Introduction of RTM Forming Process
Resin transfer molding referred to as RTM, starting in the 50s, is the hand lay-up molding process improved a closed-form technology, can produce two-sided light products.
The basic principle of RTM is to put glass fiber reinforced material in the closed mold cavity, with special pressure equipment to inject resin glue into the mold cavity, soaked glass fiber reinforced material, and then solidify, demolding molded products
RTM Process-Standard RTM
The upper and lower (yin and yang) modules of the standard RTM are reinforced with a metal frame, and the perimeter is tightly locked by a metal fastener.
The resin is imported through a medium pressure injection machine.
The resin is injected by the center injection port and flows to the periphery vent.
Standard RTM Mould
RTM Process-Lightweight RTM
The lower mould of the light RTM (Yin die) has a rigid mold reinforced by a metal frame, the upper Die (master) is a semi-rigid die, through the flanging of a negative pressure at the same time on the mold cavity after the two-level (half negative pressure) vacuum-assisted resin through the low-pressure injection machine into the resin by the peripheral resin flow channel injection Nozzle, Suction port flow to the center
Light RTM Mould
Wide Application of Light Weight RTM
Because lightweight RTM is a low-pressure vacuum-assisted molding process, compared with the traditional RTM, the mold making process is greatly simplified, convenient and fast. The mold does not need to strengthen the steel structure as the traditional RTM.
The lower mould is sandwich structure with high rigidity to prevent the resin from any deformation during injection, while sandwich core structure can effectively save the heat produced during the solidification of the product, which is beneficial to the rapid solidification of subsequent products and shorten the production cycle.
The upper die is more simple, can be made into lightweight, semi-rigid structure, so it is very conducive to frequent demoulding, die-closing operation
Main Problems in RTM Molding Process
No doubt RTM process comparison and hand lay-up process, it is closed mode operation, does not pollute the environment, does not damage the health of workers, to a certain extent, improve production efficiency, and can make two-sided light products.
But in the actual production process, There are many problems: how to let the RTM mold meet the requirements of high temperature and high pressure? How to ensure that the size of molds and even products are accurate? How to ensure the uniformity of product thickness? How to improve the surface quality of products?
The following will be from the production of molds, molding materials selection, and equipment, such as the matching to answer the above questions.
Mould and Manufacture of Light RTM
(1) The flanging structure treatment and surface treatment of the light RTM original touch.
(2) Lightweight RTM mold structure design.
(3) Lightweight RTM mold layer design.
Structural Design of Lightweight RTM
The Flanging Detail of the Light RTM Mould
Structural Treatment of the Flanging of Lightweight RTM Mould
The problem of clamping stability: because the upper and lower mold is based on a negative pressure to close the mold, flanging die cavity size determines the clamping force of the size and the stability of the mold, according to the size of the product to measure the width of the flanging, generally around 250mm.
The problem of sealing: because the upper and lower mold by a negative pressure through the sealing tape, the entire flanging can not have perpendicular to the plane of the right angle, gradient angle of these structures, encountered this situation need to do a certain radian transition processing.
Surface Treatment of Light RTM Original Mould
A high surface quality of the product needs a high surface quality of the mold, to achieve high surface quality of the mold, the original touch needs to be necessary surface treatment:
1, Surface repair: Easy to polish the use of plastic materials, because easy to burnish the bottom of the gum easily polished, the original mode of repair has a great help, at the same time easy to polish the bottom of the pinhole rate is very low, for the original mode to provide a dense uniform surface layer.
2, the surface of the high brightness requirements: the use of high light plastic clothing, high viscosity low, good leveling, pinhole rate is very low, after polishing up to the a-level surface. In addition, reduce the grinding capacity of the mold layer, at the same time reach the high light surface requirements of products.
Design of Mould Layer for Lightweight RTM
The upper mold layer is relatively simple, the use of transparent mold plastic clothing with better toughness of vinyl mold resin, mold thickness design around 10mm. Therefore, the upper die is relatively lightweight, using the opening and closing mode.
The lower die layer is designed to sandwich structure: provide enough rigid support to ensure the exact size.
