce the part. It is important to select the heating and cooling system, whether it be electrical, heated oil, or steam, that is best suited for the application for both energy and cost efficiencies. Heated platen presses are used across a wide range of industries and materials, and possible temperatures can range from at or near room temperature, to 1500 °F or higher.

 

In many cases, cooling requirements will also be a factor that can be programmed into the press to ensure appropriate curing conditions and to ensure parts and molds can be safely handled afterwards. The part geometry, size, and material properties will have the largest impact on the necessary cooling times.

Stroke and Daylight

Heated platen presses can be configured with single or multiple opening (daylights).  This allows for the forming process to produce multiple parts during the same pressing cycles as multiple molds can be used in a single press. Applications where cure times may be lengthy, the versatility of a heated platen press can reduce the overall number of presses required to achieve the desired production output.

 

Enough daylight must be available between the fully retracted tool faces to allow removal of the finished part from the press. In practice, this translates to daylight that is approximately triple the press stroke. If a press will be used to produce more than one part, stroke and daylight should accommodate the largest expected tooling. Additional clearances may be required to accommodate in die cooling, in die heating, quick-change tooling, and loading/unloading systems.

Fig. 6: A 7500 Ton, with 10 daylight, heated platen press with vacuum enclosure and loading/unloading systems

Hydraulic Heated Platen Presses

Hydraulic heated platen presses are extremely versatile pieces of machinery. Not only are they widely used to form production parts that require both a controlled temperature and forming pressure across many industries, but they can also be used in testing and laboratory environments. For example, platen presses can be used in impact and crush testing, and to prototype heat seals of plastic packaging.

 

With properly integrated hydraulic systems, heated platen presses can produce extreme levels of pressure that are necessary to form, compact and bond various materials together. Larger presses can be equipped with oversized bolsters to ensure the movement of the platens is smooth and minimize deflection, resulting in accurate and precise parts. For many forming applications, it is extremely important to have square and flat platens, coinciding with reliable and repeatable pressing motions for operational efficiencies. This is often a requirement for parts used in automotive, aerospace and other applications that make use of heated platen presses where high precision is paramount.

 

Custom hydraulic heated platen presses can be designed and manufactured for the specific process. They can include single opening, multiple openings, up or down acting platens, and many other options. To ensure successful part results and to further focus on maximizing efficiencies in time and operational costs, the press can be fitted with a variety of frame styles and include features such as:

  • Gas or electrically fired heating systems
  • Platen cooling systems
  • Vacuum enclosures and systems
  • Insulated heat enclosures
  • Platen cleaners
  • Temperature sensors
  • LCD displays
  • High Speed data acquisition systems
Fig. 7: A 1000 Heated Platen Press

Advantages

Some of thew advantages and abilities of a hydraulic heated platen press are summarized here:

  • Stable and uniform distribution of forming pressure
  • Controlled temperatures – allows for flexibility of materials used on the same press
  • Are suitable to be used in lab and testing environments
  • Ability to form multiple parts to maximize production capabilities
  • Fully configurable to meet forming requirements with ability to adjust; temperature, pressure, position, cure times, and press speed
  • Custom machined platens with integrated mounting and cooling features
  • Precision and accuracy of parts

 

Visit our Heated Platen Presses page to learn more about custom Hydraulic Heated Platen Presses.

 

Contact us about your hydraulic press needs.

Image References

  1. Fig 1: HPP-F1, Precision machined platens, with slots, grooves and other cut-outs, Macrodyne
  2. Fig 2: HPP-F2, High Density Polyethylene (HDPE), Polymer Shapes, (https://www.polymershapes.com/product/high-density-polyethylene-hdpe/)
  1. Fig 3: HPP-F3, Rajput, K., MDF vs Plywood | What Is MDF | What is Plywood (https://civiljungle.com/mdf-vs-plywood/)
  1. Fig 4: HPP-F4, A 225 Ton Multi-Frame Heated Platen Press, Macrodyne
  2. Fig 5: HPP-F5, A 1500 Ton, with 4 daylight, heated platen press with automated loading/unloading systems, Macrodyne
  3. Fig 6: HPP-F6, A 7500 Ton, with 10 daylight, heated platen press with vacuum enclosure and loading/unloading systems, Macrodyne
  4. Fig 7: HPP-F7, A 1000 Heated Platen Press, Macrodyne