A batch of white polycarbonate plates comes off the press with silver streaks around the gate, and the resin bag has been open beside the hopper since the morning shift. That is a drying problem, not a machine problem. A 100 t switch plate making machine can suit plates and small accessories, provided cavity count, flame-retardant grade and drying are matched to it.
This article covers those three, plus the BIS rules your parts must help the finished product meet.
Key Takeaways
- Two cavities of an 86 × 86 mm PC plate with a large window can need about 43 to 72 t; four cavities can need about 84 to 140 t.
- Flame ratings depend on thickness. Covestro rates its Makrolon 6555 UL 94 V-0 at 3.0 mm but V-2 at 1.0 mm.
- Dry PC to 0.02% moisture or less. Covestro gives 120 °C for 2 to 3 hours in a dry air dryer.
- Switches are under compulsory BIS certification to IS 3854, so the moulded part must let the finished switch pass its heat, fire and mechanical tests.
What Should a Switch Plate Making Machine Deliver?
It must hold the mould shut for every cavity you plan, deliver enough melt pressure to fill thin, flat walls, and keep barrel and mould at the resin's settings. On flat plates with large windows, clamp force can limit cavity count before shot size does, so size the clamp first.
Plates are wide and thin, and their window openings come off the projected area. A plate's outline can look large while the clamp only sees the plastic around the window. The calculation method is set out in the article in this series on what a 100 ton machine can make.
Polycarbonate needs more clamp per square centimetre than PP. A Bayer MaterialScience (now Covestro) datasheet for Makrolon 2558, a general-purpose PC, gives a clamp tonnage of 3 to 5 US t/in². The worked example below shows what that range means for cavity count on a 100 t clamp.
Pressure is the second check. A thin plate filled from one gate has a long flow path for its wall, and PC resists flow, so the injection unit needs pressure in reserve. How screw size trades pressure against shot volume is covered in the screw diameter article in this series.
Mould temperature is the other equipment point. Covestro recommends 80 to 120 °C for Makrolon 6555, well above chilled water, so plan a mould temperature controller with the machine.
Why Does Wall Thickness Matter for Flame-Retardant Plates?
Flame ratings are tied to thickness. Covestro rates Makrolon 6555 UL 94 V-0 at 3.0 mm but only V-2 at 1.0 mm, and its glow wire flammability index drops from 960 °C at 1.5 mm to 875 °C at 0.75 mm. Thinning a wall can change the rating.
Flame-retardant PC data that matter on the shop floor (Makrolon 6555, Covestro)
| Property | Value | What it means for moulding plates |
|---|---|---|
| UL 94 rating | V-0 at 3.0 mm, V-2 at 1.0 mm | Check the rating at the thinnest wall you mould, not the nominal one |
| Glow wire flammability index | 960 °C at 1.5 and 3.0 mm, 875 °C at 0.75 mm | Very thin ribs and edges can fall to the lower value |
| Drying | 120 °C, 2 to 3 h, moisture 0.02% max | Dry every lot in a dry air dryer before it reaches the hopper |
| Water absorption at 23 °C, 50% RH | 0.12% at equilibrium | Six times the drying limit, so an open bag soon becomes wet resin |
| Mould temperature | 80 to 120 °C | Needs a mould temperature controller |
| Moulding shrinkage | 0.60 to 0.80% | Set cavity sizes for this grade, not for general PC |
IEC 60695-2-12 defines the glow wire flammability index as the highest test temperature at which the material does not ignite, or self-extinguishes within 30 seconds without its drips igniting the tissue below. It is a materials test, so the finished product is still tested on its own.
So a redesign to save resin is also a compliance change. A plate thinned from 3 mm to 2 mm saves material and cycle time but moves the part away from the thickness at which the V-0 rating was earned.
How Should You Dry Polycarbonate for Switch Plates?
Dry it every time, in a dry air dryer, to the resin maker's limit. For Makrolon 6555, Covestro gives 120 °C for 2 to 3 hours and a maximum moisture content of 0.02%. Moisture in PC can show up as surface streaks, and that damage cannot be fixed after moulding.
The datasheet explains why care pays. Its equilibrium water absorption at 23 °C and 50% relative humidity is 0.12%, six times the drying limit. During the monsoon, when shop air can be more humid than that, an open bag at the hopper can pass the limit well before the shift ends.
Size the dryer from the machine, not the other way round. If a job uses 6 kg of PC an hour and the resin needs 2 to 3 hours at temperature, the drying hopper must hold 12 to 18 kg, so that every granule has had its full time before it reaches the screw.