Surface Layer + Transition layer
Structure reinforced layer + bonding layer + structure sandwich
Bonding layer + structure enhancement layer
Sandwich mold Structure: From the design point of view to ensure the accuracy of the mold rigidity and size
Surface Layer + Transition layer
Sandwich Mold Structure:
From the design point of view to ensure the accuracy of the mold rigidity and size.
Mold Surface Design: From the point of view of high temperature to choose the mold plastic clothing
As the RTM molding process after the overall reaction of the resin injection, because the heat generated by the reaction is more concentrated, so the demand for mold plastic clothing has relatively high-temperature resistance requirements. Usually, choose vinyl mold adhesive as the RTM mold plastic clothing, not only to meet the requirements of heat resistance but also to meet the frequent use of thermal shock and a large amount of service life
Selection of resin system for transition layer and bonding layer:
Vinyl Mold Resin System
Also as a tool for the transition of plastic clothing needs to meet the requirements of heat resistance and continuous thermal shock, as well as the structure of the reinforcement layer and the structure of the bonding layer, the need for good bonding performance
Precision control of mold size: 0 shrinkage die resin application,
An indispensable reinforcement layer in the sandwich structure design.
One-Shot 0 shrinkage mold resin system mold size requirements of the high and large-scale mold production can be a very good control of the shrinkage of the mold
Sandwich selection in structure design: application of light wood sandwich
1, super compression performance, very good to improve the mold rigidity and compressive capacity
2, reduce the weight of the mold
3, at the same time play the role of insulation
Selection of RTM Molding Materials
Matrix resin System:
Resin can be an unsaturated polyester resin, can also be vinyl or epoxy resin, the main requirements:
1, low viscosity, can be very good in the preformed body flow, infiltration, immersion. (Viscosity index 180-300)
2, longer gel time, faster-curing speed, this is conducive to soak, exhaust.
Reinforcement Materials: mainly with a variety of axial cloth, combination mat with the corresponding diversion materials(PP).
Diversion Material:
1, Closed Mould Mat: a combination mat, mainly by the PP fiber as a diversion medium on both sides of the composite chopped strand, the thickness can be adjusted according to requirements.
2, Continuous Filament Mat: there are continuous fiber strands in a random manner in the form of a ring-shaped distribution on the mesh belt made of felt.
Thin-layer Sandwich Material:
Soric series of strong core felt, the use of Soric series of strong core felt in RTM process, not only as an enhanced system of diversion medium, making the molding process become simple and efficient, but also can improve the product’s rigidity to reduce the weight of products and achieve uniformity of product thickness control.
Structure Clip Core:
PVC foam, light wood, such as the use of sandwich. For large-scale products such as bunker hull Shell, and so on, structural design using structural sandwich materials, these materials after drilling, slotting processing, not only meet the design requirements, effectively guarantee the uniformity of product thickness, but also as a diversion medium, making the molding faster.
How to improve the surface quality of products: application of polyester surfacing mat
DymPet: is a special RTM polyester surfacing veil, providing a dense and homogeneous resin-rich surface layer for the products to provide a perfect surface quality. It’s helpful to airtightness in some packing products.
Auxiliary Materials:
Semi-permanent release agent Axel 802, 807, 818
800 Series Release Agent application:
1, in the products after spraying, bonding, and other processing to avoid a large number of grinding and other post-processing processes.
2, the effect of multiple demoulding can improve production efficiency.
Auxiliary Materials:
Stereotypes spray glue
Lida Spray Glue (Ledafix) is a special resin-based spray glue for the positioning and bonding of fiberglass and core materials, which is widely used in the RTM process.
Standard RTM Injection Equipment
Traditional RTM injection equipment:
Technical parameters:
Air Source requirements: 481 l/min 6.8 bar
1 Liquid gas ratio: 11:1
heory of material pump max output: 9.46 l/min, 182 ml/stroke
0.5-3.5% Curing Agent Range: 0.5-3.5%
Feed pipe Length: 7.5 m
Light RTM Injection Equipment
Technical parameters:
Air Source requirements: 481 l/min 6.8 bar
1 Liquid gas ratio: 11:1
Theory of material pump max output: 9.46 l/min, 182 ml/stroke.
Curing Agent Range: 0.5-3.5% feeding pipe Length: 7.5 meters.
Accurate pressure feedback system.
Flow and Pressure Control of RTM Injection System
High-Tech Automatic RTM Matching System
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