Want to save 90% of the energy and reduce the wastage of material by up to 40% in your thermoforming plant?
The secret is the use of contact heat thermoforming machines from GN of Canada.
Below is a reprint of an article published in 2009 in SA Plastics and Rubber, which explains how and why these machines are the competitive choice.
Opportunities in Thermoforming for the small converter
"The use of OPS (Biaxially oriented polystyrene) and contact heat systems for thermoforming offers a number of advantages" - says Tim Forshaw
The thermoforming of plastic sheeting for a number of diverse industries has for many years been a favoured process. Where large volume production is required and where lower tooling costs are important, thermoforming is the choice. It has therefore developed strongly in the packaging market, and remains highly competitive for the production of open-top containers of all types. Typical products are tubs, trays, cups, clamshells and blisters made from a variety of different polymers. It is particularly cost effective for thin mouldings such as cup and tray lids.
Thermoforming production is a single-stage process where a roll of plastic sheet is heated to its softening point and then forced over or into a mould either by pressure or vacuum or a combination of both.
Assistance with “plugging” of the mould is frequently used for deeper draw products.
The products which are formed are punched out of the sheet using a die or a cutting knife. This results in a significant proportion of unformed webbing, which can either be sold as scrap or reprocessed into sheet. Larger thermoforming companies, using big volumes of material, prefer to invest in flat sheet extrusion machinery to manufacture the sheeting from both the in-house scrap and new polymer beads.
Sheet extrusion is a high throughput, high capital cost business. With new equipment ranging in price from R10-million upwards, it can only be justified in operations processing thousands of tons of material per annum. Some companies attempt to reduce this investment by purchasing old equipment, generally from abroad. This is a risky strategy and usually results in poor quality sheet, lots of waste and very high maintenance costs.
The dilemma for the smaller company wishing to start thermoforming with one or two machines, and who cannot justify in-house extrusion, is how to be competitive with the larger companies while scrapping 35-50% of the sheet that is purchased. There are three ways in which the playing field can be levelled:
Contact Heat Thermoformers
(GN Thermoforming of Canada)
The contact heat machine has major cost saving advantages over “normal” radiant heat machines. Firstly, it has no chain rails to transport the sheet through the machine, thus saving a significant amount of waste at the edges of the mouldings; and secondly, because of its heating method and tooling operation, it is possible to layout the mould cavities for the container in a nested fashion rather than in rows.
For a round container, the typical sheet waste on a contact heat machine is 25-35% versus 50% on a chain driven radiant heat machine. This means a saving of approximately 40% of the total sheet scrap. Additionally, the contact heat machine has the advantage that it uses low cost steel rule or forged knife cutting within the forming mould, providing uniform and identical products. In traditional thermoforming, second station cutting is less accurate and can cause significant product/lid fit problems, and the alternative of in-mould cutting requires matched punch and die tools which are much more expensive. Contact heat machines are also simpler and have lower maintenance costs.
Contact heat thermoformers use only 5-10% of the electricity consumed by a similarly sized radiant heat machine. With the cost of energy in South Africa rising at 30% per annum, this saving will amount to R130 000 per annum for a small to medium size machine.
A new innovation just announced by GN thermoforming is a tool specific heater platen for the contact heat machine. The effect of this is to improve the quality of the thermoformed articles as well as increasing production speeds by 30%. To download the brochure for this clickhere
OPS (Oriented Polystyrene)
The second area in which smaller thermoforming businesses can gain an advantage is through the use of oriented polystyrene. OPS is the most commonly used clear polymer for thermoforming in the United States and Japanese markets, having about 70% of the market for clear products. It has hardly ever been seen in South Africa, largely because the convertors who could benefit most by using it (the smaller companies without in-house extrusion) do not have the right equipment to process OPS.
OPS is converted most easily on contact heating machines and can also be run on newer technology radiant heat machines. The benefits of OPS over its clear competitors (PVC, PET) are that it is clearer, more rigid, higher gloss and has a higher service temperature.
Most significantly, OPS has a 30% density advantage – so, for the same thickness, one ton of sheet will be 30% greater in area.
Recent initiatives in the recycling of Polystyrene in South Africa mean that it is no longer a perceived environmentally unfriendly material. A further benefit for the converter is that the waste sheet is pure crystal polystyrene of high molecular weight which can easily be used in other applications, for example in Injection molding.
One far-sighted company in South Africa has recently recognised the opportunity and started forming a new range of products in OPS, using the waste for injection molding existing products. This strategy has made them extremely cost competitive in thermoforming.
Cost Savings Calculated
Let’s assume that our start-up entrepreneur has one machine producing a transparent round container. He can use either OPS or PET or PVC. A comparison of the contact heat plus OPS option with the radiant heat plus PVC (or PET) option is given in the table below.
|Material Machines||OPS Contact||PET/PVC Radiant|
|Sheet cost (R/kg)||14||14|
|Value of waste (R’000)||840||1890|
Savings - R1 million/annum, for equal numbers of units of product
The above assumes that the materials are of equal cost (OPS may be cheaper at present). It doesn’t take into account the savings to be made with lower maintenance costs, lower energy consumption and lower downtime for the contact machine.
GN Thermoforming philosophy is “horses for courses”. The technology used in the machine ranges is designed to optimise the production of specific types of products. Not all packaging items can be made on contact heating machines, so GN offer two other types of machine to address this.
The first of these is a small platen, tilting mould thermoformer (TM series) capable of speeds up to 45 cycles per minute and ideal for the production of deeper drawn cups, and cup lids. Cup lids which must be liquid tight need to be made using a drape (male) mold so that the critical inside dimensions of the lid are always constant and do not vary with the thickness variations in the sheet. The machines are designed to use PS, OPS, PET, or PP sheet and have the advantage over their competitors in being significantly smaller and cheaper while producing high quality moldings at high speed.
The second new development is the new Dual Mould (DM) concept. This is designed to produce high outputs (up to 40 cycles per minute) with in-mould cutting tools of moderate cost, allowing the production of deep draw (up to 150mm) articles, using PP material. The DM arrangement comprises two forming/cooling sections of the mould mounted on a swinging platen, operating under a single plugging and cutting platen. The additional cooling significantly improves the output of slow cooling materials such as thick PP products. The machine is relatively small in size, with a forming area of 550 x 400 mm, and has integrated robotic stacking and discharge conveyors.
Why are these machines important? Because they offer high productivity at relatively low cost, lowering the cost of production and thereby improving the competitiveness of the converter.
Additionally small versatile fast machines allow greater flexibility in production, shorten lead times and reduce the incidence of stock shortages.