Our position is firm: never mould flame-retardant PC from an open bag. Feed it from the dryer, keep the hopper lid closed and log the dryer temperature every shift. A switch plate rejected for streaks costs the same resin and machine time as a good one.
Which Indian Certification Rules Apply to Switches and Sockets?
Switches for domestic and similar purposes are under compulsory BIS certification to IS 3854, through the Electrical Wires, Cables, Appliances and Protection Devices and Accessories (Quality Control) Order, 2003. Plugs and socket-outlets are covered by IS 1293. Your moulded parts must let the finished product pass.
BIS explains what these standards test. A resistance to abnormal heat and fire clause checks that insulating material does not deteriorate or start a fire under overload or a loose connection. Mechanical strength is checked with blows from a pendulum hammer, and plugs and sockets are checked by inserting and withdrawing a plug 10,000 times.
BIS also notes that these accessories are made from both thermoset and thermoplastic materials. Thermoset parts need equipment built for thermosets, so a standard thermoplastic machine fits only the thermoplastic side of that range, such as PC and PC blends.
Parts moulded alongside plates, such as switch frames, socket covers and grid plates, follow the same logic. Confirm the resin's flame data at the moulded thickness, dry it the same way and keep its lot numbers traceable to the batch of plates.
The brand owner holds the BIS licence, but the moulder controls what testing will find: wall thickness, weld lines near screw bosses, gate marks and moisture in the resin.
What Should You Send for a Switch Plate Machine Check?
Send the plate drawing with window, rib and boss details, the resin grade and its flame rating, the number of cavities you want, the runner type and your monthly volume. With those, clamp, shot and drying needs can be worked out together. See the 100 ton horizontal injection moulding machine page.
Frequently Asked Questions About Switch Plate Making Machines
Is a UL 94 V-0 material enough to pass IS 3854?
No. UL 94 is a material flammability rating on test bars of a stated thickness. IS 3854 tests the finished switch, including resistance to abnormal heat and fire and mechanical strength. A well-rated material helps, but the moulded product, with its real walls, ribs and inserts, still has to pass the standard's own tests.
What mould temperature does flame-retardant PC need?
Covestro recommends 80 to 120 °C for Makrolon 6555. That is far above what plain chilled water gives, so plan a mould temperature controller with oil or pressurised water. Running the mould too cold to save cycle time can leave moulded-in stress around windows and screw bosses.
Does a bigger window reduce the clamp force needed?
Yes. Through-openings are removed from projected area, so a plate with a larger window needs less clamp per cavity. Ribs, frames and bosses in the parting plane still count. Measure the actual plastic outline from the drawing, not the outside size of the plate, before you decide on cavity count.
What does the glow wire flammability index tell me?
It is the highest glow wire temperature at which test plaques of a material do not ignite, or self-extinguish within 30 seconds without their drips igniting the tissue below, under IEC 60695-2-12. Covestro lists 960 °C at 1.5 mm for Makrolon 6555. Product standards set what the finished part must withstand.
Can the same machine run sockets and plug tops?
It can, if the parts fit the clamp and shot and the resin suits a thermoplastic machine. Sockets and plug tops can carry metal contacts, so insert loading time and the choice between a horizontal and a vertical machine can matter as much as tonnage. IS 1293 sets the tests these products must pass.
Related Articles
- What Can You Make on a 100 Ton Injection Moulding Machine?
- Choosing Between the 32 mm and 35 mm Screw on a 100 Ton Machine
- 100 Ton Injection Moulding Machine Running Costs: Power, Cycle and Output
Sources & References
- Bureau of Indian Standards: Scheme I (ISI Mark Scheme): products under compulsory certification
- Bureau of Indian Standards (BIS Blog), N. Agarwal: Standards for Plugs-Socket-Outlets and Switches
- IEC: IEC 60695-2-12:2021 Glow-wire flammability index (GWFI) test method for materials
- Covestro: Makrolon 6555 product data
- Bayer MaterialScience (now Covestro) via IDES: Makrolon 2558 technical data sheet
Technical Disclaimer
Disclaimer: The information provided in this document is for general informational and educational purposes only. It is based on technical references and industry information available at the time of preparation and may be subject to change. It does not constitute engineering, technical, commercial or professional advice, nor does it constitute a quotation, specification, warranty or contractual commitment by Pratishna Engineers.
Actual injection moulding machine and process requirements vary according to the component design, material, mould, production volume, machine configuration and operating conditions. The information, examples, calculations and recommendations provided should be independently evaluated and verified for the specific application before making any equipment, process or production decision. Information obtained from third-party sources remains subject to the accuracy and limitations of those sources.
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